Metal Detector Resistant RFID Tags

Abstract

Disclosed herein is a conductive structure for use with an RFID device having a metal mass below the standard detection threshold of a metal detector, and a method for fabricating the same. The conductive structure preferably includes a pair of dipole arms extending from a tuning loop, where each of the pair of dipole arms terminates in a load end. The conductive structure can be fabricated from a printed metal ink or by cutting, laser machining, or etching a metal foil. The conductive structure is modified to reduce the overall thickness and metal mass of the device as much as possible while maintaining an acceptable level of performance. A portion of the load end can also be hollowed out to further reduce the metal mass of the conductive structure.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 954,909, filed December 30, 2019, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates generally to metal detector resistant tags (e.g., to avoid detecting or inducing false positives when passing through a metal detector) and methods of making and using the same. More specifically, the improved RFID devices are for use with consumer food products and associated packaging materials that are scanned by a metal detector to detect metallic foreign objects that may be contained therein. The improved RFID tags of the present invention are particularly suited to direct and indirect food contact applications including, but not limited to, transportation, storage, handling and movement, and therefore this specification makes specific reference thereto. However, it should be understood that aspects of the present invention are applicable to other similar applications and devices as well. [Background technology]

[0003] Radio frequency identification is the use of electromagnetic energy to stimulate a responding device (known as an RFID "tag" or transponder) to identify itself and possibly provide additional information and / or data stored in the tag. RFID tags and / or labels typically include a combination of an antenna and analog and / or digital electronics, which may include, for example, semiconductor devices commonly referred to as "chips," communication electronics, data memory, and control logic. A typical RFID tag has a microprocessor electrically coupled to an antenna and acts as a transponder, providing information stored in the chip memory in response to radio frequency interrogation signals received from a reader, also known as an interrogator. In the case of passive RFID devices, the energy of the interrogation signal also provides the energy required to operate the RFID tag device.

[0004] RFID tags can be embedded in or attached to the desired article that a user wishes to later identify and / or track. In some cases, the tag can be attached to the outside of the article by clips, adhesives, tape, or other means, and in other cases, the RFID tag can be inserted into the article so that it is included in packaging or placed within a container of the article or multiple articles. RFID tags are also manufactured with a unique identification number, which is usually a simple serial number of a few bytes with a check digit appended. This identification number is usually integrated into the RFID tag during the manufacturing process. Users cannot change this serial number / identification number, and manufacturers ensure that each RFID tag serial number is unique since it is only used once. Such read-only RFID tags are usually permanently attached to the article to be identified and / or tracked, and once attached, the tag's serial number is associated with the host article in a computer database.

[0005] Ready-to-eat food items or other packaged foods are generally manufactured or prepared in factories or commercial kitchens using machines that contain metal components as part of the manufacturing process, causing the food to become contaminated with metal particles. Metals can also be intentionally included in foods. Although food manufacturers generally have very strict environmental regulations in place in their facilities and packaging processes, metal items can be broken off and inadvertently get into the food or packaging. One common low-cost method of detecting unwanted and / or unintended metals is to pass packaged foods through a metal detector. If metal is detected, the food can be segregated or otherwise discarded to remove the metal contaminants from the food. Unfortunately, as explained in more detail below, using metal detectors for such purposes has many limitations when used in conjunction with RFID devices.

[0006] More specifically, it is desirable to use RFID devices in connection with food products to allow for better control of transportation, traceability, inventory, and other supply chain requirements. RFID devices have the potential to increase profitability by allowing food manufacturers to continuously monitor food supplies throughout the entire supply chain. RFID tags also allow manufacturers to quickly respond to low inventory and avoid the risk of overstocking certain food items without having to physically count inventory to ensure adequate supplies of food. For example, a sales floor can monitor the supply of food they have and easily predict when to order more food to maintain adequate supplies and facilitate use of the food at the point of sale. Therefore, ideally, RFID devices should be attached to food products as early in the supply chain as possible to aid in traceability and production, or incorporated into food packaging materials before they are used to package the food.

