Abstract:
A magnetomechanical EAS tag having a bias magnet made of a high magnetostrictive material so that stress, which is a result of ordinary use of an article incorporating the tag, demagnetizes the bias rending the EAS tag inactive is provided. In an alternate embodiment a mechanical mechanism is incorporated with a conventional EAS tag to deactivate the tag upon ordinary use of an article to which the tag is associated. In yet another embodiment, a combination of the bias magnet made of a high magnetostrictive material and a mechanical deactivation mechanism is used to deactivate an EAS tag during ordinary use of an article to which the tag is associated.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    This invention relates to deactivatable magnetomechanical markers and labels for electronic article surveillance (EAS) systems, and more particularly to using a mechanical mechanism and a high magnetostrictive material as a deactivatable bias to reduce tag pollution due to magnetomechanical EAS markers.  
           [0005]    2. Description of the Related Art  
           [0006]    EAS systems are typically used to prevent unauthorized removal of items from a designated area. In a retail environment, EAS labels are attached to articles for sale, and when active, will trigger an alarm if carried through interrogation zones typically located at the store exits. After an authorized sale of an article, store personnel deactivate the attached EAS label so the article can be removed from the store without triggering the EAS system. As used herein, the terms “markers”, “labels”, and “tags” are used interchangeably and refer to markers, labels, tags, and the like, used to trigger EAS systems.  
           [0007]    Presently, many items of merchandise are source tagged. Source tagging is the attachment of EAS labels at the manufacturing or distribution site. Source tagging can result in an increase in a problem known as “tag pollution”. Tag pollution refers to active or partially active labels inadvertently being carried into EAS equipped stores triggering the EAS alarm. When articles are source tagged with EAS labels, some of the tagged merchandise may be shipped to stores that are not equipped with EAS systems. With no EAS system in the store, when these tagged products are legitimately sold the EAS labels are not deactivated. The active EAS labels can trigger EAS alarms when the customer carries or wears an article, having an active label attached, into a store equipped with an EAS system.  
           [0008]    Solutions to the tag pollution problem include providing security personnel at the store entrance to appropriately handle inadvertent EAS alarms. For example, EAS labels that alarm the system can be deactivated at the door. This solution can increase personnel costs and inconvenience to the customers. Alternately, the problem can be handled at the distribution point by properly deactivating EAS labels that are attached to products intended for stores without the appropriate EAS equipment. However, this can increase the time and costs associated with distribution. As more and more articles are source tagged with EAS labels, tag pollution will be an increasing problem.  
           [0009]    U.S. Pat. No. 5,574,431 (the &#39;431 patent) discloses a security tag that is deactivatable as a result of stress induced by ordinary use of the article. The &#39;431 patent is directed to radio frequency (RF) tags, which work in RF EAS systems. RF EAS systems transmit and respond to RF energy in the interrogation zone. RF tags are comprised of a resonant circuit that detectably responds to the RF energy transmitted into the interrogation zone. The &#39;431 patent is directed to a mechanical stress concentrator that breaks the resonant circuit at a stress concentration point due to the stress caused by ordinary use of the article. The resonant circuit is opened and becomes disabled preventing the circuit from resonating when exposed to the interrogating RF energy. Thus, normal wearing of RF EAS tagged articles deactivates the attached RF EAS tags reducing the tag pollution problem.  
           [0010]    Magnetomechanical EAS markers do not contain resonant circuits in an analogous manner to RF tags. A magnetomechanical EAS marker is made of an elongated strip of magnetostrictive ferromagnetic material, the “resonator”, disposed adjacent a hard ferromagnetic element that, when magnetized, magnetically biases the strip and arms it to resonate mechanically at a preselected magnetic resonant frequency. The resonator is captured within a cavity in the marker housing so that it is free to mechanically vibrate. The hard ferromagnetic element, or bias, is a high coercivity biasing magnet that is capable of applying a DC magnetic bias field to the resonator. The bias magnet is positioned adjacent the resonator, but not in direct contact. The marker resonates when subjected to a magnetic interrogation field at a frequency at or near the marker&#39;s resonant frequency. The response of the marker at the marker&#39;s resonant frequency can be detected by EAS receiving equipment, thus providing an electronic marker for use in magnetomechanical EAS systems. Demagnetizing the bias magnet deactivates the marker. U.S. Pat. No. 4,510,489 discloses further information about magnetomechanical EAS systems.  
