Bulk-acoustic waves radiated from low-loss surface-acoustic-wave resonators

The bulk-acoustic conductance in low-loss surface-acoustic-wave filters utilizing leaky surface-acoustic waves is significant for the device operation. Here we directly measure the bulk acoustic wave radiation pattern on the backside of the piezoelectric substrate with the help of a scanning laser-interferometer probe. For the case studied, a leaky surface-acoustic wave resonator on 36°YX–LiTaO3, a numerical calculation is carried out and the different bulk-wave modes arriving at the substrate bottom are identified by comparing the measured and computed energy-flow angles. The results are expected to lead to improved models for describing the operation of low-loss surface-acoustic-wave filters.