[0007] Unfortunately, the mass of conductive materials used as antennas in RFID devices is generally larger than the detection threshold of metal detectors for foreign metal objects. This deficiency forces manufacturers to either reduce the detection threshold of the metal detectors, thereby reducing their ability to detect foreign metal objects, or to apply RFID devices after scanning food with a metal detector, thus losing the benefits of more accurate tracking and use of RFID devices throughout the entire manufacturing or production process.

[0008] Thus, there is a long felt need in the art for improved RFID devices that can be used in association with food items throughout the manufacturing or production process, including before the food is scanned for metallic foreign objects with a metal detector, and that are metal detector "proof," meaning that their antennae or other metallic parts do not cause false positives from a metal detector. Summary of the Invention [Means for solving the problem]

[0009] The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed invention. This summary is not extensive, and is not intended to identify key / critical elements or to delineate the scope. Its sole purpose is to present some concepts in a simple form as a prelude to the more detailed description that is presented later.

[0010] Described herein are RFID devices / antennas that are below the standard detection threshold of most metal detectors commonly used in food manufacturing and / or production, and methods of using the same. More specifically, the RFID device can be placed on a food item or its packaging prior to being scanned by a metal detector and will not generate false positives based on the metal components of the RFID device. In one embodiment, the RFID device includes an antenna structure designed for a metal mass below the detection threshold of a metal detector, yet maintains a suitable level of performance for tracking food items through the supply chain, including, by way of non-limiting example, point of sale inventory.

[0011] In some embodiments, the RFID device further comprises a conductive structure. In some embodiments, the conductive structure comprises a pair of dipole arms extending from the tuning loop, where each of the dipole arms terminates in a load end. In some embodiments, the conductive structure is further configured to have a metallic mass below a standard detection threshold of a metal detector used to scan the food items and their packaging.

[0012] In some embodiments, the conductive structures are as described above and have an area large enough to achieve the required or desired performance, yet still below the typical standard detection threshold associated with scanning food items or packaging for foreign metal objects of approximately 1 mm diameter metal balls.

[0013] The conductive structures can be fabricated by any technique known in the art, including, but not limited to, printing a conductive ink or cutting (e.g., laser and / or die cutting) a metal foil. In some embodiments, the thickness of the overall conductive structure is reduced by more than a skin depth calculated for the respective conductive structure material and frequency.

[0014] In some embodiments, portions of each load end can be hollowed out such that areas of the conductive structure with lower current flow are removed while minimizing the impact on overall RFID performance, resulting in a conductive structure with a mass below the detection threshold of a metal detector.

[0015] In further embodiments, an RFID device contemplated for use in food item and food packaging applications is disclosed. The RFID device preferably includes an RFID chip and a conductive structure electrically coupled to the RFID chip. In some embodiments, the conductive structure includes a pair of dipole arms extending in opposite directions from a tuning loop, where each of the dipole arms terminates in a load end. The conductive structure is configured to have a metal mass less than the standard detection threshold of a metal detector used to scan the food items and their respective packaging.

[0016] The improved RFID devices described herein may be fabricated by removing or eliminating portions of the metallic conductive structures of the RFID device, e.g. cavity By hollowing out the metal conductive structure, the spark hazards associated with microwaving food products having RFID devices attached thereto can be reduced or eliminated. Similar results can also be achieved, in part, by reducing the thickness of the metallic conductive structure. Yet another advantage of the improved RFID devices described herein is that such reduction in structure and mass produces an RFID device that does not block detection of high density materials when the RFID device is x-rayed.

[0017] Also described herein is a method for reducing the metal mass of a conductive structure for use with an RFID device. In some embodiments, the method includes the steps of: (1) providing a designed conductive structure with an initial area large enough to adequately perform its intended function; (2) determining a skin depth for the conductive structure based on material and / or frequency; and (3) reducing the overall thickness of the conductive structure as much as possible to maintain an adequate level of performance (preferably down to the calculated skin depth).

