Patent Description:
The present subject matter relates to radio frequency identification ("RFID") devices capable of sensing a temperature. More particularly, the present subject matter relates to environmental shielding and/or enhancement of RFID devices capable of sensing a temperature.

Electrically powered devices for sensing a material or condition are well known. This includes RFID devices incorporating sensors for determining and communicating the temperature of an article to which the RFID device is associated, such as the temperature of a food item or article, including packaged articles intended to be stored under certain environmental conditions and to which the RFID device is secured. Such an RFID device is described in <CIT>, which is hereby incorporated herein by reference.

One challenge with devices of the type described in <CIT> is ensuring that the measured temperature corresponds to the temperature of the article to which the device is secured, rather than the temperature of the local environment, which can vary rapidly. Contrary to this prior art, the present subject matter presents the improvement of providing embodiments in which temperature-sensing RFID devices are shielded from environmental conditions that would affect measurement of the temperature of an article to which the device is secured and/or are otherwise configured for enhanced detection of the temperature of an associated article itself.

<CIT> relates to a body temperature measuring system including a clinical thermometer for measuring the body temperature of an object and a data reading device for reading data from the clinical thermometer. The clinical thermometer is adhesive and comprises a wireless tag having an RFID function) and a semiconductor temperature sensor. <CIT> relates to a composite of a noncontact IC tag module and a biocompatible adhesive label. The noncontact IC tag module may be equipped with an NFC compatible temperature sensor chip.

A temperature-sensing RFID device according to the present invention is defined in claim <NUM>. Advantageous features of the present invention are defined in the dependent claims.

<FIG> shows an RFID device, generally designated at <NUM>, according to an aspect of the present disclosure, which is not part of the claimed invention. The RFID device <NUM> includes an RF communication chip <NUM>, which may include an integrated circuit for controlling RF communication and other functions of the RFID device <NUM>. The RFID chip <NUM> further includes a temperature sensor configured and oriented to determine the temperature of an article to which the RFID device <NUM> is secured, such as a food item to provide information concerning possible food safety parameters for the particular food item, such as having its temperature raised to a level triggering a potential concern.

The RF chip <NUM> is electrically connected or coupled to an antenna, generally designated at <NUM>. The RFID chip <NUM> and the antenna <NUM> may be at least partially formed of a reflective material, such as aluminum foil. The illustrated antenna <NUM> has first and second conductors <NUM> and <NUM>, respectively, positioned at opposite lateral sides of the RFID chip <NUM>, with the conductors <NUM> and <NUM> being electrically coupled to the RFID chip <NUM> by a strap <NUM>. In one embodiment, the RFID chip <NUM> is attached to the strap <NUM> by an anisotropic conductive paste, such as an adhesive with particles such as ceramics and/or metals. The antenna <NUM> is configured to receive energy from an RF field and produce a signal that is transmitted to one or more external devices (not shown), such as a controller or reader or detector, configured to receive and analyze the signal. The RF field may be generated by the device to which the antenna <NUM> transmits the signal, or it may be generated by a different external device.

While the temperature sensor of the RFID chip <NUM> is configured to detect the temperature of the article to which the RFID device <NUM> is secured, it is possible for environmental factors to interfere with detection of the proper temperature. Accordingly, to protect the RFID chip <NUM> from such environmental factors, the RFID device <NUM> of this embodiment is provided with a shielding structure <NUM> positioned between the RFID chip <NUM> and the outside environment (i.e., with the RFID chip <NUM> positioned between the shielding structure <NUM> and the article to which the RFID device <NUM> is secured). The shielding structure <NUM> may be variously configured, such as being configured to overlay the entire RFID chip <NUM> and a portion of the strap <NUM> (as in <FIG>) or being limited to the bounds of the RFID chip <NUM> (as in <FIG>). In other embodiments, the shielding structure <NUM> may overlay only a portion of the RFID chip <NUM>, though it may be preferred for the shielding structure <NUM> to overlay and protect the entire RFID chip <NUM>.

