Deactivatable fequency-dividing-transponder tag

• US 4,882,569 A
• Filed: 07/26/1988
• Issued: 11/21/1989
• Est. Priority Date: 07/26/1988
• Status: Expired due to Term

• Current Assignee: Sensormatic Electronics Corporation (Johnson Controls International plc)
• Original Assignee: Security Tag Systems, Inc. (Johnson Controls International plc)
• Inventors: Dey, Subrata
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Chen, Hollis
• Application Number:
  US07/224,326
• Time in Patent Office: 483 Days
• Field of Search: 340/551, 340/572
• US Class Current: 340/572.2
• CPC Class Codes: G08B 13/2411 Tag deactivation
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/2448 Tag with at least dual detection means, e.g. combined inductive and ferromagnetic tags, dual frequencies within a single technology, tampering detection or signalling means on the tag

Abstract

A presence-detection-system tag in which a frequency-dividing transponder may be decisively deactivated notwithstanding the intensity of the ambient magnetic field. The tag includes a frequency-dividing transponder including an active strip of magnetic material that, when magnetically biased to be within a predetermined magnetic field intensity range, responds to excitation by electromagnetic radiation of a first predetermined frequency by radiating electromagnetic radiation of a second predetermined frequency that is a frequency-divided quotient of the first predetermined frequency; a first bias strip of magnetic material disposed in relation to the active strip of magnetic material for biasing the active strip of magnetic material to be within the predetermined magnetic field intensity range only when the first bias strip of magnetic material is magnetized; and a second bias strip of magnetic material disposed in relation to the active strip of magnetic material for further biasing the active strip to be outside of the predetermined magnetic field intensity range to thereby prevent the active strip of magnetic material from radiating electromagnetic radiation of the second predetermined frequency in response to excitation by electromagnetic radiation of the first predetermined frequency when the first and second bias strips of magnetic material are both magnetized. A coded tag includes two such active strips having different magnetomechanical resonant frequencies. Either tag may be detected in a presence detection system that includes means for transmitting an electromagnetic radiation signal of a first predetermined frequency into a surveillance zone; and means for detecting electromagnetic radiation of the second predetermined frequency within the surveillance zone. The system further includes a magnetizer for magnetizing the second bias strip to thereby deactivate the frequency-dividing transponder of the tag.

Claims

1. A tag for attachment to an article to be detected within a surveillance zone, comprising

a frequency-dividing transponder including an active strip of magnetic material that, when magnetically biased to be within a predetermined magnetic field intensity range, responds to excitation by electromagnetic radiation of a first predetermined frequency by radiating electromagnetic radiation of a second predetermined frequency that is a frequency-divided quotient of the first predetermined frequency,

a first bias strip for magnetic material disposed in relation to the active strip of magnetic material for biasing the active strip of magnetic material to be within the predetermined magnetic field intensity range only when the first bias strip of magnetic material is magnetized;

and

a second bias strip of magnetic material disposed in relation to the active strip of magnetic material for further biasing the active strip to be outside of the predetermined magnetic field intensity range to thereby prevent the active strip of magnetic material from radiating electromagnetic radiation of the second predetermined frequency in response to excitation by electromagnetic radiation of the first predetermined frequency when the first and second bias strip of magnetic material are both magnetized.

2. A tag according to claim 1, wherein the first and second bias strip of magnetic material have different magnetic properties.

3. A tag according to claim 2, wherein the first and second bias strips of magnetic material have different dimensions.

4. A tag according to claim 1, wherein the first and second bias strips of magnetic material have different dimensions.

5. A tag according to claim 1, wherein the active strip of magnetic material is a thin, flat ribbon of low coercivity magnetostrictive amorphous magnetic material having a transverse uniaxial magnetic anisotropy defining a magnetomechanical resonant frequency "f₁ " equal to one-half the first predetermined frequency in accordance with the dimensions of the ribbon, wherein when the ribbon is in the presence of a magnetic bias field within the predetermined magnetic field intensity range, the ribbon responds to the detection of electromagnetic radiation of a frequency "2f₁ " by transmitting electromagnetic radiation of the second predetermined frequency, which is a frequency divided quotient of the frequency "2f₁.

