Metal detector resistant RFID tags

Abstract

A conductive structure for a radio frequency identification (RFID) device (having a metal mass below the standard detection threshold of a metal detector) and a method for producing the same are disclosed. The conductive structure preferably includes a pair of dipole arms extending from a tuning loop, wherein each dipole arm terminates at a load end. The conductive structure may be made using printed metallic ink, or by cutting, lasering or etching a metal foil. The conductive structure may be modified to minimize the overall thickness and metal mass of the device while still retaining an acceptable level of performance. The load end portion may also be hollowed out to further reduce the metal mass of the conductive structure.

Description

[0001] Cross-references to related patent applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 954,909, filed on December 30, 2019, which is incorporated herein by reference in its entirety and becomes a part of the present invention. Technical Field

[0003] The present invention generally relates to a metal detector resistant tag (e.g., to avoid detection or triggering false positives when passing through a metal detector) and methods of producing and using the same. More specifically, the improved radio frequency identification (RFID) device is intended for use with fast moving consumer foods and related packaging that are scanned using a metal detector to detect metallic foreign matter that may be included therein. The improved radio frequency identification tag of the present invention is particularly suitable for direct and indirect food contact applications, including but not limited to the transportation, storage, handling and movement of food. Therefore, specific reference is made to this in the present specification. However, it should be understood that aspects of the present invention are also equally suitable for other similar applications and devices. Background Art

[0004] RFID refers to the use of electromagnetic energy to emulate a responding device (called an RFID "tag" or transponder) to identify itself and, in some cases, provide additional information and / or data stored in the tag. An RFID tag typically contains an antenna and analog and / or electronic components, which may include a semiconductor device commonly called a "chip", communication electronics, data storage, and control logic. A typical RFID tag typically has a microprocessor electrically connected to the antenna, which acts as a transponder and provides information stored in the chip's memory in response to a radio frequency interrogation signal received from a reader (also called an interrogator). For passive RFID devices, the energy from the interrogation signal also provides the necessary energy for the RFID tag device to operate.

[0005] RFID tags may be included in or affixed to merchandise that a user wants to later identify and / or track, such as various food items. In some cases, the RFID tag may be affixed to the exterior of the merchandise using a clip, adhesive, tape, or other means, and in other cases, the RFID tag may be inserted into the merchandise, such as contained within packaging, or within a container of an item or items. Further, RFID tags are typically manufactured with a unique identification number, which is typically a simple serial number consisting of a few bytes, with a check digit attached. This identification number is typically incorporated into the RFID tag during manufacture. This serial / identification number cannot be changed by the user, and the manufacturer guarantees that each RFID tag serial number is used only once and is therefore unique. Such read-only RFID tags are typically permanently affixed to the merchandise to be identified and / or tracked, and once affixed, the tag's serial number is associated with the primary merchandise in a computer database.

[0006] Foods, such as ready-to-eat foods or other packaged foods, are often produced or prepared in factories or commercial kitchens that use machinery with metal components during the production process, which can result in the food being contaminated with metal particles. In addition, there is the possibility that metal may be placed in the food maliciously. While food producers typically employ very strict environmental controls over their facilities and packaging processes, metal items may break off and accidentally enter the food or its packaging. A common, low-cost method of detecting unintended and / or unexpected metal is to pass the packaged food through a metal detector. If metal is detected, the food can be separated to remove the metal contaminant from the food, or otherwise disposed of. Unfortunately, as explained in detail below, metal detectors used for such purposes have a number of limitations when used in conjunction with RFID devices.

[0007] More specifically, the use of RFID devices in food is needed to better control transportation, traceability, inventory and other supply chain needs. RFID devices can enable food producers to continuously monitor the supply of food throughout the supply chain, thereby improving the profit margins of food producers. The use of RFID devices can also allow producers to respond quickly to low inventory without having to conduct inventory counts to ensure adequate supply of food while avoiding the risk of overstocking of specific foods. For example, stores can monitor the supply of existing food and easily predict when to order more food to maintain an appropriate supply and have the food available at the point of sale. Therefore, ideally, the RFID device should be connected to the food as early as possible in the supply chain to assist with traceability and production, or placed in the food packaging before the food is packaged.

