METAL DETECTOR RESISTANT RFID TAGS

Abstract

A conductive structure for use with a RFID device having a metallic mass that is below a standard detection threshold of a metal detector and a method of manufacturing the same is disclosed herein. The conductive structure preferably comprises a pair of dipole arms extending from a tuning loop, wherein each of the pair of dipole arms terminates in a load end. The conductive structure may be manufactured from a printed metallic ink, or by cutting, lasering, or etching a metal foil. The conductive structure is modified to reduce overall thickness and metallic mass of the device as much as possible, while still maintaining an acceptable level of performance. Portions of the load ends may also be hollowed out to further reduce the conductive structure's metallic mass.

Claims

1. A metal detector-resistant RFID device comprising: an RFID chip; and a conductive structure electrically coupled to the RFID chip, wherein the conductive structure has a metallic mass that is below the standard detection threshold.

2. The RFID device of claim 2, wherein a thickness of the conductive structure is greater than a skin depth for the conductive structure.

3. The RFID device of claim 1 wherein the conductive structure comprises a pair of dipole arms extending oppositely from a tuning loop, and further wherein each of said pair of dipole arms terminates in a load end.

4. The RFID device of claim 3, wherein each load end is hollowed out.

5. The RFID device of claim 1wherein a portion of the conductive structure has a lower current flow than a second portion of the conductive structure and the first portion is removed.

6. The RFID device of claim 1wherein the RFID device does not block detection of high-density materials when x-rayed.

7. The RFID device of claim 11, wherein the standard detection threshold is a total metallic volume of 0.52 mm.sup.3 or greater.

8. A method of reducing a metallic mass of a RFID device comprising: providing a conductive structure; reducing a thickness of the conductive structure to achieve a reduced thickness; and hollowing out a portion of the conductive structure, wherein a current flow of the portion is less than the current flow of a second portion of the conductive structure.

9. The method of claim 8 further comprising the step of calculating a skin depth of the conductive structure.

10. The method of claim 8, wherein the reduced thickness is not less than the skin depth of the conductive structure.

11. The method of claim 8, wherein the conductive structure comprises a pair of dipole arms extending from a tuning loop and terminating in a load end.

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

13. A conductive structure for use with a RFID device that will be subject to a metal detector having a standard detection threshold, wherein the conductive structure has a metallic mass that is below the standard detection threshold and is electrically coupled to the RFID device.

14. The conductive structure of claim 13, wherein the standard detection threshold is a 1 mm diameter metal sphere.

15. The conductive structure of claim 13, wherein the standard detection threshold is a total metallic volume of 0.52 mm.sup.3 or greater.

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

17. The conductive structure of claim 13, wherein an overall thickness of the conductive structure is greater than a skin depth for the conductive structure.

18. The conductive structure of claim 13, wherein a portion of the conductive structure is removed.

19. The conductive structure of claim 13, wherein a conductive structure thickness is achieved by vapor deposition.

20. The conductive structure of claim 13 wherein the conductive structure is manufactured by either printing a conductive ink or by cutting a foil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] FIG. 2 illustrates a side perspective view of a RFID device attached to a food packaging in accordance with the disclosed architecture.

[0022] FIG. 3A illustrates a top view of an RFID device prior to removing portions of a conductive structure of the RFID device in accordance with the disclosed architecture.

[0023] FIG. 3B illustrates a top view of the RFID device of FIG. 3A after removing portions of the conductive structure of the RFID device in accordance with the disclosed architecture.

[0024] FIG. 4A illustrates a side elevational view the conductive structure having a starting thickness in accordance with the disclosed architecture.

[0025] FIG. 4B illustrates a side elevational view the conductive structure having a reduced thickness in accordance with the disclosed architecture.

[0026] FIG. 5A illustrates a top view of an RFID device having an initial conductive structure in accordance with the disclosed architecture.

[0027] FIG. 5B illustrates a top view of the RFID device having a modified conductive structure in accordance with the disclosed architecture

[0028] FIG. 6 illustrates a method of reducing a mass of a conductive structure for use with an RFID device in accordance with the disclosed architecture.

DETAILED DESCRIPTION

[0029] The innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding thereof. It may be evident, however, that the innovation can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate a description thereof.

