초록 ▼

An EAS presence detection system includes a transmitter 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, the tag containing a transponder including a mater

An EAS presence detection system includes a transmitter 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, the tag containing a transponder including a material that, when in the presence of a magnetic bias field within a predetermined magnetic field intensity range, responds to detection of electromagnetic radiation of the said first predetermined frequency by transmitting electromagnetic radiation of a second predetermined frequency that is either a multiple harmonic or a frequency-divided quotient of the first predetermined frequency or at the first frequency; a detection system disposed for detecting radiation of the second predetermined frequency within the surveillance zone; and a magnetic field source for providing a magnetic bias field within the predetermined magnetic field intensity range within the surveillance zone. The magnetic field source includes a coil disposed in or adjacent the surveillance zone and an adjustable current source for causing a current to flow through the coil to provide a magnetic bias field within the surveillance zone. The coil is a large aperture solenoid coil wound on a core of metallic material of high permeability and high magnetic saturation. The core may be shielded from the electromagnetic radiation field of the first predetermined frequency by a non-ferrous electrically conductive tube disposed around the coil. The amplitude of the current is adjusted to provide a magnetic bias field within said predetermined magnetic field intensity range within the surveillance zone. The amplitude of the current is varied to sweep the intensity of the magnetic bias field through such a range of magnetic field intensities as to cause the magnetic bias field within each portion of the surveillance zone to be within said predetermined magnetic field intensity range during at least a portion of said sweep. A control system is coupled to the detection system and the adjusting means to determine whether detection by the detection means of electromagnetic radiation at the second predetermined frequency is due to the movement of a tag through the surveillance system or is due to the presence of a stationary tag in or near the surveillance zone.

대표청구항 ▼

A presence detection system, comprising means for transmitting an electromagnetic radiation signal of a first predetermined frequency into a surveillance zone; a tar for attachment to an article to be detected within the surveillance zone, the tag containing a transponder including a material that,

A presence detection system, comprising means for transmitting an electromagnetic radiation signal of a first predetermined frequency into a surveillance zone; a tar for attachment to an article to be detected within the surveillance zone, the tag containing a transponder including a material that, when in the presence of a magnetic bias field within a predetermined magnetic field intensity range, responds to detection of electromagnetic radiation of the said first predetermined frequency by transmitting electromagnetic radiation of a second predetermined frequency that is related to the first frequency; detection means disposed for detecting radiation of the second predetermined frequency within the surveillance zone; and means for providing said magnetic bias field within said predetermined magnetic field intensity range within the surveillance zone; wherein the means for providing said magnetic bias field include adjusting the intensity of said magnetic bias field within the surveillance zone to be within said predetermined magnetic field intensity range; and wherein the adjusting means are adapted for sweeping the intensity of said magnetic bias field through such a range of magnetic field intensities as to cause the magnetic bias field within each portion of the surveillance zone to be within said predetermined magnetic field intensity range during at least a portion of said sweep.