This PDF file contains the front matter associated with SPIE Proceedings Volume 10164, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Researchers have performed theoretical investigations of flow induced limit cycle oscillations (LCOs) of tensioned ribbons. Furthermore, attempts have been made to tap into the energy harvesting capability of such ribbons, owing to its structural simplicity, low weight and ease of fabrication. However, in order to tune the ribbon to perform optimally at a given location, a robust, reliable model of the ribbon is essential to predict the limit cycle behavior. The model needs validation across a broad spectrum of its operating envelope based on experimentally obtained results. This paper seeks to provide experimental data for a sample tensioned ribbon in cross flow to serve as basis for validation of an aeroelastic model. This paper experimentally characterizes a PTFE (polytetrafluoroethylene) ribbon of aspect ratio 18 across a range of applied axial preload tension and wind speeds.

Piezoelectric polymers, such as the Emfit polypropylene piezoelectret foam investigated in this study, have distinct advantages over traditional piezoceramics. Although piezopolymers have a smaller piezoelec tric coupling coefficient when compared to piezoceramics, they are well suited for in vivo applications , having a lead - free composition, for applications with curved or flexible surfaces, being flexible, or where weight or large shocks are factors, being l ight weight and r esilient. Presented here is an improved electromechanical multiple degree of freedom (MDOF) model of a mult ilayer piezoelectret foam stack that implements a complex stiffness damping model as a function of measureable material properties , as well as an updated stack configuration which makes use of lighter and more fle xible materials than the author’s previous configuration. The model predicts the energy harvesting performance of the stack at varying excitation frequencies and for varying s tack properties. Finally, the stack model parameters are validated with experimentally determined foam material properties .

In elastic dielectrics, piezoelectricity is the response of polarization to applied mechanical strain, and vice versa. Piezoelectric coupling is controlled by a third-rank tensor and is allowed only in materials that are non-centrosymmetric. Flexoelectricity, however, is the generation of electric polarization by the application of a non-uniform mechanical strain field, i.e. a strain gradient, and is expected to be pronounced at submicron thickness levels, especially at the nano-scale. Flexoelectricity is controlled by a fourth-rank tensor and is therefore allowed in materials of any symmetry. As a gradient effect, flexoelectricity is size dependent, while piezoelectric coupling has no size dependence. Any ordinary piezoelectric cantilever model developed for devices above micron-level thickness has to be modified for nano-scale piezoelectric devices since the effect of flexoelectric coupling will change the electroelastic dynamics at such small scales. In this work, we establish and explore a complete analytical framework by accounting for both the piezoelectric and flexoelectric effects. The focus is placed on the development of governing electroelastodynamic piezoelectric-flexoelectric equations for the problems of energy harvesting, sensing, and actuation. The coupled governing equations are analyzed to obtain the frequency response. The coupling coefficient for the bimorph configuration is identified and its size dependence is explored.

This study examines the potential of the Electro-Mechanical Impedance (EMI) method to provide an estimation of the developed thermal stress in constrained bar-like structures. This non-invasive method features the easiness of implementation and interpretation, while it is notoriously known for being vulnerable to environmental variability. A comprehensive analytical model is proposed to relate the measured electric admittance signatures of the PZT element to temperature and uniaxial stress applied to the underlying structure. The model results compare favorably to the experimental ones, where the sensitivities of features extracted from the admittance signatures to the varying stress levels and temperatures are determined. Two temperature compensation frameworks are proposed to characterize the thermal stress states: (a) a regression model is established based on temperature-only tests, and the residuals from the thermal stress tests are then used to isolate the stress measurand; (b) the temperature-only tests are decomposed by Principle Components Analysis (PCA) and the feature vectors of the thermal stress tests are reconstructed after removal of the temperaturesensitive components. For both methods, the features were selected based on their performance in Receiver Operating Characteristic (ROC) curves. Experimental results on the Continuous Welded Rails (CWR) are shown to demonstrate the effectiveness of these temperature compensation methods.

Structural traveling waves have potential applications in numerous areas such as propulsion and skin friction drag reduction. Recent research has shown that via the two-mode excitation method, traveling waves can be generated in both one- and two-dimensional structures via the use of low-profile piezoelectric actuators. Traveling waves on a one-dimensional beam propagate in a single direction, while those on a two-dimensional structure, such as a plate, do not necessarily propagate uniformly across the surface. The propagation patterns can include unidirectional traveling waves with spatial phase shifts, wave fronts moving in opposing directions, or even rotationally moving waves. These propagation patterns depend on the participating modes and vary based on the excitation frequency, thus if multiple frequency traveling waves are generated on a plate, multiple propagation patterns are superimposed. In this study, traveling waves were generated in a plate at two different frequencies. Those frequencies were then simultaneously excited on the plate to generate a propagation pattern containing traveling waves at both frequencies. The superimposed propagation pattern was then analyzed by comparing it with a numerical combination of the individual frequency patterns. The experimentally superimposed traveling waves were found to be a linear combination of the individual frequency waves. In addition, by combining multiple frequency waves, the percentage of the plate containing traveling waves increased.

Crack detection on pressed panel during the press forming process is an important step to ensure the quality of panel products. Traditional crack detection technique has been generally performed by experienced human inspectors, which is subjective and expensive. Therefore, the implementation of automated and accurate crack detection is necessary during the press forming process. In this study, we performed an optimal camera positioning and automated crack detection using two image processing techniques with multi-view-camera system. The first technique is based on evaluation of the panel edge lines which are extracted from a percolated object image. This technique does not require a reference image for crack detection. Another technique is based on the comparison between a reference and a test image using the local image amplitude mapping. Before crack detection, multi-view images of a panel product are captured using multiple cameras and 3D shape information is reconstructed. Optimal camera positions are then determined based on the shape information. Afterwards, cracks are automatically detected using two crack detection techniques based on image processing. In order to demonstrate the capability of the proposed technique, experiments were performed in the laboratory and the actual manufacturing lines with the real panel products. Experimental results show that proposed techniques could effectively improve the crack detection rate with improved speed.

This paper proposes a full-field pulse-echo ultrasonic propagation imaging (FF-PE-UPI) system for non-destructive evaluation of structural defects. The system works by detection of bulk waves that travel through the thickness of a specimen. This is achieved by joining the laser beams for the ultrasonic wave generation and sensing. This enables accurate and clear damage assessment and defect localization in the thickness with minimum signal processing since bulk waves are less susceptible to dispersion during short propagation through the thickness. The system consists of a Qswitched laser for generating the aforementioned waves, a laser Doppler vibrometer (LDV) for sensing, optical elements to combine the generating and sensing laser beams, a dual-axis automated translation stage for raster scanning of the specimen and a digitizer to record the signals. A graphical user interface (GUI) is developed to control all the individual blocks of the system. Additionally, the software also manages signal acquisition, processing, and display. The GUI is created in C++ using the QT framework. In view of the requirements posed by the Korean Air Force(KAF), the system is designed to be compact and portable to allow for in situ inspection of a selected area of a larger structure such as radome or rudder of an aircraft. The GUI is designed with a minimalistic approach to promote usability and adaptability while masking the intricacies of actual system operation. Through the use of multithreading the software is able to show the results while a specimen is still being scanned. This is achieved by real-time and concurrent acquisition, processing, and display of ultrasonic signal of the latest scan point in the scan area.

The bistability and snap through capability of an unsymmetric laminate consisting of only Macro Fiber Composites (MFC) are investigated. The non-linear analysis predicts two cylindrically stable configurations when strain anisotropy is piezoelectrically induced within a [0MFC/90MFC]T laminate. This is achieved by bonding two MFCs in their actuated states and releasing the voltage post cure to create in-plane residual stresses. The minimization of total potential energy with the Rayleigh-Ritz method are used to analytically model the resulting laminate. A finite element analysis is conducted in MSC Nastran using the piezoelectric-thermal analogy approach to verify the analytical results. The effects of adhesive properties, bonding cure cycles, MFC layup, and its geometry on the curvatures, displacements, and bifurcation voltages are characterized. Finally, the snap through and reverse snap through capabilities with piezoelectric actuation are demonstrated. This adaptive laminate functions as both the actuator and the primary structure and allows large deformations under a non-continuous energy input. Its snap through capability allows full configuration control necessary in morphing applications.

Active Fluid Flow Control (AFFC) has received great research attention due to its significant potential in engineering applications. It is known that drag reduction, turbulence management, flow separation delay and noise suppression through active control can result in significantly increased efficiency of future commercial transport vehicles and gas turbine engines. In microfluidics systems, AFFC has mainly been used to manipulate fluid passing through the microfluidic device. We put forward a conceptual approach for fluid flow manipulation by coupling multiple vibrating structures through flow interactions in an otherwise quiescent fluid. Previous investigations of piezoelectric flaps interacting with a fluid have focused on a single flap. In this work, arrays of closely-spaced, free-standing piezoelectric flaps are attached perpendicular to the bottom surface of a tank. The coupling of vibrating flaps due to their interacting with the surrounding fluid is investigated in air (for calibration) and under water. Actuated flaps are driven with a harmonic input voltage, which results in bending vibration of the flaps that can work with or against the flow-induced bending. The size and spatial distribution of the attached flaps, and the phase and frequency of the input actuation voltage are the key parameters to be investigated in this work. Our analysis will characterize the electrohydroelastic dynamics of active, interacting flaps and the fluid motion induced by the system.

Distributions of piezoelectric patches bonded to structures provide a means to alter or control, through active or passive means, the dynamic response of the host structure. Numerous active control schemes for such composite structures have been explored. Alternatively, for certain structures, a passive electrical network may be implemented which presents an electrical analog of the modal response of the structure, effectively providing a multi-modal, distributed passive tuned mass modal damper capability. Numerous tuned-mass damper design concepts (“tunings”) may be applied to such a passive network. Further, the distributed network analog, when coupled with active control concepts, permits a hybrid distributed passive-active modal control capability. This paper explores this hybrid distributed network control concept applied to a clamped rectangular plate. A unit-cell discrete representation of the plate leads to an electrical analog comprised of passive inductors, transformers and resistors. Addition of synthetic (or controlled) impedances at a limited set of points within the network permits dynamic adjustment of the frequency response of the system.

This work presents a theoretical study of the effects on stiffness and deflection of embedding piezoelectric fibers within glass fiber reinforced polymer beams. Through this study, enhancements to the beam stiffness and flexural capabilities are analyzed as a result of the piezoelectric effect of the embedded piezoelectric fibers. Fiber orientation of glass fiber reinforced polymer laminated beams is optimized based on stiffness requirements following classical lamination theory. The piezoelectric effect on the glass fiber reinforced polymer beam is analyzed for simply-supported mechanical boundary conditions. The symmetric unidirectional general stacking sequence laminates are shown to have optimal stiffness and deflection behavior. The addition of piezoelectric fibers with d₃₃₃ piezoelectric actuation mode further increases stiffness and reduces deflection. This enables tuning of the mechanical properties of the laminate beam. Introducing piezoelectric fibers to the reinforcing phase further optimizes the deflection range under bending while additionally minimizing the weight of the structure. The strengthening effect of the piezoelectric fibers can reduce the required number of laminate layers while maintaining optimal behavior.

