The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 21, 1989
Filed:
Jul. 26, 1988
Subrata Dey, St. Petersburg, FL (US);
Security Tag Systems, Inc., St. Petersburg, FL (US);
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.