[0018] In some embodiments, certain areas of the conductive structure having relatively low current flow are then hollowed out to remove additional mass. The hollowed out areas are preferably located at the pair of loaded ends of the overall thickness of the conductive structure. In some embodiments, it is preferred to remove enough material to reduce the overall thickness and ensure that the conductive structure has a mass below the standard detection threshold of metal detectors used in food processing screening processes, but has sufficient mass to function effectively as an RFID device.

[0019] To the accomplishment of the foregoing and related ends, certain illustrative aspects of the disclosed invention are described in this specification by reference to the following description and the annexed drawings. These aspects are, however, inclusive of but a few of the various ways in which the principles disclosed herein can be employed and are intended to include all such aspects and their equivalents. Other advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a side view of a food item being scanned for foreign objects by a metal detector in accordance with the disclosed architecture.

[0021] [Diagram 2] FIG. 2 is a side perspective view of an RFID device attached to a food package according to the disclosed architecture.

[0022] [Figure 3A] FIG. 2 is a plan view of an RFID device before removing portions of the conductive structures of the RFID device according to the disclosed architecture.

[0023] [Figure 3B] FIG. 3B is a top view of the RFID device of FIG. 3A after removing portions of the conductive structures of the RFID device according to the disclosed architecture.

[0024] [Figure 4A] FIG. 2 is a side view of a conductive structure having an initial thickness according to the disclosed architecture.

[0025] [Figure 4B] 1 is a side view of a conductive structure having a reduced thickness according to the disclosed architecture.

[0026] [Figure 5A] 1 is a plan view of an RFID device having an initial conductive structure according to the disclosed architecture;

[0027] [Figure 5B] FIG. 1 is a plan view of an RFID device having a conductive structure modified according to the disclosed architecture.

[0028] [Figure 6] 13A-13C illustrate a method for reducing the mass of conductive structures for use with RFID devices according to the disclosed architecture. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will now be described with reference to the drawings, in which like reference numerals are used to refer to like elements throughout the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding thereof. However, it will be apparent that the present invention may be practiced without such specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description.

[0030] As mentioned above, one common low-cost method of detecting unwanted and / or unintended metals in food items or their associated packaging is to pass the food and / or packaging through a metal detector. If metal is detected, the food can be segregated or otherwise discarded to remove the metal contaminants from the food. The use of RFID devices is also a common method of tracking food throughout the food supply chain. Unfortunately, to date, RFID devices have not worked well with metal detectors, often resulting in false readings from metal detectors in response to metal components in the RFID device. More specifically, RFID devices typically contain antennas large enough to be detected by metal detectors, necessitating individual inspections that cause false readings and defeat the purpose of the metal detector. Smaller RFID tags can be used to offset this problem, but the use of smaller RFID tags often results in a significant reduction in the performance levels of the RFID device, defeating the purpose of the RFID device. Other options include reducing the sensitivity of the detector, which would reduce the ability of the metal detector to detect smaller metal objects, or applying RFID devices to the food after scanning for metal objects, which would reduce the functionality of the RFID devices since they would not be present in the entire manufacturing or production process.

[0031] Thus, there is a long felt need in the art for improved RFID devices that can be used in association with food items throughout the entire manufacturing or production process and where the antennae or other metal parts do not cause false positives from metal detectors.

[0032] Referring first to the drawings, FIG. 1 illustrates the use of a metal detector 30 for use in the food industry. More specifically, food items 10, such as ready-to-eat, frozen foods, and the like, pass through a metal detector 30 before being shipped. Metal detectors generally have a tunnel configuration. Metal detectors 30 used in food scanning operations are often configured to have a detection threshold for metal. If a mass of detectable metal 40 is detected above the set detection threshold, the food item 10 can be rejected, discarded, or diverted to a separate production or inspection area for further investigation into the cause of the metal detection. While this outcome is favorable in cases where the food item 10 has metal contamination, false positive detections can cause manufacturing / production delays and require human intervention, neither of which are efficient or favorable.

