Thickness Mode Piezoelectric Transducers Research Articles

A numerical investigation of power loss in a thickness-mode piezoelectric transducer

Power loss reduction in piezoelectric transducers has been attracting the attention of diverse researchers and the ultrasonic technology manufactures for years. In this context, fundamentally two frequencies have been profusely investigated to excite these transducers, namely the resonance and antiresonance ones. However, more recently other operation points have been examined. This article presents a numerical investigation of power loss in a thickness-extensional mode piezoelectric transducer, excited at its fundamental resonance, and designed with the data compatible with a very-high mechanical quality factor (Q m) piezoceramic. Additionally, harmonic electric excitations of the device and a constant velocity of its front face were supposed, when it was acoustically coupled to air or water loads, i.e. in real loading conditions for numerous applications. In this investigation it was found an optimal operation point where a remarkable power loss reduction may be obtained regarding excitations at the resonance or antiresonance frequencies. Finally, it was discovered that power loss frequency spectrum depends on the external acoustic load for this type of transducers. In simulations, a linear piezoelectrics was assumed.

An underwater parametric array source transducer composed of PZT/thin-polymer composite

The source transducers for parametric array (PA) sound are required to radiate the primary wave with high intensity and directivity so as to generate nonlinear interactions between strong acoustic waves at different frequencies effectively, resulting in so-called PA sound. Thickness-mode piezoelectric transducers using 1–3 lead zirconate titanate (PZT) polymer composites were used to produce wide-bandwidth PA sound due to their ability to generate high-intensity, high-frequency sound beams over a relatively wide frequency band. The small mechanical quality factor of 1–3 PZT polymer composites results in high damping of the polymer matrix leading to a transducer with relatively flat frequency response but yet decreased-power efficiency. A PZT polymer composite that can enhance the power efficiency of a PA source transducer over a wide frequency bandwidth was proposed. This is achieved by adopting thinner polymer matrix layers and PZT rods with dual resonance frequencies. A transducer demonstrated ultrasonic sound up to 197 and 203 dB (re = 1 μP) at 98 and 135 kHz, respectively. The power efficiencies were 50% at 98 kHz and 33% at 135 kHz. PA sound was successfully generated up to 150 dB (re = 1 μP) at 30 kHz with a half-power beam width of 3.4°.

Research Papers. An Approach to Design Broadband Air Backed Piezoelectric Sensor

Abstract In this work, an approach to the design of broadband thickness-mode piezoelectric transducer is pre- sented. In this approach, simulation of discrete time model of the impulse response of matched and backed piezoelectric transducer is used to design high sensitivity, broad bandwidth, and short-duration impulse response transducers. The effect of matching the performance of transmitting and receiving air backed PZT-5A transducer working into water load is studied. The optimum acoustical characteristics of the quarter wavelength matching layers are determined by a compromise between sensitivity and pulse duration. The thickness of bonding layers is smaller than that of the quarter wavelength matching layers so that they do not change the resonance peak significantly. Our calculations show that the −3 dB air backed transducer bandwidth can be improved considerably by using quarter wavelength matching layers. The computer model developed in this work to predict the behavior of multilayer structures driven by a transient waveform agrees well with measured results. Furthermore, the advantage of this this model over other approaches is that the time signal for optimum set of matching layers can be predicted rapidly

Dynamic modeling of thickness-mode piezoelectric transducer using the block diagram approach

This paper aims to provide an alternative method to determine the characteristics of a piezoelectric transducer from measurement. A block diagram approach is proposed to analyze the dynamic characteristics of a thickness-mode piezoelectric transducer at its resonance frequency. Based on the feedback loop framework, the input–output relations of the electromechanical interaction of the transducer are described in terms of linear block diagram models. Furthermore, the closed-loop relations from external force to vibration velocity and electric current from generated voltage are easily found by Mason’s rule to characterize the equivalent mechanical admittance and electrical impedance, respectively. An example of a Langevin transducer with 28.15 kHz resonance frequency is illustrated for dynamics analysis. The frequency responses of the piezoelectric transducer, resulting from a force and current input, are respectively measured to identify the system parameters of the feedback model. The experimental results demonstrate the effectiveness of the proposed method.