To assist surgeons and physicians in percutaneous needle based interventional procedures, a shape memory alloy (SMA) actuated smart needle has been developed. A promising approach for surgeons and physicians to accurately reach target locations in soft tissues is to use flexible active needles in surgical procedures such as brachytherapy and sample biopsy. In the past decade, for an enhanced flexibility of needles, different methods have been proposed. These methods include bevel-tip needles, kinked needles and flexure-based needles. After inserting these needles into soft materials, a curved path was aimed to achieve instead of common straight path. The focus of this study is another control approach of achieving a desired curved path. In this study, the needle body is attached with a SMA actuator close the needle tip that when actuated bends the needle, and thereby leads to a curved path inside soft tissue. As an experiment, a prototype of the SMA actuated needle has been developed and the behaviors of the needle have been evaluated in two different environments: air, and a tissue-mimicking gel.

As one of the most crucial part of the unmanned underwater vehicle (UUV), the composite propeller plays an important role on the UUV’s performance. As the composite propeller behaves excellent properties in hydroelastic facet and acoustic suppression, it attracts increasing attentions all over the globe. This paper goes a step further based on this idea, and comes up with a novel concept of “morphing composite propeller” (MCP) to improve the performance of the conventional composite propeller (CCP) to anticipate the improved propeller can perform better to propel the UUV. Based on the new concept, a novel MCP is designed. Each blade of the propeller is assembled with an active rotatable flap (ARF) to change the blade’s local camber with flap rotation. Then the transmission mechanism (TM) has been designed and housed in the propeller blade to push the ARF. With the ARF rotating, the UUV can be propelled by different thrusts under certain rotation velocities of the propeller. Based on the design, the Fluent is exploited to analyze the fluid dynamics around the propeller. Finally, based on the design and hydrodynamic analysis, the structural response for the novel morphing composite propeller is calculated. The propeller blade is simplified and layered with composite materials. And the structure response of an MCP is obtained with various rotation angle under the hydrodynamic pressure. This simulation can instruct the design and fabrication techniques of the MCP.

This study is concerned with the activation energy threshold of bistable composite plates in order to tailor a bistable system for specific aeronautical applications. The aim is to explore potential configurations of the bistable plates and their dynamic behavior for designing novel morphing structure suitable for aerodynamic surfaces and, as a possible further application, for power harvesters. Bistable laminates have two stable mechanical shapes that can withstand aerodynamic loads without additional constraint forces or locking mechanisms. This kind of structures, when properly loaded, snap-through from one stable configuration to another, causing large strains that can also be used for power harvesting scopes. The transition between the stable states of the composite laminate can be triggered, in principle, simply by aerodynamic loads (pilot, disturbance or passive inputs) without the need of servo-activated control systems. Both numerical simulations based on Finite Element models and experimental testing based on different activating forcing spectra are used to validate this concept. The results show that dynamic activation of bistable plates depend on different parameters that need to be carefully managed for their use as aircraft passive wing flaps.

A major technological driver in current aircraft and other vehicles is the improvement of fuel efficiency. One way to increase the efficiency is to reduce the skin friction drag on these vehicles. This experimental study presents an active drag reduction technique which decreases the skin friction using spanwise traveling waves. A novel method is introduced for generating traveling waves which is low-profile, non-intrusive, and operates under various flow conditions. This wave generation method is discussed and the resulting traveling waves are presented. These waves are then tested in a low-speed wind tunnel to determine their drag reduction potential. To calculate the drag reduction, the momentum integral method is applied to turbulent boundary layer data collected using a pitot tube and traversing system. The skin friction coefficients are then calculated and the drag reduction determined. Preliminary results yielded a drag reduction of ≈ 5% for 244Hz traveling waves. Thus, this novel wave generation method possesses the potential to yield an easily implementable, non-invasive drag reduction technology.

To meet the requirements for the next generation of space missions, a paradigm shift is required from current structures that are static, heavy and stiff, toward innovative structures that are adaptive, lightweight, versatile, and intelligent. A novel morphing structure, the thermally actuated anisogrid morphing boom, can be used to meet the design requirements by making the primary structure actively adapt to the on-orbit environment. The anisogrid structure is able to achieve high precision morphing control through the intelligent application of thermal gradients. This active primary structure improves structural and thermal stability performance, reduces mass, and enables new mission architectures. This effort attempts to address limits to the author's previous work by incorporating the impact of thermal coupling that was initially neglected. This paper introduces a thermally isolated version of the thermal morphing anisogrid structure in order to address the thermal losses between active members. To evaluate the isolation design the stiffness and thermal conductivity of these isolating interfaces need to be addressed. This paper investigates the performance of the thermal morphing system under a variety of structural and thermal isolation interface properties.

Metamaterial possesses a number of attractive features such as frequency filtering, wave guiding, wave focusing, etc. Conventionally, the realization of metamaterial is through the careful design of unit-cell of a mechanical structure which typically exhibits spatial periodicity. In this research, we propose the development of adaptive metamaterial beams with coupled circuits between adjacent piezoelectric transducers to realize multi-targeted bandgaps. To characterize the wave propagation attenuation, a numerical model based on the transfer matrix method and Bloch theory is formulated to predict the complex band structure of the infinite periodic structure. It is shown theoretically that three separate bandgaps can be generated compared to only one in the conventional LC-shunt since three resonating loops can be formed in the circuit due to the coupling effect. Consequently, wave propagation or vibration can be suppressed effectively inside those bandgap frequencies when the structure is subjected to vibration sources with multiple frequency components.

In this paper, some numerical tools for dispersion analysis of periodic structures are presented, with a focus on the ability of the methods to deal with dissipative behaviour of the systems. An adaptive phononic crystal based on the combination of metallic parts and highly dissipative polymeric interface is designed. The system consists in an infinite periodic bidirectional waveguide. The periodic cylindrical pillars include a layer of shape memory polymer and Aluminum. The mechanical properties of the polymer depend on both temperature and frequency and can radically change from glassy to rubbery state, with various combination of high/low stiffness and high/low dissipation. A fractional derivative Zener model is used for the description of the frequency-dependent behaviour of the polymer. A 3D finite element model of the cell is developed for the design of the metamaterial. The ”Shifted-Cell Operator” technique consists in a reformulation of the PDE problem by ”shifting” in terms of wave number the space derivatives appearing in the mechanical behaviour operator inside the cell, while imposing continuity boundary conditions on the borders of the domain. Damping effects can easily be introduced in the system and a quadratic eigenvalue problem yields to the dispersion properties of the periodic structure. In order to validate the design and the adaptive character of the metamaterial, results issued from a full 3D model of a finite structure embedding an interface composed by a distributed set of the unit cells are presented. Various driving temperature are used to change the behaviour of the system. After this step, a comparison between the results obtained using the tunable structure simulation and the experimental results is presented. Two states are obtained by changing the temperature of the polymeric interface: at 25°C, the bandgap is visible around a selected frequency. Above the glass transition, the phononic crystal tends to behave as an homogeneous plate.

A Helmholtz resonator is a passive acoustic resonator classically used to control a single frequency resulting from the cavity volume and the resonator neck size. The aim of the proposed study is to present a new concept and strategy allowing real-time tunability of the Helmholtz resonator in order to enhance acoustic absorption performances at low frequencies (< 500 Hz). The proposed concept consists in replacing the resonator rigid front plate by an electroactive polymer (EAP) membrane. The first proposed strategy consists on a change in the mechanical properties of the membrane resulting from the applied electric field. This induces a resonance frequency shift. A second strategy is based on a well-located spring, which could direct the membrane deformation following the axis of the resonator to obtain a cavity volume variation. Both strategies allow variation of the resonance frequency of the device. Experimental measurements are performed to determine the potential of this concept for improvement of low-frequency performances of the acoustic devices.

In most aviation applications, a major cost benefit can be achieved by a reduction of the system weight. Often the acoustic properties of the fuselage structure are not in the focus of the primary design process, too. A final correction of poor acoustic properties is usually done using insulation mats in the chamber between the primary and secondary shell. It is plausible that a more sophisticated material distribution in that area can result in a substantially reduced weight. Topology optimization is a well-known approach to reduce material of compliant structures. In this paper an adaption of this method to acoustic problems is investigated. The gap full of insulation mats is suitably parameterized to achieve different material distributions. To find advantageous configurations, the objective in the underlying topology optimization is chosen to obtain good acoustic pressure patterns in the aircraft cabin. An important task in the optimization is an adequate Finite Element model of the system. This can usually not be obtained from commercially available programs due to the lack of special sensitivity data with respect to the design parameters. Therefore an appropriate implementation of the algorithm has been done, exploiting the vector and matrix capabilities in the MATLABQ environment. Finally some new aspects of the Finite Element implementation will also be presented, since they are interesting on its own and can be generalized to efficiently solve other partial differential equations as well.

In this paper the structural behavior of reinforced concrete (RC) beams with smart rebars under three point loading system has been numerically studied, using Finite Element Method. The material used in this study is Superelastic Shape Memory Alloy (SE SMA) which contains nickel and titanium. Shape memory alloys (SMAs) are a unique class of materials which have ability to undergo large deformation and also regain their un-deformed shape by removal of stress or by heating. In this study, a uniaxial SMA model is able to reproduce the pseudo-elastic behavior for the reinforcing SMA wires. Finite element simulation is developed in order to study the load-deflection behavior of smart concrete beams subjected to three-point bending tests.

An artificial muscle for a human arm-like manipulator with high strain and high power density are under development, and an SMA(Shape memory alloy) spring is a good actuator for this application. In this study, an artificial muscle composed of a silicon tube and a bundle of SMA(Shape memory alloy) springs is evaluated. A bundle of SMA springs consists of five SMA springs which are fabricated by using SMA wires with a diameter of 0.5 mm, and hot and cool water actuates it by heating and cooling SMA springs. A faucet-like valve was also developed to mix hot water and cool water and control the water temperature. The mass of silicon tube and a bundle of SMA springs is only 3.3 g and 2.25 g, respectively, and the total mass of artificial muscle is 5.55 g. It showed good actuating performance for a load with a mass of 2.3 kg and the power density was more than 800 W/kg for continuous valve switching with a cycle of 0.6 s. The faucet-like valve can switch a water output from hot water to cold water within 0.3s, and the artificial muscle is actuated well in response to the valve position and speed. It is also presented that the temperature of the mixed water can be controlled depending on the valve position, and the displacement of the artificial muscle can be controlled well by the mixed water. Based on these results, SMA spring-based artificial muscle actuated by hot and cool water could be applicable to the human arm-like robot manipulators.

