This PDF file contains the front matter associated with SPIE Proceedings Volume 11376, including the Title Page, Copyright information, and Table of Contents.

The inherent randomness and non-tunability associated with turbulent flow usually make it a poor candidate as an energy source for piezoelectric harvesters. We have shown in prior work that when the turbulence is generated by a grid, however, there are certain predictable relationships between the power output and the turbulent flow that could potentially make the deployment of piezoelectric harvesters in such settings viable. In this paper, we look at the voltages recorded from harvesters placed in turbulence generated by passive rectangular, fractal I, fractal cross, semi-passive and active grids and statistically characterize the coherent “beats” present in these “random” signals. The effects of beam distance from the grid, average flow velocity, grid type and separation between multiple beams have been considered in this analysis. An important conclusion from this work is that the beat duration distribution pattern of a beam that is close to or has entered into flutter vibration is clearly identifiable, potentially providing an opportunity to use piezoelectric materials as sensors to detect flutter.

A compact bistable galloping oscillator is proposed for enhanced power generation from concurrent wind and base vibration. The harvester consists of a D-shaped bluff body attached to a piezoelectric cantilever. Repulsive magnetic interaction is introduced between the bluff body and a fixed windward support to bring nonlinear bistability. An aeroelectro- mechanically coupled model is established and experimentally validated. Both experimental measurements and model predictions demonstrate that the synchronization bandwidth for efficient energy harvesting from concurrent wind and base vibration can be substantially extended.

Many researchers have been focused on energy harvester for the tire over the past decade. In this paper, we propose a self-tuning stochastic resonance energy harvester for a smart tire with the circuit integration. Compared to existing harvesters, the energy harvester shows large power and wide bandwidth due to stochastic resonance and passive selftuning. The harvester consists of an inward rotating cantilever beam with an electromagnetic transducer. The tuning performance is verified by analysis of Kramers rate and signal-to-noise ratio (SNR). In addition to energy harvester, we implemented the energy harvesting circuit to achieve data acquisition and energy storage. Circuit includes a rectifier, buck-boost converter, wireless communication module, microprocessor and temperature monitoring sensor. In lab test and field test are conducted to performance of self-tuning energy harvester. Circuit assembly is attached to the rim hub while harvester assembly is installed inside the tire with a tire pressure monitoring sensor (TPMS). The results the feasibility of the self-tuning harvesting strategy on the smart tire application.

In this paper, a tapered beam piezoelectric energy harvester attached with a tip mass whose centroid does not coincide with the attaching point is investigated. First, the consideration of the geometric dimensions of the tip mass is embodied in the calculation of its rotational inertia and the determination of its centroid. Subsequently, a single-degree-of-freedom representation method is developed on the basis of a derived analytical governing equation. Finally, by shunting to the P-SSHI interface circuit, using an improved equivalent impedance modelling method, the mechanical and electrical domains are bridged to provide a comprehensive analysis of the practical energy harvesting system.

Due to its multidisciplinary nature, the power behavior of a piezoelectric vibration energy harvester depends on system properties in multiple domains such as material, mechanical and electrical. This paper presents a dimensionless maximum power equation that integrates these effects into a simple model, which serves as a convenience tool for the design and analysis of piezoelectric vibration energy harvesters. The model is given as a closed-form relationship between the dimensionless maximum power (maximum power normalized by the power limit) and the normalized electromechanical coupling coefficient with respect to the critical coupling coefficient, which is the minimum coupling to reach the power limit of a system. In addition, this integrated design equation can be applied to different energy harvesting interface circuit types such as resistive and standard AC-DC with a simple change of the critical coupling expression in the equation. The application of this equation is illustrated by a detailed design example of a bimorph beam harvester for fixed target natural frequency and length given a base motion excitation. It is found that under the same level of excitation, there is an optimal PZT thickness for maximum power. In addition, overall, it is beneficial to make the system of low damping to yield a larger structural response and more power. However, this also leads to a higher bending stress, which is an important design consideration due to the relatively brittle nature of PZT materials.

The article presents the study of a novel self-powered SECE (synchronized electric charge extraction) circuit for scavenging piezoelectric energy under low-frequency shock excitation. Specifically, the device consists of a piezoelectric cantilever beam whose tip magnet is impulsively excited by a rotating magnet. It is attached to a load-independent SECE circuit with the advantage of power enhancement at low-level output voltage. The proposed circuit includes an envelope detector for voltage detection, a voltage divider for minimizing the switching delay and a diode for recovering the charge on the detection capacitance. The result shows that the predicted harvested power agrees well with the experimental observations. In addition, the power ripples are significantly reduced due to the larger electric-induced damping drawn from the SECE technique. Finally, the load-independent property makes the observed SECE power remain constant within the output voltage operated at around 2-5 volt, and therefore outperforms the standard DC power.

Piezoelectric materials have found numerous applications in sensors with the characteristic of flexibility and sensitivity. Taking advantage of their characteristic, we fabricate a multi-layered cross-shaped piezoelectric sensor for torsional load analysis. It consists of a polyethylene terephthalate substrate and two piezoelectric layers placed in the crossed form. From the crossed shape of two piezoelectrics, various conditions of torsional loading can be analyzed by simply measuring load voltage amplitudes and phases. We derive a modeling framework of the cross-shaped piezoelectric sensor under torsional loading to expect the sensing response of the sensors. Also, an experimental setup is established to verify the modeling statement.

Piezoelectric actuators have been applied to various applications due to its compact configuration, high force to volume ratio and high precision. In this paper, we present a planar type piezoelectric actuator that has two-dimensional (2-D) motorization capability. This 2-D piezoelectric actuator is constructed by a 0.5 mm thick stainless-steel plate with one 45 mm by 31.8 mm by 0.2 mm piezoelectric PZT that attached on its surface. Using this PZT sheet and driving at two different resonant frequencies with a relationship of integer multiples and a phase difference, traveling waves can be generated to drive the 2-D piezoelectric actuator moving in x- or in y- directions. This driving method is called two-frequency-two-mode. Setting driving frequencies of activated modes to be integer multiples is to stabilize the period of the generated traveling wave and thus increase the propelling efficiency. In addition, the input signal is superposed by the two resonant frequencies on two specific bending modes to selectively drive the 2-D piezoelectric actuator to move in a particular direction. Furthermore, to assist the chosen of the driving voltage ratio and phase difference, Hilbert transform was applied. The weight of the piezoelectric actuator is 17.4 g, and the average moving velocity can reach 1.60 mm/s in x direction and 0.93 mm/s in y direction, where the driving voltage was 100 Vpp. In this paper, numerical studies and experimental studies are presented to verify the performance of this 2-D piezoelectric actuator.

This paper presents a rheological model that was developed to stimulate the experimental behavior of magnetorheological elastomers (MREs) under varying loading conditions (magnetic field, strain amplitude and frequency). Magnetorheological elastomers (MREs) were fabricated and tested using double lap shear experiment setup under different strain amplitudes, magnetic fields and frequencies. A linear visco-elastic rheological model consists of seven parameters to represent both viscous and elastic behavior of MREs. The parameters under varying loading conditions were identified and optimized using the data recorded from experiments. The experimental results were then compared with model predicted values which demonstrate that the seven-parameter model predicts MRE behavior well.

In this presentation, principles visualizing propagation of structurally guided waves are first introduced and then several setups and their features are explained. For decades, various wave propagation imaging system has been developed and commercialized for different fields like laser induced ultrasound, microwave, pyroshock, and acoustic emission. Depending on the structures and materials, system variation, especially scanning mechanism is also interested and some examples on real world applications of these systems deepen understanding on the applicability and provides inspiration on potential applications. Lastly, suggestion on the smart hangar and smart twin will be followed.

