SAW velocity measurements by using interdigital bulk wave transducers.

Abstract

A simple method of measuring the phase velocity of surface acoustic waves(SAW's) is proposed. The fundamentals of this method are based on the frequency dependence of radiation angle of an interdigital bulk wave transducer(IDBT) and the incident angle selection in bulk-to-surface mode conversion. The angle beam of bulk waves generated by a sending IDBT impinges onto the surface of a solid passing through a suitable acoustic coupling material and is converted to SAW's on the surface. The SAW's reradiate bulk waves. This signal is detected with a receiving IDBT. The transmission response between the sending and receiving IDBT's indicates a frequency f_0 at which the incident angle of bulk waves coincides with the Rayleigh critical angle. The SAW velocity can be calculated as a product of f_0 and the interdigital period. SAW velocities for various materials are measured by the proposed method. The results of measurements are shown to be in reasonable agreement with the calculated velocities. The method facilitates rapid evaluation of substrate meterials for use in SAW devices.