Unauthorized personnel detection system
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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Abstract
A detection system for a doorway discriminates between persons who are authorized to go through the doorway and those who are not. An oscillator with a resonant L-C circuit includes metallic capacitor plates on opposite sides of the doorway to reduce the oscillator frequency when a person walks through and to provide a transient frequency increase if the person wears or carries a small metal object. A discriminating circuit is connected to the oscillator output to discriminate between persons in the doorway with and without such a metal object.
37 Citations
8 Claims
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1. A detection system comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification