The Design of Broadband and Efficient Acoustic Wave Transducers

Abstract

The basic design criteria for SAW transducers is typically a flat frequency response. design criteria for bulk wave t.ransducers in nondestructive evaluation and medical imaging is the compactness of the impulse response. This criteria is different from the usual flat frequency response criteria because a flat bandwidth does not necessarily imply a compact impulse response. Aniterative optimization program, based on a least mean square algorithm, has been developed and used to simultaneously optimize matching metworks and acoustic parameters to achieve either of the above design criteria. The optimization is first illustrated in t he frequency domain for an IDT transducer. Then the optimization is done in the time domain for a bulk wave transducer with the criterionof reducing the length of the impulse response. The impulse response is thus reduced from about 15 cycles to 3 cycles and has an almost Gaussian frequency response. The increase in t he round trip insertion loss of the transducer due to the tuning is of the order of a few dB. Transducers have been constructed at 5 and 35 Wz (Z = 3 kg/n?-sec) and no front matching layer. The agreement between theory and experiment is excellent. The basic