LECTURE 9 
HIGH-INTENSITY SOUND IN LIQUIDS 
E. Meyer 
Ill Physikalisches Institut 
der Universitat Gottingen 
Gottingen, West Germany 
When speaking of the generation of high sound intensities, we are inclined 
to think of explosions and atom bombs. These produce enormous intensities in 
water as well as in air. We will, however, exclude such generators from this 
report because it is still rather difficult and dangerous to explode atom bombs 
in the laboratory. We will limit ourselves to conventional methods of sound 
generation and will discuss the generation and measurement of high acoustic 
power in water and the effects observed, when intense sound waves are propa- 
gated through liquids. 
9.1. GENERATION OF HIGH ACOUSTIC POWER 
9.1.1. Continuous Wave Transducers 
In the generation of sound, it is appropriate to distinguish between sinu- 
soidal, more or less stationary excitation, and pulse excitation. It is obvious 
that sinusoidal sound sources radiate high power only if operated at resonance. 
It is also evident that only magnetostrictive and piezoelectric transducers are 
of interest in this connection. We will not consider the generation of the lower 
frequencies up to some kcps. High frequencies, or rather small wavelengths, 
are preferred since still another condition must be fulfilled for the generation 
of high intensities, i.e., the radiated sound has to be focused. This is achieved 
either by using large radiating areas or, even better, spherical or cylindrical 
radiating areas. 
If we use a quartz plate as a sound source and if we are able to prevent 
cavitation in the liquid, we can generate sound intensities of up to about 60 w/cm?, 
It has been reported that, under exceptionally favorable conditions, intensities 
of up to 300 w/cm? may be generated at 1.5 Mcps [1]. These figures show, by 
the way, that the maximum attainable sound intensities do not nearly reach the 
theoretical limit given by the tensile strength of the quartz itself. A practical 
limit is determined by the fact that it is impossible to completely prevent 
breakdown of the high electric tension at the boundaries of the quartz plate. 
With barium titanates as piezoelectric transducer material, the intensities 
which can be obtained are much smaller than can be obtained with quartz; 
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