Abstract:
According to one exemplary embodiment, an RFID device is disclosed. The RFID device includes a substrate, an antenna structure having a first sheet of electrically conductive material including two parts and an elongated slot extending therebetween, a wireless communications device coupled to the substrate, and an environmentally-responsive material disposed within a portion of the elongated slot.

Description:
FIELD OF THE INVENTION 
     The field of the invention relates to the use of environmentally sensitive materials and conductive antennas for radio frequency identification based sensing applications and constructions related thereto. 
     BACKGROUND OF THE INVENTION 
     The use of radio frequency identification (RFID) to identify one of a plurality of items is well known. Typical RFID tags or integrated circuits include a microprocessor, also known as a microchip, electrically connected to an antenna. Alternatively, the microchip is first attached to a pad having electrical leads that provides a larger attachment of “landing” area. This is typically referred to as a “strap” or “interposer.” The strap is then attached to the antenna. 
     The microprocessor stores data, which can include identifying data unique to a specific item, which is transmitted to an external receiver for reading by an operator and processing of the item. RFID tags can be attached to items for inventory control, shipment control, and the like. RFID tags are particularly useful in identifying, tracking and controlling items such as packages, pallets, and other product containers. The location of each item can be tracked and information identifying the owner of the item or specific handling requirements, can be encoded into the RFID and later read by a scanning device capable of decoding and displaying the information. 
     Accordingly, RFID tags can be attached to items entering or within a supply chain and the identifying information received can be processed for various reasons in a variety of manners. RFID tags are particularly useful in identifying, tracking and controlling items such as pallets, packages and individual product containers. In many instances, it is desirable to monitor and obtain information regarding the environmental conditions to which the items are exposed. For example, certain items may be sensitive to fluctuations in temperature, humidity, pressure, or other physical parameters, and certain items may be sensitive to the presence or absence of chemical or biological materials. As with many products contained in individual containers within supply chains, obtaining environmental conditions information at the item-level is beneficial within supply chains where the quality, safety, lifespan, or other characteristics of the items may be affected by environmental conditions. 
     SUMMARY OF THE INVENTION 
     The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention. 
     According to one exemplary embodiment, an RFID device is disclosed. The RFID device can include a substrate, an antenna structure having a first sheet of electrically conductive material including two parts and an elongated slot extending therebetween, a wireless communications device coupled to the substrate, and an environmentally-responsive material disposed within a portion of the elongated slot. 
     According to another exemplary embodiment, an antenna structure is disclosed. The antenna structure can include a sheet of electrically conductive material having a first part and a second part, and the first and second parts may be coupled together reactively, conductively or through a combination of both reactive and conductive coupling such that an operating parameter of the antenna structure varies in relation to an environmental condition. 
     In another exemplary embodiment, an RFID device is described. The RFID device can include a substrate, an antenna structure having a sheet of electrically conductive material having a first part and a second part, the two parts being capacitively coupled together such that an operating parameter of the antenna structure varies in relation to an environmental condition and a wireless communications device coupled to the antenna structure. 
     Yet another exemplary embodiment can describe a method of forming an RFID device. The method of forming an RFID device can include steps for depositing a first electrically conductive material on a substrate; defining an elongated slot in the first electrically conductive material; depositing an environmentally responsive material at a location along the elongated slot; and coupling a wireless communications device to the antenna structure. 
     Another exemplary embodiment describes a method of detecting an environmental condition, which can include wirelessly communicating with an RFID device having an antenna structure and varying an operating parameter of the antenna structure in relation to the environmental condition. 
     Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description of the various embodiments and specific examples, while indicating preferred and other embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by referring to the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings, of which: 
         FIG. 1   a  is an oblique view of an exemplary embodiment of an RFID device; 
         FIG. 1   b  is a plan view of an exemplary embodiment of an RFID device; 
         FIG. 1   c  is a cutaway view of an exemplary embodiment of an RFID device; 
         FIG. 2  is a plan view of another exemplary embodiment of an RFID device; 
         FIG. 3   a  is a plan view of another exemplary embodiment of an RFID device; and 
         FIG. 3   b  is a cutaway view of another exemplary embodiment of an RFID device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatuses and methods disclosed in this document are described in detail by way of examples and with reference to the figures. Unless otherwise specified, like numbers in the figures indicate references to the same, similar, or corresponding elements throughout the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatuses, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific shapes, materials, techniques, arrangements, etc. are either related to a specific example presented or are merely a general description of such a shape, material, technique, arrangement, etc. Identifications of specific details or examples are not intended to be, and should not be, construed as mandatory or limiting unless specifically designated as such. Selected examples of apparatuses and methods are hereinafter disclosed and described in detail with reference made to FIGURES. 
     As used herein, the word “exemplary” means “serving as an example, instance or illustration.” The embodiments described herein are not limiting, but rather are exemplary only. It should be understood that the described embodiment are not necessarily to be construed as preferred or advantageous over other embodiments. Moreover, the terms “embodiments of the invention”, “embodiments” or “invention” do not require that all embodiments of the invention include the discussed feature, advantage or mode of operation. 
     Generally referring to  FIGS. 1   a  through  3   b , a RFID device including an antenna structure and at least one environmentally-sensitive or responsive material is disclosed. The at least one environmentally-sensitive material may be configured to be responsive to an ambient environmental condition such as a physical parameter or to the presence or absence of a chemical or biological material. The antenna structure may be locally modified or otherwise enhanced in order to achieve an optimized interaction between the environmentally-sensitive material, and the antenna structure. To that end, the RFID device may also include a secondary conductive element. 
     Turning to  FIGS. 1   a  through  1   c , an exemplary embodiment of an RFID device  100  is shown. The RFID device  100  can have a variety of components. The RFID device  100  may include a substrate  102 , and an antenna structure  104  disposed thereon. Substrate  102  can be any material, for example paper, coated paper, polyethylene terephthalate (PET), laminations of film and paper or any other suitable substrate that can be desired. Antenna structure  104  can be any of a variety of materials, for example aluminum, copper, silver or another thin, conductive material, for example etched or hot-stamped metal foil. The foregoing RFID device  100  can be provided as part of a preformed RFID inlay. Exemplary RFID inlays for use in accordance with the present invention are available from Avery Dennison RFID Company of Clinton, S.C. 
     The antenna structure  104  may alternately be a conductive ink, consisting of one or more types of conductive particles suspended in a suitable matrix, an inorganic semiconductor material such as doped amorphous silicon, an organic conductor such as polyaniline, or a combination of multiple layers of any of the above conductors to give the desired electrical and mechanical characteristics. 
     Antenna structure  104  may be coupled to a wireless communications device, such as an RFID chip  108  that may be part of an RFID strap or interposer  106 . Strap or interposer  106  may further include conductive leads  110 ,  112  to facilitate coupling between antenna structure  104  and RFID chip  108 . In some embodiments, strap or interposer  106  may also include a substrate to facilitate supporting RFID chip  108  and conductive leads  110 . 
     Antenna structure  104  may be a continuous, unitary layer of conductive material, and may have an elongated slot  114  defined therein. Elongated slot  114  may partition antenna structure  104  such that on either side of elongated slot  114  may be portions  116 ,  118 . Each of portions  116 ,  118  may be coupled to each of the conductive leads  110 ,  112 , respectively. The conductive leads  110 ,  112  may in turn be coupled to contact points or areas disposed on RFID chip  108 . A strap or interposer  106  may further be disposed proximate to the open end of elongated slot  114  of the antenna structure such that it bridges the elongated slot  114  and facilitates coupling between portions  116 ,  118  via strap or interposer  106 . A current passing through antenna structure  104  may pass from one contact point on RFID chip  108 , through conductive lead  110 , portion  116 , portion  118 , conductive lead  112 , and to another contact point on the RFID chip  108 . Furthermore, portions  116  and  118  may be capacitively or inductively coupled via elongated slot  114 . Coupling between antenna structure  114  and strap or interposer  106  may be a direct, conductive coupling or may be an indirect, reactive coupling, such as, for example, capacitive or inductive coupling. The antenna structure  104  may therefore act as a hybrid slot-loop antenna, such as that described in U.S. Pat. No. 7,298,343, the contents of which are hereby incorporated by reference in their entirety. 