By way of example, if the active components of the RFID chip <NUM> (which may include transistors, diodes, the temperature sensor, etc.) are exposed to infrared light, the components may become heated or the infrared light may cause other effects due to photoelectric effects, which may affect the temperature sensed by the temperature sensor. For example, exposure of the silicon of the RFID chip <NUM> to infrared radiation can cause the RFID chip <NUM> to heat up and increase the temperature detected by the temperature sensor. Accordingly, it may be advantageous for the shielding structure <NUM> to be comprised of a material configured to reflect infrared radiation away from the RFID chip <NUM>. This may include the shielding structure <NUM> being at least partially formed of an aluminum material. Alternatively or additionally, at least a portion of a surface of the shielding structure <NUM> facing the outside environment may be configured with an infrared-reflecting color, such as white. For example, at least a portion of an outwardly facing surface of the shielding structure <NUM> may be formed of an opaque, white material, such as plastic or dense paper.

According to another aspect of the present disclosure, the shielding structure <NUM> may be at least partially formed of a thermally non-conductive material to prevent, or at least significantly or extensively retard, the temperature of the outside environment from affecting the temperature detected by the temperature sensor. For example, the shielding structure <NUM> may be at least partially formed of a foam material or a corrugated cardboard material. Such a shielding structure <NUM> reduces the thermal coupling between the RFID chip <NUM> and the outside environment (which may have a temperature that changes rapidly), thus increasing the accuracy of the temperature sensor in measuring the temperature of the article to which the RFID device <NUM> is secured. It might be considered that such an approach in effect modifies the thermal properties of the label, tag, sticker, etc. associated with the RFID chip <NUM> having the temperature sensor.

These different configurations of shielding structures <NUM> may be employed separately or in any combination. Additionally, the antenna <NUM> can be directly cut onto the shielding structure <NUM> (e.g., using a laser), rather than being separately provided.

It will be seen that shielding structures <NUM> according to the present disclosure will improve the performance of a temperature-sensing RFID device <NUM> by protecting the RFID chip <NUM> of the RFID device <NUM> from environmental factors external to the article itself that is the object of temperature monitoring. Another aspect or embodiment of the present disclosure (which may be practiced either separately or in combination with a shielding structure <NUM>) is a thermally conductive or absorbent structure that enhances the thermal coupling between the temperature sensor and the article to which the RFID device is secured. <FIG> and <FIG> show examples of such a thermally conductive or absorbent structure, which is positioned between at least a portion of the RFID chip <NUM> and the article to which the RFID device is secured.

In the example of <FIG>, the RFID device <NUM> includes both a shielding structure <NUM> positioned above or outwardly of the RFID chip <NUM> and a thermally conductive or absorbent structure <NUM> positioned below or inwardly of the RFID chip <NUM> (and preferably in direct contact with both the RFID chip <NUM> and the article to which the RFID device <NUM> is secured). It should be understood that these two structures <NUM> and <NUM> may be separately incorporated into an RFID device, though providing both may be advantageous for improved shielding and/or a combination of shielding and enhanced thermal coupling between the temperature sensor and the article to which the RFID device is secured.

The thermally conductive or absorbent structure <NUM> may be variously configured. In one example, at least a portion of the thermally conductive or absorbent structure <NUM> has an infrared-absorbing color, such as black. The thermally conductive or absorbent structure <NUM> may include an adhesive comprising particles having a greater thermal conductivity than the remainder of the adhesive, such as metallic particles and/or certain ceramic particles to increase the thermal coupling between the RFID chip <NUM> and the article to which the RFID device <NUM> is secured. The thermally conductive or absorbent structure <NUM> may also (or additionally) have a thermal mass selected for enhanced tracking of the temperature of the article to which the RFID device <NUM> is secured. For example, a thermal mass that tends to average the internal temperature of the article may be selected, such that transient temperature fluctuations are smoothed out. As the RFID device <NUM> only reports temperature when read, this may result in a more reliable thermal history.