The new era in energy-efficiency building is to integrate automatic occupancy detection with automated heating, ventilation and cooling (HVAC), the largest source of building energy consumption. By closing off some air vents, during certain hours of the day, up to 7.5% building energy consumption could be saved. In the past, smart vent has received increasing attention and several products have been developed and introduced to the market for building energy saving. For instance, Ecovent Systems Inc. and Keen Home Inc. have both developed smart vent registers capable of turning the vent on and off through smart phone apps. However, their products do not have on-board occupancy sensors and are therefore open-loop. Their vent control was achieved by simply positioning the vent blade through a motor and a controller without involving any smart actuation. This paper presents an innovative approach for automated vent control and automatic occupancy (human subjects) detection. We devise this approach in a smart register that has polydimethylsiloxane (PDMS) frame with embedded Shape memory alloy (SMA) actuators. SMAs belong to a class of shape memory materials (SMMs), which have the ability to ‘memorise’ or retain their previous form when subjected to certain stimulus such as thermomechanical or magnetic variations. And it can work as actuators and be applied to vent control. Specifically, a Ni-Ti SMA strip will be pre-trained to a circular shape, wrapped with a Ni-Cr resistive wire that is coated with thermally conductive and electrically isolating material. Then, the SMA strip along with an antagonistic SMA strip will be bonded with PZT sensor and thermal sensors, to be inserted into a 3D printed mould which will be filled with silicone rubber materials. In the end, a demoulding process yields a fully integrated blade of the smart register. Several blades are installed together to form the smart register. The PZT sensors can feedback the shape of the actuator for precise shape and air flow control. The performance and the specification of the smart registers will be characterized experimentally. Its capacity of regulating airflow, forming air curtain will be demonstrated.

In this paper, we present modeling and characterization of coiled SMA spring actuators that are fabricated by coiling cylindrical SMA wires on to a threaded screw mandrel and applying heat treatment. Here, we evaluate a theoretical model that describes the actuation behavior of SMA coiled springs based on the constitutive model of SMA. We have experimentally verified the developed theoretical model and analyzed various parameters with respect to temperature change during actuation. The model was coded in Simulink® and the effects of various parameters with respect to temperature change were investigated. Simulations were compared with experiments and good agreement was obtained. We also show, how the high tension winding of SMA on the mandrel help in better performance and understanding of the fabricated coiled SMAs.

Brachytherapy is one of the most effective modalities for treating early stage prostate cancer. In this procedure, radioactive seeds are being placed in the prostate to kill the tumorous cells. Inaccurate placement of seeds can underdose the tumor and dangerously overdose the critical structures (urethra, rectum, bladder) and adjacent healthy tissues. It is very difficult, if not impossible, for the surgeons to compensate the needle misplacement errors while using the conventional passive straight needles. The smart needles actuated by shape memory alloy (SMA) wires are being developed to provide more actuation and control for the surgeons to achieve more geometric conformity. In our recent work, a prototype of a smart needle was developed where not only the actuation of SMA wires were incorporated, but also shape memory polymers (SMPs) were included in the design introducing a soft joint element to further assist the flexibility of the active surgical needles. The additional actuation of shape memory polymers provided the capability of reaching much high flexibility that was not achievable before. However, there are some disadvantages using this active SMP component compared to a passive Nylon joint component that are discussed in this work. The utilization of a heated SMP as a soft joint showed about 20% improvement in the final needle tip deflection. This work presents the finite element studies of the developed prototype. A finite element model that could accurately predict the behavior of the smart needle could be very valuable in analyzing and optimizing the future novel designs.

This work addresses two issues in lightweight structural composites suitable for aerospace systems. The first is to add additional functionality to multifunctional composites and the second is to provide damping in structures that cover a wide range of frequencies and temperatures. Passive damping in all materials suffer from failing at certain temperature and in certain frequency ranges. The extreme environments often seen by aerospace structures provide high temperature, which is exactly where damping levels in structures reduce causing unacceptable vibrations. In addition, as loading frequencies decrease damping levels fall off, and many loads experienced by aerospace structures are low frequency. This work looks at the implementation of a control system to a longitudinal metastructure bar. A metastructure is a structure which has distributed vibration absorbers which provide passive damping to the system. The active control system will be implemented by adding piezoelectric materials to one of the absorbers to make the absorber active. The structure with the active vibration absorber will be compared to a structure of equal weight with no active components. Since the two comparison structures are of equal weight, the performance improvements are strictly due to the control system and not at the cost of additional weight.

We present a metamaterial beam based on a piezoelectric bimorph with segmented electrodes. Previously, we found the theoretical response of the beam using the assumed-modes method, and derived the effect of the shunt circuit impedance applied to each pair of electrodes. The structural response is governed by a frequency- dependent stiffness term, which depends on a material/geometry-based electromechanical coupling parameter and the impedance of the shunt circuits. A simple way to interpret the response of the system with frequency- dependent stiffness is the root locus method, which immediately yields the poles of each mode of the system using simple geometric rules. Case studies are shown for creating locally resonant bandgap with or without negative capacitance. To justify the use of these admittances that often require power input to the system, the concept of synthetic impedance is extended to symmetric voltages, as are encountered in series-connected piezoelectric bimorphs. Synthetic impedance or admittance is a method for obtaining an arbitrary impedance across a load by measuring the voltage and applying the corresponding current using digital signal processing and an analog circuit. Time domain simulations using these synthetic impedance circuits are compared to the ideal frequency domain results with good agreement. Surprisingly, the necessary digital sampling rate for stability is significantly higher than the Nyquist frequency.

In this paper, a tunable metamaterial consisting of periodic layers of steel, polyurea and piezoelectric ceramic transducer (PZT) was presented. The PZT layer in this structure was connected to an inductor L. Transfer matrix method was used to calculate the band structure of the sample. It was observed that an extremely narrow stop band was induced by the PZT layer with inductor L. This narrow stop band was attributed to the resonance circuit constituted by the piezoelectric layer, for the piezoelectric layer with electrodes could be seen as a capacitor. Further, homogenization was used to calculate the effective elastic constants of the sample. Results showed that the effective parameters of this structure behaved negative in the narrow stop band. The location of the narrow stop band was in the charge of inductor L, which could be used to design acoustic filters or noise insulators by changing the parameters of structure.

In this research, we present a novel approach to achieve adaptive nonreciprocal wave propagation by exploiting the concept of metastable modular metastructures or metamaterials. Numerical studies on a 1D metastable chain provide clear evidence that such unconventional wave transmission characteristics is facilitated through both nonlinearity and spatial asymmetry of strategically configured constituents. Due to a synergistic product of assembling together metastable modules, modules that exhibit coexisting stable states for the same topology, recent investigations have demonstrated remarkable programmability of properties afforded via transitioning amongst these metastable states. In the context of wave transmission, such massive property adaptation provides unprecedented bandgap tuning opportunities and therefore enables the adaptivity of nonreciprocal wave propagation. In addition to metastable states, influence of wave amplitude and frequency on the existence and adaptation of nonreciprocal wave transmission is also parametrically explored. Overall, this investigation elucidates the rich dynamics achievable by nonlinearity and metastabilities, and creates a new class of adaptive structural and material systems capable of achieving tunable bandgaps and nonreciprocal wave transmissions.

In this contribution, we explore the use of locally resonant metamaterials for multi-functional structural load- bearing concepts using analytical, numerical, and experimental techniques. Locally resonant metamaterials exhibit bandgaps at wavelengths much larger than the lattice dimension. This is a promising feature for low- frequency vibration attenuation. The presented work aims to investigate highly integrated structural concepts and experimentally validated prototypes for vibration reduction in load-bearing applications. The goal is to explore and extend the design space of lightweight structural systems, by designing multi-functional periodic structural elements, preserving structural stiffness while concurrently enabling sufficiently wideband damping performance over a target frequency range of interest. Following a generalized theoretical modeling framework for bandgap design and analysis in finite structures, the focus is placed on the design, fabrication, and analysis of a load-carrying frame development with internally resonant components. Finite-element modeling is employed to design and analyze the frequency response of the frame and simplified analytical solution is compared with this numerical solution. Experimental validations are presented for a 3D-printed prototype. The effects of various parameters are reported both based on numerical and experimental findings.

Earthworms possess extraordinary on-ground and underground mobility, which inspired researchers to mimic their morphology characteristics and locomotion mechanisms to develop crawling robots. One of the bottlenecks that constrain the development and wide-spread application of earthworm-like robots is the process of design, fabrication and assembly of the robot frameworks. Here we present a new earthworm-like robot design and prototype by exploring and utilizing origami ball structures. The origami ball is able to antagonistically output both axial and radial deformations, similar as an earthworm’s body segment. The origami folding techniques also introduce many advantages to the robot development, including precise and low cost fabrication and high customizability. Starting from a flat polymer film, we adopt laser machining technique to engrave the crease pattern and manually fold the patterned flat film into an origami ball. Coupling the ball with a servomotor-driven linkage yields a robot segment. Connecting six segments in series, we obtain an earthworm-like origami robot prototype. The prototype is tested in a tube to evaluate its locomotion performance. It shows that the robot could crawl effectively in the tube, manifesting the feasibility of the origami-based design. In addition, test results indicate that the robot’s locomotion could be tailored by employing different peristalsis-wave based gaits. The robot design and prototype reported in this paper could foster a new breed of crawling robots with simply design, fabrication, and assemble processes, and improved locomotion performance.

Skeletal muscle mechanics exhibit a range of noteworthy characteristics, providing great inspiration for the development of advanced structural and material systems. These characteristics arise from the synergies demonstrated between muscle’s constituents across the various length scales. From the macroscale oblique orientation of muscle fibers to the microscale lattice spacing of sarcomeres, muscle takes advantage of geometries and multidimensionality for force generation or length change along a desired axis. Inspired by these behaviors, this research investigates how the incorporation of multidimensionality afforded by oblique, pennate architectures can uncover novel mechanics in structures exhibiting multistability. Experimental investigation of these mechanics is undertaken using specimens of molded silicone rubber with patterned voids, and results reveal tailorable mono-, bi-, and multi-stability under axial displacements by modulation of transverse confinement. If the specimen is considered as an architected material, these results show its ability to generate intriguing, non-monotonic shear stresses. The outcomes would foster the development of novel, advanced mechanical metamaterials that exploit pennation and multidimensionality.

Bio-implantable medical devices need a reliable and stable source of power to perform effectively. Although batteries can be the first candidate to power implantable devices as they provide high energy density, they cannot supply power for long periods of time and therefore, they must be periodically replaced or recharged. Battery replacement is particularly difficult as it requires surgery. In this paper, we develop a micromachined ultrasonic power generating receiver with a size of 3.5mmx3.5mm capable of providing sufficient power for implantable medical devices. The ultrasound receiver takes the form of a unimorph diaphragm consisting of PZT on silicon. We dice bulk PZT with a thickness of 127 μm and bond the diced pieces to a silicon wafer. In order to get a 50 μm thick PZT layer, which is needed for optimal power transfer, we mechanically lap and polish the bonded PZT. We numerically investigate the performance of the fabricated receiver with inner and outer electrodes on the surface of the PZT. Using COMSOL simulations, we analyze the effect of different sizes of inner and outer electrodes under the actuation of the inner electrode in order to find the optimum electrode sizes. We show that when the transmitter is generating an input power less than Food and Drug Administration limits, the receiver can provide sufficient voltage and power for many implantable devices. Furthermore, the process developed can be used to fabricate significantly smaller devices than the one characterized, which enables further miniaturization of bio-implanted systems.

