Showing papers on "Piezoelectric sensor published in 2001"

PVDF piezoelectric polymer

Abstract: PVDF piezo polymers are new, valuable materials for sensing and actuating applications. These materials are strong candidates for new sensors that cannot be realised with piezoceramics or single crystals. The combination of the mechanical properties of a plastic material with those of a piezoelectric material led to new sensors and transducers whose design is not easy. For this reason, the characteristics and properties of piezo polymer are described as well as basic knowledge that engineers need for technical use.

A novel thick-film piezoelectric micro-generator

Abstract: The use of alternative electrical energy sources to batteries is of particular significance to remote sensor systems. A vibration-powered micro-generator, based on a screen printed piezoelectric material, is proposed for this purpose. Theoretical and experimental results show that 2 µW can be generated for a vibration frequency of only 80 Hz. The device is not optimized and significant improvements are envisaged in the future.

Analysis of piezoelectric coupled circular plate

Abstract: This paper deals with the vibration analysis of a circular plate surface bonded by two piezoelectric layers, based on the Kirchhoff plate model. The form of the electric potential field in the piezoelectric layer is assumed such that the Maxwell static electricity equation is satisfied. The validation of the theoretical model is done by comparing the resonant frequencies of the piezoelectric coupled circular plate obtained by the theoretical model and those obtained by finite-element analysis. The mode shape of the electric potential obtained from free vibration analysis is generally shown to be non-uniform in the radial direction in contrast to what is commonly assumed. The piezoelectric layer is shown to have an effect on the frequencies of the host structure. The proposed model for the analysis of a coupled piezoelectric circular plate provides a means to obtain the distribution of electric potential in the piezoelectric layer. The model provides design reference for piezoelectric material application, such as an ultrasonic motor.

Diagnostic Lamb waves in an integrated piezoelectric sensor/actuator plate: analytical and experimental studies

Abstract: The objective of this study is to model the diagnostic transient waves in an integrated piezoelectric sensor/actuator plate with a view to using it as a first step towards establishing an entire structural health monitoring system and to provide experimental verification of the proposed models. PZT ceramic disks are surface mounted on an aluminum plate acting as both actuators and sensors to generate and collect A0 mode Lamb waves. Mindlin plate theory is adopted to model the propagating waves by taking both transverse shear and rotary inertia effects into account. Actuator and sensor models are both proposed. The interaction between an actuator and the host plate is modeled based on classical lamination theory. The converse piezoelectric effect of the actuator is treated as an equivalent bending moment applied to the host plate. The sensor acts as a capacitor that converts the sensed strain change into a voltage response. An analytical expression for the sensor output voltage in terms of the given input excitation signal is derived, and then experimental work is performed to verify the accuracy of the analytical model. Experimental results show that single-mode Lamb waves in the plate can be successfully generated and collected through the integrated PZT disks. The experiment also shows that the predicted sensor output for both amplitude and phase agrees well with experimentally collected data.

Active control of FGM plates subjected to a temperature gradient: Modelling via finite element method based on FSDT

Abstract: An efficient finite element formulation based on a first-order shear deformation theory (FSDT) is presented for the active control of functionally gradient material (FGM) plates with integrated piezoelectric sensor/actuator layers subjected to a thermal gradient; this is accomplished using both static and dynamic piezothermoelastic analyses. The formulation based on FSDT can be applied to a range of relatively thin-to-moderately thick plates. A constant displacement-cum-velocity feedback control algorithm coupling the direct and inverse piezoelectric effects is applied to provide active feedback control of the integrated FGM plate in a self-monitoring and self-controlling system. Numerical results for the control of bending and torsional deflections and/or vibrations are presented for a FGM plate comprising zirconia and aluminium. The effects of constituent volume fraction and the influence of feedback control gain on the static and dynamic responses of the FGM plates are examined in detail. Copyright © 2001 John Wiley & Sons, Ltd.

Vibration control of smart piezoelectric composite plates

Abstract: This study on the vibration control of smart piezoelectric composite plates investigates the effect of the stretching-bending coupling of the piezoelectric sensor/actuator pairs on the system stability of smart composite plates. Based on first-order shear theory and consistent methodology, a smart isoparametric finite element is formulated and the classical negative velocity feedback control method is adopted for the active vibration control analysis of smart composite plates with bonded or embedded distributed piezoelectric sensors and actuators. It is shown mathematically and demonstrated numerically that generally the coupling effect tends to result in system instability unless the sensor/actuator pairs are collocated or the plate simply supported. The result of this study can be used to aid the placement of piezoelectric sensor/actuator pairs of smart composite plates as well as for robust controller design.