<FIG> illustrates an example having a differently configured thermally conductive or absorbent structure. In the example of <FIG>, a portion of the antenna <NUM> acts as a thermally conductive or absorbent structure, preferably being in direct contact with at least a portion of the RFID chip <NUM> and configured to be in direct contact with the article to which the RFID device <NUM> is secured. As a metallic material with a relatively large area, the antenna <NUM> is a relatively good thermal conductor, such that the temperature of the article to which the RFID device <NUM> is secured is readily transferred to the temperature sensor. For example, increased efficiencies in thermally coupling the article (e.g. a food article) can be achieved by antenna structures having an especially large area, such as through the use of an antenna of a sloop type of structure. Such efficiencies include enhancing the transmission of a changing heat condition or temperature of the article to the RFID chip <NUM> and its temperature sensor. In contrast, in an RFID device omitting a thermally conductive or absorbent structure, the RFID chip may be separated from the article by a pressure-sensitive adhesive (PSA) or other securement materials that are poor thermal conductors compared to the metallic material of an antenna.

In the example of <FIG>, the antenna <NUM> includes a conductive loop generally designated at <NUM>, with a portion of the conductive loop <NUM> serving as the thermally conductive or absorbent structure. The conductive loop <NUM> may be variously configured, but in the illustrated example, the conductive loop <NUM> extends between the first conductor <NUM> and the second conductor <NUM> and is at least partially formed of a metallic material, such as an aluminum foil. The illustrated conductive loop <NUM> includes a bridge <NUM> spaced away from the RFID chip <NUM> and both of the first and second conductors <NUM> and <NUM>. A first leg <NUM> of the conductive loop <NUM> extends between the first conductor <NUM> and the bridge <NUM>, while a second leg <NUM> of the conductive loop <NUM> extends between the second conductor <NUM> and the bridge <NUM>. An extension <NUM> of the conductive loop <NUM> extends between the bridge <NUM> and the RFID chip <NUM>, with a portion of the extension <NUM> preferably being in direct contact with the RFID chip <NUM> and with the article to which the RFID device <NUM> is secured and/or to be monitored.

In the illustrated example, the extension <NUM> is associated with a midsection of the bridge <NUM>, while the first and second legs <NUM> and <NUM> are associated with first and second ends of the bridge <NUM>, respectively. It should be understood that the illustrated configuration of the conductive loop <NUM> shown in <FIG> is merely exemplary of this concept and that the conductive loop may be differently configured from that specifically designated at <NUM> in <FIG>.

<FIG> shows a temperature-sensing RFID device <NUM> according to the claimed invention. In the embodiment of <FIG>, the antenna <NUM> is not monolithically formed or configured as a singular structure, but rather is composed of a first or minor portion <NUM> and a separate second or major portion <NUM>. The minor portion <NUM> is physically connected to the RFID chip <NUM>, while the major portion <NUM> is physically separated from the minor portion <NUM> of the antenna <NUM> and from the RFID chip <NUM> by a gap <NUM>. Due to the major portion <NUM> of the antenna <NUM> being separated from the minor portion <NUM> of the antenna <NUM> and from the RFID chip <NUM>, it is coupled to the RFID chip <NUM> at RF frequencies (e.g., <NUM>) by either magnetic fields, electric fields, or both.

In the illustrated embodiment, the minor portion <NUM> of the antenna <NUM> comprises a pair of similarly shaped foil elements <NUM> (connected to the RFID chip <NUM> by pads, for example) extending in opposite directions from the RFID chip <NUM>, with the major portion <NUM> of the antenna <NUM> also comprising a pair of similarly shaped foil elements <NUM>. Each foil element <NUM> of the major portion <NUM> of the antenna <NUM> is generally aligned with a corresponding foil element <NUM> of the minor portion <NUM> of the antenna <NUM>, but separated from the associated foil element <NUM> of the minor portion <NUM> by the gap <NUM> (across which the major portion <NUM> of the antenna <NUM> is coupled to the RFID chip <NUM> by either magnetic fields, electric fields, or both). It should be understood that the embodiment of <FIG> is merely exemplary and that the antenna <NUM> may be differently configured, such as with the individual foil elements <NUM>, <NUM> being differently shaped and/or positioned and/or for either or each portion <NUM>, <NUM> of the antenna <NUM> being defined by a different number of foil elements.

