Wear, K A; Shah, A (2023) Nominal Versus Actual Spatial Resolution: Comparison of Directivity and Frequency-Dependent Effective Sensitive Element Size for Membrane, Needle, Capsule, and Fiber-Optic Hydrophones. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 70 (2). pp. 112-119.

Full text not available from this repository.

Abstract

Frequency-dependent effective sensitive element radius aeff(f) is a key parameter for elucidating physical mechanisms of hydrophone operation. In addition, it is essential to know aeff(f) to correct for hydrophone output voltage reduction due to spatial averaging across the hydrophone sensitive element surface. At low frequencies, aeff(f) is greater than geometrical sensitive element radius ag. Consequently, at low frequencies, investigators can overrate their hydrophone spatial resolution. Empirical models for aeff(f) for membrane, needle, and fiber-optic hydrophones have been obtained previously. In this article, an empirical model for aeff(f) for capsule hydrophones is presented, so that models are now available for the four most common hydrophone types used in biomedical ultrasound. The aeff(f) value was estimated from directivity measurements (over the range from 1 to 20 MHz) for five capsule hydrophones (three with dg = 2ag = 85 μm and two with dg = 2ag = 200 μm). The results suggest that capsule hydrophones behave according to a “rigid piston” model for k ag ≥ 0.7 (k = 2π/wavelength). Comparing the four hydrophone types, the low-frequency discrepancy between aeff(f) and ag was found to be greatest for membrane hydrophones, followed by capsule hydrophones, and smallest for needle and fiber-optic hydrophones. Empirical models for aeff(f) are helpful for choosing an appropriate hydrophone for an experiment and for correcting for spatial averaging (over the sensitive element surface) in pressure and beamwidth measurements. When reporting hydrophone-based pressure measurements, investigators should specify aeff at the center frequency (which may be estimated from the models presented here) in addition to ag.

Item Type:	Article
Keywords:	Acoustic output measurement, directivity, hydrophone, spatial averaging
Subjects:	Acoustics > Ultrasound
Divisions:	Medical, Marine & Nuclear
Identification number/DOI:	10.1109/TUFFC.2022.3211183
Last Modified:	25 Feb 2025 09:22
URI:	https://eprintspublications.npl.co.uk/id/eprint/10116