SYMPOSIUM REPORT: Summarized Proceedings of Symposium on Applications of Ultrasonics

A symposium of the Acoustics Group of the Physical Society, held on 18th February 1949, surveyed recent advances in (a) the investigation of the fundamental structure of matter; (b) telecommunication and allied applications; (c) use of mechanical forces set up by intense waves. In (a) derivation of elastic constants of matter was an important field especially as small samples such as single crystals could be used. Losses incurred in propagating waves were surveyed with the help of an electrical transmission line model and simple versions of this were established to represent relaxation phenomena based on Maxwell's hypothesis of shear elasticity as a time function and on Kneser's treatment of loss due to delay in a storage process. There was excellent agreement of the latter with recent results on acetic acid. Available sources of ultrasonic power were surveyed and the importance of barium titanate as a powerful and strongly coupled piezoelectric transducer was emphasized. An expression for the receiver/transmitter power ratio in telecommunications systems was examined for gaseous, liquid and solid media and, from available data, optimum frequencies for various ranges were deduced. These were found to be in accord with experience in echo-sounding, earth exploration and in propagation in metals. Accounts were given of experience with flaw detectors and echo-sounding which showed that these were becoming important industrially and in navigation; work on blind aids was unpromising. Advances in timing and time delay devices were described. There is a dearth of important industrial applications of the use of intense waves in spite of the interesting phenomena which have been demonstrated in the laboratory. The importance of the study of cavitation was pointed out. Results were discussed for killing bacteria, disintegrating proteins, emulsifying, soldering aluminium and refining the crystalline structure in solidification of light alloys. Stress was laid on the wideness of the frequency spectrum over which these phenomena occurred and on the difficulties and importance of maintaining temperature constant and of measuring intensities during investigations.