Proceedings Volume 4334

Smart Structures and Materials 2001: Smart Electronics and MEMS

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Proceedings Volume 4334

Smart Structures and Materials 2001: Smart Electronics and MEMS

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Volume Details

Date Published: 16 August 2001
Contents: 9 Sessions, 43 Papers, 0 Presentations
Conference: SPIE's 8th Annual International Symposium on Smart Structures and Materials 2001
Volume Number: 4334

Table of Contents

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Table of Contents

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  • Keynote Papers
  • Smart Electronics and RF MEMS
  • Accelerometers and Gyroscopes
  • Smart Skin Antenna and Frequency Selective Surface (FSS) I ARO/NATO Invited Session
  • Keynote Papers
  • Smart Skin Antenna and Frequency Selective Surface (FSS) II ARO/NATO Invited Session
  • Wireless Telemetry
  • Fabrication and Characterization
  • Smart Devices and Systems I
  • Smart Devices and Systems II
  • Smart Skin Antenna and Frequency Selective Surface (FSS) II ARO/NATO Invited Session
Keynote Papers
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Recent progress in MEMS technology development for military applications
The recent progress of ongoing efforts at the Army Aviation and Missile Command (AMCOM) to develop microelectromechanical systems (MEMS) technology for military applications is discussed in this paper. The current maturity level of low cost, low power, micro devices in industry, which range from simple temperature and pressure sensors to accelerometers in airbags, provides a viable foundation for the development of rugged MEMS devices for dual-use applications. Early MEMS technology development efforts at AMCOM emphasized inertial MEMS sensors. An Army Science and Technology Objective (STO) project was initiated to develop low cost inertial components with moderate angular rate sensor resolution for measuring pitch and yaw of missile attitude and rotational roll rate. Leveraging the Defense Advanced Research Projects Agency and other Government agencies has resulted in the development of breadboard inertial MEMS devices with improved robustness. During the past two years, MEMS research at AMCOM has been expanded to include environmental MEMS sensors for missile health monitoring, RF-MEMS, optical MEMS devices for beam steering, and micro-optic 'benches' for opto-electronics miniaturization. Additionally, MEMS packaging and integration issues have come into focus and are being addressed. Selected ongoing research efforts in these areas are presented, and some horizon MEMS sensors requirements for Army and law enforcement are presented for consideration.
MEMS for high-frequency applications
In this paper, we reviewed some of the microelectromechanical system (MEMS) research efforts for high frequency applications. The efforts can generally be divided into two areas: planar reconfigurable transceivers and phased arrays using MEMS devices. For the planar transceivers, the interest is in demonstration of RF MEMS devices with a focus on integration issues including architectures and fabrication. Our goal is to establish building blocks for compact, smart transceivers that have beam forming and tuning functionality. For phased-array applications, system architectures were demonstrated for quasi-optical systems and phased arrays. The purpose is to demonstrate beam forming and steering functionality using MEMS devices instead of expensive phase shifters.
Smart Electronics and RF MEMS
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Laterally movable gate FET (LMGFET) for on-chip integration of MEMS with electronics
Operation of a new device structure called Laterally Movable Gate Field Effect Transistor (LMGFET) is reported here. The device drain current changes linearly with lateral gate motion. A prototype test device was designed and fabricated in our laboratory. A novel three-mask LIGA compatible process was used for device fabrication. A comb drive structure was used to drive the movable gate. On the unoptimized test device, static sensitivity to gate position of 6.4 A/m was observed in saturation with zero gate to source voltage. For the ac drive voltage on the comb drive, a sensitivity of 3.2 nA change in drain current per volt of ac drive voltage were observed at a dc bias of 38 V. Significant improvement in device performance are possible with changes in device design. This, to our knowledge, is the first report on the operation of a LMGFET with a driven gate.
Performance improvement of rf MEMS capacitive switches with high-dielectric-constant materials
Hargsoon Yoon, Yanan Sha, Pramod K Sharma, et al.
A novel approach to improve the performance of a capacitive shunt switch using high dielectric constant materials and monolithic integration based on copper interconnection process is investigated here. To get a high isolation and low actuation voltage, a high dielectric constant material (Ba0.65Sr0.35TiO3) was used in the MIM (metal- insulator-metal) structure, which determines switching isolation characteristics. The realized dielectric constant of this BST thin film was 367 for a thickness of 1500Å. When the BST film is used between the membrane and transmission line instead of silicon nitride, the air gap can be reduced into 1.85 μm with isolation ratio of 4500:1 and actuation voltage of 18 V. In case of 0.85 μm air gap, it is expected to give the isolation ratio of over 2000:1 and actuation voltage less than 7 V. We have also investigated a monolithic integration process of RF MEMS switch with CMOS circuitry using a back-end-of-line process of Cu interconnection technology. This process integration is based on the 6 level Cu interconnection process that includes the MIM capacitor structure.
Analysis of imperfections in a micromachined tunable-cavity interferometer
Jung-sik Moon, Andrei M. Shkel
An alternative to a classical wavelength interferometer (an array of hand-assembled etalons consisting of two semi-transparent mirrors separated by a fixed-cavity) is the implementation of wide band tunable filter using Micro-Electro-Mechanical Systems (MEMS) technology. This approach will allow a single tunable device to replace an array of fixed-cavity filters reducing cost and parts. MEMS technology offers many advantages, including scalability for wide tuning range, sensitivity for precision sensing, and batch fabrication capability for cost reduction While at the same time, MEMS technology introduces many new challenges, which include fabrication yield, device reproducibility, and fabrication imperfections - all are factors seriously limiting performance of MEMS interferometers. Without defects, reflectance must be greater than 99.69% in order to achieve finesse of 1000 to be useful for DWDM applications. Though, the presence of defects limits performance and becomes more pronounced at higher reflectance values. For example, component misregistration while fabricating MEMS interferometer with 95% and 98% reflectance values, result in the reduction of effective finesse of 10% and 42%, respectively. This paper discusses several models for analyzing imperfections in MEMS tunable-cavity interferometers. Based on thermal expansion and component misregistration analysis, we conclude that a passive MEMS-based filter cannot achieve performance required for DWDM applications.
