EP4643269A1

EP4643269A1 - Radio-frequency identification inlays for use with or incorporated into microwavable food packages

Info

Publication number: EP4643269A1
Application number: EP24704399.5A
Authority: EP
Inventors: Mohammed RAMZAN
Original assignee: SML Brand Identification Solutions Ltd; Sml Brand Identification Solutions Ltd
Current assignee: SML Brand Identification Solutions Ltd; Sml Brand Identification Solutions Ltd
Priority date: 2023-02-09
Filing date: 2024-02-08
Publication date: 2025-11-05
Also published as: WO2024165690A1; CN120917449A

Abstract

Radio-frequency identification (RFID) inlay designs for packages to contain food products intended for microwave preparation. In general, the RFID inlay designs include a substrate on which an antenna structure is formed; the antenna structure having an impedance matching loop and a dipole antenna. The impedance matching loop includes an integrated circuit (IC) chip bond region characterized by a gap in the loop, wherein ends of the loop on either side of the gap form first and second IC bonding points; an IC is physically positioned within the IC chip bond region and electrically coupled to the first and second IC bonding points. The impedance matching loop further comprises a modified contour element that extends from a fist internal side of the loop to a second internal side, the modified contour element characterized by a lower impedance at microwave frequencies than an impedance through the chip bond region. The dipole antenna comprises first and second elements extending outwardly from the impedance matching loop. The antenna structure is characterized by an operational frequency suitable for activating and reading information stored in the IC, but currents induced in the antenna structure when exposed to microwave frequencies are substantially diverted through the modified contour element, away from the chip bond area, whereby electrical arcing across the gap in the loop is mitigated.

Description

RADIO-FREQUENCY IDENTIFICATION INLAYS FOR USE WITH OR INCORPORATED INTO MICROWAVABLE FOOD PACKAGES

The present invention claims priority from and 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, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure is directed, in general, to Radio Frequency Identification (RFID) inlays and, more specifically, to RFID inlays for use with or incorporated into packages for food products intended for microwave preparation.

BACKGROUND

Radio frequency identification (RFID) uses electromagnetic fields to identify and track tags attached to objects. An RFID tag, or “inlay”, consists of three different components: an RFID “chip”, which is an integrated circuit (IC), and an antenna, both affixed to a substrate. When activated by an electromagnetic interrogation pulse from an RFID reader device, the tag transmits digital data, usually an identifying inventory number, back to the reader; the number can be used, for example, to inventory goods, track their movement, and register the sale of a product to which they are attached. There are two types of RFID tags; passive tags are powered by energy from an RFID reader's interrogating radio waves, and active tags are powered by a battery and can be read at a greater range from the RFID reader (up to hundreds of meters). Unlike a barcode, an RFID tag does not need to be within the line of sight of the reader, so it may be embedded in a tracked object.

An RFID tag IC has a logic unit that makes decisions and provides memory for stored data, such as a unique product ID. An RFID tag antenna, connected to the tag IC, is the largest part of the tag. The geometry of an antenna is determined by the frequency at which the tag operates; variations in antenna design allow tags to have different properties and behaviors. The antenna can be shaped, for example, as a spiral coil, a single dipole, dual dipoles (one perpendicular to other), or a folded dipole. The antenna is designed for a specific frequency of operation and the designated frequency determines an effective antenna length. A substrate holds the RFID IC and antenna together; an antenna can be deposited or printed on the substrate, and the IC is then attached to the antenna and the substrate. A substrate can be made from flexible material such as thin plastic, but it may also be made from rigid material. Most passive tags use substrates made from flexible material with a thickness of 100 to 1000 nm. Suitable materials for a substrate include polymer, PVC, Polyethylenetherephtalate (PET), phenolics, polyesters, styrene, and even paper. The substrate material may affect the design frequency of the antenna; therefore, the effect of substrate material must be considered during proper tuning of the antenna.