[0008] Unfortunately, the mass of the conductive material used as the antenna in an RFID device is usually greater than the detection threshold of metallic foreign bodies in a metal detector. This deficiency requires manufacturers to either lower the detection threshold of the metal detector, thereby reducing its ability to detect metallic foreign bodies, or apply the RFID device after scanning the food with a metal detector, thereby losing the more accurate traceability and advantages of using the RFID device throughout the production process.

[0009] Therefore, there is a long-felt need in the art for an improved RFID device that can be used throughout the food production process, including before the food is scanned for metallic foreign matter with a metal detector. There is also a long-felt need in the art for an improved RFID device that is "metal detector resistant" (i.e., its antenna or other metal components will not trigger a false positive in a metal detector). Summary of the invention

[0010] A brief summary of the invention is given below to provide a basic understanding of some aspects of the disclosed invention. The summary of the invention is not an extensive overview, nor is it intended to identify the key / important elements of the invention, or to define its scope. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the detailed description of the embodiments that follow.

[0011] The present invention describes an RFID device / antenna that is below the standard detection threshold of most metal detectors commonly used in food production, and methods of using the device / antenna. More specifically, the RFID device can be placed on a food product or its packaging before 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 that is designed to have a metal mass that is below the detection threshold of a metal detector, but still maintains a sufficient performance level to track food through the supply chain, including but not limited to store inventory.

[0012] 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, wherein each dipole arm terminates at a load end. In some embodiments, the metal mass of the conductive structure is further less than a standard detection threshold of a metal detector used to scan food and its packaging.

[0013] In certain embodiments, the conductive structure is as described above and has an area sufficient to achieve the desired or required performance, but still below the standard detection threshold associated with scanning food or packaging to detect metallic foreign objects of approximately 1 mm diameter metal spheres.

[0014] The conductive structure can be produced using techniques known in the art, including but not limited to printing conductive ink or by cutting (e.g., laser and / or die cutting) metal foil. In certain embodiments, the thickness of the overall conductive structure is reduced to no less than the skin depth calculated for the respective conductive structure material and frequency.

[0015] In some embodiments, a portion of each load terminal may be hollowed out to remove the conductive structure area with low current and minimize the impact on the overall RFID performance, while also achieving a conductive structure with a metal mass below the detection threshold of the metal detector.

[0016] In another embodiment, the present invention discloses a radio frequency identification device intended for use in food and food packaging applications. The radio frequency identification device preferably includes a radio frequency identification chip and a conductive structure electrically coupled to the radio frequency identification chip. In certain embodiments, the conductive structure includes a pair of dipole arms extending in opposite directions from a tuned loop, wherein each dipole arm terminates at a load end. The metal mass of the conductive structure is less than a standard detection threshold of a metal detector used to scan food and its packaging.

[0017] The improved RFID device of the present invention can reduce or eliminate the risk of sparks when heating food with the RFID device in a microwave oven by eliminating or removing (e.g., hollowing out) the metal conductive structure portion of the RFID device. A similar result can also be achieved in part by reducing the thickness of the metal conductive structure. Another advantage of the improved RFID device of the present invention is that this reduction in structure and mass does not prevent the detection of high-density materials when the RFID device is subjected to X-ray inspection.

[0018] The present invention also describes a method for reducing the metal mass of a conductive structure of an RFID device. In certain embodiments, the method includes (1) providing a conductive structure having an initial area sufficient to fully function as intended; (2) determining a skin depth of the conductive structure based on the 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 to the depth of the calculated skin thickness).

[0019] In certain embodiments, specific areas of the conductive structure having relatively low current are hollowed out and additional mass is removed. The specific areas of the hollowing out are preferably located at a pair of load ends of the overall thickness of the conductive structure. In certain embodiments, it is preferred to remove enough material so that when combined with the reduced overall thickness, the mass of the conductive structure is below the standard detection threshold of metal detectors used in food processing screening, but the mass is sufficient to operate effectively as an RFID device.

[0020] To achieve the above and related purposes, the present invention describes certain illustrative aspects of the disclosed invention and provides the following description and drawings. However, these aspects are only illustrative of a few of the various ways in which the principles disclosed in the present invention may 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 in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A side view of a metal detector used in the disclosed architecture to scan food for foreign objects.