Fabrication and characterization of annular thickness mode piezoelectric micro ultrasonic transducers

Micromachining techniques, in combination with low temperature ceramic composite sol-gel processing, have been used to fabricate annular array thickness-mode piezoelectric micro ultrasonic transducers (Tm-pMUTs). The processing techniques of low temperature (710 degrees C) composite sol-gel ceramic (sol + ceramic powder) deposition and wet etching were used to deposit and structure 27-microm thick lead zirconate titanate (PZT) films on silicon substrates to produce annular array Tm-pMUTs. Using these techniques, high quality PZT materials with near bulk permittivity have been obtained. The Tm-pMUT devices were shown to resonate at approximately 60 MHz in air and 50 MHz in water. From resonance measurements k(t) values ranging between 0.2 and 0.47 have been calculated and shown to depend on the level of porosity within the film. Lower values of kt were observed for films with higher levels of porosity, which was attributed to the relative decrease in the effective piezoelectric coefficient epsilon(33) with respect to stiffness and permittivity as a function of increasing porosity. This paper presents the successful micro-fabrication of a Tm-pMUT device and discusses the optimization of the poling conditions and effect of PZT microstructure on the coupling coefficient k(t). Pulse echo measurements in water, showing a -6 dB center frequency of 53 MHz and 47% -6 dB bandwidth, using a target 15 mm away from the transducer, have been included to demonstrate successful operation of the device. Full analysis of these results will be conducted in later publications.

PATTERNED HIGH FREQUENCY THICK FILM MEMS TRANSDUCER

ABSTRACT This paper describes the resonant behaviour of PZT (lead zirconate titanate) micro electromechanical systems (MEMS) based thickness mode piezoelectric transducers fabricated using an innovative low temperature method. The results obtained from transducers with different thicknesses (23 to 42 μ m) on silicon and alumina substrates, were compared to the results obtained from an analytical MASON model. The composite sol gel and wet etching process used to fabricate the MEMS transducers has been described in previous work [1]. It involves producing a PZT powder/sol composite slurry which, when spun down, yields films a few micrometers thick. Repeated layering and infiltration produces PZT films up to 30 μ m thick. The low firing temperature used in this process (< 720°C) allows the use of silicon as a substrate, which offers the possibility to incorporate piezoelectric ceramics into MEMS. The PZT thick films are shaped using a wet etching technique, using a HF/HCl solution diluted in water. The stress dependency of the thickness and porosity of the film have been demonstrated to be the major issue regarding the cracking behavior of such film thicknesses. An investigation into the curvature of the wafer study was performed using a Veeco Dektak stylus profiler. Results obtained for a resonating device with a diameter of 635 μ m on two different substrates, such as silicon and alumina, are presented. After removal of the silicon substrate support devices were tested to determine the resonance and antiresonance frequencies. Theses were found to occur at approximately 69 and 73 MHz respectively for the 22 μ m thick PZT device. Resonance and antiresonace peaks can be observed at 70 and 77 MHz respectively for the 23 μ m thick PZT device. Estimated values of keff calculated from the positions of resonance and anti-resonance peaks show the keff to be approximately between 0.2 and 0.42 as a fonction of the film density. A 30 μ m thick film resonates at 50 MHz. This device has direct applications for near surface medical imaging. The spin coating technique used for the fabrication opens a new field of possibilities regarding the 3D structure of such transducers.

