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CONTROLLED WAVE PATTERN ULTRASONIC BURGLAR ALARM

  • US 3,781,859 A
  • Filed: 04/19/1972
  • Issued: 12/25/1973
  • Est. Priority Date: 04/19/1972
  • Status: Expired due to Term
First Claim
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1. A burglar alarm system for detecting intrusion into a protected enclosure comprising:

  • oscillator means to generate an ultrasonic signal of predetermined frequency;

    a directional, wide-beam transmitter means, connected to said oscillator means and located inside said protected enclosure with its transmitting axis directed toward the floor of said enclosure, to emit an ultrasonic sound at said predetermined frequency in a beam toward said floor;

    directional receiver means, located inside said protected enclosure, with its sensitive axis directed toward said floor of said enclosure to receive and convert said ultrasonic sound to an electrical signal, the communication path between said transmitter means and said receiver means being other than the line of sight, such that said sound emitted from said transmitter means must be reflected a plurality of times between said floor and the ceiling of said enclosure before it can be received by said receiver means;

    decoupler means, connected to said receiver means, to present an input impedance to said electrical signal;

    filter means, connected to said decoupler means, to filter extraneous electrical noise from said electrical signal;

    phase detector means, connected to said filter means and said oscillator means, to mix said electrical signal and said ultrasonic signal, and to generate a doppler signal from the phase difference between said electrical signal and said ultrasonic signal;

    intrusion detection means, connectEd to said phase detector means, to generate an alarm actuating signal upon reception of a doppler signal of predetermined frequency and amplitude indicative of human movement inside the protected enclosure;

    alarm means, connected to said intrusion detection means, to render an alarm upon receipt of said alarm actuating signal;

    fail safe means, connected to said oscillator means and said alarm means, to generate an alarm actuating signal upon failure of said oscillator means to generate said ultrasonic signal of predetermined frequency;

    turbulence circuit means connected to said phase detection means and said intrusion detection means to remove from said doppler signal electrical noise due to random noise and air turbulence in said protected enclosure;

    memory logic means to delay rendering of said alarm; and

    a walk test switch causing any alarm to be controllably rendered instantly, so that installation and adjustment of said system is facilitated.

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