Abstract:
A tamper resistant electronic tag that wirelessly receives and transmits unique subscriber information to and from a transceiver so that financial transactions can occur quickly and seamlessly. In a preferred embodiment, the tag works in conjunction with a roadway toll booth and is mounted onto a flat interior surface of a vehicle, where it can receive and transmit electronic information to and from a toll booth. That allows a driver to pay the toll fee without having to stop his vehicle. The electronic tag includes a plastic protective card for carrying a circuit. The circuit includes an integrated circuit that is adhesively attached to the protective card. The protective card and circuit are then attached to the flat surface. When the protective card is removed, the integrated circuit is pulled off with the protective card while the rest of the circuit remains attached to the flat surface, thereby severing the circuit, and rendering it inoperable. This prevents the unwanted tampering and unauthorized use of the electronic tag.

Description:
FIELD OF INVENTION 
     The present invention is directed to a tamper resistant electronic tag that attaches to the inside of an automobile, preferably the front windshield, so that unauthorized removal of the tag will render the tag inoperable. The tag is preferably part of a highway toll collection system that allows a vehicle to automatically pay toll fees, by transmitting a signal incorporating unique subscriber information to a transceiver at a toll booth so that the vehicle may pass through the toll booth without having to stop the vehicle. The tag may also be used for other RF-identification applications, such as in parking facilities, vehicle registration and retail stores. Additionally, the tag may provide RF-identification for security and access control applications. 
     BACKGROUND OF THE INVENTION 
     Use of toll booths for collecting fees along heavily trafficked highways and roadways is a common practice for generating revenue for many jurisdictions. In order to facilitate the quick and efficient collection of these fees and to prevent “bottlenecking” at the toll booths, many jurisdictions have incorporated wireless electronic tags that seamlessly transmit subscriber information to a transceiver at the toll booth, which then automatically deducts the appropriate fees from an existing account established by the tag owner. In that way, a driver may simply pass a toll booth and have the appropriate fees paid without having to bring his vehicle to a stop. 
     The electronic tags are typically small portable units that are placed inside a vehicle so that when a toll booth is passed, the tag retransmits signals to a transceiver at a toll booth. Oftentimes, the tags are attached to a front windshield of a vehicle so that its signal to the toll booth is unobstructed. However, this often leaves the tag in open view making it highly susceptible to theft. 
     One solution to this problem is to embed the electronic tag in between two layers of glass in a vehicle&#39;s windshield, as disclosed in U.S. Pat. No. 6,275,157 to Mays et al. This prevents unwanted tampering, but also bars access to the tag. If the tag malfunctions or otherwise becomes inoperative, or if the vehicle is sold, it is impossible to access the tag without destroying the windshield. It would also be advantageous to provide an electronic tag that can be accessed without having to destroy or break portions of the vehicle. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an electronic tag that transmits subscriber information to allow quick and efficient financial transactions to occur. It is a further object of the present invention to provide a tag that can be attached to a surface, particularly a vehicle&#39;s windshield, to prevent unauthorized tampering with the tag. It is still a further object of the present invention to provide an electronic tag that will become inoperable when tampered with. 
     The present invention is directed to a tamper resistant electronic tag that wirelessly retransmits subscriber information to a transceiver when interrogated, so that financial transactions can occur quickly and seamlessly. A preferred embodiment mounts the tag onto a relatively flat surface, typically the front windshield of a vehicle, where it receives an interrogation signal from a “reader” system and retransmits a modified signal carrying subscriber information back to the reader system. 
     The tag may include a card like structure that prevents access to the internal structures of the tag. This protective card is generally flat, rectangular shaped laminate with a hole therein for holding the integrated circuit. The integrated circuit is encapsulated or affixed in the hole, causing it to be securely held within the hole and further making it difficult to remove the integrated circuit from the card without causing it to become inoperable. 
