Patent Description:
It is known for packages for microwavable food items to include cooking aids that are to be placed into the microwave oven with the food item for cooking/heating the food item. For example, foods having crusts, such as frozen pies or stuffed bread, may benefit from "crisping sleeves," which are paper items that at least partially surround the food item during microwaving. Typically, a "crisping sleeve" has a paper substrate, with a susceptor incorporated into the inner surface of the "crisping sleeve," facing and preferably in contact with the food item. The susceptor, which may be a metallized film, absorbs microwave energy and converts it into heat, which crisps and/or browns the crust or surface of the food item, thus improving the look and texture of the food item. Due to the absorbing nature of the film used as the susceptor, relatively low levels of energy are reflected by it, such that it does not strike an arc due to generating high differential voltages between adjacent parts of the film, which could otherwise cause the packaging to catch fire.

It is also known to incorporate RFID technology, such as an RFID tag, into product packaging for various purposes, including inventory management and theft prevention. <FIG> shows an RFID tag T according to conventional design, which may be secured to or otherwise associated with an enclosure like that of enclosure <NUM> of <FIG> (typically, a paper or cardboard sleeve or box) of the package <NUM> for a microwavable food item in respect to <FIG>. The entirety of the packaging <NUM> of <FIG> is not intended to be microwaved, but rather the food item (and, optionally, a "crisping sleeve" or the like) is removed from the enclosure <NUM> of <FIG> and inserted into the microwave oven for heating/cooking.

The RFID tag T of <FIG> includes an RFID chip C, with an associated dipole antenna A for transmitting information to and/or receiving information from an RFID reader (not illustrated). The RFID chip C is electrically coupled to the antenna A across a gap G defined by the antenna A between two conductor pad areas P.

RFID tags inherently must, at some point, have a gap across which the RFID chip is placed that has a voltage at the intended frequency of operation when in the field of a reader device. The power required incident on the RFID chip C may be as low as <NUM> microwatts, whereas a microwave oven may typically operate at a power level in excess of <NUM> watts, which can generate very high voltages across the gap G and the associated RFID chip C. The antenna A is designed to operate at a first frequency F1, for example in the range of approximately <NUM> to <NUM>, with the antenna A taking incident power at the first frequency F1 from an RFID reader and converting it to a voltage across the RFID chip C to allow it to operate.

A second frequency applied by the microwave oven, identified in <FIG> at F2, typically on the order of approximately <NUM>,<NUM>, may also be incident on the antenna A when the RFID tag T is placed into the microwave oven. The antenna A is not designed to operate at the second frequency F2, as the very high power levels incident at second frequency F2 will generate high voltages on the antenna A. These high voltages can appear at a number of places on the antenna A; however, by methods such as introducing large gaps L between antenna elements and controlled radii (identified generally at R in <FIG>), a voltage across said elements that would generate a high voltage breakdown and, hence, arc can be avoided. However, the gap G bridged by the RFID chip C is necessarily relatively small and, hence, a high voltage arises at the second frequency F2, which high voltage may cause a breakdown and generate an arc. Similarly depicted in <FIG>; the dipole antenna <NUM> can receive microwave energy (identified in <FIG> at M) and reflect the microwave energy (represented in <FIG> at R) into the microwave source. There is the possibility that an arc may be created between adjacent sections of the dipole antenna <NUM> (which location may be between the two conductive elements of the dipole antenna <NUM>, as identified in <FIG>at <NUM>). Additionally, referring to <FIG> the dipole antenna <NUM> of the conventional RFID tag <NUM> is formed of relatively thick, low resistance conductor, which has different properties than the metallic film used to define a typical susceptor. For example, common susceptors are made from metal-coated films with optical densities ranging from <NUM> to <NUM>, corresponding to a sheet resistance of <NUM> ohms to <NUM> ohms, whereas a material of less than <NUM> ohm per square is commonly used to form the antenna <NUM> of the RFID tag <NUM>. On account of the characteristics of the dipole antenna <NUM>, the RFID tag <NUM> can cause issues if it is not dissociated from the food item prior to microwaving the food item (i.e., if the entire package <NUM> of <FIG> is placed into the microwave oven).

