Deactivatable resonant marker for use in RF electronic article surveillance system

• US 4,689,636 A
• Filed: 03/15/1985
• Issued: 08/25/1987
• Est. Priority Date: 03/15/1985
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Lemberger, Richard R., Tait, William C.
• Primary Examiner(s): Wise, Robert E.
• Application Number:
  US06/712,415
• Time in Patent Office: 893 Days
• Field of Search: 343/895, 340/572
• US Class Current: 343/895
• CPC Class Codes: H01Q 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence

Abstract

A deactivatable marker for use in an RF electronic article surveillance system is disclosed, which marker includes a resonant circuit having at least one inductive component and one capacitive component. The circuit further comprises a component having two conductive layers separated only by an insulative thin-film which breaks down when at least a predetermined potential is applied across it to form a conductive path which changes the resonant frequency of the circuit. The two conductive layers are preferably configured to form a spiral multi-turn inductor and capacitor pads on opposing surfaces of a dielectric sheet, and to be embossed at a localized area, thereby contacting the layers except for the presence of the insulating thin-film.

Claims

1. A deactivatable marker for use in an electronic article surveillance system having a transmitter for producing an electromagnetic field within an interrogation zone and a receiver for detecting the marker when excited by the field, said marker including at least one inductive component, one capacitive element and a third component comprising a pair of conductive layers, at least one of which is metallic, said layers being separated at at least one location by only an insulative thin-film formed on the surface of the metallic layer, said components being coupled together to form a circuit resonant at at least one frequency, whereby deactivation of the marker may be effected by developing across the thin-film at least a predetermined potential to thereby breakdown the thin-film and to form a conductive path between the conductive layers which alters the resonant frequency of the circuit to prevent detection thereof by said receiver.

2. A marker according to claim 1, wherein said thin-film comprises an oxide layer formed on the surface of the metal layer.

3. A marker according to claim 2, wherein said oxide layer is less than one micrometer thick.

4. A marker according to claim 1, wherein each of said conductive layers extends over an area and is juxtaposed from an area of the opposite layer, separated therefrom by a substantially uniformly thick dielectric layer to form one capacitive component.

5. A marker according to claim 4, wherein said thin-film extends over an area over which said conductive layers are nominally separated by said dielectric layer, but wherein said sheet is deformed to cause the conductive layers to be separated only by the insulating thin-film.

6. A marker according to claim 4, wherein said thin-film separates opposing areas of the conductive layers forming the capacitive component such that resonant oscillations built up in the circuit may cause a potential to be induced across the capacitive component which exceeds said predetermined potential.

7. A marker according to claim 6, wherein both of said conductive layers are separated by a substantially uniformly thick dielectric layer and are configured to provide substantially inductive multi-turn spiral paths, each turn of the spiral paths being juxtaposed from a like turn of the path in the other conductive layer, such that the opposing portions and dielectric layer sandwiched therebetween forms a distributed capacitive element.

8. A marker according to claim 1, wherein at least one of said conductive layers of said third component is configured to provide one inductive component.

9. An electronic article surveillance system comprising

a transmitter for producing an electromagnetic field within an interrogation zone,

a marker including at least one inductive component, one capacitive component and a third component comprising a pair of conductive layers, at least one of which is metallic, which layers are separated at at least one location by only an insulative thin-film formed on the surface of the metallic layer, said components being coupled together to form a circuit having at least one resonant frequency,

a receiver for detecting oscillations at at least said one resonant frequency produced by the marker when excited by the field, and for producing an alarm signal in response thereto, and

means for deactivating the marker to inhibit the detection thereof by the receiver, said means comprising means for applying at least a predetermined electrical potential across said thin-film to thereby breakdown the thin-film and create a conductive path between the conductive layers, which path alters the resonant frequency of the circuit and inhibts the detection by said receiver.

10. A system according to claim 9, wherein said means for applying said predetermined potential includes means for inducing oscillations in said marker circuit of sufficient intensity to develop across said thin-film at least said predetermined potential.

11. A system according to claim 10, wherein said marker includes said capacitive component and said third component in parallel such that resonant oscillations induced in the circuit by said applying means causes a potential across the capacitive and third components which exceeds the predetermined potential.