Low-Temperature Ultrasonic Attenuation in Tin and Aluminum

According to theory based on an ideal metal, the ultrasonic attenuation should be proportional to the square of the frequency and to the electrical conductivity of the metal. Experiments were performed to compare theoretical and experimental values of attenuation in a frequency range from 100 kc/sec to 1 Mc/sec.A long wire sample coupled to a barium titanate transducer was suspended in a chamber, which in turn was placed in a liquid helium bath. A short train of sine waves was sent through the wire and the amplitude of successive reflections was measured as a function of temperature and frequency. The electrical conductivity of the sample was also measured.Two samples were investigated. High-purity tin yielded experimental results in excellent agreement with theory. The attenuation in high-purity aluminum was proportional to the electrical conductivity but averaged 45% higher than theoretically predicted.