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Combined radio and magnetic energy responsive surveillance marker and system

  • US 4,413,254 A
  • Filed: 09/04/1981
  • Issued: 11/01/1983
  • Est. Priority Date: 09/04/1981
  • Status: Expired due to Fees
First Claim
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1. A marker comprising in combination first passive means including at least one conductive antenna element and being responsive to the energy in a field of radio waves when immersed therein for reradiating a portion of said energy as a detectable and distinguishable radio signal, and second passive means including at least one body of high permeability and low coercivity material and being responsive to the energy in a field of low frequency electromagnetic waves when immersed therein for reradiating a separately detectable signal, both said passive means being united in a common tag structure with said antenna element and said body of high permeability material interrelated for independent electrical operation in spite of electromagnetic coupling therebetween.

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