Impedance Of Transducer Research Articles

Ultrasonic Nondestructive Measurement Systems – Models and Measurements

The electroacoustic measurement model is an explicit model of an entire ultrasonic measurement system, including the pulser/receiver, cabling, and transducers. A summary is given of the measurement procedures needed for characterizing all the system elements contained in this measurement model, including a description of a new pulse-echo method for obtaining the sensitivity and impedance of an ultrasonic transducer. It is demonstrated that these models and measurement procedures can be combined to accurately simulate the measured voltage of a pulseecho immersion system.

Designing and evaluating transducers for narrowband ultrasonic spectroscopy

Introduction of new composite materials in aerospace applications has created a demand for an efficient NDE technique. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered structures. In our previous work we have described the principle of narrowband ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. This paper is concerned with optimizing the NBUS setup consisting of a piezoelectric transducer coupled to a multi-layered structure. Differences in the electrical impedance of a piezoelectric transducer caused by variations of parameters of the inspected structure are estimated using an equivalent circuit model and a finite element analysis. The theoretical analysis presented in the paper results in design guidelines for NBUS transducers.

Planning to improve the mechanical quality factor in the transducer impedance matchers for Mario Schenberg detector

"Mario Schenberg" is a spherical resonant-mass gravitational wave (GW) detector that will be part of a GW detection array of two detectors. Another one is been built in The Netherlands. Their resonant frequencies will be around 3.2 kHz with a bandwidth of about 200 Hz. This range of frequencies is new in a field where the typical frequencies lay below 1 kHz, making the transducer development much more complex. Some studies indicated that using low mass mechanical resonators (used for impedance matching to the parametric transducer, in a cold damping regime) allow the detector to reach the standard quantum limit. In this work we describe the procedures that are being developed to quickly test the mechanical quality factor of a very small resonator in the quest to find the best machining method and thermal annealing for the impedance matching resonator, one key part that makes a good coupling between the sphere and the transducer. The main goal is to optimize the mechanical quality factor in a reasonable time.

Calibration of Current Measurement Transducers in Oversized Calibration Fixtures

A simple one-dimensional (1D) transmission line model has previously been used to derive improved estimates for the transfer impedance of current transducers at high frequencies by taking account of the finite reflections that occur at the ports of the calibration fixture. This approach is further extended to take account of the additional reflections that occur in the system when an oversized calibration fixture is used. The success of this method is also assessed, for frequencies up to 600 MHz, using measured and computed results for the current induced on a wire inside a cavity backed aperture illuminated by a nearby antenna.

Structural Health Monitoring by Piezo-Impedance Transducers. I: Modeling

The electromechanical impedance (EMI) technique, which employs piezoelectricceramic leadzirconatetitarate (PZT) patches as impedance transducers, has emerged as a powerful nondestructive evaluation...

Structural Health Monitoring by Piezo–Impedance Transducers. II: Applications

This paper, the second in a two-part series, presents a new methodology for structural identification and nondestructive evaluation by piezo–impedance transducers. The theoretical development and experimental validation of the underlying lead–zirconium–titanate (PZT)–structure interaction model was presented in the first part. In our newly proposed method, the damage in evaluated on the basis of the equivalent system parameters “identified” by the surface-bonded piezo–impedance transducer. As proof of concept, the proposed method is applied to perform structural identification and damage diagnosis on a representative lab-sized aerospace structural component. It is then extended to identify and monitor a prototype reinforced concrete bridge during a destructive load test. The proposed method was found to be able to successfully identify as well as evaluate damages in both the structures.

Lump Circuit Modeling and Matching Consideration on Acoustical Transmitters for Underwater Application

In underwater environment the acoustical wave can transmit a long ranges away from the transmitter than the electromagnetic wave does. So far, the piezoelectric ceramic is still the best candidate as acoustical telemetry transmitters in underwater applications. The impedance matching on the interface between electro-acoustical transducer and electrical transmitter has been the most important subject to confirm the high transmitting efficiency. In this research, a lumped equivalent circuit of electro-acoustic transducer is proposed. Then, the network theorem is implemented to design a high power transformer for impedance matching, and to improve the electro-acoustic efficiency of the transducer. In the developing procedure, the transducer's impedance is measured and the circuit element of equivalent circuit is deduced from the measured data to correlated the simulated values of the equivalent circuit. Then the matching transformer is developed to meet the specifications of impedance matching and high power operation. The equivalent circuit of the electro-acoustic transducer with matching transformer was developed and simulated using Hp-Vee program. The simulated results quite agree with the measured results. This approach really develops an effective method for impedance matching design and reduced the time for trial and error.