A block diagram model of the thickness mode piezoelectric transducer containing dual oppositely polarized piezoelectric zones

A unidimensional, linear systems, block diagram model of a two-layer thickness mode piezoelectric transducer is presented. The layers are subject to opposing piezoelectric polarization and the device is assumed to be loaded by semi-infinite isotropic media at the two principal faces. Block diagram representations of the transducer acting as both a generator and a receiver of ultrasound are developed in conjunction with the equivalent model of the electrical admittance. When expressed in this manner, the underlying cause and effect relationships are identified, with the important contribution of the piezoelectric boundary highlighted. Comparisons with the conventional single-layer transducer are made throughout and the major physical differences in terms of transduction performance are discussed. The new model is compared with finite element analysis and good agreement is also demonstrated with experimental data. A key aspect of the methodology is the provision of a more intuitive understanding of such device behavior. Accordingly, emphasis has been placed on the physical relationships and this is considered a major contribution of the work.

Computer Modeling and Simulation of Thickness Mode Piezoelectric Transducers Under Different Driving Conditions

A global model for the pulsed ultrasonic responses of piezoelectric probes is presented. It allows the evaluation of transducers electrical impedance, transfer functions, impulse responses, emission and pulse-echo transient responses (neglecting diffraction effects) for different electrical pulsed driving waveforms (spike, sine-wave burst, square-wave burst, …). In addition, an approximate approach allows the computation of transient responses of piezoelectric transducers driven by efficient pulsers, which usually include a power switching device (e.g. SCR elements or nowdays MOS-FET transistors) and some rectifier components. Attenuation of ultrasonic waves in the different piezoelectric and non-piezoelectric layers are taken into account. A Visual Fortran Program has been developed for computer simulation. This program, with an interactive graphic interface, allows an easy simulation of electrical and ultrasonic responses of thickness mode piezoelectric transducers having different structures, material parameters, dimensions, tuning components, coaxial cables and electrical driving conditions.

Measurement Technique for Mechanical Vibration Using a Thickness-Mode Piezoelectric Transducer with Two Comb-Shaped Electrodes

A technique for measuring mechanical vibration is proposed using a thickness-mode piezoelectric transducer. The transducer has three electrode groups, which are an interdigital arrangement of two comb-shaped electrodes mounted on one surface of a piezoelectric ceramic plate and a counter electrode on the other surface of the ceramic plate. A combination of one of the two comb-shaped electrodes and the counter electrode operates as a thickness-mode vibrator for radiating a longitudinal wave into a water layer. The other comb-shaped electrode is used to detect a reflected ultrasound beam from the vibrating diaphragm, and is also applicable for receiving an electromagnetically coupled signal from an electric signal applied to the input comb-shaped electrode. Interference between the reflected signal and the coupled signal results in a change of the amplitude of the output signal, corresponding to the mechanical displacement of the diaphragm. This technique has the advantages of excellent transducer performance and concise signal processing.

Design and fabrication of an ultrasonic speaker with thickness mode piezoceramic transducers

Until now, most ultrasonic speakers have utilized piezoelectric buzzer-like radial mode transducers, which necessitates a complicated signal processing circuit to overcome the narrow frequency bandwidth of the transducers. We designed an ultrasonic speaker with thickness mode piezoceramic transducers, and fabricated an ultrasonic speaker system working at a frequency of 650 kHz. The design method of an individual in-air piezoceramic transducer is presented, followed by the design of the parallel combination of many transducers that are used to make the speaker. The performance of the speaker was measured experimentally to verify its unique features; i.e. a high directivity and a wide frequency bandwidth. The ultrasonic speaker developed in this study preserved all the unique features of an ultrasonic speaker without the use of complicated electronic signal processing circuits by virtue of the broadband frequency characteristics of thickness mode piezoelectric transducers.