Piezoelectric identification device and applications thereof

Abstract: An identification device having a piezoelectric sensor array is used to obtain biometric data. In one embodiment, a piezo ceramic sensory array is used to obtain biometric data. In another embodiment, a multi-layer sensor array structure having a PVDF layer in between two conductor grids orthogonal to one another is used to obtain biometric data. Urethane can be added to one side of the sensor array where a finger is placed. A foam substrate can be used as a support. Multiplexers are switched to control the sensor. The device has several operating modes for obtaining a variety of biometric data, including an impedance detection mode, a voltage detection mode, an imaging mode, and a Doppler-shift detection mode. The presence of a fingerprint on the sensor can be used to turn-on the device. The device is capable of capturing a fingerprint, forming a three-dimensional map of a finger bone, and/or determining the direction and speed of arteriole and/or capillary blood flow in a finger. A single pixel or a group of pixels can be detected and readout to a memory. The device can be used as an electronic signature device. The device can operate as part of a personal area network, using a public service layer according to the invention.

Health monitoring of concrete structures strengthened with advanced composite materials using piezoelectric transducers

Abstract: An active damage interrogation (ADI) method which uses an array of piezoelectric (PZT) transducers attached to a structure was used to detect and localize disbonds and delaminations of advanced composite reinforcement from concrete structures. The ADI system provides the ability to detect, localize, and estimate the extent of the disbond by actively exciting the structure with PZT transducers and processing the structural response as measured by the PZT transducers. The ADI system makes use of both amplitude and phase information from various actuator/sensor transfer functions, and also provides a unique method for determining when the transducer/structure bond has degraded. This paper investigates the feasibility of using the ADI method for health monitoring of concrete structures repaired with composite materials, and the advantages and limitation of this method are discussed.

Vibration Control of Plates Using Discretely Distributed Piezoelectric Quasi-Modal Actuators/Sensors

Abstract: A novel approach is presented for vibration control of smart plates using discretely distributed piezoelectric actuators and sensors. The new method consists of techniques for designing quasi-modal sensors and quasi-modal actuators. The modal coordinates and the modal velocities are obtained approximately from the outputs of the discretely distributed piezoelectric sensor elements, whereas the modal actuators are implemented by applying proper voltages on each actuator element. The observation error of the modal sensor is analyzed, and an upper bound for the observation error is determined. The control spillover of the modal actuator is also estimated, and an upper bound of the control spillover is also found. The criteria are developed for finding the optimal locations and sizes of both piezoelectric sensor and actuator elements. In the optimality criteria the optimal locations and sizes of the sensor elements can be found by minimizing the observation error of the modal sensor, and those of the actuator elements can be obtained by minimizing both the control energy and the control spillover. The results obtained using the present optimal criteria show that they do not depend on the initial condition of vibration of the structures, nor do they depend on the control gains.

Piezoelectric energy harvester and method

Abstract: A self contained device for harvesting electrical energy from linear and rotary motion has a sensor with amplifiers (104, 106) for tensile stretching of a piezoelectric body (100) with magnification of the applied force. The piezoelectric body is a monolithic plate with surface electrodes (120, 122) covering its top and bottom surfaces.

Exact Solution for Rectangular Sandwich Plates with Embedded Piezoelectric Shear Actuators

Abstract: Anexact solution isobtainedforthethree-dimensional deformationsofsimplysupported laminated rectangular thick plates with embedded shear mode piezoelectric actuators, subjected to mechanical and electrical loading on the upper and lower surfaces. Each layer of the laminate is made of either an orthotropic elastic material or a piezoelectric material whose poling direction lies in the plane of the plate, with perfect bonding between the adjoining layers. The exact displacements and stresses for a homogeneous piezoelectric plate for various lengthto-thickness ratios are compared with those obtained by the erst-order shear deformation theory. Results are also presented for asandwich plateconsistingofashearmodepiezoelectriccoresandwiched between twoelastic layers. A comparison of the stresses with those in the corresponding surface-mounted extension actuation cone guration shows that for the same transverse deeection of the plate centroid, the maximum longitudinal stress within the actuator is signie cantly smaller for the shear actuation mechanism. The exact results presented here can be used to assess the accuracy of different plate theories and/or for validating enite element codes.

On the correction of the Bernoulli-Euler beam theory for smart piezoelectric beams

Abstract: The present paper is devoted to the development of a simple Bernoulli-Euler type beam theory for smart piezoelectric composite beams. It is the scope of this paper to formulate a formally purely mechanical beam theory taking into account the coupling to the electric field by means of the direct piezoelectric effect. Different electric boundary conditions, electroded layers with either the electric potential or the total charge being prescribed, or non-electroded layers, are considered. Approximations for the electric field depending on the actually realized electric boundary conditions are then utilized in the present formulation. Finally a beam model is obtained taking into account the electromechanical coupling by means of effective stiffness parameters. Results obtained by using this simple model are compared to two-dimensional electromechanically coupled finite element calculations. A very good agreement for both the mechanical and the electrical response is found, showing that the accuracy of the present one-dimensional theory is comparable to that of the two-dimensional finite element calculations.

