A multi-frequency resonant tag circuit for use with an electronic security system having improved noise discrimination

• US 3,967,161 A
• Filed: 07/19/1974
• Issued: 06/29/1976
• Est. Priority Date: 06/14/1972
• Status: Expired due to Term

• Current Assignee: George Jay Lichtblau
• Original Assignee: George Jay Lichtblau
• Inventors: Lichtblau, George Jay
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Wannisky, William M.
• Application Number:
  US05/490,011
• Time in Patent Office: 711 Days
• Field of Search: 340/280, 340/258 R, 340/258 C, 343/6.5 SS, 317/101 R, 317/101 B, 336/200, 336/232
• US Class Current: 361/765
• CPC Class Codes: G06K 19/067 Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
• CPC Class Codes: G06K 19/0672 with resonating marks
• CPC Class Codes: G08B 13/242 Tag deactivation
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
• CPC Class Codes: H01L 27/01 comprising only passive thin-film or thick-film elements formed on a common insulating substrate passive two-terminal components without a potential-jump or surface barrier for integrated circuits, details thereof and multistep manufacturing processes therefor H01L28/00

Abstract

An electronic security system adapted for use in a controlled area such as a retail store and employing a multi-frequency resonant tag circuit having distinct frequencies for detection and discrimination. An electromagnetic field is provided within the controlled area at a frequency which is swept through a range including the detection frequency of the resonant tag circuit. In the presence of a tag circuit within the controlled area, pulses are detected by a receiver which includes noise rejection circuitry for discriminating true signals from noise. The noise rejection circuitry is sensitive to expected signals and operative to discriminate true signals from noise on the basis of several different criteria, resulting in substantially reduced false alarm actuation.

Claims

1. For use in an electronic security system which includes means for providing an electromagnetic field of a frequency which is swept within a predetermined range, means for detecting a first frequency within said range, and means for providing an electromagnetic field at a second frequency outside of said range, a multi-frequency resonant tag circuit containing at least first and second tuned circuits respectively resonant at said first and second frequencies comprising:

a planar substrate of electrically insulative material;

a first conductive path formed on a surface of said substrate in a configuration to define a first inductor;

a second conductive path formed on said substrate in a configuration to define a second inductor;

first and second pairs of conductive areas formed on said substrate, each pair having conductive areas in alignment on respective opposite surfaces of said substrate to define a capacitor, the conductive areas on the substrate surface containing said first and second conductive paths being electrically connected to said paths at selected points to define said first and second tuned circuits;

a conductive path of predetermined size provided in circuit with said tag circuit on a surface of said substrate and operative to fuse upon application of electromagnetic energy at said second resonant frequency to thereby destroy the resonant properties of said tag circuit at said first frequency; and

a conductive path provided through said substrate and completing at least one of said tuned circuits by interconnection of said first or second conductive path and one of said conductive areas.

2. For use in an electronic security system which includes means for providing an electromagnetic field of a frequency which is swept within a predetermined range, means for detecting a first frequency within said range, and means for providing an electromagnetic field at a second frequency outside of said range, a multi-frequency resonant tag circuit containing at least first and second tuned circuits respectively resonant at said first and second frequencies comprising:

a planar insulative substrate having formed on one surface thereof

a first conductive area centrally formed on said substrate surface;

a second conductive area formed along one side of said substrate surface;

a first conductive path arranged on said substrate surface between and in electrical connection with said first and second conductive areas;

a second conductive path formed on said substrate surface between and in electrical connection with said second conductive area and a third conductive area formed on said substrate surface near a corner thereof; and

wherein the opposite surface of said substrate includes;

fourth, fifth and sixth conductive areas each in alignment and substantially coextensive with said respective first, second and third conductive areas formed on said one substrate surface;

a conductive path connecting said fourth and fifth conductive areas;

a conductive path through said substrate connecting said third and sixth conductive areas; and

a conductive path interconnecting said fifth and sixth conductive areas and dimensioned to fuse upon application of an electromagnetic field of predetermined power at said second frequency to thereby destroy the resonant properties of said tag circuit at said first frequency.

3. For use in an electronic security system which includes means for providing an electromagnetic field of a frequency which is swept within a predetermined range, means for detecting a first frequency within said range and means for providing an electromagnetic field at a second frequency, a multi-frequency resonant tag circuit containing at least first and second tune circuits respectively resonant at said first and second frequencies comprising:

a planar substrate of electrically insulative material;

a first conductive path formed on a surface of said substrate in a configuration to define a first inductor;

a second conductive path formed on said substrate in a configuration to define a second inductor;

first and second pairs of conductive areas formed on said substrate, each pair having conductive areas in alignment on respective opposite surfaces of said substrate to define a capacitor, the conductive areas on the substrate surface containing said first and second conductive paths being electrically connected to said paths at selected points to define said first and second tuned circuits; and

a conductive path provided through said substrate and completing at least one of said tuned circuits by interconnection of said first or second conductive path and one of said conductive areas.

4. For use in an electronic security system which includes means for providing an electromagnetic field of a frequency which is swept within a predetermined range, means for detecting a first frequency with said range and means for providing an electromagnetic field at a second frequency, a multi-frequency resonant tag circuit containing at least first and second tuned circuits respectively resonant at said first and second frequencies comprising:

a planar insulative substrate having formed on one surface thereof;

a first conductive area;

a second conductive area;

a first conductive path in electrical connection with said first and second conductive areas arranged in a configuration to define a first inductor;

a third conductive area;

a second conductive path in electrical connection with said second conductive area and said third conductive area and formed in a configuration to define a second inductor;

said planar insulative substrate having formed on a second surface thereof;

fourth, fifth and sixth conductive areas each in alignment and substantially co-extensive with said respective first, second and third conductive areas formed on said one substrate surface, said first and fourth conductive areas and said second and fifth conductive areas comprising respective first and second capacitors;

a conductive path connecting said fourth and fifth conductive areas;

a conductive path through said substrate connecting said third and sixth conductive areas; and

a conductive path interconnecting said fifth and sixth conductive areas;

said first inductor, second inductor and second capacitor being electrically connected to form said first tuned circuit; and

said first capacitor, second inductor and second capacitor being electrically connected to form said second tuned circuit.

5. A multi-frequency resonant tag according to claim 4 wherein said conductive path interconnecting said fifth and sixth conductive areas is dimensioned to fuse upon application of an electromagnetic field of predetermined power at said second frequency.

6. A multi-frequency resonant tag according to claim 4 wherein in said second frequency is an ISM frequency.