Showing papers in "Sensors and Actuators A-physical in 2007"

Squeeze film air damping in MEMS

Abstract: The paper presents an overview and reports the recent progress of research on squeeze film air damping in MEMS. The review starts with the governing equations of squeeze film air damping: the nonlinear isothermal Reynolds equation and various reduced forms of the equation for different conditions. After the basic effects of squeeze film damping on the dynamic performances of micro-structures are discussed based on the analytical solutions to parallel plate problems, recent research on various aspects of squeeze film air damping are reviewed, including the squeeze film air damping of perforated and slotted plate, the squeeze film air damping in rarefied air and the squeeze film air damping of torsion mirrors. Finally, the simulation of squeeze film air damping is reviewed. For quick reference, important equations and curves are included.

Electromechanical coupling in dielectric elastomer actuators

Abstract: In this paper the electromechanical coupling in dielectric elastomer actuators is investigated. An equation proposed by Pelrine et al. [R.E. Pelrine, R.D. Kornbluh, J.P. Joseph, Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation, Sens. Actuators A 64 (1998) 77–85] is commonly used for the calculation of the electrostatic forces in dielectric elastomer systems. This equation is analyzed here with (i) energy consideration and (ii) numerical calculations of charge and force distribution. A new physical interpretation of the electrostatic forces acting on the dielectric elastomer film is proposed, with contributions from in-plane and out-of-plane stresses. Representation of this force distribution using Pelrine's equation is valid for an incompressible material, such as the acrylic elastomer VHB 4910. Experiments are performed for the measurement of the dielectric constant ɛ r of the acrylic elastomer VHB 4910 for different film deformations. The values of ɛ r are shown to decrease with increasing pre-stretch ratio λ p , from 4.7 for the un-stretched film, down to 2.6 for equi-biaxial deformation with λ p = 5. This result is important in that it corrects the constant value of 4.7 largely applied in literature for pre-stretched dielectric elastomer actuator modeling. With the results of this work the predictive capabilities of a model describing the three-dimensional passive and active actuator behavior are remarkably improved.

Principles and features of Single Photon Avalanche Diode Arrays

Abstract: This is the first of two serial papers dealing on single-photon avalanche diode (SPAD) topics. Aim of the series is to discuss in depth the design and fabrication of our SPAD-A array system for two-dimensional single-photon imaging, able to count and time-tag single photons by means of a monolithic array sensor. This paper deals with the device structure and characterization. The second paper will present the developed fast electronics and will show the overall performance reached in passive, active, and gated regimes. In this first paper we review the working principle and the features of single-photon detector pixels, with particular attention to the monolithic array integration. Then we discuss design criteria, trade-offs, and how to chose operating conditions to attain best performances out of individual pixels. Finally, experimental data will be thoroughly discussed.

Mechanical behavior of an acrylic elastomer used in dielectric elastomer actuators

Abstract: The paper reports on extensive experimental work for the characterization of a dielectric elastomer used as base material for electroactive polymer (EAP) actuators. The mechanical behavior of the acrylic elastomer VHB 4910 is characterized using large strain experiments (uniaxial and equibiaxial deformation) under force and displacement controlled loading conditions. Next to tensile and relaxation tests, experiments were conducted also using the so-called circular actuators. Over 40 actuators were produced (with different in-plane pre-strain levels) and activated with voltages between 2000 and 3500 V. The experimental data are useful for determining constitutive model parameters as well as for validating models and simulation procedures for electromechanical coupling in EAP actuators. A novel approach is proposed for finite element analysis of dielectric elastomer actuator, which has been used in the present work for the evaluation of the experimental observations from circular actuators. Material parameters of different visco-hyperelastic models have been determined from a subset of the experimental data and the predictive capabilities of the models evaluated through comparisons with the remaining data. The prediction of the circular actuator behavior was satisfactory so that the proposed models might be useful for actuator design and optimization purposes. Limitations of the proposed constitutive model formulation are presented.

