Log-periodic transducers for acoustic surface waves

Nonuniform interdigital transducers, i.e. those in which the periodicity and aperture may vary, can be used to obtain a response not available from uniform transducers. Here, the log-periodic type, which is designed to give a large bandwidth, is investigated, and a bandwidth of 39% is achieved experimentally. Using certain assumptions, a simplified theory for nonuniform transducers is developed. The theory gives results in good agreement with the experiments. It is shown that it is necessary to profile the transducer if the passband ripple is to be minimised.