This study utilize the simple fabrication method for graphene oxide (GO) sheet preparation, their controllable modification using surface initiated atom transfer radical polymerization (SI-ATRP) technique and thus suitable interaction with elastomeric matrix for final enhancement and controlling of the sensing capability upon light stimulus. GO particles and their grafted analogues were characterized by Fourier transform infrared spectroscopy, Thermogravimetric analysis and Raman spectroscopy to properly see the controllable coating as well as reduction of GO during the single-step synthesis. The composites containing various amounts of GO, controllably modified GO and elastomeric matrix poly(vinylidene-co-hexafluoropropylene) elastomer were characterized by dynamic mechanical analysis and thermal conductivity. The phenomenon how the GO and modified GO particles influence the mobility of the polymer chains and thermal conductivity will be investigated. The impact on change of the material properties with respect to the light-responsive and sensing capabilities is discussed.

This article proposes a framework for determining the types of nonlinearity observed in the frequency response of microscale energy harvesters made of a piezoelectric film deposited on a stainless-steel substrate. The model accounts for inertial, geometrical and material nonlinearities due to amplified excitation and induced hysteresis. The simulations based on the multiple scale analysis reveals the softening type of nonlinearity for the case of a 15 μm PZT thick film deposited on a 60 μm stainless-steel substrate. They agree quite well with the experimental observations. In addition, the further investigation shows the existence of the critical film thickness such that the hardening (softening) nonlinearity is observed if the film thickness is below (above) this critical value. It is also found that such a key parameter is mainly affected by the ratio of the bending stiffness due to material nonlinearity to that based on linear moduli. Finally, the hardening type of nonlinearity was also observed in different samples with very small film thickness, as predicted by the proposed framework.

Effective development of vibration energy harvesters is required to convert ambient kinetic energy into useful electrical energy as power supply for sensors, for example in structural health monitoring applications. Energy harvesting structures exhibiting bistable nonlinearities have previously been shown to generate large alternating current (AC) power when excited so as to undergo snap-through responses between stable equilibria. Yet, most microelectronics in sensors require rectified voltages and hence direct current (DC) power. While researchers have studied DC power generation from bistable energy harvesters subjected to harmonic excitations, there remain important questions as to the promise of such harvester platforms when the excitations are more realistic and include both harmonic and random components. To close this knowledge gap, this research computationally and experimentally studies the DC power delivery from bistable energy harvesters subjected to such realistic excitation combinations as those found in practice. Based on the results, it is found that the ability for bistable energy harvesters to generate peak DC power is significantly reduced by introducing sufficient amount of stochastic excitations into an otherwise harmonic input. On the other hand, the elimination of a low amplitude, coexistent response regime by way of the additive noise promotes power delivery if the device was not originally excited to snap-through. The outcomes of this research indicate the necessity for comprehensive studies about the sensitivities of DC power generation from bistable energy harvester to practical excitation scenarios prior to their optimal deployment in applications.

Energy harvesting employing non-linear systems offers considerable advantages over linear systems given the broadband resonant response which is favorable for applications involving diverse input vibrations. In this respect, the rich dynamics of bi-stable systems present a promising means for harvesting vibrational energy from ambient sources. Harvesters deriving their bi-stability from thermally induced stresses as opposed to magnetic forces are receiving significant attention as it reduces the need for ancillary components and allows for bio- compatible constructions. However, the design of these bi-stable harvesters still requires further optimization to completely exploit the dynamic behavior of these systems. This study presents a comparison of the harvesting capabilities of non-magnetic, bi-stable composite laminates under variations in the design parameters as evaluated utilizing established power metrics. Energy output characteristics of two bi-stable composite laminate plates with a piezoelectric patch bonded on the top surface are experimentally investigated for variations in the thickness ratio and inertial mass positions for multiple load conditions. A particular design configuration is found to perform better over the entire range of testing conditions which include single and multiple frequency excitation, thus indicating that design optimization over the geometry of the harvester yields robust performance. The experimental analysis further highlights the need for appropriate design guidelines for optimization and holistic performance metrics to account for the range of operational conditions.

Many vibration energy harvesters have been developed in the past to harvest energy from rotating systems. Yet most of these harvesters are linear resonance-based harvesters whose output power drops dramatically under random excitation. This poses a serious problem because a lot of vibrations of rotating systems are stochastic. In this paper, an advanced energy harvesting mechanism is proposed to magnify power output when the excitation is random. Large power output can be produced with stochastic resonance by inputting weak periodic signal and noise excitation into a bistable system. Stick-slip and whirling vibrations which are inherently existing in various rotating shaft systems, are used to make periodic signal and noise excitation. Energy harvester with external magnet was used to compensate biased periodic force from rotating shaft. The proposed energy harvesting approach is particularly useful for high friction and low speed application such as oil drilling. Detailed analysis is conducted to prove the effectiveness of the proposed energy harvesting concept. In addition, experiments were performed to verify the feasibility of this energy harvesting strategy.

To enhance the output power and broaden the operation bandwidth of vibration energy harvesters (VEH), nonlinear two degree-of-freedom (DOF) energy harvesters have attracted wide attention recently. In this paper, we investigate the performance of a nonlinear VEH with magnetically coupled dual beams and compare it with the typical Duffing-type VEH to find the advantages and drawbacks of this nonlinear 2-DOF VEH. First, based on the lumped parameter model, the characteristics of potential energy shapes and static equilibriums are analyzed. It is noted that the dual beam configuration is much easy to be transformed from a mono-stable state into a bi-stable state when the repulsive magnet force increases. Based on the equilibrium positions and different kinds of nonlinearities, four nonlinearity regimes are determined. Second, the performance of 1-DOF and 2-DOF configurations are compared respectively in these four nonlinearity regimes by simulating the forward sweep responses of these two nonlinear VEHs under different acceleration levels. Several meaningful conclusions are obtained. First, the main alternative to enlarge the operation bandwidth for dual-beam configuration is chaotic oscillation, in which two beams jump between two stable positions chaotically. However, the large-amplitude periodic oscillations, such as inter-well oscillation, cannot take place in both piezoelectric and parasitic beams at the same time. Generally speaking, both of the magnetically coupled dual-beam energy harvester and Duffingtype energy harvester, have their own advantages and disadvantages, while given a large enough base excitation, the maximum voltages of these two systems are almost the same in all these four regimes.

Non-harmonic excitations are widely available in the environment of our daily life. We could make use of these excitations to pluck piezoelectric energy harvesters. Plucking piezoelectric energy harvesting could overcome the frequency gap and achieve frequency-up effect. However, there has not been a thorough analysis on plucking piezoelectric energy harvesting, especially with good understanding on the plucking mechanism. This paper is aimed to develop a model to investigate the plucking mechanism and predict the responses of plucking piezoelectric energy harvesters under different kinds of excitations. In the electromechanical model, Hertzian contact theory is applied to account for the interaction between the plectrum and piezoelectric beam. The plucking mechanism is clarified as a cantilever beam impacted by an infinitely heavy mass, in which the multi-impact process prematurely terminates at separation time. We numerically predict the plucking force, which depends on piezoelectric beam, Hertzian contact stiffness, overlap area and plucking velocity. The energy distribution is investigated with connected resistor.

Interest in clean, stable, and renewable energy harvesting devices has increased dramatically with the volatility of petroleum markets. Specifically, research in aero/hydro kinetic devices has created numerous new horizontal and vertical axis wind turbines, and oscillating wing turbines. Oscillating wing turbines (OWTs) differ from their wind turbine cousins by having a rectangular swept area compared to a circular swept area. The OWT systems also possess a lower tip speed that reduces the overall noise produced by the system. OWTs have undergone significant computational analysis to uncover the underlying flow physics that can drive the system to high efficiencies for single wing oscillations. When two of these devices are placed in tandem configuration, i.e. one placed downstream of the other, they either can constructively or destructively interact. When constructive interactions occurred, they enhance the system efficiency to greater than that of two devices on their own. A new experimental design investigates the dependency of interaction modes on the pitch stiffness of the downstream wing. The experimental results demonstrated that interaction modes are functions of convective time scale and downstream wing pitch stiffness. Heterogeneous combinations of pitch stiffness exhibited constructive and destructive lock-in phenomena whereas the homogeneous combination exhibited only destructive interactions.

Vibration energy harvesting has been shown as a promising power source for many small-scale applications mainly because of the considerable reduction in the energy consumption of the electronics, ease of fabrication and implementation of smart materials at small scale, and scalability issues of the conventional batteries. However, conventional energy harvesters are not quite robust to changes in excitation or system parameters, suffer from narrow bandwidth, and are very inefficient at small scale for low frequency harvesting. In addition, they have a low power to volume ratio. To remedy the robustness issues, improve their effectiveness, and increase their power density, we propose to exploit structural instabilities, in particular instabilities in multi-layered composites which are inherently non-resonant. The induced large strains as a result of the structural instability could be exploited to give rise to large strains in an attached piezoelectric layer to generate charge and, hence, energy. The regular high-strain morphological patterns occur throughout the whole composite structure that in turn enable harvesting at a larger volume compared to conventional harvesters; hence, harvesting via structural instabilities can significantly improve the harvested power to volume ratio. In this study, we focus on harvesting from wrinkling type of instabilities.

We explore the potential of human-scale motion energy harvesting toward enabling self-powered wearable electronic components to avoid the burden of battery replacement and charging in next-generation wireless applications. The focus in this work is piezoelectric transduction for converting human motion into electricity. Specifically, we explore three piezoelectric energy harvesting approaches experimentally and numerically: (1) Direct base excitation of a cantilevered bimorph configuration without/with a tip mass; (2) plucking of a bimorph cantilever using a flexible/nonlinear plectrum; and (3) direct force excitation of a curved unimorph. In all cases, electromechanical models are developed and experimental validations are also presented. Specifically a nonlinear plectrum model is implemented for the plucking energy harvester. Average power outputs are on the order 10-100 uW and can easily exceed mW in certain cases via design optimization.

In this paper, we investigate the feasibility of energy harvesting from the mouse click motion using a piezoelectric energy transducer. Specifically, we use a robotic finger to realize repeatable mouse click motion. The robotic finger wears a glove with a pocket for including the piezoelectric material as an energy transducer. We propose a model for the energy harvesting system through the inverse kinematic framework of parallel joints in the finger and the electromechanical coupling equations of the piezoelectric material. Experiments are performed to elucidate the effect of the load resistance and the mouse click motion on energy harvesting.

A power-generated magnetorheological (MR) damper with integrating a controllable damping mechanism and a power-generation mechanism is proposed in this paper. The controllable damping mechanism is realized by an annular rotary gap filled with MR fluids working in pure shear mode. The rotary damping moment is transformed to a linear damping force via a ball-screw mechanism. The power-generation mechanism is realized via a permanent magnet rotor and a stator with winding coils, which transforms the vibration energy of the system into electric power or directly to power the controllable damping mechanism. The characteristics of the controllable damping force and the power-generated performance are theoretically analyzed and experimentally tested.

