Radio frequency identification insert for use with or embedded in a microwave heatable food package

Abstract

The invention relates to a radio frequency identification (RFID) insert design for microwave preparation of food packages. In general, an RFID insert design includes a substrate having an antenna structure formed thereon; an antenna structure has an impedance matching loop and a dipole antenna. The impedance matching loop includes an integrated circuit (IC) chip bonding region characterized by a gap in the loop, wherein loop ends on both sides of the gap are formed with first and second IC bonding points; the IC is physically disposed within the IC chip bonding area and electrically coupled with the first and second IC bonding points. The impedance matching loop further includes an improved profile element extending from the loop first interior side to the second interior side, the improved profile element characterized as having an impedance lower than an impedance of the chip bonding region at the microwave frequency. The dipole antenna includes first and second elements extending outwardly from an impedance matching loop. The antenna structure is characterized to have an operating frequency adapted to activate and read information stored in the IC, but when exposed to microwave frequencies, the current induced in the antenna structure is directed substantially through the improved profile element away from the chip bonding area, thereby mitigating arcing of the gaps in the loop.

Description

[0001] This application claims priority to U.S. Provisional Application No. 63 / 484,182, filed February 9, 2023, and U.S. Provisional Application No. 63 / 509,147, filed June 20, 2023, which are both hereby incorporated by reference in their entirety. TECHNICAL FIELD

[0002] The present disclosure relates generally to radio frequency identification (RFID) inlays, and more particularly to RFID inlays for use with, or embedded into, microwaveable food packaging. BACKGROUND

[0003] Radio frequency identification (RFID) uses electromagnetic fields to identify and track tags attached to objects. An RFID tag, or “inlay,” is composed of three distinct components: an RFID “chip,” which is an integrated circuit (IC), and an antenna, both of which are affixed to a substrate. When activated by an electromagnetic interrogation pulse from an RFID reader device, the tag transmits digital data back to the reader, typically an inventory identification number; this number can be used, for example, to take inventory, track the flow of goods, and register the sale of the product to which the number is attached. There are two types of RFID tags; passive tags are powered by the energy of the interrogation radio frequency wave from the RFID reader, while active tags are powered by a battery and can be read at a greater range, up to hundreds of meters, from the RFID reader. Unlike a bar code, an RFID tag does not need to be in the line of sight of the reader, and thus can be embedded in the object being tracked.

[0004] An RFID tag IC has logic to make decisions and provides memory for storing data, such as a unique product ID. The RFID tag antenna, which is connected to the tag IC, is the largest part of the tag. The geometry of the antenna is determined by the operating frequency of the tag; variations in antenna design allow the tag to have different characteristics and behaviors. The antenna can be made, for example, as a spiral coil, a single dipole, a double dipole (one perpendicular to the other), or a folded dipole. The antenna is designed for a specific operating frequency, and the frequency of that design determines the effective antenna length. The substrate combines the RFID IC and the antenna together; the antenna can be deposited or printed on the substrate, and then the IC is connected to the antenna and the substrate. The substrate can be made of a flexible material such as thin plastic, but can also be made of a rigid material. Most passive tags use a substrate made of a flexible material that is 100 to 1000 nm thick. Suitable substrate materials include polymers, PVC, polyethylene terephthalate (PET), phenolic, polyester, styrene, and even paper. The substrate material can affect the design frequency of the antenna; therefore, the effects of the substrate material must be considered when properly tuning the antenna.

[0005] RFID tags can be embedded or attached to microwaveable food packaging; however, doing so can cause unwanted arcing, potentially leading to a fire, if proper precautions are not taken. U.S. Patent Application No. 17 / 787,667 (hereinafter “667 Patent Application”), entitled “Two-part RFID tag for embedding into microwaveable food packaging,” describes the problem that:

[0006] “

[0006] An RFID tag comprises an RFID chip, and an associated antenna for transmitting information to and / or receiving information from an RFID reader. The RFID chip is electrically coupled to the antenna through a gap defined by the antenna between two conductor pads areas. Such an RFID tag must inherently have a gap somewhere, with the RFID chip placed at a location across the gap, which gap has a voltage at the intended operating frequency when in the field of a reader device. The required power applied to the RFID chip can be as low as 10 microwatts, while a microwave oven typically operates at power levels exceeding 800 watts, which can create very high voltages across the gap and associated RFID chip.