Nano electromechanical sensors based on carbon nanotubes

Abstract: Sensors are key components in an overwhelming wealth of systems for industrial and consumer applications. Further system miniaturization will demand for continuous down-scaling of sensor functions in such systems most likely towards nanoscale. Then new sensor device concepts will emerge to improve performance, e.g. sensitivity, or to utilize unique functional properties of nanoscale structures. This paper presents concepts and demonstrators of nano electromechanical sensors based on carbon nanotubes (CNTs). First, different transducer concepts based on the unique electrical, mechanical and electromechanical properties of single-walled carbon nanotubes (SWNTs) are addressed and discussed. Second, fabrication techniques and methods for the integration of SWNTs in micro or nanosystems are presented. Finally, demonstrators of suspended SWNT-based cantilever structures and a membrane-based nanotube pressure sensor are introduced and evaluated. Electromechanical measurements on these test devices prove SWNTs as exceptional piezoresistive electromechanical transducers with gauge factors far above the values of state-of-the-art strain gauges.

Review of MEMS-based drug delivery and dosing systems

Abstract: Micro-dosing/drug delivery control system is a bio-chip in practice. It is mostly developed by Micro-electro-mechanical Systems (MEMS) technology. In micro-dosing or drug delivery control systems, the driving power source with driving methodology and bio-compatibility are the two key issues that a great deal of researchers are truly interested in. Since the micro-dosing and drug delivery systems are applied on human bodies, there inevitably exist inherent limitations. Our study is aimed at driving technology review from all aspects. Comparisons are made to unveil the advantages and shortcomings of different driving designs. In addition, bio-compatibility is addressed and discussed, especially upon the currently-used and potential bio-materials in bio-MEMS.

Embedded piezoresistive cement-based stress/strain sensor

Abstract: In order to develop one type of embedded piezoresistive cement-based stress/strain sensor (PCSS) to monitor the local compressive stress/strain of concrete structures, we explore the piezoresistivity of cement-based material with carbon fiber and carbon black under single compressive loading and repeated compressive loads at different loading amplitudes, and find it is reversible and stable within the elastic regime. This justifies the use of cement-based material with carbon fiber and carbon black in the manufacture of embedded PCSS. PCSS based on the piezoresistivity of cement-based material with carbon fiber and carbon black is tested with compressive stress/strain in the range 0 MPa (0 μɛ) to 8 MPa (476 μɛ) for performance evaluation. Results indicate that PCSS can be used to achieve a sensitivity of 1.35% MPa−1 (0.0227% μɛ−1, gage factor of 227), linearity of 4.17% (4.16%), repeatability of 4.05% (4.06%) and hysteresis of 3.61% (3.62%), and the relationship between its input (compressive stress/strain) and output (fractional change in electrical resistivity) is Δρ = −1.35σ (Δρ = −0.0227ɛ). These findings suggest that this newly developed sensor can be used as one of the alternatives to monitor the compressive stress/strain of concrete structures.

Mechanical properties of ZnO nanowires

Abstract: One-dimensional solids like nanowires and nanotubes are potential materials for future nanoscale sensors and actuators. Due to their unique length scale, they exhibit superior mechanical properties and other length scale dependent phenomena. In this paper, we report experimental investigations on the mechanical properties of ZnO nanowires. We have designed a MEMS test-bed for mechanical characterization of nanowires. The MEMS device exploits the mechanics of post-buckling deformation of slender columns to achieve very high force and displacement resolution. The small size of the test-bed allows for in situ experimentation inside analytical chambers, such as SEM and TEM. We present microscale version of pick-and-place as a generic specimen preparation and manipulation technique for experimentation on individual nanostructures. We performed experiments on ZnO nanowires inside a scanning electron microscope (SEM) and estimated the Young's modulus to be about 21 GPa and the fracture strain to vary from 5% to 15%.

Calibration and data fusion solution for the miniature attitude and heading reference system

Abstract: Development, calibration and alignment of a miniature magnetic and inertial measurement unit, which is used as an attitude and heading reference system, are presented. Several guidelines were followed during the design process to make the magnetic and inertial measurement unit suitable for various kinds of applications, thus the system is designed both as small as possible but still modular, consisting of three inertial sensor units, a magnetic sensor unit and a control unit. Complete calibration and alignment procedure is described and an adaptive Kalman filter concept for fusing various sensors’ attitude and heading data is introduced and discussed. The characteristics of the magnetic and inertial measurement unit as an attitude and heading reference system are evaluated. The algorithm showed remarkable performance in the orientation determination as the average root mean square error was less than 1.2° over the entire appliable operating range.

