Abstract:
In the embodiments described herein, a RFID enabled license plate is constructed by using the license plate, or a retro-reflective layer formed thereon as part of the resonator configured to transmit signals generated by and RFID chip integrated with the license plate. Such an RFID enabled license plate can include a metal license plate with a slot formed in the metal license plate, and a RFID tag module positioned in the slot. The RFID tag module can include a chip and a loop, and the loop can be coupled with the metal license plate, e.g., via inductive or conductive coupling. In this manner, the metal license plate can be configured to act as a resonator providing increased performance.

Description:
RELATED APPLICATIONS INFORMATION 
       [0001]    This application claims the benefit under 35 U.S.C. 120 to U.S. patent application Ser. No. 11/962,047, filed Dec. 20, 2007, and entitled “Method and Apparatus for RFID Enabled Metal License Plates”, which in turn claims the benefit under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 60/871,273, filed Dec. 21, 2006, and entitled “Method and Apparatus for RFID Enabled Metal License Plates”, all of which are incorporated herein by reference in their entirety as if set forth in full. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The embodiments described herein relate generally to electronic vehicle registration and tracking systems, and more particularly to the use of Radio Frequency Identification (RFID) in such systems. 
         [0004]    2. Background of the Invention 
         [0005]    RFID technology has long been used for electronic vehicle tolling applications. In such applications, an RFID reader or interrogator is position over or near a road way at a point where a toll is to be collected. An RFID tag is then place in each vehicle that includes an identifier by which the vehicle can be recognized, e.g., the vehicle&#39;s license plate number. The interrogator then uses RF signals to interrogate the tag and obtain the identifier so that the toll can be applied to the correct vehicle, or account. 
         [0006]    Generally, the tag to interrogator communication is achieved through a form of modulation known as backscatter modulation. In a backscatter modulation system, the tag does not generate its own RF carrier signal when transmitting information to the interrogator. Rather, the interrogator generates an RF carrier and modulates the carrier with data intended for the tag, e.g., a request for the tags identifier information. The tag receives the modulated signal decides the data and then performs actions in accordance therewith e.g., accesses the memory and obtains the requested identifier information. The interrogator continues to transmit the RF carrier, now with no data on it. The tag receives this un-modulated carrier and reflects it back to the interrogator. This is called backscatter. In order to send data back to the interrogator, e.g., identifier, the tag modulates the reflected, or backscatter signal with the data. 
         [0007]    For example, the tag will alternately backscatter and not backscatter the RF carrier signal for a certain period of time in order to transmit a digital “0” an “1” respectively. Thus, the tag modulates the backscatter signal by reflecting or not reflecting the signal based on the data, i.e., “1s” and “0s,” to be sent. The interrogator receives the modulated backscatter signal and decodes the information received thereon. 
         [0008]    Early on, such tags were active device, meaning they possessed their own power source, such as a battery. An active tag was necessary, for example, in order to generate enough power in the reflected signal to transmit information over extended distances. But more recently, passive tag technology has become more viable. A passive tag does not include a battery or power source of its own. Rather, energy in the RF signals received from the interrogator is used to power up the tag. For example, the received RF signal can be rectified and used to charge up a capacitor that is then used to power the tag. 
         [0009]    As antenna and integrated circuit technology has evolved, larger and larger distances can be achieved with passive tags of smaller and smaller dimensions. Accordingly, small, thin, light weight tags can be used in a wide variety of applications. Often these tags are referred to as sticker tags or RFID labels, because of their dimensions and the fact that they can be manufactured to include an adhesive layer so that they can be applied to the outside of containers, the surface of documents, inventory, etc. In other words the tags can be applied like a label or sticker. 
         [0010]    The emergence of passive, sticker tag technology has also greatly reduced the cost of implementing an RFID system. As a result, new applications, such as Electronic Vehicle Registration (EVR) using RFID, have emerged. Currently, e.g., in the United States, a vehicle owner registers their vehicle with the State government and pays a fee. The owner is then provider a sticker, which is applied to the vehicle license plate, to evidence the valid registration of the vehicle; however, these stickers can easily be counterfeited or stolen, i.e., removed and applied to another vehicle. Such activity is difficult to detect, because the only way to determine that a registration sticker does not belong on a certain vehicle is to access a database and check the corresponding information. 