To avoid problems of this nature, the RFID tag T and <NUM> of <FIG> respectively, are typically configured to be readily removable or otherwise dissociable from the food item, such as by securing it to the enclosure of the package, which may include instructions to not microwave the enclosure. However, it is possible that a user failing to take proper care could place the entire package (including the RFID tag T and <NUM> shown in <FIG> respectively) into the microwave oven with the food item, thereby failing to dissociate the RFID tag T or <NUM> from the food item. Accordingly, it would be advantageous to provide an RFID tag that may be microwaved without resulting in the problems associated with microwaving a conventional RFID tag T or <NUM>.

<CIT> describes a plurality of antennas for receiving the radio wave, the IC portion for signal-processing the received radio wave, and thermal fuses arranged in connection portions between the antenna and the IC portion. The thermal fuse detects and cuts-by-melt a heat according to a heat-generation of the IC portion accompanied with the reception of the radio wave with a non-intentional and intensive level and separates the antenna and the IC portion. As the antenna is separated non-reciprocally, a surplus feed to the IC portion is stopped compulsorily and a breakage of the IC portion by heat is avoided.

<CIT> describes a microwavable package including one or more microwave-absorbing regions, microwave-shielding regions, and/or embossed regions designed to enhance microwave cooking of food products including raw meat, poultry, and fish as well as breaded, battered, and dough containing items. Microwave-absorbing regions (i.e., solid susceptors) may promote thermal cooking, browning, and/or crisping of food products. Microwave-shielding regions (i.e., patterned susceptors) may promote uniform cooking and inhibit overcooking of food products.

<CIT> describes a Radio Frequency Identification (RFID) tag including an integrated circuit (IC) chip and an antenna. The IC chip is enclosed inside a coating of endothermic material. The endothermic material includes silicon resin or ceramic resin or both.

There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as may be set forth in the claims appended hereto.

The underlying technical problem is solved by an RFID tag and a package for a microwavable food item comprising the RFID tag having the features of claims <NUM> and <NUM>, respectively. Additional embodiments are defined in the dependent claims.

<FIG> and <FIG> show an RFID tag <NUM> according to the present disclosure, while <FIG> shows the RFID tag, generally designated at <NUM>, secured to the enclosure <NUM> (e.g., a paper box) of packaging, generally designated at <NUM>, for a microwavable food item. The packaging <NUM> may include other items, such as a "crisping sleeve" configured to be microwaved with the food item. The RFID tag <NUM> may be incorporated into the packaging <NUM> by any suitable approach and, while the RFID tag <NUM> is secured to the enclosure <NUM> in the embodiment of <FIG>, the RFID tag <NUM> may be associated with another portion of the packaging <NUM> (e.g., a "crisping sleeve" housed within the enclosure <NUM>) in other embodiments. Further, while RFID tags are described herein as being incorporated into the packaging of a microwavable food item, it should be understood that RFID tags according to the present disclosure may be useful in any of a number of possible applications, particularly when it is contemplated that they may be exposed to frequencies (referred to herein as a "second frequency") that are significantly higher than the frequency (referred to herein as a "first frequency") at which an antenna of the RFID tag is intended to operate.

The RFID tag <NUM> includes an antenna <NUM> with an RFID chip <NUM> electrically coupled thereto. The antenna <NUM> is provided as a dipole antenna, which is formed of a conductor defining a gap <NUM> between two conductor pad areas <NUM> (<FIG>), which is bridged by the RFID chip <NUM>. The antenna <NUM> and RFID chip <NUM> may be provided generally according to conventional design (e.g., as described above with respect to the embodiment of <FIG>), with the antenna <NUM> being designed to operate at a first frequency, which may be in the range of approximately <NUM> to <NUM>. As in the conventional RFID tag T, the antenna <NUM> takes incident power at the first frequency and converts it to a voltage across the RFID chip <NUM> to allow it to operate.

The RFID chip <NUM> may take any of a number of forms (including those of the type commonly referred to as a "chip" or a "strap" by one of ordinary skill in the art), including any of a number of possible components and being configured to perform any of a number of possible functions. For example, in one embodiment, the RFID chip <NUM> includes an integrated circuit for controlling RF communication and other functions of the RFID tag <NUM>.

