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Finger surface image enhancement having a liquid layer on the finger touching surface of the platen

  • US 5,051,576 A
  • Filed: 07/31/1990
  • Issued: 09/24/1991
  • Est. Priority Date: 07/31/1990
  • Status: Expired due to Fees
First Claim
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1. In an optical fingerprint imaging system having at least one interrogating light beam for illuminating a finger placed against a finger touching surface of a platen to provide a modulated light beam, the system having an imaging segment for imaging the modulated beam onto a photo-electric transducer, the improvement comprising:

  • a layer of liquid on the finger touching surface of the platen,said layer of liquid being thick enough so that a liquid-to-air interface is formed in the valley zones.the interrogating light beam having an axis at the finger touching surface such that the angle of said axis is greater than the critical angle,the axis of said imaging segment being positioned in a zone between said axis of said interrogating light beam and the mirror axis of said interrogating light beam,the photo-electric transducer receiving scattered light from the ridges of a finger placed against the liquid covered touching surface of the platen and receiving substantially none of the light reflected along said mirror axis.

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