Apparatus for deactivation of electronic article surveillance tags

Abstract: A deactivation device for deactivating electronic article surveillance tags comprises a housing, a coil supported in the housing and having opposed first and second sides and energizable to generate a magnetic field issuing from both the first and second sides thereof and a shielding unit supported in the housing in juxtaposition with the coil second side. The shielding unit includes a succession of magnetically permeable members and lessens magnetic fields exteriorly of a portion of the housing juxtaposed with the last of magnetically permeable members in the succession and otherwise functions as a pole piece for the coil and enhances the magnetic field generated by the coil. Plural coil pairs may be provided in the housing about an interior compartment receiving tagged articles and each coil pair provided with the shielding unit.

Description: FIELD OF THE INVENTION This invention relates generally to electronic article surveillance and pertains more particularly to so-called "deactivators" for rendering electronic article surveillance tags inactive. BACKGROUND OF THE INVENTION It has been customary in the electronic article surveillance (EAS) industry to apply to articles to be monitored either hard, reusable EAS tags or disposable adhesive EAS labels, both functioning as article monitoring devices. At article checkout stations in retail stores, a checkout clerk passes the article over or into deactivation apparatus which deactivates the monitoring device. Known deactivation apparatus includes coil structure energizable to generate a magnetic field of magnitude sufficient to render the monitoring device inactive, i.e., no longer responsive to incident energy to itself provide output alarm or to transmit an alarm condition to an alarm unit external to the tag or label (hereinafter "tag"). One commercial deactivator of the assignee hereof employs one coil disposed horizontally within a housing and tagged articles are moved across the horizontal top surface of the housing such that the tag is deactivated regardless of its orientation. Another commercial deactivator of the assignee hereof employs a housing having an open side with a plastic bucket inserted in the housing such that an article or a plurality of articles may be made resident in the bucket. Three coil pairs are disposed about the bucket in respective x-, y- and z-axis planes. The coil pairs of each of the two described deactivators generate a low frequency decaying magnetic field of substantial strength. In the first deactivator, the field necessarily is exteriorly above the upper horizontal surface thereof to perform deactivation. However, the field escapes the housing in other directions, particularly downwardly of the housing. In the second deactivator, while the fields are necessarily needed only in the bucket, they undesirably escape the housing. Thus, in use of either type of deactivator, it is necessary to keep the deactivator at a safe distance from other sensitive devices, such a monitors, magnetic stripe readers and the like. The known deactivators place an undesirable constraint on EAS system checkout stations, i.e., the stations can not be as compact as desired, and otherwise usable space at the stations need be dedicated to the EAS system. Further, the known deactivators exhibit relatively high power needs to generate the deactivating fields. While shielding has been successfully used in the EAS industry to overcome interference problems, for example, in transmitting antenna shielding, as in commonly-assigned U.S. Patent No. 4,769,631, a new approach is requisite due to the extraordinarily strong fields and low frequencies involved in tag deactivation. An "evident solution" to the problem would be to select a suitable shielding material of acceptable thickness, driven usually by weight and cost considerations, which would be placed around the interfering unit. In the case of the known deactivators, this approach would have required a substantial gap between the deactivating coils and the shield to prevent saturation and the addition of a second layer in a nested arrangement. This would have resulted in a greatly increased overall size and some magnetic leakage due to the gap without significant improvement in efficiency. SUMMARY OF THE INVENTION The present invention has as its primary object a solution to the above-discussed problems attending the described prior art deactivators. One more particular object of the invention is to provide enhanced constraints on magnetic fields unnecessarily exterior to the described prior art deactivators. Another more particular object of the invention is lessen power needs of the described prior art deactivators. In attaining the above and other objects, in one embodiment thereof, relating to the first described prior art deactivation device for deactivating electronic article surveillance tags, the invention provides a housing, a single coil supported in the housing and having opposed first and second sides and energizable to generate a magnetic field issuing from both the first and second sides thereof and a shielding unit supported in the housing in juxtaposition with the coil second side, the shielding unit comprising a succession of magnetically permeable members. The shielding unit lessens magnetic