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On measurement of the acoustic nonlinearity parameter uisng the finite amplitude insertion substitution (FAIS) technique.

Zeqiri, B; Cook, A; Retat, L*; Civale, J*; ter Haar, G* (2015) On measurement of the acoustic nonlinearity parameter uisng the finite amplitude insertion substitution (FAIS) technique. Metrologia, 52 (2). pp. 406-422.

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The acoustic nonlinearity parameter or B/A, is an important parameter which defines the way a propagating finite amplitude acoustic wave undergoes progressive time-domain distortion when travelling through any medium. A measurement technique for determining its value is the so-called Finite Amplitude Insertion Substitution (FAIS) technique. The method is versatile and has been applied to and range of liquid, tissue and tissue-like media. Importantly, it is a relative technique. This paper presents a detailed study of the FAIS method, employing a number of novel features. The first of these is the implementation of a large area membrane hydrophone (30 mm detector aperture) which is used to record the plane-wave component of the acoustic field. This reduces the influence of diffraction on measurements, enabling studies to be carried out in the transducer near-field, with the interrogating transducer, test cell and detector positioned closely together, a feature which additionally assists in controlling potential errors arising from nonlinear distortion through the water path. A second novel feature is the development of a model which estimates the influence of finite-amplitude distortion as the acoustic wave travels from the rear surface of the test cell to the detector. It is demonstrated that this effect can lead to a significant systematic error in B/A measurement whose magnitude and direction depends on the contrast in acoustic properties between the test material and the water-filled equivalent cell. Good qualitative agreement between the model and experiment is reported. Studies of B/A undertaken at a temperature of 20 ± 0.5ºC are presented on two fluids commonly employed as reference materials within the technical literature: Corn Oil and Ethylene Glycol; as well as samples of an IEC standardised agar-based tissue-mimicking material. A systematic assessment measurement uncertainties is presented giving expanded uncertainties in the range ±7% to ±14%, expressed at a confidence level close to 95%, dependent on the test cell thickness and material properties.

Item Type: Article
Keywords: Ultrasound, nonlinearity parameter, tissue-mimicking materials, reference fluids
Subjects: Acoustics
Acoustics > Ultrasound
Identification number/DOI: 10.1088/0026-1394/52/2/406
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/6635

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