Barely visible impact damage (BVID) due to low velocity impact events in composite aircraft structures are becoming extremely prevalent. BVID can have an adverse effect on the strength and safety of the structure. During aircraft inspections it can be extremely difficult to visually detect BVID. Moreover, it is also a challenge to ascertain if the BVID has in-fact caused internal damage to the structure or not. In this paper, multiple 2-mm quasi-isotropic carbon fiber reinforced polymer (CFRP) composite coupons were impacted using the ASTM D7136 standard in a drop weight impact testing machine to determine the mass, height and energy parameters to obtain approximately 1" impact damage size in the coupons iteratively. For subsequent impact tests, four piezoelectric wafer active sensors (PWAS) were bonded at specific locations on each coupon to record the acoustic emission (AE) signals during the impact event using the MISTRAS micro-II digital AE system. Impact tests were conducted on these instrumented 2-mm coupons using previously calculated energies that would create either no damage or 1" impact damage in the coupons. The obtained AE waveforms and their frequency spectrums were analyzed to distinguish between different AE signatures. From the analysis of the recorded AE signals, it was determined if the structure had indeed been damaged due to the impact event or not. Using our proposed structural health monitoring technique, it could be possible to rapidly identify impact events that cause damage to the structure in real-time and distinguish them from impact events that do not cause damage to the structure. An invention disclosure describing our acoustic emission structural health monitoring technique has been filed and is in the process of becoming a provisional patent.

This research investigates the effect of the geometric parameters of origami crease patterns on their deployment dynamics. In this study, we construct a dynamic model of a non-rigid Miura origami sheet based on the bar-and-hinge approach, capturing panel flexibility and inertial effects. These effects are critical in describing the dynamics of origami deployment, which are ignored in the state of the art rigid folding kinematics model. Deployment is facilitated by strain energy stored in the torsional springs at the hinged creases, and a controlled deployment velocity at one end of the Miura sheet. We theoretically and numerically analyze the deployment process of integrated Miura sheets with various geometries. Eigenvalue decomposition at different stages during the quasi-static deployment process shows that the Miura pattern’s crease length ratio and panel section angle affect the fundamental natural frequency and damping ratio. Numerical studies show that changing the crease pattern geometries results in deployment paths that may substantially deviate from a nominal Miura unfolding path under rigid folding assumptions. Examination of the theoretical model reveals how crease pattern geometries affect the apparent stiffness, offering insight into this behavior. The findings of this research enable a deeper understanding of the physics behind origami deployment and pave the way for new applications of origami-based deployable structures.

Morphing is an increasingly investigated topic in aeronautics due to the performance improvements brought by aerodynamic shapes adaptivity on large aircraft. Being aerodynamics mainly driven by geometry, a structure that can modify its shape may achieve tremendous capability enhancement, especially if its operating scenario is wide. However, the implementation of morphing structures leads to many issues that still need to be properly solved to make the technology fully operative in real application scenarios. For instance, additional DOFs generate systems with increased modal density and then with more complex aeroelastic behaviour, and premature onset of dynamic instabilities. The authors of the present paper have dealt with this problem in other publications, in cooperation with several colleagues, and interesting results are available in literature, to some extent. In this general framework, there are peculiar aspects that only recently have started to catch the attention of the scientific community. Among those, a particular one is the objective of the present work, referring to the numerical simulation strategy of adaptive devices. The kinematic system at the basis of a wide class of morphing structures is driven by an actuation chain, which gives an important contribution to the already cited aeroelastic behaviour. For safety-critical embedded subsystems, it is crucial to detect potential failures and predict their impacts since the early design stages. Now, kinematic components significantly affecting the structural dynamics, as torsion bars and bearings, are assumed rigid in the traditional simulation strategy. If such a concept may be supposed valid for standard layouts (as in the case of flap, ailerons and other moveable systems), it cannot be held for architectures integrating hundreds of those mechanical parts. This work addresses preliminary investigations on systematic analyses carried out on detailed simulations of selected components of aircraft morphing structures, trying to evaluate the effects of elasticity of bearings and hinged connections on the global dynamic response.

There has been increasing demand for larger space structures to satisfy the requirements of astrophysics missions. However, storage space for payloads in satellites is limited, so deployable structures are used in most space missions to minimize storage space and consequently, to reduce launch costs. This work proposes a deployable truss structure which can improve the packaging efficiency of the existing truss structure. The main feature of the proposed structure is that it can be stored in a flat form. Each unit consists of Scissor-like Elements (SLEs) and the whole structure is deployed in a three-dimensional form with a simple mechanism. The detailed configurations and mechanism of the proposed structure are discussed. The geometric constraints for folding the proposed structure into a planar form were analyzed. A kinematic analysis to describe the motion of the structure was also performed. Then the packaging efficiency with respect to length, which is an important performance index of such deployable structures, was analyzed and compared with a typical truss structure.

The Structural Health Monitoring (SHM) is a key technology to detect and prevent critical damages in different kind of structures. Corrosion is one of the main issues affecting metallic structures exposed to wet environments or affected by high levels of moisture, such as in offshore aerogenerators or aircrafts, and, therefore, is a critical parameter to be monitored. In this work, an on-line SHM sensor is presented, based on impedance spectroscopy techniques, which can be used to continuously measure corrosion in the surface of different kind of structures, and which could be implemented in airframe and wind energy generation structures. The impedance of an interdigitated sensor is measured in a frequency range between 16mHz and 200kHz, with resulting impedance values up to 100GOhm. The impedance sensor aims at being a completely wireless and autonomous solution: the sensor integrates wireless data communication and is self-powered by two independent energy harvesting systems. An RF antenna is used to harvest energy from a RF emitter in static and low range applications, while a flexible PV panel is installed to directly harvest energy from the environment, also in moving applications such as wind generator blades. Moreover, the use of thin-film and flexible electronics facilitates the integration of the sensor into any surface with very little aerodynamic impact. All the interdigitated sensor, the associated control electronics and the energy harvesting system can be implemented in polymeric thin flexible substrates, combining printed and hybrid electronics and allowing curved and complex geometries for the sensor device.

Non-contact and non-destructive usages of laser ultrasonic have been researched actively nowadays. Specifically, there are some studies about Lamb wave inverse problems, which is the research about inversely calculating material properties from Lamb wave dispersion curve. In this study, measurement system of Lamb wave phase velocity and method of inversely calculating elastic modulus of isotropic metal plate from the experimental dispersion curve of A0 mode. Ultrasounds are induced with a pulsed laser and detect them with a laser Doppler vibrometer, and measured the velocities of them in non-contact and non-destructive way. Then, calculating method of phase velocity distribution of A0 mode is introduced. By using characteristic equation of A0 mode, the sum of squares of residuals, SSR, is defined to represent how close the bulk wave velocities expectations are close to the right values when dispersion curve is experimentally given. Also, this study verified that assuming Poisson's ratio cannot affect inverse calculation results, which allows to roughly assume the ratio for the calculation. For the aluminum 0.5 mm plate, Lamb wave measurement system, phase velocity calculation method, and inversely calculation method by assuming Poisson's ratio roughly are verified by success of inversely calculating the elastic modulus of aluminum specimen accurately.

In this paper, we propose a piezoelectric actuator-sensor pair that can classify several objects. It consists of two polyvinylidene-fluoride films above a polyethylene-terephthalate substrate. Herein, the actuator is connected to an voltage supplier, and the sensor output signal is acquired through a measuring equipment. Specifically, this pair is installed on a robot hand. When the objects are grasped by the robot hand in static state, the actuator oscillates as sinusoidal input voltages with frequency sweep are applied for a few seconds. At the same time, the sensor data is obtained and undergoes preprocessing procedure for learning process. The neural network classifier model is trained by learning process. After conducting the learning process, we test the feasibility of the actuator-sensor pair by demonstrating the real-time recognition system.

This paper focuses on using two developed imaging methods to localize the impact points on a composite plate. The first developed imaging method (Method 1) was firstly investigated on a metallic plate. A network of nine piezoelectric wafer active sensors (PWAS) was instrumented on an aluminum plate to receive impact signals. Based on Method 1, we need at least three sensors, which can be used to determine two hyperbolic paths, to localize an impact point on a metalic plate with known group velocities of generated waves (known its material properties). The observed results indicate that Method 1 can be used successfully to localize the impact points on a metallic plate. These successful results motivated us to investigate Method 1 on a composite plate. A second experiment of impact localization was implemented on a composite plate. Two clusters of sensors (every cluster has three PWAS transducers) were instrumented on the composite specimen to receive the generated acoustic waves due to break pencil leads at different points. The received signals were anaylized using a wavelet transform to determine the time of flight. The group velocity profile of antisymmetric Lamb wave mode was determined analytically at certain frequency. Based on Method 1, two hyperbolic paths, which are generated by four sensors, can be used successfully to localize the impact points on a composite plate with known its material properties. The second developed imaging method (Method 2) was investigated on the same composite specimen with assumption of unknown its material properties (unknown group velocity profile of generated wave). Based on Method 2, we need six sensors distributed on two clusters to determine two straight line paths. The intersection point of these two lines represents the impact point. The results showed that Method 2 can successfully localize the impact points on a composite plate.