RFID tags can be incorporated into, or attached to, packages containing a food product intended for microwave preparation; doing so without proper precautions, however, can cause undesired electrical arcing, potentially resulting in a fire. United States Patent Application No. 17/787,667 (hereinafter the “’667 patent application”), entitled “Two-Part RFID Tags for Incorporation into Microwavable Food Packaging” describes the problem, to wit:

“[0006] [An] RFID tag includes an RFID chip, with an associated antenna for transmitting information to and/or receiving information from an RFID reader. The RFID chip is electrically coupled to the antenna across a gap defined by the antenna between two conductor pad areas. Such 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 may be as low as 10 microwatts, whereas a microwave oven may typically operate at a power level in excess of 800 watts, which can generate very high voltages across the gap and the associated RFID chip.

“[0007] The antenna is designed to operate at a first frequency, for example in the range of approximately 860 MHz to 930 MHz, with the antenna taking incident power at the first frequency from an RFID reader and converting it to a voltage across the RFID chip to allow it to operate.

“[0008] A second frequency applied by the microwave oven, typically on the order of approximately 2,450 MHz, may also be incident on the antenna when the RFID tag is placed into the microwave oven. The antenna is not designed to operate at the second frequency, as the very high power levels incident at second frequency will generate high voltages on the antenna. These high voltages can appear at a number of places on the antenna; however, by methods such as introducing large gaps between antenna elements and controlled radii, a voltage across said elements that would generate a high voltage breakdown and, hence, arc can be avoided. However, the gap bridged by the RFID chip is necessarily relatively small and, hence, a high voltage arises at the second frequency, which high voltage may cause a breakdown and generate an arc.

“[0009] To avoid problems of this nature, [an] RFID tag is 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) into the microwave oven with the food item, thereby failing to dissociate the RFID tag from the food item.

“[0010] Even if the RFID tag is properly dissociated from the food item prior to microwaving the food item, the RFID tag has certain limitations. For example, if the RFID tag is secured to an enclosure of the packaging, it is impossible to track the food item using an RFID reader before the food item is placed into the enclosure. However, it may be advantageous to be able to read and/or write to the RFID tag before the food item is placed into the enclosure to provide traceability of the ingredients, the machinery used, etc. Similarly, it becomes impossible to track the food item after it has been removed from the enclosure. This is disadvantageous when the food item is intended to be removed from the enclosure, heated in a microwave, and then paid for, which may include communicating with the RFID tag for pricing and/or inventory purposes at a cash register or similar point of sale terminal.”

The solution proposed in the ‘667 patent application is to utilize a two-part package, wherein a first package member (containing a food product) is configured to be microwaved while a second package member is configured to be dissociated from the first package member prior to microwaving the first package member; according to the Abstract of the ‘667 patent application:

“The RFID tag includes a reactive strap associated with the first member and a far-field antenna associated with the second member. The reactive strap is coupled to the antenna when the packaging is intact, while being decoupled from the antenna when the second member has been dissociated from the first member. The RFID tag is capable of far-field communication when the reactive strap is coupled to the antenna, while the reactive strap is capable of only near-field communication when decoupled from the antenna.”

The proposed solution, however, will be ineffective if a user forgets to remove the second package member prior to placing the food product in a microwave. Furthermore, a smart microwave appliance could utilize the presence of an RFID tag on a product placed inside to automatically set the appropriate cooking temperature and time; thus, a solution that mandates removal of a portion of a food product package, including all or part of an associated RFID tag, prior to placement in a microwave could be undesirable. Furthermore, the ‘667 patent application itself recognizes that problem, to wit:

“[0033] . . . it is possible that a user will not so dissociate the second package member 16 (and associated far-field antenna 22) from the first package member 14, the far-field antenna 22 may be configured to ensure that microwaving the assembled RFID tag 18 will not create smoke or fire or an unsafe condition. This may be achieved according to any suitable approach, which may include the far-field antenna 22 being configured to fracture when microwaved, such as by configuring the far-field antenna 22 to expand at a different rate than the second package member 16 when heated, thereby causing the far-field antenna 22 to fracture. Alternatively, the far-field antenna 22 may be configured such that it is allowed to overheat, possibly damaging the second package member 16, but not creating an arc or fire or smoke.”

