Comparison of acoustic fields radiated from piezoceramic and piezocomposite focused radiators

The acoustic field radiated from piezoelectric transducers is usually predi cted supposing that the transducer vibrates in thickness mode. However, dif ferent reports have shown that not only thickness vibrations were excited, but also plate waves. These waves are responsible for discrepancy between t he experimental acoustic fields and those predicted by the Rayleigh integra l. It could be supposed that the plate waves are strongly attenuated in pie zocomposite materials, as mechanical cross-talk between neighboring element s of the composite structure is fairly weak. A similar effect could be achi eved in piezoceramic material by employing a heavy backing, which partially damps the plate waves. These opportunities of plate wave damping are inves tigated in the present paper. Three transducers are studied, which have ide ntical geometrical characteristics, but are made from different materials. The plate waves in these transducers are indirectly compared by measuring c orresponding ultrasound fields and comparing them with theoretically predic ted field. It is shown that plate wave patterns are strongly material depen dent and that it is only for piezocomposite sources (even when highly focus ed) that Rayleigh integral modeling can accurately predict the pressure fie ld distribution. (C) 1999 Acoustical Society of America. [S0001-4966(99)041 05-3].