[0007] “

[0007] The antenna is designed to operate at a first frequency, for example in the range of about 860 MHz to 930 MHz, the antenna picks up incident power at the first frequency from an RFID reader and converts it to a voltage across the RFID chip to enable it to operate.

[0008] “

[0008] When the RFID tag is placed in a microwave oven, a second frequency, typically about 2,450 MHz, is also incident on the antenna, applied by the microwave oven. The antenna is not designed to operate at the second frequency, as the extremely high power level incident at the second frequency can create high voltages across the antenna. These high voltages can occur at multiple places in the antenna; however, by methods such as introducing larger gaps between antenna elements, and controlled radii, the voltage across elements can be avoided from creating high voltage breakdown, and thus arcing. However, the gap bridged by the RFID chip must necessarily be relatively small, and thus at the second frequency, high voltages can occur there, which can lead to breakdown and arcing.

[0009] “

[0009] To avoid such problems, RFID tags are typically configured to be easily removable or otherwise separable from the food item, for example by being affixed to an outer packaging of the packaging, which outer packaging can contain instructions prohibiting microwave heating of the outer packaging. However, it is possible that a user, by failing to take proper care, can place the entire packaging, including the RFID tag, into the microwave oven along with the food item, failing to separate the RFID tag from the food item.

[0010] "

[0010] Even if the RFID tag is properly separated from the food item prior to microwave heating of the food item, the RFID tag has certain limitations. For example, if the RFID tag is affixed to the outer packaging of the package, the food item cannot be tracked using an RFID reader prior to placement of the food item in the outer packaging. However, it can be advantageous if the RFID tag could be read and / or written to prior to placement of the food item in the outer packaging, in order to trace ingredients, machines used, etc. Likewise, after the food item is removed from the outer packaging, it becomes impossible to track the food item. This would be disadvantageous when the food item is intended to be removed from the outer packaging, heated in a microwave oven, and subsequently paid for, at which point it can be necessary to communicate with the RFID tag at a cash register or similar point-of-sale terminal for pricing and / or inventory purposes."

[0011] The solution proposed in the '667 patent application is to utilize a two-part package, where a first package component (containing the food item) is configured to be microwaveable, and a second package component is configured to be separable from the first package component prior to microwave heating of the first package component; according to the abstract of the '667 patent application:

[0012] "The RFID tag includes a reactive strap associated with the first component and a far-field antenna associated with the second component. When the package is in its intact state, the reactive strap is coupled to the antenna, and when the second component has been separated from the first component, the reactive strap is decoupled from the antenna. When the reactive strap is coupled to the antenna, the RFID tag is capable of far-field communication, and when decoupled, the reactive strap is only capable of near-field communication."

[0013] However, if the user forgets to remove the second package component prior to placing the food item in the microwave, the proposed solution above would be ineffective. Furthermore, a smart microwave appliance can automatically set the appropriate cooking temperature and time using the presence of an RFID tag on a product placed in the smart microwave appliance; thus, a solution that forces removal of part of the food package (including all or part of the associated RFID tag) prior to placement in the microwave can not be desirable. Furthermore, the '667 patent application itself recognizes this problem, namely:

[0014] "

[0033] ... A user can not separate the second packaging component 16 (and associated far-field antenna 22) from the first packaging component 14, and the far-field antenna 22 can be configured to ensure that microwave heating of the assembled RFID tag 18 does not result in smoke or flame or unsafe conditions. This can be accomplished in any suitable manner, which can include configuring the far-field antenna 22 to break when subjected to microwave heating, such as by configuring the far-field antenna 22 to expand at a different rate than the second packaging component 16 when heated, thereby causing the far-field antenna 22 to break. Alternatively, the far-field antenna 22 can be configured such that it is allowed to overheat, thereby potentially damaging the second packaging component 16, but without creating an electrical arc or flame or smoke."

