Deactivatable radio frequency security label

[0001] Not Applicable

[0002] Not Applicable

[0003] 1. Field of the Invention

[0004] The invention relates to radio frequency (RF) security labels having a deactivatable resonant circuit.

[0005] 2. Description of the Related Art

[0006] Electronic article surveillance (EAS) systems are widely used in commercial and retail establishments to deter theft or other unauthorized removal of articles from the surveillance area. In one commonly used EAS system, each article or item to be protected carries a security tag or label, which may be affixed on or inside packaging or as a label for the article or item, or on or inside the article or item itself, containing an electronic circuit, such as an inductor/capacitor resonant circuit. The resonant tag circuit is detected or identified by equipment for establishing an RF electromagnetic field in a surveillance zone at the exit of the surveillance area.

[0007] The detectable resonant circuit of the EAS tag is a small, generally planar, multi-layer structure having a dielectric substrate and conductive layers on opposite sides of the substrate that define an inductor and at least one capacitor that provide a circuit resonant at at least one predetermined detection frequency.

[0008] Removal of a tagged article from the surveillance area is typically authorized at a checkout counter, where the clerk deactivates the tag. The security tag may be deactivated by changing the resonant frequency of the tag so that the tag resonates outside of the predetermined detection frequency or by altering the resonant circuit so that the circuit no longer resonates.

[0009] A typical deactivation technique is accomplished electronically, by passing the tag through a deactivating RF field that disables the detectable resonant circuit. Such deactivation involves exposing the resonant tag circuit to an RF field having a predetermined minimum energy level sufficient to cause either short-circuiting of the resonant circuit or creation of an open circuit and thereby preventing the circuit from resonating at the predetermined detection frequency.

[0010] In a typical implementation of deactivation a portion of one conductor in a multi-layer resonant tag circuit is indented or “dimpled”. Deactivation is accomplished by exposure of the tag to a specific RF field at a predetermined energy level that causes a short circuit at the indent or dimple, which results in the desired deactivation of the resonant circuit being targeted. Examples of “dimpled” deactivation tag devices are shown in U.S. Pat. Nos. 4,567,473 and 5,841,350. Other deactivation techniques include the use of fuseable links as shown in U.S. Pat. Nos. 4,802,944 and 5,059,950.

[0011] The present invention is a deactivation apparatus for an electronic article surveillance tag having a plurality of layers and an equivalent resonant circuit containing an inductor and a capacitor. The apparatus includes: a capacitor formed by a pair of conductive capacitor plates separated apart by a dielectric layer; an inductor connected to each of the pair of capacitor plates where an electromagnetic field of a preselected frequency at a first magnitude impinging upon the tag causes the equivalent resonant circuit to resonate and produce a detectable response from the tag; and, an electrically weakened area in the dielectric layer between the pair of conductive capacitor plates where the electromagnetic field at a second magnitude higher than the first magnitude impinging upon the tag causes a conductive path through the weakened area electrically connecting the pair of capacitor plates together and deactivating the tag.

[0012] The electrically weakened area can be a mixture of a conductive material and a nonconductive binder disposed in a void area of the dielectric layer between the pair of capacitor plates.

[0013] The electrically weakened area can alternately include an oxide layer between each of the pair of capacitor plates and the dielectric layer, and a conductive material disposed in a void area of the dielectric material between the pair of capacitor plates.

[0014] Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.

[0020] Referring to FIG. 1, the basic resonant circuit associated with the present invention includes capacitor C1 and inductor L1. A conductor coil on one or more layers of a multi-layered EAS label typically forms inductor L1. Two conductive plates separated by a dielectric material form capacitor C1.

[0021] Referring to FIG. 2, inductor L1 is connected to conductive capacitor plates 2 and 4 as shown in the illustration of the relevant portions of an RF EAS tag 1, according to one embodiment of the present invention. Capacitor plates 2 and 4 of capacitor C1 are separated by dielectric material 6. Dielectric material 6 can be an adhesive layer that retains plates 2 and 4 in their desired position. Inlaid in a cutout or void area of dielectric material 6 is a matrix made of a conductive material in a nonconductive binder 8. The conductive material can be any suitable conductive material that is adapted to be mixed with a binder, and can include, but is not limited to, a metal such as copper, aluminum, bronze, and the like, or a conductive material such as carbon. The nonconductive binder can be made of, but is not limited to, varnish, polymers, polyurethane, and other nonconductive materials, the selection of which is well known in the art. Upon exposure to an electromagnetic field of sufficient magnitude and at the appropriate frequency and duration, the matrix of conductive material and nonconductive binder 8 forms a carbonized or conductive path between capacitor plates 2 and 4. The carbonized path shorts plates 2 and 4 of capacitor C1 rendering the EAS tag 1 non-resonant at its operating frequency, or deactivated. The field level required to resonate tag 1 for normal operation is lower than the magnitude required to short capacitor C1. Normal operation means that when tag 1 resonates it produces a signal detectable by an electronic article surveillance receiver (not shown). Deactivation occurs only when tag 1 is radiated with a field level of sufficient magnitude required for deactivation, which shorts plates 2 and 4.

[0022] Referring to FIG. 3, a top plan view of one embodiment of the present invention shows inductor L1 may be formed by a coil of copper or other suitable conductor material on adhesive dielectric material 6, which also carries conductor plate 2 of capacitor C1. Additional layers may be present, but are not shown. Inductor L1 is connected to through contact 9.

[0023] Referring to FIG. 4, a bottom plan view of the embodiment illustrated in FIG. 3 shows through contact 9 in electrical connection with conductor plate 4 of capacitor C1. The electrical circuit is thus completed as illustrated in FIG. 1. As stated, additional layers may be present, as well as other physical implementations of coil L1 and capacitor plates 2 and 4.

[0024] Referring to FIG. 5, the relevant portions of an alternate embodiment of RF EAS tag 10 is illustrated. In tag 10, conductive capacitor plates 12 and 14 are both separated from dielectric material 6 by an oxide layer 16. A conductive material 18, which can be a conductive material as described hereinabove or another conductive material, is inlaid in an opening or void area in dielectric material 6. Exposing tag 1 to an electromagnetic field of sufficient magnitude, frequency, and duration causes a carbonizing path through oxide layer 16 between the conductive plates 12 and 14 and conductive material 18. The resulting short circuit of capacitor C1 renders tag 10 non-resonating at the intended operating frequency, and deactivates tag 10.

[0025] In the present invention, one resonant frequency selection is about 8 MHz, but the invention is not so limited and can be used at other frequencies. The desired deactivation electromagnetic field can be a similar RF field but of relatively high magnitude, and can be an RF pulse. The invention can be implemented at other frequencies as long as a suitable shorting deactivation mechanism can be implemented by an electrically weakened area as disclosed herein.

[0026] It is to be understood that variations and modifications of the present invention can be made without departing from the scope of the invention. It is also to be understood that the scope of the invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the forgoing disclosure.