Development of a high intensity focused ultrasound (HIFU) hydrophone system.

Abstract

The growing use of high intensity focused Ultrasound (HIFU) has driven a need for reliable, reproducible measurements of HIFU acoustic fields. A reflective scatterer approach, incorporating several novel features for improved bandwidth, reliability, and reproducibility has been demonstrated [M. E. Schafer, J. Gessert, and W. Moore, Proc. IEEE Ultrasonics Symposium, 1739–1742 (2005)]. Several design improvements which have increase the signal‐to‐noise ratio of the system, and potentially reduced the cost of implementation, are now presented. For the scattering element, an artificial sapphire material is used to provide a more uniform radiating surface. The receiver is a segmented, truncated spherical structure with a 10 cm radius, made from 25 micron thick, biaxially stretched PVDF, with a Pt‐Au electrode on the front surface. A specialized backing material provides the stiffness required to maintain structural stability, while at the same time providing both electrical shielding and ultrasonic absorption. This new receiver design has improved the noise performance by 8–12 dB; the new scattering sphere has reduced the scattering loss by another 14 dB, producing an effective sensitivity of −298 dB re 1 microVolt/Pa. The design trade‐off still involves receiver sensitivity with effective spot size. However, the reduced cost and improved repeatability makes the overall design more robust for routine HIFU system measurements.