With increasing popularity of portable devices for outdoor activities, portable energy harvesting devices are coming into spot light. The next generation energy harvester which is called hybrid energy harvester can employ more than one mechanism in a single device to optimize portion of the energy that can be harvested from any source of waste energy namely motion, vibration, heat and etc. In spite of few recent attempts for creating hybrid portable devices, the level of output energy still needs to be improved with the intention of employing them in commercial electronic systems or further applications. Moreover, implementing a practical hybrid energy harvester in different application for further investigation is still challenging. This proposal is projected to incorporate a novel approach to maximize and optimize the voltage output of hybrid energy harvesters to achieve a greater conversion efficiency normalized by the total mass of the hybrid device than the simple arithmetic sum of the individual harvesting mechanisms. The energy harvester model previously proposed by Larkin and Tadesse [1] is used as a baseline and a continuous unidirectional rotation is incorporated to maximize and optimize the output. The device harvest mechanical energy from oscillatory motion and convert it to electrical energy through electromagnetic and piezoelectric systems. The new designed mechanism upgrades the device in a way that can harvest energy from both rotational and linear motions by using magnets. Likewise, the piezoelectric section optimized to harvest at least 10% more energy. To the end, the device scaled down for tested with different sources of vibrations in the immediate environment, including machinery operation, bicycle, door motion while opening and closing and finally, human motions. Comparing the results from literature proved that current device has capability to be employed in commercial small electronic devices for enhancement of battery usage or as a backup power source. [1] Larkin, Miles, and Yonas Tadesse. "HM-EH-RT: hybrid multimodal energy harvesting from rotational and translational motions." International Journal of Smart and Nano Materials 4.4 (2013): 257-285.

In this manuscript, we investigate the use topology optimization to design planar resonators with modal fre- quencies that occur at 1 : n ratios for kinetic energy scavenging of ambient vibrations that exhibit at least two frequency components. Furthermore, we are interested in excitations with a fundamental component containing large amounts of energy and secondary component with smaller energy content. This phenomenon is often seen in rotary machines; their frequency spectrum exhibits peaks on multiple harmonics, where the energy is primarily contained in the rotation frequency of the device. Several theoretical resonators are known to exhibit modal frequencies that at integer multiples 1:2 or 1:3. However, designing manufacturable resonators for other geometries is still a daunting task. With this goal in mind, we utilize topology optimization to determine the layout of the resonator. We formulate the problem in its non-dimensional form, eliminating the constraint on the allowable frequency. The frequency can be obtained a posteriori by means of linear scaling. Conversely, to previous research, which use the clamped beam as initial guess, we synthesize the final shape starting from a ground structure (or structural universe) and remove of the unnecessary beams from the initial guess by means of a graph-based filtering scheme. The algorithm determines the simplest structure that gives the desired frequency’s ratio. Within the optimization, the structural design is accomplished by a linear FE analysis. The optimization reveals several trends, the most notable being that having members connected orthogonally as in the L-shaped resonator is not the preferred topology of this devices. In order to fully explore the angle of orientation of connected members on the modal characteristics of the device; we derive a reduced-order model that allows a bifurcation analysis on the effect of member orientation on modal frequency. Furthermore, the reduced order approximation is used solve the coupled electro-mechanical equation of a vibration based energy harvester (VEH). Finally, we present the performance of the VEH under various base excitations. These results show an infinite number of topologies that can have integer ratio modal frequencies, and in some cases harvest more power than a nominal L shaped harvester, operating in the linear regime.

In this paper, we explore 3D-printed Gradient-Index Phononic Crystal Lens (GRIN-PCL) for structure-borne focusing both numerically and experimentally. The proposed lens consists of an array of nylon stubs with different heights which is fabricated by 3D printing the PA2200 nylon. The orientation and height of the stubs are determined according to the hyperbolic secant gradient distribution of refractive index which is guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. The fabricated lens is then bonded to an aluminum plate to focus the wave energy in the structure. The wave focusing performance is simulated in COMSOL Multiphysics® under plane wave excitation from a line source indicating that the focal points are consistent with the analytical beam trajectory results. Experiments are conducted with a scanning laser vibrometer and experimentally measured wave field successfully validates the numerical simulation of wave focusing within the 3D-printed GRIN-PCL domain. With a piezoelectric energy harvester disk located at the focal region of the GRIN-PCL larger power output is obtained as compared to the baseline case of energy harvesting without the GRIN-PCL on the uniform plate counterpart for the same incident plane wave excitation.

In this paper, a new type of haptic system for surgical robot application is proposed and its performances are evaluated experimentally. The proposed haptic system consists of an effective master device and a precision slave robot. The master device has 3-DOF rotational motion as same as human wrist motion. It has lightweight structure with a gyro sensor and three small-sized MR brakes for position measurement and repulsive torque generation, respectively. The slave robot has 3-DOF rotational motion using servomotors, five bar linkage and a torque sensor is used to measure resistive torque. It has been experimentally demonstrated that the proposed haptic system has good performances on tracking control of desired position and repulsive torque. It can be concluded that the proposed haptic system can be effectively applied to the surgical robot system in real field.

In this research, a new configuration of bidirectional actuator featuring MR fluid (BMRA) is proposed for haptic application. The proposed BMRA consists of a driving disc, a driving housing and a driven disc. The driving disc is placed inside the driving housing and rotates counter to each other by a servo DC motor and a bevel gear system. The driven shaft is also placed inside the housing and next to the driving disc. The gap between the two disc and the gap between the discs and the housing are filled with MR fluid. On the driven disc, two mutual magnetic coils are placed. By applying currents to the two coils mutually, the torque at the output shaft, which is fixed to the driven disc, can be controlled with positive, zero or negative value. This make the actuator be suitable for haptic application. After a review of MR fluid and its application, configuration of the proposed BMRA is presented. The modeling of the actuator is then derived based on Bingham rheological model of MRF and magnetic finite element analysis (FEA). The optimal design of the actuator is then performed to minimize the mass of the BMRA. From the optimal design result, performance characteristics of the actuator is simulated and detailed design of a prototype actuator is conducted.

In this study, a 7-DOF slave robot integrated with the haptic master is designed and its dynamic motion is controlled. The haptic master is made using a controllable magneto-rheological (MR) clutch and brake and it provides the surgeon with a sense of touch by using both kinetic and kinesthetic information. Due to the size constraint of the slave robot, a wire actuating is adopted to make the desired motion of the end-effector which has 3-DOF instead of a conventional direct-driven motor. Another motions of the link parts that have 4-DOF use direct-driven motor. In total system, for working as a haptic device, the haptic master need to receive the information of repulsive forces applied on the slave robot. Therefore, repulsive forces on the end-effector are sensed by using three uniaxial torque transducer inserted in the wire actuating system and another repulsive forces applied on link part are sensed by using 6-axis transducer that is able to sense forces and torques. Using another 6-axis transducer, verify the reliability of force information on final end of slave robot. Lastly, integrated with a MR haptic master, psycho-physical test is conducted by different operators who can feel the different repulsive force or torque generated from the haptic master which is equivalent to the force or torque occurred on the end-effector to demonstrate the effectiveness of the proposed system.

Due to the attractive potential in elastic wave attenuation and wave guiding, acoustic metamaterials have received much attention. Different from the more conventional metamaterials that possess only mechanical displacement/deformation, the electro-mechanical metamaterials analyzed in this paper utilize the two-way electromechanical coupling of piezoelectric transducers and local resonance induced by LC (inductor-capacitor) shunt circuits, which features enlarged design space as well as adaptivity. We report an adaptive piezoelectric gradient index (GRIN) lens featuring focusing acoustic wave. The proposed GRIN lens is comprised of arrayed piezoelectric unit-cells with individually connected inductive shunt circuits. Taking advantage of wave velocity shifting in the vicinity of local resonant frequency of unit-cell and specifically arranged LC shunt circuits, we can focus the transverse wave adaptively by adjusting the inductive loads, i.e., tuning the inductances. Analytical investigations and finite element simulations are performed. This tunable GRIN lens can be used as acoustic metamaterial for various acoustic devices operating with broadband frequencies.

Vibration energy is one of the most common sources of energy that can be harvested from. Two vibration-to-energy conversion mechanisms are piezoelectric and electromagnetic [1,3]. The vibration of a cantilever beam is a popular method to harvest energy from piezoelectric and electromagnetics. When a cantilever beam vibrates from an external force the beam deflects back and forth. A piezoelectric material produces energy from the strain the beam is under. An electromagnetic array produces energy as a coil that is attached to the beam moves across the magnetic field of the array. More energy can be produced when a coil moves through a larger and more concentrated magnetic field. We propose a two degree of freedom aeroelastic energy harvester that uses a Halbach electromagnetic array and microfiber composite (MFC) piezoelectric patches, shown in Fig. 1. A Halbach array is a specific arrangement of magnets that focuses the magnetic field onto one side of the array while negating the field on the other side [2] whereas a normal alternating array has its magnetic field even distributed both sides of the array. The microfiber composite (MFC) patch is primarily for increasing the stiffness while negligibly increasing the mass of the cantilever beam. Wind tunnel test results are presented to characterize power output and the flutter speed of the energy harvester at different wind speeds. The harvester reaches the flutter speed at 3.5 m/s and operates up to 5 m/s and produces a power of 300 mW. The harvester is compact and fits inside an 8in square duct.

In this paper, a Luneburg lens is explored for omnidirectional structure-borne wave focusing both numerically and experimentally. The proposed lens is formed by radially distributed blind holes with different diameters based on the gradient index phononic crystal theory. The radial orientation and diameter of the holes are determined according to the refractive index distribution which is guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. According to this design, the wave travels slower at the center of the lens and converges at the focal spot which is on the circular lens boundary. Wave simulations are performed in COMSOL Multiphysics® under plane wave excitation from a line source and wave focusing is observed at the opposite border of the lens with respect to the incoming wave direction. Experimentally measured wave fields with a scanning laser vibrometer successfully validate simulated wave focusing. Furthermore, omnidirectionality is verified by testing the lens under plane wave excitation from different directions. With piezoelectric energy harvesters located at the boundary of the Luneburg lens substantially larger power output can be obtained as compared to the baseline case of energy harvesting without the lens on the uniform plate counterpart for the same incident plane wave excitation.

Piezoelectric-based, semi-active vibration reduction approaches have been studied for over a decade due to their potential in controlling vibration over a large frequency range. Previous studies have relied on a discrete model when switching between the stiffness states of the system. In such a modeling approach, the energy dissipation of the stored potential energy and the transient dynamics, in general, are not well understood. In this paper, a switching model is presented using a variable capacitance in the attached shunt circuit. When the switch duration is small in comparison to the period of vibration, the vibration reduction performance approaches that of the discrete model with an instantaneous switch, whereas longer switch durations lead to less vibration reduction. An energy analysis is then performed that results in the appearance of an energy dissipation term due to the varying capacitance in the shunt circuit.