On-chip 3D air core microinductor for high-frequency applications using deformation of sacrificial polymer
A novel on-chip 3D air core micro-inductor, utilizing deformation of sacrificial thick polymer and conformal photoresist electrodeposition techniques, is reported. The bottom conductors are formed on silicon or glass substrate by metal electroplating through SU-8 polymeric mold. A thick SJR 5740 photoresist is then spun on and patterned to be a supporting mesa. Hard curing of such polymer mesa could significantly deform it into a cross-sectional bell-shape sacrificial core with graded profile in which is used to support top conductors formation. A layer of conformal electrodeposited photoresist (PEPR 2400) is then coated along the core's surface profile, patterned by standard optical lithography and filled up by metal electroplating. Finally, all polymeric molds including significantly deformed sacrificial core and electroplating bases are removed, resulting in an on-chip solenoid-type 3D air core micro-inductor. Since this new inductor has an air core and has only two contact points per turn, the core loss and equivalent series resistance are expected to be small, and hence, to give higher quality factor at high-frequency operation. Currently, high-frequency characterization of this on-chip inductor is under way.
Smart-power integrated circuits to drive piezoelectric actuators for a cm3 microrobot system
Manel Puig-Vidal, J. Lopez-Sanchez, P. Miribel-Catala, et al.
Today, the use of robots for self acting tasks in applications ranging from biology and medicine to microsystems technology demand miniaturized dimensions and high-precision handling techniques. A lot of these tasks have been carried out by humans, but the manual capabilities are restricted to certain tolerances. Transport and manipulation of biological cells or assembly of micromechanical parts are the best suited applications for microrobots with sizes about cm3. Low cost and high-resolution actuators are critical performances which determine to choose piezoceramic materials as more suitable for micropositioning and micromanipulation units of a cm3 microrobot. Smart Piezoactuator Unit (SPUs) as a basic element of a new generation of cm3 microrobots have been developped. The main characteristic of this proposed Smart Piezoactuator Unit system is the integration of driving circuitry with the piezoelectric actuators and to include a serial communication interface to minimize the number of power and command wires. Micropositioning and micromanipulation units are developed combining properly 6 Smart Piezoactuator Units each one. A BCD technology (Bipolar, CMOS, DMOS) is used to design high voltage smart power integrated circuit for these Smart Piezoactuator Units. Using this technology we integrate in the same chip 4 power drivers with its control and protection circuitry.
Accelerometers and Gyroscopes
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Micromachined gyroscopes: challenges, design solutions, and opportunities
Micromachined gyroscopes are probably the most challenging type of transducers ever attempted to be designed in micro-world. A nail-size dynamic system integrated with control electronics on the same silicon chip is designed to be a very sensitive sensor which is potentially able to detect maneuvers and motions beyond human perception. Along with exciting opportunities which MEMS gyroscopes could bring to everyday life, the miniaturization introduces many new technical challenges. Multi-degree of freedom dynamics, sensitivity to fabrication imperfections, dynamic instability, limited control resources - all these raise a number of fundamentally challenging issues in the design, analysis, and control of micromachined gyroscopes. In this paper, we summarize principles of operation, review recent research and development efforts, and discuss potential applications and the future market of silicon based micromachined gyroscopes.
Structural and thermal analysis of a MEMS angular gyroscope
This paper describes the structural and thermal modeling of a Micro Electro Mechanical System (MEMS) z-axis angular gyroscope. The gyroscope consists of a oscillating proof mass supported by a suspension made up of six concentric interconnected rings rigidly attached to an anchored frame. The device is capable of measuring angular displacement through precession of the proof mass line of oscillation in the presence of rotation induced Coriolis force. Using a strain energy method, a closed form solution for the effective stiffness of the suspension system is developed, which is confirmed using finite element modeling. A comparative study of the suspension with a commonly used serpentine spring suspension demonstrates that the studied device is robust to thermal fluctuations and residual stresses. A parametric analysis is used to identify an appropriate micromachining technology suitable for the fabrication of the angular gyroscope.
Design, simulation, and testing of IDT-based MEMS gyroscope
William D Suh, K. A. Jose, Pascal B Xavier, et al.
The design and simulation of a Surface Acoustic Wave (SAW) MEMS gyroscope using HP EESOF is presented in this paper. This SAW gyroscope is an integration of a SAW resonator and a SAW sensor. The SAW resonator is designed and optimized using coupling-of-modes theory. The SAW resonator is used to setup the stable reference vibration. A SAW sensor arranged in orthogonal to the resonator. Further to this resonator, strategically positioned metallic dots that form an array along the standing wave anti-node locations are subjected to the reference vibratory motion. These vibrating dot arrays through the Coriolis effect will generate secondary SAW in orthogonal direction under rotation, which can then be picked up by the SAW sensor. Numerical simulation using HP EESOF is used to optimize this gyroscope. This SAW gyroscope can be competitively priced, inherently rugged, reliable and very sensitive, which is capable of being wirelessly interrogated, without any sensor power source. In view of its one-layer planar configuration, this gyroscope can be implemented easily for applications requiring conformal mounting onto a surface of interest.
