Rfid tag for bonding to microwaveable food packaging with a shielding structure

Abstract

The present application relates to RFID tags for incorporation into microwaveable food packaging having a shielding structure. An RFID tag is provided for incorporation into packaging of a microwaveable food, where the RFID tag is configured to be safely microwaved. The RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric positioned at least partially between the shielding conductor and the RFID chip. The shielding structure is configured to limit a voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency. The RFID tag includes an RFID chip and an antenna electrically coupled to the RFID chip.

Description

[0001] This application is a divisional application. The original application was filed on December 28, 2017, with application number 201780081477.9, and the invention title was "RFID tag with shielding structure for integration into microwaveable food packaging".

[0002] Cross-references to related applications

[0003] This application claims priority and benefit to U.S. Provisional Patent Application No. 62 / 440,408, filed December 29, 2016, and U.S. Provisional Patent Application No. 62 / 539,817, filed August 1, 2017, each of which is incorporated herein by reference in its entirety. Technical Field

[0004] This subject matter relates to packaging for microwaveable foods. More specifically, this subject matter relates to radio frequency identification (“RFID”) tags incorporated into the packaging of microwaveable foods. Background Technology

[0005] As is well known, packaging for microwaveable foods includes cooking aids that are placed in a microwave oven with the food for cooking / heating. For example, foods with a crust (crust) such as frozen pies or filled breads can benefit from "crisping sleeves," which are paper articles that at least partially surround the food during microwave cooking. Typically, the "crisping sleeve" has a paper base in which receptors are incorporated into the inner surface of the sleeve, facing and preferably in contact with the food. The receptors can be metallized films that absorb microwave energy and convert it into heat, causing the crust or surface of the food to become crisp and / or brown, thereby improving the appearance and texture of the food. Due to the absorptive nature of the membrane used as a receptor, a relatively low level of energy is reflected, preventing it from triggering an arc due to a high differential voltage between adjacent portions of the membrane, which could otherwise cause the packaging to catch fire.

[0006] It is also known to incorporate RFID technology, such as RFID tags, into product packaging for various purposes, including inventory management and anti-theft. Figure 1 shows an RFID tag T of conventional design, which can be attached to or otherwise attached to a housing similar to the housing 13 of Figure 1A (typically a paper or cardboard sleeve or box) of the microwaveable food packaging 9 of Figure 1A. The packaging 9 of Figure 1A is not intended to be microwaved as a whole, but rather to remove food (and optionally, a “brittle sleeve” or similar) from the housing 13 of Figure 1A and insert it into a microwave oven for heating / cooking.

[0007] The RFID tag T in Figure 1 includes an RFID chip C with a coupled dipole antenna A for transmitting and / or receiving information from an RFID reader (not shown). The RFID chip C is electrically coupled to the antenna A across a gap G defined by the antenna A between two conductive pad regions P.

[0008] At certain times, the RFID tag itself must have a gap across which the RFID chip is placed. This gap has a voltage at the intended operating frequency when the reader device is in the field. The incident power required on the RFID chip C can be as low as 10 microwatts; however, microwave ovens typically operate at power levels exceeding 800 watts, which can generate very high voltages across the gap G and the coupled RFID chip C. Antenna A is designed to operate at a first frequency F1 (e.g., in the range of approximately 860 MHz to 930 MHz). Antenna A takes the incident power at the first frequency F1 from the RFID reader and converts it into a voltage across the RFID chip C to allow its operation.