[0015] Thus, the inventors of the '667 patent application recognized that the proposed solution can still initiate an electrical arc or fire if no auxiliary measures are taken to prevent or mitigate such problems. The inventors are also co-inventors of U.S. Patent No. 11,308,379 B2 (hereinafter the " '379 patent") entitled "RFID Tag with Shielding Structure for Embedding in Microwaveable Food Packaging." The '379 patent describes a solution that requires a shielding structure that is coupled across a gap to the antenna and covers the RFID chip. As the '379 patent abstract states:

[0016] "An RFID tag for embedding in microwaveable food item packaging is provided that is configured to be safely microwaveable. The RFID tag includes an antenna defining a gap and configured to operate at a first frequency. An RFID chip is electrically coupled across the gap to the antenna. A shielding structure is electrically coupled across the gap to the antenna and covers the RFID chip. The shielding structure includes a shielding conductor and a shielding medium 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."

[0017] While the solution proposed in the '379 patent can effectively overcome the problems inherent in the solution proposed in the '667 patent application, it requires additional components and adds complexity to the design of RFID inlays suitable for microwave applications. Thus, there remains a need in the art for improved RFID inlay designs that overcome the deficiencies of existing RFID designs for use with, or embedded in, microwaveable food packaging. SUMMARY

[0018] To address the shortcomings of the prior art, a radio frequency identification (RFID) inlay design for microwaveable food packaging is disclosed. Generally, the RFID inlay design includes a substrate having an antenna structure formed thereon; the antenna structure having an impedance matching loop and a dipole antenna. The impedance matching loop includes an integrated circuit (IC) die bond area characterized by a gap in the loop, where the loop ends on either side of the gap are formed with first and second IC bond points; an IC is physically disposed within the IC die bond area and electrically connected to the first and second IC bond points. The impedance matching loop further includes a modified contour element extending from a first interior side of the loop to a second interior side, the modified contour element being characterized by having an impedance at microwave frequencies that is lower than the impedance of the die bond area. The dipole antenna includes first and second elements extending outwardly from the impedance matching loop. The antenna structure is characterized by having an operating frequency suitable for activating and reading information stored in the IC, but when exposed to microwave frequencies, current induced in the antenna structure is directed substantially through the modified contour element away from the die bond area, thereby mitigating arcing at the gap in the loop.

[0019] Generally, the modified contour elements of the disclosed microwaveable RFID inlays include at least one central gap. In exemplary embodiments, the at least one central gap has a length that is greater than a width of the modified contour element. For example, the at least one central gap can be curvilinear; for example, it can be substantially sinusoidal. In alternative embodiments, the modified contour element includes two central gaps and an elliptical portion therebetween, the two central gaps being formed by opposing arcs at ends of first and second portions of the contour element extending inwardly from the impedance matching loop; the elliptical portion can be circular. Due to the novel design aspects of the modified contour elements of the present disclosure, they can all be formed on the substrate concurrently with the impedance matching loop and the dipole antenna, thereby avoiding the need for a separately created shielding layer as described in the '379 patent; however, they can also be made as separate layers above or below the impedance matching loop and the dipole antenna so long as they are electrically conductively coupled.

[0020] In typical embodiments, each of the first and second elements of the dipole antenna is characterized by a linear portion having a circular lobe termination. Preferably, the linear portions of the first and second elements of the dipole antenna are characterized by a smooth contour from the junction near where the linear portions extend outwardly from the impedance matching loop.

[0021] The substrate of the RFID inlay can include, for example, polyethylene terephthalate (PET). In addition to separately manufacturing the RFID inlays for use with food packaging, the substrate can also include a portion of and be manufactured concurrently with such packaging.

[0022] While the disclosed microwaveable RFID inlay has proven to significantly reduce the risk of arcing, the inlay can further include a layer of flame retardant material overlying at least a portion of the antenna structure proximate the IC chip bond area; further, the inlay can include a second layer of flame retardant material beneath the IC chip bond area beneath the substrate. The layer of flame retardant material can be bonded to the antenna structure and / or the substrate by an adhesive, which can also be flame retardant.

