Piezoelectric Ceramic Elements Research Articles

Study on the prestressed sandwich piezoelectric ceramic ultrasonic transducer of torsional-flexural composite vibrational mode.

Based on the classical torsional and flexural vibrational theory of a slender rod, the prestressed sandwich torsional-flexural composite mode piezoelectric ceramic ultrasonic transducer is studied. This type of transducer consists of the slender metal rods and the longitudinally and tangentially polarized piezoelectric ceramic rings. The resonance frequency equations for the torsional and flexural vibrations in the transducers are derived. The simultaneous resonance of the torsional and flexural vibrations in the transducer is acquired by correcting the length of the metal slender rods resulting from the piezoelectric ceramic elements. The experimental results show that the measured resonance frequencies of the transducers are in good agreement with the computed ones, and the measured resonance frequencies of the torsional and the flexural vibrations in the composite transducers are also in good agreement with each other.

AN ACTIVELY TUNED SOLID-STATE VIBRATION ABSORBER USING CAPACITIVE SHUNTING OF PIEZOELECTRIC STIFFNESS

A tunable solid-state piezoelectric vibration absorber and an active tuning method were developed and demonstrated. A passive vibration absorber generally acts to minimize structural vibration at a specific frequency associated with either a tonal disturbance or a lightly damped structural vibration mode. Because this frequency is rarely stationary in real applications, damping is usually added to ensure some level of effectiveness over a range of frequencies. Maximum response reductions, however, are achieved only if the absorber is lightly damped and accurately tuned to the frequency of concern. Thus, an actively tuned vibration absorber should perform better than a passive one and, furthermore, could be made lighter. In its simplest form, a vibration absorber consists of a spring–mass combination. A key feature of the tunable vibration absorber described herein is the use of piezoelectric ceramic elements as part of the device stiffness. The effective stiffnesses of these elements were adjusted electrically, using a passive capacitive shunt circuit, to tune the resonance frequency of the device. The tuning range of the absorber is thus bounded by its short- and open-circuit resonance frequencies. An alternative tuning approach might employ resistive shunting, but this would introduce undesirable damping. Another feature of the device is the ability to use the piezoelectric elements as sensors. A control scheme was developed to estimate the desired tuning frequency from the sensor signals, to determine the appropriate shunt capacitance, and then to provide it. The shunt circuit itself was implemented in 10 discrete steps over the tuning range, using a relay-driven parallel capacitor ladder circuit. Experimental results showed a 20 dB maximum, and a 10 dB average improvement in vibration reduction across the tuning range, as compared to a pure passive absorber tuned to the center frequency, with additional benefit extending beyond the tuning range.

A catheter tactile sensor for measuring hardness of soft tissue: measurement in a silicone model and in an in vitro human prostate model.

Tissue hardness is related to tissue composition, and this is often changed by disease. It is therefore of interest to measure the hardness in an objective and non-invasive way. A tactile sensor based on a vibrating piezoelectric ceramic element in a feedback loop is described. When the sensor touches an object it produces a frequency shift related to the hardness of the object. The aim of this study was to develop an in vitro hardness measurement method using a catheter type version of the sensor. The method was evaluated in an established silicone tissue model and on human prostate tissue in vitro. A linear relationship was found with a high degree of explanation (R2 = 0.98) between a cone penetration hardness standard (DIN ISO 2137) applied to the silicone model and the corresponding frequency shift. The results from measurements on a human prostate tissue sample, fixed with formalin, showed that the relative hardness measured with the tactile sensor correlated (R = -0.96, p < 0.001, N = 60) with the proposed hardness related to the histological composition of the prostate tissue. The results indicated that hardness of prostate tissue, and maybe hardness of human tissue in general, can be expressed according to the cone penetration standard and that the hardness can be measured with this tactile sensory system. These findings hold the promise of further development of a non-invasive tool for hardness measurement in a clinical situation.

