Ultrasonic studies of solids

Ultrasonics is being used in many areas in solid-state physics. One is Fermi surface mapping of normal metals by the magnetoacoustic technique. The detailed knowledge gleaned is valuable in theoretical calculations of many of the electrical and optical properties of metals. Another area is that of ``hard'' superconductors. Measurements of ultrasonic attenuation in the study of the metallurgical microstructure of high-field superconducting alloys (such as the Nb-Zr alloys) could have technological significance, especially in the field of power transmission. A new ultrasonic tool has been developed to aid investigations-the depletion layer transducer. It has prominent advantages over a conventional quartz piezoelectric transducer, including a higher fundamental frequency and the ability to change the resonant frequency by varying the dc bias level. Along with the new transducer, a new piezoelectric semiconductor amplifier produces substantial amplification of ultrasonic waves in photoconductive CdS by applying a dc electric field in the direction of wave propagation. This feature could find use in acoustic delay line technology.