Various equivalent circuits for thickness mode piezoelectric transducers

AbstractThe equivalent transmission line model originally proposed by Nukiyama [5] and applied to the thickness mode piezoelectric transducers by Kikuchi et al. [6] is reviewed and its characteristics are described. The model is compared with those proposed by Mason [4] and by Krimholz et al. [2]. The equivalent transmission line model developed by Kikuchi et al. [6] was derived from the fundamental piezoelectric equation and Newton's equation of motion via the Laplace transformation. A new equivalent circuit in a time domain was derived as well. By comparing the equivalent circuit in a time domain with the equivalent transmission line model [6], it was demonstrated that the equivalent transmission line model is a fundamental equivalent circuit that is effective both for analyses in a time domain and for conventional analyses in a frequency domain. It is also demonstrated that, when the simultaneity between electric and acoustic signals is neglected, the equivalent circuits [2, 4] can be derived from the equivalent transmission line model.

Controlled-source analogous circuits and SPICE models for piezoelectric transducers

Transmission line analogous circuits for piezoelectric transducers are developed which employ controlled sources rather than the traditional transformer to model the coupling between the electrical and the mechanical systems. A novel method is used to derive each model that consists of adding a term that is equal to zero to one of the device electromechanical equations. When this is done, it is shown that the equations can be cast into the form of the familiar telegraphist's equations for the voltage and current on an electrical transmission line. The circuits are derived for both the thickness-mode piezoelectric transducer and the side-electrode bar piezoelectric transducer. SPICE models of the analogous circuits are presented and an example simulation is given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An ultrasonic spike pulse emission circuit.

For many ultrasonic testing instruments, the piezoelectric transducers are working under a pulse situation. To improve the resolution of these instruments, the designs of the transducers must be considered. Recently, some ultrasonic instruments such as blood flow instruments, a Doppler system that uses ultrasonic pulsed random signals, and spectral analysis in food ultrasonography all emit and receive wideband spike pulses, so that they need piezoelectric transducers and emission circuits with a wider frequency band and higher efficiency. In this paper use is made of a Redwood equivalent circuit and a Laplace transform to analyze the impulse response of the emitting and receiving networks for the thickness mode piezoelectric transducers. The theoretical analysis shows that the sensitivity of the acoustic system is proportional to the square of the electromechanical coupling coefficient and inverse to the flight time of the ultrasonic wave within the transducer. An ultrasonic spike pulse emission circuit for thickness mode piezoelectric transducers was installed on the basis of theoretical analysis. The experimental results are in good agreement with the theoretical results.

Experimental determination of the three-port impedance matrix for an array of transflexural elements.

A transducer has been built that consists of an array of transflexural piezoelectric disks embedded in a soft potting material. This transducer can be configured as a thin layer yet exhibits significant low-frequency (audio band) sensitivity. It has been modeled as a general three-port transducer, and an experimental determination of the three-port impedance matrix over a range of frequencies for a prototype transducer has been made. The matrix is expressed in terms of effective constants (the electromechanical coupling constant, the clamped dielectric constant, and the elasticity constant) of a thickness mode piezoelectric transducer. Predictions of the frequency response of the transducer and its performance as an active surface have been made using the measured impedance matrix. These predictions have been compared to its actual performance as an active surface.

Back-Face Only Electrical Connections of Thickness Mode Piezoelectric Transducers

The radiation patterns of disk transducers connected in a recently reported novel manner by Laughlin, Drews, and Wilson is studied. In this connection, the back-face plating of a transducer is divided into two electrodes which constitute the only transducer-to- transceiver connection, and a dual-beam radiation pattern resulted. However, we found that repolarizing one half of the transducer re- stored a single beam pattern. This method of connection and regionally repolarizing the piezoelectric transducer appears highly advantageous for use in fabrication of both miniature transducers and various trans- ducer arrays (e.g., linear, annular, and matrix).