Microgyroscopes with dynamic disturbance rejection
This paper reports a novel micromachined gyroscope design with inherent disturbance-rejection capabilities. The proposed approach is based on increasing the degrees-of-freedom (DOF) of the oscillatory system by the use of two independently oscillating proof masses. Utilizing dynamical amplification in the 4-DOF system, inherent disturbance rejection is achieved, providing reduced sensitivity to structural and thermal parameter fluctuations and damping changes over the operating time of the device. In the proposed system, the first mass is forced to oscillate in the drive direction, and the response of the second mass in the orthogonal direction is sensed. The response has two resonant peaks and a flat region between peaks. Operation is in the flat region, where the gain is insensitive to frequency fluctuations. Simulations indicate over 15 times increase in the bandwidth of the system due to the use of the proposed architecture. In addition, the gain in the operation region has low sensitivity to damping changes. Consequently, by utilizing the disturbance-rejection capability of the dynamical system, improved robustness is achieved, which can relax tight fabrication tolerances and packaging requirements and thus result in reducing production cost of micromachined gyroscopes.
Hybrid MEMS-IDT-based accelerometer and gyroscope in a single chip
Vijay K. Varadan, William D Suh, K. A. Jose, et al.
In this paper, recent advances made on wireless MEMS-IDT (Interdigital Transducer) based accelerometers and gyroscopes at Penn State and HVS are presented. The concept and design principles are based on using surface acoustic waves (SAW) and polysilicon seismic mass for acceleration and proof mass for gyro. By designing the seismic mass of the accelerometer to float just above a high frequency Rayleigh Surface Acoustic Wave Sensor (SAWS), we are able to realize the accuracy and versatility required for the measurement of accelerations from 10-6 g to 100 g. The gyro design is based on the combination of Surface Acoustic Wave Resonator (SAWR) and Surface Acoustic Wave Sensor, which operates at the Rayleigh mode. The transmitter IDT creates SAW that propagates back and forth between the reflectors and forms a standing wave pattern within the cavity space between the IDTs. The particles at the anti-nodes of standing wave pattern experience large amplitude of vibration perpendicular to the plane of the substrate, which serves as the reference vibrating motion for the gyroscope. A number of metallic (proof) masses are strategically positioned at the anti-node locations so that the effect of the Coriolis force can be used to sense the gyroscopic motion.
Smart Skin Antenna and Frequency Selective Surface (FSS) I ARO/NATO Invited Session
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Electronically reconfigurable and mechanically conformal apertures using low-voltage MEMS and flexible membranes for space-based radar applications
Jennifer T. Bernhard, Nan-Wei Chen, Randall Clark, et al.
The University of Illinois and Northrop Grumman Corporation have teamed to integrate a wide band reconfigurable aperture array with associated wide band T/R functions on a flexible and foldable/rollable substrate for space based radar applications. Advanced MEMS and packaging techniques are used to make the antenna array lightweight, reliable, and reproducible. Soft flexible substrates make the antenna foldable/rollable with the associated electronics below the ground plane of the antenna elements. The individually reconfigurable antenna element uses MEMS switches to select between two broad frequency bands of operation. These MEMS switches have low actuation voltages and stress-free operation, improving the array's reliability. The reconfigurable antenna element is based on a low-profile radiator that provides greatly increased instantaneous bandwidth over microstrip patch antennas currently in place for phased array applications. Voltage-controlled MEMS switches are utilized to switch between stacked layers of elements that operate in the S- and X-bands. In each band, the antenna elements provide at least 25% instantaneous bandwidth. The challenges presented by the flexible substrate and the array design as well as experimental and simulated results for the antenna elements and switches are discussed.
Overview of the DoD's rf multifunction structural aperture (MUSTRAP) program
Kevin H. Alt, Allen J. Lockyer, Daniel P. Coughlin, et al.
The proliferation of antenna systems of state-of-the-art military aircraft has challenged major airframe manufacturers to provide additional outer surface platform space for antenna placement while still maintaining a flightworthy structure. The solution is to design antennas that can sustain severe structural load. The recently completed 'RF Multifunction Structural Aperture (MUSTRAP),' contract number F33615-97-2- 3807 performed by Northrop Grumman Corporation (NGC), El Segundo, California and TRW/ASD, Rancho Bernardo, San Diego, California, together with their DoD customer have met this challenge by conceiving the novel technology of Conformal Load-bearing Antenna Structures (CLAS). Under the Air Force Research Laboratory, Air Vehicles Directorate, Structures Division's leadership and direction, the MUSTRAP team have developed multifunction, broadband, structurally integrated, low cost antennas for communications, navigation, identification (CNI) and electronic warfare (EW) applications in the 0.03 to 2.0 GHz range. Two concepts, a fuselage and a vertical tail installation, were designed, analyzed, fabricated, and tested. The fuselage demonstration article was a load bearing multifunction (UHF/SATCOM) antenna 35 by 37 inch panel subjected to combined axial and shear loading, which replicated realistic flight conditions. Ultimate failure loads imposed on the panel were 1,800 pounds per inch axial loading and 600 pounds per inch shearing loading, after successfully withstanding a single lifetime (6,000 hours) of fatigue. Electrical performance was validated using anechoic chamber measurements. The vertical tail concept was a structural excitation multifunction (VHF/UHF) antenna element that can be tailored to fit in virtually any end cap vertical tail configuration. Designed to endure the severe acoustic environment associated with empennage noise sources, the end cap was successfully flight tested on NASA/Dryden's Systems Research Aircraft (SRA) to validate the structural and electrical performance. Highlights of the program are presented in the text.