fields exteriorly of a portion of the housing juxtaposed with the last of magnetically permeable members in the succession and otherwise enhances the magnetic field. In a second embodiment thereof, relating to the second described prior art deactivation device for inactivating electronic article surveillance tags, the invention provides a housing, at least first and second pairs of coils supported in the housing each coil having opposed first and second sides. The coil pairs are independently energizable to generate respective first and second magnetic fields issuing from both the first and second coil sides and shielding units are supported in the housing respectively in juxtaposition with the second sides of each coil, each shielding unit comprising a succession of magnetically permeable members. The shielding units lessen magnetic fields exteriorly of respective portions of of the housing juxtaposed with the last of magnetically permeable members in the respective successions and enhance the magnetic field inside of the housing. The magnetically permeable members are comprised of magnetic steel, preferably, silicon iron. In contrast to the "evident solution" to the prior art problem above addressed, the invention overcomes the problem by placing a heavier shield in very close proximity to the coils (zero gap in the case of the first embodiment) making it an integral part of the magnetic circuit where it acts as a pole piece as well as a shield. The resulting deactivators are only slightly larger that than the prior art deactivators and are much more efficient due to the improved flux path without the leakage of the "evident solution". The reduction of the undesirable external field is achieved in part through a reduction in coil current proportional to the enhancement of the internal field so that the same deactivation field is maintained. The foregoing and other objects and features of the invention will be further understood from the following detailed description of preferred embodiments thereof and from the drawings, wherein like reference numerals identify like components throughout. DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded, perspective view of a first embodiment of a deactivator in accordance with the invention. Fig. 2 is a perspective view of the single deactivating coil of the first embodiment. Fig. 3 is front elevational view of the shielding unit of the first embodiment. Fig. 4 is an exploded, perspective view of a second embodiment of a deactivator in accordance with the invention. Fig. 5 is a left side elevational and schematic view of the Fig. 4 deactivator. Fig. 6 is front elevational view of one of the four identical panels of the shielding units of the second embodiment. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PRACTICES Referring to Fig. 1, deactivator 10 includes a housing jointly defined by cover 12 and base 14. A product identifier/logo decal 12a is seatable in a circular open recess 12b of cover 12. Transmit/receive coil structure 16 is disposed adjacently interiorly of cover 12 for effecting communication with a tag prior to deactivation to initiate the same and following deactivation thereof to assure, through associated processing circuitry known in the EAS art in the described prior art deactivators, that the tag is indeed deactivated. Deactivation coil 18 is disposed interiorly of transmit/receive coil structure 16. As is seen in Figs. 1 and 2, deactivation coil 18 is energized through conductors 22 and 24 and generates a necessary magnetic field above its upper side, i.e., to deactivate tags disposed adjacent the outer surface of cover 12. Shielding unit 34 has an upper side thereof in Fig. 1 juxtaposed with the lower side of coil 18. Base 14 includes various registration and assembly securing members 36 and, on assembly of deactivator 10, they extend through holes 38 in shielding unit 34 and holes 40 in transmit/receive coil structure 16, and abuttingly bound coil 18, to maintain the various components of the deactivator in desired position. Members 36 are exteriorly threaded at free ends thereof and interiorly threaded securement members (not shown) are secured to members 36 atop transmit/receive coil structure 16 to assemble the deactivator. Referring to Fig. 3, shielding unit 34 will be seen to be comprised of ten layers, 34a, 34b,...34j. As is indicated for layer 34a (all layers are identical), it includes an exterior coating layer 34a-1, in the nature of the material of a transformer lamination, i.e., electrically insulative material, such as C5 type inorganic matter in a very thin coating of about two ten thousandths of an inch, an interior layer 34a-2, comprised of magnetically permeable matter, preferably commercially-available #24 gauge .025", 64mm) M19 grade, non-oriented silicon steel (SiFe), and an interior layer 34a-3, constituted identically with layer 34a-1. Layers 34a and 34b are mutually secured, as are all juxtaposed layers of shielding unit 34, by a double-sided adhesive film 42, forming shielding unit 34 as a laminated structure. Each deactivation cycle requires an amount of energy (power-time product) which is measured in watt seconds. The first described prior art deactivator, i.e., without shielding unit 34, requires two hundred watt seconds per deactivation, or a power consumption of two hundred watts for deactivation