[0023] The essential features of the various embodiments to be described hereinafter in detail and optional features are summarized above; these essential features and certain optional features form the subject matter of the appended claims. Those skilled in the art will appreciate the principles of the specifically disclosed microwaveable RFID inlay as a basis for similar inlays, tags and products within the scope of the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0024] For a full understanding of the present disclosure, reference is now made to the following detailed description, taken in connection with the accompanying drawings, in which:

[0025] FIG. 1 illustrates a prior art RFID inlay;

[0026] Figure 2 A microwave-induced electric field in the prior art RFID inlay of FIG. 1 is illustrated;

[0027] Figure 3 Basic design features of a microwaveable RFID inlay according to the principles of the present disclosure are illustrated;

[0028] Figure 4 A second exemplary microwaveable RFID inlay with a ruler is illustrated;

[0029] Figure 5 A second exemplary microwaveable RFID inlay for microwaveable food packaging is illustrated;

[0030] Figure 6A And Figure 6B An exemplary layered structure of a microwaveable RFID inlay according to the principles of the present disclosure is illustrated;

[0031] Figure 7 A first equivalent circuit of an RFID antenna structure with improved profile elements according to the principles of the present disclosure is illustrated;

[0032] Figure 8 A second equivalent circuit of an RFID antenna structure with improved profile elements according to the principles of the present disclosure is illustrated;

[0033] Figure 9 First, second, third and fourth exemplary embodiments of a microwaveable RFID inlay according to the principles of the present disclosure are illustrated;

[0034] Figure 10 It shows Figure 9 The microwave-induced electric field in the first exemplary microwave-heatable RFID insert shown;

[0035] Figure 11 It shows Figure 9 Port impedance of the first exemplary microwave-heatable RFID insert shown.

[0036] Figure 12 It shows Figure 9 The microwave-induced electric field in the second exemplary microwave-heatable RFID insert is shown.

[0037] Figure 13 It shows Figure 9 Port impedance of the second exemplary microwave-heatable RFID insert shown;

[0038] Figure 14 It shows Figure 9 The microwave-induced electric field of the third exemplary microwave-heatable RFID insert is shown.

[0039] Figure 15 It shows Figure 9 Port impedance of the third exemplary microwave-heatable RFID insert shown.

[0040] Figure 16 It shows Figure 9 The microwave-induced electric field of the fourth exemplary microwave-heatable RFID insert is shown.

[0041] Figure 17 It shows Figure 9 The port impedance of the fourth exemplary microwave-heatable RFID insert is shown.

[0042] Figure 18 It shows Figure 9 The exemplary microwave-heatable RFID insert shown exhibits a microwave-induced electric field without improved contour elements.

[0043] Figure 19 A fifth exemplary embodiment of an RFID insert designed according to the principles of this disclosure is shown;

[0044] Figure 20 It shows Figure 19 The microwave-induced electric field in the fifth exemplary microwave-heatable RFID insert shown; and,

[0045] Figure 21 It shows Figure 20 The port impedance of the fifth exemplary microwave-heatable RFID insert is shown. Detailed Implementation

[0046] The following discloses design principles for microwaveable radio frequency identification (RFID) antennas, as well as exemplary RFID inlays suitable for use in microwave oven cooking of products or product packaging. To better understand the need for improved RFID inlay designs, reference is first made to FIG. 1, which illustrates a prior art RFID inlay 100. The RFID inlay 100 features a central impedance matching loop 110 and a dipole antenna, which includes a first leg 120-A and a second leg 120-B extending outwardly from the central impedance matching loop 110. A gap exists in the impedance matching loop 110 to form a die bonding area comprised of first and second integrated circuit (IC) bonding pads 111-A and 111-B. An RFID IC 130 is physically mounted within the die bonding area and is electrically connected to the bonding pads 111-A and 111-B, respectively. As can be seen, such prior art inlays contain multiple 90 degree corners to (1) improve impedance matching in the chip matching loop and the main antenna dipole (sharper corners increase the reactive impedance); and (2) efficiently utilize available space. Figure 2 The microwave induced electric field in the prior art RFID inlay 100 of FIG. 1 is shown. As can be seen, at the 90 degree corners and the corners, the electric field strength at these points is higher than other areas of the antenna geometry. However, the antenna structures disclosed herein are able to mitigate the high electric field strength induced by the microwaves, particularly in the vicinity of the die bonding area.

[0047] Turning now to Figure 3Fig. 3 shows the basic design features of a microwaveable RFID inlay 300 in accordance with the principles of the present disclosure. Similar to prior art inlay 100, RFID inlay 300 includes an impedance matching loop 310 and a dipole antenna composed of first and second elements 320-A and 320-B that extend linearly outward from the central impedance matching loop 310 and each terminate in a circular lobe. Preferably, the connection between the linear portions of the first and second elements of the dipole antenna near where they extend outward from the impedance matching loop is characterized by a smooth profile. A gap exists in the impedance matching loop 310 to form a die bonding area composed of first and second integrated circuit (IC) bonding pads 311-A and 311-B. An RFID IC (not shown) can be physically mounted within the die bonding area and electrically connected to bonding pads 311-A and 311-B, respectively. Unlike prior art inlay 100, RFID inlay 300 is composed of gentle and smooth curves and there is no antenna meandering in the dipole antenna portions 320-A and 320-B. More importantly, RFID inlay 300 includes an additional feature, an "improved profile element" 330 within the impedance matching loop 310; the improved profile element extends from a first interior side of the loop to a second interior side of the loop and is characterized by having an impedance at microwave frequencies that is lower than the impedance of the die bonding area. As will be described in more detail below, improved profile element 330 includes at least one central gap 333 between first and second portions 331 and 332. Lowering the impedance of improved profile element 330 at typical microwave oven frequencies (2.45 GHz) serves to draw higher currents away from the die bonding area, thereby mitigating arcing at the gap within impedance matching loop 310.

[0048] The technical and functional principles of the RFID inlay 300 and similar embodiments disclosed hereinafter for use in a microwave oven are three-fold. First, the antenna geometry is designed to eliminate and / or significantly reduce sharp corners and small bend radii features. These elements exhibit higher surface energy and also increase the risk of arcing at the higher voltage microwave (2.45 GHz) frequency. Therefore, the RFID inlay 300 and similar embodiments are designed to have only smooth curves and gentle bends as much as possible. Second, the overall antenna structure of the RFID inlay 300 is tuned to achieve performance maximization in the conventional RFID operating frequency range (860 - 960 MHz) while presenting an impedance mismatch at the microwave (2.45 GHz) frequency band. This reduces the formation of resonances inside and around the antenna structure and the excessive voltage and current that can lead to arcing. In particular, the antenna structure of the RFID inlay 300 contains a "modified profile element" that presents a lower impedance at the microwave (2.45 GHz) frequency band compared to the adjacent chip bonding area. This lower impedance diverts the excessive voltage and current away from the chip bonding area and towards the lower impedance modified profile. To further guard against the risk of arcing, the RFID inlay 300 can be converted to a tag structure that uses a flame retardant material, which will be described with reference to FIG. 6; this prevents and / or significantly reduces the formation and spread of any flames initiated by arcing in the event that the previous preventive design elements are insufficient.

[0049] Figure 4 A second exemplary microwaveable RFID inlay 400 with a scale is shown. The RFID inlay 400 is substantially similar to the RFID inlay 300, except that the modified profile element includes two center gaps. The RFID inlay 400 is designed as a tag with an adhesive layer 401 for sticking it to a product package; Figure 5 A second exemplary microwaveable RFID inlay 400 on a food package 500 for microwave preparation is shown. Rather than building the RFID inlay 400 with an adhesive layer 401 for sticking it to the food package 500 separately, the substrate of the RFID inlay 400 can be part of such a food package, so that the RFID inlay can be embedded directly into the package without the need to stick it to the package.