Point-actuated aperture antenna development
Marc Angelino, Gregory N. Washington
Consistent changes in both commercial and military satellite needs have created the need for antennas with additional flexibility. Military surveillance may require the ability to focus the radiation pattern to increase the bandwidth or resolution in a certain area. Commercial satellites may need to change coverage area to meet evolving consumer needs or to compensate for adverse weather or atmospheric conditions. Recent studies on active antennas have shown that the far field radiation pattern can be changed by altering the shape of the sub reflector. In this research, we control the antenna far field radiation pattern by controlling the shape of the sub reflector using numerous point actuators placed perpendicular to the reflector surface. The PZT stack coupled with a stick-slip mechanism give the point actuators used in this design an advantage over similar studies using PZT bimorph or PVDF actuators to generate the actuation force in that the displacement can be maintained without the continuous application of voltage. An electromechanical model is used to describe the motion of the stack, and the stick slip mechanism is modeled similar to power screw-type actuators. A combined finite element/electromagnetic analysis code is used to determine the desired shape of the reflector, and the corresponding actuator displacements. The final shape of the reflector is verified using stereo photogrammetry.
Micromachined systems for rf and microwave antenna applications
K. J. Vinoy, Pramod K Sharma, K. A. Jose, et al.
This paper provides a brief review of applications for MEMS based systems in microwave and millimeter wave systems. MEMS based switches, capacitors, inductors, phase shifters and micromachined transmission lines and antennas find increasing applications in recent years. Approaches towards the design and fabrication of two MEMS components such as phase shifters and switches, both making use of high dielectric barium strontium titanate (BST) thin films to improve the performance characteristics are also presented. Electrostatic micro switches made with this approach can be actuated with very low voltages.
Shape control of distributed parameter reflectors using sliding mode control
Fukashi Andoh, Gregory N. Washington, Vadim Utkin
Sliding mode control has become one of the most powerful control methods for variable structure systems, a set of continuous systems with an appropriate switching logic. Its robustness properties and order reduction capability have made sliding mode control one of the most efficient tools for relatively higher order nonlinear plants operating under uncertain conditions. Piezo-electric materials possess the property of creating a charge when subjected to a mechanical strain, and of generating a strain when subjected to an electric field. Piezo-electric actuators are known to have a hysteresis due to the thermal motion and Coulomb interaction of Weiss domains. Because of the thermal effect the hysteresis of piezo-electric actuators is reproducible only with some uncertainty in experiments. The robustness of sliding mode control under uncertain conditions has an advantage in handling the hysteresis of piezo-electric actuators. In this research sliding mode control is used to control the shape of one- and two-dimensionally curved adaptive reflectors with piezo-electric actuators. Four discrete linear actuators for the one-dimensionally curved reflector and eight actuators for the two-dimensionally curved reflector are assumed.
Optimized multilayered wideband absorbers with graded fractal FSS
K. J. Vinoy, K. A. Jose, Vijay K. Varadan, et al.
Various approaches have been followed for the reduction of radar cross section (RCS), especially of aircraft and missiles. In this paper we present the use of multiple layers of FSS-like fractal geometries printed on dielectric substrates for the same goal. The experimental results shown here indicate 15 dB reduction in the reflection of a flat surface, by the use of this configuration with low loss dielectrics. An extensive optimization scheme is required for extending the angle coverage as well as the bandwidth of the absorber. A brief investigation of such a scheme involving genetic algorithm for this purpose is also presented here.
Keynote Papers
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MEMS and nanotechnology research for the electronics industry
Y. Eugene Pak
The 20th Century has witnessed breathtaking developments in the miniaturization and the large-scale integration of microelectronic devices that have had an enormous impact on human affairs. The same miniaturization paradigm can be applied to mechanical devices using MEMS technology leading to ultra small micromachines that cannot otherwise be fabricated using conventional machining and assembly techniques. The MEMS technology is expected to have a great impact in the 21st century by enabling many complex electromechanical systems to be fabricated and integrated. In this paper, applications of MEMS to many areas relating to information and biotechnology are discussed. These topics are presented in the context of ongoing research at the Samsung Advanced Institute of Technology (SAIT). SAIT is the central research laboratory for the Samsung Corporation whose charter is to develop breakthrough technologies to be the leader in the 21st century.
Smart Skin Antenna and Frequency Selective Surface (FSS) II ARO/NATO Invited Session
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Planar reconfigurable slot antenna for communications
Dimitrios Peroulis, Kamal Sarabandi, Linda P.B. Katehi, et al.
A new approach for implementing electronically tunable antennas is presented in this paper. The basic concept is to vary the effective electrical length of the antenna by controlling the bias conditions of solid state switches mounted on the slot. The implemented antennas is resonating at three different frequencies spanning the range of 550 to 700 MHz with no matching networks required.
Distortion of conformal antennas on aircraft structures
Harmen Schippers, Hans van Tongeren, Jaco Verpoorte, et al.
Conformal antennas on aircraft allow the use of non-conventional antenna locations such as the skin of the aircraft. However, when antennas are installed at these locations they are subject to steady and unsteady aerodynamic loads. The inertial forces and these aerodynamic loads will cause deformations and vibrations of the total antenna surface. The effect of these distortions on antenna performance will be most significant on highly directional antennas. The aim of the present paper is to describe technology development for estimating the effects of surface distortion on antenna performance. The technology is applied to a Side-Looking Airborne Radar (SLAR) antenna on a reconnaissance pod mounted on a fighter type aircraft. This generic SLAR antenna is a phased array antenna covering two faces of the pod: one part on the vertical side face and one part on the lower face of the pod. Radiation patterns are computed for distorted antenna surfaces. The computational model for the determination of the disturbed radiation pattern is based on geometrical parameterisation of the Stratton-Chu integral equations.
