Wave propagation generated by piezoelectric actuators attached to elastic substrates

Summary Piezoelectric actuators can be used to generate high-frequency elastic waves for damage identification of materials. This paper provides a comprehensive theoretical study of the electromechanical behavior of surface-bonded or embedded piezoelectric actuators under inplane electric fields. A modified one-dimensional actuator model is introduced, from which arbitrarily distributed electric fields along the actuator can be considered. The model is used to simulate the dynamic load transfer between the actuator and the host medium and the resulting elastic wave propagation by using the integral transform method and solving the resulting singular integral equations. Of particular interest is the generated waveform away from the actuator under different electric fields. An asymptotic analysis is conducted to obtain the far-field solution of the wave field. The property of the resulting waveform is studied, and the simulation shows that the direction of wave propagation can be adjusted by controlling the phase distribution of the applied electric field along the actuator.     

A dynamic linearization concept for piezoelectric actuators

We present a linearization circuit based on a capacitive Wheatstone bridge that is able to set a desired polarization in a piezoactuator. The system is meant to be used for dynamic actuation in a broad frequency range. A general nonlinear model for piezoactuators is presented in which two nonlinear sub-systems are cascaded: the electric-field-to-polarization (E-P) and the polarization-to-strain (P-x) blocks. The inversion of the latter sub-system in combination with the linearization bridge results in a reduction of up to 19 dB of the harmonic distortion of the actuator's mechanical displacement.     

Optically addressed microelectromechanical systems driven with high-frequency modulated light

We propose and analyze a new mode of operation for an optically addressed deformable mirror device. The device consists of an array of metallized membrane mirrors supported above an optically addressed photoconductive substrate. A conductive transparent electrode is deposited on the backside of the substrate. A variable polarity voltage is applied between the membrane and the back electrode of the device accompanied with high-frequency modulated light. The membrane is deformed when a modulated light illuminates the backside of the device. This occurs due to impedance and bias redistribution between the two cascaded impedances. This operating mechanism of a microelectromechanical systems device is suitable for detecting moving targets.     

Net shape formed spiral and helical piezoelectric actuators

Piezoelectric actuators tend to be made from relatively simple shapes such as blocks, plates and beams. These shapes allow for a range of displacements from key actuation modes but, in order to expand this range, complex structures are required that cannot be made via conventional means. This study presents a novel manufacturing method for such structures using a green ceramic tape lamination process followed by plastic deformation. Furthermore, a helix and a spiral are introduced as examples of initially curved structures. Their actuated behaviour is described by simple but effective models in terms of the standard linear piezoelectric coefficients and is compared to experiments. It is shown that displacements are produced by actuation mechanisms not previously reported in the literature.     

Numerical modelling of piezoelectric actuators exposed to hydrogen

Modern fuel injectors have been developed based on piezoelectric stack actuators. Performance and durability of actuators in a hydrogen environment are important considerations in the development of hydrogen injectors. 2D plane stress and 3D models for analysis of coupled diffusion and thermo-electromechanical response of actuators are presented. Chemical potential, electric field and temperature gradients are taken as driving forces for hydrogen transport. The explicit Euler finite difference method is used to solve the nonlinear diffusion governing equation. The finite element method is used for time-dependent analysis of fully coupled mechanical, electric and thermal fields. The diffusion process and thermo-electromechanical deformations are coupled through the dependence of piezoelectric properties on hydrogen concentration. Experimental results for the piezoelectric coefficient d ₃₃ of PZT ceramics exposed to different hydrogen concentrations are used. A comparison of a fully coupled 2D model with 2D and 3D models with reduced coupling is made to examine the significance of coupling and computational efficiency. Selected numerical results are presented for time histories of hydrogen concentration, temperature and stroke of an idealized actuator unit cell to obtain a preliminary understanding of the performance of actuators exposed to hydrogen.     

Solid freeform fabrication of piezoelectric sensors and actuators

The last two decades have witnessed the proliferation piezoelectric composite transducers for an array of sensor and actuator applications. In this article, a concise summary of the major methods used in composite making, with special emphasis on Solid Freeform Fabrication (SFF), is provided. Fused Deposition of Ceramics (FDC) and Sanders Prototyping (SP) are two SFF techniques that have been utilized to make a variety of novel piezocomposites with connectivity patterns including (1-3), (3-2), (3-1), (2-2) and (3-3). The FDC technique has also been used to prototype a number of actuators such as tube arrays, spiral, oval, telescoping, and monomorph multi-material bending actuators. It has been demonstrated that SFF technology is a viable option for fabricating piezocomposite sensors and actuators with intricate geometry, unorthodox internal architecture, and complex symmetry. The salient aspects of processing of such composite sensors and actuators are summarized, and structure-processing-property relations are elaborated on.     