[0033] 2 shows a side perspective view of an RFID device 100 including an RFID chip 110 and a conductive structure 120. While the RFID device 100 is affixed to the food package 20 according to the disclosed architecture, it is also contemplated that the RFID device 100 can be affixed directly to the food item 10. Common applications for affixing the RFID device 100 to the food item 10 or associated package 20 include food traceability, where the RFID device 100 is used in conjunction with a database to store information, for example, to precisely record when and where the food was produced and the identity of the source of the food item, to associate the food item 10 with ingredients, to track the expiration date or "use by" date of the food item 10, and any other traceable factors that suit the needs and / or preferences of the user. The food package 20 can be microwaveable or frozen depending on the requirements of the enclosed food item 10.

[0034] FIG. 3A shows a plan view of an RFID device 100 including an RFID chip 110 and a conductive structure 120. More specifically, the RFID chip 110 is electrically coupled to the conductive structure 120. However, the metallic mass of the conductive structure 120 of the RFID device 100 would cause a false positive in a metal detector, such as the metal detector 30 shown in FIG. 1. In comparison, FIG. 3B shows a plan view of the RFID device 100 of FIG. 3A, but after removing portions of the conductive structure 120 of the RFID device according to the disclosed architecture. More specifically, the RFID device 100 of FIG. 3 also includes an RFID chip 110 electrically coupled to a metallic conductive structure 120, but now portions 128 of the conductive structure 120 have been removed to reduce the overall metallic mass of the RFID device 100 without affecting its overall performance (i.e., to be successfully interrogated by an RFID reader (not shown) throughout the food supply chain). The portions 128 of the conductive structure 120 that are removed or hollowed out are selected based on locations where current flow through the conductive structure 120 is relatively low compared to the remainder of the conductive structure 120, and are selected so that removing the portions 128 does not significantly affect the performance of the RFID device 100. While this reduction in material is advantageous, other adjustments or other aspects of the RFID device 100 design may be necessary to provide optimal sensitivity.

[0035] In a further embodiment, as shown in Figures 4A and 4B, the metal mass of the conductive structure 120 can also be reduced by reducing the thickness of all or part of the conductive structure 120. More specifically, the conductive structure 120 shown in Figure 4A has an initial thickness a. It is known to those skilled in the art that RF currents in the ultra-high frequency (UHF) frequency range in the 915 MHz region flow primarily at the surface of a conductor or antenna. Moreover, the current decreases exponentially with the depth of the conductor. A representation of such a current reduction effect is known as the skin depth, and the conductive structure 120 of Figure 4A has a skin depth 130, as will be described in more detail below.

[0036] As best shown in FIGS. 4A and 4B, another way to reduce the total metal mass of the conductive structure 120 is to reduce the initial thickness a (shown in FIG. 4A) to a reduced thickness b (shown in FIG. 4B). In some embodiments, the reduced thickness b is at least a skin depth 130 thick. More specifically, the skin depth 130 is a measure of the current density and is defined as the distance from the outer edge of the conductor to the point where the current density drops to 1 / e of the current value at the conductor surface. For example, at 4 skin depths from the conductor surface, approximately 98% of the current flows in the conductor. As a further example, for a UHF RFID antenna made from aluminum, the skin depth is 2.65×10 -8 The skin depth based on the resistivity of the ohm-meter and the frequency of 915 MHz is calculated to be 2.7 μm. Therefore, for a rectangular cross-section conductor, if the thickness is reduced to less than 5.4 μm, the resistance at 915 MHz will be higher than the DC resistance, causing additional loss or reduction in antenna and RFID device performance.