Small resonant fractal antennas
K. J. Vinoy, K. A. Jose, Vijay K. Varadan, et al.
Reducing the size of an antenna has significant impact on their applications in modern communications system and in wireless sensors. However, as the antenna size is reduced, the real part of its input impedance reduces to near zero, and the imaginary part becomes very large. Meander line and zig-zag antennas have been used whenever small resonant antennas were required. Antennas using fractal geometry have been pursued in recent years for various advantages such as scale invariance and self-similarity. The apparent increase in the effective length of wire segments constituting the antenna forces the antenna to resonate at a lower frequency. In this paper we present the numerical studies on reducing the resonant frequency of a fractal geometry within a finite area, by the increase in fractal iteration order.
Wireless Telemetry
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Microsystems engineering
The early '70s witnessed the introduction of the 'ion- selective field-effect transistor,' ISFET, which melded ion- selective electrode technology with standard microfabricated electronics and subsequently ushered in the era of integrated transducers. The futuristic allure of integrated transducers soon permeated the literature generating a literal zoo of unique sensors and actuators all purporting a litany of 'smaller, cheaper, better.' Capitalizing on the forte of microfabrication, the simple microdevice quickly evolved into arrays of microdevices and then on to integrated microsystems, complete with multiple transducers, actuators, and controls. However, the initial visions for integrated microsystems far outstripped available technical resources. For example, the simple ISFET required over twenty years to realize even limited commercialization. Process incompatibilities, materials issues, and fabrication limitations still present formidable challenges to any practical commercialization of most academic microsystem concepts. These limitations have generally mandated two strategic adaptations: (1) Limit products to simple, single-function/process microdevices such as in ink-jet printers, solid state pressure sensors, etc., or (2) Follow the example of high speed electronics and adopt a hybrid approach where the individual microdevices are individually fabricated and later assembled/packaged into the complex system. The latter approach is particularly apropos to optical microsystems which inherently demand a diverse range of nontraditional materials, photonic, and electro-optical components.
Surface-conforming MEMS: a new approach for vehicle dynamics monitoring
Jeffrey N. Schoess
Future advanced fixed- and rotary-wing aircraft, launch vehicles, and spacecraft will incorporate smart microsensors to provide vehicle dynamics monitoring. Qualitative measurement of vehicle aerodynamics properties, including airflow, surface pressure distribution, and thermal profiling, are becoming increasingly important. This paper presents a new packaging concept for integrating MEMS sensors into aircraft coating protectant systems to perform conformal sensing and characterize vehicle aerodynamics. A low profile 0.1-in. elastomeric packaging technique will be presented that enables assessment of vehicle low-speed air data parameters and structural integrity.
Telemetered sensors for dynamic activity and structural performance monitoring
The development of improved structures requires knowledge of their dynamic behavior. Minimally intrusive wireless systems, capable of monitoring vibration and impact, are needed in order to provide this knowledge. Our objective was to design, build, and test a high speed data collection and wireless data communications system, including microsensors, and capable of being embedded or externally worn. Our previous transmitter designs were small and could be used to transmit multichannel digital data, but they were not capable of fast data transmission rates. The addition of a remotely triggered datalogger allowed us to overcome the limitations of our earlier designs. A bi-directional RF communications link was used to trigger a sample to be logged (from 30 meters), as well as to request data to be transmitted to the host PC for data acquisition/analysis. Sweep rates of 2000 Hz were successfully demonstrated from a triad of MEMs accelerometers. The remote datalogger and transceiver and accelerometer package measured 12 mm by 24 mm by 6 mm thick; these were mounted to the feet of thoroughbred horses to study their impact levels. These small, fast, wireless data recording systems can be used to monitor rotating/ vibrating machinery and civil/automotive/aerospace structures.
Web-controlled wireless network sensors for structural health monitoring
Kyle Mitchell, Nghia Dang, Pengxiang Liu, et al.
Wireless network sensors are being implemented for applications in transportation, manufacturing, security, and structural health monitoring. This paper describes an approach for data acquisition for damage detection in structures. The proposed Web-Controlled Wireless Network Sensors (WCWNS) is the integration of wireless network sensors and a web interface that allows easy remote access and operation from user-friendly HTML screens. The WCWNS is highly flexible in terms of functions and applications. Algorithms and tools for data analysis can be directly installed on and executed from the web server. This means WCWNS will have unlimited capabilities in performing data analysis. Data can be analyzed for damage detection either on site distributed amongst the intelligent sensors or off site either in the web server or at an end users location after downloading from the web server. This feature allows for a variety of health monitoring algorithms to be investigated by researchers of all backgrounds and abilities. In addition, both short-range and long-range communications devices handle data exchange and communications in WCWNS. The system can be setup to operate efficiently in any topological arrangement. Short-range communications devices facilitate fast and low-power local data transfer, while long-range communications devices support high quality long-distance data exchange. The proposed system is demonstrated on an experimental setup.
MEMS high-speed angular-position sensing system with rf wireless transmission
Winston Sun, Wen Jung Li
A novel surface-micromachined non-contact high-speed angular-position sensor with total surface area under 4mm2 was developed using the Multi-User MEMS Processes (MUMPs) and integrated with a commercial RF transmitter at 433MHz carrier frequency for wireless signal detection. Currently, a 2.3 MHz internal clock of our data acquisition system and a sensor design with a 13mg seismic mass is sufficient to provide visual observation of a clear sinusoidal response wirelessly generated by the piezoresistive angular-position sensing system within speed range of 180 rpm to around 1000 rpm. Experimental results showed that the oscillation frequency and amplitude are related to the input angular frequency of the rotation disk and the tilt angle of the rotation axis, respectively. These important results could provide groundwork for MEMS researchers to estimate how gravity influences structural properties of MEMS devices under different circumstances.