Thermal analysis of high drive transducer elements

The increasing demand for high-power, low-cost, compact transducer packages for underwater acoustic applications is leading to concerns of overheating in the active driving piezoelectric ceramic (lead zirconate titanate) elements and the associated passive materials (epoxies and polyurethanes). Pushing a design to its thermal limits can lead to reduced acoustic performance and reliability. There is not much guidance to be found in the literature that provides an analytical approach to cope with thermal issues of piezoelectric ceramics in the design phase. An analytic modeling effort is presented that addresses the thermal issues for compact high drive 31-mode free-flooded ring underwater sonar transducers. In this particular case, the thermal issues proved to be the limiting design concerns over the field and stress-limited cases. However, with modeling (analytical and finite element) and bench testing of components, the proper choice of materials and configuration parameters were determined and the performance goals were subsequently achieved. The approach addresses both the transient thermal response and the steady-state temperature profile that results from high-power, high duty cycle drive. These results may prove useful for other similar designs. [Work supported by ONR.]

Influence of Static Prestress on the Characteristics of Bolt-Clamped Langevin-Type Transducers

Bolt-clamped Langevin-type transducers (BLTs) are widely used as powerful vibration sources in high-power ultrasonic applications. In the structure of a BLT, static compressional prestress is imposed on piezoelectric ceramic elements by clamping, to compensate for their weakness to tensile stress. Nevertheless, no report has been made about the clamping effects on the characteristics of a BLT with a reasonable estimation of the prestress. Previous works on material property change of piezoelectric ceramics caused by static compressional stress have always presumed a groundless uniformity of stress distribution in the objects examined. The authors have investigated the effects by some experiments and numerical simulations with the use of the finite-element analysis system to estimate precisely the prestress. As a result of these experiments, the prestress has been found to reduce the electromechanical coupling factor of the BLT. Estimation of the prestress is considered indispensable for designing BLTs, although the microscopic mechanism of the piezoelectricity reduction is not yet clarified.

Study on the vibrational characteristics of ultrasonic transducers using tapered piezoelectric ceramic elements

Any nonuniformity in the flatness of a crystal element used in an ultrasonic transducer may lead to significant variations in transducer response. An accurate estimation of such variations could obviously be a measure of the nonuniformity involved, whatever its extent may be. Studies are reported on the effect of nonparallelism between two major plane surfaces of the crystal element on transducer response by studying the normal displacement amplitude pattern and its distribution over one of the vibrating (plane) surfaces at resonance. Measurements are carried out in air using a phase-locked laser interferometry technique where the effect of tapering in disk thickness on the transducer performance is manifested through the variation in vibrational patterns. Results of these measurements are compared with those obtained from electrical (conductance) response to highlight the importance of the former. Other comparison measurements, such as the conventional method of determination of acoustic response and pulse waveforms of the radiated signals in water, are also reported as a function of tapering in disk thickness. A correlation is discussed between results obtained from different measurements.

Study on the multifrequency Langevin ultrasonic transducer

Langevin ultrasonic transducers are widely used in high-power ultrasonics and underwater sound. In ultrasonic cleaning, a matching metal horn rather than a metal cylinder is used as the radiator in order to enhance the radiating surface and improve the acoustic matching between the transducer and the processed medium. To raise the effect of ultrasonic cleaning, the standing wave in the cleaning tank should be eliminated. One method to eliminate the standing wave in the tank is to use the multifrequency ultrasonic transducer. In this paper, the Langevin ultrasonic horn transducer, with two resonance frequencies, is studied. The transducer consists of two groups of piezoelectric ceramic elements: the back metal cylinder, the middle metal cylinder and the front matching metal horn. The vibrational modes of the transducer are analysed, and resonance frequency equations of the transducer in the half-wave and the all-wave vibrational modes are derived. According to the resonance frequency equations, transducers with two resonance frequencies are designed and made. The resonance frequencies, the effective electromechanical coupling coefficients and the equivalent electric impedances of the transducers are measured. It is shown that the measured resonance frequencies are in good agreement with the computed results, and the transducer can be excited to vibrate at two resonance frequencies, which correspond to the half-wave and the all-wave vibrational modes of the transducer.

圧電素子を用いた内耳インピーダンスの測定 イヌによる実験的研究

Inner ear impedance was measured in 17 ears of 13 dogs using a newly developed device with piezoelectric ceramic elements. The device was composed of two elements, one for activation of the stapes and the other for recording vibrations of the former element in the form of an electric output, which varies in accordance with the magnitude of the inner ear impedance.Under general anesthesia, the animal was fixed in a prone position and the middle ear was exposed. Then, the malleus and incus were carefully removed and the measuring device was positioned on the head of the stapes. Average impedances in 10 ears were 3.99M ohm at 1kHz, 4.43M ohm at 2kHz and 13.05M ohm at 4kHz. Experimental rupture or closure of the round window did not cause significant change in inner ear impedance values. However, fixation of the stapes increased the values in the frequency range between 1 and 6kHz up to a peak of 36.54M ohm.