Attenuation and localization of wave propagation in rods with periodic shunted piezoelectric patches

Abstract: Shunted piezoelectric patches are periodically placed along rods to control the longitudinal wave propagation in these rods. The resulting periodic structure is capable of filtering the propagation of waves over specified frequency bands called stop bands. The location and width of the stop bands can be tuned, using the shunting capabilities of the piezoelectric materials, in response to external excitations and to compensate for any structural uncertainty. A mathematical model is developed to predict the response of a rod with periodic shunted piezoelectric patches and to identify its stop band characteristics. The model accounts for the aperiodicity, introduced by proper tuning of the shunted electrical impedance distribution along the rod. Disorder in the periodicity typically extends the stop-bands into adjacent propagation zones and more importantly, produces the localization of the vibration energy near the excitation source. The conditions for achieving localized vibration are established and the localization factors are evaluated for different levels of disorder on the shunting parameters. The numerical predictions demonstrated the effectiveness and potentials of the proposed treatment that requires no control energy and combines the damping characteristics of shunted piezoelectric films, the attenuation potentials of periodic structures, and the localization capabilities of aperiodic structures. The theoretical investigations presented in this work provide the guidelines for designing tunable periodic structures with high control flexibility where propagating waves can be attenuated and localized.

Practical issues in the detection of damage in beams using wavelets

Abstract: Wavelet transform of dynamic response data, experimentally acquired using a piezoelectric sensor, is presented as a local non-destructive evaluation technique for locating damage in a beam. The higher consistency and accuracy of the results based on data from a piezoelectric sensor over a conventional strain gauge are demonstrated. The allowable range of wavelet scale to process the data is shown to be dependent on the sampling rate, filter frequency and length of signal, where edge effects due to transformation must also be considered in the latter. By estimating the wave arrival times based on theoretical flexural wave velocity, the approximate wavelet scale to process the data can be determined. Further processing of the signal at a finer wavelet scale is necessary to improve the accuracy. Based on experimental data, the method is shown to be robust with respect to boundary and damage conditions as well as impact position.

The investigation of three-dimensional vibration for piezoelectric rectangular parallelepipeds using the AF-ESPI method

Abstract: Electronic speckle pattern interferometry (ESPI) is a powerful tool for the full-field measurement of a deformed body. In this paper, a three-dimensional vibrating block that couples the out-of-plane and in-plane motions is investigated using the amplitude-fluctuation ESPI (AF-ESPI). This method demonstrates the advantages of combining high processing speed, such as in the subtraction method, with high fringe sensitivity, such as in the time-averaged method. The optical system for AF-ESPI is then employed to analyze the volume vibration of piezoelectric material for a rectangular parallelepiped configuration. Based on the fact that fringe patterns measured by the AF-ESPI method appear as a clear picture only at the resonant frequency, both the natural frequencies and the out-of-plane and in-plane vibration mode shapes are successfully obtained in this study. Finally, the impedance analysis as well as the finite element method (FEM) with three-dimensional model are also conducted to compare with the result obtained by AF-ESPI. It is shown that the numerical calculation and the experimental result agree fairly well for both the resonant frequency and the mode shape in three-dimensional configurations.

A piezoelectric sensor in a living organism for fluid pressure measurement.

Abstract: The invention relates to a fluid pressure sensor for a lead (18) or catheter preferably intended to be placed in a living organism, such as the heart of a human being, said sensor comprising a piezoelectric element (4, 10, 11, 14) delivering an electric signal when subjected to a pressure variation, said piezoelectric element (4, 10, 11, 14) being designed to exhibit circumferential sensitivity and being disposed on at least parts of the outer surface of a rigid annular or tubular supporting structure (2). The rigidity of said sensor is such that the signal from the sensor relating to the pressure transferred to the sensor through an ongrowth of for instance tissue on the sensor would be at least 90 % of the signal from the sensor without the ongrowth.

Method and apparatus for regulating voltages and voltage gradients for driving piezoelectric elements

Abstract: The invention describes a method and an apparatus for a fuel injection system with a piezoelectric element for controlling the amount of injected fuel by charging and/or discharging the piezoelectric element, wherein the fuel injection system comprises a current flow controller for charging and/or discharging the piezoelectric element based upon the gradient of a voltage across the piezoelectric element due to a charge the piezoelectric element is carrying.

Piezoelectric element for injector

Abstract: A piezoelectric element, for generating drive force for an injector, is provided with a plurality of alternately stacked piezoelectric layers expanding and contracting in accordance with application of voltage and internal electrode layers for supplying the applied voltage. The piezoelectric layers contain voids, but the total thickness in the stacking direction of the voids contained in any one piezoelectric layer is not more than ⅓ of the thickness in the stacking direction of the piezoelectric layer and the thickness in the stacking direction of each of the voids is not more than 50 μm.

