Combined radio and magnetic energy responsive surveillance marker and system
First Claim
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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Accused Products
Abstract
A surveillance marker has a semiconductor connected between arms of a dipole antenna, one arm being of non-ferrous conductive material and the other of high permeability low coercivity material such as permalloy. Higher coercivity magnetizable pieces are disposed adjacent the low coercivity arm, and all is sandwiched between paper or other insulating layers. The marker is detected by a combination of RF field and low frequency magnetic field generating and receiving units that energize a master alarm only when both units simultaneously detect the marker signals. Magnetizing the higher coercivity pieces suppresses a signal that would otherwise be reradiated by the marker from the high permeability arm thereby rendering the marker undetectable.
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Citations
15 Claims
- 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.
- 6. A marker comprising in combination a non-linear impedance element connected to at least one conductive antenna element, and a body of high permeability and low coercivity material dimensioned and configured to reradiate a separately detectable signal when immersed in a low frequency electromagnetic field, said body being electrically connected to said impedance element so as to constitute another conductive antenna element, said impedance element with its connected antenna elements 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, said elements and body being united in a single structure.
- 10. A marker comprising in combination of non-linear impedance element connected to a body of high permeability and low coercivity material, the latter being dimensioned and configured to reradiate a separately detectable signal when immersed in a low frequency electromagnetic field and simultaneously to constitute a conductive antenna element which is combination with said impedance element responds 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, said elements and body being united in a single structure.
Specification