[0030] As noted above, one common low-cost method of detecting undesirable and/or unintended metal in a food product item or its associated packaging is to pass the food product and/or packaging through a metal detector. If metal is detected, the food product can be segregated to remove the metal contaminant from the food product, or otherwise disposed of. The use of RFID devices is also a common way of tracking food products throughout the food supply chain. Unfortunately, heretofore, RFID devices have not worked well with metal detectors and oftentimes result in the generation of false positive readings by the metal detector in response to the metallic components in the RFID device. More specifically, RFID devices typically contains antennas that are metallic and large enough to be detectable by a metal detector, thereby triggering a false positive reading and requiring an individual inspection which defeats the purpose of the metal detector. While a smaller RFID tag could be used to offset this problem, the use of smaller RFID tags oftentimes results in a significant drop in the level of performance of the RFID device, thereby defeating the purpose of the RFID device. Other options include decreasing the detector's sensitivity, which reduces the ability of the metal detector to detect smaller metal objects and is undesirable, or to apply the RFID devices to the food products after scanning for metal objects, which reduces the functionality of the RFID device because it wasn't present throughout the entire manufacturing or production process.

[0031] Accordingly, there is a long felt need in the art for an improved RFID device that can be used in relation to food product items throughout the entire manufacturing or production process, and whose antenna or other metal components will not trigger a false positive from the metal detector.

[0032] Referring initially to the drawings, FIG. 1 illustrates the use of a metal detector 30 for use in the food industry. More specifically, a food item 10, such as a ready to eat meal, frozen food, etc., is passed through the metal detector 30 prior to shipping. The metal detector is typically in the form of a tunnel. Metal detectors 30 used in food scanning operations are oftentimes configured with a detection threshold for metal. In the event that a detectable mass of metal 40 is detected in excess of the set detection threshold, the food item 10 may be rejected, disposed of, or diverted to a separate production or inspection area for further investigation into the source of the metal detection. While this outcome is desirable in the event that the food product item 10 has metal contamination, false positive detections result in manufacturing/production delays, and the need for human intervention, neither of which are efficient or desirable.

[0033] FIG. 2 illustrates a side perspective view of a RFID device 100 containing a RFIF chip 110 and a conductive structure 120. The RFID device 100 is attached to a food product packaging 20 in accordance with the disclosed architecture, though it is also contemplated that RFID device 100 may be directly attachable to the food product item 10. Typical applications for attaching the RFID device 100 to food product item 10 or its associated packaging 20 include food product traceability, where the RFID device 100 is used in conjunction with a database for storing information, for example, to record exactly where and when the food product item 10 was produced, the identity of the source of the food product item 10, to associate the food product item 10 with its raw ingredients, to track the food product item 10 expiration or the "best by" dates, and any other trackable element that suits user need and/or preference. The food product packaging 20 may be microwavable or freezable depending on the requirements of the enclosed food product item 10.

[0034] FIG. 3A illustrates a top view of RFID device 100, which contains an RFID chip 110 and conductive structure 120. More specifically, RFID chip 110 is electrically coupled to conductive structure 120. However, the mass of the metal of conductive structure 120 of RFID device 100 will likely trigger a false positive in a metal detector, such as metal detector 30 shown in FIG. 1. By comparison, FIG. 3B illustrates a top view of the RFID device 100 of FIG. 3A but after removing portions of the conductive structure 120 of the RFID device in accordance with the disclosed architecture. More specifically, the RFID device 100 of FIG. 3 also contains a RFID chip 110 electrically coupled to a metallic conductive structure 120, but wherein a plurality of portions 128 of 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 product supply chain). The portions 128 of conductive structure 120 to be removed or hollowed out are chosen based on where the current flow through conductive structure 120 is relatively low compared to the rest of the conductive structure 120, and such that the result of the removal of portions 128 does not significantly affect performance of the RFID device 100. While this reduction in material is beneficial, other adjustments or other aspects of the RFID device 100 design may be required to provide optimal sensitivity.

[0035] In further embodiments, as illustrated in FIGS. 4A and 4B, the metal mass of the conductive structure 120 may also be reduced by reducing the thickness of either all or part of the conductive structure 120. More specifically, the conductive structure 120 illustrated in FIG. 4A has an initial thickness (a). It is known to those of ordinary skill in the art that RF currents in the ultra-high frequency (UHF) frequency range in the region of 915 MHz flow primarily on the surface of the conductor or antenna. Additionally, said currents reduce exponentially with the depth of the conductor. An expression of this current reducing effect is known as skin depth, and the conductive structure 120 of FIG. 4A has a skin depth 130, as explained more fully below.

