Improved hydrophone calibration by combining acoustic holography with the radiation force balance measurements

Abstract

Ultrasound sources are frequently characterized by the radiation force (RF) balance method that is based on the relation between the total acoustic power and RF on absorbing or reflecting targets. This relation is usually taken from the plane-wave approximation or with a geometrical correction for focused sources. However, real sources emit inhomogeneous acoustic beams. Acoustic holography is a method of recording the true field by measuring both pressure magnitude and phase over a 2D surface (a hologram). The hologram makes it possible to accurately calculate the radiation stress tensor on the surface of the absorbing target. Such measurements allow the relation of hydrophone sensitivity with measured RF based on the known exact expression for RF as a function of the 2D pattern of acoustic pressure and particle velocity. This suggests an improved approach for single-frequency hydrophone calibration that benefits from the inherent accuracy of mass balances as well as the fact that pressure approximately scales with one half of the accuracy of the RF measurement. In the current study this approach was used to calibrate a hydrophone by characterizing a 1-MHz flat piezoceramic source in water using acoustic holography and a RF balance. [Work supported by RFBR and NIH EB007643.]