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.