     It is another object of the invention to provide a multi-layered tag with an easily damaged substrate that will become inoperable upon removal or attempted removal. The strength of adhesion between the various layers and components of the tag is controlled to allow the circuit to be easily and permanently separated from the tag&#39;s receiving antenna and capacitive coupling element upon removal of the tag. 
     The tag is meant to be easily destructible upon tampering or attempted removal from a surface. However, the tag is also meant to be durable for its intended use. The tag is designed to give reliable and long lasting use up until the point at which it is tampered with or removed. 
     With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view drawing of an electronic tag of the present invention attached to a windshield of a vehicle; 
         FIG. 2  is an exploded view of an embodiment of the electronic tag comprising multiple layers; 
         FIG. 3   a  is a cross section view of an embodiment of a protective card of the invention with a closed-top hole for receiving the integrated circuit; 
         FIG. 3   b  is a cross section view of an embodiment of a protective card of the invention with a open-top hole for receiving the integrated circuit; 
         FIG. 4  is a schematic view of the pattern of adhesive failure during an attack on the tag of  FIG. 8  by hand; 
         FIG. 5  is an exploded view of an embodiment of the electronic tag comprising multiple layers and lacking a strap subassembly component; 
         FIG. 6  is an exploded view of an embodiment of the electronic tag comprising multiple layers and including a smaller substrate; and 
         FIG. 7  is a schematic view of a alternate protective card of the invention which eliminates that need for an annularly shaped adhesive layer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now in detail to the drawings,  FIG. 1  shows an electronic tag  120  of the present invention mounted on the inside of a vehicle&#39;s front windshield  110 . The tag  120  can be mounted anywhere inside the vehicle, but the front windshield  110  provides a preferred location because it permits a clear and unobstructed path for signals to be sent between the tag  120  and a data processing station (not shown). In addition to being mounted onto the windshield  110 , the tag  120  may be embedded into the windshield of new cars. 
     In a preferred embodiment of the invention, the tag  120  is used in conjunction with roadway toll booths, so that subscribed information can be relayed to the toll booth and the proper fee electronically paid without having to stop the vehicle. However it is also envisioned that the tag  120  be used in a variety of other environments to eliminate cash transactions, thereby increasing the speed and efficiency at which these financial transactions can occur. For example, it is contemplated that the tags be used in conjunction with fast food drive-throughs, gas stations, parking facilities, or any other location where cash is exchanged. Additionally, the tag is not limited to the transfer of electronic financial information, but can be used to transfer any information which needs to be quickly and accurately relayed. The tag  120  also provides a level of security for these transactions by limiting the access to the tag  120 , thereby preventing their fraudulent use. 
       FIG. 2  shows an embodiment of the invention in which multiple layers are employed to make a thin electronic tag  120  with low manufacturing costs. In this embodiment, the electronic tag consists of a first pressure sensitive adhesive layer (PSA)  150  which allows the tag to be affixed to the windshield of the vehicle. During manufacture of the tag, the first PSA  150  is covered with a release liner  152 , that must be removed in order to expose the adhesive. The first PSA  150  is attached to a substrate  154  that allows for the printing of custom graphics on the face of the substrate that faces the windshield. On the opposite face of the substrate  154  is an antenna  156  that receives an interrogation signal from a toll booth reader/transceiver. 
     The substrate  154  is attached to the protective card  158  by the second PSA  160 , which, preferably, is annular in shape and has a center opening  161 . The strap subassembly (SS) is affixed between the substrate  154  and protective card  158 . The SS consists of strap subassembly PSA (SSPSA)  162 , a SS substrate  164  bearing a SS capacitive coupling element  165 , and an integrated circuit  166 . Collectively, the antenna  156 , SSPSA  162 , SS substrate and SS capacitive element  165  form the coupling circuitry of the tag, with the SSPSA  162  and the SS substrate  164  acting together as a dielectric. 