[0009] When the RFID tag T is placed in a microwave oven, a second frequency (identified as F2 in Figure 1, typically on the order of approximately 2,450 MHz) applied by the microwave oven can also be incident on antenna A. Antenna A is not designed to operate at the second frequency F2 because the very high power levels incident at F2 would generate high voltages on antenna A. These high voltages could occur at many locations on antenna A; however, by introducing large gaps L and controlled radii (typically identified as R in Figure 1) between antenna elements, voltages across the elements that would generate high breakdown voltages and thus arcing can be avoided. However, the gap G bridged by the RFID chip C is necessarily relatively small, thus generating high voltages at the second frequency F2, which could lead to breakdown and arcing. Similarly depicted in Figure 1A, dipole antenna 17 can receive microwave energy (identified as M in Figure 1A) and reflect microwave energy (indicated as R in Figure 1A) into the microwave source. An electric arc may occur between adjacent sections of the dipole antenna 17 (this location can be identified between the two conductive elements of the dipole antenna 17, marked 19 in FIG. 1A). Additionally, referring to FIG. 1A, the dipole antenna 17 of a conventional RFID tag 11 is formed of a relatively thick, low-resistance conductor, which has different characteristics from the metal film used to define a typical sensor. For example, a typical sensor is made of a metal-coated film with an optical density ranging from 0.18 to 0.29, corresponding to a sheet resistance of 100 ohms to 230 ohms; however, materials with a resistance of less than 1 ohm / cube are typically used to form the antenna of the RFID tag 11. Due to the characteristics of the dipole antenna 17, the RFID tag 11 may cause problems if it is not separated from the food before microwaved (i.e., if the entire package 9 of FIG. 1A is placed in a microwave oven).

[0010] To avoid problems of this nature, the RFID tags T and 11 of Figures 1 and 1A are typically configured to be easily removed from or otherwise separated from the food, such as by attaching them to the outer shell of the packaging, which may include instructions not to microwave the outer shell. However, users may fail to take proper care and may place the entire package (including RFID tags T and 11 shown in Figures 1 and 1A, respectively) in a microwave oven with the food, thus failing to separate the RFID tag T or 11 from the food. Therefore, it would be beneficial to provide RFID tags that can be microwaved without causing the problems associated with microwaved conventional RFID tags T or 11. Summary of the Invention

[0011] Several aspects of this subject matter may be embodied, alone or together, in the apparatuses and systems described and claimed below. These aspects may be used alone or in combination with other aspects of the subject matter described herein, and the joint description of these aspects is not intended to exclude the individual use of these aspects or the claims, either alone or in different combinations as may be made in the appended claims.

[0012] In one aspect, the RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip and the antenna are electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric, the shielding dielectric being at least partially positioned between the shielding conductor and the RFID chip. The shielding structure is configured to limit the voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency.

[0013] On the other hand, packaging for microwaveable food is provided. The packaging includes a shell and an RFID tag attached to the shell. The RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric, the shielding dielectric being at least partially positioned between the shielding conductor and the RFID chip. The shielding structure is configured to limit the voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency.

[0014] On the other hand, the RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric, the shielding dielectric being at least partially positioned between the shielding conductor and the RFID chip. A second shielding structure is electrically coupled to the antenna across the gap, located below the RFID chip. The shielding structure is configured to limit the voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency.

[0015] On the other hand, packaging for microwaveable food is provided. The packaging includes a shell and an RFID tag attached to the shell. The RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric, the shielding dielectric being at least partially positioned between the shielding conductor and the RFID chip. A second shielding structure is electrically coupled to the antenna across the gap, located below the RFID chip. The shielding structure is configured to limit the voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency.

[0016] On the other hand, the antenna consists of a thin-film antenna with a resistance ranging from approximately 100 ohms to approximately 230 ohms. On the other hand, the RFID tag includes an RFID chip and an antenna electrically coupled to the RFID chip. The antenna is composed of a conductor formed of a base material and a second material with different coefficients of thermal expansion, configured to break the antenna into multiple pieces upon heating.

[0017] In another aspect, packaging for microwaveable food is provided. This packaging includes a shell, an RFID tag, and a joiner material sandwiched between the RFID tag and the shell. The RFID tag includes a substrate and an RFID tag attached to the substrate. The RFID tag includes an RFID chip and an antenna electrically coupled to the RFID chip. The joiner material has a higher resistance than the antenna. Attached Figure Description

[0018] Figure 1 is a top view of an RFID tag designed according to conventional methods;

[0019] Figure 1A is a perspective view of microwaveable food packaging incorporating RFID tags according to a conventional design;

[0020] Figure 2A A top plan view of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0021] Figure 2B It is attached to the packaging of microwaveable food. Figure 2A A cross-sectional side view of a portion of an RFID tag;

[0022] Figure 3A A top plan view of another embodiment of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0023] Figure 3B It is attached to the packaging of microwaveable food. Figure 3A A cross-sectional side view of a portion of an RFID tag;

[0024] Figure 4A A top plan view of a third embodiment of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0025] Figure 4B yes Figure 4A A cross-sectional side view of a portion of an RFID tag;

[0026] Figure 5A top plan view of a fourth embodiment of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food.

[0027] Figure 6A A top plan view of a fifth embodiment of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0028] Figure 6B It is attached to the packaging of microwaveable food. Figure 6A A cross-sectional side view of a portion of an RFID tag.

[0029] Figure 7A A top plan view of a sixth embodiment of an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0030] Figure 7B yes Figure 7A A cross-sectional side view of a portion of an RFID tag; and

[0031] Figure 8 A basic equivalent circuit of a portion of an RFID tag according to aspects of this disclosure is illustrated.

[0032] Figure 9 This is a perspective view of microwaveable food packaging incorporating RFID tags according to aspects of this disclosure.

[0033] Figure 10 A top plan view of an alternative embodiment of an antenna for an RFID tag according to aspects of this disclosure that can be incorporated into the packaging of microwaveable food;

[0034] Figure 10A It is after heating Figure 10 Top view of the antenna; and

[0035] Figure 11 This is an exploded perspective view of an alternative embodiment of microwaveable food packaging incorporating RFID tags according to aspects of this disclosure. Detailed Implementation

[0036] Detailed embodiments of the invention have been disclosed herein as needed; however, it should be understood that the disclosed embodiments are merely examples of the invention, which may be embodied in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but merely as the basis for the claims and as a representative basis for instructing those skilled in the art to refer to the invention differently in virtually any suitable manner.

[0037] Figure 2A and 2B An RFID tag 10 according to this disclosure is shown, while Figure 2B An RFID tag (typically designated 10) is shown attached to the outer shell 12 (e.g., a cardboard box) of microwaveable food packaging (typically designated 14). Packaging 14 may include other items configured to be microwaved with the food, such as a "brittle sleeve." RFID tag 10 can be incorporated into packaging 14 by any suitable method, although RFID tag 10 is attached to... Figure 2B The housing 12 in the embodiments described herein, however, the RFID tag 10 may be coupled to another part of the packaging 14 in other embodiments (e.g., a “brittle sleeve” housed within the housing 12). Furthermore, while the RFID tag is described herein as being incorporated into the packaging of microwaveable food, it should be understood that the RFID tag according to this disclosure can be used in any of many possible applications, particularly when considering that they may be exposed to frequencies (referred to herein as the “second frequency”) significantly higher than the frequency at which the RFID tag’s antenna is expected to operate (referred to herein as the “first frequency”).

[0038] The RFID tag 10 includes an antenna 16 to which an RFID chip 18 is electrically coupled. The antenna 16 is provided as a dipole antenna, formed by a conductor defining a gap 20 bridged by the RFID chip 18 between two conductor pad regions 22. Figure 2A Antenna 16 and RFID chip 18 can typically be provided according to conventional designs (e.g., as described above with respect to the embodiment of FIG1), wherein antenna 16 is designed to operate at a first frequency that can be in the range of approximately 860 MHz to 930 MHz. As in a conventional RFID tag T, antenna 16 takes incident power at the first frequency and converts it into a voltage across RFID chip 18 to allow it to operate.

[0039] The RFID chip 18 can take any of a variety of forms (including those commonly referred to by those skilled in the art as "chip" or "strap"), include any of a variety of possible components, and be configured to perform any of a variety of possible functions. For example, in one embodiment, the RFID chip 18 includes an integrated circuit for controlling RF communication and other functions of the RFID tag 10.

[0040] The RFID tag 10 further includes a shielding structure (generally designated 24) comprising a shielding conductor 26 and a shielding dielectric 28. The shielding conductor 26 is formed of a material having conductive properties and, as will be described in more detail, can be configured in various ways without departing from the scope of this disclosure. The shielding dielectric 28 is formed of a material having dielectric properties and, as will be described in more detail, can be configured in various ways without departing from the scope of this disclosure. For example, in Figure 2A and Figure 2BIn one embodiment, the shielding conductor 26 and the shielding dielectric 28 are generally flat or planar, substantially identical in shape, and oriented with the periphery of the shielding conductor 26 coinciding with the periphery of the shielding dielectric 28. In other embodiments, the shielding conductor and the shielding dielectric may be configured and / or oriented differently, at least partially misaligned (i.e., with portions of the shielding conductor extending beyond the periphery of the shielding dielectric and / or portions of the shielding dielectric extending beyond the periphery of the shielding conductor).

[0041] The shielding structure 24 is electrically coupled to the antenna 16 across the gap 20, and capacitively coupled to the conductor pad region 22 on either side of the gap 20. Figure 2A ).like Figure 2B As shown, the shielding structure 24 covers the RFID chip 18, wherein the shielding dielectric 28 is at least partially positioned between the RFID chip 18 and the shielding conductor 26. The shielding structure 24 may cover or obscure the entire gap 20 (e.g., Figure 2A and 2B (in the middle) or only the part with a 20-degree gap.

[0042] As described above, the RFID tag 10 can be exposed to signals operating at a first or second frequency. When the RFID tag 10 is exposed to the first frequency, the shielding structure 24 forms a partial short circuit across the gap 20. However, the antenna 16 is configured to compensate for the presence of the partial short circuit, thereby allowing the RFID tag 10 to operate normally.

[0043] As described above, when a conventional RFID tag T is exposed to the second frequency F2, a large voltage rises across the gap G, creating a risk of arcing. If the voltage and power at the second frequency F2 are sufficiently limited, the RFID chip C can survive, but the primary purpose is to prevent an arc that could ignite the RFID tag T or its associated packaging 14. When the RFID tag 10 is exposed to the second frequency, Figure 2A and Figure 2B The shielding structure 24 provides this function by "shorting" the high voltage generated across the gap 20 (and therefore the RFID chip 18), thereby reducing the voltage below levels that could lead to breakdown and possible arcing (which prevents ignition). Therefore, unlike conventional RFID tags T, the RFID tag 10 can be placed in a microwave oven and exposed to the accompanying high-frequency signals (which can be on the order of approximately 2,450 MHz) without the risk of ignition.

[0044] As shown above, the shielding structure can be configured differently without departing from the scope of this disclosure. For example, Figure 3A and 3B An implementation of an RFID tag (typically designated 10a) is shown (and) Figure 3BThe package of the connection in the middle, usually designated as 14a), wherein the shielding structure 24a includes shielding dielectrics 28a in different configurations ( Figure 3B ).exist Figure 3A and 3B In this embodiment, the shielding dielectric 28a is bonded to an over-lamination layer that covers at least a portion of the RFID chip 18, the gap 20, and at least a portion of the conductor pad region 22 of the antenna 16. Figure 3A The shielding conductor 26a may include a patterned conductor to provide the desired bridging and shielding effect. For example... Figure 3B As shown in the best embodiment, the size and shape of the shielding conductor 26a and the shielding dielectric 28a can be different, wherein the shielding conductor 26a is smaller than the shielding dielectric 28a in which the imprinted laminate is bonded.

[0045] Figure 4A and 4B Another implementation of an RFID tag (typically designated 10b) according to this disclosure is illustrated. Figure 4A and 4B In this embodiment, a shielding structure (typically designated 24b) is bonded across gap 20 to an RFID strip comprising a strip conductor 30 and a strip substrate 32 (together with the RFID chip 18), the RFID strip being electrically coupled to antenna 16. The shielding structure 24b may consist of a shielding conductor 26b applied to the strip substrate 32, which serves as a shielding dielectric 28b. The strip substrate 32 (and any other shielding dielectric described herein) may be formed of any of a variety of materials, such as polyethylene terephthalate.

[0046] Figure 5 Another implementation of an RFID tag (typically designated as 10c) with a shielding structure 24c having a different configuration is illustrated. Figure 5 In one embodiment, the shielding conductor 26c includes an extension region 34, which allows the size of the shielding conductor 26c to be increased beyond the size of the connected shielding dielectric (in Figure 5 The dimensions are not visible in the image. In other embodiments—where the shielding structure is primarily configured and oriented to cover or obscure the gap 20—in contrast, the extension region 34 of the shielding conductor 26c is oriented not to cover the gap 20 (or antenna 16), but is positioned on the side of the antenna 16 and the gap 20, extending away from the antenna 16. Without departing from the scope of this disclosure, the dimensions and configuration of the extension region 34 of the shielding conductor 26c may differ; in one embodiment, the dimensions are... Figure 2A and Figure 2B The shielding conductor 26 is approximately the same, but in another embodiment is larger. Figure 2A and 2BThe shielding conductor 26, and in another embodiment smaller than Figure 2A and 2B Shielding conductor 26.

[0047] Regardless of the specific size and configuration of the extension region 34 of the shielding conductor 26c, the extension region 34 helps dissipate heat generated on the gap 20. Since this effect is enhanced by increasing the size of the extension region 34, a relatively large extension region 34 may be advantageous for improving heat dissipation. The extension region 34 (along with the remainder of the shielding conductor 26c and any of the other shielding conductors described herein) may be formed of non-combustible materials, such as, but not limited to, aluminum, heat-resistant, flame-retardant paper (Flex Dura HR, http: / / www.flexlinkllc.com / heat-resistant-paper.html), and non-combustible adhesives (Eclectic E6000 Adhesive, http: / / eclecticproducts.com / products / e6000.html), to provide a barrier against any arc that may be generated across the gap 20, thereby preventing the spread of fire.

[0048] Figure 6A and 6B Examples are shown of RFID tags with different configurations of shielding structure 24d (typically specified as 10d) (and linked packages typically specified as 14d), in Figure 6B Another implementation method (in China). Figure 6A and 6B In this embodiment, the shielding dielectric 28d is formed of a material that undergoes reversible or irreversible dielectric breakdown under high voltages induced by high-power microwave fields. This configuration enhances the short-circuit effect provided by the shielding structure 24d in the presence of a second frequency (e.g., in a microwave field). In this embodiment (and in other embodiments described herein), the shielding conductor 26d can be formed by printing a conductive material (which becomes and defines the shielding conductor 26d) onto the shielding dielectric 28d (e.g., by imprinting lamination).

[0049] A single RFID tag can include more than one shielding structure, such as Figure 7A and 7B As shown in the implementation method. In Figure 7A In this context, RFID tags (typically designated 10e) are provided with information typically based on prior... Figure 3A and 3B The first shielding structure described in the implementation description (typically designated as 24e). The antenna 16 of the RFID tag 10e can be freely and directly connected to the outer shell of the packaging (e.g., Figure 3BThe first shielding structure is a secondary shielding structure (usually specified as 24f). Figure 7B The second shielding structure 24f is connected to the lower side of the antenna 16, wherein the second shielding structure 24e and 24f are located below the RFID chip 18 (i.e., the shielding structures 24e and 24f are electrically coupled to the opposite sides of the antenna 16). The shielding dielectric 28f of the second shielding structure 24f contacts the lower side of the antenna 16, while the connected shielding conductor 26f is freely fixed or otherwise connected to the outer shell of the packaging of microwaveable food, etc.

[0050] In the example implementation, the second shielding structure 24f is substantially the same as the first shielding structure 24e; however, within the scope of this disclosure, the shielding conductor 26f and / or shielding dielectric 28f of the second shielding structure 24f are configured differently from the shielding conductor 26e and shielding dielectric 28e of the first shielding structure 24e. Regardless of the specific configuration of the two shielding structures 24e and 24f, additional shielding is provided by providing them on both sides of the antenna 16. This additional shielding involves additional "short circuits" because there are now two local short circuits across the gap 20. However, according to the previous... Figure 2A and 2B As described in the implementation description, antenna 16 is configured to compensate for the presence of local short circuits, thereby allowing RFID tag 10e to operate normally when exposed to a first frequency.

[0051] Figure 8 This represents the basic equivalent circuit of the basic components of the RFID tag 10 according to this disclosure. Figure 8 In the process, the gap 20 defined by antenna 16 is bridged by RFID chip 18 (represented by resistor Rp and capacitor Cp) and shielding structure 24, which includes shielding conductor 26 and shielding dielectric 28 (composed of two identical series capacitors Cp). B (Indicated). The total capacitance of the shielding dielectric 28 is used for indication. Figure 8 Individual capacitor C with shielding dielectric 28 in B Half of the capacitance. This is calculated using the standard formula, where the total capacitance of a series capacitor is the reciprocal of the sum of the reciprocals of all the capacitances.

[0052] The impedance of the shielding dielectric 28 is equal to the reciprocal of the product of 2 × π × F × total capacitance, where F is the frequency at which the RFID tag 10 is powered. Therefore, if the first frequency is on the order of approximately 800 MHz and the second frequency is on the order of approximately 2,400 MHz, the impedance drops to approximately one-third between the first and second frequencies, which enhances the "short circuit" and, therefore, enhances the shielding effect at the second frequency.

[0053] Additionally, arcing may occur between adjacent segments (i.e., gap G and the connected RFID chip C). This is partly due to the adjacent segments being surrounded by material (i.e., air or other components) having a lower dielectric strength than the electric field obtained by the differential voltage across the adjacent segments. Arcing may also occur and be exacerbated—partly due to the material surrounding the segment reaching a certain temperature as the RF current flows / flows through the gap G and chip C, which reduces the dielectric strength of the surrounding material and generates flammable / flammable volatiles. Such arcing can be avoided without utilizing shielding created by surrounding the segment with materials possessing properties such as dielectric strength capable of withstanding the electric field at the segment, and heat-resistant, flame-retardant, and non-flammable properties, i.e., heat-resistant and flame-retardant paper and non-flammable adhesives (one or more).

[0054] Furthermore, other embodiments are disclosed within the same scope of the present invention. Figure 9 In the example implementation, the housing 23 is coupled to an RFID tag 25, which includes an RFID chip 27—with an antenna 29 electrically coupled to it. The antenna 29 is formed of a conductor 31 with a resistance greater than that of a conventional RFID tag 11's antenna, allowing the package 21 (including the RFID tag 25) to be safely microwaved. For example, the conductor 31 may have a sheet resistance comparable to that of a sensor (i.e., in the range of approximately 100 ohms to approximately 230 ohms). Similar to a sensor, the conductor 31 may also have an optical density in the range of approximately 0.18 to 0.29. With this configuration, when the RFID tag 25 is microwaved, it functions in the same way a sensor functions when microwaved—by absorbing microwave energy M and heating up, and reflecting minimal energy R', rather than reflecting high levels of energy back to the microwave source or generating an electric arc.

[0055] The higher sheet resistance of conductor 31 compared to the dipole antenna 17 of a typical RFID tag 11 can affect the performance of antenna 29. While the sheet resistance of the material (measured in ohms per square block for a given thickness) is a fixed value, the resistance experienced by RF current flowing through conductor 31 can be effectively reduced by increasing the area of ​​conductor 31 (e.g., by increasing its thickness). This is particularly effective in reducing resistance for RF current because skin depth is a more significant factor than for DC current due to the tendency of RF current to flow through the outer surface of conductor 31 (i.e., as conductor thickness decreases relative to skin depth, RF resistance becomes higher than DC resistance). Therefore, having a relatively large area or thickness for antenna 29 to reduce RF resistance may be advantageous.

[0056] Compared to dipole antennas, slot-loop hybrid antennas typically have a larger conductor area, making it possible to provide antenna 29 as a slot-loop hybrid antenna (sometimes referred to as a "sloop" antenna). Figure 9 (As shown) This may be advantageous. Such a slot-loop hybrid antenna 29 can be formed from a conductor 31 comprising a conductor sheet, which in the example embodiment is typically rectangular, with a slot 33 defined therein and positioned at an edge or end 35 of the conductor sheet 31. As shown, the slot 33 may extend between a closed end 37 and an open end 39, which is coupled to an end or edge 35 of the conductor sheet 31. While configuring the antenna 29 as a slot-loop hybrid antenna has various advantages, antennas 29 configured differently are also within the scope of this disclosure.

[0057] Looking further into the RFID chip 27, it can take any of a variety of forms (including those commonly referred to by those skilled in the art as "chips" or "bands"), include any of a variety of possible components, and be configured to perform any of a variety of possible functions. For example, in one embodiment, the RFID chip 27 includes an integrated circuit for controlling RF communication and other functions of the RFID tag 25. In an example embodiment, two ends or two points of the RFID chip 27 are connected to the conductor sheet 31 near the opening end 39 of the slot 33 on opposite sides of the slot 33, which serves to electrically couple the RFID chip 27 to the conductor sheet 31.

[0058] According to another aspect of this disclosure—it can be incorporated into Figure 9 The RFID tag 25 may be implemented in the antenna 29 or separately, suitable for integration into the RFID tag 41 of microwaveable food packaging. Figure 10 and 10A The RFID tag 41 can be configured to break into multiple pieces or otherwise separate after being heated in a microwave oven. This breaking reduces interaction with the microwave field, thus avoiding potential problems of excessive reflection of microwave energy and / or arcing when the RFID tag 41 is heated in a microwave oven. If desired, this configuration allows the resistance of the conductor 43 of the antenna 45 of the RFID tag 41 to be lower than [value missing]. Figure 9 Implementation methods (e.g., thin-film resistors with less than 100 ohms).

[0059] according to Figure 9 The foregoing description of the RFID tag 25 provides Figure 10 The RFID tag 41 shown has an RFID chip 47 electrically coupled to the conductor sheet 43 of the slot-loop hybrid antenna 45, but the antenna 45 may be configured differently without departing from the scope of this disclosure.

[0060] Regardless of the specific configuration of antenna 45, its conductor sheet 43 is preferably formed of at least two materials (a base material and a second material—which may be provided in a smaller quantity than the base material) with different coefficients of thermal expansion. With this configuration, the materials expand at different rates when heated (e.g., in a microwave oven) until the conductor sheet 43 breaks into multiple pieces or otherwise separates. The magnitude of the difference in the coefficients of thermal expansion of the materials can vary without departing from the scope of this disclosure, although a relatively large difference may be advantageous to cause the conductor sheet 43 to break or otherwise separate more quickly upon heating.

[0061] In one exemplary embodiment, the conductor sheet 43 may be 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 specifically, the base material may be polyethylene terephthalate (which has a coefficient of thermal expansion of approximately 60 m / (mK)), while the second material is aluminum (which has a coefficient of thermal expansion of approximately 22 m / (mK)). When bonded together and heated, the aluminum eventually breaks, causing the RFID tag 41 to not operate or at least operate at a lower level, which reduces the interaction between the RFID tag 41 and the microwave field. Although in this example the base material has a larger coefficient of thermal expansion than the second material, the second material has a larger coefficient of thermal expansion within the scope of this disclosure. Furthermore, in one embodiment, it can be formed by including one or more weak particles or lines (in... Figure 10A (The obvious) such as the reduced thickness of the grooves or thinned areas promotes this fracture, which causes the conductor sheet 43 to break at one or more specific locations.

[0062] If you wish to use the RFID tag 11 which is designed according to standard specifications, you can modify how you integrate it into the packaging 49 of microwaveable food. Figure 11 An example is shown of a package 49 incorporating an RFID tag 11 (as shown in Figure 1A) of a conventional design, but the RFID tag 11 is as follows: Figure 9 and Figure 10 The configuration of the central location is also within the scope of this disclosure.

[0063] The outer casing 51 of package 49 is provided with one or more (in) applied to its surface. Figure 11The bonding material 53 (exemplified in the example as the outer surface) may exist as a relatively thin layer or sheet of material, with a resistance higher than that of the antenna 17 of the RFID tag 11 (e.g., a thin layer resistance in the range of approximately 100 ohms to approximately 230 ohms). Preferably, the bonding material 53 has a substantially uniform thickness, but a non-uniform thickness is also within the scope of this disclosure. It may be advantageous for the average thickness of the bonding material 53 to be less than the thickness of the antenna 17 of the RFID tag 15 (e.g., for a bonding material 53 comprising aluminum, the average thickness of the bonding material 53 may be in the range of approximately 10 nm to approximately 100 nm).

[0064] In one embodiment, the bonding material 53 comprises a metal film. In another embodiment, the bonding material 53 comprises ink with suitable conductivity. In other embodiments, the bonding material 53 may be configured differently, provided that it has a suitablely high resistance (i.e., a resistance at least greater than the resistance of the antenna 17 of the coupled RFID tag 11, and more preferably, the sheet resistance is in the range of about 100 ohms to about 230 ohms).

[0065] exist Figure 11 In this embodiment, the substrate 55 of the RFID tag 11 (on which the RFID chip 15 and antenna 17 are mounted) is coupled to the housing 51 in such a way that the bonding material 53 is sandwiched or inserted between the RFID tag 11 and the housing 51. The bonding material 53 itself may have adhesive properties to secure the RFID tag 11 relative to the housing 51, or a separate device may be provided to secure the RFID tag 11 to the bonding material 53 (e.g., adhesive applied to the underside of the substrate 55). Therefore, separating the housing 51 from the bonding material 53 and the manufacture of the RFID tag 11 allows for greater flexibility in manufacturing. By providing the bonding material 53 with relatively high resistance, the effective sheet resistance of the RFID tag 11 is increased, thereby increasing the tendency to absorb RF energy and heat up rather than generate an electric arc.

