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Unauthorized personnel detection system

  • US 4,684,933 A
  • Filed: 05/15/1986
  • Issued: 08/04/1987
  • Est. Priority Date: 05/15/1986
  • Status: Expired due to Fees
First Claim
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1. A detection system comprising:

  • a pair of metallic plates adapted to be mounted on the opposite sides of a passageway to form a capacitor whose reactance depends upon the effective dielectric constant of what is in the space between said plates;

    an oscillator which includes said capacitor, said oscillator having a frequency which varies with the reactance of said capacitor;

    and a discriminating circuit connected to the output of said oscillator and having means responsive to the oscillator frequency for discriminating between the presence of a person'"'"'s body without an electrically conductive article in said passageway between said plates and the presence of a person'"'"'s body with an electrically conductive article in said passageway between said plates.

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