     Optionally, the SSPSA  162  is covered with a release liner (not shown) to protect the adhesive until the SS is assembled into the tag. In the embodiment shown in  FIG. 2 , the components of the strap subassembly fit within the opening  161  of the second PSA layer  160 . 
     The protective card  158 , is punched with a hole  159 , in which the integrated circuit  166  fits. A preferred embodiment of the protective card  158  containing a hole  159  that does not go all the way through the card, is shown in  FIG. 3   a . In the embodiment of  FIG. 3   a , the outer surface of integrated circuit  166   a  is attached with an adhesive (not shown) to the protective card. This adhesive can be of any type suitable for use with the integrated circuit  166 . Preferably, the adhesive will have properties that make the adhesion between the integrated circuit  166  to the protective card  158  stronger than the adhesion between the integrated circuit  166  and the SS substrate  164 . The adhesive will be sufficiently strong to make it difficult to remove the integrated circuit  166  from the protective card  158  without damaging the integrated circuit. 
     A further embodiment of the protective card  158  with a hole  159  that goes all the way through the card is shown in  FIG. 3   b . In the embodiment of  FIG. 3   b , the integrated circuit  166  is secured to the support card  158  by filling the empty space of the hole with a fill material such as an adhesive. This fill material can be of any type suitable for use with the integrated circuit  166 . Preferably, the fill material will have properties that make the adhesion between the integrated circuit  166  to the protective card  158  stronger than the adhesion between the integrated circuit and the SS substrate  164 . The fill material should also preferably be sufficiently strong to make it difficult to remove the integrated circuit  166  from the protective card  158  without damaging the integrated circuit. The integrated circuit  166  is fixed within the protective card so that the outer surface of the integrated circuit  166   a  does not protrude beyond the outer surface  158   a  of the protective card  158 . In an embodiment where there is fill material present on the outer surface  166   a  of the integrated circuit, the level of the fill material does not protrude beyond the outer surface  158   a  of the protective card  158 . Further, the thickness of the second PSA  160  in combination with the thickness of the protective card  158  will also be sufficient to ensure that the outer surface of the integrated circuit  166   a  does not protrude beyond the outer surface of the protective card  158   a . Accordingly, a flush surface is presented for application of the optional label  170 . As shown in  FIG. 2 , the outer layer  158   a  of the protective card  158  is optionally covered with a third PSA  168  to which an optional label  170  may be affixed. 
     If someone tries to remove the integrated circuit  166  for illicit purposes, they must remove it from the protective card  158 . However, this process would result in the integrated circuit  166  (which is susceptible to mechanical damage or electrostatic discharge) being rendered inoperable. 
     Tamper resistance of the tag embodied in  FIG. 2  is achieved through the use of destructable substrates, by varying the adhesion between the various layers and components, and by preventing access to internal structures. Examples of certain features of the tag of the invention are described in detail below. The features described below are merely illustrative and are not intended to be limiting, and it should be apparent to one of skill in the art that there are further features of the tag which fall within the scope and spirit of the invention. 
     In a preferred embodiment, the release liner  152  covering the first PSA  150  is made of polyethylene terephthalate (PET). Further, the release liner  152  may be transparent, allowing for inspection of the optional customer graphics on the substrate  154 . In one embodiment of the invention, the release liner  152  is printed with the words “Remove this Liner,” or other similar instructions to facilitate end-use installation. 
     The two sides of the first PSA  150  have different adhesive properties that make the adhesion of the substrate  154  to the windshield  110  stronger than that adhesion of the substrate  154  to the protective card. This difference in adhesion between varying surfaces is important for the tamper resistance of the tag. Further, it is desirable that the first PSA  150  be optically clear, so that any graphics printed on the substrate  154  are visible through it. Ideally, the first PSA  150  is also resistant to discoloration or loss of adhesion upon long term exposure to sunlight and heat, as it is this layer that makes contact with the windshield of the automobile. Preferably, the first PSA  150  is an acrylic transfer adhesive, but it could also be any type of adhesive that satisfies the adhesion properties necessary for the tamper resistance of the tag. 
