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Dec 2011

Volume 130, Issue 6, pp. EL373-4184

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Localization of a small change in a multiple scattering environment without modeling of the actual medium

S. T. Rakotonarivo, S. C. Walker, W. A. Kuperman, and P. Roux

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3566-3573 (2011); (8 pages)

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A method to actively localize a small perturbation in a multiple scattering medium using a collection of remote acoustic sensors is presented. The approach requires only minimal modeling and no knowledge of the scatterer distribution and properties of the scattering medium and the perturbation. The medium is ensonified before and after a perturbation is introduced. The coherent difference between the measured signals then reveals all field components that have interacted with the perturbation. A simple single scatter filter (that ignores the presence of the medium scatterers) is matched to the earliest change of the coherent difference to localize the perturbation. Using a multi-source/receiver laboratory setup in air, the technique has been successfully tested with experimental data at frequencies varying from 30 to 60 kHz (wavelength ranging from 0.5 to 1 cm) for cm-scale scatterers in a scattering medium with a size two to five times bigger than its transport mean free path.
Show PACS
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Fn Scattering of acoustic waves

Impact of attenuation on guided mode wavenumber measurement in axial transmission on bone mimicking plates

Jean-Gabriel Minonzio, Josquin Foiret, Maryline Talmant, and Pascal Laugier

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3574-3582 (2011); (9 pages) | Cited 2 times

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Robust signal processing methods adapted to clinical measurements of guided modes are required to assess bone properties such as cortical thickness and porosity. Recently, an approach based on the singular value decomposition (SVD) of multidimensional signals recorded with an axial transmission array of emitters and receivers has been proposed for materials with negligible absorption, see Minonzio et al. [J. Acoust. Soc. Am. 127, 2913–2919 (2010)]. In presence of absorption, the ability to extract guided mode degrades. The objective of the present study is to extend the method to the case of absorbing media, considering attenuated plane waves (complex wavenumber). The guided mode wavenumber extraction is enhanced and the order of magnitude of the attenuation of the guided mode is estimated. Experiments have been carried out on 2 mm thick plates in the 0.2–2 MHz bandwidth. Two materials are inspected: polymethylacrylate (PMMA) (isotropic with absorption) and artificial composite bones (Sawbones, Pacific Research Laboratory Inc, Vashon, WA) which is a transverse isotropic absorbing medium. Bulk wave velocities and bulk attenuation have been evaluated from transmission measurements. These values were used to compute theoretical Lamb mode wavenumbers which are consistent with the experimental ones obtained with the SVD-based approach.
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43.20.Ye Measurement methods and instrumentation
43.80.Vj Acoustical medical instrumentation and measurement techniques
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.60.Fg Acoustic array systems and processing, beam-forming
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