Measuring with strain gages has a limitation of consuming time to prepare for the experiment and attaching near the MLCCs, making it does not represent the physical quantities of the MLCCs itself. In this study, we propose a ‘failure criteria for a crack in MLCCs soldered on a Print-Circuit-Board by ball drop test’ based on the acceleration measured by Laser Doppler Vibrometers. By drawing a Shock Response Spectrum, we can find the dominant frequency for the failure of MLCCs. In addition, we present a suitable deformation form of the Print-Circuit-Board by using a high-speed camera.

When considering damping in the design of a vibration system, magnetorheological (MR) fluids can provide an alternative to more traditional dampers that can take up unnecessary mass and volume on aircraft and space missions. The goal of this paper is to study the effects of transient magnetic fields on vibration systems in order to allow the system to reach its equilibrium position. These effects are modeled using a sandwich beam with an MR fluid core. A numerical and experimental modal analysis is conducted on the beam to measure the properties of the first mode, which are then used for a transient finite element model where multiple transient magnetic fields influence the beam’s motion. Comparing the modal analysis results reveals that both analyses are in agreement, as they offer similar modal parameters for the first mode. The free-decay numerical simulation shows that transient magnetic fields allow the sandwich beam to return to equilibrium, while also doing so quickly. Among other steps, future work will primarily consist of replicating the numerical transient results experimentally.

Vibration of the automotive engine has the characteristics of wide frequency band, multi-vibration sources and multi-main frequencies. Limited capability of passive mounting systems can be provided for engine vibration isolation. A MR semiactive mounting system for automotive engines is investigated in this paper. The dynamic model of the vertical vibration isolation system for the engine and an efficient damping control model of the MR mount are established. The frequency characteristics of the engine vibration are analyzed. The fuzzy control algorithm for the MR mounting system is designed, and the isolation performance of the MR mounting system is analyzed based on the developed experimental setup in Hefei University of Technology.

Locally resonant metamaterials are capable of producing frequency attenuation regions that are not dependent on the lattice size and have been object of several studies since the 2000s. Most recently, flexible structures with periodically distributed piezoelectric attachments combined to resonant circuits have been studied as locally resonant piezoelectric metamaterials. In this work the authors use a genetic algorithm to optimize each unit cell of a piezoelectric metamaterial in order to obtain wider attenuation bands. An assumed-modes solution for a piezoelectric bimorph beam with segmented electrodes under transverse vibrations is presented. Although the unit cells of the optimized configurations have the same length (periodically distributed along the length), the target frequency of each cell varies, leading to optimal non-uniform configurations that exhibit wider attenuation bands than the uniform ones. The optimization of the proposed objective function converges to a non-uniform configuration that displays an attenuation band 56% wider than the reference case.

Breaking reciprocity in wave propagation problems is of great interest within the research community, given the opportunity to design new devices for one-way communication with unprecedent performances. In the context of mechanics and phonon transport, directional wave manipulation can be achieved exploiting space-time periodic materials. Namely, structures whose elastic or physical properties are functions of space and time. In this work we experimentally study nonreciprocal wave propagation in a space-time modulated beam based on piezoelectric actuation. The system is made of an aluminum beam with an array of piezoelectric patches bonded on its top and bottom surface. Each patch is attached to a negative capacitance (NC) shunt driven by switching circuit, which is able to provide a square-wave stiffness profile in time to the layered material. Spatiotemporal modulation is induced by phase shifting the temporal modulation law of three consecutive piezo-elements, generating a traveling Young’s modulus that mimics the propagation of a wave along the beam dimension. As a result, we achieved 1kHz directional bandgaps, i.e. bandgaps at different frequencies for counter propagating waves, which can be moved in a range spanning 8-11 kHz.

Interplanetary missions have had many challenges associated with several coupled issues. The Mars Curiosity rover mission represents the limit of the current technology using rigid “aeroshells” and supersonic parachutes. One of the main challenges to overcome in these missions is the Entry, Descent, and Landing (EDL) phase. The Martian atmosphere does not contain the density to provide enough drag to slow down a heavy entry vehicle using conventional designs. As a result, Mars entry vehicles have been constrained to land at lower surface elevations. The landing uncertainty of those entry vehicles represents a limitation that needs to be improved upon by several orders of magnitude. Therefore, we need to consider the unique and unusual designs that will provide significant improvements in landing accuracy. Mainly in maximizing aerodynamic braking and minimizing the complexity associated with retro-propulsion. In this research, we focus on characterizing the aerodynamic performance, such as lift and drag forces and moments, on the new concept design like a Badminton Shuttle using Computational Fluid Dynamics (CFD) simulations. Due to limited resources, a two-dimensional shuttle is considered at the different range of Reynolds numbers, which is consistent with wind tunnel data. The results depict specific vorticity contours to understand the flow characteristics of the vortex shedding behind the shuttle. The time history of the lift-coefficient shows a link between the vortex generation and shedding at the instant time. The results indicate the 2D shuttle is inherently stable, just like its 3D geometric counterpart. Force and moments show similar consistent trends when compared to the 3D model.

The biomimicking and understanding of the dynamics of insect flyers is important in developing agile and efficient MAVs. The present study is based on the development of dragonfly inspired MAV and investigation of its motion characteristics. Initially, a tethered two-winged MAV model is constructed, composing of two flapping wings, a flapping mechanism, a chassis, and an external power supply with a function generator. The wings are fabricated with composite stiffeners and membrane. The material of the wings consists of carbon nanotubes (CNTs)/polypropylene (PP) nanocomposite and low density polyethylene (LDPE). The wings are thus lightweight, thin, flexible, and can generate large amplitude bending-twisting motion. The flapping mechanism is constructed with a cantilever type piezoelectric actuator, a mediator mechanism having CNTs/PP nanocomposite flexure joints, and carbon fiber/epoxy composite linkages. The assembled two-winged MAV model has a total mass, body length, wingspan, and aspect ratio of 0.61g, 60.46mm, 90.14mm, and 10.06, respectively. The characteristic flapping frequency of the model is 20Hz, as compared to the wingbeats (or characteristic frequency) of 27.53Hz of an actual dragonfly species, i.e., the Anax Parthenope Julius. Measured via digital image correlation (DIC) technique, the fabricated wings exhibit a bending dominated motion during downstroke as well as upstroke. The combined design of flapping wings and flexure joint mechanism is also computationally studied for their structural dynamic characteristics (performed using ANSYS). The first resonance mode or the characteristic frequency, at which the wings have highest deflections, is 17.25Hz. The flexure mechanism is able to generate very large wing deflections (maximum deflection 22.7mm at wing tip) with a sinusoidal heaving input excitation of very small amplitude (0.1mm given at the actuator attachment location). This is useful to generate higher aerodynamic forces and improve efficiency. The maximum stresses and strains are found at flexure-rigid link and wing stiffener attachment, respectively. Finally, a dragonfly-inspired four-winged MAV is developed. It consists of two pairs of nanocomposite wings with independently actuated flapping mechanisms. Like a natural dragonfly, the forewing and hindwing pairs can be controlled independently and operated at different characteristic frequencies as well as relative phase angles.

In this research, the application of an existing morphing wing technology, known as the Spanwise Morphing Trailing Edge (SMTE), is investigated further to identify the optimal morphing geometries for a subsonic Reynolds number regime. The new morphing wing model considers generating a variety of n-th root function (e.g., square root) geometries along the spanwise trailing edge of the wing to provide optimal aerodynamic results. The degree of the root function, control deflection of the trailing edge, and the angle of attack are parameterized to investigate the detailed aerodynamic characteristics. This research was conducted numerically through Computational Fluid Dynamics (CFD) simulations. The CFD simulations are performed using the three-dimensional (3D) Reynolds-Average Navier-Stokes (RANS) equations with the k - ω Shear Stress Transport (SST) turbulence model. The results show that the aerodynamic performance improves as the n-th root function geometries approach to the shape of an elliptic curve, which is a special case of the square root function. The results also indicate that the wing geometries of lower control deflection are more beneficial than those of higher control deflection to generate the same amount of lift when the angle of attack can vary freely.

