Attenuation of Microwave Acoustic Surface Waves Due to Gas Loading

Abstract

Experimental measurements of microwave acoustic surface‐wave attenuation due to propagation at the boundary of a solid and a monatomic gas are presented. Data illustrate attenuation as a function of frequency, molecular weight, pressure, and temperature. Experimental results are compared to both an approximate and a continuum mechanical theory. For the frequencies of interest (500–2500 MHz) the approximate theory gives better agreement with experiment. A summary of data of attenuation due to air loading at 1 GHz is presented for a number of low‐loss acoustic surface‐wave substrates. Of practical interest is the fact that microwave acoustic surface‐wave delay lines and other signal‐processing devices must be encapsulated in either helium or vacuum if minimum insertion loss is desired.