[0037] Many approaches can be taken to reduce the metal mass of the conductive structure 120 to overcome the limitations of the prior art. For example, one can consider selecting an RFID device with a relatively small antenna having a metal mass that is below the detection threshold of a metal detector and therefore does not cause detection. However, RFID devices with reduced RFID antenna size or relatively small RFID devices are generally associated with lower and less acceptable RF performance.

[0038] FIG. 5A shows a plan view of an RFID device 100 having an initial conductive structure 120(a), and FIG. 5B shows a plan view of an RFID device 100 having a conductive structure 120(b) modified according to the disclosed architecture. More specifically and as shown in FIG. 5A, the conductive structure 120(a) in its initial, unmodified form can be a dipole-type antenna, such as the AD238 RFID tag manufactured and sold by Avery Dennison, Inc., of Glendale, California. However, this example is used for illustrative purposes only, as many different initial unmodified RFID tag designs that can be used in connection with food production are contemplated herein. In some embodiments, the conductive structure 120(a) includes a tuning loop 122 and a pair of dipole arms 124, each extending from the tuning loop 122 in generally opposite directions. More specifically, each of the dipole arms 124 can be a meander-line type arm that terminates at a respective load end 126. Each load end 126 is the maximum load area for the conductive structure 120 which enhances broadband.

[0039] The standard detection threshold for a detectable mass 40 (shown in FIG. 1) of a metal detector 30 (shown in FIG. 1) of the type commonly used in the food production industry is a sphere with a diameter of approximately 1 mm. In this embodiment using an AD238 RFID tag, the material used for the conductive structure 120 is aluminum, and the detection threshold volume is approximately 0.52 mm. 3 Therefore, in this example, the standard detection threshold is a total metal volume of 0.52 mm 3 The undeformed conductive structure 120(a), fabricated from aluminum with an initial thickness of 15 μm, has a length of approximately 8.6 mm. 3 and 573mm 2 , which is much higher than the detection threshold and may result in a false positive by the metal detector 30. However, reducing the conductive structure 120 from its initial thickness to a reduced thickness of 1 μm reduces the volume of the conductive structure 120 to approximately 0.57 mm 3, which is much closer to the detection threshold, and does not change the total conductive structure area. Unfortunately, the reduced thickness of 1 μm is less than the skin depth 130 of aluminum, so a reduction in RF performance must be expected.

[0040] In comparison, Figure 5B shows the results of modifications to the antenna design that reduce the overall metal mass while still maintaining an acceptable level of performance. The modified conductive structure 120(b) has a mass that is less than the standard detection threshold of the metal detector 30. More specifically, the overall conductive structure 120(b) ideally has a thickness that is greater than the skin depth 130 for the construction material and frequency. In this example, the skin depth 130 for aluminum at a frequency of 915 MHz is approximately 2.7 μm.

[0041] To achieve a desired level of performance from the RFID device 100, it may be necessary to remove or hollow out portions of the 15 μm thick conductive structure 120 that have lower or relatively low current flows. More specifically, the pair of loaded ends 126 are the areas of the conductive structure 120 in this example that have the lowest surface current flows. These are the most highly loaded areas that enhance broadbandwidth. Thus, portions 128 can be removed or hollowed out from the pair of loaded ends 126. Removing such portions of the most highly loaded areas from the pair of loaded ends 126 reduces the volume of the conductive structure 120(b) to approximately 5.44 mm in this example. 3 and 363 mm 2 10 and 110dB, and with proper design will have a relatively minimal impact on RFID performance. Hollowing out or removing portion 128 will thus have the effect of maintaining or improving the wide bandwidth while reducing the overall antenna size requirements. Unfortunately, this volume is still above the detection threshold for a metal detector and will likely generate false positive readings by metal detector 30.

[0042] However, the thickness of the conductive structure 120(b) is set to 363 mm. 2 1 μm thick aluminum having a pair of loading ends 126 with multiple hollow portions 128, the area is approximately 0.36 mm, which is below the detection threshold of the metal detector 30.3 If the thickness is further reduced to 500 nm, the volume will be reduced to about 0.18 mm 3 The conductive structures 120 can be manufactured by printing conductive inks such as copper, silver, graphene, cutting or etching metal foils with a rotary cutting system or laser, but can also be manufactured to smaller thicknesses by deposition.