Regardless of the particular configuration of the minor and major portions <NUM> and <NUM> of the antenna <NUM>, the gap(s) <NUM> between the minor and major portions <NUM> and <NUM> serve to reduce the amount of heat transfer from the antenna <NUM> to the RFID chip <NUM>. As shown in <FIG>, the major portion <NUM> of the antenna <NUM> is significantly larger than the minor portion <NUM> of the antenna <NUM>. The relatively large major portion <NUM> of the antenna <NUM> will have a tendency to pick up unwanted thermal energy, which would be transferred to the RFID chip <NUM> (thereby affecting the performance of a temperature sensor of the RFID chip <NUM>) if the major portion <NUM> were physically coupled to the RFID chip <NUM>. However, reducing the size of the antenna <NUM> (to reduce the amount of unwanted thermal energy picked up by the antenna <NUM>) may be impracticable due to a reduction in size also hampering the performance of the antenna <NUM>. By providing a gap <NUM> between the minor portion <NUM> of the antenna <NUM> (which will transfer less heat to the RFID chip <NUM> due to being relatively small) and the major portion <NUM>, the major portion <NUM> may remain sufficiently large to ensure proper operation of the antenna <NUM> without any unwanted thermal energy picked up by the major portion <NUM> being transferred to the RFID chip <NUM> (which is prevented by the presence of the gap(s) <NUM>).

<FIG> shows an RFID device <NUM> that is a variation of the RFID device <NUM> of <FIG>. In the embodiment of <FIG>, the RFID device <NUM> includes a reactive strap <NUM>, which is comprised of an RFID chip <NUM> connected to a conductive ring or loop of conductor <NUM>. The reactive strap <NUM> may include thermal insulators, conductors, or a combination of both in order to control its coupling to a sensed material. In addition to the reactive strap <NUM>, the RFID device <NUM> of <FIG> includes an antenna component <NUM> that is separated from the reactive strap <NUM> by a thermally isolating gap <NUM>, with the antenna component <NUM> being coupled to the RFID chip <NUM> across the gap <NUM> by a magnetic field.

The RFID device <NUM> of <FIG> may be understood as being a variation of the RFID device <NUM> of <FIG>, with the conductive ring or loop of conductor <NUM> corresponding to the first or minor portion <NUM> of the antenna <NUM> of <FIG> and the antenna component <NUM> corresponding to the second or major portion <NUM> of the antenna <NUM> of <FIG>. As in the embodiment of <FIG>, the antenna component/antenna major portion <NUM> is relatively large to enhance operation of the RFID device <NUM>, while the gap <NUM> serves to thermally isolate the antenna component/antenna major portion <NUM> from the conductive ring or loop of conductor/antenna minor portion <NUM> and from the RFID chip <NUM>, thereby preventing unwanted thermal energy picked up by the antenna component/antenna major portion <NUM> from being transferred to the RFID chip <NUM>.

<FIG> illustrates another variation of the RFID device <NUM> of <FIG>. As in the embodiment of <FIG>, the RFID device <NUM> of <FIG> includes an RFID chip <NUM> directly connected to a first portion <NUM> of an antenna <NUM>, while being separated from a second portion <NUM> of the antenna <NUM> by a gap <NUM> (which also separates the two portions <NUM> and <NUM> of the antenna <NUM>). Unlike the embodiment of <FIG>, the first portion <NUM> of the antenna <NUM> is not configured to have an especially small size (to minimize any thermal connection to the RFID chip <NUM>), but rather has a size and shape that are selected in order to provide a desired thermal connection between the associated RFID chip <NUM> and an article to which the RFID device <NUM> is to be secured for sensing the temperature of the article. Also unlike the embodiment of <FIG>, the first portion <NUM> of the antenna <NUM> is shown in <FIG> as being comprised of a pair of foil elements <NUM> and <NUM> that are differently configured. One of the foil elements <NUM> is illustrated as being sized and shaped like a foil element <NUM> of the first portion <NUM> of the antenna <NUM> of <FIG>, while the other foil element <NUM> is illustrated as being significantly larger (on the order of the size of one of the foil elements <NUM> of the major portion <NUM> of the antenna <NUM> of <FIG>). As the larger foil element <NUM> will be more greatly affected by temperature changes than the smaller foil element <NUM>, it will be understood that the larger foil element <NUM> plays a greater role in providing the RFID chip <NUM> with a desired thermal connection.

