The bulk acoustic waves launched in a piezoelectric crystal by an interdigital transducer, considered earlier as a spurious response in SAW devices, are now usefully employed in planar bulk acoustic wave (BAW) devices. This paper presents the results of a theoretical analysis of bulk wave response in a material. The analysis enables one to design BAW devices with a more desirable response than those obtained so far. Copyright © 1988, The Institution of Electrical Engineers. All rights reserved.