Abstract
This paper presents an optimization design strategy for wideband piezoelectric transducers based on a kerfless multifrequency annular array with two elements, made out of a 1-3 connectivity piezo-composite disk. The disk is machined by reducing the thickness within a circular section at the centre of the disk faces, so that two elements are obtained: an inner and thinner disk and an outer ring. They are designed to meet two main criteria: i) both elements present a different resonant frequency, being the inner disk the higher frequency element and ii) the individual frequency bands of the elements overlap to build up an overall frequency response that approximate to the sum of the individual frequency bands. The objective of this research is to determine the optimum configuration of both elements, in particular the relative elevation of the inner disk, so that cross-talk between elements and the appearance of undesired modes is minimized while frequency bandwidth is optimized. Towards this end, the response of different configurations is calculated using a finite element method. DOI: http://dx.doi.org/10.5755/j01.eie.22.5.16350
Highlights
Ultrasonic transducers based on piezoelectric materials are normally based on the excitation of geometrical resonances of the piezoelectric element
Frequency bandwidth of piezoelectric transducers can be enhanced by different means: i) selecting piezoelectric materials having higher electromechanical coupling factors [6] or higher mechanical losses or acoustic impedance value closer to that of the medium the transducer is going to be coupled to, ii) using a high impedance backing block, iii) using specially designed matching layers [7], [8] and iv) by acting on the electrical
Successful solutions in this case have been the use of multiple matching layers [10]– [13], wider bandwidth piezoelectric materials [14] and active materials with acoustic impedance closer to the air, examples are the use of ferroelectret films [13], [15], [16] and PVDF [17]
Summary
Ultrasonic transducers based on piezoelectric materials are normally based on the excitation of geometrical resonances of the piezoelectric element. Some of these solutions cannot be used for the case of air-coupled transducers, where achieving wideband response is an even more challenging problem due to the huge acoustic impedance difference between the air and the piezoelectric element Successful solutions in this case have been the use of multiple matching layers [10]– [13], wider bandwidth piezoelectric materials (like 1-3 connectivity composites based on PMN-PT single crystals) [14] and active materials with acoustic impedance closer to the air, examples are the use of ferroelectret films [13], [15], [16] and PVDF [17]
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