Abstract
The acoustic nonlinearity parameter B/A is an important parameter for characterizing acoustic propagation in fluids. Recent developments in the fields of shock waves and biomedical ultrasonics have necessitated an accurate method for measuring this quantity. This paper presents a new technique based on an ultrasonic interferometer that allows accurate measurements of the change in sound speed within a liquid cavity. The system makes use of a novel continuous wave phase locking principle, which has the effect of nullifying many of the nonlinearities inherent in the acoustic interferometer. The phase lock circuitry automatically adjusts the frequency so as to keep an exact integer number of waves in the cavity regardless of changes in sound speed. Using this principle, B/A is determined by relating a small change in ambient pressure (less than 2 bar) to a change in frequency under isentropic conditions. B/A values are calculated using this experimental setup for several liquids including two slow sound-speed fluorocarbon liquids, FC-43 and FC-75. These liquids are unique in that they have the lowest range of sound speeds of any organic liquids and in that they have the highest values of B/A recorded thus far.
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