Ultrasonic attenuation measurements in metals at low temperatures

The experimental techniques are reviewed for making ultrasonic measurements at frequencies from 10 MHz to 10 GHz in metals at temperatures down to 25 mK. The principles of attenuation measurements by the pulse-echo method and the electronic equipment for low temperature measurements are described. The theory and design of sample holders using nonresonant, re-entrant and helical cavities at ultralow temperatures are discussed. The generation of longitudinal and transverse phonons in metals with thin film CdS transducers, piezoelectric rods and electromagnetic radiation is explained. The preparation of thin flat samples of soft single crystals for these studies is described and the techniques necessary to extend ultrasonic measurements to higher frequencies and lower temperatures are considered.