Functionalized nano interdigitated electrodes arrays on polymer with integrated microfluidics for direct bio-affinity sensing using impedimetric measurement

Abstract: This paper presents a fully integrated nano interdigitated electrodes array (nIDA) and microfluidic system on polymer substrate. It can be used as a miniaturized, sensitive, and easy-to-use impedimetric sensor for genomics, proteomics, and cellular analysis. The benefits gained from a nanoscale IDA is very high sensitivity for monitoring protein binding behavior. With the intention of integrating this nano biosensor into a lab-on-a-chip device, a gold nIDA has been successfully patterned on polymer (cyclic olefin copolymer, COC) substrate, which has been widely used for disposable lab-on-a-chip applications. The fabricated device has been characterized in deionized (DI) water and different concentrations of KCl salt solution ranging from 10−1 to 10−5 M using electrochemical impedimetric spectroscopy (EIS). Experimental and theoretical impedance responses are well matched. The preliminary test shows that the impedance from the same buffer solution increases after protein binding (mouse monoclonal anti-rabbit immunoglobulin, IgG) at the gold electrode surface and the impedance change is directly related to the IgG concentration. These results support the feasibility of applying the proposed device as a sensitive protein immunosensor on a disposable polymer substrate.

Determining refractive index of single living cell using an integrated microchip

Abstract: We report a novel method for measuring the effective refractive index (RI) of single living cell using a small integrated chip, which might be an efficient approach for diseases diagnosis. This microchip is able to determine the refractive index of single living cell in real time without any extra cell treatments such as fluorescence labelling, chemical modification and so forth, meanwhile, providing low cost, small size, easy operation and high accuracy. The measurement system integrates an external cavity laser, a microlens, and some microfluidic channels onto a monolithic chip. In the experiments, two standard polystyrene beads with nominal RI are utilized to calibrate the measurement system and five different types of cancerous cells are subsequently measured in the chip. The experimental results show that the refractive indices of the cancerous cells tested ranges from 1.392 to 1.401, which is larger than typical value of normal cell of 1.35–1.37. This integrated chip potentially has a serial of applications on biodefense, disease diagnosis, biomedical and biochemical analysis.

A microgripper using piezoelectric actuation for micro-object manipulation

Abstract: Design, fabrication and tests of a monolithic compliant-flexure-based microgripper were performed. The geometry design and the material stresses were considered through the finite element analysis. The simulation model was used to study in detail profiles of von Mises stresses and deformation. The maximum stress in the microgripper is much smaller than the critical stress values for fatigue. The microgripper prototype was manufactured using micro-wire electrode discharge machining. A displacement amplification of 3.0 and a maximum stroke of 170 μm were achieved. The use of piezoelectric actuation allowed fine positioning. Micromanipulation tests were conducted to confirm potential applications of the microgripper with piezoelectric actuation in handling micro-objects. The simulation and experimental results have proven the good performance of the microgripper.

Electrode design, measuring method and data acquisition system of carbon fiber cement paste piezoresistive sensors

Abstract: Carbon fiber cement paste piezoresistive sensors (CFCPS) are made of piezoresistivity of carbon fiber cement paste and mainly used for local monitoring of concrete structures. Two electrode fixing styles for measuring the resistance of CFCPS are compared and the conception of embedded gauze electrode is put forward. The characteristics, layout styles and configuration parameters of embedded gauze electrode and the methods for measuring the resistance of CFCPS are studied. The mould of sensors is designed and the data acquisition system based on voltage signal is developed. It is revealed that the four-pole layout is suitable for setting embedded gauze electrode and the direct-current four-pole method adapts to measure the resistance of CFCPS. The resistivity of CFCPS is independent of the area of voltage pole and the mesh size of gauze electrode. The space between current pole and voltage pole does not influence the resistivity of CFCPS when more than a critical value. The developed data acquisition system has many advantages such as simple circuit, good practicability, high precision and ability to realize real-time, on-line and multi-channel acquisition.

