Determination of the velocity of ultrasound by short pulse switched sinusoidal excitation and phase-sensitive detection by a computer-controlled pulse-echo system

摘要

For the determination of the velocity and the attenuation of acoustic waves, the resonances caused by reflections from both surfaces of plane parallel transducers and diffraction effects arising from the limited size of the transducers lead towell-known phase shifts of the signal. To avoid the build-up of these effects, fast-switched ultrasonic pulses with a pulse width shorter than the transit time of the transducers are employed. For these excitation conditions, contributions from internalreflections and diffraction can be separated in time. This allows the generation and detection of acoustic signals in an extremely wide frequency range. A fully automatic computer-controlled measuring system including a temperature-controlled samplechamber for the range 1.5-400 K has been constructed for high-accuracy generation and detection of short pulsed ultrasonic signals in the frequency regime 2-500 MHz.