Design of piezoelectric actuators for measurement technology instruments

Engineering methods are presented for calculating mechanical stresses and deformations in homogeneous piezoceramic plates having a nonuniform polarization across their thickness. A detailed examination is made of the design of a piezoceramic modulator for a pyroelectric temperature transducer. The results of numerical calculations are compared with experimental data. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 48–52, July, 1998.     

Compact piezoelectric stacked actuators for high power applications

Small, hollow, multilayer actuators with a diameter of 3 mm were fabricated by the stacking method from piezoelectric hard lead zirconate titanate (PZT) ceramics. Langevin vibrators were also constructed with the hollow multilayer actuators. The performance capabilities of the actuator and Langevin vibrator samples were examined under high-power conditions. The high-power vibration level at a given sinusoidal drive voltage was significantly enhanced by using a multilayer structure under either a nonresonance or resonance condition. A maximum vibration velocity of 0.17 m/sec was obtained for the 9-layer actuator sample under nonresonance conditions. The vibration velocity was further improved with the Langevin vibrator driven at the resonance frequency. The temperature rise due to heat generation under high-power conditions was the immediate limitation on the maximum accessible vibration velocity for the stacked actuators.     

On the elastic wave propagation induced by a network of piezoelectric actuators

Summary.  This paper provides a comprehensive analysis of the two-dimensional wave propagation in an elastic medium induced by embedded multiple piezoceramic actuators. Based on a new actuator model, which involves the deformation in both the transverse and longitudinal directions of the actuator, the actuation process and the dynamic load transfer between multiple actuators and the host medium is studied. The formulation of the problem is established using the analytical solution of the single actuator problem and a pseudo-incident wave method. Detailed numerical simulation is conducted to study the electroelastic behavior of this composite system. Attention is focussed on the properties of generated waveforms for different actuator arrangements. Received March 5, 2002; revised July 24, 2002 Published online: January 16, 2003     

Study of elastic wave propagation induced by piezoelectric actuators for crack identification

The current paper provides a theoretical study of elastic wave propagation in a cracked elastic medium induced by an embedded piezoelectric actuator. The formulation of the problem is based on a newly developed actuator model and the solution of coupled crack and actuator problems. The interaction between an actuator and a crack is studied to develop basic understanding of the effect of the crack upon the wave field generated. The resulting wave field is used to simulate 'sensor signals'. Scattered wave from the crack is then regenerated by solving a reverse elastodynamic problem and used in an imaging technique to identify the crack.     

Characteristics of chemo-mechanically driven polyacrylonitrile fiber gel actuators

Pure polyacrylonitrile (PAN) fiber gels, exhibiting effective actuation forces and displacements through muscle-like contractile behavior during the volume change when subjected to environmental stimuli, are prepared by electrospinning, twisting (strand creation) and activation process to investigate performance characteristics of chemo-mechanically driven PAN gel actuators. Single PAN strand (yarn) having a dimension of 210 μm in diameter is used. A typical hysteresis loop is observed for the length change (∼ 38%) of PAN gels with respect to pH variation. Diameter and volume changes are observed as greater than 100% and greater than 720%, respectively, for pH activated systems. Chemically induced force generation of pure PAN fiber gel is completed within a few seconds. The average maximum force is 0.002 N, implying that the force generation of a single PAN filament is 6.7 × 10^{− 6} N. A linear relation between force and strain is observed. It is found that PAN fiber gels in contracted state have stronger force and strain (0.043 N/0.112) than those (0.015 N/0.002) in elongated state. The actuation stress of pure PAN is in the range of moving coil transducer and commercial PAN but the actuation strain is better than moving coil transducer and similar to natural muscle.     

Widely tunable optical bandpass filter by use of polymer long-period waveguide gratings

We report the design and fabrication of a widely tunable optical bandpass filter based on using two identical long-period gratings formed along a polymer channel waveguide with a section of the waveguide core removed. The peak transmission of the passband of the fabricated filter is approximately 60% and the bandwidth of the passband is approximately 6 nm. The filter is thermally tunable over the C + L band (1520-1610 nm) for both TE and TM polarizations with a temperature control of approximately 30 degrees C.     

Real-time calibration of open-loop piezoelectric actuators for interferometric applications

In the present paper a piezoelectric actuator realized for interferometric applications is described, together with a numerical model to simulate its electro-mechanical behavior. The actuator is an open-loop device made up of three piezoelectric ceramics glued into a stainless steel case and connected directly to the parallel port of a personal computer by control electronics developed on purpose. It consists of a 16 bit digital-to-analog converter whose voltage is fixed by the parallel port, a charge amplifier which provides the voltage to the piezoelectric ceramics and a current divider for the control of the voltage on each channel. The layout based on three active elements has allowed to obtain a device which is able to perform a straight expansion with a negligible tilting, a desirable feature for an actuator used for interferometric applications. The hysteretic behavior, a typical characteristic of this kind of actuator, was simulated by a numerical model, based on the Prandtl–Ishlinskii hysteresis operator, which shows a high capability to predict the input–output response at any level of the input signal, and it is efficient enough for use in real-time applications.     