The RFID tag <NUM> further includes a shielding structure, generally designated at <NUM>, which is comprised of a shield conductor <NUM> and a shield dielectric <NUM>. The shield conductor <NUM> is formed of a material having conductive properties and, as will be described in greater detail, may be variously configured without departing from the scope of the present disclosure. The shield dielectric <NUM> is formed of a material having dielectric properties and, as will be described in greater detail, may be variously configured without departing from the scope of the present disclosure. For example, in the embodiment of <FIG> and <FIG>, the shield conductor <NUM> and shield dielectric <NUM> are generally flat or planar, substantially identically shaped, and oriented with the perimeter of the shield conductor <NUM> coinciding with the perimeter of the shield dielectric <NUM>. In other embodiments, the shield conductor and shield dielectric may be differently configured and/or oriented at least partially out of alignment (i.e., with a portion of the shield conductor extending beyond the perimeter of the shield dielectric and/or a portion of the shield dielectric extending beyond the perimeter of the shield conductor).

The shielding structure <NUM> is electrically coupled to the antenna <NUM> across the gap <NUM>, being coupled by capacitance to the conductor pad areas <NUM> on either side of the gap <NUM> (<FIG>). As shown in <FIG>, the shielding structure <NUM> overlays the RFID chip <NUM>, with the shield dielectric <NUM> at least partially positioned between the RFID chip <NUM> and the shield conductor <NUM>. The shielding structure <NUM> may overlay or cover all (as in <FIG> and <FIG>) or only a portion of the gap <NUM>.

As described above, it is possible for the RFID tag <NUM> to be exposed to signals operating at first or second frequencies. When the RFID tag <NUM> is exposed to the first frequency, the shielding structure <NUM> forms a partial short circuit across the gap <NUM>. However, the antenna <NUM> is configured so as to compensate for the presence of the partial short circuit, thereby allowing the RFID tag <NUM> to operate properly.

As described above, when a conventional RFID tag T is exposed to the second frequency F2, a large voltage arises across the gap G, which risks the creation of an arc. If the voltage and power at the second frequency F2 are limited sufficiently, the RFID chip C may survive, but the main objective is to prevent an arc that could ignite the RFID tag T or the packaging <NUM> into which it is incorporated. The shielding structure <NUM> of <FIG> and <FIG> provides this function by "shorting" the high voltage generated across the gap <NUM> (and, hence, the RFID chip <NUM>) when the RFID tag <NUM> is exposed to the second frequency, thereby reducing the voltage below the level that can cause a breakdown and possible arc, which prevents ignition. Accordingly, the RFID tag <NUM> may be placed into a microwave and exposed to the attendant high-frequency signals (which may be on the order of approximately <NUM>,<NUM>) without the risk of ignition, unlike a conventional RFID tag T.

The shielding structure may be variously configured without departing from the scope of the present disclosure, as noted above. For example, <FIG> show an embodiment of an RFID tag, generally designated at 10a, (and associated packaging, generally designated at 14a, in <FIG>) in which the shielding structure 24a includes a differently configured shield dielectric 28a (<FIG>). In the embodiment of <FIG>, the shield dielectric 28a is incorporated into an over-lamination layer, which overlays the RFID chip <NUM>, at least a portion of the gap <NUM>, and at least a portion of the conductor pad areas <NUM> of the antenna <NUM> (<FIG>). The shield conductor 26a may comprise a patterned conductor to provide the desired bridging and shielding effects. As best seen in <FIG>, the shield conductor 26a and shield dielectric 28a may be differently sized and shaped, with the shield conductor 26a being smaller than the over-lamination layer into which the shield dielectric 28a is incorporated.