Thus, it was recognized by the inventor of the ‘667 patent application that the proposed solution could still potentially cause arcing or fire without the use of a secondary means to prevent or mitigate such problems. That inventor is also a named inventor of United States Patent No. 11 ,308,379 B2 (hereinafter the “’379 patent”), entitled “RFID Tags with Shielding Structure for Incorporation into Microwavable Food Packaging”; that patent describes a solution that requires a shielding structure coupled to the antenna across the gap and overlaying the RFID chip. As described in the Abstract of the ‘379 patent:

“RFID tags are provided for incorporation into the packaging of a microwavable food item, with the RFID tag being 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 overlays the RFID chip. The shielding structure includes a shield conductor and a shield dielectric at least partially positioned between the shield 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 that is greater than first frequency.”

Although the solution proposed in the ‘379 patent might be effective to 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 tags suitable for microwavable applications. Accordingly, there remains a need in the art for improved RFID inlay designs that can overcome the deficiencies of prior art RFID designs for use with or incorporated into a package containing a food product intended for microwave preparation.

SUMMARY

To address the deficiencies of the prior art, disclosed herein are radio-frequency identification (RFID) inlay designs for packages to contain food products intended for microwave preparation. In general, the RFID inlay designs include a substrate on which an antenna structure is formed; the antenna structure having an impedance matching loop and a dipole antenna. The impedance matching loop includes an integrated circuit (IC) chip bond region characterized by a gap in the loop, wherein ends of the loop on either side of the gap form first and second IC bonding points; an IC is physically positioned within the IC chip bond region and electrically coupled to the first and second IC bonding points. The impedance matching loop further comprises a modified contour element that extends from a fist internal side of the loop to a second internal side, the modified contour element characterized by a lower impedance at microwave frequencies than an impedance through the chip bond region. The dipole antenna comprises first and second elements extending outwardly from the impedance matching loop. The antenna structure is characterized by an operational frequency suitable for activating and reading information stored in the IC, but currents induced in the antenna structure when exposed to microwave frequencies are substantially diverted through the modified contour element, away from the chip bond area, whereby electrical arcing across the gap in the loop is mitigated. In general, the modified contour element of the disclosed microwavable RFID inlays comprises at least one central gap. In exemplary embodiments, the at least one central gap has a length greater than the width of the modified contour element. For example, the at least one central gap can be curvilinear; e.g., it can be substantially sinusoidal. In alternative embodiments, the modified contour element comprises two central gaps formed by opposing arcs in the ends of first and second portions of the contour element extending inwardly from the impedance matching loop and an elliptic portion centered therebetween; the elliptic portion can be circular. Because of the novel design aspects of the modified contour elements disclosed herein, they can all be formed on the substrate simultaneously with the impedance matching loop and the dipole antenna, which obviates the need for a separately-created shield layer, such as described in the ‘379 patent described supra; such elements, however, can be created as a separate layer above or below the impedance matching loop and the dipole antenna provided they are conductively coupled.

In general embodiments, each of the first and second elements of the dipole antenna are characterized by a linear portion terminated with a rounded lobe. Preferably, junctions proximate the location the linear portions of the first and second elements of the dipole antenna extend outwardly from the impedance matching loop are characterized by smooth contours.

The substrate of the disclosed RFID inlays can comprise, for example, polyethylenetherephtalate (PET). Rather than separately manufacturing RFID inlays for use with food packages, the substrate can also comprise a portion of such packages and be manufactured simultaneously.

Although the disclosed microwavable RFID inlays have been shown to substantially mitigate the risk of arcing, an inlay can further include a layer of fire retardant material overlaying at least a portion of the antenna structure proximate the IC chip bond region; additionally, an inlay can include a second layer of fire retardant material underlaying the IC chip bond region below the substrate. The layer(s) of fire retardant material can be bonded to the antenna structure and/or substrate by an adhesive, which can also be fire retardant.

