Patent Description:
Radio-frequency identification is the use of electromagnetic energy to stimulate a responsive device (known as an RFID "tag" or transponder) to identify itself and, in some cases, provide additional information and/or data stored in the tag. RFID tags and/or labels typically contain a combination of antennas and analog and/or digital electronics, which may include, for example, a semiconductor device commonly referred to as the "chip", communications electronics, data memory, and control logic. Typical RFID tags have a microprocessor electrically connected to an antenna, and act as transponders, providing information stored in the chip memory in response to a radio frequency interrogation signal received from a reader, also referred to as an interrogator. In the case of passive RFID devices, the energy of the interrogation signal also provides the necessary energy to operate the RFID tag device.

RFID tags may be incorporated into or attached to articles that a user wishes to later identify and/or track, such as various food products. In some cases, the RFID tag may be attached to the outside of the article with a clip, adhesive, tape, or other means and, in other cases, the RFID tag may be inserted within the article, such as being included in the packaging, or located within the container of the article or plurality of articles. Further, RFID tags are manufactured with a unique identification number which is typically a simple serial number of a few bytes with a check digit attached. This identification number is typically incorporated into the RFID tag during its manufacture. The user cannot alter this serial/identification number, and manufacturers guarantee that each RFID tag serial number is used only once and is, therefore, unique. Such read-only RFID tags typically are permanently attached to an article to be identified and/or tracked and, once attached, the serial number of the tag is associated with its host article in a computer database.

Food product items, such as ready to consume meals or other packaged food products are commonly manufactured or prepared in factories or commercial kitchens that utilize machinery with metal components as part of the production process, and that could result in the food product becoming contaminated with metal particles. Additionally, it is possible for metal to be maliciously placed into a food product. While food manufacturers typically have very stringent environmental controls in place within their own facilities and packaging processes, metal items can break and accidentally still enter the food product or its packaging. One common low-cost method of detecting the undesirable and/or unintended metal is to pass the packaged food product 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. Unfortunately, as explained more fully below, the use of metal detectors for such purposes have a number of limitations when used with RFID devices.

More specifically, to allow for better control of shipping, traceability, inventory, and other supply chain needs, it is desirable to use RFID devices in relation to food products. RFID devices have the potential to increase profitability for a food manufacturer by allowing the food manufacturer to continuously monitor the supply of food product throughout the entire supply chain. Using RFID tags also allows the manufacturer to quickly respond to low inventory without the need for a physical inventory count to ensure an adequate supply of food product, while avoiding the risks of overstocking particular food product items. For example, a store can monitor the supply of food products on hand and easily predict when to order more food product to maintain an appropriate supply and to have food products readily available at the point of sale. Ideally, the RFID devices should therefore be attached to the food product as early as possible in the supply chain to assist in traceability and production, or integrated with the food product packaging before it is used to package the food item.

Unfortunately, the mass of conductive material used as an antenna in an RFID device is typically greater than the detection threshold for a foreign metal object of a metal detector. This deficiency requires a manufacturer to either reduce the detection threshold of the metal detector, thereby reducing its ability to detect a foreign metal object, or to apply an RFID device after scanning the food product with the metal detector, thereby losing the benefits of more accurate traceability and use of the RFID device throughout the entire manufacturing or production process.

<CIT> relates to an electronic identifier for packaging where the antenna for the electronic identification device is formed of a non-metallic material which is printed directly onto a surface of a packaging film or a surface of a package. <CIT> relates to robust washable tags using a large area antenna conductor. The robust merchandise tags combine a hybrid-slot loop antenna structure with a large area conductor sheet in the nature of a foil or the like. <CIT> relates to a method of manufacturing a radio frequency identification device where a web of material is provided to at least one cutting station in which a first pattern is generated in the web of material. A further cutting may occur to create additional modifications in order to provide a microchip attachment location and to selectively tune an antenna for a particular end use application.