A lattice model of the thickness-mode piezoelectric transducer

Abstmct-The development of a new three-port model of the thickness-mode piezoelectric transducer, employing linear systems theory, is presented. A discrete bidirectional lattice is used to describe mechanical wave propagation and continuous transfer functions to represent the electrical parameters. When presented in block-diagram format, an extremely valuable insight is gained into the nature of piezoelectric interaction. The lattice concept is extended to the analysis of multilayered structures and, when implemented in the discrete time domain, close agreement with experimental data is obtained. A number of experimental and simulation results are included for comparison. I. INTRODUCTION ONVENTIONAL models of the thickness-mode piezoelectric transducer invariably utilize transmissionline analogs in which the electromechanical properties of the system are evaluated by means of electrical network concepts. Examples of this include the equivalent circuits of Mason [l] and the more recent KLM [2] model, which uses a center-tapped transmission line to model acoustic wave propagation. In this form both models are also readily adapted for the analysis of multilayered transducer structures. However, electrical analogs possess some disadvantages which limit their flexibility when applied to piezoelectric transducer modelling [3]. Physical insight into the nature of the transduction process is often masked, and as a'result the influence of external electrical and mechanical load conditions on transducer behaviour is difficult to determine. To overcome this, an alternative strategy has been proposed by Hayward [3] who adopted a systems feedback approach to

Lightweight, broadband Rayleigh wave transducer

A broadband angle-beam transducer system for producing and/or receiving Reigh waves on the surface of a metal medium comprising a thickness mode piezoelectric polymer transducer element embedded within and impedance matched to a plastic wedge. The transducer element is oriented at an angle determined to be the critical angle for Rayleigh waves in the metal structure to be tested. As a transmitter, the transducer element generates discrete dilatational wave pulses, one of which propagates within the plastic wedge to the plastic face in contact with the metal structure. At this face some of the wave energy is reflected as dilatational and shear waves within the wedge and the remainder of the wave energy passes through a coupling medium into the metal structure producing a Rayleigh wave traveling along the surface of the structure. When the system is used as a receiver, a Rayleigh wave propagating on the surface of the metal structure is received by the polymer element which then generates a voltage proportional to the Rayleigh waveform.

A systems model of the thickness mode piezoelectric transducer

A new model for piezoelectric ultrasonic transducers is proposed. Using a systems engineering approach, the concept of feedback is used to explain secondary piezoelectric effects and to clearly describe electromechanical interaction. The model is derived from the fundamental piezoelectric equations and it embraces the relevant practical situations where the transducer is subject to arbitrary electrical and mechanical loading. Block diagram representations of the piezoelectric transducer acting as a generator and receiver of ultrasound are developed. The physical significance of each element in the block diagrams are explained to provide a clear and distinct relationship between electrical and mechanical quantities. This permits the factors which control secondary piezoelectric action to be readily defined, along with the importance of this effect on the overall transfer function. It is considered that no other transducer model illustrates these concepts with the same degree of clarity and the technique offers significant advantages over existing transducer analogies. A number of computer simulations and experimental water tank measurements of acoustic wave profiles are presented. Close substantiation of the theoretical analysis is shown.

A systems feedback representation of piezoelectric transducer operational impedance

An analysis of thickness-mode piezoelectric transducer impedance under a variety of mechanical load conditions is presented. A wideband, systems model is used to describe this impedance, which is representative of the electrical input impedance in the transmitting mode and the electrical output impedance for the receiving mode. For a fixed input voltage, the total current flowing through the transducer is considered as the vector sum of two current quantities. Firstly, an input current arising directly from the applied voltage source and secondly, a feedback current, which is generated by secondary piezoelectric action. By treating the problem in this manner, an extremely valuable insight into the nature of the electrical characteristics is provided. Complex variations in the impedance behaviour are readily explained and the physical processes that contribute to such deviations are clearly isolated.

Discrete-Time Modeling of the Thickness Mode Piezoelectric Transducer

The validity of using r-transform techniques to model piezoelectric thickness mode transducer behavior is demonstrated. By modeling the transducer as a recursive digital fiiter, the response to a variety of arbitrary input functions may be evaluated directly in the time domain. This eliminates the need for more conventional trans- formation techniques which are limited in extent or distort the time domain response under some conditions. The technique has been successfully employed to model transducer behavior over a wide range of practical operating conditions and this is verified by the experimen- tal results.