Detection and Imaging in Complex Media with the D.O.R.T. Method
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Acoustic waves are used for detection, localization and sometimes destruction of passive targets. In most fields of acoustics, arrays of transmitters and arrays of receivers are available, and if not synthetic aperture techniques can be used. With such arrays, a great amount of data can be collected, and the general problem is to extract the relevant information from these data to detect (or to form an image of) a scattering object. This problem appears in applications ranging from medical imaging to underwater acoustics and even in seismology. The D.O.R.T. method is a new approach to active detection and focusing of acoustic waves using arrays of transmitters and receivers. This method was derived from the theoretical study of iterative time-reversal mirrors. It consists essentially of the construction of the invariants in the time-reversal process. After explaining the basic theory of the D.O.R.T. method, several experimental results are shown: (a) detection and selective focusing through an inhomogeneous medium; (b) detection and focusing in a water waveguide, where high resolution is achieved by taking advantage of the multiple paths in the guide; (c) an analysis of scattering by a thin hollow cylinder, where the various components of the elastic waves circumnavigating in the shell are separated; and (d) in some cases the eigenvectors obtained at different frequencies can be combined to obtain the time-domain Green’s function of each scatterer.
KeywordsSingular Value Decomposition Transfer Matrix Complex Medium Lamb Wave Impulse Response Function
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