The present paper investigates the nonlinear dynamic electromechanical conversion capability of axially prestressed piezoelectric strips, vibrating under transverse mechanical impulsive forces. A computational structural dynamics framework is adopted, comprising a mixed-field laminate plate theory together with an eight-node coupled plate finite element, that encompass nonlinear effects due to large rotations and initial stresses. The dynamics incorporate all linear and nonlinear coupling terms between mechanical and electric fields, and emphasis is given on the presentation and analysis of nonlinear stiffness and electromechanical coupling terms that affect the electric charge and energy in the piezoelectric devices. The resultant discretized equations of motion are finally linearized and solved using the Newmark implicit time integration scheme in combination with the Newton-Raphson iterative technique. Numerical evaluation cases investigate the nonlinear vibratory response and the electromechanical energy conversion capacity of prestressed vibrating piezoelectric strips excited by transverse impulsive forces. The effect of axial preloading and transverse dynamic loading on both the nonlinear dynamic electromechanical response and electromechanical energy conversion is quantified.

To quantitatively evaluate the output performance of triboelectric nanogenerators (TENG), the figure-of-merits (FOM) have been developed. However, the current version of FOM has limitations in applications, especially, it does not consider the breakdown effect that seriously affects the effective maximized energy output. At the same time, the standardized method to evaluate output capability that can be universally applied for all nanogenerators is missing. Here, a standardized assessment method is firstly proposed for output capability assessment of nanogenerators, in which the breakdown limits have been considered. Contact separation (CS) and contact freestanding-triboelectric-layer (CFT) modes TENGs are used to demonstrate this method, and the maximized effective energy output and revised FOM are calculated based on the experimental results. These results are consistent with that theoretically calculated based on Paschen’s law. The standardized evaluation on a film-based piezoelectric nanogenerator is also conducted based on this method, demonstrating its universal applicability for nanogenerators. This study proposes a standardized method for evaluating the effective output capability of nanogenerators considering the breakdown effect, which is crucial for standardized evaluation and applications of nanogenerator technology.

Total knee replacement (TKR) surgeries have been increasing tremendously in the past few years particularly among active young people and elderly people suffering from knee pain. Hence, continuous monitoring of the load on the knee after the knee surgery is highly desirable for designing an efficient and more functional smart knee implant. In this paper, we demonstrate a smart knee implant system which consists of a triboelectric harvester and a front-end electronic system which continuously monitors the load on the knee by relying only on the power harvested by the triboelectric harvester. The TKR system consists of the femoral, tibial tray, and the ultra high mechanical polyethylene (UHMWPE) bearing parts. The designed triboelectric harvesters are placed between the tibial tray and the UHMWPE bearing for perfect load monitoring. The frontend electronic system is placed on the tibial tray to be powered by the harvester. The triboelectric harvester produces an AC signal which is processed using our proposed frontend electronic system to monitor the load on the knee. For instance, at a knee cyclic load of around 230 N, the harvester produces 6.5 μW power and 18 V RMS signal at a frequency of 1 Hz. The frontend electronic system consists of a LC filter to process the high voltages from the harvester, a rectifier to convert the AC signal into a DC signal, a regulator to convert this DC signal into a stabilized and ripple free DC signal to provide biasing to the final stage, Delta-Sigma ADC, which finally converts the analog signal into digital bits. The power consumption of the proposed design is approximately 5 uW. According to the proposed design, monitoring the load several times a day is feasible by relying only on the harvested power. The prototype of the proposed system has been fabricated on a printed circuit board (PCB) and tested with the designed harvester. The test results demonstrate that triboelectric energy harvesting is a promising technique for self-monitoring the load inside knee implants. Through this research, the knee implants could be improved and failures can be detected at an early stage.

Rotational energy harvesting has received massive attractions due to the abundance and availability of rotational motions in ambient environments. This paper considers a rotational impact energy harvester by utilizing the static instability of a centrifugal softening beam. During the rotation, two rigid piezoelectric beams are impacted by the centrifugal softening driving beam to generate electric energy. When the rotational frequency is increased, with the centrifugal effect, the amplified relative motion between the driving and generating beams significantly contributes to the increase of the impact force and in turn the output power. The theoretical model is developed and used for numerical simulation. It is shown that the output voltage can be significantly improved with the centrifugal softening effect. Furthermore, the impact force is demonstrated to prevent the driving beam from continuously deflecting and suffering the mechanical failure.

For piezoelectric sensors, the usage of flexible substrates can achieve better performance with higher strain comparing to using rigid substrates. However, most of flexible substrates are plastic based materials which cannot be sustained under high temperature greater than 300°C during the sintering or annealing process which will up to more than 800°C in the fabrication process. Moreover, the cracks are easily formed during transferring when the thickness of PZT film is larger than 10 μm. Although, there are transferring technique in flexible electronics process such as epitaxial lift-off (ELO) and water-assisted transfer printing (WTP) developed by other groups, but the target film should be soaked into the etchant or other solvent to achieve transferring which may affect the performance of PZT film. Nowadays, there still have no suitable method to transferring the PZT thick film with standardized process. In this research, we modify and improve the transferring technique by adding sacrificial metal layer without solvent-assisted that the thick PZT film deposited by screen-printing method can be transferred to flexible substrates successfully. Also, the PZT film by screen-printing method can achieve greater than 10 μm thickness without cracks before and after transferred. Finally, the transferring technique used for batched thick PZT film deposited by screen-printing method is proved by simple piezoelectric cantilever output performance characterization.

In the past decade, nonlinearity has been introduced into piezoelectric energy harvesters (PEH) for power performance enhancement and bandwidth enlargement. While a great emphasis has been placed on the structural design and the effect of electrical part on the nonlinear dynamics of the system, the maximum power and power limit, an important aspect for performance optimization of nonlinear PEHs, are rarely studied, especially their relationship with that of linear PEHs. To this end, this paper is motivated to investigate the maximum power and power limit of a representative type of nonlinear PEHs, i.e., monostable. An equivalent circuit is proposed to analytically study and explain the behaviors of monostable PEHs, and reveals the connection between linear and monostable PEHs. The effect of nonlinearity, e.g., due to the additional magnetic force, is modeled as a nonlinear stiffness element mechanically and a nonlinear capacitive element electrically, based on the harmonic balance method. Facilitated by this equivalent circuit and the impedance matching technique, clear closed-form solutions of power limit and critical electromechanical coupling, i.e., minimum coupling to reach the power limit, of monostable PEHs are obtained. Then the effect of excitation level and magnetic field on the power and electromechanical coupling of the system is investigated. Though this paper uses monostable PEHs as an example, the results and technique can be extended to other similar types of nonlinear PEH systems as well, for example, bistable.

Internet of things (IoTs) enables a cloud of physical devices to be network-connected, providing real-time information of the physical environment for decision-making [1,2]. The recently advocated 5th-generation (5G) communication with nearly zero time-delay has greatly contributed the development of IoTs. It is estimated that 20.4 billion connected items will be in use by 2020, forecasted by Gartner, Inc [3]. An IoT system usually consists of sensors, actuators, controlling and communication circuits. Each sensor serves as a node in the network, and there are usually more than ten thousand sensor nodes in an IoT system. It is a challenging issue to supply electrical power to a cluster of sensor nodes. The employment of battery in a sensor will greatly affect the device reliability and durability where the battery replacement is usually difficult, and the chemical substances in batteries are normally harmful to environments [4,5]. To solve this issue, self-powered electronic devices have emerged as an alternative approach to operate without external electrical power supply, where the electrical power can be harvested from the ambient environment energy including solar, thermal and mechanical energies

6], [7], [8], [9

. Among various paradigms for energy harvesting, the recently proposed triboelectric nanogenerator (TENG) has capacity to harvest the mechanical energy from the ambient environment by coupling the triboelectrification and electrostatic induction effects, where the extremely high voltage can be attained and the thickness of the device can be shrank down to be an extremely small size

