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Measurement of low‐intensity highly focused ultrasound
Abstract   Open access

Measurement of low‐intensity highly focused ultrasound

George H. Myers, Peter A. Lewin and Mark E. Schafer
The Journal of the Acoustical Society of America, v 79(S1), pp S45-S45
May 1986
DOI: https://doi.org/10.1121/1.2023235
url
https://doi.org/10.1121/1.2023235View
Published, Version of Record (VoR)Maybe Open Access (Publisher Bronze),  Open

Abstract

The requirements for precise determination of acoustic output for different types of medical diagnostic equipment have made it important to develop methods of measuring ultrasonic field parameters at high megahertz range of frequencies. More specifically, of particular interest here is the measurement of pulsed beams of small focal diameters (of the order of a wavelength), generated by the low total power output devices. These low power levels are in general on the order of 50 pW, which is below the sensitivity of current acoustic power measurements methods including radiation force balances and calorimeters. While the miniature wideband polymer hydrophones have the requisite voltage sensitivity and bandwidth to correctly record the pressure waveforms, their finite dimensions, typically 0.5 to 1.0 mm in diameter, lead to spatial averaging effects. To overcome this problem, a technique has been developed, and is now being tested which permits hydrophones to be used in these applications. The measurement procedure is based on the fact that: (a) the entire beam is intercepted by the hydrophone and, (b) the beam profile can be accurately determined by pulse-echo techniques. The pressure waveform is recorded from a calibrated hydrophone of known effective area, located at the focus of the beam. The total force on the hydrophone is determined by numerically integrating the beam profile. The peak pressure, intensity, and total transmitted power can then be directly determined. Experimental results will be presented and both the advantages and limitations of the proposed measurement procedure will be discussed.

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