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Apparatus and method for detecting a magnetic marker

  • US 4,710,752 A
  • Filed: 08/08/1986
  • Issued: 12/01/1987
  • Est. Priority Date: 08/08/1986
  • Status: Expired due to Term
First Claim
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1. A system for detecting the presence of a ferromagnetic marker in an interrogation zone, comprising:

  • first generating means for generating a first magnetic field in the interrogation zone at a first frequency,second generating means for generating a second magnetic field in the interrogation zone at a second frequency,said second frequency having a value less than approximately one-fifth of said first frequency andmeans for detecting amplitude modulated signals produced by a magnetic marker present in the interrogation zone when said first and second magnetic field generating means are enabled.

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