The foregoing has broadly outlined the essential and optional features of the various embodiments that will be described in detail hereinafter; the essential and certain optional features form the subject matter of the appended claims. Those skilled in the art should recognize that the principles of the specifically disclosed microwavable RFID inlays can be utilized as a basis for similar inlays, tags and products that are within the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

For a complete understanding of the present disclosure, reference is now made to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 illustrates a prior art RFID inlay;

FIGURE 2 illustrates microwave-induced electric fields in the prior art RFID inlay illustrated in FIGURE 1 ;

FIGURE 3 illustrates the basic design features of microwavable RFID inlays in accordance with the principles disclosed herein;

FIGURE 4 illustrates a second exemplary microwavable RFID inlay with a ruler for scale;

FIGURE 5 illustrates the second exemplary microwavable RFID inlay on a food package intended for microwave preparation;

FIGURES 6A and 6B illustrate exemplary layered constructions for microwavable RFID inlays according to the principles disclosed herein;

FIGURE 7 illustrates a first equivalent circuit for an RFID antenna structure having a modified contour element according to the principles disclosed herein;

FIGURE 8 illustrates a second equivalent circuit for an RFID antenna structure having a modified contour element according to the principles disclosed herein;

FIGURE 9 illustrates first, second, third and fourth exemplary embodiments of RFID inlays designed in accordance with the principles disclosed herein;

FIGURE 10 illustrates microwave-induced electric fields in the first exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 11 illustrates the port impedance for the first exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 12 illustrates microwave-induced electric fields in the second exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 13 illustrates the port impedance for the second exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 14 illustrates microwave-induced electric fields in the third exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 15 illustrates the port impedance for the third exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 16 illustrates microwave-induced electric fields in the fourth exemplary microwavable RFID inlay illustrated in FIGURE 9; FIGURE 17 illustrates the port impedance for the fourth exemplary microwavable RFID inlay illustrated in FIGURE 9;

FIGURE 18 illustrates microwave-induced electric fields in the exemplary microwavable RFID inlays illustrated in FIGURE 9 without a modified contour element;

FIGURE 19 illustrates a fifth exemplary embodiment of an RFID inlay designed in accordance with the principles disclosed herein;

FIGURE 20 illustrates microwave-induced electric fields in the fifth exemplary microwavable RFID inlay illustrated in FIGURE 19; and,

FIGURE 21 illustrates the port impedance for the fifth exemplary microwavable RFID inlay illustrated in FIGURE 20.

DETAILED DESCRIPTION

Disclosed hereinafter are principles for the design of microwaveable radio-frequency identification (RFID) antennas and exemplary RFID inlays suitable for use on products, or product packaging, that are to be cooked in a microwave oven. To better understand the need for the improved design of RFID inlays, reference is first made to FIGURE 1 , which illustrates a prior art RFID inlay 100. RFID inlay 100 is characterized by a central impedance matching loop 110 and a dipole antenna comprising first and second legs 120-A and 120- B extending outwardly from the central impedance matching loop 110. A gap exists in the impedance matching loop 110 to form a chip bond region consisting of first and second integrated circuit (IC) bonding points 111-A and 111-B. An RFID IC 130 is physically mounted in the chip bond region and electrically coupled to bonding points 111-A and 111- B. As can be seen, such prior art inlays contain many 90 degree bends in order to (1 ) improve impedance matching (sharper bends increase reactive impedance) both in the chip matching loop and the main antenna dipole; and (2) make efficient use of available space. FIGURE 2 illustrates microwave-induced electric fields in the prior art RFID inlay 100 illustrated in FIGURE 1. As can be seen, with 90 degree bends and corners, the electric field strengths are higher at these points compared to other areas of the antenna geometry. The antenna structures disclosed herein, however, can mitigate the high electric field strengths, induced by microwaves, particularly proximate the chip bond region.

Turning now to FIGURE 3, illustrated are the basic design features of a microwavable RFID inlay 300 in accordance with the principles disclosed herein. RFID inlay 300, similar to prior art inlay 100, includes an impedance matching loop 310 and a dipole antenna comprising first and second elements 320-A and 320-B extending linearly outward from the central impedance matching loop 310 and each terminated with a rounded lobe. Preferably, junctions proximate the location the linear portions of the first and second elements of the dipole antenna extend outwardly from the impedance matching loop are characterized by smooth contours. A gap exists in the impedance matching loop 310 to form a chip bond region consisting of first and second integrated circuit (IC) bonding points 311-A and 311-B. An RFID IC (not shown) can be physically mounted in the chip bond region and electrically coupled to bonding points 311-A and 311-B. Unlike prior art inlay 100, RFID inlay 300 consists of gentle and smooth curves with no antenna meandering in the dipole antenna portions 320-A and 320-B. More importantly, the RFID inlay 300 includes an additional feature of a “modified contour element” 330 within the impedance matching loop 310; the modified contour element extends from a fist internal side of the loop to a second internal side of the loop and is characterized by a lower impedance at microwave frequencies than an impedance through the chip bond region. As will be described in more detail hereinafter, the modified contour element 330 includes at least one central gap 333 between first and second portions 331 and 332. Decreasing the impedance at the frequency of typical microwave ovens (2.45GHz) through the modified contour element 330 functions to divert higher currents away from the chip bond area, whereby electrical arcing across the gap in the impedance matching loop 310 can be mitigated.

The technical and functional principles of RFID inlay 300, and similar embodiments disclosed hereinafter, for use within a microwave oven are three-fold. First, the antenna geometry is designed to eliminate and/or significantly reduce sharp angles and low bend radii features. These elements tend to exhibit high surface energies and also increase arcing at higher voltage microwave (2.45GHz) frequencies. Thus, RFID inlay 300, and similar embodiments, are designed to have only smooth curves and gentle bends wherever possible. Second, the general antenna structure of RFID inlay 300 is tuned to maximise performance within the conventional RFID operating frequency range (860-960MHz), whilst presenting an impedance mismatch within the microwave (2.45GHz) band. This reduces resonances and excessive voltages and currents being formed within and around the antenna structure which can lead to arcing. In particular, the antenna structure of RFID inlay 300 incorporates a ‘modified contour element’ which presents a lower impedance to the microwave (2.45GHz) band than the nearby chip-bond area. This lower impedance diverts excessive voltages and currents away from the chip-bond area and towards the lower impedance modified contour. To further protect against the risk of arcing, the RFID inlay 300 can be converted into a label construction, as will be described with reference to FIGURE 6, using fire retardant materials; this prevents and/or significantly reduces the formation and progression of any flames resulting from arcing in circumstances where the previously mentioned preventative design elements are insufficient.

FIGURE 4 illustrates a second exemplary microwavable RFID inlay 400 with a ruler for scale. RFID inlay 400 is substantially the same as RFID inlay 300, except the modified contour element includes two central gaps. The RFID inlay 400 is constructed as a label having an adhesive layer 401 for affixing the RFID inlay to a product package; FIGURE 5 illustrates the second exemplary microwavable RFID inlay 400 on a food package 500 intended for microwave preparation. Rather than separately constructing RFID inlay 400, having an adhesive layer 401 for affixing to food package 500, the substrate for RFID inlay 400 can be a portion of such food package, whereby the RFID inlay is directly incorporated into the package rather than requiring it to be affixed thereto.

Turning now to FIGURES 6A and 6B, illustrated are exemplary layered constructions for microwavable RFID inlays; the constructions are substantially similar, except the orientation of the RFID inlay (consisting of a substrate layer and antenna layer formed thereon) are flipped. First, an antenna structure 600 is formed on a substrate 610 according to methods known in the art. The antenna structure 600 is configured as described previously with respect to exemplary RFID inlays 300 and 400 (or other embodiments described hereinafter); in particular, the impedance matching loop, modified contour element, and dipole antenna are preferably simultaneously formed on the substrate. Next, if warranted by the intended application, a first adhesive layer 620-A can be utilized to bond a first fire retardant (FR) material layer 630-A to one side of the RFID inlay. Similarly, if warranted by the intended application, a second adhesive layer 620-B can be utilized to bond a second FR material layer 630-B to the opposite side of the RFID inlay. The FR materials are selected to have suitable RF (dielectric) properties as well as their ability to reduce / eliminate potential fire hazards if arcing should occur; in addition, the adhesive layer can also be fire retardant. For applications where the RFID inlay will be affixed to a product, an additional adhesive layer 640 and release liner 650 can be added; the release liner can subsequently be removed to expose the adhesive layer for affixing the RFID inlay to a product.

The exemplary microwaveable RFID antenna structures disclosed herein are each characterized by a low impedance “modified contour element”, designed in accordance with the following principles.

• The purpose of the modified contour is to produce a low impedance path in parallel to the chip bond area, such that microwave-induced currents are diverted through this preferential path, rather than through the gap in the impedance matching loop which can induce arcing.

• The modified contour element consists of a relatively narrow gap at the center of the dipole, which is preferably as long as possible and remissive of sharp corners and low bend radii. In the simplest form, this can be realized by a single sinusoidally shaped gap as illustrated in FIGURE 3. Alternatively, two (or more) sequential gaps or two opposing arcs, which form a solid ellipse at the center can be utilized, as described hereinafter.

• The resulting low impedance arises from two factors:

The narrow and long length of the gap(s) increases the leakage current through the underlying PET dielectric substrate, and is represented by Z c, which is purely real, therefore Z c = RLC; and,

The modified contour introduces a large parallel electrical capacitance, which is represented by Zee-

Note that the thickness of the modified contour gap is preferably optimised such that the above characteristics become significant, without the gap becoming too narrow. If the gap is too narrow, the probability of dielectric breakdown significantly increases, far negating the advantages of this design element.

FIGURE 7 illustrates a first equivalent circuit 700 for an RFID antenna structure having a modified contour element according to the principles disclosed herein. The equivalent circuit is composed of the impedance (Z_CG) of the chip gap area 710 in parallel with the impedance of the modified contour area 720, where RLC represents the real impedance in relation to the leakage current via the modified contour element and Z_Cc is the impedance due to the contour element capacitance. The contour capacitance impedance (Z_Cc), is a function of frequency as well as electrical capacitance:

1

Zee = - ja>C sA where, a) = 2nf and C = — , and, d where d is the thickness of the contour element gap, and A is the product of the length of the modified contour by the thickness of the aluminium antenna, which is a constant (10 rm).

Therefore, it can be seen that Z_Cc is inversely proportional to the frequency, f, and the electrical capacitance, C. Thus, in order to lower the Z_Cc imaginary impedance, the capacitance is increased by either: reducing d, making the contour gap thinner; or,

■ increasing A, by making the contour gap length longer.

For designs having multiple gaps in the modified contour element, FIGURE 8 illustrates a second equivalent circuit 800 for an RFID antenna structure having a modified contour element according to the principles disclosed herein. In such embodiments, the modified contour area impedance includes two resistance (RLCI and RLCS) and two capacitance (Z_Cci and Zees) components.

A number of different prototype versions, described hereinafter with reference to FIGURES 9-21 , were designed and tested in order to arrive at optimum antenna geometries for peak UHF RFID performance whilst sufficiently lowering Zee in order to reduce current density at the chip gap area. FIGURE 9 illustrates first 910, second 920, third 930 and fourth 940 exemplary embodiments of RFID inlays designed in accordance with the principles disclosed herein. The prototypes are substantially similar, but vary in the shape of the central modified contour element; in particular, the embodiments differ in the shape and number of gaps.