     It is preferred that the substrate  154  be opaque to be able to obscure the internal parts of the tag from view while further providing a good background for optional customer graphics. As graphics can be printed on the substrate  154 , it is desirable that the substrate  154  be white or of a light color to make the graphics easier to see. In a preferred embodiment, graphics, if desired by the customer, may be applied to the substrate  154  by a pad printing process. Further, the material for the substrate  154  may be chosen to allow for the application of the antenna  156  on one of its surfaces. 
     The substrate  154  can be made from a wide variety of materials, with the destructibility of the substrate  154  being a desirable property. As a non-limiting example, the substrate  154  may be made out of a low melting point material that is easily destroyed upon tampering with the tag, such as polyethylene terephthalate (PET) or polyethylene napthalate (PEN). As a further non-limiting example, the substrate may be made out of paper. Generally, the substrate may be made out of a material that rips, tears or breaks easily, such as a flexible vinyl. Further, the substrate may be of a thickness that causes it to be easily destroyed by tampering. 
     In a preferred embodiment, the antenna  156  of the invention is printed onto the inside-facing surface of the substrate  154 , preferably through a screen printing process. In one embodiment, the antenna  156  is composed of a conductive thermoset ink containing silver. It is also preferred that the antenna  156  have geometric features that increase the likelihood that the antenna  156  will be destroyed if the invention is removed from a windshield. These geometric features may include, reduced surface area of the antenna (such as antennas with an annular shape), specific shapes that concentrate the stresses placed upon the antenna during tampering (such as notches in the edges of the antenna), and/or orientation of the antenna so that the stresses placed upon the antenna occur across areas of shorter geometry (i.e. the antenna is oriented so that the stresses occur across the antenna in the direction of its smallest dimension). It is also preferred that the antenna  156  have an aperture-based design that is optimized for use with the integrated circuit  166  of the invention. An example of an antenna that can be used in the invention is described in U.S. patent application “RFID Tag With Small Aperture Antenna,” Ser. No. 11/121,140, which is hereby incorporated by reference herein. 
     The second PSA  160  preferably consists of acrylic double-coated tape. As will be discussed below, it is important that the second PSA  160  have adhesive properties that make substrate-to-protective card adhesion weaker than the substrate-to-windshield adhesion caused by the first PSA  150 . It is also preferred that the second PSA  160  have an annular shape to facilitate tag destruction by reducing the adhesive surface area between the substrate  154  and the second PSA  160  and between the second PSA  160  and the protective card  158 . As mentioned, the second PSA layer  160  should be thick enough so that the outer surface of the integrated circuit  166   a  does not protrude past the outer surface  158   a  of the protective card  158 . 
     Turning to the strap subassembly (SS) part of the invention, it is preferred that the SS substrate  164  is made of polyimide. Preferably, the SS substrate  164  serves to not only accept the integrated circuit  166  and coupling circuitry, but also serves as one part of the dielectric of the circuitry coupling the antenna  156  to the SS capacitive coupling element  165 . Further, the SS substrate  164  may have destructibility properties similar to those of the substrate  154 . The SS substrate  164  should be as thin as possible, without detracting from the function of the tag. 
     The strap subassembly PSA (SSPSA)  162  is preferably made of an acrylic transfer adhesive. The SSPSA  162  serves to not only attach the SS securely to the antenna  156 , but also serves as the second part of the dielectric of the circuitry coupling the antenna  156  to the SS capacitive coupling element  165 . It is preferable that the SSSPSA  162  adhere the antenna  156  to the SS substrate  164  with enough strength so that the bond between the integrated circuit  166  and the SS capacitive coupling element  165  will fail before the bond between the antenna  156  and the SS substrate  164  fails. Preferably, the SSPSA  162  is an acrylic transfer adhesive, but it could also be any type of adhesive that satisfies the adhesion properties necessary for the tamper resistance of the tag. 