     The characteristics that may be exhibited by hybrid slot-loop antennas include, but are not limited to, increased readability characteristics in substantially any direction within or parallel to the plane of antenna structure  104  or RFID device  100  as a whole, as well as improved readability performance at short ranges in any direction, such as above or below the plane of antenna structure  104  or RFID device  100  as a whole. Furthermore, antenna structure  104  may be tuned as desired via any variation or combination of length, width, positioning and shape of elongated slot  114 . An additional characteristic of hybrid slot-loop antennas is that the sensitivity of antenna structure  104  to the presence of a dielectric material varies along the length of elongated slot  106 . Thus, by placing a dielectric material across a desired portion of elongated slot  106 , the gain, near field performance and far field performance of antenna structure  104  may be optimized, and such optimization effects may vary in relation to the positioning of the dielectric material along the length of elongated slot  106 . 
     Still referring to  FIGS. 1   a  through  1   c , RFID device  100  may further include an environmentally-responsive or sensitive material  120 . In some embodiments, environmentally-responsive material may be a coating. Environmentally-responsive material  120  may have dielectric, magnetic or conductive properties that vary in response to environmental parameters, or to the presence or absence of a chemical or biological material. For example, environmentally-responsive material  120  may be a polymer-based material having polar or dipole characteristics. As an exemplary and non-limiting list, environmentally-responsive material  120  may have dielectric, magnetic or conductive properties that vary in response to temperature, humidity, pressure, or other environmental factors; environmentally-responsive material  120  may also have dielectric properties that vary in response to the concentration of particular compounds in the ambient environment. 
     Examples of some environmentally sensitive materials are described below. The sensing material may be selected to detect a particular environmental condition. For example, in order to detect a chemical or biological entity, a material whose complex dielectric constant and conductivity or other electrical parameter changes in response to exposure (e.g., absorption) of the chemical or biological entity may be selected. Similarly, to detect exposure to radiation a material whose electrical performance degrades in response to alpha, beta, gamma, X-ray or ultraviolet radiation may be used. As discussed, the sensing material may comprise one or more layers and in which only one layer, any combination of layers, or all layers have an electrical parameter that changes in response to the same or different environmental condition. In addition, the pattern of the sensing material may be of any suitable pattern to provide the desired coupling. 
     In one embodiment material  120  is a foam or elastic material that has conductive particles, such as carbon, embedded into its structure. It is known that physical deformation of such materials, by varying the separation and hence the probability of contact between adjacent particles, changes the conductivity of the material. For example, a material of thickness 4 mm may have a resistivity of 1000 ohms per square but, when compressed to 2 mm thickness, this may drop to 200 ohms per square. 
     Changing the physical dimensions of the foam, and hence altering the resistivity, can be achieved in a number of ways and the following represent a non-exhaustive listing of examples;
         physical compression, for example in response to an object being placed on top of element  120  or forcing the element  120  on to itself;   bending, for example in response to a lid of a container being opened, or, when coupled to a material that has a defined deformation with temperature;   stretching, due to an object being hung on a tether or fastener formed partially of the material or exerting opposing forces on an object to cause the object to elongate and place stresses on the internal components;   compression or stretching caused by an external environmental parameter such as air pressure (for a foam filled with a gas when the pressure exceeds the internal pressure of the foam cells they will compress, when the pressure is below the internal pressure they will expand).       

     Another example of a chemically responsive material is the organic polymer, polyaniline. This materials conductivity is strongly related to its oxidation state, which, in turn, via an appropriate chemical environment, may be made to respond to factors such as the presence of a gas, liquid and parameters such as pH. A range of alternate organic conductors, such as polythiophene, polyacetylene, polypyrrole and PEDOT:PSS (Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)) exist and have known changes in electrical and dielectric properties in response to a range of physical, chemical and biological states. 
     The environmental response of these materials may be include reversible parameters, where, for example, in the case of a conductive foam to which pressure is applied, the resistivity return to close to its original value when the pressure is removed or irreversible responses, such as, in the case of the conductive foam, the pressure has reached a point that the cells of the foam are ruptured and the resistivity will not return to its original state when pressure is removed. An additional form of response, important for sensing parameters such as temperature of exposure to chemical agents, is where the sensing material integrates exposure over a defined time. For example, in the case of temperature, the material parameter maybe the integral of the materials response over a period of days, and may emulate the response of, for example, the growth of bacteria in a product. Environmentally-responsive material  120  may be disposed across and/or within elongated slot  114 , as shown in  FIGS. 1   a  and  1   c . Suitable methods of applying the responsive material  120  would include printing, laminating a film, vapor deposition, coating, spreading, spraying, sputtering, or, in the case of a discrete physical element by such methods as pick and place or pattern application with a suitable adhesive or by using strap attach technology. The presence of environmentally responsive or sensitive material  120  within elongated slot  114  may alter the level of interaction between portions  116 ,  118  across elongated slot  114 , and, therefore, may alter the gain, far field performance and near field performance of RFID tag  100 . Furthermore, it should be appreciated that the interaction between portions  116 ,  118  can vary along the length of slot  114 . Therefore, as an illustrative example and as shown in  FIG. 1   b , the effect of environmentally responsive or sensitive material  120  disposed at point A along slot  114  may not be equivalent to the effect of material  120  disposed at point B along slot  114 . Thus, the interactions between antenna structure  104  and environmentally responsive or sensitive material  120 , and, consequently, the operating characteristics of RFID device  100  may be optimized by selectively choosing the position of material  120  along slot  114  or alternatively modified to react in a particular manner depending on the position of the material  120 . 
     In operation, the dielectric, magnetic or conductive properties of environmentally responsive or sensitive material  120  may vary in response to a particular ambient environmental factor, as described above. Such a variation may in turn induce a variation in the interaction between portions  116 ,  118  at the location of material  120 , and may likewise induce a variation in the interaction between environmentally responsive or sensitive material  120  and antenna structure  104 . Thus, operating properties of antenna structure  104  such as gain, near field performance and far field performance may vary in real time in response to the particular environmental or sensing factor. In addition, changes in the antenna complex impedance will interact with the complex impedance of the RFID device  110  to later the near and far field performance and characteristics. 
     Turning to  FIG. 2 , another exemplary embodiment of RFID device  100  may include an interdigitated region  202 . Interdigitated region  202  may include a plurality of fingers  204 ,  206  jutting out from portions  116 ,  118 , respectively, into elongated slot  114 . Fingers  204  of portion  116  may interdigitate with corresponding fingers  206  of portion  118 , thereby defining a substantially serpentine gap  208  therebetween. Capacitive or inductive coupling may occur across gap  208 , thereby indirectly coupling portions  116 ,  118 . Environmentally responsive or sensitive material  120  may be disposed across interdigitated region  202 , within gap  208 , and within elongated slot  114  proximate to interdigitated region  202 . 
     Turning to  FIGS. 3   a  through  3   b , in another exemplary embodiment the RFID device  100  may include an additional conductive layer  302 . The conductive layer  302  can be any of a variety of materials, for example aluminum, copper, silver or another thin, conductive material, for example etched or hot-stamped metal foil. Conductive layer  302  may be disposed on top of environmentally responsive material  120 , which may in turn be disposed at a desired location across and within elongated slot  114 . Conductive layer  302  may therefore be capacitively coupled to portions  116 ,  118  of antenna structure  104 . Consequently, two capacitive couplings, in an effective serial arrangement, may effectively be created at the desired location across environmentally responsive material  120 . 
     During the manufacture of RFID tag  100 , in some embodiments, environmentally-responsive layer  120  may be applied to antenna structure via methods such as printing, vacuum deposition, or other methods known in the art. In such embodiments, the environmentally responsive layer  120  may be applied at a desired position or location across and within elongated slot  114 . A conductive layer  302  having similar or substantially similar dimensions to the environmentally responsive layer  120  may then be applied to the exposed surface of layer  120  with its position or location registered to layer  120 . In other embodiments, the environmentally responsive or sensitive layer  120  may be applied as a coating covering the antenna structure  104  substantially in its entirety. In such embodiments, an additional conductive layer  302  (or layers) may be applied to the exposed surface of environmentally responsive or sensitive layer  120  (or layers when provided) only at the desired position or location across the elongated slot  114 . The desired variation in the operating characteristics of antenna portion  104  may thus be achieved by positioning additional conductive layer  302  or layers at a corresponding desired location or position. 
     The foregoing description and accompanying figures illustrate the principles, preferred embodiments and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art. 
     Therefore, the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.