6. A coded tag for attachment to an article to be detected within a surveillance zone, comprising

a first frequency-dividing transponder including a first active strip of magnetic material that, when magnetically biased to be within a predetermined magnetic field intensity range, responds to excitation by electromagnetic radiation of a first predetermined frequency by radiating electromagnetic radiation of a second predetermined frequency that is a frequency-divided quotient of the first predetermined frequency;

a second frequency-dividing transponder including a second active strip of magnetic material that, when magnetically biased to be within the predetermined magnetic field intensity range, responds to excitation by electromagnetic radiation of a third predetermined frequency by radiating electromagnetic radiation of a fourth predetermined frequency that is a frequencydivided quotient of the third predetermined frequency;

a first bias strip of magnetic material disposed in relation to the first and second active strips of magnetic material for biasing the first and second active strips of magnetic material to be within the predetermined magnetic field intensity range when the first bias strip of magnetic material is magnetized; and

a second bias strip of magnetic material disposed in relation to the first and second active strips of magnetic material for further biasing the first and second active strips to be outside of the predetermined magnetic field intensity range to thereby prevent the first and second active strips of magnetic material from respectively radiating electromagnetic radiation of the second and fourth predetermined frequencies in response to excitation by electromagnetic radiation of the first and second predetermined frequencies when the first and second bias strips of magnetic material are both magnetized.

7. A tag according to claim 6, wherein the first and second bias strips of magnetic material have different magnetic properties.

8. A tag according to claim 7, wherein the first and second bias strips of magnetic material have different dimensions.

9. A tag according to claim 6, wherein the first and second bias strips of magnetic material have different dimensions.

10. A coded tag according to claim 6,

wherein the first active strip of magnetic material is a thin, flat ribbon of low coercivity magnetostrictive amorphous magnetic material having a transverse uniaxial magnetic anisotropy defining a magnetomechanical resonant frequency "f₁ " equal to one-half the first predetermined frequency in accordance with the dimensions of the ribbon, wherein when the ribbon is in the presence of a magnetic bias field within the predetermined magnetic field intensity range, the ribbon responds to the detection of electromagnetic radiation of a frequency "2f₁ :

by transmitting electromagnetic radiation of the second predetermined frequency, which is a frequency divided quotient of the frequency "2f₁ ; and

wherein the second active strip of magnetic material is a thin, flat ribbon of low coercivity magnetostrictive amorphous magnetic material having a transverse uniaxial magnetic anisotropy defining a magnetomechanical resonant frequency "f₂ " equal to one-half the third predetermined frequency in accordance with the dimensions of the ribbon, wherein when the ribbon is in the presence of a magnetic bias field within the predetermined magnetic field intensity range, the ribbon responds to the detection of electromagnetic radiation of a frequency "2f₂ " by transmitting electromagnetic radiation of the fourth predetermined frequency, which is a frequency divided quotient of the frequency "2f₂.

11. A presence detection system, comprising

means for transmitting an electromagnetic radiation signal of a first predetermined frequency into a surveillance zone;

a tag for attachment to an article to be detected within the surveillance zone, comprising a frequency-dividing transponder including an active strip of magnetic material that, when magnetically biased to be within a predetermined magnetic field intensity range, responds to excitation by electromagnetic radiation of a first predetermined frequency by radiating electromagnetic radiation of a second predetermined frequency that is a frequency-divided quotient of the first predetermined frequency;

a first bias strip of magnetic material disposed in relation to the active strip of magnetic material for biasing the active strip of magnetic material to be within the predetermined magnetic field intensity range only when the first bias strip of magnetic material is magnetized; and

a second bias strip of magnetic material disposed in relation to the active strip of magnetic material for further biasing the active strip to be outside the predetermined magnetic field intensity range to thereby prevent the active strip of magnetic material from radiating electromagnetic radiation of the second predetermined frequency in response to excitation by electromagnetic radiation of the first predetermined frequency when the first and second bias strips of magnetic material are both magnetized.

means for detecting electromagnetic radiation of the second predetermined frequency within the surveillance zone; and

means for magnetizing the second bias strip.