         [0011]    For example, in the United States, an estimated five to ten percent of motorists fail to legally register their vehicles, resulting in lost annual state revenues of between $720 million and $1.44 billion. Outside of the United States, some government agencies report the problem at 30-40% of the vehicles. 
         [0012]    Deploying an Electronic Vehicle Registration system can help Motor Vehicle Administrators achieve increases in vehicle compliance and associated revenues by eliminating the need to rely on inefficient, manual, visual-based compliance monitoring techniques. EVR uses RFID technology to electronically identify vehicles and validate identity, status, and authenticity of vehicle data through the use of interrogators and tags that include data written into the tag memory that matches the vehicle registration data. Fixed, e.g., roadside, or handheld interrogators can then be used to read the data out when required. Thus, RFID technology can enable automated monitoring of vehicle compliance with all roadway usage regulations, e.g., vehicle registration, tolling, etc., through a single tag. 
         [0013]    There are two common ways of attaching a RFID tag to a vehicle, one is using an RFID label tag attached to the windshield of the vehicle. The tag can then be read by a roadside or handheld reader. A second method of attaching the tag to a vehicle is to embed the RFID tag into the license plate. This has the convenience an continuity of replicating the application of current registration stickers; however, such a solution can also suffer from reduced transmission, i.e., communication distance due to the effects the metal license plate has on the performance of the tag antenna. 
         [0014]    For example, as illustrate in  FIG. 1 , a RFID tag  100  consisting of a RFID chip  102  and an antenna  104  can be mounted on the vehicle license plate  110 . As mentioned, however, license plate  110  is usually made from metal. As a result, the tag information may not be readable due to the shielding effects of metal surrounding tag  100 . Moreover, if tag  100  is directly applied to the metal surface of license plate  110 , then tag antenna  104  can be shorted or severely detuned by the metal surface. As a result, tag  100  will not be read, or will only be readable at very short distance. 
         [0015]    A conventional approach to overcoming this issue is to leave some spacing  202  between tag  100  and metal license plate  110  as shown in  FIG. 2 . Such a solution has an added benefit in that metal license plate  110  can also serve as a back plane for tag antenna  104 . For example, as illustrated in  FIG. 3 , an RFID tag  100  can be housed within an non-metal enclosure  302 , e.g., formed from a low dielectric material that includes a spacer  304  such as an air gap or foam material. 
         [0016]    One problem with such a conventional solution is the increased dimension, i.e., thickness of the resulting license plate assembly. Accordingly, conventional approaches force a tradeoff between reduced performance, or increased size and dimensions, which can have a negative impact. 
       SUMMARY 
       [0017]    In the embodiments described herein, a RFID enabled license plate is constructed by using the license plate, or a retro-reflective layer formed thereon as part of the resonator configured to transmit signals generated by and RFID chip integrated with the license plate. 
         [0018]    For example, in one aspect, such an RFID enabled license plate can include a metal license plate with a slot formed in the metal license plate, and a RFID tag module positioned in the slot. The RFID tag module can include a chip and a loop, and the loop can be coupled with the metal license plate, e.g., via inductive or conductive coupling. In this manner, the metal license plate can be configured to act as a resonator providing increased performance. 
         [0019]    In another aspect, the RFID tag module can be positioned substantially within the slot such that the addition of the RFID tag module does not increase the thickness of the license plate. 
         [0020]    In still another aspect, the RFID enabled license plate can comprise a RFID tag module, positioned in the slot, which includes a chip and contacts. The contacts connected with the metal license plate, e.g., via a conductive paste or a solder connection. 
         [0021]    In still another aspect, the RFID enabled license plate can comprise a license plate and a retro-reflective layer formed over the license plate. A slot can then be formed in the retro-reflective layer, and a RFID tag module can be positioned in the slot. The RFID tag module can include a chip and a loop, and the loop coupled with the retro-reflective layer, e.g., via inductive or conductive coupling. 