10], [11], [12

. A TENG is intrinsically a self-powered mechanical sensor with a high signal to noise ratio owing to its high-voltage output. In this case, a variety of self-powered TENG stress sensors have been proposed including seawater pressure sensor, human-machine interface, smart keyboard, etc

13], [14], [15

. However, even though TENG can achieve extremely high voltage owing to the nature of the low capacitance, the transferred charge between electrodes is very small where the short-circuit current is usually lower than 100 μA. This causes the design of signal processing circuits to be difficult, where extremely high sensitivity is needed. Furthermore, cable connection is usually needed to transfer the mechanical signal detected by a TENG to the control panel, however, for several specific applications including infrastructure health monitoring in severe environments, turbulence detection in the deep sea, wireless smart keyboard, and so forth, cables for electrical connection are not allowed. Thus, cable-free self-powered TENG based mechanical sensing is desirable. Free-space optical communication (FSOC) is an effective approach for the wireless sensing, where information can be carried through the light [16,17]. Optical switch is a key component for the FSOC, where the signal can be loaded by switching on and off

18], [19], [20

Optical switching have been achieved by various physical mechanisms including twisted nematic (TN) cells, surface-stabilized ferroelectric liquid crystals (SSFLCs), polymer-dispersed liquid crystals (PDLCs), electrowetting actuation, etc

20], [21], [22], [23], [24], [25

. Among these approaches, electrowetting optical switch (EOS) presents several advantages such as low manufacturing cost, high reliability as well as long lifetime

25], [26], [27

. The majority of raw materials including conducting fluids, insulating oils for EOS are all available from daily life, which are inexpensive and non-toxic. The fabrication of the EOS is simple, where chemical reactions and micro-fabrications are not needed. In order to actuate the liquid by varying the interfacial tension between the conducting droplet and the dielectric substrate or oil, high-voltage outputs are required. Conventional high-voltage sources are usually bulky, bringing difficulties in system integrations, and dangerous in several specific situations. Circuit design for connecting the high-voltage source and the mechanical sensor is extremely complicated. TENGs, in contrast, can achieve high voltages and mechanical sensing at the same time, of which the structure can be very compact. In this study, it is the first time ever that a TENG-driven electrowetting optical switch was developed by a combination of a freestanding sliding mode triboelectric nanogenerator (FS-TENG) and an electrically tunable liquid lens (ETULL). The ETULL was fabricated by a conducting fluid, an insulating oil, an acrylic cylindrical spacer as well as two indium tin oxide (ITO) electrodes. Upon applying a voltage on the ETULL, the interface between two liquids was curved due to the electrowetting effect, forming an insulating oil based concave lens. The light propagation through the ETULL could be switched between the on state, which means no light diverging at the flat interface, and the off state, where the light was diverged by the concave lens. The switch was controlled by the voltage generated by the FS-TENG. To verify the effectiveness of the proposed self-powered EOS, a wireless sensing system was performed and the mechanical motions were remotely detected. Such a mechanical-electrical-optical signal conversion enabled the wireless sensing, which can be applied for various fields such as human-machine interfaces, remote monitoring of the infrastructure health, security detections, wireless smart keyboard, etc. Reference [1] J Gubbi, R Buyya, S Marusic, M Palaniswami. Internet of Things (IoT): A vision, architectural elements, and future directions, Future Generation Comput.Syst. 29 (2013) 1645-1660. [2] L Tan, N Wang, Future internet: The internet of things, 5 (2010) V5-376-V5-380. [3] https://www.gartner.com/en [4] D Aurbach, I Weissman, A Zaban, P Dan. On the role of water contamination in rechargeable Li batteries, Electrochim.Acta. 45 (1999) 1135-1140. [5] P Onianwa, SO Fakayode. Lead contamination of topsoil and vegetation in the vicinity of a battery factory in Nigeria, Environ.Geochem.Health. 22 (2000) 211-218. [6] A Das, Y Gao, TT Kim. A 220-mV power-on-reset based self-starter with 2-nW quiescent power for thermoelectric energy harvesting systems, IEEE Transactions on Circuits and Systems I: Regular Papers. 64 (2017) 217-226. [7] P Gardonio, M Zilletti. Vibration energy harvesting from an array of flexible stalks exposed to airflow: a theoretical study, Smart Mater.Struct. 25 (2016) 035014. [8] P Glynne-Jones, NM White. Self-powered systems: a review of energy sources, Sens Rev. 21 (2001) 91-98. [9] FK Shaikh, S Zeadally. Energy harvesting in wireless sensor networks: A comprehensive review, Renewable and Sustainable Energy Reviews. 55 (2016) 1041-1054. [10] Y Chen, Y Zhang, T Zhan, Z Lin, SL Zhang, H Zou, et al. An Elastic Triboelectric Nanogenerator for Harvesting Random Mechanical Energy with Multiple Working Modes, Advanced Materials Technologies. (2019) 1900075. [11] F Fan, Z Tian, ZL Wang. Flexible triboelectric generator, Nano energy. 1 (2012) 328-334. [12] G Zhu, J Chen, T Zhang, Q Jing, ZL Wang. Radial-arrayed rotary electrification for high performance triboelectric generator, Nature communications. 5 (2014) 3426 [13] P Bai, G Zhu, Q Jing, J Yang, J Chen, Y Su, et al. Membrane‐based self‐powered triboelectric sensors for pressure change detection and its uses in security surveillance and healthcare monitoring, Advanced Functional Materials. 24 (2014) 5807-5813. [14] J Luo, FR Fan, T Zhou, W Tang, F Xue, ZL Wang. Ultrasensitive self-powered pressure sensing system, Extreme Mechanics Letters. 2 (2015) 28-36. [15] M Xu, S Wang, SL Zhang, W Ding, PT Kien, C Wang, et al. A highly-sensitive wave sensor based on liquid-solid interfacing triboelectric nanogenerator for smart marine equipment, Nano Energy. 57 (2019) 574-580. [16] VW Chan. Free-space optical communications, J.Lightwave Technol. 24 (2006) 4750-4762. [17] K Kiasaleh. Performance of APD-based, PPM free-space optical communication systems in atmospheric turbulence, IEEE Trans.Commun. 53 (2005) 1455-1461. [18] A Boucouvalas, P Chatzimisios, Z Ghassemlooy, M Uysal, K Yiannopoulos. Standards for indoor optical wireless communications, IEEE Communications Magazine. 53 (2015) 24-31. [19] BR Moss, JS Orcutt, VM Stojanovic. Devices and techniques for integrated optical data communication. (2018). [20] Y Silberberg, P Perlmutter, J Baran. Digital optical switch, Appl.Phys.Lett. 51 (1987) 1230-1232. [21] W Lee, C Wang, Y Shih. Effects of carbon nanosolids on the electro-optical properties of a twisted nematic liquid-crystal host, Appl.Phys.Lett. 85 (2004) 513-515. [22] C Zhang, H Wang, S Guan, Z Guo, X Zheng, Y Fan, et al. Self‐Powered Optical Switch Based on Triboelectrification‐Triggered Liquid Crystal Alignment for Wireless Sensing, Advanced Functional Materials. (2019) 1808633. [23] S Shoarinejad, A Sadeghisahebzad. Threshold properties of nanodoped surface stabilized ferroelectric liquid crystals under electric and magnetic fields, Journal of Molecular Liquids. 220 (2016) 1033-1041. [24] R Sutherland, V Tondiglia, L Natarajan, T Bunning, W Adams. Electrically switchable volume gratings in polymer‐dispersed liquid crystals, Appl.Phys.Lett. 64 (1994) 1074-1076. [25] L Li, C Liu, Q Wang. Optical switch based on tunable aperture, Opt.Lett. 37 (2012) 3306-3308. [26] C Murade, J Oh, D Van den Ende, F Mugele. Electrowetting driven optical switch and tunable aperture, Optics express. 19 (2011) 15525-15531. [27] J Wu, Y Du, J Xia, W Lei, T Zhang, B Wang. Optofluidic system based on electrowetting technology for dynamically tunable spectrum absorber, Optics express. 27 (2019) 2521-2529.

