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Body movement detector

  • US 4,474,185 A
  • Filed: 05/12/1982
  • Issued: 10/02/1984
  • Est. Priority Date: 05/12/1982
  • Status: Expired due to Term
First Claim
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1. A device for monitoring an apnea episode or the like of a person wherein the dielectric constant of said person varies with breathing comprising:

  • a pad formed from an electrically conductive material having two sides, a first side thereof for positioning adjacent to a person to be monitored;

    a single ended voltage follower preamplifier having an input connected to said pad, said preamplifier having a circuit ground floating with respect to earth ground;

    a guard shield disposed on the second side of said pad and insulated therefrom, said guard shield connected to the output of said preamplifier;

    a carrier oscillator having a common circuit ground with said preamplifier and having a carrier output signal connected to said earth ground whereby said oscillator pumps said preamplifier at the frequency of oscillation whereby breathing movements of said person produce changes in dielectric constant between said grid and said earth ground thereby modulating said carrier signal;

    demodulator means connected to said preamplifier output for extracting a time varying signal from such modulated carrier signal proportional to such breathing movements;

    detection means connected to said demodulator means for determining the presence or absence of said time varying signal;

    a low frequency amplifier capacitively coupled to said demodulator means;

    first comparator means having an adjustable threshold for producing a HIGH output in the absence of a demodulated signal and a LOW output in the presence of a demodulated signal;

    integrator means connected to the output of said first comparator means for producing a voltage proportional to the time of absence of a demodulated signal;

    discharge means for rapidly discharging said integrator in the presence of a demodulated signal;

    indicating means connected to the output of said integrator for indicating the presence of a demodulated signal and for indicating the absence of a demodulated signal for a preselected period of time.

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