Elastic metamaterials can be used for vibration control where environmental vibrations exist. While, vibration energy harvesters can be designed to harness the environmental vibrations and convert them into useful electricity. These facts inspire us to develop a system with simultaneous vibration suppression and energy harvesting ability by combining them together. A piezoelectric metamaterial beam is presented in this paper to achieve dual functionalities. First, an analytical model of this system is developed and analyzed. Regarding the location of the metamaterial section on the beam, two configurations are proposed and studied. In order to achieve good dual functionalities, covering the beam with the metamaterial section from the free end should be given the priority. A parametric study is then performed to investigate the effect of the number of piezoelectric oscillators on the performance of the system. The result shows that by adding more oscillators, the system performance in terms of both vibration suppression and energy harvesting can be enhanced. Finally, a finite element model is developed with the consideration of implementing a realistic structure. The finite element results are in good agreement with the analytical results.

Since weakly-coupled bladed disks are highly sensitive to the presence of uncertainties, they can easily undergo vibration localization. When vibration localization occurs, vibration modes of bladed disk become dramatically different from those under the perfectly periodic condition, and the dynamic response under engine-order excitation is drastically amplified. In previous studies, it is investigated that amplified vibration response can be suppressed by connecting piezoelectric circuitry into individual blades to induce the damped absorber effect, and localized vibration modes can be alleviated by integrating piezoelectric circuitry network. Delocalization of vibration modes and vibration suppression of bladed disk, however, require different optimal set of circuit parameters. In this research, multi-objective optimization approach is developed to enable finding the best circuit parameters, simultaneously achieving both objectives. In this way, the robustness and reliability in bladed disk can be ensured. Gradient-based optimizations are individually developed for mode delocalization and vibration suppression, which are then integrated into multi-objective optimization framework.

Synchronized Switch Damping control is one of the most interesting solutions for vibration suppression proposed in the last years. It is based on the electromechanical coupling provided by piezoelectric actuators. By connecting the piezoelectric actuator to a shunting circuit (typically a RL one) and properly switching between open and closed circuit, an equivalent hysteresis cycle is created and the structure energy is dissipated. It is known that, in order to maximize the damping effect the resistance of the circuit must be reduced. Anyway, as shown in literature, this effect is limited by the presence of a beating effect when the resistance is lower than a certain threshold. The aim of this paper is to analyse the beating phenomenon in order to propose new solutions to cancel it. The paper will show some innovative solutions modifying the shunting circuit to avoid the beating phenomenon and thus increase the control performance. These solutions will be described from a theoretical point of view and then tested to demonstrate their effect.

A solid mechanical spring generally exhibits uniform stiffness. This paper studies a mechanical spring filled with magnetorheological (MR) fluid to achieve controllable stiffness. The hollow spring filled with MR fluid is subjected to a controlled magnetic field in order to change the viscosity of the MR fluid and thereby to change the overall stiffness of the spring. MR fluid is considered as a Bingham viscoplastic linear material in the mathematical model. The goal of this research is to study the feasibility of such spring system by analytically computing the effects of MR fluid on overall spring stiffness. For this purpose, spring mechanics and MR fluid behavior are studied to increase the accuracy of the analysis. Numerical simulations are also performed to generate some assumptions, which simplify calculations in the analytical part. The accuracy of the present approach is validated by comparing the analytical results to previously known experimental results. Overall stiffness variations of the spring are also discussed for different spring designs.

Semi-active tuned mass dampers (STMDs) with magnetorheological (MR) dampers are becoming promising alternative to passive tuned mass dampers (TMDs) and active tuned mass dampers (ATMDs). In this paper, a new control algorithm for STMDs with acceleration feedback is experimentally evaluated in a laboratory wind tower - nacelle model equipped with a prototype STMD. The control algorithm adopts an existing acceleration feedback control approach which was originally proposed for ATMDs. The STMD consists of a mass, passive springs and an MR damper. The fail-safe operation of the STMD is reported due to both an internal friction of the STMD and a residual force of the MR damper at its off-state. The paper compares the simulated performance of the STMD with the measured performance of the fail-safe STMD under harmonic force excitation and discusses the major deteriorating factors that limit the measured performance. Despite the limitations, the paper reports that at low excitation the fail-safe STMD acts similarly to the TMD with same mass, while already at moderate excitation its performance is almost equally good as that of the TMD with two times larger mass.

This study presents the design, development, testing, and performance evaluation of a scaled bridge bearing utilizing magnetorheological elastomer (MRE) layers as adaptive elements, which allow for a varying stiffness under a magnetic field. The adaptive bridge bearing system incorporates a closed-loop magnetic circuit that results in an enhanced magnetic field in the MRE layers. A new design is introduced and optimized using structural and magnetic finite element analyses. Two bearings and a test setup for applying simultaneous variable shear, constant compression, and a variable magnetic field on the bearing are fabricated. The adaptive bridge bearing results demonstrate the stiffness change of the bearing under different strain levels and loading frequencies, as well as the ability of the bearing to change its stiffness under different applied electric currents, which can be correlated to the applied magnetic field.

The application of origami-inspired designs to engineered structures and materials has been a subject of much research efforts. These structures and materials, whose mechanical properties are directly related to the geometry of folding, are capable of achieving a host of unique adaptive functions. In this study, we investigate a three-dimensional multistability and variable stiffness function of a cellular solid based on the Miura-Ori folding pattern. The unit cell of such a solid, consisting of two stacked Miura-Ori sheets, can be elastically bistable due to the nonlinear relationship between rigid-folding deformation and crease material bending. Such a bistability possesses an unorthodox property: the critical, unstable configuration lies on the same side of two stable ones, so that two different force-deformation curves co-exist within the same range of deformation. By exploiting such unique stability properties, we can achieve a programmable stiffness change between the two elastically stable states, and the stiffness differences can be prescribed by tailoring the crease patterns of the cell. This paper presents a comprehensive parametric study revealing the correlations between such variable stiffness and various design parameters. The unique properties stemming from the bistability and design of such a unit cell can be advanced further by assembling them into a solid which can be capable of shape morphing and programmable mechanical properties.

The trend in future space high precision reflectors is going towards large aperture, lightweight and actively controlled deformable antennas. An adaptive shape control system for a Carbon Fiber Reinforced Composite (CFRC) reflector is conducted by Piezoelectric Ceramic Transducer (PZT) actuators. This adaptive shape control system has been shown to effectively mitigate common low order wave-front error, but it is inevitably plagued by high order wave-front error control. In order to improve the controllability of the adaptive CFRC reflector control system for high order wave-front error, the design of adaptive CFRC reflector requires optimizing further. According to numerical and experimental results, the print-through error induced by manufacturing and PZT actuators actuation is a type of predominant high order wave-front error. This paper describes a design which some secondary rib elements are embedded within the triangular cells of the primary ribs. These small secondary ribs are designed to support the reflector surface’s weak region. Controllability of this new adaptive CFRC reflector control system with small secondary ribs is evaluated by generalized Zernike functions. This new design scheme can reduce high order residual error and suppress the high order wave-front error such as print-through error. Finally, design parameters of the adaptive CFRC reflector control system with small secondary ribs, such as primary rib height, secondary rib height, cut-out height of primary rib, are optimized.

Partial or total upper extremity impairment affects the quality of life of a vast number of people due to stroke, neuromuscular disease, or trauma. Many researchers have presented hand orthosis to address the needs of rehabilitation or assistance on upper extremity function. Most of the devices available commercially and in literature are powered by conventional actuators such as DC motors, servomotors or pneumatic actuators. Some prototypes are developed based on shape memory alloy (SMA) and dielectric elastomers (DE). This study presents a customizable, 3D printed, a lightweight exoskeleton (iGrab) based on recently reported Twisted and Coiled Polymer (TCP) muscles, which are lightweight, provide high power to weight ratio and large stroke. We used silver coated nylon 6, 6 threads to make the TCP muscles, which can be easily actuated electrothermally. We reviewed briefly hand orthosis created with various actuation technologies and present our design of tendon-driven exoskeleton with the muscles confined in the forearm area. A single muscle is used to facilitate the motion of all three joints namely DIP (Distal interphalangeal), PIP (Proximal Interphalangeal) and MCP (Metacarpophalangeal) using passive tendons though circular rings. The grasping capabilities, along with TCP muscle properties utilized in the design such as life cycle, actuation under load and power inputs are discussed.

The requirements for transmission and coupling elements in hybrid powertrains are rising continuously. Our previous investigations were focused on the elimination of viscous induced drag torques in switch elements based on magnetorheological fluids by a MR-fluid movement control. MRFs are highly qualified for the utilization in powertrains considering their particular characteristics of changing their apparent viscosity significantly under influence of a magnetic field by fast switching times and a smooth torque control. In this contribution a further developed design of the magnetic circuit will be presented to reduce the weight and space requirements of energy- efficient MRF-based actuators. These requirements are satisfied by a serpentine flux guidance resulting also in a reduction of the excitation energy. A simulation of the transient torque transmission shows fast response times of the novel design. Due to the new design of the magnetic circuit it is also possible to create novel, space-saving combinations of a MRF-based brake and clutch and a well-defined torque transmission.

An accurate position control is demanded in the current hydraulic lifter used for vehicle maintenance. This work presents a new type of vehicle lifter for precision position control using a magnetorheological valve system. In the first step, the principal design parameters such as gap size of oil passage, length and depth of coil part, and distance coil part from the end of valve are considered to achieve the objective function for getting the highest position accuracy under current input constraint. After determining the optimized design values, the field-dependent pressure drops of the optimized valve system are experimentally evaluated and compared to those obtained from the initial design. Subsequently, the position of the vehicle lifter is controlled by change of pressure drop using a simple PID controller. It is demonstrated that the proposed vehicle lifter can be effectively applied to vehicle service center for more accurate tasks under proper height.

Recently, it is very popular in medical field to adopt robot surgery such as robot-assisted minimally invasive surgery (RMIS). However, there are some problems in the robot surgery. It is very hard to get the touch feeling of the organs during the surgical operation because the surgeons cannot touch and feel repulsive force from the organs directly. So, this work proposes a squeeze mode of single magneto-rheological (MR) sponge to realize viscoelastic property of human organs or skins and undertake a theoretical analysis of MR sponge. In addition, its effectiveness is verified through experimental tests. The similarity between MR sponge and real organs is identified and desired repulsive force of each organs can be achieved by proper selection of MR sponge cell associated with controlled input current.

This paper presents a 7 degrees-of-freedom (7-DOF) haptic master which is applicable to the robot-assisted minimally invasive surgery (RMIS). By utilizing a controllable magneto-rheological (MR) fluid, the haptic master can provide force information to the surgeon during surgery. The proposed haptic master consists of three degrees motions of X, Y, Z and four degrees motions of the pitch, yaw, roll and grasping. All of them have force feedback capability. The proposed haptic master can generate the repulsive forces or torques by activating MR clutch and MR brake. Both MR clutch and MR brake are designed and manufactured with consideration of the size and output torque which is usable to the robotic surgery. A proportional-integral-derivative (PID) controller is then designed and implemented to achieve torque/force tracking trajectories. It is verified that the proposed haptic master can track well the desired torque and force occurred in the surgical place by controlling the input current applied to MR clutch and brake.