<FIG> illustrate another embodiment of an RFID tag, generally designated at 10b, according to the present disclosure. In the embodiment of <FIG>, the shielding structure, generally designated at 24b, is incorporated into an RFID strap comprised of a strap conductor <NUM> and strap substrate <NUM> (along with the RFID chip <NUM>), which is electrically coupled to the antenna <NUM>, across the gap <NUM>. The shielding structure 24b may be comprised of a shield conductor 26b applied to the strap substrate <NUM>, which serves as the shield dielectric 28b. The strap substrate <NUM> (and any of the other shield dielectrics described herein) may be formed of any of a variety of materials, such as polyethylene terephthalate.

<FIG> illustrates another embodiment of an RFID tag, generally designated at 10c, with a differently configured shielding structure 24c. In the embodiment of <FIG>, the shield conductor 26c includes an extended area <NUM>, which may increase the size of the shield conductor 26c beyond that of the associated shield dielectric (which is not visible in <FIG>). In contrast to other embodiments, in which the shielding structure is primarily configured and oriented to overlay or cover the gap <NUM>, the extended area <NUM> of the shield conductor 26c is oriented so as not to overlay the gap <NUM> (or the antenna <NUM>), but rather is positioned laterally of the antenna <NUM> and the gap <NUM>, extending away from the antenna <NUM>. The extended area <NUM> of the shield conductor 26c may be variously sized and configured without departing from the scope of the present disclosure, being approximately the same size as the shield conductor <NUM> of <FIG> and <FIG> in one embodiment, larger than the shield conductor <NUM> of <FIG> and <FIG> in another embodiment, and smaller than the shield conductor <NUM> of <FIG> and <FIG> in yet another embodiment.

Regardless of the particular size and configuration of the extended area <NUM> of the shield conductor 26c, the extended area <NUM> assists in dissipating heat generated across the gap <NUM>. This effect is enhanced by increasing the size of the extended area <NUM>, so it may be advantageous for the extended area <NUM> to be relatively large for improved heat dissipation. The extended area <NUM> (along with the remainder of the shield conductor 26c, as well as any of the other shield conductors described herein) may be formed of a non-flammable material, such as but not limited to, an aluminum material, heat resistant, flame resistant paper (Flex Dura HR, http://www. flexlinkllc. com/heat-resistant-paper. html), and non-flammable adhesive (Eclectic E6000 Adhesive, http://eclecticproducts. com/products/e6000. html) to provide a barrier to any arc that may be generated across the gap <NUM> to prevent a fire from spreading.

<FIG> illustrate yet another embodiment of an RFID tag, generally designated at 10d, (and associated packaging, generally designated at 14d, in <FIG>) with a differently configured shielding structure 24d. In the embodiment of <FIG>, the shield dielectric 28d is formed of a material which undergoes reversible or non-reversible dielectric breakdown at high voltages of the type induced by a high-power microwave field. By such a configuration, the shorting effect provided by the shielding structure 24d in the presence of a second frequency (e.g., in a microwave field) may be enhanced. In this embodiment (as well as in other embodiments described herein), the shield conductor 26d may be formed by printing a conductive material (which becomes and defines the shield conductor 26d) onto the shield dielectric 28d, such as an over-lamination.

A single RFID tag may include more than one shielding structure, as shown in the embodiment of <FIG> and <FIG>. In <FIG>, the RFID tag, generally designated at 10e, is provided with a first shielding structure, generally designated at 24e, in general accordance with the preceding description of the embodiment of <FIG>. Rather than the antenna <NUM> of the RFID tag 10e being free for direct connection to the enclosure of packaging (as in <FIG>), a second shielding structure, generally designated at 24f, (<FIG>) is associated with an underside of the antenna <NUM>, with the second shielding structure 24f underlying the RFID chip <NUM> (i.e., with the shielding structures 24e and 24f electrically coupled to opposing faces of the antenna <NUM>). The shield dielectric 28f of the second shielding structure 24f contacts the underside of the antenna <NUM>, while the associated shield conductor 26f is free to be secured or otherwise associated to the enclosure of a package for microwavable food or the like.