The first exemplary embodiment 910 is characterized by a contour element having a single narrow sinusoidal gap; as such, the gap has a length that is greater than the width of the modified contour element. Those skilled in the art will recognize that other linear or curvilinear gaps might also be utilized to satisfy the design principles disclosed herein; i.e., which present a lower impedance at the microwave (2.45GHz) band.

The second exemplary embodiment 920 is characterized by a contour element having two narrow sinusoidal gaps. The third exemplary embodiment 930 is characterized by a contour element having a two gaps formed by opposing arcs in the ends of first and second portions of the contour element extending inwardly from the impedance matching loop and an elliptic portion centered therebetween. The fourth exemplary embodiment 940 is characterized by a single wide sinusoidal gap.

The exemplary embodiments illustrated in FIGURE 9 were each modelled to determine both the microwave-induced electric fields and port impedances. First, FIGURE 10 illustrates microwave-induced electric fields in the first exemplary microwavable RFID inlay 910 illustrated in FIGURE 9. As can be seen, at microwave (2.45GHz) frequencies, the lower impedance modified contour element diverts current densities away from the chip bond area and towards the modified contour and lower sections of the loop antenna. FIGURE 11 illustrates the port impedance for the first exemplary microwavable RFID inlay 910 illustrated in FIGURE 9, in comparison to the original port impedance (i.e., without the modified contour element). As can be seen, the chip port impedance is significantly higher (1 144 Q) than the modified contour port element (623 Q) at the microwave (2.45GHz) band. This acts to reduce the voltages and subsequent current densities at the chip port area at the microwave band, which ultimately helps to reduce the formation of arcing at the chip bond area.

FIGURE 12 illustrates microwave-induced electric fields in the second exemplary microwavable RFID inlay 920 illustrated in FIGURE 9. As can be seen again, the lower impedance modified contour element diverts current densities away from the chip bond area and towards the modified contour element and lower sections at microwave frequencies. Similarly, with reference to FIGURE 13, it can be seen that the chip port impedance is significantly higher (-715 Q) than the modified contour port element (-354 Q) at the microwave (2.45GHz) band, which will result in a lower potential for arcing in the chip bond area.

FIGURE 14 illustrates microwave-induced electric fields in the third exemplary microwavable RFID inlay 930 illustrated in FIGURE 9. As with the prior embodiments, the lower impedance modified contour element diverts current densities away from the chip bond area and towards the modified contour element and lower sections at microwave frequencies. Likewise, FIGURE 15 illustrates that the port impedance for the third exemplary microwavable RFID inlay 930 is significantly higher (-672 Q) than the modified contour port element (-339 Q) at the microwave (2.45GHz) band.

FIGURE 16 illustrates microwave-induced electric fields in the fourth exemplary microwavable RFID inlay 940 illustrated in FIGURE 9; again, it can be seen that the lower impedance modified contour element diverts current densities away from the chip bond area and towards the modified contour element and lower sections at microwave frequencies. Similarly, with reference to FIGURE 17, it can be seen that the port impedance for the fourth exemplary microwavable RFID inlay 940 is significantly higher (-677 Q) than the modified contour port element (-332 Q) at the microwave (2.45GHz) band.

For comparison to the embodiments 910, 920, 930 and 940, FIGURE 18 illustrates microwave-induced electric fields in the exemplary microwavable RFID inlays illustrated in FIGURE 9 without a modified contour element. Those skilled in the art will recognize that, without the modified contour element as disclosed herein, the current density in the entire loop is greatly increased; in particular it is 10-15 times greater in the chip bond area, which has the potential to generate sparking and/or breakdown at microwave (2.45GHz) band.

