Microwave acoustics

During the last few years, generation and propagation of acoustic waves have been extended to frequencies high into the gigacycle region. This paper deals with microwave acoustics, with emphasis on effects and techniques utilized at cryogenic temperatures. The extremely short wavelengths require the use of single crystal propagation media, free from defect scattering, supercooled to reduce wave attenuation from phonon interactions. Interactions of acoustic phonons with other phonons, electrons or holes, and spin waves are possible, with interchanges of energy that can produce attenuation or amplification of acoustic waves. The fundamental characteristics of acoustic wave propagation in crystanine media are discussed, with a review of experimental techniques and results. Microwave acoustic waves in solids and transducers suited to generation and detection are discussed, and a basic analysis of plane wave piezoelectric coupling is presented.