In the illustrated embodiment, the second shielding structure 24f is substantially identical to the first shielding structure 24e, but it is within the scope of the present disclosure for the shield conductor 26f and/or the shield dielectric 28f of the second shielding structure 24f to be differently configured from the shield conductor 26e and shield dielectric 28e of the first shielding structure 24e. Regardless of the particular configurations of the two shielding structures 24e and 24f, by providing them on both faces of the antenna <NUM>, additional shielding is provided. This additional shielding involves additional "shorting," as there are now two partial short circuits across the gap <NUM>. However, in accordance with the preceding description of the embodiment of <FIG> and <FIG>, the antenna <NUM> is configured so as to compensate for the presence of the partial short circuits, thereby allowing the RFID tag 10e to operate properly when exposed to the first frequency.

<FIG> is a basic equivalent circuit representing the basic components of an RFID tag <NUM> according to the present disclosure. In <FIG>, the gap <NUM> defined by the antenna <NUM> is bridged by an RFID chip <NUM> (represented by a resistor RP and a capacitor CP) and a shielding structure <NUM> comprising a shield conductor <NUM> and a shield dielectric <NUM> (represented by two identical capacitors CB in series). The total capacitance of the shield dielectric <NUM> is half of the capacitance of the individual capacitors CB used to represent the shield dielectric <NUM> in <FIG>. This is calculated using the standard formula in which the total capacitance of a series of capacitors is the inverse of the sum of all inverse capacitances.

The impedance of the shield dielectric <NUM> is equal to the inverse of the product of <NUM> × π × F × total capacitance, in which F is the frequency at which the RFID tag <NUM> is powered. Thus, if the first frequency is on the order of approximately <NUM> and the second frequency is on the order of approximately <NUM>,<NUM>, then impedance drops by a factor of approximately three between the first and second frequencies, which enhances the "shorting" and, hence, shielding effect at the second frequency.

Additionally, there is the possibility that an arc may be created between adjacent sections namely gap G and associated RFID chip C. This is in part due to adjacent sections being surrounded by a material (i.e. air or other elements) having a dielectric strength lower than that of the electric field achieved by said differential voltages across said adjacent sections. Also an arc may be created and exacerbated in part due to materials surrounding said sections that reach a temperature, due to RF current flowing along/through said adjacent sections gap G and chip C, that lowers dielectric strength of the surrounding material as well as creates flammable/combustible volatiles. This arc can be avoided without the use of a shield by surrounding said sections with a material having the properties such as; a dielectric strength that can withstand the electric field at said sections, along with having heat resistant, flame resistant and non-flammable properties i.e. heat resistant and flame resistant paper and non-flammable adhesive(s).

In the illustrated embodiment of <FIG>, the enclosure <NUM> is associated with the RFID tag <NUM> includes an RFID chip <NUM> with an antenna <NUM> electrically coupled thereto. The antenna <NUM> is formed of a conductor <NUM> having a resistance that is greater than the resistance of the antenna <NUM> of a conventional RFID tag <NUM>, which allows the package <NUM> (including the RFID tag <NUM>) to be safely microwaved. For example, the conductor <NUM> may have a sheet resistance that is comparable to that of the sheet resistance of a susceptor (i.e., in the range of approximately <NUM> ohms to approximately <NUM> ohms). The conductor <NUM> may also have an optical density in the range of approximately <NUM> to <NUM>, similar to a susceptor. By such a configuration, when the RFID tag <NUM> is microwaved, it acts in the way that a susceptor does when being microwaved, by absorbing microwave energy M and heating up and reflecting minimal energy R', rather than reflecting high levels of energy to the microwave source or creating an arc.

The higher sheet resistance of the conductor <NUM> may affect the efficiency of the antenna <NUM> compared to the dipole antenna <NUM> of a typical RFID tag <NUM>. While the sheet resistance of the material (measured in ohms per square at a given thickness) is a fixed value, the resistance experienced by an RF current flowing through the conductor <NUM> may be effectively decreased by increasing the area of the conductor <NUM> (e.g., by increasing its thickness). This is particularly effective in reducing the resistance for an RF current, as skin depth is more of a factor than for a DC current, due to the tendency of an RF current to flow in the outer surface of the conductor <NUM> (i.e., as conductor thickness is reduced with respect to the skin depth, RF resistance becomes higher than DC resistance would be). Accordingly, it may be advantageous for the antenna <NUM> to have a relatively large area or thickness to decrease the RF resistance.