Piezoelectric ultrasonic motor using longitudinal-torsional composite resonance vibration

A piezoelectric ultrasonic motor, which uses longitudinal and torsional composite vibration, is examined in order to obtain high torque characteristics with small diameter. Piezoelectric ceramic elements, oscillating in both longitudinal and torsional modes, respectively, are used as piezoelectric stiffened modes having high electromechanical coupling factors k(33) and k(15), respectively. It is found that the resonant frequencies for longitudinal mode and torsional mode could coincide with each other in the ultrasonic motor, according to finite element method analysis and experimental measurement. The motor operating in both resonant vibrations indicated good performance. The 20-mm diameter motor exhibited 4 kgfcm maximum torque, 450 r/min maximum rotational speed, 40% maximum efficiency, and quick responsiveness, within 2.5 ms.

Tuning of a Surface Acoustic Wave Resonator Formed of Lithium Tetraborate Substrate Combined with Piezoelectric Ceramic Element

Tuning of resonant characteristics, especially of resonant frequency, was studied on surface acoustic wave resonator, which was formed on a lithium tetraborate substrate and adhered to a poled piezoelectric ceramic element. The resonant frequency was tunable when a electric field (up to 1.5 kV/mm) was applied to the piezoelectric element. The magnitude of resonant frequency tunining was about 600 ppm, so that the temperature coefficient of resonant frequency change could be tuned to be constant or almost zero ppm/°C over the experimental temperature range between 0 and 75°C. The mechanism of tuning is considered to be that the distance between interdigital electrodes on the resonator was changed as the piezoelectric ceramic element was actuated and deformed with the application of electric field.

Piezoelectrically Assisted Ultrafiltration

Abstract We have demonstrated the feasibility of using piezoelectrically assisted ultrafiltration to reduce membrane fouling and enhance the flux through ultrafiltration membranes. A preliminary economic evaluation, accounting for the power consumption of the piezoelectric driver and the extent of permeate flow rate enhancement, has also shown that piezoelectrically assisted ultrafiltration is cost effective and economically competitive in comparison with traditional separation processes. Piezoelectric transducers, such as a piezoelectric lead zirconate titanate (PZT) disc or a piezoelectric horn, driven by moderate power, significantly enhance the permeate flux on fouled membranes, presumably because they promote local turbulence. Several experiments were conducted on polysulfone and regenerated cellulose UF membranes fouled during filtration of model feed solutions. Solutions of poly(ethylene glycol) and of high-molecular weight dextran were used as models. We found that we could significantly increase the permeate flux by periodically driving the piezoelectric transducer, horn or PZT disc, by application of moderate power over short periods of time, from 20 to 90 seconds. Enhancements as high as a factor of 8 were recorded within a few seconds, and enhanced permeate fluxes were maintained over a prolonged period (up to 3 hours). The prolonged flux enhancement makes it feasible to drive the piezoelectric transducer intermittently, thereby reducing the power consumption of the piezoelectric driver. As piezoelectric drivers of sonically assisted ultrafiltration, PZT disc transducers are preferred over the piezoelectric horn because of their small size and ease of adaptability to ultrafiltration test cells. The horn transmits sonic energy to the UF membrane through a titanium element driven by a separate piezoelectric transducer, but a piezoelectric ceramic disc transmits energy directly to the UF membrane. Moreover, because piezoelectric ceramic elements can be fabricated in several configurations, they are potentially feasible for piezoelectrically driven ultrafiltration spiral-wound membrane modules.

Applications of laser holography in vibratory analysis of piezoelectric ceramics and transducers

Abstract In this paper the vibratory holograms of piezoelectric elements and transducers under resonance state are investigated by means of the time-average method of laser holography. Also investigated are a series of dynamic vibratory characteristics calculated from holograms, such as vibratory type, amplitude, relations between amplitude and excitation voltage, relations between amplitude and frequencies, amplitude distribution on the vibratory face etc. Suggestions are made on using the holography to examine the effects of transducer design, the improvement of technology, property and unanimity transducers, the determinations of various vibratory models of piezoelectric ceramic elements and the evaluations of qualities of piezoelectric elements.