     The SS capacitive coupling element  165  of the invention serves at least two purposes. First, it carries electrical signals between the integrated circuit  166  and the coupling circuitry, and second, it comprises one side of the coupling circuitry. In a preferred embodiment, the SS capacitive coupling element  165  is made of copper and is patterned in a subtractive etching process. The SS capacitive coupling element  165  may also have a coating to prevent corrosion and to facilitate reflow solder processing. It should be appreciated that the integrated circuit  166  may also be non-capacitively coupled to the antenna  156  with a connection that is mechanically weak to satisfy the tamper resistant properties of the tag. 
     The integrated circuit  166  of the present invention is attached to the SS in a manner that gives the attachment a minimal mechanical strength needed to operate under normal conditions. Because of this, the circuit  166  is more likely to become separated from the coupling circuitry if an attempt is made to remove the tag  120 . In a preferred embodiment, the integrated circuit  166  is attached with a lead-free solder, and only the Input and Ground pins of the circuit are soldered to the SS capacitive coupling element  165 . It is contemplated that the integrated circuit  166  can be attached by the soldering of additional pins to the SS capacitive coupling element. Further, the use of other attachment means, such as conductive epoxies, are also contemplated by the invention. It is preferred that the integrated circuit  166  be attached to the SS capacitive coupling element  165  in the weakest manner possible that does not interfere with the reliability of the tag for normal everyday use. 
     A primary purpose of the protective card  158  of the invention is to prevent the removal of the tag  120  for unauthorized uses. This is preferably done by preventing access to the first PSA  150 . In a preferred embodiment, the protective card  158  is made of polycarbonate, but it may also be made of other plastics or materials. In one embodiment, the protective card  158  is white in color, although other colors are contemplated by the invention. It is important that the protective card  158  be of a significant thickness to reduce access to the first PSA  150 . Preferably, the protective card  158  is about 0.04 inches thick, but could be thicker or thinner depending on the other components of the tag. It is also preferable that, after application, the protective card  158  is separated from the windshield by approximately 0.004 inches. This separation can be varied by varying the thickness of the first PSA  150  and the substrate  154 . Although greater separation from the windshield is contemplated by the invention, separation of 0.004 inches or less is ideal for preserving the tamper resistant features of the tag. 
     The differences in the adhesion properties between different layers of the tag may be further enhanced by varying the surfaces of the protective card  158 . In a preferred embodiment, the outer surface  158   a  of the protective card  158  is smooth, while the inner surface  158   b  is rough. The rough inner surface  158   b  of the protective card  158  reduces the surface area of contact between the protective card  158  and the second PSA  160 , further enhancing the destructibility of the tag. As a non-limiting example, the inner surface  158   b  of the protective card  158  may be made with a stippled surface during the molding of the card. It should be apparent that other variations in the surface of the protective card  158  that change its adhesion properties are also contemplated by the invention. 
     The optional label  170  conceals the internal features of the tag while also providing a surface for the optional display of graphics and/or information identifying the tag. The label  170  may be made of PET. Ideally, the label  170  is purchased with customer specific graphics already printed on it, and can easily be dispensed from a roll for application during manufacturing of the tag. During the manufacturing process, the identification information specific to that tag may be printed on the label  170 , such as an identification number. As the label  170  is likely purchased, the third PSA  168  will typically be pre-applied to the label  170 . 
