The thermal pulse decay technique for measuring ultrasonic absorption coefficients

The classic method for measuring absorption coefficients ofmaterials requires adetermination 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 egions. A thermal pulse-decay technique is proposed and evaluated which allows for the separation, intime 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 osmaller beamwidths and higher frequencies and intensities than were previously possible.