Optimisation using measured Green's function for improving spatial coherence in acoustic measurements

Matthew Clark, Steve D. Sharples, Michael Geoffrey Somekh

Research output: Journal article publicationConference articleAcademic researchpeer-review

3 Citations (Scopus)

Abstract

Aberrating materials can degrade acoustic measurements by distorting the acoustic wavefront and causing acoustic speckle (as opposed to speckle noise which is a manifestation of coherent backscatter). The amplitude and phase fluctuations associated with acoustic speckle can introduce considerable measurement uncertainty which is difficult to deal with. This paper demonstrates a new technique which optimises the spatial distribution of the generation of the ultrasound to compensate for the aberration. This technique uses experimentally measured Green's functions to allow the calculation of the field resulting from the generation wavefront during optimisation. The technique is used to improve the accuracy of velocity measurements in a steel sample using 82 MHz SAW waves. This is achieved by optimising for improved spatial coherence in the measurement region which suppresses the speckle noise. Experimental evidence of acoustic aberration arising from grain structure is shown for steel and aluminium and the measured Green's function optimisation technique is shown to overcome the resulting acoustic speckle. The technique was performed using the Adaptive Optical Scanning Acoustic Microscope (AOSAM) at Nottingham University, UK.
Original languageEnglish
Pages (from-to)205-212
Number of pages8
JournalUltrasonics
Volume42
Issue number1-9
DOIs
Publication statusPublished - 1 Apr 2004
Externally publishedYes
EventProceedings of Ultrasonics International 2003 - Granada, Spain
Duration: 30 Jun 20033 Jul 2003

Keywords

  • Acoustic aberrations
  • Optimisation
  • Scattering
  • Stochastic media
  • Velocity measurement

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Acoustics and Ultrasonics

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