The thermal pulse decay technique for measuring ultrasonic absorption coefficients

The classic method for measuring absorption coefficients of materials requires a determination of the temperature rise within a medium during ultrasonic irradiation. Serious errors may result from a viscous heating effect around the required thermocouple probe, and from heat lost by conduction to surrounding, cooler regions. A thermal pulse-decay technique is proposed and evaluated which allows for the separation, in time and space, of the viscous heating artifact and the true absorptive heating of a medium. In addition, the pulse-decay method explicitly accounts for heat conduction and the ultrasonic beam patterns used in experiments. The inherent advantages of the new technique allow for an extension of absorption measurements to smaller beamwidths and higher frequencies and intensities than were previously possible.