Keyless entry system having remote marker for motor vehicles

  • US 4,868,915 A
  • Filed: 07/20/1988
  • Issued: 09/19/1989
  • Est. Priority Date: 02/23/1984
  • Status: Expired due to Fees
First Claim
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1. A keyless entry system, comprising:

  • (a) a means for defining an interrogation zone;

    (b) generating means for generating a magnetic field having a frequency band within said interrogation zone, said generating means including an interrogating coil;

    (c) activating means for detecting the presence of an object within said interrogation zone and activating said generating means in response to the presence of said object;

    (d) a marker responsive within said interrogation zone to undergo a substantial change in its effective magnetic permeability at preselected frequencies within said frequency band that provides the marker with signal identity, said marker comprising a plurality of strips of magnetostrictive, ferromagnetic material, each of said strips being adapted to be magnetically biased and thereby armed to resonate mechanically at a different frequency within the frequency band of said magnetic field;

    (e) detecting means for detecting resonances of said marker within said interrogation zone, said detecting means comprising an antenna coil and said interrogating coil and said antenna coil being coplanar;

    (f) decoding means for comparing said detected marker resonances against a predefined code to verify parity therebetween; and

    (g) actuating means for enabling said entry system in response to an indication of parity from said entry system in response to an indication of parity from said decoding means.

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