Design, simulation, and testing of wireless temperature sensor
William D Suh, K. A. Jose, Vijay K. Varadan, et al.
Remote monitoring and control of temperature is very important for many industrial applications. This paper presents the numerical simulation and its comparison with measurement of phase response from a wireless Surface Acoustic Wave temperature sensor. This wireless microsensor consists of two or more arrays of IDTs and reflectors on a piezoelectric substrate with different IDT-reflector spacing. Pulse modulated signals are transmitted from a remote reader system and their echoes are returned after traveling through the device with different time delays. The same reader is used to receive the signal and corresponding IF signals are generated in a mixer and their phase differences are calibrated to temperature values. Using coupled-mode theory, the phase characteristics relative to temperature was analyzed. The effect of relative distance between the two reflector arrays is demonstrated. The influence of phase reversal location, which produces multiple temperature values for a given phase difference, is also discussed and a simple solution is illustrated. This sensor is coupled with a small planar antenna, which will be well suited for applications that require passive and conformal sensors. The analysis has shown that a very high sensitivity of 20.74°/°C or a temperature resolution of 0.05°C with 1° phase measurement resolution can be achieved using the present measurement system.
Fabrication and Characterization
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Fabrication of microstructures and microdevices by the particle assemblage
Mikihiko Kobayashi, Norio Shinya, Takehiro Dan, et al.
We aim to fabricate microstructure and microdevices by integrating and arranging powder particles, i.e., the particle assemblage. We have developed three assembling techniques of the particles. The details of the assembling techniques and samples of the assembled microstructures are introduced. A manipulator is developed to manipulate and to weld metal particles by using a tungsten probe. Nickel alloy particles of 50 micrometers were piled on a gold substrate by the manipulator, and a leaning tower of the particles is fabricated. The array of the leaning tower is considered to act as an actuator. For the integration of a great number of particles, we developed another method based on the principle with the xerography. An electron beam or an ion beam is irradiated on an insulating substrate. An electrified pattern is formed on the substrate by the doped electron or doped ion. Fine particles are attracted to the pattern by the electrostatic force. Thus, we can arrange particles by immersing the substrate in the suspension of particles. The third is a productive method of ordered mixture by the electrostatic force. A self- thermostatic heater is made from the composite particles of BaTiO3 and In produced by the method.
Massive replication of polymeric high-aspect-ratio microstructures using PDMS casting
Sangwon Park, Kabseog Kim, Harish M. Manohara, et al.
This paper presents a rapid replication technique for polydimethylsiloxane (PDMS) high aspect ratio microstructures (HARMs) and a pattern transfer technique for replication of metallic HARMs on other substrates (such as circuit containing substrates) using such replicated PDMS HARMs. A high aspect ratio metallic micromold insert, featuring a variety of test microstructures made of electroplated nickel, has been fabricated by the standard deep X-ray lithography (DXRL) process. Mixed pre-polymer PDMS with a curing agent has been cast onto the metallic micromold insert test patterns to create replicated polymeric HARMs. The replicated PDMS HARMs could be used to massively reproduce high aspect ratio metallic microstructures on other substrates using a pattern transfer technique. In order to demonstrate the concept, an experiment has been carried out to attach the replicated PDMS HARMs onto a silicon substrate which has pre-deposited photoresist and metallic seed layer. Electrodeposition has been carried out through the attached PDMS HARMs mold followed by the subsequent removal of the PDMS, resulting in high aspect ratio metallic microstructures on the silicon substrate. This technique could be used to massively reproduce metallic HARMs on circuit containing substrates to create 3-D integrated MEMS devices.
Micro stereo lithography for 3D MEMS devices
Micro Stereo Lithography (MSL) is a poor man's LIGA for fabricating high aspect ratio MEMS devices in UV curable semiconducting polymers using either two computer-controlled low inertia galvanometric mirrors with the aid of focusing lens or an array of optical fibers. This technique has also been successfully used recently for fabricating 3D metallic and ceramic MEMS devices. Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: (1) these techniques are very expensive and need specific installations as well as a cleanroom environment, (2) the materials that can be used up to now are restricted to silicon and metals, (3) the manufacture of 3D parts having curved surfaces or an important number of layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide. It is thus natural for the researchers to 'look' for alternative methods to make 3D sensors and actuators using polymeric based materials. For MSL techniques to be successful as their silicon counterparts, one has to come up with multifunctional polymers. These multifunctional polymers have not only a high sensing capability but also a high strain and actuation performance. With the invention of organic thin film transistor, now it seems possible to fabricate polymeric based MEMS devices with built-in- electronics. Moreover, with combined architecture techniques, one can integrate silicon devices with the polymeric ones without much difficulty. In this paper, the applications of MSL for polymer and ceramic based microstructures and MEMS are discussed with some examples.
Smart Devices and Systems I
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Mechatronics: the future of mechanical engineering; past, present, and a vision for the future
M. K. Ramasubramanian
Mechatronics is the synergistic integration of precision mechanical engineering, electronics, computational hardware and software in the design of products and processes. Mechatronics, the term coined in Japan in the '70s, has evolved to symbolize what mechanical design engineers do today worldwide. The revolutionary introduction of the microprocessor (or microcontroller) in the early '80s and ever increasing performance-cost ratio has changed the paradigm of mechanical design forever, and has broadened the original definition of mechatronics to include intelligent control and autonomous decision-making. Today, increasing number of new products is being developed at the intersection between traditional disciplines of Engineering, and Computer and Material Sciences. New developments in these traditional disciplines are being absorbed into mechatronics design at an ever-increasing pace. In this paper, a brief history of mechatronics, and several examples of this rapid adaptation of technologies into product design is presented. With the ongoing information technology revolution, especially in wireless communication, smart sensors design (enabled by MEMS technology), and embedded systems engineering, mechatronics design is going through another step change in capabilities and scope. The implications of these developments in mechatronics design in the near future are discussed. Finally, deficiencies in our engineering curriculum to address the needs of the industry to cope up with these rapid changes, and proposed remedies, will also be discussed.