[0043] In a further contemplated embodiment, an RFID device 100 for use with a food item includes an RFID chip 110 and a conductive structure 120 electrically coupled to the RFID chip 110. The conductive structure 120 includes a tuning loop 122 and a pair of dipole arms 124. Each dipole arm 124 extends outwardly from the tuning loop 122 in generally opposite directions and terminates in a loaded end 126. Each loaded end 126 is the highest loaded area for the conductive structure 120, and the conductive structure 120 is fabricated to have a metal mass below the standard detection threshold of a metal detector 30 of the type commonly used in the food production industry.

[0044] Additionally, the conductive structure 120 is configured to have an overall thickness that is ideally slightly greater than the skin depth 130 for the conductive structure material and frequency. Based on standard detection thresholds commonly used to scan food items for foreign metals, the conductive structure 120 is ideally configured to have an overall thickness that is slightly greater than the skin depth 130 for the conductive structure material and frequency. 3 1. The conductive structure 120 may have a total metal volume of less than 100 .mu.m. To obtain such a small volume, portions of the conductive structure 120 that have lower or relatively low current flow and minimal impact on RF performance are removed or hollowed out, such as portions of a pair of load ends 126. More specifically, each load end 126 is hollowed out to create a plurality of openings or portions 128 within the load end 126.

[0045] Alternative techniques for detecting foreign metals include x-ray analysis, etc. As previously mentioned, in some embodiments, the RFID device 100 described herein is fabricated to have reduced mass distributed throughout the conductive structure 120. In this manner, the RFID device 100 should not produce a high density "lump" and should produce a relatively diffuse image on an x-ray. More specifically, a relatively diffuse image would not block or impede the detection of high density materials such as foreign metals since the RFID device 100 is relatively "transparent". Ideal materials for the conductive structure 120 for x-ray applications include, but are not limited to, graphene (2.267 g / cm 3 ), aluminum (2.7g / cm 3 ) and copper (8.96 g / cm 3 ), which are materials with relatively low density, including graphene. Therefore, it would be advantageous to construct the conductive structure 120 from a low density and high conductivity material, such as aluminum or graphene for x-ray applications. Metal detection is more related to electrical conductivity. Aluminum is a good choice, but graphene, copper and silver are better conductors. Also, an added benefit of a small metal volume is that the RFID device 100 is ideally "microwaveable." More specifically, the RFID devices described herein can also reduce or eliminate the risk of sparking associated with using microwaves to cook food to which the RFID device is attached, by removing or removing, e.g., hollowing out, portions of the metal conductive structure of the RFID device.

[0046] 6 illustrates a method for reducing the metal mass of a conductive structure 120 of an RFID device 100. More specifically, the method 200 begins in step 202 by providing a conductive structure 120 having an initial area and volume large enough to properly perform RFID functions in accordance with user instructions. In step 204, a skin depth 130 can be calculated based on the material and frequency of the conductive structure as previously described, and in step 206, the method continues by reducing the total initial thickness of the conductive structure 120 in one of the manners previously described to obtain the profile shown in FIG. 4B. In general, the reduced thickness of the conductive structure 120 should not be less than the skin depth 130 calculated for the particular material and frequency of the conductive structure.

[0047] At step 208, areas of reduced current flow along the conductive structure 120 are identified that have little or no effect on the performance of the conductive structure 120 and the RFID device 100. In some embodiments, the particular areas of the conductive structure 120 that have low current flow are located at a pair of load ends 126 of the conductive structure 120. Thus, at step 210, the portions 128 of the conductive structure 120 that have low current flow are hollowed out to reduce the overall metal mass of the conductive structure 120 and the RFID device 100. By removing this metal mass, the overall area of ​​the conductive structure 120 has been reduced as much as possible without significantly affecting the performance of the RFID device 100. The methods described herein provide an optimal solution for the design of a conductive structure 120 that provides the required performance and is suitable for use with a food product 10 or its packaging 20, and a metal detector 30.