         [0022]    In still another aspect, the RFID enabled license plate can include a retro-reflective layer formed over the license plate and a slot formed in the metal license plate. A RFID tag module can be positioned in the slot. The RFID tag module can comprise a chip and contacts, and the contacts connected with the metal license plate, e.g., via a conductive paste or a solder connection. 
         [0023]    These and other features, aspects, and embodiments of the invention are described below in the section entitled “Detailed Description.” 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Features, aspects, and embodiments of the inventions are described in conjunction with the attached drawings, in which: 
           [0025]      FIG. 1  is a diagram illustrating an exemplary license plate comprising an RFID module; 
           [0026]      FIG. 2  is a diagram illustrating a side view of the license plate of  FIG. 1 ; 
           [0027]      FIG. 3  is a diagram illustrating a RFID module that can be used in conjunction with the license plate of  FIGS. 1 and 2 ; 
           [0028]      FIGS. 4A and 4B  are diagrams illustrating an example RFID enabled license plate in accordance with one embodiment; 
           [0029]      FIGS. 5A and 5B  are diagrams illustrating methods for coupling an RFID module with the license plate of  FIGS. 4A and 4B ; 
           [0030]      FIGS. 6A-C  are diagrams illustrating an example RFID enabled license plate in accordance with another embodiment; 
           [0031]      FIGS. 7A-C  are diagrams illustrating example RFID enabled license plate in accordance with another embodiment; 
           [0032]      FIG. 8  is a diagram illustrating another example RFID enabled license plate in accordance with another embodiment; and 
           [0033]      FIG. 9  is a diagram illustrating another example RFID enabled license plate in accordance with another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The embodiments described below are directed to system and methods for a RFID enabled license plate in which a metal layer of the license plate is actually used to radiate backscattered energy generated by a RFID tag positioned within a slot created in the license plate. Accordingly, not only does the metal license plate not interfere with the operation of the tag, it actually assists. 
         [0035]    Certain embodiments described herein are directed to methods for creating an antenna structure directly on (1) a metal license plate, (2) a metalized retro-reflective foil covering a non-metal license plate, or (3) a metalized retro-reflective foil covering the metal license plate. Depending on the embodiment, the RFID chip can be directly connected to or electrically coupled, either capacitive or inductively, with the antenna structure. The antenna structure can be a single or multi-frequency resonant structure. 
         [0036]      FIG. 4 , comprising  FIGS. 4A and 4B , is a diagram illustrating an example license plate  400  comprising an RFID tag in accordance with one embodiment. As shown in  FIG. 4A , license plate  400  can comprise an open area, or slot  402 . For example, slot  402  can be cut into metal license plate  400 . Alternatively, slot  402  can be punched out of plate  400 . As shown in  FIG. 4B , a RFID tag module  406  comprising an enclosure around tag  404  can then be positioned within slot  402 . The dimensions of slot  402  and module  406  can be designed such that module  406  fits within slot  402  creating a substantially planar surface with the surface of metal license plate  400 . It should be noted that the top of module  406  is shown extending beyond the surface of license plate  400  in  FIG. 4B , creating a non-planar surface; however, this is purely for illustration. In practice, module  406  can be made extremely thin allowing for a substantially planar surface across all of plate  400 , including slot  402 , even when module  406  is installed therein. 
         [0037]    For example, module  406  can be similar to the module illustrated in  FIG. 3 . Thus, module  406  can include an enclosure if required. Module  406  can then be configured to include a feeding loop that can couple tag  404  with metal license plate  400 . In this manner, the entire license plate  400  can then serve as an effective radiator via inductive coupling through the feeding loop. 
         [0038]      FIGS. 5A and 5B  illustrate two example implementations of the embodiment illustrated in  FIG. 4 . In  FIG. 5A , module  406  comprises a chip  502  coupled with a feeding loop  504 . Slot  402  is then positioned such that feeding loop  504  will be inductively coupled with metal license plate  400 . In  FIG. 5B , slot  403  is positioned such that feeding loop  504  is capacitively coupled with metal license plate  400 . 
