Problems in the propagation of ultrasonic pulses in solids

Abstract

The ultrasonic pulse technique in solids almost always makes use of a short-duration train of sinusoidal oscillations. The number of oscillations in this train may vary considerably, from the one or two employed in flaw detectors and for velocity measurements on small specimens at low frequencies to the hundred or more used in absorption measurements at the higher ultrasonic frequencies. A basic problem in the use of the pulse technique is that of change of shape of the pulse arising from effects other than the absorption of energy by the material. Some of the more prominent causes of this change of shape are discussed. They include reflections at the detecting transducer; the electrical termination at the detecting transducer; the coupling film between transducer and specimen; frequency dependent absorption in the specimen; misorientation of crystalline specimens; diffraction; guided wave propagation, mode interference and secondary pulses. References to detailed discussions of these effects are provided. The paper was presented at the Symposium on Sonic Investigations on Internal Damping in Solids in London in August 1964. The symposium was organized by the Acoustics Group of the Institute of Physics and the Physical Society