High-aspect-ratio integrated force arrays
Stephen M. Bobbio, Stephen W. Smith, Jason M. Zara, et al.
The Integrated Force Array (IFA) is a metallized polyimide actuator made up of a large array of capacitive cells that deform when voltage is applied. The deformations of the individual cells add to produce an overall muscle-like compression of the array. In previously reported work deformations of up to 30% have been realized and the IFAs have been used as mechanical scanners in ultrasound imaging systems. The gaps of the capacitive cells are etched directly into the polyimide and oriented perpendicular to the plane of the array. Metal is deposited on the sidewalls of the etched features in order to form the plates of each capacitor. The force associated with the IFA motion is directly proportional to the height of the sidewall metal and thus to the thickness of the membrane. Until now, the thickness has been 2μm with gap widths of 1μm. In recent work, much higher aspect ratio IFAs (thicker but with the same gap width) have been fabricated in order to produce devices that operate with greater force and are much more robust devices.
MEMS pressure belt with sensor interface and communication architecture
Lee H. Eccles, Wayne Catlin, Mark J. Holland, et al.
Boeing utilizes many different sensor types and their associated electronic systems for aircraft testing. An array of sensors are being used to determine the load on the wings of an aircraft. We have developed a MEMS sensor network, which takes advantage of this technology. In this paper, we report the development of a 'pressure belt' containing a electronic packaging configuration incorporating MEMS pressure sensors and multi-chip modules. A thin profile of less than 0.070 inch was required for aerodynamic reasons. The MCM substrate was fabricated on oxidized silicon using copper as the conductor and photo-sensitive polyimide as the dielectric material. Direct-chip-attachment (flip chip) process was used to bond the MEMS device to the module and the bus connection was conducted through embedded copper on a flex PCB to the host computer. An encapsulation material for the protection of the bare electronic components was selected for improving the reliability of the module. Improvements in the signal conditioning and processing are being incorporated into the pressure belt. The design includes a signal conditioning unit that includes analog to digital conversion, a digital filter, temperature compensation and conversion to engineering units.
Development of active PBG structures for realizing novel MOEMS based on transparent metals
Salvatore Baglio, Mark J. Bloemer, Nicolo Savalli, et al.
This work deals with the development of a novel class of smart opto-electro-mechanical devices that are based on Photonic Band Gap materials consisting of several periods of suitable metal-dielectric couples. Innovative devices with electrically controllable optical properties are obtained that can be used both as sensors with optical output signals for application in hostile environments and as controlled optical filters. Theoretical models of such novel devices together with experimental prototypes have been developed and characterization of the devices has been performed. Finally an integrated device, realized by using standard CMOS technologies and compatible micromachining processes, in being developed.
Comparative study of 2-DOF micromirrors for precision light manipulation
Johanna I Young, Andrei M. Shkel
Many industry experts predict that the future of fiber optic telecommunications depends on the development of all-optical components for switching of photonic signals from fiber to fiber throughout the networks. MEMS is a promising technology for providing all-optical switching at high speeds with significant cost reductions. This paper reports on the the analysis of two designs for 2-DOF electrostatically actuated MEMS micromirrors for precision controllable large optical switching arrays. The behavior of the micromirror designs is predicted by coupled-field electrostatic and modal analysis using a finite element analysis (FEA) multi-physics modeling software. The analysis indicates that the commonly used gimbal type mirror design experiences electrostatic interference and would therefore be difficult to precisely control for 2-DOF motion. We propose a new design approach which preserves 2-DOF actuation while minimizing electrostatic interference between the drive electrodes and the mirror. Instead of using two torsional axes, we use one actuator which combines torsional and flexural DOFs. A comparative analysis of the conventional gimbal design and the one proposed in this paper is performed.
Capacitive micropressure sensors with underneath readout circuit using a standard CMOS process
Shihchen Chang, Chingliang Dai, Jinghung Chiou, et al.
A capacitive micropressure sensor with readout circuits on a single chip is fabricated using commercial 0.35micrometers CMOS process technology and post-processing. The main break through feature of the chip is the positioning of its readout circuits under the pressure sensor, allowing the chip to be smaller. Post-processing included anisotropic dry etching and wet etching to remove the sacrificial layer, and the use of PECVD nitride to seal the etching holes of the pressure sensor. The sacrificial layer was the metal 3 layer of the standard 0.35 micrometers CMOS process. In addition, the readout circuit is divided into analog and digital parts, with the digital part being an alternate coupled RS flip- flop with four inverters that sharpened the output wave. Moreover, the analog part is employed switched capacitor methodology. The pressure sensor contained an 8 X 8 sensing cells array, and the total area of the pressure sensor chip is 2mmx2 mm. In addition to illustrating the design and fabrication of the capacitive pressure sensor, this investigation demonstrates the simulation and testing results of the readout circuit.