Non-traditional information storage has become increasingly ubiquitous as a means of providing interactive, environment-specific information. Two popular examples of this are Optical Quick Response (QR) codes and Radio-Frequency Identification (RFID) tags, which are used in product tags, anti-theft systems, tamper-evident seals, logistics, etc. From a security point-of-view though, these two examples have unique drawbacks. Optical QR codes can be easily viewed and replicated because they are limited to the surface of objects, and RFID tags are prone to remote RFID skimming. With this in mind, we are investigating a PZT-based information storage method which has visibly indistinguishable features, is incompatible with skimming, and can be used with a QR-type encoding scheme. This information storage method involves a frequency-dependent array of transducers with engineered resonance profiles. In this proceedings, we investigate methods of engineering these resonance profiles for the case of a square PZT wafer. Specifically, we investigate the use of non-uniform poling to enhance specific resonances. Simulation results and a discussion of changes to the resonance characteristics resulting from non-uniform poling are included.

In this paper, we present a gradient-index (GRIN) metamaterial lens design toward enhanced sensing by amplifying ultrasonic guided wave signal carrying defect information in pipelines. The curved GRIN lens conforms over the steel pipe and consists of cylindrical steel stubs with varying height according to the hyperbolic secant profile of the refractive index around the circumference of the pipe. We design the lens to perform above the audible frequency range as utilized in ultrasonic inspection of pipelines. By tailoring the dispersion curves of the longitudinal and torsional pipe modes that are commonly used in guided wave testing elastic wave focusing is successfully achieved at focal spots of the lens. Amplification of the multi-mode guided wave signals is validated through experiments performed on a lab scale steel pipe.

The flexoelectric effect of solids represents a new branch of research. As an electromechanical conversion mechanism, it occurs in all dielectric materials. This offers new applications based on a large number of possible materials. Based on that, an investigation of properties and conversion conditions are of great importance. It is important to find out the significance of flexoelectric energy conversion in relation to other conversion mechanisms. This paper attempts to verify the flexoelectric effect in simple dielectric materials and to investigate the applicability in the area of energy harvesting (EH). In our studies, dielectric Polyethylene-Terephthalate (PET) polymer films were used in two different plate capacitor configurations. Two different measurement setups were built to enable the evaluation of polymer films under changing conditions. Main verification parameter of the energy conversion is the electrical voltage change in a differential measurement setup. Changing strain gradients, the basis of the flexoelectric conversion, were generated in two separate ways in thin PET-films. First results clearly show the presence of flexoelectric conversion. The height of the voltage pulses by mechanical loading of the samples cannot be explained by capacitive energy conversion only. Another effect is required to explain the electrical response - FLEXOELECTRICITY

This paper introduces a transient-motion-powered IoT sensor node, which is called ViPSN-E. It can carry out motion detection and wireless communication by making good use of the energy harvested from an instantaneous unidirectional motion. The mechanical energy harvester is composed of a piezoelectric cantilever and a pair of repelling magnets, which realize the plucking excitation under low-speed movement. Different from the system under periodic excitation, whose energy can be continuously accumulated over time, a single plucking motion only inputs a limited amount of energy to the system. An asymmetric structure is designed for identifying the open-door and close-door paths based on the differences between the amounts of their harvested energy. The working mechanism of the magnetic plucking motion is analyzed considering the potential wells variation during the open-door and close-door movements. On the other hand, efficient conversion and utilization of the limited amount of energy are challenging. The prototyped ViPSN-E includes an efficient power management unit, therefore can make good use of the energy harvested from each transient plucking motion. Only one plucking can fulfill the tasks of temperature sensing, motion direction detection, and several rounds of wireless transmissions. The harvested energy and consumption of the IoT node are analyzed to validate the feasibility of this design. The proposed ViPSN-E provides valuable guidance towards the design of self-powered ubiquitous motion-sensing systems.

The nonlinear energy sink (NES) is becoming increasingly accepted as a promissory noise and vibration technique, mainly due to its multi-mode reduction capability and its improved robustness. To realize an NES, however, sophisticated arrangements and sub-systems have to be implemented in the structure to be controlled. For instance, in slender, elastic structures treated with piezoelectric attachments, the need for canceling the linear term that accounts for the stiffness in the electrical domain makes the use of so-called negative capacitance (NC) circuits to be compulsory. In this line, this paper scrutinizes the effects of negative capacitance circuits on the residual piezoelectric capacitance and the electromechanical coupling term. In special, the effects of the linear S and H circuits are thoroughly examined through numerical investigations, based on a finite element of a piezoelectric plate, on which a pair of piezoelectric patches have been placed on top and bottom of a cantilevered aluminum structure. Whilst the S circuit leaves a residual positive capacitance in the electrical domain of the system, the H circuit realizes a residual negative capacitance with which the effect and benefits of adding a nonlinear cubic force in the system become apparent. The numerical results also show that the multi-mode performance of the piezoelectric NES can be significantly improved by reducing the mass term of the electrical domain to an infimum fraction of the inductance previously tuned using a linear resistance-inductance (RL) reference circuit. The piezoelectric NES is eventually submitted to a number of elastic system de-tuning scenarios, from which its robustness against environmental perturbations has been verified.

A lamb wave is a guided wave that propagates along a plate-like structures in various systems. Particularly, in space structures where weight saving is very important, various vibrations are often transmitted as Lamb waves; therefore, control and mitigation of Lamb waves are important issue. Since the high frequency components included in the pyroshock can be fatal to electronic devices, many engineers have studied shock isolators for mounting and protecting such electronic devices. Lamb waves, as with light, are refracted with a certain angle due to the difference in wave speed between the two media. Using the refraction of the lamb waves, shock response for selected region can be reduced by changing direction of the wave. Theoretically, this effect can be achieved by simply attaching a thin elastic material on the host plate to change flexural stiffness. Thus, it would be a very efficient solution to reduce shock response in a specific area behind the patch on the wavefront path by attaching one elastic patch on the path of the Lamb wave. In this study, we proposed elastic patches of various shapes for shock reduction, and the shock reduction characteristics of several patches were numerically and experimentally confirmed. The plane Lamb waves generated from the array of piezoelectric disk attached to the thin metal plate were refracted when passing through the elastic patch; as a result, the shock response was decreased in the area behind the patch.

High-performance control systems (HPCSs) are sophisticated vibration mitigation strategies that include active, semi-active and hybrid systems. They generally outperform passive supplemental damping systems by relying on a feedback mechanism enabling adaptability, resulting in better control reachability over a wide excitation frequency bandwidth. HPCSs are therefore ideal for multi-hazard mitigation. However, the performance of these systems is highly dependent on the controller design, which requires appropriate tuning based on assumptions or on knowledge of dynamic parameters, long-term performance of sensors, excitations, etc. The quantification of performance based on possible uncertainties on such assumptions and/or knowledge could be a powerful tool in financially or technically justifying the use of an HPCS, or simply to benchmark the long-term performance of a given control algorithm. This paper investigates a methodology to assess the performance of control algorithms under various sources of uncertainties. To reduce the computational demand of the uncertainty quantification process, surrogate models are employed to map the nonlinear relationship between structural response and controller configurations. Long-term performance is quantified using life-cycle cost analysis. The investigation is conducted on a 39-story building, located in Boston (MA), and equipped with a set of semi-active friction devices. Results demonstrate that the proposed framework can be used to assess the performance of a given control algorithm considering various sources of uncertainties.

Noise is often generated in different parts of a structure than where it is perceived, e.g. cabin noise caused by engine or APU of aircraft. Passive materials can reduce noise, but are mainly effective in a higher frequency range and require additional mass. Active systems in turn address low frequency noise, targeting different measures (sound pressure, vibration velocity, radiated sound power). Another approach is the focus on structural intensity (SI), i.e. transmitted power per unit area. Hereby, an active barrier for structure-borne sound can attenuate the downstream structure and avoid noise emission. Therefore, a real-time measurement of SI is crucial. It can be estimated using accelerometer arrays with different levels of simplifications. The presented numerical study assesses these methods, addressing the actuator and error sensor placement on a plate structure. A linear feed-forward filter is implemented, hence the SI it is split into its linearly dependent components. The necessary amount of control forces and virtual error sensors is assessed, with respect to dependencies on wavelength and the type of SI components. The study shows an advantage of SI control compared to a conventional velocity control. A small number of error sensor positions and actuators can achieve a higher global attenuation. Simplified and more robust methods for SI estimation are favorable for a practical implementation. For example by controlling only velocity and angular rate or bending moments, a rather high attenuation can be achieved.