           [0011]    U.S. Pat. No. 5,729,200, (the &#39;200 patent) the disclosure of which is incorporated herein by reference, discloses that conventional magnetomechanical EAS markers use amorphous metal alloys such as Metglas 2628CoA, having a composition of Fe 32 Co 18 Ni 32 B 13 Si 5 , and Metglas 2826MB, both available from Honeywell AlliedSignal, Inc. Parsippany, N.J., and VC4613 available from Vacuumschmelze GmbH, Grüner Weg 37, D-63450, Hanau, Germany, and other similar alloys for the active resonator. The bias magnet can be formed from a semi-hard magnetic material, such as SemiVac 90 available from Vacuumschmelze, Hanau, Germany, having a coercivity of around 70 to 80 Oersteds (Oe), and which requires an AC deactivation magnetic field of about 200 Oe. Alternately, a low coercivity material, such as Sensor Vac, also available from Vacuumschmelze, having a coercivity of about 20 Oe, can be used for the bias magnet, which requires a lower deactivation field that is useful for source tagged articles as described in the &#39;200 patent. A characteristic of all conventional bias magnet materials is that they are selected to have low magnetostriction so that stress induced by normal handling of the markers, and the articles to which the markers are attached, does not cause deactivation.  
           [0012]    A method of deactivating a magnetomechanical EAS marker attached or contained within an article by stress induced by ordinary use of the article is needed.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    A first aspect of the present invention is a deactivatable magnetomechanical electronic article surveillance marker with a magnetostrictive resonator adapted to mechanically resonate at a frequency within a preselected detection frequency range provided by an incident magnetic field. A magnetizable bias magnet is disposed adjacent the resonator that, when magnetized, biases the resonator with a magnetic field having a predetermined field strength to arm the resonator to resonate at the frequency. The bias magnet is magnetostrictive and demagnetizable by stress, such that normal use of an article incorporating the marker deactivates the marker. The marker can be incorporated into the article during manufacturing, or subsequent to manufacturing of the article.  
           [0014]    The bias magnet can be made of an alloy composition containing a saturation magnetostriction of about 25 to about 50 parts per million (ppm). In one embodiment, the bias magnet is made of an alloy composition containing a saturation magnetostriction of about 50 ppm.  
           [0015]    A second aspect of the present invention is a deactivatable magnetomechanical electronic article surveillance marker having a marker housing attachable to an article, a magnetostrictive resonator adapted to mechanically resonate at a frequency within a preselected detection frequency range provided by an incident magnetic field is disposed within the marker housing. A magnetizable bias magnet is disposed adjacent said resonator that, when magnetized, biases said resonator with a magnetic field having a predetermined field strength to arm the resonator to resonate at the frequency. A mechanism as described herein is disposed adjacent the marker housing for compressing the marker housing during ordinary usage of the article to dampen the mechanical resonance of the magnetostrictive resonator.  
           [0016]    A mechanical deactivator can be attached to the marker housing and has a moveable member with a free end terminating in a pointed protrusion. The moveable member is adapted to move towards the marker housing forcing the pointed protrusion into the marker housing during ordinary usage of the article to dampen the resonance of the magnetostrictive resonator.  
           [0017]    The bias magnet can be magnetostrictive and demagnetizable by stress, wherein normal use of the article incorporating the marker deactivates the marker, so that the marker includes both modes of deactivation.  
           [0018]    Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a plot showing the effect on magnetic flux as a result of bending various bias magnet compositions.  
         [0020]    [0020]FIG. 2 is a bottom plan view of one embodiment of the present invention.  
         [0021]    [0021]FIG. 3 is an rear elevational view, in cross-section, taken along line  3 - 3  in FIG. 2.  
         [0022]    [0022]FIG. 4 is a top plan view an alternate view of the present invention.  
         [0023]    [0023]FIG. 5 is a front elevational view of that of FIG. 4.  
         [0024]    [0024]FIG. 6 is a front elevational view of that of FIG. 5 after deactivation.  
         [0025]    [0025]FIG. 7 is an alternate embodiment of that shown in FIG. 5.  
         [0026]    [0026]FIG. 8 is a block diagram of an electronic article surveillance system incorporating the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring to FIG. 1, the number of bends versus the percent change in magnetic flux from 100% of the maximum bias level to the deactivation specification  1  of 30% of maximum is illustrated for various bias magnet compositions. The maximum magnetic bias level depends on the particular bias material selected. For example, for resonators made of VC4613, the 100% magnetic bias level is preferably in the range of about 5.85 to 7.15 Oe. The &#39;200 patent discloses magnetic properties of various conventional bias materials. The required bias level range is dependent upon the resonator material selected. Curve  2  and curve  4  show the change in magnetic flux for a conventional bias magnet material, such as the Sensor Vac material described hereinabove, for a 2 inch and a 1 inch bend diameter, respectively. Curve  6  and curve  8  show the change in magnetic flux for a material that is similar to the Sensor Vac material but which has high magnetostrictive properties. High magnetostrictive properties is defined by an alloy composition containing a saturation magnetostriction of about 25 to about 50 parts per million (ppm). Saturation magnetostriction is the amount of elongation a material exhibits from its demagnetized state to fully magnetized state along the magnetization direction. The elongation is expressed, in parts per million, as the ratio of the change in length upon magnetization to the length of the material in the demagnetized state. The effect the invention makes use of is the inverse magnetostrictive effect, where mechanical stress affects the magnetization of the material. The higher the saturation magnetostriction, the stronger the inverse effect, and the larger demagnetization of material possible given the same amount of stress applied to the material. In the example, the bias magnet is made of an alloy composition containing a saturation magnetostriction of about 50 ppm.  