[0036] As best illustrated in FIGS. 4A and 4B, another way of reducing the overall metallic mass of the conductive structure 120 is to decrease the initial thickness (a) (as shown in FIG. 4A) to a reduced thickness (b) (as shown in FIG. 4B). In some embodiments, reduced thickness (b) is at least the thickness of skin depth 130. More specifically, skin depth 130 is a measure of the current density, and is defined as the distances from the outer edges of a conductor to the point at which the current density falls to ⅟e of the value of the current at the surface of the conductor. For example, in a layer four times the skin depth from the surface of a conductor, approximately 98% of the current will flow in the conductor. In a further example, for a UHF RFID antenna made from aluminum, skin depth, based on a resistivity of 2.65×10.sup.-8 ohm-meter and a frequency of 915 MHz, is calculated as 2.7 .Math.m. Therefore, as a rectangular cross-section conductor, once thickness drops below 5.4 .Math.m, the resistance at 915 MHz increases above the DC resistance, introducing additional loss and reduction of antenna and hence RFID device performance.

[0037] A number of approaches may be taken to reduce the metallic mass of the conductive structure 120 to overcome the limitations of the prior art. For example, the selection of a RFID device with a relatively small antenna having a metal mass that is below the detection threshold of the metal detector and therefore, would not trigger a detection may be considered. However, RFID devices with reduced or relatively small RFID antenna sizes are commonly associated with lower and unacceptable RF performance.

[0038] FIG. 5A illustrates a top view of an RFID device 100 having an initial conductive structure 120(a), and FIG. 5B illustrates a top view of the RFID device 100 having a modified conductive structure 120(b) in accordance with the disclosed architecture. More specifically and as illustrated in FIG. 5A, the conductive structure in an initial unmodified configuration 120(a) may be a dipole type antenna, such as an AD238 RFID tag manufactured and sold by Avery Dennison, of Glendale, California. However, the example is used for exemplary purposes only, as many different initial unmodified RFID tags designs that may be used in relation to food production are contemplated herein. In some embodiments, the conductive structure 120(a) contains 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 may be meander-line type arms that each terminate in a load end 126. Each load end 126 is an area of top load for the conductive structure 120, which strengthens broadband.

[0039] A standard detection threshold for a detectable mass 40 (as shown in FIG. 1) for a metal detector 30 (also shown in FIG. 1) of the type commonly used in the food production industry is a sphere approximately 1 mm in diameter. In the present example, which utilizes an AD238 RFID tag, the material used for the conductive structure 120 is aluminum and the volume of the detection threshold is approximately 0.52 mm.sup.3. Therefore, the standard detection threshold in this example has a total metallic volume of 0.52 mm.sup.3 or greater. The unmodified conductive structure 120(a) made with a starting thickness of 15 .Math.m aluminum has a volume of approximately 8.6 mm.sup.3, and an area of 573 mm.sup.2, which is well above the detection threshold and would likely result in a false positive by metal detector 30. However, reducing the conductive structure 120 from the starting thickness to a reduced thickness of 1 .Math.m will reduce the volume of the conductive structure 120 to approximately 0.57 mm.sup.3, which is much close to the detection threshold and does not change the overall conductive structure area. Unfortunately, the reduced thickness of 1 .Math.m is less than a skin depth 130 of the aluminum, so a reduction in RF performance should be expected.

[0040] By comparison, FIG. 5B illustrates the result of a modification to the antenna design that results in a reduced overall metallic mass, while still maintaining an acceptable level of performance. The modified conductive structure 120(b) has a mass below the standard detection threshold of metal detector 30. More specifically, the overall conductive structure 120(b) ideally has a thickness greater than the skin depth 130 for the constructive material and frequency. In this example, the skin depth 130 for aluminum at a frequency of 915 MHz is approximately 2.7 .Math.m.

