Optimal focusing through aberrating media: a comparison between time reversal mirror and time delay correction techniques
ABSTRACT The problem of focusing an ultrasonic beam through an
inhomogeneous medium was investigated experimentally for conventional
time delay focusing, adaptive time delay focusing, and time reversal
focusing. It is shown that neither time delay based technique gives a
properly focused beam for all aberrator locations. Only time reversal
focusing allows a robust focusing regardless of the aberrator location.
The matched filter theory of signal processing allows an interpretation
of this result: time reversal focusing provides the optimal input to the
linear system consisting of the acousto-electric and diffraction impulse
Article: Fluid mechanicsSERBIULA (sistema Librum 2.0).
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ABSTRACT: Methods for correction of phase aberrations induced by near-field variations in the index of refraction are explored. Using signals obtained from a sampled aperture (i.e. transducer array), phase aberrations can be accurately measured with a correlation approach similar to methods used in adaptive optics and radar. However, the method presented here has no need for a beacon or an ideal point reflector to act as a source for estimating phase errors. It uses signals from random collections of scatterers to determine phase aberrations accurately. Because there is no longer a need for a beacon signal, the method is directly applicable not only to medical ultrasound imaging but also to any coherent imaging system with a sampled aperture, such as radar and sonar.IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/1988; 35(6):758-67. · 1.82 Impact Factor
- Journal of The Acoustical Society of America - J ACOUST SOC AMER. 01/1991; 90(2):1119-1129.