     The embodiment of the tag shown in  FIG. 2  operates in the following manner. An interrogator, such as from a toll booth reader/transceiver, transmits an interrogation signal to the tag. The antenna  156  converts the electromagnetic energy into alternating currents. The antenna  156  is capacitively coupled to the integrated circuit  166 , with the SSPSA  162  and SS substrate  164  acting as a dielectric. This entire capacitive coupling forms the circuit of the invention. The alternating current on the antenna  156  side of the circuit results in time-varying electromagnetic (EM) fields appearing across the circuit. The EM fields induce an alternating current on the integrated circuit  166  side of the circuit. The alternating current is then rectified by the integrated circuit  166 . The integrated circuit  166  detects that modulation is absent from the signal and begins to modulate the intrinsic impedance of the antenna  156 . This results in a modulated backscatter from the tag that is detected by the interrogator and processed. In a preferred embodiment, the tag in powered by energy conveyed in the interrogation signal. However, separate power sources, such as a battery or solar cell, are also contemplated by the invention. 
     The tamper resistance of the embodiment of the tag of  FIG. 2  will now be described. In one scenario, an attempt is made to remove the tag using only the fingers. The tag is thin, fits close to the windshield, and lacks the topographical features necessary for gripping and removing the tag. As such, it becomes necessary to insert the fingernails between the tag and the windshield to begin to peel the tag away. 
     The first PSA  150  is made up of a strong adhesive, so the tag is securely adhered to the windshield, requiring successive force to peel it away. For example, the first PSA  150  may be made up of an adhesive layer that has a peel adhesion strength to stainless steel of about 1200 N/m. By contrast, the second PSA  160  is made up of a weaker adhesive that, upon tampering, will fail before the first PSA  150 . For example, the second PSA  160  may be made up of an adhesive layer that has a peel adhesion strength to stainless steel of about 650 N/m. It should be appreciated that adhesive layers with different peel adhesion strengths are also contemplated by the invention, with the primary concern that the first PSA  150  has a higher peel adhesion strength than the second PSA  160 . 
     The protective card  158  is separated from the windshield by the first PSA  150  and the substrate  154  by a distance of approximately 0.004 inches. A fingernail is approximately 0.012 inches thick and is somewhat blunt edged. As such, force applied with a fingernail will not be able to be directed to the first PSA  150 , but will instead be directed to the protective card  158 . The initial sequence of events that occur during an attack by hand to the bottom right corner of the tag are shown schematically in  FIG. 4 . Once the wedge force applied by the fingernail exceeds the stiffness of the protective card  158 , the protective card  158  will begin to flex locally away from the windshield. As the protective card  158  flexes, the first PSA  150  and second PSA  160  are put in tension. The tension in the first PSA  150  is counterbalanced by its adhesion to the windshield and the substrate  154 , while the tension in the second PSA  160  is counterbalanced by its adhesion to the substrate  154  and the protective card  158 . 
     As the person attacking the tag begins to apply a pulling force away from the windshield, the protective card  158  continues to flex and the tension increases in the first PSA  150  and second PSA  160 . As diagrammed in  FIG. 4 , the tension in the second PSA  160  eventually exceeds the adhesive strength between the second PSA  160  and its adjacent layers. At this point, the protective card  158  begins to locally come away from the substrate  154 , which remains adhered to the windshield, while a propagation front of adhesive failure  190  (delamination) forms (see  FIG. 4 ). As the pulling force continues, the delamination progresses along the width of the second PSA  160  until the front reaches the center opening  161 , when the tensional forces are transferred to the SS. The tension across the SSPSA  162  is balanced with the integrated circuit&#39;s  166  attachment to the SS substrate  164  and with the adhesion between the integrated circuit  166 , encapsulant for the integrated circuit and the protective card  158 . 
     As the tension across the SSPSA  162  and the integrated circuit  166  attachment increases, one of two things will happen. Most likely, the integrated circuit  166  attachment will fail, leaving the SS capacitive coupling element  165  and SS substrate  164  attached to the windshield while the integrated circuit  166  remains encapsulated in the now separated protective card  158 . This is the preferred destruct mode. If the pulling force is released before complete separation of the tag layers, the performance of the tag will be at least severely limited if the protective card  158  is somehow stuck back down to the substrate  154 . Once the protective card  158  and integrated circuit  166  are pulled completely away from the substrate  154  and SS, the tag will be rendered inoperable, because the integrated circuit  166  will no longer communicate with the coupling element  165  and the antenna  156 . Further, if the protective card  158  and integrated circuit  166  are removed and applied, through whatever means, to the windshield of another automobile, it will be visibly obvious that the tag has been tampered with. 