[0022] Figure 2 is a side perspective view of an RFID device coupled to a food product in the disclosed architecture.

[0023] Figure 3A FIG. 1 is a top view of the RFID device in the disclosed architecture before a portion of the conductive structure of the RFID device is removed.

[0024] Figure 3B For the disclosed architecture Figure 3A A top view of the RFID device after removing a portion of the conductive structure of the RFID device.

[0025] Figure 4A FIG. 1 is a side elevation view of a conductive structure having a starting thickness in the disclosed architecture.

[0026] Figure 4B is an elevational side view of a conductive structure with reduced thickness in the disclosed architecture.

[0027] Figure 5A FIG. 4 is a top view of an RFID device having an initial conductive structure in the disclosed architecture.

[0028] Figure 5B FIG. 4 is a top view of an RFID device with an improved conductive structure in the disclosed architecture.

[0029] Figure 6 A method of reducing the mass of a conductive structure of an RFID device in the disclosed architecture is shown. DETAILED DESCRIPTION

[0030] The present invention is described with reference to the accompanying drawings, wherein the same reference numerals represent the same components throughout. In the following description, for the purpose of explanation, many specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent that the present invention can be practiced without these specific details. In other examples, well-known structures and devices are shown in block diagram form in order to describe the present invention.

[0031] As discussed above, a common, low-cost method of detecting unintended and / or unexpected metal in food or its associated packaging is to pass the food and / or packaging through a metal detector. If metal is detected, the food can be separated to remove the metal contaminant from the food, or otherwise processed. The use of RFID devices is also a common way to track food through the food supply chain. Unfortunately, to date, RFID devices do not work well with metal detectors and often result in metal detectors generating false positive readings of metal components in the RFID device. More specifically, RFID devices often contain metal antennas that are large enough to be detected by metal detectors, thereby triggering false positive readings and requiring separate inspection, which defeats the purpose of metal detectors. While this problem can be addressed by using smaller RFID tags, using smaller RFID tags often results in a significant reduction in RFID performance levels, rendering the RFID device ineffective. Other options include reducing the sensitivity of the detector, which reduces the ability of the metal detector to detect smaller metal objects and is undesirable, or applying the RFID device to the food after scanning for metal objects, which reduces the functionality of the RFID device because the RFID device is not always present throughout the production process.

[0032] Therefore, there is also a long-standing need in the art for an improved radio frequency identification device that can be used throughout the food production process (whose antenna or other metal components will not trigger a false positive in a metal detector).

[0033] First, refer to the accompanying drawings. Figure 1 The use of a metal detector 30 in the food industry is shown. More specifically, food 10 (such as ready-to-eat food, frozen food, etc.) passes through the metal detector 30 before transportation. The metal detector is usually in the form of a tunnel. The metal detector 30 used for food scanning operations is usually configured with a detection threshold for the metal. If the detectable mass of metal 40 detected exceeds the set detection threshold, the food 10 is rejected, disposed of, or transferred to a separate production or inspection area for further investigation of the source of the metal detection. Although this result is desirable in the case where the food 10 contains metal contamination, false positive detections can cause production delays and require human intervention, both of which are not effective and desirable.

[0034] Figure 21 is a side perspective view of an RFID device 100 including an RFID chip 110 and a conductive structure 120. In the disclosed architecture, the RFID device 100 is connected to a food package 20, but it is also contemplated that the RFID device 100 may be directly connected to the food 10. Typical applications for connecting the RFID device 100 to the food 10 or its associated packaging 20 include food traceability, where the RFID device 100 is used in conjunction with a database to store information, for example, to accurately record the location and time of production of the food 10, the identity of the source of the food 10, so as to associate the food 10 with its raw materials, and to track the shelf life or "best before" date of the food 10, as well as any other traceable elements suitable for the needs and / or preferences of the user. The food package 20 may be heated or frozen using a microwave oven, depending on the food 10 in the package.

