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ENCAPSULATED ELECTRICALLY RESONANT CIRCUIT AND INTERROGATING APPARATUS AND METHOD FOR FINDING SAME IN VARIOUS LOCATIONS

  • US 3,836,842 A
  • Filed: 01/22/1973
  • Issued: 09/17/1974
  • Est. Priority Date: 01/22/1973
  • Status: Expired due to Term
First Claim
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1. A passive marking device for placement in a location so that the location is thereafter identifiable with the use of an appropriate interrogating instrument, the marking device comprising:

  • an elongated core in the form of a sintered body of ferrite magnetically soft material;

    a coil of conductive material encircling a portion of the core;

    a capacitor connected across the coil, the assembly of the core, the coil and the capacitor providing a resonant circuit;

    an encapsulation, encapsulating the resonant circuit, the encapsulation bonded to the surface of the core and being of a magnetically transparent material at least as brittle as the sintered ferrite material, the core, mechanically reinforced by the encapsulation and co-acts therewith to fracture as would a unitary body in the event of mechanical damage, evidence of sUch fracture being detectable by visual inspection of the marking device.

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