Index of content:
Volume 115, Issue 6, June 2004
- TRANSDUCTION 
115(2004); http://dx.doi.org/10.1121/1.1739486View Description Hide Description
To aid the design of linear arrays, it is quite important to have a detailed understanding of the elementary transducer behavior. These transducer bars must be backed and matched. The aim of this work is to characterize and to optimize layers that are used to match such transducer bars. In order to show the influence of these layers, the acoustical (acoustical power, far-field directivity pattern), electrical (electrical impedance) and mechanical (displacement field) parameters of the transducer are computed using the finite element method.Numerical studies of several transducers with different ideal matching layers which satisfy the one-dimensional criterion are presented and carefully analyzed. These studies show the existence of parasitic modes in the desired operating band of the transducer, due to shear wave propagation in the matching layer. A simple choice criterion of the matching material suggesting no parasitic mode in the desired operating band of the transducer bar has been defined. This criterion is given by where W is the width of the transducer and is the shear wavelength of the matching layer at the working frequency. Finally, experimental results of a matched transducer bar are successfully compared with numerical ones.
1-3 piezoelectric composite transducers for swept-frequency calibration of hydrophones from 100 kHz to 2 MHz115(2004); http://dx.doi.org/10.1121/1.1707090View Description Hide Description
Rapid calibration of hydrophones used in biomedical ultrasound is possible with swept frequency techniques such as time delay spectrometry. However, calibrations below 2 MHz largely have been neglected because of insufficient transmitting transducer bandwidth, even though important medical applications operate in this range. To address this deficiency, several transmitting transducer designs were developed and tested, and two 1-3 piezoelectric composite designs were found to have the requisite bandwidth and uniformity of response. In one the element has a plane front face and spherically concave back face (plano-concave), and in the second both faces are concave, but with different radii of curvature (biconcave). The nonuniform thickness disperses the thickness resonance, and the composite structure suppresses radial-mode resonances. Also, the composite’s lower acoustic impedance provides a more efficient match to water. The piezoelectric composite transducers were found to have transmitting pressure sensitivities superior to ceramic single-element and segmented designs having similar dimensions, and their responses were significantly more uniform variation from 0.1–2 MHz, with fine structure variation), likely due to decreased contributions from radial modes.
115(2004); http://dx.doi.org/10.1121/1.1737738View Description Hide Description
Cones or wedges inserted between an ultrasonic transducer and a specimen enhances certain characteristics of the transducers. Such an arrangement is useful in that the transducer can be used for transmitting and receiving signals on a point (or line) source, which can eliminate the undesirable aperture effect that makes the transducer blind to waves traveling in certain directions and to those of certain frequencies. In this paper, a comprehensive numerical analysis based on a wave propagationmodel is carried out to study the characteristics and parameters of wedges. We study the effect of dimensions, shape and aperture on frequency response and directivity. For computational accuracy and efficiency, the boundary element method is used in the analysis.