As in the embodiment of <FIG>, the second portion <NUM> of the antenna <NUM> is coupled to the first portion <NUM> across the gap <NUM> (e.g., by an electric field), with the gap <NUM> thermally isolating the second portion <NUM> from the RFID chip <NUM> and from the first portion <NUM> of the antenna <NUM> in order to control the nature of thermal coupling to the RFID chip <NUM>. In the embodiments of <FIG> and <FIG>, the various portions of the antennas are configured to provide each gap <NUM> with a generally uniform or constant width, but it should be understood that the portions of the antennas may be differently configured to provide one or more gaps <NUM> with a non-uniform or varying width, as in the embodiment of <FIG>.

<FIG> illustrates another RFID device <NUM> employing the principles described above with respect to the embodiment of <FIG>. In the embodiment of <FIG>, the RFID device <NUM> includes a ground plane <NUM> formed of a conductive material and having a first surface (the bottom surface in the orientation of <FIG>) configured to be placed into contact with a surface or article. A non-conductive spacer <NUM> is secured to the surface of the ground plane <NUM> opposite the first surface (which opposing surface is the upper surface of the ground plane <NUM> in the orientation of <FIG>). In one embodiment, the non-conductive spacer <NUM> is formed of a foam material, but other non-conductive materials may instead be employed.

A first antenna portion <NUM> (illustrated as a pair of foil elements <NUM> and <NUM>) is secured to the surface of the non-conductive spacer <NUM> opposite the ground plane <NUM> (which opposing surface is the upper surface of the non-conductive spacer <NUM> in the orientation of <FIG>), with the first antenna portion <NUM> being connected and coupled to an RFID chip <NUM> associated with the same surface of the non-conductive spacer <NUM>. A second antenna portion <NUM> is mounted to the same surface of the non-conductive spacer <NUM> as the RFID chip <NUM>. As in the embodiments of <FIG>, the second antenna portion <NUM> is separated from the RFID chip <NUM> and from the first antenna portion <NUM> by a thermally isolating gap <NUM>, with the second antenna portion <NUM> being coupled (via electrical field, magnetic field, or both) to the RFID chip <NUM>, while being thermally isolated therefrom. Optionally, the RFID chip <NUM> may be shielded against heat and light, as described above, for example.

The first antenna portion <NUM> is thermally coupled to the ground plane <NUM> by a conductor <NUM>. By thermally coupling the ground plane <NUM> to the first antenna portion <NUM>, the temperature of the ground plane <NUM> (and, hence, of the article or surface to which the ground plane <NUM> is secured) will be transferred to the first antenna portion <NUM> for detection by the temperature sensor of the RFID chip <NUM>. The conductor <NUM> may be integrally formed with one or both of the first antenna portion <NUM> and the ground plane <NUM> or provided as a separate component. In the illustrated embodiment, the conductor <NUM> extends along or wraps around an edge of the non-conductive spacer <NUM> (being secured by a crimp or the like, for example), but it should be understood that it may associate the ground plane <NUM> and the first antenna portion <NUM> in some other way (e.g., by passing through the non-conductive spacer <NUM>, rather than being wrapped around it).

Claim 1:
A temperature-sensing RFID device (<NUM>, <NUM>, <NUM>, <NUM>), comprising:
an RFID chip (<NUM>) including a temperature sensor;
an antenna (<NUM>, <NUM>) adapted to receive energy from an RF field and produce a signal and including
a first portion (<NUM>, <NUM>, <NUM>) directly coupled to the RFID chip (<NUM>), and
a second portion (<NUM>, <NUM>, <NUM>) separated from the RFID chip (<NUM>) and from the first portion (<NUM>, <NUM>) of the antenna (<NUM>) by a thermally isolating gap (<NUM>) and configured to be coupled to the RFID chip (<NUM>) by a magnetic field, an electric field, or both a magnetic field and an electric field.