Residual magnetic field sensing for stress measurement

Abstract: The evaluation of both applied and residual stresses in engineering structures to provide early indications of stress status and eventual failure is a fast growing area in non-destructive testing. Much work has been done in recent years in the development of magnetic stress measurement techniques for ferromagnetic materials using applied magnetic fields to monitor changes in the magnetic properties of materials, such as variations in the hysteresis curve or Barkhausen emission. But the area of passive field measurement is relatively unexplored. When magnetic metals are strained, they irreversibly transformed from a non-magnetic state to a magnetic state, this is referred to as metal magnetic memory (MMM) or the residual magnetic field (RMF). This paper investigates the phenomena under different circumstances and applies the residual magnetic field technique to stress measurement. A three axis magneto-resistive magnetic field sensor is used to measure the residual magnetic fields parallel to the applied stress and the material surface (Bx) and perpendicular to the material surface (Bz), generated by the magneto-mechanical effect without the application of an external field, using steel samples exposed to stresses. The test results show that without using an applied field, the stresses in a sample can be measured using magnetic field sensing, with Bx showing particularly good correlation. The work concludes that the novel passive field technique including analysis of the magnetic field pattern and magnetic field variation rate, would prove advantageous in certain circumstances, for example in-service inspection of structures with complex geometries. Further research directions are also highlighted.

Fabrication and characterization of bismuth–telluride-based alloy thin film thermoelectric generators by flash evaporation method

Abstract: Bismuth–telluride-based alloy thin film thermoelectric generators are fabricated by a flash evaporation method. We prepare Bi 0.4 Te 3.0 Sb 1.6 (p-type) and Bi 2.0 Te 2.7 Se 0.3 (n-type) powders for the fabrication of the flash evaporated thin films. The overall size of the thin film thermoelectric generators, which consist of seven pairs of legs connected by aluminum electrodes, is 20 mm by 15 mm. Each leg is 15 mm long, 1 mm wide and 1 μm thick. We measure the output voltage and estimate the maximum output power near room temperature as a function of the temperature difference between hot and cold junctions of the thin film thermoelectric generators. In order to improve the performance of the generators, a hydrogen annealing process is carried out at several temperatures from 25 °C to 250 °C. The highest output voltage of 83.3 mV and estimated output power of 0.21 μW are obtained from a hydrogen annealing temperature of T a = 250 °C and a temperature difference of Δ T = 30 K. The hydrogen annealing temperature of T a = 250 °C also results in the best electrical performance for both p-type thin film (Seebeck coefficient = 254.4 μV/K, resistivity = 4.1 mΩ cm, power factor = 15.9 μW/cm K 2 ) and n-type thin film (−179.3 μV/K, 1.5 mΩ cm, 21.5 μW/cm K 2 ).

Fabrication of multilayer passive and active electric components on polymer using inkjet printing and low temperature laser processing

Abstract: The low temperature fabrication of passive (conductor, capacitor) and active (field effect transistor) electrical components on flexible polymer substrate is presented in this paper. A drop-on-demand (DOD) ink-jetting system was used to print gold nano-particles suspended in Alpha-Terpineol solvent, PVP (poly-4-vinylphenol) in PGMEA (propylene glycol monomethyl ether acetate) solvent, semiconductor polymer (modified polythiophene) in chloroform solution to fabricate passive and active electrical components on flexible polymer substrates. Short pulsed laser ablation enabled finer electrical components to overcome the resolution limitation of inkjet deposition. Continuous argon ion laser was irradiated locally to evaporate the carrier solvent as well as sinter gold nano-particles. In addition, selective ablation of multilayered gold nanoparticle film was demonstrated using the novel SPLA-DAT (selective pulsed laser ablation by different ablation threshold) scheme for sintered and non-sintered gold nanoparticles. Finally, selective ablation of multilayered film was used to define narrow FET (field effect transistor) channel. Semiconductor polymer solution was deposited on top of channel to complete OFET (organic field effect transistor) fabrication.

Design and optimization of a linear vibration-driven electromagnetic micro-power generator

Abstract: We present design and optimization of a linear electromagnetic generator suitable to supply power to body-worn sensor nodes. The design is based on an air-cored tubular architecture and a flexible translator bearing. A two-stage procedure is used to optimize the generator. First, the geometric parameters of stator and translator are optimized for maximum electromagnetic force capability based on magnetostatic finite element simulations. Second, mechanical resonance frequency and load resistance are optimized regarding maximum output power using lumped-parameter simulations and measured acceleration data from human walking motion. When worn on the body during walking, the optimized generator has an output power of 2–25 μ W, depending on its position on the human body. Stator and translator occupy a volume of 0.25 cm3. We have built a working generator prototype and validated the simulations.

