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Digital time-delay acoustic imaging

  • US 5,793,703 A
  • Filed: 11/12/1996
  • Issued: 08/11/1998
  • Est. Priority Date: 03/07/1994
  • Status: Expired due to Term
First Claim
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1. An acoustic imaging method comprising the steps of periodically transmitting wideband acoustic pulses to insonify a target area, detecting reflections of said pulses at a first set of at least two receiving positions using at least one receiver transducer to generate transducer output signals, and processing the transducer output signals corresponding to the set of receiving positions so as to produce an image of the target area, said processing step comprising:

  • (a) sampling said transducer output signals at a predetermined rate during an interval between the transmitted pulses;

    (b) digitizing the sampled signals by an analog-to-digital conversion;

    (c) quadrature match filtering the digitized sampled signal for each receiving position using a complex kernel derived from an estimated signature of each of the transmitted pulses, sampled at a same rate as the transducer output signals, so as to generate a set of complex filtered samples for each receiving position;

    (d) taking, for each pixel in a required image, a weighted sum of selected phase-shifted complex filtered samples for the first set of receiving positions to form a complex composite signal by;

    (i) selecting from said sets of complex filtered samples, samples whose echo times are closest to an estimated time of flight of the transmitted pulse to the point in the target area corresponding to the pixel and back to the transducer, and(ii) interpolating the selected complex samples by phase-shifting to compensate for a difference between required and selected time delays, wherein all phase-shifts are determined from the time differences using a single frequency.

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