| 摘要 |
A frequency-dividing transponder for detecting electromagnetic radiation of a first predetermined frequency and responding to said detection by transmitting electromagnetic radiation of a second predetermined frequency that is a frequency-divided quotient of the first predetermined frequency, includes an active strip of amorphous magnetic material having a transverse uniaxial anisotropy defining a magnetomechanical resonant frequency in accordance with the dimensions of the strip at the second predetermined frequency when magnetically biased to be within a predetermined magnetic field intensity range so as to respond to excitation by electromagnetic radiation of the first predetermined frequency by transmitting electromagnetic radiation of the second predetermined frequency; and a tripole strip of magnetic material of such coercivity and so disposed in relation to the active strip of magnetic material as to create a magnetomechanical resonance in the active strip at the first predetermined frequency when the active strip is magnetically biased to be within the predetermined magnetic field intensity range. The transponder is used as a component of a tag that is attached to an article to be detected within a surveillance zone of a presence detection system, such as an electronic article surveillance (EAS) system utilized for theft deterrence. The presence detection system further includes a transmitter for transmitting electromagnetic radiation of a first predetermined frequency into a surveillance zone and a detection system for detecting electromagnetic radiation of the second predetermined frequency within the surveillance zone. The transponder may also include a bipolar bias strip of such coercivity and so disposed in relation to the active strip as to cause the active strip to be within the predetermined magnetic field intensity range at which the active strip has magnetomechanical resonance at the first and second predetermined frequencies. Alternatively, a magnetic field source, such as an electromagnetic bar magnet of high flux density core material that transmits electromagnetic radiation at a frequency in a range of from 1 to 100 Hertz, provides a magnetic field within the predetermined magnetic field intensity range within the surveillance zone so that when a tag including a transponder not having a bias strip is within the surveillance zone, the active strip of the transponder is within the predetermined magnetic field intensity range.
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