[0050] Now turning to Figure 6A and Figure 6BFig. 6 shows an exemplary layered structure of a microwaveable RFID inlay; these structures are substantially similar except that the orientation of the RFID inlay (consisting of a substrate layer and an antenna layer formed thereon) is flipped. First, an antenna structure 600 is formed on a substrate 610 according to methods known in the art. The configuration of the antenna structure 600 is as described previously for exemplary RFID inlays 300 and 400 (or other embodiments described hereafter); in particular, it is preferred to simultaneously form an impedance matching loop, a modified profile element, and a dipole antenna on the substrate. Next, a first layer of flame retardant (FR) material 630-A can be adhered to one side of the RFID inlay using a first adhesive layer 620-A, if desired for the intended application. Similarly, a second layer of flame retardant material 630-B can be adhered to the opposite side of the RFID inlay using a second adhesive layer 620-B, if desired for the intended application. The flame retardant material selected should have suitable radio frequency (dielectric) properties, and should reduce / eliminate the potential for fire hazard if an arc occurs; in addition, the adhesive layers can also be flame retardant. For applications where the RFID inlay is to be adhered to a product, an additional adhesive layer 640 and release liner 650 can be added; the release liner can then be removed to expose the adhesive layer for adhering the RFID inlay to the product.

[0051] The exemplary microwaveable RFID antenna structures disclosed herein all feature a "modified profile element" of low impedance, which is designed following the principle that:

[0052] The purpose of the modified profile is to create a low impedance path parallel to the chip bonding area, so that microwave induced current is directed through this preferred path, rather than through the gap in the impedance matching loop which can induce arcing.

[0053] The modified profile element consists of a relatively narrow gap at the center of the dipole, which is preferably as long as possible, and avoids sharp corners and small bend radii. In the simplest form, this can be achieved by a single sinusoidal gap, as shown in Figure 3 Alternatively, two (or more) consecutive gaps, or two opposing arcs, can be employed, as described below, which form a solid ellipse at the center.

[0054] The resulting low impedance is due to two factors:

[0055] The narrow and long gap increases the leakage current through the underlying PET media substrate, which is represented by Z LC , which is a pure real number, so that Z LC = R LC ; and,

[0056] The modified profile introduces a larger parallel capacitance, which is represented by Z CC .

[0057] It is important to note that preferably, the thickness of the improved profile gap is optimized so that the above-mentioned characteristics become significant without making the gap too narrow. If the gap is too narrow, the probability of dielectric breakdown increases significantly, thus greatly negating the advantages of the design element.

[0058] Figure 7 A first equivalent circuit 700 for an RFID antenna structure with an improved profile element according to the principles of the present disclosure is shown. The equivalent circuit is composed of the impedance (Z CG ) of the chip gap region 710 in parallel with the impedance of the improved profile region 720, where R LC represents the real part impedance associated with the leakage current through the improved profile element, and Z CC is the impedance resulting from the profile element capacitance. The profile capacitance impedance (Z CC ) is a function of frequency and capacitance:

[0059]

[0060] where ω = 2πf and and,

[0061] where d is the thickness of the profile element gap, and A is the product of the length of the improved profile and the aluminum antenna thickness, which is a constant (10 um).

[0062] Thus, it can be seen that Z CC is inversely proportional to the frequency f and the capacitance C. Therefore, to reduce the imaginary part of Z CC , the capacitance can be increased by:

[0063] making the profile gap thinner to reduce d; or,

[0064] increasing A by making the profile gap length longer.

[0065] For designs with multiple gaps in the improved profile element, Figure 8 A second equivalent circuit 800 for an RFID antenna structure with an improved profile element according to the principles of the present disclosure is shown. In such embodiments, the improved profile region impedance includes two resistance (R LC1 and R LC2 ) and two capacitance (Z CC1 and Z CC2 ) components.

[0066] To obtain the optimal antenna geometry to achieve peak UHF RFID performance while sufficiently reducing the zero current (ZCC) to reduce the current density in the chip gap region, a number of different prototype versions were designed and tested (described below with reference to Figures 9-21 Figure 9 ​Exemplary embodiments 910, 920, 930, and 940 of RFID inserts designed according to the principles of this disclosure are shown. These prototypes are generally similar, but differ in the shape of the central improved contour element; specifically, the embodiments vary in the shape and number of gaps.