Mechanical metamaterials can be designed to give rise to exotic properties such as negative stiffness, negative Poisson’s ratio (auxeticity), and tailorable buckling by selectively designing the geometry of the host material. However, these behaviors are typically fixed and cannot be changed once the metamaterial has been fabricated. Motivated by the goal of post-manufactured application-specific adaptability, we present a soft mechanical metamaterial with pressurized circular voids for in-situ tunable mechanical properties. Prototypes are created by curing a two-component silicone rubber in a 3D printed mold. The circular voids are sealed at one end and independently connected to a pressure source on the opposite side, allowing any subset of the voids to be pressurized. Uniaxial compression tests are then conducted on a universal testing machine. Through selective pressurization of the voids, we demonstrate tunability of the material’s stiffness profiles and the critical loads that lead to the onset of auxeticity and/or buckling. Numerical investigations allow deeper insight, revealing that selective pressurization affects the qualitative shape of the first buckling mode and illustrating how pressurization can break the auxetic behavior of the nominal, unpressurized specimen. Overall, the outcomes demonstrate that soft elastomers with selectively pressurized voids can express quantitatively and qualitatively tunable responses, offering potential for new types of mechanical metamaterials with predictable, in-situ tunability.

This paper presents a fabrication method for polymer films with programmable self-folding behavior. The target shape of the films is provided as a polygonal mesh. The unfolding polyhedra method is used to determine the layout of the folds and faces forming a planar origami sheet which can be folded towards the target shape. Photolithographic masks are printed with the determined layout and used in a photolithography process that produces polymer films with compliant folds of low cross-linking density and stiff faces of high cross-linking density. During the development step in the photolithography process, the films exhibit inhomogeneous developer absorption at the folds, with a higher concentration on the side of the folds that is in direct contact with the developer solution. The non-uniformly absorbed developer is removed upon heating the films, causing inhomogeneous strains across the thickness of the folds which leads to thermally-driven self-folding. The folded configuration of the films is made permanent by subsequently cooling the folded films to room temperature and saturating their cross-linking density through UV exposure. In the fabrication method, the fold angle achieved by each fold in the films is modulated by adjusting their width. A formula relating fold angle and fold width is calibrated using experimental data and incorporated into the computational implementation of the unfolding polyhedra method to precisely size the folds when creating the templates for the photolithographic masks. This method thus produces polymer films that are programmed to accurately self-fold into a target shape when heated. The fabrication method is demonstrated by producing various three-dimensional shapes. Potential applications of the fabricated programmable films include packaging of micro-systems and entrapment of cells.

In this work, the vibration transmissibility behavior of novel dome shaped auxetic structures with different cellular configurations are simulated using Abaqus 6.14 and subsequently studied experimentally. The dynamic behavior of domes and hourglass shape auxetic structures are studied within the frequency bandwidth of 5-500 Hz by using base excitation technique. The auxetic samples are subjected to broadband excitation at low dynamic strain, followed by sine sweep around the resonance of the system. The dynamic and modal behaviors are experimentally analyzed by using 3D Laser Doppler Vibrometer. The system is shown to develop specific wave propagation and attenuation bands, outline of which is important for developing strategies for damping/energy harvesting. Further, analysis has been carried out to analyze the mechanical wave propagation behavior when the system is subjected to broadband excitation frequency at low dynamic strains. Here, we have arranged a large periodic repeating units of hourglass shape auxetics with lumped mass inside it placed at the center. The equivalent spring-mass-damper mechanical circuit has been developed for the shake of simplifying our system. The Non-linear stiffness of hourglass structure depend upon constitutive cellular cells i.e. auxetic, regular honeycomb and plane, which is evident for getting broader bandgap formation than the linear one. The lumped mass is considered here as locally resonating metamaterial enabling low-frequency vibration attenuation. Furthermore, the analysis is being done for bandgap expressions depending upon the added mass ratio and target frequency. Further study is proposed for attenuation and transmission band analysis to steer the waves which roots the idea of vibration sink, in which we can damp the mechanical waves effectively at a specific location. The Auxetic meta-materials are envisaged to have a significant role in wave attenuation and wave steering, and can be used effectively for vibration control.

In this research, we propose a novel and comprehensive origami-based solution to the long-standing challenge regarding lattice-based mechanical metamaterials: how to systematically construct a lattice and transform it among different symmetric configurations in a predictable, scalable, and reversible manner? By bridging the lattice geometry and rigid-folding kinematics, we reveal that origami can be used as a versatile scaffold to construct all types of 2D and 3D Bravais lattices. Via rigid folding, the origami lattices can undergo all diffusionless phase transformations, which can trigger fundamental lattice-symmetry switches. The proposed theoretical framework of origami lattice can open up new avenues towards engineering metamaterials and metastructures that can alter their underlying lattice structures on-demand, which will create new applications beyond what has been explored.

In this paper, we report a non-prismatic one-dimensional piezoelectric linear motor driven by a new method called “Multi- Integer-Frequency Multi-Mode.” The non-prismatic structure of the piezoelectric linear motor is constructed by a 180mm long by 17mm wide by 0.4mm thick stainless steel plate with two30mm long by 17mm wide by 0.6mm thick PZT actuators attached on the top and bottom of the stainless steel plate on two ends. To enable multiple bending modes can be superimposed equally, the ratio of driving voltage and the phase difference between modes are designed to make all of activated modes to have similar amplitudes. Thus, we can activate multiple bending modes for generating traveling waves on the piezoelectric motor. Furthermore, the driving frequencies are made to have a relationship of integer multiplication, and it can improve the efficiency of traveling wave generations. Applying this concept, we developed analytical and a simulation method to analyze the formation of traveling waves. It was identified numerically and verified experimentally that traveling waves can be excited by using the first to the fourth bending modes. We also introduced Hilbert Transform as the design tool for driving optimization and successfully found the most efficient traveling wave driving parameters. Using identified parameters, traveling waves were sufficient induced to push a 5.6g object on the piezoelectric motor in the region between 69.7mm and 122.6mm with an average velocity of 3.1mm/s.

Though there exist numerous researches concentrating on theoretical modelling of an electret-based vibration energy harvester (eVEH) connected with a pure load resistor, holistic modelling of eVEH with DC interface circuits is rarely studied. In this paper, a theoretical model of the eVEH connected to a DC interface circuit with a full bridge rectifier is proposed and validated by simulation and experiment. The power loss of eVEHs due to the reverse current leakage of diodes in the rectifier is investigated. The results show that the diodes with large reverse current are not recommended to construct the rectifier for eVEHs, due to the large impendence feature of the eVEH.

Tensairity refers to a class of lightweight structure which has a wide range of interesting applications such as temporary bridges, inflatable kites, of unmanned aerial vehicle wings and mainsail in sailing boats. A Tensairity structure has three main components, namely tension element, compression element and air beam. The primary purpose of the air beam is to stabilise the compression element under loading. The combination of these elements results in a structure which has lightweight compared to conventional structures for the same strength and vice versa. In this study, we explore a new concept of meta tensairity beam. Air is modelled as spring, and an additional torsional spring has been used between the two beams and this structure has been repeated periodically. Both tension and compression elements have been modelled as Euler Bernoulli beam. The unwanted vibration which occurs in the tensairity structure can be attenuated by varying the stiffness of torsional spring. Band structure of meta tensairity beam has been obtained by using Bloch theorem and transfer matrix method. The phenomenon of frequency band attenuation has been incorporated in the Tensairity structure, and it gives rise to a new set of design potentials for lightweight structures. Real-time health monitoring of tensairity structures can also be done by harvesting energy from meta tensairity, which makes it a self-sustaining system.

Bistable fiber composite laminates have promising capabilities for shape morphing and have found applications in advanced airframes, energy harvesting, and robotics. Their bistability originates from an asymmetric ply layout and can create highly complex deformations during the snap-through from one stable state to the other. There- fore, it is essential to understand the transient behaviors of these laminates under different loading conditions. Although simple symmetric loading conditions are well understood, asymmetric loading conditions received far less attention. In this study, we investigate the transient deformation of a [0°/90°] square laminate subjected to an asymmetric point load at different locations. Finite element simulation and experimental testing both show that, depending on the loading position, snap-through can either be a one-step or two-step process, while each step is related to the curvature change of a laminate edge. Also, at some loading positions, snap-through is unattainable regardless of the input magnitude. The results of this study would help us obtain a more comprehensive understanding of the nonlinear mechanics of bistable composite laminates showing transient response to different external forces.

