Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-01-13
2001-01-23
Wu, Daniel J. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572100, C340S572700
Reexamination Certificate
active
06177870
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electronic article surveillance (EAS) systems.
BACKGROUND OF THE INVENTION
It is well known to provide electronic article surveillance systems to prevent or deter theft of merchandise from retail establishments. In a typical system, markers designed to interact with an electromagnetic field placed at the store exit are secured to articles of merchandise. If a marker is brought into the field or “interrogation zone”, the presence of the marker is detected and an alarm is generated. Some markers are intended to be removed at the checkout counter upon payment for the merchandise. Other types of markers remain attached to the merchandise but are deactivated upon checkout by a deactivation device which changes a characteristic of the marker so that the marker will no longer be detectable at the interrogation zone.
A known type of EAS system employs markers which include an LC resonant circuit. An example of such a system is disclosed in U.S. Pat. No. 3,810,147. The circuit is typically formed on a substrate by printed or etched circuit techniques and includes a conductive path to form a coil on one side of the substrate. The coil is connected to a capacitor formed of capacitor plates that are on opposite sides of the substrate. The resonant circuit of the marker is tuned to a predetermined frequency. The detection equipment of the EAS system includes a transmitter which radiates an interrogation signal in the interrogation zone. The interrogation signal is swept through a frequency range which includes the predetermined tuning frequency of the marker. When an active marker is present in the interrogation zone, receiving equipment at the zone detects a change in the interrogation field at the tuned frequency because of the resonance of the resonant circuit of the marker.
It is known to provide a resonant circuit marker that can be deactivated by including in the marker circuitry a fusible link. The fusible link can be caused to fuse upon being energized by application of an electromagnetic field at a predetermined frequency, which may be the resonant frequency of the marker circuit itself, or the resonant frequency of a deactivation circuit associated with the fusible link. When the fusible link is energized and caused to fuse, an open circuit is formed in the resonant circuit of the marker, causing the marker to be detuned and no longer detectable by the detection portion of the EAS system.
As an alternative technique for deactivating resonant circuit markers, the dielectric between the capacitor plates may be broken down by application of a high energy pulse at the marker's tuned frequency. It is known, for example, to provide dimples in one of the capacitor plates, or to provide other structure which facilitates formation of a breakdown path between the capacitor plates.
Some improvements in known resonant circuit EAS markers are desirable. For example, it would be worthwhile to increase the reliability with which markers of this type can be detected. Further, it would be desirable to provide a marker that can be detected without using a swept-frequency interrogation transmitter. Furthermore, known techniques for deactivating resonant circuit markers are irreversible, in that once a fusible link is fused or the capacitor is broken down, the marker cannot be reactivated. It would be useful to provide a resonant circuit EAS marker that can be restored to an active condition after the marker has been deactivated.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a resonant circuit EAS marker that can be more reliably detected than resonant circuit markers provided according to the prior art.
It is a further object of the invention to provide resonant circuit EAS markers that can be detected at a greater distance than prior art resonant circuit markers.
It is still another object of the invention to provide a resonant circuit EAS marker that can be restored to an activated condition after it has been deactivated.
It is yet another object of the invention to provide a resonant circuit EAS marker that can be deactivated by more than one technique.
According to a first aspect of the invention, there is provided a resonant EAS marker of the radio-frequency type, including a substrate, a coil formed on the substrate and including a magnetic element, and a capacitor formed on the substrate and connected to the coil.
According to a preferred embodiment of the invention, the magnetic element included in the coil exhibits a giant magneto-impedance (GMI) effect when a bias magnetic field is applied to the magnetic element. A marker of this type may be interrogated by simultaneously transmitting a carrier signal at the marker's resonant frequency and a low frequency alternating magnetic field. Because of the presence of the GMI element, the marker functions to mix the carrier frequency and the low frequency of the magnetic field, forming a sideband of the carrier frequency that can be detected by suitable receiving equipment provided as part of the EAS system.
According to a second aspect of the invention, there is provided an EAS marker which includes a support member sized for application to an article of merchandise, and circuitry on the support member for performing a first function of receiving and re-radiating a first signal at a first frequency and a second function of receiving a second signal at a second frequency that is lower than the first frequency and mixing the second signal with the first signal, wherein the portion of the circuitry for performing the first function includes a conductive layer formed on said support member and the portion of the circuitry for performing the second function includes a magnetic element.
According to a third aspect of the invention, there is provided a resonant EAS marker of the radio-frequency type, including an inductive element, a capacitive element connected to the inductive element, a first deactivation mechanism associated with at least one of the inductive element and the capacitive element, for reversibly deactivating the marker, and a second deactivation mechanism, associated with at least one of the inductive element and the capacitive element, for irreversibly deactivating the marker.
A resonant circuit EAS marker provided in accordance with the invention, by virtue of including a GMI magnetic element, generates a marker signal in the form of sidebands of a carrier RF signal. A marker signal of this type can be detected more reliably and at a greater distance than the signals provided by conventional resonant circuit markers.
Furthermore, deactivation elements may be provided in association with the GMI element and may be selectively magnetized to inhibit the GMI effect. When this occurs, the marker no longer generates the sideband signal and cannot be detected, thus being rendered deactivated. The marker may be restored to its active state by degaussing the deactivation elements. A conventional, irreversible, deactivation feature may also be provided, such as a fusible link or a breakdown path between capacitor plates, in accordance with conventional practice.
The foregoing, and other objects, features and advantages of the invention will be further understood from the following detailed description of preferred embodiments and from the drawings, wherein like reference numerals identify like components and parts throughout.
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Lian Ming-Ren
Patterson Hubert A.
Robin Blecker & Daley
Sensormatic Electronics Corporation
Tweel , Jr. John
Wu Daniel J.
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