Hydrophone Measurements for Biomedical Ultrasound Applications: A Review

Abstract

This article presents basic principles of hydrophone measurements, including mechanisms of action for various hydrophone designs, sensitivity and directivity calibration procedures, practical considerations for performing measurements, signal processing methods to correct for both frequency-dependent sensitivity and spatial averaging across the hydrophone sensitive element, uncertainty in hydrophone measurements, special considerations for high-intensity therapeutic ultrasound, and advice for choosing an appropriate hydrophone for a particular measurement task. Recommendations are made for information to be included in hydrophone measurement reporting.

Fig. 1.

Typical diagnostic ultrasound imaging pulse (normalized) showing peak compressional pressure (p_c) and peak rarefactional pressure (p_r).

Fig. 2.

Membrane hydrophones. a-c: coplanar designs with differential amplifiers, d: bilaminar design. A typical membrane hydrophone frame diameter is approximately 10 cm.

Fig. 3.

Capsule hydrophone. The length is approximately 6 cm.

Fig. 4.

Needle hydrophones.

Fig. 5.

Measurement of directional response of membrane hydrophone by rotating about two orthogonal axes.

Fig. 6.

Beamwidths (full width half maxima) at fundamental and harmonic frequencies for Sonic Concepts H101 Transducer (3.3 MHz, F/1) (black asterisks). Frequency-dependent effective sensitive element diameters deff (f) for five membrane hydrophones withgeometrical sensitive element diameters d_g of 200 through 1000 μm (dashed lines) are also shown. Reprinted from [118].

Fig. 7.

A pressure waveform measured using membrane (NT, S5, ST), needle (ON, DI), capsule (GL), and Fabry-Perot fiber optic (PA) hydrophones before and after sensitivity deconvolution. Some signals are shifted in time, but this does not affect measurements of peak compressional pressure or peak rarefactional pressure. Reprinted (after reformatting) from [98],

Fig. 8.

A pressure waveform measured using reflectance-type fiber optic (HFO) and needle (HNA) hydrophones before and after spatial averaging corrections. Reprinted from [117].

Fig. 9.

HIFU membrane hydrophone stainless steel front protection layer and a silicone oil backing (GAMPT mbH, SI04)

Fig. 10.

Magnitude and phase of frequency response for HIFU membrane hydrophone in Fig. 9. Expanded uncertainty of the calibration data for k = 2 (95% confidence). Reprinted from [135]. ©2019 IEEE.