Elastic mechanical metamaterials exhibit unusual frequency contingent properties like negative mass, negative Young’s modulus, and negative Poisson’s ratio in a particular band of the excitation frequency. Locally resonant units in the designed metamaterial enable bandgap formation virtually at any frequency for wavelengths much higher than the lattice length of the unit. Due to out of phase motion of multiple resonating units with lattice, there is a change in the dynamic properties (stiffness or mass or density) of the material as these properties become frequency-dependent.On another side, at higher frequencies for wavelengths equal to the lattice size of the medium, the Bragg scattering phenomenon occurs, which also helps in the bandgap formation. Therefore, these extreme frequency contingent physical properties modulate wave propagation through designed metama- terials. In this research, the band structure of piezo-embedded negative stiffness metamaterial is derived using generalized Bloch theorem. Bloch theorem is used to solve various periodic media problems in different fields. The relationship between frequency and wave number can be established using this theory. The results elucidate that the insertion of the piezoelectric material in the resonating unit can provide not only better tunability but also several unusual band structures that can be perceived. The attenuation bandwidth of the designed metamaterial can be tailored through critical parameters derived from the extensive non-dimensional study of the system. This research can be considered as a contribution towards designing the active elastic mechanical metamaterials.

In this paper, we report our work on developing a film-type speaker based on a porous ferroelectret film. This speaker was made of a micro-porous polypropylene film. The advantage of this porous PP film is that it is lightweight and flexible and contains multiple void structures which allow it to store a large number of space charges and to have a piezoelectric effect. Even though microporous polypropylene film has been used in many applications for sensors and actuators, the application for speakers has been limited as it has a poor low frequency response. To break through this limitation, we developed two fixtures which can introduce tension for changing the void structure and for changing the density of the porous film for enhancing the acoustic intensity and overcoming the low frequency response. The two PMMA fixtures possessed an array of rectangular or circular holes to create the ferro-electret film array. They contain a sealed cavity to create negative pressure which can be used to create a curvature to each film for changing the void structure and film density. Our experimental finding showed that the acoustic response at low frequency was successfully enhanced and became smoother after introduction of curvature to the film. We found that the acoustic response of a 12.5mm diameter film was better than film with a diameter of either 10mm and 7.5mm. The optimization of the array fixture and experimental studies are discussed in this paper.

Robot inverse kinematic problem is a widely studied problem. In this paper, we present a numerical method to solve robot inverse kinematic problem based on screw theory. In this method, we transform the inverse kinematic problem into optimization problem and a damping term is introduced. It combine the advantages of Newton method and gradient descent method improve the shortcomings of both methods. At last, we use this method to solve the inverse kinematics problem of JARI 6R serial industry robot and the calculation result is shown.

In the recent past, bistable laminates have been widely studied for their potential in wing morphing applications. The existence of multiple stable states makes them extremely viable as structural elements. However, for successful deployment, these laminates must be integrated into a larger mechanism. For integration, the bistable laminates are required to be clamped to a larger structure without the loss of bistability. In this work, an attempt has been made to understand the effect of integration (i.e., using different structural constraints and clamping) on the bistability and the snapthrough performance of a special class of hybrid bistable symmetric laminates (HBSLs). The structural analysis has been carried out using FEA software ABAQUS. Subsequently, a conceptual design of a morphing wing is proposed based on the insights gained from the numerical analysis that uses two HBSLs as skin with a corrugated core. Finally, using the analysis guidelines, two HBSL skins and a circular corrugated core are manufactured and integrated to show the possibility of using such bistable laminates as skin.

Inertial actuators are widely used in active vibration control, since they don’t need to react off the base structure. Then, unlike reactive actuators, they can be used as modules that can be directly installed on a vibrating structure. In many cases, inertial actuators are used to develop some stand-alone active dampers. Such devices are embedded with sensors and a microcontroller, in order to independently perform the vibration control task. This kind of control unit is commonly adopted to implement decentralized architectures. In this work, the main goal was to limit instability phenomena related to the dynamics of inertial actuators. The proposed solution also aims to improve the performance of a decentralized control strategy through a partial sharing of data between devices, without the use of cables. First, the formulation of the modified Negative Derivative Feedback resonant controller is derived; then, the steps of the control strategy are explained, which are based on a preliminary modal identification of the structure and the assignment of a compensator for each resonance frequency to be controlled. Finally, the proposed method is validated with experimental results from a clamped-clamped beam.

As a new type of energy harvester that is based on the Maxwell’s displacement current, the unique capacitive model of nanogenerators makes traditional characterization methods unsuitable for unveiling the output capability. Among different nanogenerators, triboelectric nanogenerator (TENG) has been intensively studied due to its high output and high energy conversion efficiency, with area power density reaching 500 W/m2 and the total energy conversion efficiency of up to 85%. However, it should be noticed that with traditional approaches, only a small portion of the maximized energy per cycle (Em) of TENG can be outputted, which cannot reflect its real output capability. To address this issue, the figure-of-merits have been developed. However, the current version of figure-of-merits has limitations in applications, without considering the breakdown effect that seriously affects the effective maximized energy output. Meanwhile, the method to evaluate output capability of nanogenerators is missing. Here, a standardized method is proposed for evaluating the output performance of TENG, which can correctly measure the output capability with the breakdown effect considered. To develop such kind of universal standardized method, we have developed the process flow of the measurement on the maximized effective energy output Eem per cycle. The trickiest part is how to measure the breakdown limits, which can be solved through the measurement circuit developed. The measurement circuit is composed of a TENG as the high voltage source, a targeted device and several electric meters to control the surface charge density and quantitively measure the breakdown point. The targeted device will be powered by the high voltage source TENG and then be triggered to the breakdown condition with typical output characteristic. Through this method, we firstly show the measurement results of breakdown points in the Q-V curves which illustrate sudden changes in both charge and voltage, where the slope before the breakdown point is the measured capacitances at a certain displacement of TENG, and the first inflection point of the Q-V curve is the threshold breakdown point of the device. Based on this, V-Q plots with breakdown points of contact separation and contact freestanding-triboelectric-layer modes TENG are derived through experiments to demonstrate this method, which are consistent with that calculated by Paschen’s law. During the experiments, visible sparks were generated and recorded by video, showing the existence of breakdown. The maximized effective energy output Eem are calculated based on the measured results. And then the standardized evaluation of a PVDF film-based PENG is conducted to further demonstrate the broad applicability of this method. The FOM was revised based on Eem, and calculated for each nanogenerator to enable the comparison across different mechanisms and structures since the former definition of FOM did not consider the breakdown effect, limitating its wide application. This study proposes a standardized method for evaluating the effective output capability of nanogenerators, which is crucial for standardized evaluation and applications of nanogenerator technology.

Dielectric elastomer generation is a power generation method that converts various mechanical energies into electric energy by using a dielectric elastomer. Dielectric elastomer generation can harvest electric energy from renewable energy sources such as sea wave power, hydraulic power (Karman vortex), and wind power. Practical application of dielectric elastomer generation faces various issues; however, this paper will focus on an electrical problem of a dielectric elastomer generation circuit. The dielectric elastomer generation circuit needs an external power supply to charge the dielectric elastomer before starting the electric generation. Additionally, the dielectric elastomer generation circuit requires a high DC voltage. In this paper, we propose a self-excited dielectric elastomer generation circuit using piezoelectric elements. The proposed circuit consists of piezoelectric elements, the Cockcroft-Walton circuit, the dielectric elastomer, and the ringing choke converter. In the proposed circuit, the piezoelectric element is vibrated to generate a voltage, and the generated voltage is boosted to a high voltage value for charging the dielectric elastomer by the Cockcroft-Walton circuit. After the dielectric elastomer generation is completed, the ringing choke converter circuit steps down the generated voltage to a predetermined value, and the generated power is the output to a load. Furthermore, operations of the circuit are confirmed by the simulation and experimental results. The experimental results are obtained by using a test bench. The test bench uses a piston machine driven by a DC motor for the purpose of stretching and shrinking the dielectric elastomer.