This study aims at developing a finite element model to predict the sound transmission loss (STL) of a multilayer panel partially treated with a Magnetorheological (MR) fluid core layer. MR fluids are smart materials with promising controllable rheological characteristics in which the application of an external magnetic field instantly changes their rheological properties. Partial treatment of sandwich panels with MR fluid core layer provides an opportunity to change stiffness and damping of the structure without significantly increasing the mass. The STL of a finite sandwich panel partially treated with MR fluid is modeled using the finite element (FE) method. Circular sandwich panels with clamped boundary condition and elastic face sheets in which the core layer is segmented circumferentially is considered. The MR fluid core layer is considered as a viscoelastic material with complex shear modulus with the magnetic field and frequency dependent storage and loss moduli. Neglecting the effect of the panel’s vibration on the pressure forcing function, the work done by the acoustic pressure is expressed as a function of the blocked pressure in order to calculate the force vector in the equation of the motion of the panel. The governing finite element equation of motion of the MR sandwich panel is then developed to predict the transverse vibration of the panel which can then be utilized to obtain the radiated sound using Green’s function. The developed model is used to conduct a systematic parametric study on the effect of different locations of MR fluid treatment on the natural frequencies and the STL.

Many bio-medical applications entail the problems of spatially manipulating of bubbles by means of acoustic radiation. The examples are ultrasonic noninvasive-targeted drug delivery and therapeutic applications. This paper investigates the nonlinear coupling between radial pulsations, axisymmetric modes of shape oscillations and translational motion of a single spherical gas bubble in a host liquid, when it is subjected to an acoustic pressure wave field. A mathematical model is developed to account for both small and large amplitudes of bubble oscillations. The coupled system dynamics under various conditions is studied. Specifically, oscillating behaviors of a bubble (e.g. the amplitudes and instability of oscillations) undergoing resonance and off-resonance excitation in low- and high- intensity acoustic fields are studied. Instability of the shape modes of a bubble, which is contributing to form the translational instability, known as dancing motion, is analyzed. Dynamic responses of the bubble exposed to low- and high-intensity acoustic excitation are compared in terms of translational motion and surface shape of the bubble. Acoustic streaming effects caused by radial pulsations of the bubble in the surrounding liquid domain are also reported.

High performance control systems (HPCS) are advanced damping systems capable of high damping performance over a wide frequency bandwidth, ideal for mitigation of multi-hazards. They include active, semi-active, and hybrid damping systems. However, HPCS are more expensive than typical passive mitigation systems, rely on power and hardware (e.g., sensors, actuators) to operate, and require maintenance. In this paper, a life cycle cost analysis (LCA) approach is proposed to estimate the economic benefit these systems over the entire life of the structure. The novelty resides in the life cycle cost analysis in the performance based design (PBD) tailored to multi-level wind hazards. This yields a probabilistic performance-based design approach for HPCS. Numerical simulations are conducted on a building located in Boston, MA. LCA are conducted for passive control systems and HPCS, and the concept of controller robustness is demonstrated. Results highlight the promise of the proposed performance-based design procedure.

This paper is focused on the analytical model, design, and simulation of a variable coil-based friction damper (VCBFD) for vibration control of structures. The proposed VCBFD is composed of a soft ferromagnetic plate, made of a linear magnetic material, and two identical thick rectangular air-core coils connected in parallel, each one attached to the plate through a friction pad. The friction force is provided by a normal force produced through an attractive electromagnetic interaction between the air-core coils (ACs) and the soft ferromagnetic plate when sliding relative to each other. The magnitude of the normal force in the damper is varied by a semi-active controller that controls the command current passing through the ACs. To demonstrate the efficiency of the proposed VCBFD and its semi-active controller, it has been implemented on a two-degree-of-freedom (2DOF) base-isolated model subjected to the acceleration components of three records of strong earthquakes. The results show that the performance of the proposed VCBFD in its passive-on mode is overshadowed by the undesirable effects of stick-slip motion. However, the damper in its semi-active mode is more successful in not only reducing the displacement of the base-floor but also avoiding stick-slip motion, due to acting completely in its sliding phase.

In this work, a unique magneto-mechanical energy harvester is fabricated, modeled, and investigated. The magnetomechanical energy harvester consists of a levitated magnet, forming a magnetic spring, connected to oblique, mechanical springs. Upon base-excitation, the levitated magnet experiences nonlinear forces in the direction of motion due to the mechanical and magnetic spring. Voltage is induced in a coil placed around the body of the energy harvester. Results confirm the oblique, mechanical springs and magnetic springs introduce geometric negative and hardening stiffnesses. This behavior allows for the use of disc magnets instead of ring magnets, reducing energy dissipation due to Coulomb damping. Forward and reverse sinusoidal frequency sweep measurements at a constant acceleration of 0.75g shows the characteristic backbone curve exhibited by Duffing-type nonlinear oscillators. The frequency response of the proposed device demonstrates the broadband capabilities with a measured peak power of approximately 7-mW at 15Hz. Results from the model are in good agreement with data obtained from the experiment.

This paper presents a resonance-type vibration energy harvester using a nonlinear oscillator with self-excitation circuit. The bandwidth of the resonance peak and the performance of the power generation at the resonance frequency are trade- offs for the conventional linear vibration energy harvester. A nonlinear oscillator can expand the resonance frequency band to generate larger electric power in a wider frequency range. However, it is difficult for the harmonically excited nonlinear vibration energy harvester to maintain the highest-energy response under the presence of disturbances since the nonlinear oscillator can have multiple stable steady-state solutions in the resonance band. In order to provide the global stability to the highest-energy solution, we introduce a self-excitation circuit which can destabilize other unexpected lower-energy solutions and entrain the oscillator only in the highest-energy solution. Numerical and experimental studies show that the proposed self-excitation control can provide the global stability to the highest-solution and maintain the high performance of the power generation in the widened resonance frequency band.

In the conventional model of general vibration energy harvesters, the harvesting effect was regarded as only the electrically induced damping. Such intuition has overlooked the detailed dynamic contribution of practical power conditioning circuits. This paper presents an improved impedance model for the electromagnetic energy harvesting (EMEH) system considering the detailed dynamic components, which are introduced by the most extensively used full-wave bridge rectifier. The operation of the power electronics is studied under harmonic excitation. The waveforms, energy cycles, and impedance picture are illustrated for showing more information about the EMEH system. The theoretical prediction on harvesting power can properly describe the changing trend of the experimental result.

Dedicated sensors are widely used throughout many industries to monitor everyday operations, maintain safety and report performance characteristics. In order to adopt a more sustainable solution, intensive research is being conducted for self-powered sensing. To enable sensors to power themselves, harvesting energy from environmental vibration has been widely studied, however, its overall effectiveness remains questionable due to small vibration amplitudes and thus limited harvestable energy density. This paper addresses the issue by proposing a novel vibration energy harvester in which a metal compliant mechanism frame is used to house both a linear electromagnetic generator and proof mass. Due to the compliant mechanism, the proposed energy harvester is capable of amplifying machine vibration velocity for a dedicated electromagnetic generator, largely increasing the energy density. The harvester prototype is also fabricated and experimentally characterized to verify its effectiveness. When operating at its natural frequency in a low base amplitude, 0.001 in (25.4μm) at 19.4 Hz, during lab tests, the harvester has been shown to produce up to 0.91 V AC open voltage, and a maximum power of 2 mW, amplifying the relative proof mass velocity by approximately 5.4 times. In addition, a mathematical model is created based on the pseudo-rigid-body dynamics and the analysis matches closely with experiments. The proposed harvester was designed using vibration data from nuclear power plants. Further steps for improving such a design are given for broader applications.

This paper proposes a nonlinear piezoelectric energy harvester (PEH) to scavenge energy from human limb motions. The proposed PEH is composed of a ferromagnetic ball, a sleeve, and two piezoelectric cantilever beams each with a magnetic tip mass. The ball is used to sense the swing motions of human limbs and excite the beams to vibrate. The two beams, which are sensitive to the excitation along the radialis or tibial axis, generate electrical outputs. Theoretical and experimental studies are carried out to examine the performance of the proposed PEH when it is fixed at the wrist, thigh and ankle of a male who travels at constant velocities of 2 km/h, 4 km/h, 6 km/h, and 8 km/h on a treadmill. The results indicate that the low-frequency swing motions of human limbs are converted to higher-frequency vibrations of piezoelectric beams. During each gait cycle, different excitations produced by human limbs can be superposed and multiple peaks in the voltage output can be generated by the proposed PEH. Moreover, the voltage outputs of the PEH increase monotonously with the walking speed, and the maximum effective voltage is obtained when the PEH is mounted at the ankle under the walking speed of 8 km/h.

The synchronous charge extraction (SCE) interface circuit is unique among the existing piezoelectric energy har- vesting (PEH) power conditioning circuits, for its output power is independent of the load. The previous studies about SCE have assumed lossless rectifier and ideal energy transfer through the inductor; the detailed energy flow picture in SCE was absent. This paper provides an impedance based analysis for the PEH system using SCE interface circuit. Through qualitative analysis on the energy cycle, the electrically induced dynamics of SCE is broken down into three components: the accompanied capacitance, dissipative resistance, and harvesting resis- tance, which correspond to an additional stiffness, a dissipative damper, and a regenerative damper, respectively, to the mechanical structure. Quantitative analysis on the harvested power is also carried out. Experiments on practical PEH system show good agreement with the theoretical results. The new insight provided in this study help better understand the dynamics and better evaluate the harvesting capability of the SCE circuit among those options of power conditioning towards practical PEH implementations.

In this paper, the new energy harvesting system is proposed by using wind pressure fluctuations which are one of existing energy sources that were not taken into consideration around high-rise buildings. The proposed system carries out the role of building envelope also. This research is divided in two parts. At first, Computational Fluid Dynamics (CFD) and wind tunnel experiments are performed for investigating the wind pressure that occur around the high-rise building. Secondly, based on the result of wind pressure analysis, the optimal mechanism is devised and the prototype of the energy harvesting system is designed to verify the possibility of utilization of wind pressure fluctuations through the small wind tunnel experiment, harmonic excitation experiment and numerical analysis. As a result, the performance of proposed energy harvesting system is numerically and experimentally validated.

Incorporating nonlinearities into the structures is extensively studied as an effective approach to increase the operation band of the vibration generators. Two well-known ways of obtaining nonlinearities are utilizing magnetic interaction or pre-stress effect, which brings considerable complexities for modeling and design, thus hindering the applications of the nonlinear approach. The piece-wise generator presents a simple realization of nonlinearities with good robustness. However, the available nonlinearities are limited to the combination of two linear segments of stiffness, which restricts the performance of the harvesting device. In this paper, a new piece-wise generator is proposed with more possible nonlinearities realization while keeping the advantages of simplicity and robustness. A prolonged curve fixture is introduced instead of the stopper configuration in the normal piece-wise generator, making the stiffness nonlinearity with more choice by selecting different curves of the fixture. Experimental and theoretical results show that the proposed generator possesses much better performance than the regular piece-wise generator with effectively enhanced bandwidth and resembled peak power.