     If the IC attachment does not fail, then the SSPSA  162  will begin to fail, resulting in the SS substrate  164  being held to the protective card  158  by the encapsulant and the integrated circuit  166  attachment. When the circuit  166  is pulled away from the antenna  156 , this will destroy communication between the two and render the tag inoperable. If the pulling force is released before complete separation and the protective card  158  stuck back down on the substrate  154 , the tag will function, at best with limited operability. Once the protective card  158  and the SS are pulled completely away from the substrate  154 , the tag will be rendered completely inoperable. Further, if the protective card  158  and the SS are removed and somehow applied, through whatever means, to the windshield of another automobile, it will be visibly obvious that the tag has been tampered with. 
     If the protective card  158  and the SS  162 ,  164 ,  165  are able to be removed together, the circuit may be susceptible to illicit use. Because of this, a preferred embodiment of the invention has an integrated circuit  166  attachment that is much more likely to fail than the SSPSA  162 . This makes destruction of the tag through removal of only the protective card  158  and integrated circuit  166  much more probable than the protective card  158  and the SS substrate  164  being removed together. 
     In another scenario, the embodiment of the tag of  FIG. 2  is attacked by an instrument such as a thin razor blade or flexible putty knife. This type of attack is envisioned to be directed at the first PSA  150 , as attack of any other layer would result in destruction of the substrate or delamination of the tag. 
     If the tag were attacked by a razor blade, the following sequence of events would likely occur. If the razor blade is applied at a low angle to the glass it is possible to directly apply force to the first PSA  150 , as the razor blade is thinner than the separation between the windshield and protective card  158 . Force would be applied to the blade in a direction lateral to the glass, allowing the blade edge to cut the first PSA  150  away from the windshield. As the blade continues into the tag, more of the upper face of the blade makes contact with the first PSA  150 . Adhesion between the blade surface and the first PSA  150  exerts a shear stress on the substrate  154 , which is supported by the second PSA  160 . As the blade continues laterally along the glass past the annular section of the second PSA  160  into the center section  161 , the substrate  154  is no longer supported and shear stress caused by the blade coupled through adhesion of the first PSA  150  to the blade causes the substrate  154  and antenna  156  to tear. This damage to the substrate  154  and antenna  156  will render the tag inoperable. Further, the damage to the substrate will likely be extensive enough to make it visibly obvious that the tag has been tampered with if transferred to another vehicle. 
     From the above descriptions, it should be apparent that variations in the adhesions or attachments of the various layers and components of the tag are what gives the tag its destructibility. Generally, it is important that at least the antenna  156  be attached to a windshield  110  in manner that is stronger than the attachment of the circuit  166  to one part of the coupling circuitry, i.e. stronger than the attachment of the circuit  166  to the coupling element  165  or stronger than the attachment of the circuit to the antenna  156 . These attachments can take place directly or through the sequential attachment of several layers. Once the communication between the antenna  156  and the integrated circuit  166  is destroyed, the tag will be rendered inoperable. 
       FIG. 5  shows another embodiment of a tag of the invention, in which a SS component is not incorporated. The tag shown in  FIG. 5  incorporates many of the same components as the tag shown in  FIG. 2 . Those components with the same numbers are meant to have the same attributes as already described. 
     As the embodiment of  FIG. 5  does not have a SS, the integrated circuit  166  is directly attached to the substrate  154 . Because a preferred embodiment of the antenna  156  of the invention requires capacitive coupling to the integrated circuit  166 , the surfaces of the substrate  154  may vary from those described in  FIG. 2 . In a preferred embodiment, the antenna  156  is applied on the outside surface  154   b  of the substrate  154 , while a capacitive coupling element  172  is applied on the inside surface  154   a . In this embodiment, the substrate  154  act as the dielectric in the capacitive coupling. 
