Narrow-bandwidth Rayleigh-wave filters

In order to obtain a 50 kHz bandwidth at 102 MHz with an interdigital delay-time filter, the transducers are made of a succession of elementary combs separated by an integer multiple of the acoustical wavelength. The frequency response of such a filter having two identical transducers consists of a sequence of transmission peaks, each having a bandwidth of about 50 kHz. When the two transducers are not identical, it is possible to obtain a frequency response with a small number of peaks. Such a filter is obtained when the spacing between adjacent elementary combs of each transducer is a different integer multiple of the acoustical wavelength. The design of several filters is described and some measured characteristics are presented.