Surface resistance experiments with IPMC sensors and actuators

Abstract: This paper describes experiments with the surface resistance of IPMC actuators and sensors. We measure the surface resistance of samples working as sensors or as a voltage driven actuators, as well as when insulated. The results show that in all cases the surface resistance of a sample is highly correlated to material curvature. Based on these observations we present an equivalent circuit, with variable resistors representing surface resistance, that models IPMC materials. Our simulations with SPICE show that the equivalent circuit closely models the actual behaviour of IPMC sensors and actuators. We show that since the IPMC model works as a delay line with changing resistors, the curvature of the IPMC sample at a given point depends on the surface resistance. This, in turn, affects further bending of the sample. The modified equivalent circuit also explains the hysteresis of IPMC actuators as the signals along the surface are delayed.

Liquid-level measurement system based on a remote grounded capacitive sensor

Abstract: This paper describes the design and implementation of a liquid-level measurement system based on a remote grounded capacitive sensor. The electrodes of the capacitive sensor are built with affordable materials: a rod of stainless steel and a PTFE-insulated wire. The interface circuit relies on a simple relaxation oscillator and a microcontroller. A cable with active shielding interconnects the sensor to the interface circuit. The stability of the active-shielding circuit is analysed by taking into account the parasitic components of both the interconnecting cable and the sensor. The system has been experimentally tested by measuring the level of tap water in a grounded metallic container. Over a level range of 70 cm, the system has a non-linearity error smaller than 0.35 mm and a resolution better than 0.10 mm for a measuring time of 20 ms.

Wireless flexible capacitive sensor based on ultra-flexible epoxy resin for strain measurement of automobile tires

Abstract: The measurement of strain of tires in-service is effective in improving the reliability of tires and ABS systems. Since conventional strain gages have high stiffness and require lead wires, conventional strain gages are cumbersome for the strain measurement of tires. The present study proposes a novel flexible patch-type strain sensor utilizing electric capacitance change. The sensor is made from flexible polyimide substrates and ultra-flexible epoxy resin, which makes the sensor low in stiffness and high in elongation as a whole structure. The sensor utilizes capacitance changes due to the applied strain, and wireless measurements are conducted using amplitude modulation. The sensor is applied to an automobile tire, and compression tests are performed. The effects of the temperature changes are also measured. The proposed sensor is found to successfully measure the applied strain of the tire wirelessly, and the effects of the temperature changes are minimized using a dummy sensor in a self-temperature compensation circuit.

On the performance mechanisms of Dielectric Elastomer Actuators

Abstract: Dielectric Elastomer Actuators (DEAs) show promise for robotics and mechatronics applications. They are lightweight, low costs, and have shown good performance in laboratory demonstration. However, these actuators have not been widely applied commercially after more than 10 years of development. One reason is that the mechanisms governing their performance are not completely understood. Hence designing practical actuators is difficult. This paper has the objective of understanding the dominant performance mechanisms of DEAs made with VHB 4905/4910 from 3 M. To do so, an experimental characterization of actuator performance is conducted in terms of force, power, current consumption, work output, and efficiency. Key performance mechanisms of viscoelasticity and current leakage are identified from experimental observations and analytical models are developed. The models explain well the experimental observations and should aid designers in selecting applications that are appropriate for DEAs as well as designing effective DEAs.

Photoresponsive polymer gel microvalves controlled by local light irradiation

Abstract: This paper presents independent control of multiple microvalves, which are opened by local light irradiation. The application of photoresponsive polymer gel, which was developed by our research group, to photoresponsive microvalve was systematically examined. Photoresponsive polymer gels, which were composed of poly(N-isopropylacrylamide) functionalized with spirobenzopyran chromophore (pSPNIPAAm), were fabricated by in situ photo-polymerization at the desired positions in microchannels. Blue light irradiation to the pSPNIPAAm gels induced shrinkage of the gels and caused the microvalves composed of the gels to open. Local light irradiation to the discrete microvalves enabled independent control of three photoresponsive polymer gel microvalves, which had been fabricated on a single microchip. Each microvalve was opened by 18–30 s light irradiation.