Measurements of mutual radiation impedance in arrays of piezoelectric cylindrical shell transducers

We present our recent experimental results of the mutual radiation impedance of piezoelectric cylindrical shell transducers in arrays using the Z- and V-methods previously reported by the authors [J. Acoust. Soc. Am. 112, 2407 (2002)]. The mutual radiation impedance in an array of two coaxially aligned cylindrical transducers was determined as a function of separation distance. The results obtained by both methods are in good agreement with the calculations based on the analytical equations for a similar array developed by D. H. Robey [J. Acoust. Soc. Am. 27, 706–710 (1955)]. The mutual radiation impedances in other array geometries including planar and curved arrays of cylindrical shell transducers, in which there is no known analytical solution, were also measured by the same methods in our underwater test facility. [Work supported in part by ONR 321 SS.]

P3-54 Radiation Impedance and Directivity Characteristics of Langevin Type Transducer with a Bending Board on The Radiation Surface

P3-54 Radiation Impedance and Directivity Characteristics of Langevin Type Transducer with a Bending Board on The Radiation Surface

Acoustic attenuation in the layers of a microwave transducer at the excitation of longitudinal and shear elastic waves by a piezoelectric of the 6mm symmetry class

An electroacoustic transducer in the form of a piezoelectric of the 6mm symmetry class with an arbitrary orientation of the sixfold axis and with two finite-thickness metal electrodes is considered taking into account the acoustic attenuation in the transducer layers. A system of equations is obtained to determine the impedance of the transducer, the radiation resistances for shear and longitudinal waves, the power ratio of these waves in the acoustic line, and the transformation factors for transverse and longitudinal waves. The effect of attenuation on the characteristics of a specific transducer operating in the 15-GHz frequency range is numerically analyzed.

Identification of material constants for piezoelectric transformers by three-dimensional, finite-element method and a design-sensitivity method.

In this paper, an inversion scheme for piezoelectric constants of piezoelectric transformers is proposed. The impedance of piezoelectric transducers is calculated using a three-dimensional finite element method. The validity of this is confirmed experimentally. The effects of material coefficients on piezoelectric transformers are investigated numerically. Six material coefficient variables for piezoelectric transformers were selected, and a design sensitivity method was adopted as an inversion scheme. The validity of the proposed method was confirmed by step-up ratio calculations. The proposed method is applied to the analysis of a sample piezoelectric transformer, and its resonance characteristics are obtained by numerically combined equivalent circuit method.

Оn thе influence оf acoustic attenuation in thе transducer layers under thе excitation оf thе volume elastic waves by 6mm class piezoelectric with arbitrary orientation of axis 6

An electroacoustic transducer оn the bases оf the piezoelectric class 6mm with axis 6 arbitrary orientation with electrodes of final thickness regarding the acoustic attenuation in its layers is considered. The system оf equations for the computation the transducer impedance, longitudinal and shear wave radiation resistance, power ratio of these waves in the sound conductor, and also the conversion losses for longitudinal and shear waves is obtained. The numerical analysis results of attenuation effect in the specific transducer in the range of 15 GHz are given.

New type of matching layer for air-coupled ultrasonic transducers.

This paper presents a new concept in the design of an impedance matching structure for air coupled ultrasonic transducers. A reflective layer structure is inserted between the transducer and propagation medium with a small air space. Adjusting the air space and the reflectivity of the inserted structure causes the transducer impedance to match with the impedance of the propagation medium. Two such structures were investigated as a reflector: a polymer thin film and a thick plate with many holes. Wave impedance theory was applied to these reflecting structures, and the impedance of a thin film layer at the incident surface was calculated using boundary conditions. Impedance of holed plate is calculated in a similar fashion. It was found that the calculated impedance of these structures approximately matched the impedance of the PZT air transducer (40 KHz). The acoustic pressure output was maximized by adjusting the position of the matching structure. A theoretical gain of up to 10 dB in the acoustic pressure was predicted under ideal circumstances, and the experimental observations showed a gain of 9.5 dB in the acoustic pressure for a 12 microm polyethylene film placed at a distance of approximately 0.1 mm from the transducer's surface. The increase was 9.8 dB for a polyvinylidene fluoride (PVDF) film and 9.7 dB for a 1.5 mm printed circuit board with many holes at a distance of approximately 25 microm from the transducer's surface.