once every second. With the shielding unit 34 so formed and present, experimentation has established that the deactivator of Figs. 1-3 requires only seventy watt seconds per deactivation or seventy watts for deactivation once every second. Applicants attribute such improvement to the modification of the reluctance path in the deactivator, strongly influenced by the presence of shielding unit 34, which can be regarded as a shielding unit/pole piece. A further advantage of the first embodiment is a substantial lessening of escaping magnetic field below the deactivator. Turning to Fig. 4, the second prior art deactivator above discussed includes bulk deactivator unit 44 having opening 44a and plastic bucket 46 having opening 46a. Shield unit 48 is configured as a sleeve for deactivator unit 44, having opening 48a and a rightward opening (not shown). The interior structure of deactivator unit 44 is seen in Fig. 5. One coil pair (x-axis) has coils shown at 44b-1a, 44b-1b and 44b-2a, 44b-2b. A second coil pair (y-axis) has coils shown at 44c-1a, 44c-1b and 44c-2a, 44c-2b. One coil of a third coil pair (z-axis) is shown at 44d. The three coil pairs are thus arranged in a Helmholz like configuration. The coil pairs are driven one pair at a time resulting in a three step sequence. Fig. 6 illustrates the configuration of each of the four sidewalls of shield unit 48, which will be seen to be comprised of seven layers, 48a, 48b,...48g. As is indicated for layer 48a (all layers are identical), it includes an exterior coating layer 48a-1, of material and thinness noted above for coating layer 34a-1, , an interior layer 48a-2, comprised of magnetically permeable matter, preferably commercially-available #24 gauge, M19 grade, non-oriented silicon steel (SiFe), and an interior layer 48a-3, constituted identically with layer 48a-1. Layers 48a and 48b are mutually secured, as are all juxtaposed layers of shielding unit 48, by screws passing therethrough and into securement with support member 50, which may be plywood and provides an outer wall of the shielding unit. Given that shielding unit 48 has open ends, and that the z-axis coils accordingly do not have walls juxtaposed with sides thereof but, rather are bounded perimetrically by the magnetic steel layers, the principal field containment and enhance occurs for the fields generated by the x- and y-axis coils. However, it has been found that the z-axis experiences a ten percent reduction in external field strength as well as a ten percent field strength enhancement inside the deactivation chamber. Accordingly, if the z-axis coil pair drive is reduced by ten percent, and yet the field strength of the prior art deactivator is achieved, the external z-axis field is reduced by some nineteen percent. Since only one open end is needed, for entry of tagged articles into the bucket, the invention may be practiced with a single z-axis shielding unit wall or floor as desired. The power-time product for the second above-noted prior art deactivator, i.e., without shielding unit 48, is four hundred and sixty watt seconds per deactivation. Experimentation has established that the power-time product for the subject deactivator with shielding unit 48 is two hundred watt seconds per deactivation. The invention contemplates the use of plural, spaced shielding panels for each coil. In a preferred arrangement, a first panel is configured with an inner panel comprised of five layers of #26 gauge, M 19 grade non-oriented silicon steel and an outer panel comprised of five layers of #29 gauge, M6 gauge grain oriented silicon steel. The inner panel is located 20mm from the coil and the outer panel is spaced 6mm from the inner panel. The grades and gauges are selected optimally for different fields encountered. This approach results in the highest attenuation for a given amount of magnetic material. In this connection, while the double panel arrangement maximizes shielding performance (attenuation), it is not as effective as a pole piece and therefore does not achieve the same field enhancement because only the inner shield functions as an effective pole piece. Thus, the double panel arrangement finds best usage in situations where maximum external field attenuation need be achieved at the expense of other parameters, such as efficiency, size and cost. Silicon iron emerged as applicants' principle magnetic steel choice based on its following characteristics: high permeability resulting in good shielding performance (attenuation); high intrinsic induction limit (saturation flux density) making it suitable for strong fields; low hysteresis losses and low eddy current losses; desired shielding unit thickness readily obtained by stacking thin sheets, also reducing eddy current; easily cuttable by simple shearing operations; relatively low cost, some one and one-half to two times compared to ordinary steel depending on grade; and commercially supplied annealed and with a protective coating (transformer lamination). Various changes in structure to the described systems and apparatus and modifications in the described practices may evidently be introduced without departing from the scope of the invention as defined in the appended claims. Accordingly, it is to be understood that the particularly disclosed and depicted embodiments are intended in an illustrative and not in a limiting sense.

