Broadband Generation of Line Acoustic Waves

Abstract

Abstmct-Line acoustic waves (LAW), guided acoustic modes which follow a sharp edge of a substrate, are of interest for convolver applications because their tight energy confinement produces high strains. A segmented multistrip coupler, or multistrip mode converter (MSMC), is described that converts SAW energy to LAW energy. The segmentation serves several purposes. If the LAW velocity is not precisely known, the MSMC can compensate somewhat for incorrect choice of grafting pitches in the SAW and LAW tracks. The segmentation also allows the structure to take less space on the substrate. A coupled-rnode analysis of the MSMC and results on an experimental four-segment MSMC operating at 100 MHz with 25 percent bandwidth are presented. Although the MSMC should he capable of nearly complete energy transfer, this particular design was shorter than a full transfer length and had a conversion loss of about 5 dB. The predicted value of 4.9-dB conversion loss is in good agreement with experiment.