Fabrication and Test of Integrated Micro-Scale Vibration Based Electromagnetic Generator

Abstract: This paper discusses the design, fabrication and testing of electromagnetic microgenerators on silicon. Two different designs of power generators are micro-fabricated, Prototype A having a wire-wound copper coil and Prototype B, an electrodeposited copper coil both on a Deep Reactive Ion etched (DRIE) silicon paddle. The devices were fabricated using standard Micro-Electro-Mechanical Systems (MEMS) processing techniques. For Prototype A, the maximum measured power output was 148 nW at 8.08 kHz resonant frequency and 3.9 m/s acceleration. For prototype B, the microgenerator gave a maximum load power of 23 nW for an acceleration of 9.8 m/s , at a resonant frequency of 9.83 kHz.

Actuation potentials and capillary forces in electrowetting based microsystems

Abstract: The minimum and maximum actuation voltages in electrowetting actuated microsystems are investigated in this paper. The minimum actuation voltage corresponds to the electric potential required to obtain motion of a droplet between two electrodes. Below this threshold, a droplet cannot be displaced due to contact angle hysteresis. The maximum actuation voltage corresponds to the electric potential above which there is no more gain in capillary forces because of the saturation effect. Based on the calculation of the electrocapillary forces on a drop in an EWOD system, and taking into account the contact angle hysteresis, an analytical relation is derived for the minimum actuation potential. On the other hand, the Peykov–Quinn–Ralston–Sedev model produces an approximate value of the maximum actuation voltage. Thus, a range of actuation potentials can be predicted depending on the liquid of the droplet, the surrounding gas or fluid and the nature of the solid substrate. The results of the two models are favorably compared with experimental results obtained using different liquids and substrates.

Frequency stability of wafer-scale film encapsulated silicon based MEMS resonators

Abstract: The stability of resonant frequency for single wafer, thin-film encapsulated silicon MEMS resonators was investigated for both long-term operation and temperature cycling. The resonant frequencies of encapsulated resonators were periodically measured at 25 ± 0.1 °C for >9000 h, and the resonant frequency variation remained within the measurement uncertainty of 3.1 ppm and 3.8 ppm for the two designs of resonators measured. Also, the resonators were temperature cycled for 680 cycles between −50 °C and 80 °C, measuring the resonant frequency each time the temperature reached 30 °C. Again, the change in resonant frequency was seen to remain within the measurement uncertainty. This demonstrates stability of resonant frequency for both long-term operation of more than a year and large number of temperature cycles, emphasizing the stability of both the resonator and the package.

SU-8 MEMS Fabry-Perot pressure sensor

Abstract: The biocompatible polymer, SU-8, was used to microfabricate an interferometric pressure sensor designed for invasive biomedical applications. Tests of the sensor in air and liquid environments show promising results as well as the limitations of SU-8 as a critical material in microdevices. The sensor consists of a polymer cap with a reflective, pressure-sensing diaphragm mounted onto the end of a fiber optic cable. Diaphragm deflection was measured by analyzing the spectrum reflected from the Fabry-Perot interferometer formed between the diaphragm and the fiber end. The device is fast, simple, and inexpensive to manufacture. Its small dimensions (300 μm outer diameter) reduce the risk of inflammation and infection and allow for its insertion through a catheter into small vessels and cavities. The sensor showed a linear pressure response from 0 to 125 mmHg with 1–2 mmHg resolution. The cap swelled upon immersion in a manner consistent with Fickian diffusion of water into SU-8. The interferometric displacement transducer allowed a series of measurements to characterize the drift and hysteresis of the SU-8 sensors in different environments. These results provide guidance for the design and manufacture of SU-8 microdevices.

Fiber optic in-line distributed sensor for detection and localization of the pipeline leaks

Abstract: When a gas or liquid pipeline leaks, it will generate broadband acoustic signal This acoustic pressure will induce an optical phase signal of the optical fiber fixed on the surface of pipes In this paper, we propose a hybrid configuration of Mach-Zehnder and Sagnac interferometer as sensing frame In this interferometer, there are two light paths that have the same optical length but travel different sequence paths Because the propagation lights of the two light paths pass through the leaking point at different times, the resulting phase signals differ respectively After interference, we demodulate the sensing phase signal by a broadband phase generated carrier (PGC) circuit and then the leaking point can be acquired from null frequency of the output spectrum This system has many advantages, such as its in-line configuration, all fiber structural design and polarization-insensitive for sensing fiber This system also has very wide dynamic range which can be greater than 76 dB with the minimum detectable phase signal about 33 × 10 − 4 ( rad / Hz )

Synchronized switch harvesting applied to self-powered smart systems: Piezoactive microgenerators for autonomous wireless receivers