Assessment of calibration procedures for accurate determination of thermal parameters of liquids and their temperature dependence using the photopyroelectric method

We present a systematic theoretical and experimental investigation on the accuracy of thermal diffusivity α and thermal effusivity e of liquids measured by the photopyroelectric (PPE) method in back-detection configuration (BPPE). Special cases corresponding to different cell structures are analyzed in terms of error determination of α and e for water and ethylene glycol. We propose a new normalization procedure allowing for estimation of these parameters with accuracy of 2% on α and 5% on e over extended frequency range. The normalization eliminates the frequency-dependent influence of the transducer impedance and associated electronics, reduces the errors due to coupling fluid between cell components, and reduces the number of temperature-dependent parameters that must be known in order to characterize the sample. Technical solutions for improving the performances are suggested. Another goal of the study was to demonstrate the possibility of the BPPE method to yield small variations of thermal parameters as a function of temperature. We found good agreement with the literature data for the temperature coefficients (Δα/α)/ΔT=0.267±0.015%/K for water and (Δe/e)/ΔT=0.10±0.05%/K for ethylene glycol, between 20 and 60 °C. The special case implying the normalization to a reference material and with a glass substrate for the pyroelectric sensor is shown to be the best adapted to the determination of both thermal parameters and of their temperature dependence.

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials.

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO3) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO3) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 ohms for the PZT fiber composite and PbTiO3 ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO3 and PbTiO3 transducers provided better image contrast than the other materials.

Ultrasound transmitting configuration

An ultrasound transmitting configuration includes at least one ultrasound generating device for exposing a medium which has an acoustic medium impedance and a medium speed of sound to ultrasonic waves. The ultrasound generating device has at least two ultrasound transducers which can be excited through actuating electrodes for emitting ultrasound and which have an acoustic transducer impedance. The ultrasound transducers are separated from one another and disposed alongside one another. An ultrasound lens which has an acoustic lens impedance and a lens speed of sound is disposed between the ultrasound generating device and the medium. The ultrasound generating device is acoustically coupled on a coupling side to the ultrasound lens. The ultrasound transducers extend toward the medium over a transducer depth, they extend toward one another over a transducer width, and they extend at right angles to both the transducer depth and the transducer width over a transducer length. The transducer width is maximally as great as the transducer depth, and the transducer length is considerably greater than the transducer depth. The ultrasound transducers are associated with a common actuating element for actuating the ultrasound transducers jointly and in the same way.

A new numerical method for synthesis of arbitrarily terminated lossless nonuniform transmission lines

In this paper, the synthesis of a nonuniform transmission line is treated by solving an inverse classical Sturm-Liouville problem, in which the boundary conditions are described by S-parameters. The related inverse problem is readily solvable if the terminated impedances and S-parameters satisfy some required conditions. This method can be used to design transmission-line filters and impedance transducers for almost arbitrarily provided source and load impedances.

The efficiency of ultrasonic systems in the case of piezoceramic transducers supplied with rectangular signal

The paper presents a method for the rise efficiency of ultrasonic systems—in the range 20–100 kHz—supplied by rectangular generators. The rise efficiency is important because of high power, which is working, and for optimal and reliable use of ultrasound systems. The ultrasonic systems constituted from ultrasonic piezoceramic transducers and acoustics chain (transmission, adaptation, amplifying of ultrasound vibration) are supplied from electronic generators, which works in commutation. The commutation-working regime assures a very high efficiency for an electronic generator, but generates a very large spectrum of frequency. The theoretical and experimental analysis of generated spectrum accomplished in this paper leads to very useful conclusions in order to choose an adequate matching dipole between generator and charge. Also, this analysis permits the determination of efficiency for whole ultrasonic system and it found some possibilities for it raising. This study is accomplished by the calculation programs: the efficiency as a function of harmonics, with and without matching dipole; the efficiency as a function of the acoustic charge, with matching dipole, for fundamental frequency; the input impedance of a piezoceramic transducer as a function of acoustic charge; and the total impedance of a piezoceramic transducer with matching dipole as a function of n harmonics.

The normalized electrical impedance of piezoelectric ceramic transducers as a tool for evaluation and characterization

Este trabajo ha sido realizado con financiacion de los proyectos de I+D: CICYT No TAP-97 0662-CO2-02 y CAM Ref. 07T/0031-97.

Structured-iterative design of impedance transducers invariant with respect to noninformative parameters

A structured-iterative design method of impedance transducers invariant with respect to noninformative parameters is discussed.