Active vibroacoustic control with multiple local feedback loops

Abstract: The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed under each sensor. With ideal force actuators, the plant response is passive for such an arrangement of collocated actuator/sensor pairs and so decentralized (local) feedback is guaranteed stable. This property is shown to extend to collocated velocity sensors and piezoceramic actuators over the bandwidth of interest and so multiple local feedback loops are also predicted to be stable. The performance of such a system is simulated in controlling the vibration and sound transmission through a thin plate, excited by an acoustic plane wave, with a 4 x 4 array of such actuator/sensor pairs, which are connected together with 16 local feedback control loops. Using force actuators, significant frequency-averaged reductions up to 1kHz in both the kinetic energy (28dB) and transmitted sound power (18dB) can be obtained with an appropriate feedback gain in each loop. These reductions are not so great with piezoelectric actuators (12dB and 9dB respectively) but their use allows the controller to be fully integrated in the structure.

Diagnostic Lamb waves in an integrated piezoelectric sensor/actuator plate - Analytical and experimental studies

Abstract: The objective of this study is to model the diagnostic transient waves in an integrated piezoelectric sensor/actuator plate with a view to using it as a first step towards establishing an entire structural health monitoring system and to provide experimental verification of the proposed models. PZT ceramic disks are surface mounted on an aluminum plate acting as both actuators and sensors to generate and collect A0 mode Lamb waves. Mindlin plate theory is adopted to model the propagating waves by taking both transverse shear and rotary inertia effects into account. Actuator and sensor models are both proposed. The interaction between an actuator and the host plate is modeled based on classical lamination theory. The converse piezoelectric effect of the actuator is treated as an equivalent bending moment applied to the host plate. The sensor acts as a capacitor that converts the sensed strain change into a voltage response. An analytical expression for the sensor output voltage in terms of the given input excitation signal is derived, and then experimental work is performed to verify the accuracy of the analytical model. Experimental results show that single-mode Lamb waves in the plate can be successfully generated and collected through the integrated PZT disks. The experiment also shows that the predicted sensor output for both amplitude and phase agrees well with experimentally collected data.

Cement matrix 2-2 piezoelectric composite— Part 1. Sensory effect

Abstract: Experimental results of the sensory effect of a cement matrix 2-2 piezoelectric composite are presented. The purpose of the research is to develop a self-sensing actuator exclusively for use in intelligent structures in the civil engineering field. The composite was fabricated by casting cement-based mortar into a series of pre-arranged piezoelectric thin plates. Different from most research work on piezoelectric materials, the current research focuses on the electromechanical properties and mechanical properties of the piezoelectric composite at relatively low frequencies (0.1 to 50 Hz) due to the special requirements for intelligent structures in the civil engineering field. In this frequency range, linear elastic behavior was observed for the composite. Viscosity or hysteresis, which often exists in some polymer matrix piezoelectric composites, was not observed. A complex math form was adopted to characterize the piezoelectric coefficients. It was found that the magnitude of the composite piezoelectric coefficients exhibited a linear dependency on the frequency, while the phase had an asymptotic dependency on the frequency. In the load range used, no dependency of the piezoelectric coefficients on load level was found for the composite.

Dynamic Modeling and Vibration Analysis of the Atomic Force Microscope

Abstract: The objective of this paper is to formulate the equations of motion and to investigate the vibrations of the atomic force microscope (AFM), which is divided into the contact and noncontact types. First, the governing equations of the AFM including both base oscillator and piezoelectric actuator are obtained using Hamilton's principle. In the dynamic analysis, the piezoelectric layer is treated as a sensor to measure the deflection and as an actuator to excite the AFM via an external voltage. The repulsive force and van der Waals (vdW) force are considered in the contact and noncontact types of the AFM, respectively. Some important observations are made from the governing equations and boundary conditions. Finally, numerical results using a finite element method are provided to illustrate the excitation effects of base oscillator and piezoelectric actuator on the dynamic responses.

Thermopiezoelastic snapping of piezolaminated plates using layerwise nonlinear finite elements

Abstract: The thermopiezoelastic snapping phenomena of piezolaminated plates are numerically simulated by applying a cylindrical arc-length scheme to Newton-Raphson method. Based on the layerwise displacement theory and von Karman strain-displacement relationships, nonlinear finite element formulations are derived for thermopiezoelastic composite plates. From the static and dynamic viewpoint, nonlinear thermopiezoelastic behavior and vibration characteristics are investigated for symmetric and eccentric structural models with various piezoelectric actuation modes. Present results show the possibility to enhance the performance of thermal structures using piezoelectric actuators and report new phenomena, namely thermopiezoelastic snapping, induced by the excessive piezoelectric actuation in the active suppression of thermally buckled large deflection of piezolaminated plates.