基于压电致动器的微动隔振平台系统

为实现微仪器隔振平台的自适应控制,对第三代压电致动器顶杆部件进行了改进,并将其直接应用于微隔振系统,隔振效果不是很理想。为此,对致动器进行了系统在线建模,从理论上分析了导致结果不理想的原因,给出了一种改进方法,通过理论建模分析和试验研究,结果表明:该方法虽然降低了致动器位移增益,但具有较好的隔振效果。     

Modelling and analysis of piezoelectric actuators in anisotropic structures

Summary In this paper, we examine the coupled electromechanical behaviour of a piezoceramic actuator bonded to a finite elastic medium under inplane mechanical and electric loading. The purpose of the current work is to study the suitability of using a simple actuator model to simulate the load transfer between actuators and the host medium. The actuator is characterized by an electroelastic line model with the poling direction being perpendicular to its length. The solution of this electromechanically couple problem is provided by solving singular integral equations in terms of an interfacial shear stress and conducting finite element analysis. The results show that the transfer of the actuation energy between the actuator and the host structure can be effectively simulated using the developed theoretical model. Typical examples are provided to show the effects of the geometry, the material combination and anisotropy upon the load transfer. The study is further extended to treat the interfacial debonding between the actuator and the host material.     

Tunable terahertz metamaterials based on electrically controlled piezoelectric actuators

A new concept of tunable terahertz metamaterial with electrically controlled characteristics is suggested. Two versions of creating tunable metamaterials using piezoelectric cantilevers as controllable elements are designed. Configurations of tunable metamaterials designed as planar metal-dielectric structures of arrays of U-shaped resonators and square metal patches with piezoelectric actuators are proposed.     

Electromechanical coupling and output efficiency of piezoelectric bending actuators

Electromechanical coupling mechanisms in piezoelectric bending actuators are discussed in this paper based on the constitutive equations of cantilever bimorph and unimorph actuators. Three actuator characteristic parameters, (e.g., electromechanical coupling coefficient, maximum energy transmission coefficient, and maximum mechanical output energy) are discussed for cantilever bimorph and unimorph actuators. In the case of the bimorph actuator, if the effect of the bonding layer is negligible, these parameters are directly related to the transverse coupling factor lest. In the case of the unimorph actuator, these parameters also depend on the Young's modulus and the thickness of the elastic layer. Maximum values for these parameters can be obtained by choosing proper thickness ratio and Young's modulus ratio of elastic and piezoelectric layers. Calculation results on four unimorph actuators indicate that the use of stiffer elastic material is preferred to increase electromechanical coupling and output mechanical energy in unimorph actuators.     

High-frequency vibrations of piezoelectric plates driven by lateral electric fields

We study coupled face-shear and thickness-twist motions of piezoelectric plates of monoclinic crystals driven by lateral electric fields. The first-order theory of piezoelectric plates is used. Pure thickness modes and propagating waves in unbounded plates as well as vibrations of finite plates are studied. Both free vibrations and electrically forced vibrations are considered. Basic vibration characteristics including resonant frequencies, dispersion relations, frequency spectra and motional capacitance are obtained. Numerical results are presented for AT-cut quartz plates. The results are expected to be useful for the understanding and design of resonant piezoelectric devices using lateral field excitation.     

U-type piezoelectric thin-film microactuator for hard disk drives

We have designed, fabricated, and investigated a new dual-stage actuator system based on a thin-film lead-zirconate-titanate (PZT) microactuator and a voice coil motor for positioning a magnetic head in a high-density hard disk drive (HDD). We made the PZT microactuator by using a modified sol-gel technique to deposit PZT thin film and applying reactive ion etching processes to shape the device. We studied the crystalline structure and growth behavior of the piezoelectric films by X-ray diffraction and scanning electron microscopy and found that the PZT material preferably has a composition of Pb(Zr/sub 0.52/Ti/sub 0/.48)O/sub 3/. We also tested and simulated the U-type SUS304 substrate integrated with two single-layer PZT elements in order to investigate the driving mechanics. The device performance is outstanding. With the peak-to-peak head displacement of 1.08 /spl mu/m at the applied voltage of /spl plusmn/20 V and the suspension response frequency higher than 12 kHz, both displacement/voltage sensitivity and resonant frequency are high enough for the device to be used in future high-density HDDs.     

Toward tunable thin-film filters for wavelength division multiplexing applications

We provide a detailed analysis of the various problems connected with the development of tunable thin-film filters for wavelength-division multiplexing applications. We examine the relation between the change in layer thickness and the central wavelength shift for various configurations and point out the significance of the structure of the reflectors, the spacer thickness, and the location of the active layers. We describe and compare practical arrangements using either temperature or an electric field as the driving parameter.