     The circuit attachment of the embodiment of  FIG. 5  may be achieved by a variety of methods. The circuit may be attached by soldering, as described above. However, in a preferred embodiment in which a low melting temperature substrate  154  is used, the integrated circuit  166  can alternatively be attached with a conductive epoxy and additional strain relief may be applied to the weak attach points. Further, other methods can be used to attach the integrated circuit  166  to the substrate  154 , especially methods that allow for reliable attachment of a controllable strength without the melting of the substrate. 
     As the antenna  156  is facing outward from the tag in the embodiment of  FIG. 5 , this embodiment further contemplates an optional ink flood coat. This flood coat can be used to provide a uniform color base for optional customer graphics on the substrate  154  and also can be used to hide the antenna  156  from view. 
     Upon removal of the tag shown in  FIG. 5 , the protective card  158  and integrated circuit  166  will be separated from the substrate  154 . This will cause the separation of the integrated circuit  166  from the capacitive coupling element  172 , destroying communication between the integrated circuit  166  and the antenna  156 . This type of destruction is facilitated by the fact that the attachment of the substrate  154  to the windshield  110  is stronger than the attachment of the protective card  158  to the substrate  154 . 
     A further embodiment of a tag of the invention is shown in  FIG. 6 . This embodiment incorporates a smaller substrate  174  to allow for the elimination of the second PSA  160 . Eliminating the need to manufacture the annularly shaped second PSA layer further reduces manufacturing costs. The tag shown in  FIG. 6  incorporates many of the same components as the tag shown in  FIG. 2 . Those components with the same numbers are meant to have the same attributes as already described. 
     The embodiment of  FIG. 6  eliminates the need for a second PSA by incorporating a substrate  174  with smaller dimensions than the other components of the tag (with the exception of the components of the SS). Except for its smaller dimensions, the substrate  174  has all of the same attributes as the substrate  154 , and most importantly, is highly destructible. The first PSA  150  has the same attributes as described above. However, it is important that the properties of the first PSA  150  and the protective card  158  are such that the substrate to windshield adhesion is stronger than the windshield to protective card adhesion. 
     It should also be appreciated that the embodiment shown in  FIG. 6  can be manufactured without the SS, using the antenna  156  and integrated circuit  166  attachment scheme described in  FIG. 5 . 
     The embodiment shown in  FIG. 6  will destruct upon removal in a manner analogous to the destruction of the embodiment of  FIG. 2 . Most likely, the embodiment of  FIG. 6  will be rendered inoperable by the separation of the protective card  158  and the integrated circuit  166  from the capacitive coupling element  165 . It is also possible that the tag will be rendered inoperable by the separation of the protective card  158 , integrated circuit  166  and SS substrate  164  from the substrate  174  and antenna  156 . 
     In a further embodiment, a full sheet second PSA layer may be used to reduce the costs associated with manufacturing an annular second PSA layer. As tamper resistance is partly dependant on the substrate not being supported, it would be possible to add an additional layer to block adhesion of the second PSA to the center of the protective card  158  and or the SS. In a preferred embodiment, this additional layer is made of Teflon, although it could be made of any layer that would prevent adhesion. 
     In a still further embodiment, a full sheet second PSA layer may be used with a modified protective card  178  as shown in  FIG. 7 . The modified protective card  178  also contains a center hole  179  to allow for the encapsulation of the integrated circuit  166 . Surrounding this hole is a surface  184  that is able to be contacted with the SS. A central region of the card is recessed  180  so that only the outer annular region of the card  182  makes contact with the second PSA. This type of card could be used, along with a full sheet second PSA, in embodiments similar to those shown in  FIGS. 2 and 5 . 
     Although certain presently preferred embodiments of the present invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.