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MOTION DETECTION SYSTEM

  • US 3,634,884 A
  • Filed: 03/02/1970
  • Issued: 01/11/1972
  • Est. Priority Date: 03/02/1970
  • Status: Expired due to Term
First Claim
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1. A system for detecting motion of objects within an area protected by said system, comprising:

  • a transmitter for continuously generating an ultrahigh frequency signal of sinusoidal waveform;

    an antenna coupled to said transmitter for continuously generating electromagnetic waves in response to said ultrahigh frequency signals to saturate said predetermined area and for continuously receiving electromagnetic waves of like frequency reflected from objects within said predetermined area to produce a reflected ultrahigh frequency signal of sinusoidal waveform;

    circuit means for continuously algebraically combining said generated and reflected ultrahigh frequency signals to form a third ultrahigh frequency signal of varying amplitude;

    detector means for continuously demodulating said third ultrahigh frequency signal to produce a fluctuating direct current signal;

    means connected to said detector means for filtering low- and high-frequency components from said fluctuating direct current signal and producing a low-frequency alternating current signal;

    threshold means for generating an alarm condition indicating signal when the amplitude of said fluctuating direct current signal exceeds a predetermined value indicative of movement of an object in the protected area presenting at least a predetermined minimum signal-reflective area, said threshold means including means responsive to positive- and negativegoing half-cycles of said alternating current signal for generating said alarm condition indicating signals when the magnitude of said alternating current exceeds a predetermined value during either said positive- or negative-going halfcycles; and

    means for monitoring said alarm condition indicating signals for repetitions thereof within a predetermined time interval and for developing an alarm-actuating signal in response thereto.

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