[0035] Figure 3A FIG. 1 is a top 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 metal mass of the conductive structure 120 of the RFID device 100 is likely to trigger a false positive of a metal detector, such as Figure 1 The metal detector 30 shown. In contrast, Figure 3B For the disclosed architecture Figure 3A 3 is a top view of the RFID device 100 after removing portions of the RFID device conductive structure 120. More specifically, the RFID device 100 of FIG. 3 also includes an RFID chip 110 electrically coupled to the metal conductive structure 120, wherein multiple portions 128 of the conductive structure 120 have been removed to reduce the overall metal mass of the RFID device 100 without affecting its overall performance (i.e., successful interrogation by an RFID reader (not shown) in the food supply chain). The portion 128 of the conductive structure 120 to be removed or hollowed out is selected based on the relatively low position of the current passing through the conductive structure 120 relative to the rest of the conductive structure 120 so that the result of removing the portion 128 does not significantly affect the performance of the RFID device 100. While this reduction in material is advantageous, the RFID device 100 design may require other adjustments or other aspects to provide optimal sensitivity.

[0036] In another embodiment, if Figure 4A and Figure 4B As shown, 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, Figure 4AThe conductive structure 120 is shown to have an initial thickness (a). One of ordinary skill in the art understands that RF (radio frequency) currents in the ultra-high frequency (UHF) frequency range in the 915 MHz region flow primarily on the surface of a conductor or antenna. Furthermore, the current decreases exponentially with the depth of the conductor. This expression of the current reduction effect is called skin depth, Figure 4A The conductive structure 120 has a skin depth 130, which will be explained more fully below.

[0037] like Figure 4A and Figure 4B As shown, another method of reducing the overall metal mass of the conductive structure 120 is to reduce the initial thickness (a) (e.g. Figure 4A as shown) is reduced to reduce the thickness (b) (as shown Figure 4B ). In some embodiments, the reduced thickness (b) is at least the thickness of the skin depth 130. More specifically, the skin depth 130 is a measure of 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, in a layer four times the skin depth from the conductor surface, approximately 98% of the current will flow through the conductor. In another example, for an aluminum UHF RFID antenna, based on an ohmmeter of 2.65x10 -8 The resistivity and skin depth at a frequency of 915 MHz are calculated to be 2.7 μm. Therefore, as a rectangular cross-section conductor, once the thickness drops below 5.4 μm, the resistance at 915 MHz will increase, exceeding the DC resistance, causing additional losses, reducing the performance of the antenna, and thus the performance of the RFID device.

[0038] There are a number of ways to reduce the metal mass of the conductive structure 120 to overcome the limitations of the prior art. For example, one may consider selecting an RFID device with a relatively small antenna whose metal mass is below the detection threshold of the metal detector and thus does not trigger detection. However, when the RFID antenna size is reduced or relatively small, the RF performance of the RFID device is generally low and unacceptable.

[0039] Figure 5A 1 shows a top view of an RFID device 100 having an initial conductive structure 120 (a), Figure 5B 1 shows a top view of an RFID device 100 having an improved conductive structure 120 (b) in the disclosed architecture. More specifically, Figure 5AAs shown, the conductive structure in the initial unmodified configuration 120 (a) may be a dipole antenna, such as the AD238 RFID tag manufactured and sold by Avery Dennison Corporation of Glendale, California. However, this example is for exemplary purposes only, as the present invention contemplates many different initial unmodified RFID tag designs that can be used in food production. In some embodiments, the conductive structure 120 (a) includes a tuning loop 122 and a pair of dipole arms 124, each of which extends from the tuning loop 122 in generally opposite directions. More specifically, each dipole arm 124 can be a meander-type arm, each arm terminating at a load end 126. Each load end 126 is a maximum load area of ​​the conductive structure 120 that can enhance broadband.

[0040] For metal detectors 30 commonly used in the food production industry (such as Figure 1 As shown) type, can detect quality 40 (such as Figure 1 The standard detection threshold of the sphere is about 1 mm in diameter. In this example using the AD238 RFID tag, the material used for the conductive structure 120 is aluminum, and the volume of the detection threshold is about 0.52 mm 3 Therefore, the total metal volume for the standard detection threshold in this example is 0.52mm 3 The volume of the unmodified conductive structure 120 ( a ) having a starting thickness of 15 μm and made of aluminum is approximately 8.6 mm 3 , area is about 573mm 2 , far exceeding the detection threshold and may cause a false positive in the metal detector 30. However, reducing the starting thickness of the conductive structure 120 to a reduced thickness of 1 μm will reduce the volume of the conductive structure 120 to approximately 0.57 mm 3 , which is very close to the detection threshold without changing the overall conductive structure area. Unfortunately, the 1μm reduced thickness is less than the skin depth of aluminum, 130, so degradation of RF performance can be expected.