Finally, FIGURE 19 illustrates a fifth exemplary embodiment of an RFID inlay 1900 designed in accordance with the principles disclosed herein. As with the prior embodiments, FIGURE 20 illustrates that microwave-induced current densities in the fifth exemplary microwavable RFID inlay 1900 are diverted away from the chip bond area and towards the modified contour element and lower sections of the impedance matching loop at microwave frequencies. Furthermore, as illustrated in FIGURE 21 , the port impedance for the fifth exemplary microwavable RFID inlay 1900 is significantly higher (-7491 Q) than the modified contour port element (-3584 Q) at the microwave (2.45GHz) band.

The foregoing has outlined essential and optional features of RFID inlays, tags and products according to the principles of the invention. The disclosed embodiments are provided to illustrate the essential and optional features and functions, and those skilled in the art may conceive of alternatives or modifications that do not depart from the principles of the invention as encompassed by the appended claims, and that such alternatives or modifications may be functionally equivalent.

It is to be understood that the invention is not limited to the specific details described herein which are given by way of example only and that various modifications and alterations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1 . A radio-frequency identification (RFID) inlay for a package to contain a food product intended for microwave preparation, said RFID inlay comprising: a substrate; an antenna structure formed on said substrate, said antenna structure comprising an impedance matching loop and a dipole antenna, wherein said impedance matching loop comprises an integrated circuit (IC) chip bond region characterized by a gap in said loop, wherein ends of said loop on either side of said gap form first and second IC bonding points; wherein, said impedance matching loop further comprises a modified contour element that extends from a fist internal side of said loop to a second internal side of said loop, said modified contour element characterized by a lower impedance at microwave frequencies than an impedance through said chip bond region; and, wherein said dipole antenna comprises first and second elements extending outwardly from said impedance matching loop; and, an IC physically positioned within said IC chip bond region of said central impedance matching loop and electrically coupled to said first and second IC bonding points; wherein said antenna structure is characterized by an operational frequency suitable for activating and reading information stored in said IC, and wherein currents induced in said antenna structure when exposed to microwave frequencies are substantially diverted through said modified contour element, away from said chip bond area, whereby electrical arcing across said gap in said loop is mitigated.

2. The RFID inlay recited in claim 1 , wherein said modified contour element comprises at least one central gap.

3. The RFID inlay recited in claim 1 , wherein said at least one central gap has a length greater than the width of said modified contour element.

4. The RFID inlay recited in claim 3, wherein said at least one central gap is curvilinear.

5. The RFID inlay recited in claim 4, wherein said at least one central gap is substantially sinusoidal.

6. The RFID inlay recited in claim 2, wherein said modified contour element comprises two central gaps formed by opposing arcs in the ends of first and second portions of said contour element extending inwardly from said impedance matching loop and a elliptic portion centered therebetween.

7. The RFID inlay recited in claim 6, wherein said elliptic portion is circular.

8. The RFID inlay recited in claim 1 , wherein each of said first and second elements of said dipole antenna are characterized by a linear portion terminated with a rounded lobe.

9. The RFID inlay recited in claim 8, wherein junctions proximate the location said linear portions of said first and second elements of said dipole antenna extend outwardly from said impedance matching loop are characterized by smooth contours.

10. The RFID inlay recited in claim 1 , wherein said substrate comprises polyethylenetherephtalate (PET).

11 . The RFID inlay recited in claim 1 , wherein said substrate comprises a portion of said package to contain said food product.

12. The RFID inlay recited in claim 1 , further comprising a layer of fire retardant material overlaying at least a portion of said antenna structure proximate said IC chip bond region.

13. The RFID inlay recited in claim 12, further comprising a second layer of fire retardant material underlaying at least a portion of said substrate proximate said IC chip bond region.

14. The RFID inlay recited in claim 12, wherein said layer of fire retardant material is bonded to said substrate or said antenna structure by an adhesive.

15. The RFID inlay recited in claim 14, wherein said adhesive is fire retardant.

16. The RFID inlay recited in claim 1 , wherein said modified contour element is formed on said substrate simultaneously with said impedance matching loop and said dipole antenna.