Therefore, there exists in the art a long felt need for an improved RFID device that can be used in relation to food product items throughout the entire manufacturing or production process, including prior to scanning the food products for foreign metal objects with a metal detector. There also exists a long felt need in the art for an improved RFID device that is metal detector "resistant", and whose antenna or other metal components will not trigger a false positive from the metal detector.

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

Conductive structures/antennas and RFID devices that are below the standard detection threshold of most metal detectors commonly used in food product manufacturing and/or production, and a method of using the same are described herein. More specifically, the RFID device can be placed on the food product item or its packaging prior to being scanned by a metal detector, and will not generate a false positive based on the metallic components of the RFID device. In one example, the RFID device contains a conductive/antenna structure that is designed with a metal mass below the detection threshold of the metal detector, but that still maintains an adequate level of performance to track the food product item through the supply chain including, without limitation, in a store inventory.

The extent of protection conferred is determined from the claims.

The RFID device further contains a conductive structure. The conductive structure contains a pair of dipole arms extending from a tuning loop, wherein each of said dipole arms terminates in a load end. The conductive structure is further configured to have a metal mass that is less than a standard detection threshold of a metal detector that is used to scan food product items and their packaging.

In some examples, the conductive structure is as described above and has an area large enough to achieve a required or desired performance, but still below the typical standard detection threshold associated with scanning a food item or packaging for a foreign metal object of approximately a <NUM> diameter metal sphere.

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

Portions of each load end are hollowed out so that areas of the conductive structure having a lower current flow are removed with minimal impact on overall RFID performance, while also achieving a conductive structure with a mass below the detection threshold of the metal detector.

In further examples, a RFID device is disclosed that is contemplated for use with food product items, and food packaging applications. The RFID device preferably contains a RFID chip and a conductive structure electrically coupled to the RFID chip. The conductive structure includes a pair of dipole arms extending oppositely from a tuning loop, wherein each of said dipole arm terminates in a load end. The conductive structure is configured to have a metal mass that is less than a standard detection threshold of a metal detector that is used to scan food product items and their respective packaging.

The improved RFID devices described herein may 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. A similar result may also be partially accomplished by reducing the thickness of the metal conductive structure. Yet another benefit of the improved RFID devices described herein is that this reduction of structure and mass creates a RFID device that does not block detection of high-density materials if the RFID device is x-rayed.

Methods for reducing the metal mass of a conductive structure for use with a RFID device are also described herein. In some embodiments, the method includes (<NUM>) providing a conductive structure designed with an initial area just large enough to adequately perform its intended function; (<NUM>) determine a skin depth for the conductive structure based on material and/or frequency; and (<NUM>) 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).

Specific areas of the conductive structure having a relatively lower current flow are then hollowed out to remove additional mass. The specific areas hollowed out are located on a pair of load ends of the overall thickness of the conductive structure. In some examples, enough material is preferably removed so that, in combination with the reduced overall thickness, the conductive structure has a mass below the standard detection threshold of a metal detector used in food processing screening but enough mass to function effectively as a RFID device.

To the accomplishment of the foregoing and related ends, certain illustrative aspects of the disclosed innovation are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles disclosed herein can be employed and is 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.

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 to offset this problem 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.

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.

Referring initially to the drawings, <FIG> illustrates the use of a metal detector <NUM> for use in the food industry. More specifically, a food item <NUM>, such as a ready to eat meal, frozen food, etc., is passed through the metal detector <NUM> prior to shipping. The metal detector is typically in the form of a tunnel. Metal detectors <NUM> used in food scanning operations are oftentimes configured with a detection threshold for metal. In the event that a detectable mass of metal <NUM> is detected in excess of the set detection threshold, the food item <NUM> 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 <NUM> has metal contamination, false positive detections result in manufacturing/production delays, and the need for human intervention, neither of which are efficient or desirable.