Claims: A deactivation device for inactivating electronic article surveillance tags, comprising: (a) a housing; (b) a coil supported in said housing and having opposed first and second sides and energizable to generate a magnetic field issuing from both said first and second sides thereof; and (c) a shielding unit supported in said housing in juxtaposition with said coil second side, said shielding unit comprising a succession of magnetically permeable members, said shielding unit lessening magnetic fields exteriorly of a portion of said housing juxtaposed with the last of magnetically permeable members in said succession. The deactivation device claimed in claim 1, wherein said magnetically permeable members are comprised of magnetic steel. The deactivation device claimed in claim 2, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 2, wherein said magnetically permeable members are annealed. The deactivation device claimed in claim 1, wherein said shielding unit further includes adhesive means disposed between said magnetically permeable members. The deactivation device claimed in claim 5, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 6, wherein said magnetically permeable members are annealed. A deactivation device for inactivating electronic article surveillance tags, comprising: (a) a housing; (b) at least first and second pairs of coils supported in said housing each coil having opposed first and second sides and energizable to generate respective first and second magnetic fields issuing from both said first and second sides of said coils; and (c) shielding units supported in said housing respectively in juxtaposition with said second sides of said coils, each said shielding unit comprising a succession of magnetically permeable members, each said shielding unit lessening magnetic fields exteriorly of respective portions of said housing juxtaposed with the last of magnetically permeable members in said respective successions. The deactivation device claimed in claim 8, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 9, wherein said magnetically permeable members are annealed. The deactivation device claimed in claim 8, wherein each said shielding unit further includes a support member and wherein said magnetically permeable members are stacked on said support member and are mechanically secured to said support member. The deactivation device claimed in claim 11, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 12, wherein said magnetically permeable members are annealed. A deactivation device for inactivating electronic article surveillance tags, comprising: (a) a housing defining a compartment accessible exteriorly of said housing for temporary containment of an article bearing an electronic article surveillance tag; (b) first and second coil pairs supported in said housing each coil having opposed first and second sides and energizable to generate respective first and second magnetic fields issuing from both said first and second sides of said coils; and (c) first and second shielding units supported in said housing in juxtaposition with said second sides of said respective first and second coils, each said shielding unit comprising a succession of magnetically permeable members, each said shielding unit lessening magnetic fields exteriorly of respective portions of said housing juxtaposed with the last of magnetically permeable members in said successions. The deactivation device claimed in claim 14, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 15, wherein said magnetically permeable members are annealed. The deactivation device claimed in claim 14, wherein each said shielding unit further includes a support member and wherein said magnetically permeable members are stacked on said support member and are mechanically secured to said support member. The deactivation device claimed in claim 17, wherein said magnetically permeable members are comprised of silicon iron. The deactivation device claimed in claim 18, wherein said magnetically permeable members are annealed. A deactivation device for inactivating electronic article surveillance tags, comprising: (a) a housing; (b) a coil supported in said housing and having opposed first and second sides and energizable to generate a magnetic field issuing from both said first and second sides thereof; and (c) a magnetically permeable member supported in said housing in juxtaposition with said coil second side, said magnetically permeable member functioning both as a shield for said coil and a pole piece for said coil.

Inventors: ZSCHIRNT JOERG W, ZSCHIRNT, JOERG W.
Applicants: SENSORMATIC ELECTRONICS CORP, SENSORMATIC ELECTRONICS CORPORATION
Application year: 1995
Main classification: G08B13
IPC codes: H05K9, G08B13, H01F13