[0041] To achieve the desired level of performance from RFID device 100, it may be necessary to remove or hollow out those portions of the 15 .Math.m thick conductive structure 120 that have a lower, or relatively low, current flow. More specifically, the pair of load ends 126 are the areas of the conductive structure 120 in this example where the surface current flow is at its lowest. These are areas of top load, which strengthen broadband. As such, a plurality of portions 128 may be removed from, or hollowed out of, the pair of load ends 126. Removing these portions of the top load areas from the pair of load ends 126 reduces the volume of the conductive structure 120(b) in the present example to approximately 5.44 mm.sup.3 and an area of 363 mm.sup.2, with relatively minimal impact on RFID performance with the correct design. Therefore, the hollowing out or removing of portions 128 has an effect of maintaining or improving broadband width, while decreasing overall antenna size requirements. Unfortunately, this volume is also still above the detection threshold for the metal detector, and will likely result in the generation of false positive readings by metal detector 30.

[0042] However, also reducing the thickness of the conductive structure 120(b) to approximately 1 .Math.m thick aluminum with an area of 363 mm.sup.2, with the pair of load ends 126 having the plurality of hollowed out portions 128, further reduces the volume to approximately 0.36 mm.sup.3, which is below the detection threshold of metal detector 30. A further reduction to a thickness of 500 nm has the effect of reducing volume to approximately 0.18 mm.sup.3. While the conductive structure 120 may be manufactured by printing a conductive ink based on, for example, copper, silver, or graphene, cutting a metallic foil by a rotary cutting system, or a laser, or by etching, it may also be achieved at smaller thicknesses by vapor deposition.

[0043] In an additional contemplated embodiment, a RFID device 100 for use with food product items contains a RFID chip 110 and a conductive structure 120 electrically coupled to the RFID chip 110. The conductive structure 120 contains a tuning loop 122 and a pair of dipole arms 124. Each of the dipole arms 124 extend outwardly from the tuning loop 122 in generally opposite directions and terminate in a load end 126. Each load end 126 is an area of top load for the conductive structure 120, and the conductive structure 120 is manufactured to have a metallic mass below a 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 so as to have an overall thickness that is ideally slightly greater than a skin depth 130 for the conductive structure material and frequency. Based on a standard detection threshold commonly used to scan food product items for foreign metallic objects, the conductive structure 120 will ideally have a total metallic volume of 0.52 mm.sup.3 or less. To achieve such a low volume, portions of the conductive structure 120 having lower or relatively low current flow, and that have minimal effect on RF performance, are removed or hollowed out, such as portions of the 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 ends 126.

[0045] Alternative technologies for detecting foreign metallic objects include x-ray analysis, and the like. As previously stated, in some embodiments, the RFID device 100 described herein is manufactured with a reduced mass that is spread out throughout the conductive structure 120. As such, the RFID device 100 will not produce a high density "lump", and should produce a relatively diffuse image on x-ray. More specifically, the relatively diffuse image will not block or obstruct detection of high-density materials, such as foreign metal objects, as the RFID device 100 will be relatively "transparent." Ideal materials for the conductive structure 120 for the x-ray application are materials with a relatively low density including, but not limited to, graphene (2.267 g/cm.sup.3), aluminum (2.7 g/cm.sup.3), and copper (8.96 g/cm.sup.3). Therefore, it would be advantageous to construct the conductive structure 120 from a low density, high conductivity material such as, aluminum or graphene for x-ray applications. Metal detection is better related to conductivity. Whereas aluminum is a good choice, graphene, copper, and silver are better conductors. Furthermore, an additional benefit to the low metallic volume is that the RFID device 100 will ideally be "microwave safe." More specifically, the RFID device described herein may also reduce or eliminate the sparking risks associated with using a microwave to cook a food product with an RFID device attached thereto by eliminating or removing, such as by hollowing out, a portion of the metal conductive structure of the RFID device.

[0046] FIG. 6 illustrates a method of reducing the metallic mass of a conductive structure 120 of RFID device 100. More specifically, the method 200 begins at step 202 by providing a conductive structure 120 having an initial area and volume just large enough to adequately perform RFID functions in accordance with a user's specifications. At step 204, a skin depth 130 may be calculated based on the conductive structure's material and frequency as described supra, and, at step 206, the method continues as an overall initial thickness of the conductive structure 120 is reduced in one of the manners described above to achieve the profile depicted in FIG. 4B. Typically, the reduced thickness of the conductive structure 120 should not be less than the calculated skin depth 130 for the conductive structure's specific material and frequency.

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

[0048] What has been described above includes examples of the claimed subject matter. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the claimed subject matter, but one of ordinary skill in the art may recognize that many further combinations and permutations of the claimed subject matter are possible. Accordingly, the claimed subject matter is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either 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 employed as a transitional word in a claim.