Twisting waves increase the visibility of nonlinear behaviour

Richard, G. , Lay, H. S. , Giovannini, D., Cochran, S. , Spalding, G. and Lavery, M. P.J. (2020) Twisting waves increase the visibility of nonlinear behaviour. New Journal of Physics, 22(6), 063021. (doi: 10.1088/1367-2630/ab8aab)

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Nonlinear behaviour for acoustic systems is readily measured at high acoustic pressures in gasses or bulk materials. However, at low acoustic pressures non-linear effects are not commonly observed. We find that by phase structuring acoustics beams, one observes evidence of non-linear behaviour at an acoustic pressure of 66.78 dB lower than non-structured beams in room temperature air. A bespoke 28-element ultrasonic phased array antenna was developed to generate short pulses that carry orbital angular momentum and are propagated over a short air channel. When sampling small areas of the wavefront, we observed a distinctive change in the frequency components near phase singularities. At these phase singularities the local propagation path is screwed, resulting in the collection signals from pulses traveling along different paths across the aperture of a microphone. The usually negligible frequency chirping that arises from nonlinear behaviour in air interfere at these singularity points and produce a distinctive distortion of the acoustic pulse. Simple physical movement in the system or super-sonic wave speeds do not yield similar results. Such distortions in measured frequency response near phase singularities could lead to errors for SONAR or acoustic communication systems, where received signals are integrated over a finite-area detector. With further development this behaviour could potentially lead to accurate measurement techniques for determining a material's nonlinear properties at lower acoustic pressure.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Lavery, Professor Martin and Richard, Grace and Spalding, Professor Gabriel and Cochran, Professor Sandy and Giovannini, Dr Daniel and Lay, Dr Holly
Authors: Richard, G., Lay, H. S., Giovannini, D., Cochran, S., Spalding, G., and Lavery, M. P.J.
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:New Journal of Physics
Publisher:IOP Publishing
ISSN (Online):1367-2630
Published Online:17 April 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in New Journal of Physics 22(6): 063021
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
173088EPSRC Global Challenges Research Fund Institutional Sponsorship Award 2016 - University of GlasgowJonathan CooperEngineering and Physical Sciences Research Council (EPSRC)EP/P510968/1Research and Innovation Services
173260High Dimensional Free-space Building-to-Building Link for Last-Mile CommunicationsMartin LaveryEngineering and Physical Sciences Research Council (EPSRC)EP/N032853/1ENG - Electronics & Nanoscale Engineering