         [0028]    As illustrated in FIG. 1, the conventional materials maintain over 80%, or 90%, of their maximum flux strength for 100 cycles of 2 inch, and 1 inch bends, respectively. The high magnetostriction material selected in the example reaches deactivation level  1  at 100 cycles of bending at a 1 inch diameter. The final design and the appropriate magnetostriction of the bias material depends on the required stability of the active label, the bending diameter imparted on the bias in the application, and the targeted number of cycles of bending before the label is failed.  
         [0029]    Referring to FIG. 2, one embodiment of the invention is illustrated showing EAS label  10  disposed in an article of merchandise, which in this example is shoe  12 . The exact position of label  10  will be determined according to the article to which it is to be incorporated, and the anticipated bending diameter or stress placed upon the bias during normal use of the article. FIG. 2 illustrates an example of a possible placement of label  10  for shoe  12 .  
         [0030]    Referring to FIG. 3, label  10  includes resonator cavity  14 , with resonator  16  disposed therein. Bias magnet  18  is disposed adjacent resonator cavity  14  in a suitable position to permit bending or other mechanical stress to be imparted onto the bias during normal use of the article, in this case bias magnet  18  is bent when a user walks or runs wearing shoe  12 .  
         [0031]    Referring to FIGS. 4 and 5, a magnetomechanical EAS label  20  is illustrated with a mechanical deactivator  22  attached. Magnetomechanical EAS label  20  is understood to include a marker housing having an internal cavity with a resonator disposed therein and an adjacent bias magnet. Deactivator  22  can be attached to EAS label  20  by any suitable manner such as pressure sensitive adhesive  24 . Deactivator  22  includes a hinge  26  and a movable member  28  with the free end terminating in a pointed protrusion  30 . When EAS label  20  is attached to an article by an adhesive layer  32 , under normal usage of the article, member  28  bends at hinge  26  and moves toward EAS label  20 . Once member  28  makes contact with label  20 , pressure sensitive adhesive  24  retains member  28  against label  20  to maintain contact of pointed protrusion  30  onto label  20 . With repeated use of the article, pointed protrusion  30  is forced into EAS label  20 , deforming the label housing and eventually breaking or dampening the magnetomechanical resonator contained therein. Pointed protrusion  30  may actually break the resonator or bias magnet disposed within the label housing, or it may merely crush or compress the housing into the resonator and bias. The main object is to prevent free vibration of the resonator at the resonance frequency of the label. As the resonator becomes pinched in the housing due to pointed protrusion  30  being forced into the label housing, the frequency of vibration changes and the amplitude at the marker&#39;s resonant frequency drops. Once the magnetomechanical resonator is dampened by pointed protrusion  30 , EAS label  20  is considered deactivated and will not be detected in a magnetomechanical EAS system. EAS label  20  can contain a high magnetostrictive bias, as fully described hereinabove, in additional to mechanical deactivator  22 , so that during normal usage of an attached article, the EAS label will include two modes of deactivation.  
         [0032]    In alternate embodiments of the present invention, deactivator  22  may not be separate from label  20  as label  20  can be manufactured to include a member that includes an equivalent of pointed protrusion  30  to deactivate the label upon repeated mechanical stress. Pointed protrusion  30  could take the form of a ridge formed on or within label  20 .  
         [0033]    Referring to FIG. 7, label  20  may be placed in a cavity  40  formed within an article  42  and not attached via adhesive  32  to the exterior of the article. Therefore, instead of being part of, or attaching to label  20 , a pointed protrusion  31  could be made part of, or attached to, cavity  40  manufactured in the article  42  in which label  20  is placed.  
         [0034]    The main function of pointed protrusion  30  and its equivalents is to dampen free vibrations of the resonator contained within label  20  to make the label  20  undetectable in an associated EAS system. Dampening the vibration of the resonator can be accomplished by crushing and/or compressing label  20 . As stated hereinabove, a magnetostrictive deactivateable bias can be used within a label that includes pointed protrusion  30 , or its mechanical equivalents, to incorporate two modes of deactivation.  
         [0035]    [0035]FIG. 8 illustrates an EAS system  101  used to detect or sense EAS tag  100  when passing through a surveillance zone  102 . EAS tag  100  represents a tag such as EAS tag  10  or EAS tag  20  as described hereinabove that includes the present invention. An interrogation signal is transmitted into the zone  102  via a transmitting device  103 . A signal resulting from interaction of the tag  100  with the transmitted signal is received at a receiver  104 , which communicates with a detection and alarm device  105 . The latter detects the received signal and generates an alarm indicating the presence of the tag  100  and the article  50  in the surveillance zone  102 . The particular configurations used for the devices  103 ,  104  and  105  in the system  101  will depend on the specific installation. For example, instead of a transmitter  103  and separate receiver  104 , one or more transceivers can be used.  
         [0036]    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.