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Holographic resolution of complex sound fields

  • US 4,248,093 A
  • Filed: 04/13/1979
  • Issued: 02/03/1981
  • Est. Priority Date: 04/13/1979
  • Status: Expired due to Term
First Claim
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1. Apparatus for determining the spatial distribution of an acoustic field along a boundary wall of an acoustically excited structure, said apparatus comprising:

  • a sensor array mounted to at least a portion of said boundary wall of said acoustically excited structure, said sensor array including a plurality of individual spaced apart sensors of predetermined geometry, each of said individual sensors being elastically deformable by incident acoustic energy, each of said sensors including a surface layer that is diffusely reflective to impingent light energy;

    holographic recording means for supplying at least two holographic records of light energy reflected from said sensor array, said holographic recording means including a source of monochromatic light energy for selectively generating pulses of monochromatic light in response to an applied trigger signal, first optical means for directing a portion of each pulse of said monochromatic light to said sensor array and for forming a reference beam, second optical means for receiving and combining said reference beam and at least a portion of the monochromatic light reflected from said sensor array, and photosensitive recording means for recording an image representative of said combined light supplied by said second optical means;

    detector means positioned for response to said acoustic field within said acoustically excited structure, said detector means including for supplying a signal having a frequency substantially equal to that of the dominant acoustic signal within said acoustically excited structure; and

    trigger means responsive to said signal supplied by said detector means for supplying said trigger signal to said source of monochromatic light at a frequency substantially equal to said dominant acoustic signal within said acoustically excited structure, said trigger means including means for supplying a first pair of trigger signals to said source of monochromatic light that are spaced apart in time by nT/2, where n is an odd integer and T is the period of said dominant acoustic signal, said first pair of trigger signals causing said source of monochromatic light to doubly expose said photosensitive means and form a first holographic interferogram, said trigger means further including means for supplying a second pair of trigger signals that are spaced apart in time by nT/2 with the first trigger signal of said second pair of trigger signals being spaced apart in time from the final trigger signal of said first pair of trigger signals by mT/4, where m is an odd integer, said second pair of trigger signals causing said source of monochromatic light to doubly expose said photosensitive means and form a second halographic interferogram.

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