Abstract
The decomposition of the time reversal operator (DORT) method applies to active detection and focusing of acoustic waves using arrays of transmitters and receivers. This method allows detection and selective focusing on scatterers through complex media. It consists in the construction of the invariants of the time reversal process, that are also the singular vectors of the array response matrix. The DORT method is particularly interesting for detection in inhomogeneous media when the acoustic properties are poorly known. However, if an estimate of the medium’s Green function is available, images of the medium can be formed by backpropagation of the dominant eigenvectors. For the detection of defect in scattering media like titanium, the method is useful to separate the echo of a defect from the microstructure contribution and thus to reduce speckle noise. We will also see that the time reversal operator can be interpreted as a pseudocovariance matrix like those encountered in classical array signal processing. And as shown by Anthony J. Devaney [J. Acoust. Soc. Am. 110, 2617 (2001)], nonlinear estimators like MUSIC can be applied to achieve high resolution. These different points will be illustrated through several experimental results.
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