[0067] The first exemplary embodiment 910 is characterized in that the profile element has a single narrow sinusoidal gap; therefore, the length of the gap is greater than the width of the improved profile element. Those skilled in the art will recognize that other linear or curved gaps may also be used to satisfy the design principles of this disclosure; that is, to present lower impedance in the microwave (2.45 GHz) band.

[0068] The second exemplary embodiment 920 is characterized in that the contour element has two narrow sinusoidal gaps. The third exemplary embodiment 930 is characterized in that the contour element has two gaps and an elliptical portion between the two gaps, wherein the two gaps are formed by opposing arcs at the ends of a first portion and a second portion extending inward from the impedance matching loop of the contour element. The fourth exemplary embodiment 940 is characterized in that it has a single wide sinusoidal gap.

[0069] Figure 9 Each exemplary embodiment shown has been modeled to determine the microwave induced electric field and port impedance. First, Figure 10 It shows Figure 9 The microwave-induced electric field in the first exemplary microwave-heatable RFID insert 910 is shown. It can be seen that at microwave (2.45 GHz) frequencies, the lower impedance improved profile element diverts the current density away from the chip bonding region and towards the improved profile and the lower part of the loop antenna. Figure 11 It shows Figure 9 The port impedance of the first exemplary microwave-heatable RFID insert 910 is shown and compared with the original port impedance (i.e., without the improved profile element). It can be seen that in the microwave (2.45 GHz) band, the chip port impedance (1144 Ω) is significantly higher than that of the improved profile port element (623 Ω). This helps to reduce the voltage and subsequent current density at the chip port region in the microwave band, thereby ultimately helping to reduce the formation of arc discharge in the chip bonding region.

[0070] Figure 12 It shows Figure 9 The microwave-induced electric field in the second exemplary microwave-heatable RFID insert 920 is shown. It can also be seen that at microwave frequencies, the lower impedance improved profile element draws current density away from the chip bonding region and towards the improved profile element and the underlying region. Similarly, refer to... Figure 13As can be seen, in the microwave (2.45GHz) band, the chip port impedance (approximately 715Ω) is significantly higher than that of the improved profile port element (approximately 354Ω), which will result in a lower likelihood of arc discharge in the chip bonding region.

[0071] Figure 14 It shows Figure 9 The third exemplary microwave-heatable RFID insert 930 illustrates a microwave-induced electric field. Similar to previous embodiments, at microwave frequencies, the lower impedance improved profile element draws current density away from the chip bonding region and towards the improved profile element and the underlying region. Likewise, Figure 15 It shows Figure 9 The third exemplary microwave-heatable RFID insert 930 shown has a significantly higher port impedance (approximately 672 Ω) in the microwave (2.45 GHz) band than the improved profile port element (approximately 339 Ω).

[0072] Figure 16 It shows Figure 9 The microwave-induced electric field in the fourth exemplary microwave-heatable RFID insert 940 is shown; again, it can be seen that at microwave frequencies, the lower impedance improved profile element draws current density away from the chip bonding region and towards the improved profile element and the underlying region. Similarly, see Figure 17 As can be seen, in the microwave (2.45 GHz) band, the port impedance of the fourth exemplary microwave-heatable RFID insert 940 (approximately 677 Ω) is significantly higher than that of the improved profile port element (approximately 332 Ω).

[0073] Compared with Examples 910, 920, 930 and 940, Figure 18 It shows Figure 9 The exemplary microwave-heatable RFID insert shown does not employ the improved profile element in terms of the microwave-induced electric field. Those skilled in the art will understand that without the improved profile element of this disclosure, the current density throughout the loop would increase significantly; in particular, it would increase by 10–15 times in the chip bonding region, which could potentially generate sparks and / or breakdown in the microwave (2.45 GHz) band.