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

<FIG> illustrates a top view of RFID device <NUM>, which contains an RFID chip <NUM> and conductive structure <NUM>. More specifically, RFID chip <NUM> is electrically coupled to conductive structure <NUM>. However, the mass of the metal of conductive structure <NUM> of RFID device <NUM> will likely trigger a false positive in a metal detector, such as metal detector <NUM> shown in <FIG>. By comparison, <FIG> illustrates a top view of the RFID device <NUM> of <FIG> but after removing portions of the conductive structure <NUM> of the RFID device in accordance with the disclosed architecture. More specifically, the RFID device <NUM> of <FIG> also contains a RFID chip <NUM> electrically coupled to a metallic conductive structure <NUM>, but wherein a plurality of portions <NUM> of conductive structure <NUM> have been removed to reduce the overall metallic mass of the RFID device <NUM> 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 <NUM> of conductive structure <NUM> to be removed or hollowed out are chosen based on where the current flow through conductive structure <NUM> is relatively low compared to the rest of the conductive structure <NUM>, and such that the result of the removal of portions <NUM> does not significantly affect performance of the RFID device <NUM>. While this reduction in material is beneficial, other adjustments or other aspects of the RFID device <NUM> design may be required to provide optimal sensitivity.

In further embodiments, as illustrated in <FIG>, the metal mass of the conductive structure <NUM> may also be reduced by reducing the thickness of either all or part of the conductive structure <NUM>. More specifically, the conductive structure <NUM> illustrated in <FIG> 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 <NUM> 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 <NUM> of <FIG> has a skin depth <NUM>, as explained more fully below.

As best illustrated in <FIG>, another way of reducing the overall metallic mass of the conductive structure <NUM> is to decrease the initial thickness (a) (as shown in <FIG>) to a reduced thickness (b) (as shown in <FIG>). In some embodiments, reduced thickness (b) is at least the thickness of skin depth <NUM>. More specifically, skin depth <NUM> 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 <NUM>/e 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 <NUM>% 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 <NUM>×<NUM>-<NUM> ohm-meter and a frequency of <NUM>, is calculated as <NUM>. Therefore, as a rectangular cross-section conductor, once thickness drops below <NUM>, the resistance at <NUM> increases above the DC resistance, introducing additional loss and reduction of antenna and hence RFID device performance.

A number of approaches may be taken to reduce the metallic mass of the conductive structure <NUM> to overcome the limitations of the prior art. For example, the selection of an 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.

<FIG> illustrates a top view of an RFID device <NUM> having an initial conductive structure <NUM>(a), and <FIG> illustrates a top view of the RFID device <NUM> having a modified conductive structure <NUM>(b) in accordance with an embodiment of the invention. More specifically and as illustrated in <FIG>, the conductive structure in an initial unmodified configuration <NUM>(a) is 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. The conductive structure <NUM>(a) contains a tuning loop <NUM>, and a pair of dipole arms <NUM> each extending from the tuning loop <NUM> in generally opposite directions. More specifically, each of the dipole arms <NUM> may be meander-line type arms that each terminate in a load end <NUM>. Each load end <NUM> is an area of top load for the conductive structure <NUM>, which strengthens broadband.

A standard detection threshold for a detectable mass <NUM> (as shown in <FIG>) for a metal detector <NUM> (also shown in <FIG>) of the type commonly used in the food production industry is a sphere approximately <NUM> in diameter. In the present example, which utilizes an AD238 RFID tag, the material used for the conductive structure <NUM> is aluminum and the volume of the detection threshold is approximately <NUM><NUM>. Therefore, the standard detection threshold in this example has a total metallic volume of <NUM><NUM>.

The unmodified conductive structure <NUM>(a) made with a starting thickness of <NUM> aluminum has a volume of approximately <NUM><NUM>, and an area of <NUM><NUM>, which is well above the detection threshold and would likely result in a false positive by metal detector <NUM>. However, reducing the conductive structure <NUM> from the starting thickness to a reduced thickness of <NUM> will reduce the volume of the conductive structure <NUM> to approximately <NUM><NUM>, which is much close to the detection threshold and does not change the overall conductive structure area. Unfortunately, the reduced thickness of <NUM> is less than a skin depth <NUM> of the aluminum, so a reduction in RF performance should be expected.