[0041] In contrast, Figure 5B The results of improving the antenna design to reduce the overall metal mass while still maintaining an acceptable level of performance are shown. The mass of the improved conductive structure 120 (b) is below the standard detection threshold of the metal detector 30. More specifically, in an ideal case, the thickness of the overall conductive structure 120 (b) is greater than the skin depth 130 of the conductive material and frequency. In this example, at a frequency of 915 MHz, the skin depth 130 of aluminum is approximately 2.7 μm.

[0042] To achieve the desired performance level of the RFID device 100, it may be necessary to remove or hollow out 15 μm thick portions of the conductive structure 120 that have low or relatively low current. More specifically, in this example, the load ends 126 are the areas of the conductive structure 120 where the surface current is the lowest. These are the maximum load areas that can enhance the broadband. Therefore, multiple portions 128 of the load ends 126 can be removed or hollowed out. In this example, removing these maximum load areas from the load ends 126 can reduce the volume of the conductive structure 120 (b) to approximately 5.44 mm 3 , area about 363mm 2 , with proper design, the impact on RFID performance is relatively small. Thus, hollowing out or removing portion 128 has the effect of maintaining or improving the broadband width while reducing the overall antenna size requirements. Unfortunately, this volume is still above the detection threshold of the metal detector and may cause the metal detector 30 to generate false positive readings.

[0043] However, the thickness of the conductive structure 120 ( b ) is reduced to about 1 μm and 363 mm 2 The load end 126 has a plurality of hollowed-out portions 128, which can further reduce the volume to about 0.36 mm 3 , which is below the detection threshold of the metal detector 30. A further reduction of the thickness by 500 nm can reduce the volume to about 0.18 mm 3 While the conductive structure 120 can be produced by printing conductive inks based on copper, silver or graphene, by cutting metal foils by means of a rotary cutting system or laser, or by etching, the conductive structure 120 can also be realized at a smaller thickness by vapor deposition.

[0044] In another contemplated embodiment, an RFID device 100 for food 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 at a load terminal 126. Each load terminal 126 is a maximum load region of the conductive structure 120, and the metal mass of the conductive structure 120 is below the standard detection threshold of a metal detector 30 of a type commonly used in the food production industry.

[0045] In addition, ideally, the overall thickness of the conductive structure 120 is slightly greater than the skin depth 130 of the conductive structure material and the frequency. According to the standard detection threshold commonly used to scan food metal foreign matter, ideally, the overall metal volume of the conductive structure 120 is 0.52 mm 3To achieve such a small volume, portions of the conductive structure 120 with lower or relatively lower current and portions that have the least impact on RF performance, such as portions of the load terminals 126, are removed or hollowed out. More specifically, each load terminal 126 is hollowed out to form a plurality of openings or portions 128 within the load terminal 126.

[0046] Alternative techniques for detecting metallic foreign bodies include X-ray analysis, among others. As previously discussed, in certain embodiments, the reduced mass of the RFID device 100 of the present invention is dispersed throughout the conductive structure 120. Thus, the RFID device 100 does not produce a high density "bump" that would produce a relatively diffuse image on an X-ray inspection. More specifically, because the RFID device 100 is relatively "transparent," the relatively diffuse image does not block or impede the detection of high density materials (such as metallic foreign bodies). An ideal material for the conductive structure 120 in X-ray applications is a relatively low density material, including but not limited to graphene (2.267 g / cm 3 ), aluminum (2.7 g / cm 3 ) and copper (8.96 g / cm 3 ). Therefore, it would be advantageous to construct the conductive structure 120 for X-ray applications using a low-density, high-conductivity material (such as aluminum or graphene). Metal detection is more correlated with conductivity. While aluminum is a good choice, graphene, copper, and silver are better conductors. In addition, in an ideal situation, another benefit of the smaller metal volume is that the RFID device 100 is "microwave-safe". More specifically, the RFID device described in the present invention can reduce or eliminate the risk of sparks generated when using a microwave to heat food with the RFID device by eliminating or removing (such as hollowing out) portions of the metal conductive structure of the RFID device.