[0074] at last, Figure 19 A fifth exemplary RFID insert 1900 designed according to the principles of this disclosure is shown. Similar to the previous embodiments, Figure 20 This illustrates that, at microwave frequencies, the microwave-induced current density in a fifth exemplary microwave-heatable RFID insert 1900 is diverted from the chip bonding region and directed to the lower portion of the improved profile elements and impedance matching loop. Furthermore, as... Figure 21As shown, the port impedance of the fifth exemplary microwave-heatable RFID inlay 1900 (about 7491 ohms) is significantly higher than the improved profile port element (about 3584 ohms) in the microwave (2.45 GHz) frequency band.

[0075] The essential and optional features of RFID inlays, tags, and products according to the principles of the present application are summarized above. The disclosed embodiments are intended to be illustrative of these essential and optional features and functions, and alternative or modified arrangements can be conceived by those skilled in the art without departing from the principles of the present application as encompassed by the appended claims, and these alternative or modified arrangements can be functionally equivalent.

[0076] It is to be understood that the application is not limited to the specific details described herein only in an exemplary manner, and that various modifications and changes can be made without departing from the scope of the application as defined in the appended claims.

Claims

1. An RFID inlay for microwaveable food packaging, the RFID inlay comprising: a substrate; an antenna structure formed on the substrate, the antenna structure comprising an impedance matching loop and a dipole antenna, wherein the impedance matching loop comprises an integrated circuit (IC) die bonding area characterized by a gap in the loop, wherein first and second IC bonding points are formed at ends of the loop on either side of the gap; wherein the impedance matching loop further comprises a modified profile element extending from a first interior side to a second interior side of the loop, the modified profile element characterized by an impedance at microwave frequencies that is lower than the impedance of the die bonding area; and, wherein the dipole antenna comprises first and second elements extending outwardly from the impedance matching loop; and, an IC physically disposed within the IC die bonding area of the central impedance matching loop and electrically coupled to the first and second IC bonding points; wherein the antenna structure is characterized by an operating frequency suitable for activating and reading information stored in the IC, and wherein current induced in the antenna structure when exposed to microwave frequencies is directed substantially through the modified profile element, away from the die bonding area, to reduce arcing at the gap in the loop. The modified profile element comprises at least one central gap.

2. The RFID inlay of claim 1, wherein, The at least one central gap has a length that is greater than a width of the modified profile element.

3. The RFID inlay of claim 1, wherein, The at least one central gap is curvilinear.

4. The RFID inlay of claim 3, wherein, The at least one central gap is substantially sinusoidal.

5. The RFID inlay of claim 4, wherein, The modified profile element comprises two central gaps and an elliptical portion between the two central gaps, wherein the two central gaps are formed by opposing arcs at ends of first and second portions of the profile element extending inwardly from the impedance matching loop.

6. The RFID inlay of claim 2, wherein, The elliptical portion is circular.

7. The RFID inlay of claim 6, wherein, Each of the first and second elements of the dipole antenna is characterized as having a linear portion terminated by a rounded lobe.

8. The RFID inlay of claim 1, wherein, The linear portions of the first and second elements of the dipole antenna are characterized as having a smoothly profiled junction proximate to where the linear portions extend outwardly from the impedance matching loop.

9. The RFID inlay of claim 8, wherein, The substrate comprises polyethylene terephthalate (PET).

10. The RFID inlay of claim 1, wherein, The substrate comprises a portion of the food packaging.

11. The RFID inlay of claim 1, wherein, 12. The RFID inlay of claim 1, further comprising a layer of flame retardant material over at least a portion of the antenna structure proximate to the IC die bonding area.

13. The RFID inlay of claim 12, further comprising a second layer of flame retardant material under at least a portion of the substrate proximate to the IC die bonding area. The layer of flame retardant material is bonded to the substrate or the antenna structure by an adhesive.

14. The RFID inlay of claim 12, wherein, The adhesive is flame retardant.

15. The RFID inlay of claim 14, wherein, The modified profile element is formed on the substrate concurrently with the impedance matching loop and the dipole antenna.

16. The RFID inlay of claim 1, wherein, The modified profile element is formed on the substrate concurrently with the impedance matching loop and the dipole antenna.

Images