Abstract: This paper introduces the conceptual architecture of a fully integrated, truly self-powered structural health monitoring (SHM) scheme. The challenge here is to power an array of numerous distributed actuators and sensors as well as wireless data transmission modules without recurring to heavy and costly wiring. Based on microgenerators which directly convert ambient mechanical energy into electrical energy, using the synchronized switch harvesting (SSH) method, the proposed solution allows avoiding the periodic replacement or reloading of batteries. This addresses environmental and economic issues at the same time, knowing that such elements are heavy, polluting and might be installed in rather inaccessible locations. Indeed, especially in airborne structures saving weight and maintenance cost is of priority importance. Previous work showed that such microgenerators provide a stand-alone power source, whose performances meet the requirements of autonomous wireless transmitters (AWTs) that comprise an acoustic Lamb wave's actuator and a radio frequency (RF) emitter (D. Guyomar, Y. Jayet, L. Petit, E. Lefeuvre, T. Monnier, C. Richard, M. Lallart, Synchronized switch harvesting applied to self-powered smart systems: Piezoactive microgenerators for autonomous wireless transmitters, Sens Actuators A: Phys. 138 (1) (2007) 151–160, doi:10.1016/j.sna.2007.04.009 ). Following this work, the present contribution presents a further step towards the integration of the SHM technique. It shows the ability of our microgenerators to provide enough energy to give logical autonomy to each self-powered sensing node, named autonomous wireless receiver (AWR), and thus to provide some local (decentralized) pre-processing ability to the SHM system. A preliminary design of the device using off-the-shelf electronics and surface mounted piezoelectric patches will be presented. Since the existence of a positive energy balance between the harvesting capabilities of the SSH technique and the energy requirements of the proposed device will be proved, the system formed by the combination of the AWR with the previously developed AWT, is a proof of concept of truly self-powered smart systems for damage detection in simple structures, setting apart application-specific optimization or miniaturization concerns that will be addressed in future works.

Enhanced sliding mode motion tracking control of piezoelectric actuators

Abstract: This paper proposes an enhanced sliding mode motion tracking control methodology for piezoelectric actuators to track desired motion trajectories. The proposed control methodology is established to accommodate parametric uncertainties, nonlinearities including the hysteresis effect, and other un-modelled disturbances, without any form of feed-forward compensation. The fundamental concept in this control strategy relies on the specification of a target performance and the formulation of an enhanced sliding mode control law based on the variable structure control approach. The control methodology ensures the convergence of the position tracking error to zero in the presence of the aforementioned conditions. The stability of the control methodology is proven theoretically and a precise tracking ability is demonstrated in the experimental study. One of the most important advantages of this control methodology is that the approach requires only a knowledge of the estimated system parameters together with their corresponding bounds and the bound of the non-linearities and disturbances in the physical realisation. Being capable of motion tracking, the proposed enhanced sliding mode control methodology is very attractive in the field of micro/nano manipulation through which high-precision piezoelectric actuation control applications can be realised.

A new approach to develop ionic polymer-metal composites (IPMC) actuator: Fabrication and control for active catheter systems

Abstract: The ionic polymer–metal composite (IPMC) is one type of electro-active materials with the characteristics of low electric driving potential, large deformation and aquatic manipulation. It is highly attractive to biomedical applications as an actuator or a sensor. The main purpose of this study was to develop an IPMC actuator for active catheter systems. The first step was to develop a low cost and high reliability fabrication procedure to yield an IPMC actuator. In the second step, the dynamic behavior of the actuator was tested in an aqueous environment. An empirical model was then constructed, which consisted of a fourth-order linear system, a nonlinear gain and a time delay. To linearize the dynamic behavior of this actuator for better actuating performance, a nonlinearity compensation method by a second-order polynomial was proposed. In the final step, the bending behavior of the constructed IPMC actuator with an open-loop and a closed-loop controller design was investigated. The results indicated that a low cost but reliable IPMC actuator was fabricated successfully. Its production time was less than half of current manufacturing time (more than 48 h). The bending motion at low operation frequencies was well controlled by a conventional PID controller without adding complicated control algorithm. Our proposed algorithm decreased the maximum overshot from 30 to 4.2%, and the steady-state error from 15 to 4%. Though the rise time was increased from 0.084 to 0.325 s, it was within the limit for many biomedical applications.