Compared to a dipole antenna, the conductor of a slot-loop hybrid antenna typically has a greater area, such that it may be advantageous for the antenna <NUM> to be provided as a slot-loop hybrid antenna (sometimes referred to as a "sloop" antenna), as in <FIG>. Such a slot-loop hybrid antenna <NUM> may be formed of a conductor <NUM> comprising a conductor sheet which, in the illustrated embodiment, is generally rectangular, with a slot <NUM> defined therein and positioned at an edge or end <NUM> of the conductor sheet <NUM>. As shown, the slot <NUM> may extend between a closed end <NUM> and an open end <NUM> associated with the end or edge <NUM> of the conductor sheet <NUM>. While there are various advantages to the antenna <NUM> being configured as a slot-loop hybrid antenna, it is within the scope of the present disclosure for the antenna <NUM> to be variously configured.

Further observing the RFID chip <NUM>, it may take any of a number of forms (including those of the type commonly referred to as a "chip" or a "strap" by one of ordinary skill in the art), including any of a number of possible components and configured to perform any of a number of possible functions. For example, in one embodiment, the RFID chip <NUM> includes an integrated circuit for controlling RF communication and other functions of the RFID tag <NUM>. In the illustrated embodiment, two ends or points of the RFID chip <NUM> are connected to the conductor sheet <NUM> at opposite sides of the slot <NUM>, adjacent to the open end <NUM> of the slot <NUM>, which serves to electrically couple the RFID chip <NUM> to the conductor sheet <NUM>.

According to an aspect of the present disclosure, which may be incorporated into the antenna <NUM> of the RFID tag <NUM> of <FIG> or may be separately practiced, an RFID tag <NUM> (<FIG>) that is suitable for incorporation into a package for a microwavable food item is configured to fracture into multiple pieces or otherwise dissociate upon being subjected to heating in a microwave oven. By fracturing, interaction with the microwave field is reduced, thereby avoiding the potential problems of excessive reflected microwave energy and/or the creation of an arc when the RFID tag <NUM> is heated in a microwave oven. Such a configuration allows for the resistance of the conductor <NUM> of the antenna <NUM> of the RFID tag <NUM> to be lower than in the embodiment of <FIG> (e.g., a sheet resistance of less than <NUM> ohms), if desired.

The RFID tag <NUM> shown in <FIG> is provided in accordance with the foregoing description of the RFID tag <NUM> of <FIG>, with an RFID chip <NUM> electrically coupled to the conductor sheet <NUM> of a slot-loop hybrid antenna <NUM>, although the antenna <NUM> may be differently configured without departing from the scope of the present disclosure.

Regardless of the particular configuration of the antenna <NUM>, its conductor sheet <NUM> is formed of at least two materials (a base material and a secondary material, which may be provided in a lesser quantity than the base material) having different coefficients of thermal expansion. By such a configuration, the materials expand at different rates when heated (e.g., in a microwave oven) until the conductor sheet <NUM> fractures into multiple pieces or otherwise dissociates. The magnitude of the difference in the coefficients of thermal expansion of the materials may vary without departing from the scope of the present disclosure, although a relatively large difference may be advantageous to more quickly cause the conductor sheet <NUM> to fracture or otherwise dissociate upon heating.

The conductor sheet <NUM> is formed of a base material, such as a plastic material, and a second material, such as a metallic material or conductive ink, which have different coefficients of thermal expansion. More particularly, the base material may be polyethylene terephthalate (which has a coefficient of thermal expansion of approximately <NUM>/(m K)), while the secondary material is aluminum (which has a coefficient of thermal expansion of approximately <NUM>/(m K)). When bonded together and heated, the aluminum will eventually break, thus rendering the RFID tag <NUM> inoperative or at least causing the RFID tag <NUM> to operate at a lower level, which reduces the interaction between the RFID tag <NUM> and the microwave field. While the base material has a greater coefficient of thermal expansion than the secondary material in this example, it is within the scope of the present disclosure for the secondary material to have a greater coefficient of thermal expansion. Furthermore, in one embodiment, this breakage may be promoted by including one or more points or lines of weakness (which are evident in <FIG>), such as scored or thinned areas of decreased thickness, which encourages the conductor sheet <NUM> to break at that particular location or locations.

