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Apparatus for detecting an external magnetic field

  • US 4,008,432 A
  • Filed: 12/26/1973
  • Issued: 02/15/1977
  • Est. Priority Date: 03/02/1972
  • Status: Expired due to Term
First Claim
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1. An apparatus for detecting an external magnetic field, comprising:

  • a magnetic sensor comprising an elongated member of an electrically conductive material and a thin magnetic film disposed thereabout and formed of an uniaxial magnetic anisotropic material having a magnetic hard axis disposed essentially parallel to the axis of said elongated member and a magnetic easy axis disposed about the circumference of said elongated member, and a detection coil wound about said elongated member, said magnetic sensor producing parametric oscillations and having first and second oscillation states of respectively opposite phase and a non-oscillation state, in accordance with selective magnetization of said thin film in corresponding ones of first and second oscillation domains and a non-oscillation domain,first means for producing an alternating magnetic field along said easy axis of an intensity to establish magnetization of said thin film in an oscillation domain, said first means includes further means for producing a magnetic field along said hard axis for establishing magnetization of said thin film in a desired one of said first and second oscillation states,second means for producing an external magnetic field, andthird means for moving said second means relatively to said sensor to provide adjacent positions thereof wherein the external magnetic field of said second means is coupled in the direction of said hard axis of said sensor and produces magnetization of said thin film in a different one of said domains, and a displaced position wherein the external magnetic field of said second means is not coupled to said sensor and said thin film thereof is magnetized in said given domain, whereby said magnetic sensor changes its state from that corresponding to magnetization of said thin film in said given domain to a state corresponding to magnetization of said thin film in said different domain,said second means produces an external magnetic field of an intensity and polarity such that in said adjacent position thereof to said sensor, said external magnetic field switches the magnetization of said thin film to the other of said first and second oscillation domains, whereby said sensor changes from said one to said other of said first and second oscillation states of respectively opposite phases when said magnetization switches from said one to said other of said oscillation domains,said detecting coil producing an oscillating voltage output in accordance with said sensor being in either of said first and second oscillating states and producing a zero voltage output when the sensor switches from one to the other of said first and second oscillation states of respectively opposite phase, andmeans receiving the output of said detecting coil and responding to the zero voltage output of said detecting coil when the oscillation state of said sensor changes from one to the other of said first and second oscillation states of respectively opposite phase to provide an indication of the detection by said sensor of an external magnetic field.

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