High-power piezo-drive amplifier for large stack and PFC applications
Dan J. Clingman, Mike Gamble
This paper describes the continuing development of Boeing High Power Piezo Drive Amplifiers. Described is the development and testing of a 1500 Vpp, 8 amp switching amplifier. This amplifier is used to drive a piezo stack driven rotor blade trailing edge flap on a full size helicopter. Also discuss is a switching amplifier designed to drive a Piezo Fiber Composite (PFC) active twist rotor blade. This amplifier was designed to drive the PFC material at 2000 Vpp and 0.5 amps. These amplifiers recycle reactive energy, allowing for a power and weight efficient amplifier design. This work was done in conjunction with the DARPA sponsored Phase II Smart Rotor Blade program and the NASA Langley Research Center sponsored Active Twist Rotor (ATR) blade program.
Smart Devices and Systems II
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Hybrid power systems for autonomous MEMS
Daniel M. Bennett, Richard H. Selfridge, Paul Humble, et al.
This paper describes the design of a hybrid power system for use with autonomous MEMS and other microdevices. This hybrid power system includes energy conversion and storage along with an electronic system for managing the collection and distribution of power. It offers flexibility and longevity in a compact package. The hybrid power system couples a silicon solar cell with a microbattery specially designed for MEMS applications. We have designed a control/interface charging circuit to be compatible with a MEMS duty cycle. The design permits short pulses of 'high' power while taking care to avoid excessive charging or discharging of the battery. Charging is carefully controlled to provide a balance between acceptably small charging times and a charging profile that extends battery life. Our report describes the charging of our Ni/Zn microbatteries using solar cells. To date we have demonstrated thousands of charge/discharge cycles of a simulated MEMS duty cycle.
Electromagnetic micro x-y stage with very thick Cu coil for probe-based mass data storage device
Jaejoon Choi, Hong sik Park, Kyu yong Kim, et al.
We fabricated electromagnetic micro x-y stage for application to probe based mass data storage (PDS) devices. The stage consists of Si body containing planar copper coils, glass substrate bonded to the body, and 8 permanent magnets. The dimensions of springs and copper coils were determined so that a current of 100 mA would provide 50 μm motion in x and y. For application to PDS device, electromagnetic stage should have a flat top surface and coils of low resistance. So conducting planar copper coils have been electroplated within silicon trench of high aspect ratio (5 μm in width and 30 μm in depth). As insulating layer, polyimide was used. Silicon flexures with the height of 250 μm were fabricated by using ICP-RIE (Inductively Coupled Plasma Reactive Ion Etching). The characteristics of the fabricated electromagnetic stage were measured by LDV (Laser Doppler Vibrometer) and DSA (Dynamic Signal Analyzer). DC gain was 0.16 μm/mA and the maximum displacement was 42 μm at a current of 180 mA. The natural frequency was 325 Hz.
Networked smart material actuators with rectenna array
The concept of microwave-driven smart material actuators is envisioned as the best option to alleviate the complexity associated with hard-wired control circuitry. Networked rectenna patch array receives and converts microwave power into a DC power for an array of smart actuators. To use microwave power effectively, the concept of a power allocation and distribution (PAD) circuit is adopted for networking a rectenna/actuator patch array. The PAD circuit is embedded into a single embodiment of rectenna and actuator array. The thin-film microcircuit embodiment of PAD circuit adds insignificant amount of rigidity to membrane flexibility. Preliminary design and fabrication of PAD circuitry that consists of a few nodal elements were made for laboratory testing. The networked actuators were tested to correlate the network coupling effect, power allocation and distribution, and response time. The features of preliminary design are 16- channel computer control of actuators by a PCI board and the compensator for a power failure or leakage of one or more rectennas.
New type of silicon photoelectronic negative resistance devices: PDUBAT
Photoelectronic DUal Base Transistor (PDUBAT) is a novel kind of photoelectronic negative resistance devices, which features 'N' type negative resistance and small negative resistance RN. PDUBAT consists of a vertical NPN bipolar transistor and a P type diffusion region with large area over a specific distance. The base and collector of the vertical NPN BJT with a large P diffusion region form a lateral PNP BJT. The emitter and collector of the vertical NPN BJT are connected to the ground and voltage supply respectively, while the P diffusion region is left floated to detect input light signal. When the device is exposed to light, a large number of electron-hole pairs are generated at the PN junction under the P diffusion region. The holes travel along the base of the lateral PNP BJT and become the driving current of the vertical NPN BJT. In experiments, we found that PDUBAT acts as a pulse oscillator without the load of inductors, whose frequency and magnitude are modulated by the intensity of incident light. The oscillating frequency increases while the magnitude decreases with the increasing of light intensity. The manufacturing process of PDUBAT is compatible with that of JBTs, so that it can be incorporated with the ICs.
Smart Skin Antenna and Frequency Selective Surface (FSS) II ARO/NATO Invited Session
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Antenna model for conformal array performance prediction
Peter Knott, Christoph von Winterfeld
A physical modeling method for the calculation of characteristic electromagnetic parameters of small conformal arrays is presented. The antenna array model is based on the interaction between special antenna elements composed of electrically small dipoles and loop antennas. It allows for the approximate calculation of mutual coupling effects inside the antenna array. While some system aspects (such as subarray structures, T/R-module quantization, bandwidth, driving point impedance etc.) are taken into account, the numerical complexity of exact EM modeling software (e.g. integral equation methods) is avoided. Of special interest with respect to SMART antenna structures are investigations on array bandwidth and influences of static deformations on array performance: Array performance over an increased frequency range is studied. Static deformations of the array may occur in airborne applications and can cause element dislocation and disorientation. As an effect, the resulting array far field pattern is distorted. In both cases compensation is (at least partially) possible using adapted array coefficients. The results of these calculations lead to the conclusion that in SMART antenna systems the array excitation coefficients need to be modified to increase array bandwidth and to compensate for static deformations.