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Generation of ultrasound pulses in water using granular chains with a finite matching layer
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Harput, Sevan, Cowell, David M. J. , Freear, Steven, McLaughlan, James, Gelat, Pierre, Saffari, Nader, Yang, Jia, Akanji, Omololu, Thomas, P. J. (Peter J.) and Hutchins, David A. (2017) Generation of ultrasound pulses in water using granular chains with a finite matching layer. Physical Review Applied, 8 (5). 054032. doi:10.1103/PhysRevApplied.8.054032
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WRAP-generation-ultrasound-pulses-water-chains-finite-layer-Thomas-2018.pdf - Accepted Version - Requires a PDF viewer. Available under License Creative Commons Attribution 4.0. Download (976Kb) | Preview |
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WRAP-generation-ultrasound-pulses-water-chains-finite-matching-Hutchins-2017.pdf - Accepted Version - Requires a PDF viewer. Download (1056Kb) | Preview |
Official URL: https://doi.org/10.1103/PhysRevApplied.8.054032
Abstract
Wave propagation in granular chains is subject to dispersive effects as well as to nonlinear effects arising from the Hertzian contact law. This enables the formation of wideband pulses, which is a desirable feature in the context of diagnostic and therapeutic ultrasound applications. However, coupling of the ultrasonic energy from a chain of spheres into biological tissue is a big challenge. In order to improve the energy transfer efficiency into biological materials, a matching layer is required. A prototype device was designed to address this by using six aluminium spheres and a vitreous carbon matching layer. The matching layer and the pre-compression force are selected specifically to maximise the acoustic pressure in water and its bandwidth. The designed device generated a train of wideband ultrasonic pulses from a narrowband input with a centre frequency of 73 kHz. An analytical model was created to simulate the behaviour of a matching layer as a flexible thin plate clamped from the edges. This model was then verified using free field hydrophone measurements in water, which successfully predicted the increased bandwidth by generation of harmonics. The shapes of the measured and the predicted waveforms were compared by calculating the normalised cross-correlation, which showed 83\% similarity between both. Since the generation of harmonics are of interest for this study, the total harmonic distortion (THD) and the -6~dB bandwidth of the signals were used to analyse signal fidelity between the hydrophone measurements and the model predictions. The acoustic signals in water had a root mean squared THD of 73\% and the model predicted a root mean squared THD of 78\%. The -6~dB bandwidths of individual pulses measured by a hydrophone and predicted with the model were 280~kHz and 252~kHz, respectively. At these high ultrasonic frequencies, it is the first experimental demonstration of resonant chains operating in water with a matching layer.
| Item Type: | Journal Article | ||||||||
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| Subjects: | Q Science > QC Physics | ||||||||
| Divisions: | Faculty of Science > Engineering | ||||||||
| Library of Congress Subject Headings (LCSH): | Ultrasonic waves -- Industrial applications | ||||||||
| Journal or Publication Title: | Physical Review Applied | ||||||||
| Publisher: | American Physical Society | ||||||||
| ISSN: | 2331-7019 | ||||||||
| Official Date: | November 2017 | ||||||||
| Dates: |
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| Volume: | 8 | ||||||||
| Number: | 5 | ||||||||
| Article Number: | 054032 | ||||||||
| DOI: | 10.1103/PhysRevApplied.8.054032 | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Access rights to Published version: | Open Access | ||||||||
| Funder: | EPSRC (Engineering and Physical Sciences Research Council) | ||||||||
| Grant number: | EP/K029835/1 |
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