New approaches to the use of acoustic radiation forces in the calibration of high-frequency transducers.

Abstract

A drop (of radius a) of one liquid acoustically levitated in another ‘‘host’’ liquid can be displaced from its equilibrium position by the imposition of the acoustic field of a transducer. The displacement is related to the radiation force which, in turn, can allow one to compute the acoustic pressure and thus absolutely calibrate the transducer. This approach is a variation of the sphere radiometer technique. For high-frequency calibration, however, the form function of the acoustic radiation force varies rapidly with frequency for ka≳1, where k is the wave number in the host liquid; therefore, the properties of drop and host must be known very accurately if the inversion process is to yield good estimates. If, however, the drop material is nearly impedance matched with the host, although the densities and sound velocities individually differ, the ‘‘resonances’’ in the form function are pushed to a much higher ka, and unambiguous inversion of the data over a wider frequency range to give accurate pressures is possible. Theoretical and experimental results will be presented, as will other possible acoustic radiation force configurations that overcome some of the limitations of levitation and sphere radiometry techniques. [Work supported, in part, by a U.S. National Institutes of Health Grant No. 5-RO1-CA-39374.]