[0047] Figure 6 A method for reducing the metal mass of the conductive structure 120 of the RFID device 100 is shown. More specifically, the method 200 begins with step 202, that is, providing a conductive structure 120 with an initial area and volume sufficient to fully perform the RFID function according to user requirements. In step 204, the skin depth 130 can be calculated based on the material and frequency of the conductive structure; in step 206, the method continues by reducing the overall initial thickness of the conductive structure 120 using one of the above methods to achieve Figure 4B Typically, the reduced thickness of the conductive structure 120 should not be less than the skin depth 130 calculated for the specific material and frequency of the conductive structure.

[0048] In step 208, areas of the conductive structure 120 with reduced current flow are identified that have little or no effect on the performance of the conductive structure 120 and the RFID device 100. In certain embodiments, the specific areas of the conductive structure 120 with reduced current flow are located at a pair of load terminals 126 of the conductive structure 120. Therefore, in step 210, portions 128 of the conductive structure 120 with reduced current flow are hollowed out to reduce the overall metal mass of the conductive structure 120 and the RFID device 100. Removing this metal mass minimizes the overall area of ​​the conductive structure 120 without significantly affecting the performance of the RFID device 100. The method described in the present invention provides an optimal solution for the design of a conductive structure 120 that provides the desired performance and is suitable for use with the food 10 or its packaging 20 and the metal detector 30.

[0049] Examples of the subject matter are also included above. Of course, in describing the subject matter, it is not possible to describe every possible combination of components or methods, but one of ordinary skill in the art may recognize that many further combinations and permutations of the subject matter are possible. Therefore, the subject matter is intended to cover all such changes, modifications and variations that come within the spirit and scope of the appended claims. In addition, with respect to the term "includes" used in the detailed description or the claims, this term is intended to be included in a manner similar to the term "comprising", which is used as a transitional word in the claims.

Claims

1. A metal detector-resistant radio frequency identification device, comprising: RFID chip; as well as A conductive structure electrically coupled to a radio frequency identification chip, characterized in that: The conductive structure will not be detected when passing through a metal detector having a standard detection threshold; The conductive structure includes a pair of dipole arms extending in opposite directions from the tuning loop, each dipole arm terminates at a load end, and each load end is hollowed out; wherein the current of the first portion of the conductive structure is lower than the current of other portions of the conductive structure, and the first portion of the conductive structure is removed; The device can perform the following method: include: Providing a conductive structure; Reducing the thickness of the conductive structure to achieve thickness reduction; and hollowing out a first portion of the load end of the conductive structure, The current of the first part of the load end of the hollowed-out conductive structure is smaller than the current of other parts of the conductive structure.

2. The RFID device according to claim 1, wherein: The thickness of the conductive structure is greater than the skin depth of the conductive structure.

3. The RFID device according to claim 1 or 2, wherein: The RFID device will not prevent the detection of high density materials during X-ray inspection.

4. The RFID device according to claim 1, wherein: The standard detection threshold is 0.52 mm2 of total metal volume. 3 or above.

5. A method for reducing the metal mass of a radio frequency identification device, include: Providing a conductive structure; Wherein, the conductive structure will not be detected when passing through a metal detector with a standard detection threshold, characterized in that The conductive structure includes a pair of dipole arms extending in opposite directions from the tuning loop, each dipole arm terminates at a load end, and each load end is hollowed out. Reducing the thickness of the conductive structure to achieve thickness reduction; and hollowing out a first portion of the load end of the conductive structure, The current of the first part of the load end of the hollowed-out conductive structure is smaller than the current of other parts of the conductive structure. The method according to claim 5 , further comprising the step of calculating the skin depth of the conductive structure.

7. The method according to claim 5 or 6, wherein: The reduced thickness is not less than the skin depth of the conductive structure.

8. The method according to claim 5, wherein: The portion is located on at least one of a pair of load ends of the conductive structure.

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