This article presents 3-degree-of-freedom theoretical modeling and analysis of a low-frequency vibration energy harvester based on diamagnetic levitation. In recent years, although much attention has been placed on vibration energy harvesting technologies, few harvesters still can operate efficiently at extremely low frequencies in spite of large potential demand in the field of structural health monitoring and wearable applications. As one of the earliest works, Liu, Yuan and Palagummi proposed vertical and horizontal diamagnetic levitation systems as vibration energy harvesters with low resonant frequencies. This study aims to pursue further improvement along this direction, in terms of expanding maximum amplitude and enhancing the flexibility of the operation direction for broader application fields by introducing a new topology of the levitation system.

The size of wind turbine blade has been continuously increased. Large-scale wind turbine blades induce loud noise, vibration; and maintenance difficulty is also increased. It causes the eventual increases of the cost of energy. The vibration of wind turbine blade is caused by several reasons such as a blade rotation, tower shadow, wind shear, and flow separation of a wind turbine blade. This wind speed variation changes in local angle of attack of the blades and create the vibration. The variation of local angle of attack influences the lift coefficient and causes the large change of the lift. In this study, we focus on the lift coefficient control using a flow control device to reduce the vibration. DU35-A15 airfoil was employed as baseline model. A plasma actuator was installed to generate the upwind jet in order to control the lift coefficient. Wind tunnel experiment was performed to demonstrate of the performance of the plasma actuator. The results show the plasma actuator can induce the flow separation compared with the baseline model. In addition, the actuator can delay the flow separation depending on the input AC frequency with the same actuator configuration.

The spread of smart structures has recorded a significant increase during the last decades. Nowadays these solutions are applied in various fields such as aerospace, automotive and civil constructions. This kind of structures was born in the past in order to cope with the high vibrations that every lightweight structure has to face. In order to reduce weight designers usually decide to use very thin and lightweight structures. In the automotive field, for example, a reduced fuel consumption is obtained employing lightweight materials. However, in general a worsening of the vibroacoustic comfort is obtained with undesired vibrations that can be really annoying for passengers and dangerous for the structure itself. This work presents an innovative smart plate that is able to actively vary its dynamic properties, by means of an IMSC control logic, in order to improve the acoustic performances. An investigation about the system response in the high frequency range allowed to assess the behavior in terms of absorption, reflection coefficient and transmission loss.

P(VDF-TrFE) is a ferroelectric material having a strong piezoelectric effect, a good chemical stability, chemical resistance and biocompatibility. Therefore, it is suitable for the development of flexible pressure sensors in biological applications. Using electrospinning method and a drum collector, P(VDF-TrFE) nanofibers are aligned and formed an ultrathin film sheet with a thickness of 15 to 30 μm. A 140 °C annealing process and a corona discharge poling process are conducted to increase the performance of β phase piezoelectricity. Based on this technology, a highly flexible piezoelectret pressure sensor is developed for measuring muscle movement on the surface of human body. The orientation of electrospun P(VDFTrFE) fibers and poling direction are studied to enhance the sensitivity of the piezoelectret-fiber pressure sensor. Preliminary study shows that the sensitivity of piezoelectret-fiber pressure sensor can be 110.37 pC/Pa with a high signal to noise ratio. Sensor design, experimental studies, and biological application are detailed in this paper.

Periodic structures have received large interest due to their peculiar behavior: they have band gaps, that is portions of the frequency response along with any wave incoming in the structure is reflected. Numerous are the applications, like metamaterials and locally resonant structures. Nowadays, new possibilities could come from mechanical periodic structures that are connected to an electrical transmission line, periodic in turn. Starting from this idea, this paper analyses ideal a mono-atomic spring-mass chain, considering the springs connected to a periodic electric network, composed by inductances (and resistors): these simple examples will show how the frequency response is affected. In particular, the mutual influence between the electric and mechanical domain is highlighted, and the contribution of parameters on band gap positioning and design is explored. Details are provided about vibration modes and wave transmission.

In this paper we present preliminary experimental results relative to the control of multistage seismic attenuators and inertial platforms in the band 0.01±10Hz, using open loop monolithic folded pendulums as inertial sensors. In fact, beyond the obvious compactness and robustness of monolithic implementations of folded pendulums, the main advantages of this class of sensors are the tunability of their resonance frequency and their high sensitivity over a large measurement band. The results are presented and discussed in this paper together with the planned further developments and improvements.

Helicopters are among the most complex machines ever made. While ensuring high performance from the aeronautical point of view, they are not very comfortable due to vibration mainly created by the main rotor. Traditionally this problem is solved by mounting several TMD inside the helicopter, each tuned to the frequency of the disturbance the main associated with the main rotor. In particular, this frequency is equal to the angular speed of the main rotor times the number of blades. Despite the angular speed of the main rotor is kept fixed and constant during the flight, it happens that some changes may be needed in particular situations. Therefore it happens that the mass dampers are no more tuned and thus ineffective. This leads to a significant increase of the amplitude of vibration. This work proposes to replace the purely passive systems with semi-active systems that are able to change their own natural frequency in order to be effective at each angular speed of the main rotor. The paper deals with the preliminary analysis of the project to numerically and experimentally evaluate the feasibility of this solution.

In applications of vibration suppression, control forces ideally act on the structure increasing its damping. While the frequency response of the structure is guaranteed to have a positive real part under ideal conditions, in practice a stability limit exists when inertial actuators are used. In this case the system response is no longer guaranteed to be positive real and so the control system may become unstable at high gains. Moreover, traditional approaches suggest the use of inertial actuators only if its natural frequency is well below the natural frequency of the structure, thus preventing their use at low frequencies. This paper proposes an interesting technique to enlarge the operational range to lower frequencies and to allow the use of inertial actuators. The approach is numerically tested and experimentally validated on a test rig.

A structural system consists of gravity and lateral load resisting components. Structural walls in the gravity system are typically designed to resist vertical loads only, and are assumed to be inactive to mitigate lateral loads. In this paper, we propose a novel multifunctional wall system, which is embedded with multiple-capillaries containing free-flowing fluids and can act as both a load carrying member and a Tuned Liquid Wall Damper (TLWD). Functioning similarly to a Tuned Liquid Column Damper (TLCD), the damping force of the proposed wall system is provided by the head loss of the fluid between each capillary. An analytical model is derived first to describe the dynamic behavior of the TLWD. The accuracy of the analytical model is verified using Computational Fluid Dynamics (CFD) simulations. The model is further used to compute the reduced response of an assumed primary structure attached with a TLWD to demonstrate the damping capability. Results show that TLWDs can effectively dissipate energy while occupying much less space in buildings compared to TLCDs.

Photoactuators can concern light stimuli in appropriate wavelength into mechanical response. Such reversible changes in the material shape are highly promising in their applications as remote controllers, or safety sensors. In this work we were focused on light-induced actuation and sensing performance of the prepared materials. In this case poly(dimethyl siloxane) PDMS with various amounts of silicone oil and curing agent was used as matrix. Graphene oxide (GO) as filler in its neat form as well as its modified analogue were used in concentration of 0.1 vol. %. Modified GO particles were controllably coated with poly(methyl methacrylate) polymer chains using surface-initiated atom transfer radical polymerization (SI-ATRP) approach in order improve interactions between the filler and matrix which consequently lead to the enhanced light-induced actuation performance. Generally, the both, GO particles as well as modified ones were characterized using FTIR, Raman spectroscopy and finally conductivity measurement to confirm the controllable coating and simultaneously proceeded reduction. By studying of dielectric properties (activation energies), viscoelastic properties, which were investigated using dynamic mechanical analysis, the interactions between the filler and matrix were evaluated with connection to their light-responsive and sensing capabilities.

Passive oil dampers for railway vehicles present a damping and stiffness characteristics, which depend from excitation history. This behaviour is not acceptable for many high-performance applications. A mechatronic approach, able to continuously adjust the damping coefficient according to the operation requirements, represents a very attractive and smart solution. In this paper, a control strategy for semi-active dampers of train vertical secondary suspensions is presented. The controller aims at assuring the maximum available damping at low frequencies, while at high frequencies minimizes the force transmitted to the carbody that excites the bending modes.

Piezoelectric motor is based on generating traveling waves on a finite structure. It can be classified into linear and rotary types. Among them, linear motors have an inevitable problem since finite boundaries are always exist, and reflected waves can hinder the formation of propagating waves. To solve this problem, a linear motor based on a single driving frequency and two induced resonant molds are previously reported. However, the driving frequencies are not at structure resonant frequency, the efficiency of linear motor is based on the superposition of two adjacent bending modes. The traveling wave is created by two piezoelectric actuators driven by a single frequency in between these two resonant molds with a 90° phase difference. Based on previous report, it shows that by placing these two 0.178/L length actuators at 0.22/L and 0.78/L on a one-dimensional beam with length L, an optimal performance could be reached. It suggested that the location and size of the two piezoelectric actuators can be used to optimize the performance of the linear motor. In this study, finite element simulation was used to study the contributions of the temporal and spatial correlations between the two actuators with respect to a 1-D linear motor. The position and size of these two piezoelectric actuators are studied for optimizing the performance of the linear motor.

Helicopters are among the most complex machines ever made. While ensuring high performance from the aeronautical point of view, they are not very comfortable due to vibration mainly created by the main rotor and by the interaction with the surrounding air. One of the most solicited structural elements of the vehicle are the horizontal stabilizers. These elements are particularly stressed because of their composite structure which, while guaranteeing lightness and strength, is characterized by a low damping. This work makes a preliminary analysis on the dynamics of the structure and proposes different solutions to actively suppress vibrations. Among them, the best in terms of the relationship between performance and weight / complexity of the system is that based on inertial actuators mounted on the inside of the horizontal stabilizers. The work addresses the issue of the design of the device and its use in the stabilizer from both the numerical and the experimental points of view.

This paper summarizes and extends the modeling state of the art of magnetostrictive energy harvesters with a focus on the pick-up coil design. The harvester is a one-sided clamped galfenol unimorph loaded with two brass pieces each containing a permanent magnet to create a biased magnetic field. Measurements on different pick-up coils were conducted and compared with results from an analytic model. Resistance, mass and inductance were formulated and proved by measurements. Both the length for a constant number of turns and the number of turns for a constant coil length were also modeled and varied. The results confirm that the output voltage depends on the coil length for a constant number of turns and is higher for smaller coils. In contrast to a uniform magnetic field, the maximal output voltage is gained if the coil is placed not directly at but near the fixation. Two effects explain this behavior: Due to the permanent magnet next to the fixation, the magnetic force is higher and orientates the magnetic domains stronger. The clamping locally increases the stress and forces the magnetic domains to orientate, too. For that reason the material is stiffer and therefore the strain smaller. The tradeoff between a higher induced voltage in the coil and an increasing inductance and resistance for every additional turn are presented together with an experimental validation of the models. Based on the results guidelines are given to design an optimal coil which maximizes the output power for a given unimorph.