[0066] Without departing from the scope of this disclosure, the bonding material 53 may be configured differently. For example, the bonding material 53 may have a periphery substantially overlapping the periphery of the base 55 of the coupled RFID tag 11, a periphery extending beyond the entire periphery of the base 55 of the coupled RFID tag 11, a periphery completely contained within the periphery of the base 55 of the coupled RFID tag 11, or a periphery extending beyond the periphery of the base 55 of the coupled RFID tag 11 at at least one location and contained within the periphery of the base 55 of the coupled RFID tag 11 at another location. Additionally, the periphery of the bonding material 53 may have the same shape as or a different shape from the periphery of the base 55 of the coupled RFID tag 11.

[0067] In another aspect of the same invention, not illustrated, packaging for microwaveable food is provided. The packaging includes a shell and an RFID tag attached to the shell. The RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled to the antenna across the gap. A shielding structure is electrically coupled to the antenna across the gap and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding dielectric, the shielding dielectric being at least partially positioned between the shielding conductor and the RFID chip. The shielding structure is configured to limit the voltage across the gap when the antenna is exposed to a second frequency greater than the first frequency. The shell of the packaging is provided with a previously described bonding material 53, applied to one or more of its surfaces (similarly in…). Figure 11 (Example: outer surface). The bonding material 53 may exist as a relatively thin layer or sheet of material, with a resistance higher than that of the antenna 17 of the RFID tag 11 (e.g., a thin layer resistance in the range of approximately 100 ohms to approximately 230 ohms).

[0068] The present invention also considers, but is not limited to, the microwaveable RFID testing methods described herein. The equipment used in one method includes inverter technology based on, for example, a 12000-watt furnace. For example, it can utilize... Model JE 2251SJ02. Additionally, a scale of and multiple plastic containers are used to hold the sample. In one embodiment of the test method, frozen ground beef is used as the sample. The steps of the test method using frozen ground beef are as follows: 1) Prepare the sample. Various weights can be used. In one example, a five (5) ounce sample is used. 2) Place the sample in half of the container to ensure that the sample consistently covers the bottom of the container between different tests. 3) Freeze the sample for approximately twelve (12) hours. 4) Attach at least one RFID tag to the bottom of the container holding the sample and place the sample on a rotating plate inside a microwave oven. In one embodiment, the sample is placed in the center of the rotating plate inside the microwave oven. 5) Microwave the sample at full power setting for two (2) minutes. This test method considers that several different power settings and times can be used to test the sample. 6) Determine if a “spark” or “arc” is present.

[0069] It should be understood that the above embodiments illustrate some applications of some principles of this subject matter. Many modifications can be made by those skilled in the art without departing from the spirit and scope of the claimed subject matter, including combinations of those features separately disclosed or claimed herein. For these reasons, the scope of this document is not limited to the above description, but is set forth in the appended claims, and it should be understood that the claims may relate to the features herein, including combinations of features separately disclosed or claimed herein.

Claims

1. RFID tags, including: RFID chip; and An antenna electrically coupled to the RFID chip, wherein the antenna is composed of a conductor formed of a base material and a second material having different coefficients of thermal expansion, and is configured such that the antenna breaks into multiple pieces upon being heated.

2. The RFID tag of claim 1, wherein the base material is a plastic material, and the second material is a metal material or conductive ink.

3. The RFID tag of claim 1, wherein the base material is provided in a larger quantity than the second material and has a lower coefficient of thermal expansion than the second material.

4. The RFID tag of claim 1, wherein the base material is provided in a larger quantity than the second material and has a larger coefficient of thermal expansion than the second material.

5. The RFID tag of claim 1, wherein the conductor comprises at least one weak point or line, the at least one weak point or line having a smaller thickness than another segment of the conductor.

6. The RFID tag of claim 1, wherein the antenna is configured as a slot-loop hybrid antenna.

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