By comparison, <FIG> 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 <NUM>(b) has a mass below the standard detection threshold of metal detector <NUM>. More specifically, the overall conductive structure <NUM>(b) ideally has a thickness greater than the skin depth <NUM> for the constructive material and frequency. In this example, the skin depth <NUM> for aluminum at a frequency of <NUM> is approximately <NUM>.

To achieve the desired level of performance from RFID device <NUM>, it is necessary to remove or hollow out those portions of the <NUM> thick conductive structure <NUM> that have a lower, or relatively low, current flow. More specifically, the pair of load ends <NUM> are the areas of the conductive structure <NUM> 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 <NUM> are removed from, or hollowed out of, the pair of load ends <NUM>. Removing these portions of the top load areas from the pair of load ends <NUM> reduces the volume of the conductive structure <NUM>(b) in the present example to approximately <NUM><NUM> and an area of <NUM><NUM>, with relatively minimal impact on RFID performance with the correct design. Therefore, the hollowing out or removing of portions <NUM> 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 <NUM>.

However, also reducing the thickness of the conductive structure <NUM>(b) to approximately <NUM> thick aluminum with an area of <NUM><NUM>, with the pair of load ends <NUM> having the plurality of hollowed out portions <NUM>, further reduces the volume to approximately <NUM><NUM>, which is below the detection threshold of metal detector <NUM>. A further reduction to a thickness of <NUM> has the effect of reducing volume to approximately <NUM><NUM>. While the conductive structure <NUM> 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.

In an additional contemplated embodiment, a RFID device <NUM> for use with food product items contains a RFID chip <NUM> and a conductive structure <NUM> electrically coupled to the RFID chip <NUM>. The conductive structure <NUM> contains a tuning loop <NUM> and a pair of dipole arms <NUM>. Each of the dipole arms <NUM> extend outwardly from the tuning loop <NUM> in generally opposite directions and terminate in a load end <NUM>. Each load end <NUM> is an area of top load for the conductive structure <NUM>, and the conductive structure <NUM> is manufactured to have a metallic mass below a standard detection threshold of a metal detector <NUM>, of the type commonly used in the food production industry.

Additionally, the conductive structure <NUM> is configured so as to have an overall thickness that is ideally slightly greater than a skin depth <NUM> 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 <NUM> will ideally have a total metallic volume of <NUM><NUM> or less. To achieve such a low volume, portions of the conductive structure <NUM> 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 <NUM>. More specifically, each load end <NUM> is hollowed out to create a plurality of openings or portions <NUM> within the load ends <NUM>.

Alternative technologies for detecting foreign metallic objects include x-ray analysis, and the like. As previously stated, in some embodiments, the RFID device <NUM> described herein is manufactured with a reduced mass that is spread out throughout the conductive structure <NUM>. As such, the RFID device <NUM> 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 <NUM> will be relatively "transparent. " Ideal materials for the conductive structure <NUM> for the x-ray application are materials with a relatively low density including, but not limited to, graphene (<NUM>/cm<NUM>), aluminum (<NUM>/cm<NUM>), and copper (<NUM>/cm<NUM>). Therefore, it would be advantageous to construct the conductive structure <NUM> 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 <NUM> 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.

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

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

Claim 1:
A conductive structure (120b), for use with an RFID device (<NUM>), wherein the conductive structure (120b) is not detectable when passing through a metal detector (<NUM>) having a standard detection threshold of a total metallic volume of <NUM><NUM>,
wherein
the conductive structure comprises a pair of dipole arms (<NUM>) extending oppositely from a tuning loop (<NUM>), wherein each of said pair of dipole arms terminates in a load end (<NUM>),
characterized in that each load end has a portion (<NUM>) thereof removed to form a hollow load end (<NUM>).