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Fingerprint sensing device for deriving an electric signal

  • US 4,428,670 A
  • Filed: 11/02/1981
  • Issued: 01/31/1984
  • Est. Priority Date: 08/11/1980
  • Status: Expired due to Fees
First Claim
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1. A fingerprint sensor for deriving an electric output signal according to the ridges and valleys of a finger under investigation, said sensor comprising, in combination:

  • (a) an elastic, pressure-sensitive contact surface formed by a transparent elastic material for receiving a contact pressure by said finger, thereby changing the structure of said surface in accordance with the fingerprint pattern of ridges and valleys of said finger, whereby the regions of the contact surface associated with the fingerprint valleys are not in contact with the finger and form small concave focusing mirrors, having their focal points along a focusing plane which is parallel to, and at the focal distance of said focusing mirrors away from, said contact surface;

    (b) a light source for passing substantially parallel light through said transparent elastic material to said contact surface, whereby in the presence of said finger said regions of the contact surface associated with the valleys which form said focusing mirrors reflect the light impinging on these regions and focus this light at said focusing plane, thus forming a focused light pattern at said plane in accordance with the fingerprint pattern of said finger;

    (c) photodetector means having a light sensitive area for measuring the distribution of light impinging on said area;

    (d) optical means focused on said plane for transmitting said focused light pattern to said light sensitive area of said photodetector means; and

    (e) output means associated with said photodetector means for deriving said electric output signal in response to the pattern of light falling on said light sensitive area.

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