If it is desired to employ an RFID tag <NUM> according to conventional design, the manner in which it is incorporated into the package <NUM> of a microwavable food item may be modified. <FIG> illustrates a package <NUM> incorporating an RFID tag <NUM> according to conventional design (as in <FIG>), although it is also within the scope of the present disclosure for the RFID tag <NUM> to be configured as in <FIG> or <FIG>.

The enclosure <NUM> of the package <NUM> is provided with a joinder material <NUM> applied to one or more of its surfaces (illustrated in <FIG> as an outer surface). The joinder material <NUM> may be present as a relatively thin layer or sheet of material with a resistance that is higher than the resistance of the antenna <NUM> of the RFID tag <NUM> (e.g., a sheet resistance in the range of approximately <NUM> ohms to approximately <NUM> ohms). Preferably, the joinder material <NUM> has a substantially uniform thickness, although it is within the scope of the present disclosure for the joinder material <NUM> to have a non-uniform thickness. It may be advantageous for the joinder material <NUM> to have an average thickness that is less than the thickness of the antenna <NUM> of the RFID tag <NUM> (e.g., the joinder material <NUM> may have an average thickness of in the range of approximately <NUM> to approximately <NUM> for joinder material <NUM> comprising an aluminum material).

In one embodiment, the joinder material <NUM> comprises a metallic film. In another embodiment, the joinder material <NUM> comprises an ink of a suitable conductivity. In other embodiments, the joinder material <NUM> may be differently configured, provided that it has a suitably high resistance (i.e., a resistance that is at least greater than the resistance of the antenna <NUM> of the associated RFID tag <NUM> and, more preferably, a sheet resistance in the range of approximately <NUM> ohms to approximately <NUM> ohms).

In the embodiment of <FIG>, a substrate <NUM> of the RFID tag <NUM> (to which the RFID chip <NUM> and antenna <NUM> are mounted) is associated to the enclosure <NUM> in a manner that sandwiches or interposes the joinder material <NUM> between the RFID tag <NUM> and the enclosure <NUM>. The joinder material <NUM> itself may have adhesive qualities to cause the RFID tag <NUM> to be secured with respect to the enclosure <NUM> or a separate means may be provided to secure the RFID tag <NUM> to the joinder material <NUM> (e.g., an adhesive applied to the underside of the substrate <NUM>). So separating the manufacturing of the enclosure <NUM> with the joinder material <NUM> and the RFID tag <NUM> allows for greater flexibility in manufacturing. By providing the joinder material <NUM> with a relatively high resistance, the effective sheet resistance of the RFID tag <NUM> is increased, thereby increasing the tendency to adsorb RF energy and heat up, rather than creating an arc.

The joinder material <NUM> may be variously configured without departing from the scope of the present disclosure. For example, the joinder material <NUM> may have a perimeter that substantially coincides with the perimeter of the substrate <NUM> of the associated RFID tag <NUM>, a perimeter that extends beyond the entire perimeter of the substrate <NUM> of the associated RFID tag <NUM>, a perimeter that is entirely contained within the perimeter of the substrate <NUM> of the associated RFID tag <NUM>, or a perimeter that extends beyond the perimeter of the substrate <NUM> of the associated RFID tag <NUM> in at least one location, while being contained within the perimeter of the substrate <NUM> of the associated RFID tag <NUM> at another location. Additionally, the perimeter of the joinder material <NUM> may have the same shape as the perimeter of the substrate <NUM> of the associated RFID tag <NUM> or a different shape.

Claim 1:
An RFID tag (<NUM>) comprising:
an RFID chip (<NUM>); and
an antenna (<NUM>) electrically coupled to the RFID chip (<NUM>), wherein the antenna (<NUM>) is comprised of a conductor sheet (<NUM>) formed of a base material and a secondary material having different coefficients of thermal expansion configured to cause the antenna (<NUM>) to fracture into multiple pieces upon being subjected to heating.