[0048] What has been described above includes examples of the claimed subject matter. Of course, it is not possible to describe every conceivable combination of elements or methodologies in order to describe the claimed subject matter, but one of ordinary skill in the art will recognize that many additional combinations and permutations of the claimed subject matter are possible. Accordingly, it is intended that the claimed subject matter embrace all such changes, modifications and variations that fall within the spirit and scope of the appended claims. Also, to the extent the term "includes" is used in the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when used as a transitional term in the claims.

Claims

1. An RFID chip; a conductive structure electrically coupled to the RFID chip, the conductive structure including a pair of dipole arms extending in opposite directions from a tuning loop, each of the pair of dipole arms terminating in a load end, each of the load ends having an opening hollowed out in a portion of the load end and a looped remainder of the load end surrounding the opening; 1. A metal detector resistant RFID device comprising:

2. 2. The metal detector resistant RFID device of claim 1, wherein the thickness of the conductive structure is greater than a skin depth of the conductive structure for a frequency used in the metal detector resistant RFID device.

3. 3. The metal detector resistant RFID device of claim 1, wherein a portion of the load end of the conductive structure that is hollowed out has a smaller current flow than other portions of the conductive structure, and wherein the portion of the load end that is hollowed out is removed.

4. 4. The metal detector resistant RFID device of claim 1, wherein the hollowed out loaded end of the conductive structure does not block detection of metallic foreign objects during x-ray inspection.

5. The metal detector resistant RFID device of claim 1, wherein a total metal volume of the conductive structure is less than 0.52 mm 3 .

6. 1. A method for reducing the metal mass of an RFID device, comprising: providing a conductive structure for use with an RFID device, the conductive structure including a pair of dipole arms extending in opposite directions from a tuning loop, each of the pair of dipole arms terminating in a load end; reducing a thickness of the conductive structure; and hollowing out a portion of the load end of the conductive structure to form an opening and a remainder of the load end looped around the opening; A method for reducing the metallic mass of an RFID device, wherein the current flow in the hollowed out portion of the conductive structure is less than the current flow in other portions of the conductive structure.

7. The method of claim 6 , further comprising calculating a skin depth of the conductive structure.

8. 8. The method of claim 6 or 7, wherein the thickness of the conductive structure is greater than a skin depth of the conductive structure for a frequency used in the RFID device.

9. The method of claim 6 , wherein the conductive structure includes a pair of dipole arms extending from a tuning loop and terminating in a load end.

10. The method of claim 6 , wherein the portion of the conductive structure is located at at least one of a pair of load ends of the conductive structure.

11. A conductive structure for use with a metal detector resistant RFID device, comprising: The conductive structure is electrically coupled to the RFID device and includes a pair of dipole arms extending in opposite directions from a tuning loop, each of the pair of dipole arms terminating in a load end, each of the load ends having an opening formed by hollowing out a portion of the load end and a looped remainder of the load end surrounding the opening.

12. The conductive structure of claim 11, wherein the conductive structure has a total metal volume of less than 0.52 mm 3 .

13. The conductive structure of claim 11 , wherein the conductive structure comprises aluminum.

14. 14. A conductive structure according to any one of claims 11 to 13, wherein the thickness of the conductive structure is greater than the skin depth of the conductive structure for a frequency used in the RFID device.

15. 15. The conductive structure of claim 11, wherein a portion of the conductive structure is removed.

16. 16. The conductive structure according to any one of claims 11 to 15, wherein the thickness of the conductive structure is obtained by vapor deposition.

17. 17. The conductive structure according to any one of claims 11 to 16, wherein the conductive structure is manufactured by printing a conductive ink or cutting a foil.

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