Monolaminar piezoelectric bender bar

First Page

Bessel beam ultrasonic transducer: fabrication method and experimental results : Applied physics letters, vol. 55, no. 20, pp. 2066–2071 (13 Nov. 1989)

We report experimental results from a first‐of‐a‐kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is ‘‘polarized into’’ a piezoelectric ceramic element. The resulting circular‐disk transducer has the usual full‐plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1‐in.‐diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss‐Hermite model. Bessel transducers are of particular interest in attempts to achieve ‘‘diffractionless’’ beams.

Linear type ultrasonic motor using two-dimensionally positioned piezoelectric elements

This paper deals with a linear type ultrasonic motor using two longitudinal effect piezoelectric ceramic elements which are positioned two-dimensionally. In the first part of this paper are described the vibration loci generated by the composed apparatus of two piezoelectric elements, which can vibrate independently in each direction. The second part contains a right angle construction of two piezoelectric ceramic elements and its measured vibration loci. In the third, a linear type ultrasonic motor using the composed apparatus is proposed and its measured characteristic is shown. This linear type motor has some superior features to other conventional motors.

Technique for nonuniform poling of piezoelectric element and fabrication of Gaussian transducers

A new technique has been developed to polarize piezoelectric ceramic elements with a nonuniform electric field. Used as an ultrasonic transducer, the piezoelectric element will produce a corresponding nonuniform sound field. Ultrasonic transducers for generating specific field profiles can therefore be made by having a predetermined spatial pattern of polarization strength poled into the piezoelectric element. One of the desirable beam profiles is a Gaussian; it has the advantages of being free from near-field fluctuations and far-field sidelobes, and it is much easier to model than the usual piston transducers. This method was used to fabricate Gaussian beam transducers, and their measured field profiles compared well with the Gaussian beam model. Such transducers containing the built-in Gaussian amplitude profile can be electroded and mounted in the same manner as conventional piston transducers.

Bessel beam ultrasonic transducer: Fabrication method and experimental results

We report experimental results from a first-of-a-kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is ‘‘polarized into’’ a piezoelectric ceramic element. The resulting circular-disk transducer has the usual full-plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1-in.-diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss-Hermite model. Bessel transducers are of particular interest in attempts to achieve ‘‘diffractionless’’ beams.

Finite-size effects in the frequency response of piezoelectric composite plates

The resonance spectrum of composite plates made of alternating piezoelectric ceramic and epoxy elements is studied both theoretically and experimentally in the frequency range below the thickness resonance. The transmissivity of the finite structure to plate modes is calculated, taking into account the effective plate velocities of the two constituent materials and the finite number of elements in the structure. The results are in excellent agreement with the electrically excited acoustical resonances of samples with different geometry and number of elements. In particular, the effects of the finite size on the number and frequency of modes, as well as their selection rules in the given experimental setup, are successfully interpreted. New ‘‘surface’’ resonances, attributed to the end elements, are observed in the stopbands when the surface elements have lower impedance.

Compound focus ultrasonic transducer

Improved focussing and increased bandwidth is obtained in a single-element ultrasonic transducer for non-destructive evaluation and material characterization applications. The piezoelectric ceramic element has a radius of curvature R 1 , and a combination lens and cover layer on its front surface has a radius of curvature R 2 which is less than R 1 . The depth of field of the transducer is increased and the bandwidth improved; the total thickness of the lens may be selected to control bandwidth.

External ultrasound can generate microampere direct currents in vivo from implanted piezoelectric materials.

Under development is an internal fixation plate that incorporates a piezoelectric element to generate current when excited mechanically by either weight bearing or external application of ultrasound. The intent is to deliver this current to electrodes at a fracture or osteotomy site to aid in prevention or treatment of nonunion. The present study examines quantitatively the ability of external ultrasound to generate current from small piezoelectric ceramic elements implanted in tissue. An ultrasonic transducer (2.25 MHz, 10-20 V input, less than 10 mW/cm2 output) was employed to excite small test coupons of a piezoelectric ceramic in vitro and in vivo with various materials, including water, PVC gel, cortical bone, and living soft tissues, interposed. In all instances, it was possible to generate currents of up to 20 microA after rectification; currents up to 1 mA were achieved in some cases. The work indicates that external ultrasonic energy could effectively power small internal devices designed to stimulate bone healing, without the need for implanted batteries or percutaneous leads.