         [0039]    Further, in certain embodiments, the radiation gain can be enhanced by using the metallic car frame (not shown). For example, with a properly designed tag antenna and proper consideration of the spacing between the metallic car frame and license plate  400 , the metal car frame can be used as a good antenna reflector. 
         [0040]    In another embodiment, a structure very similar to Planar Inverted-F Antenna (PIFA) can be implemented by screwing the license plate directly to the metallic car frame as illustrated in  FIG. 6 . In  FIG. 6 , which comprises  FIGS. 6A-C , metallic screws serve as shorting posts  602  and metallic car frame  600  serves as a ground plane for the antenna of tag module  406 . 
         [0041]      FIG. 7 , comprising  FIGS. 7A ,  7 B, and  7 C, is a diagram illustrating an example of a license plate  700  configured to incorporate an RFID tag in accordance with another embodiment. As shown in  FIG. 7A , an area, or slot  702  is cut, or punched, etc., in license plate  700 . As shown in  FIG. 7B , a non-metal material  704  can then be inserted into slot  702  such that both the front and rear surfaces of license plate  700  are flat. Material  704  can be stuffed, extruded, etc., into slot  702 . As shown in  FIG. 7C , an RFID “strap” comprising a chip  708  with contacts  710  can then be positioned over slot  702  as illustrated. Contacts  710  can then be connected to or capacitively coupled with metal license plate  700 . Depending on the embodiment, strap  712  can be placed on either the front surface or the rear surface of the license plate. The entire license plate  700  then becomes a slot antenna coupled with the RFID chip, which is less sensitive to the metallic car frame in terms of tag antenna detuning effect. Contacts  710  can be soldered to plate  700 , adhered using a conductive paste, or both. 
         [0042]    It should also be noted that strap  712  can be made extremely thin, such that the surface of license plate  700  is substantially planar. 
         [0043]    In certain embodiments, the dimensions of slot  702  can be altered, or multiple slots included to create a dual or multiple resonance frequency slot antenna. In such configurations, the tag will respond to multiple frequency bands, such as the Ultra High frequency (UHF) band, e.g., 900 MHz, and the microwave band, e.g. 2.45 GHz. This can allow multiple application capability. For example, depending on the application, one frequency band can be preferred for its localization characteristics and another frequency band can be preferred for its long range read capabilities. More specifically, a higher frequency band, such as a 2.45 GHz band, can be used for write applications as its limited range helps insure only the tag of interest is written to, while a lower frequency band, such as a 900 MHz band, can be used for multi-tag read applications as its greater range allows many tags to be read over a large area. In other embodiments, multiple frequency bands can be needed due to regulatory requirements that can vary the authorized frequency band based on locations, e.g., country, city, etc., and by application. 
         [0044]      FIGS. 8 and 9  are diagrams illustrating example multi-frequency RFID license plates in accordance with two example embodiments. In  FIG. 8 , two slots  802  and  804  are formed in metal license plate  800 . A strap  806  is then positioned across slot  806  as illustrated. The two slots  802  and  804  are configured, with respect to dimensions, spacing, location, etc., such that the slot antenna formed from license plate  800 , slots  802  and  804  and strap  806  will resonate at the desired frequencies, e.g., the UHF and microwave bands. 
         [0045]    In  FIG. 9 , two slots  902  and  904  are formed in license plate  900 ; however, in this example, slots  902  and  904  are connected via slot  906 . A slot  910  then extends to the edge of plate  900 . Strap  908  is then positioned across slot  910  as illustrated. Again, slots  902 ,  904 ,  906 , and  910  are configured such that the resulting slot antenna resonates at the desired frequencies. 
         [0046]    The slots of  FIGS. 8 and 9  can be filled with non-metallic material as in the example of  FIG. 7  depending on the embodiment. Further, certain parasitic elements can be included, or changed to achieve the proper multi-frequency operation. It should also be noted that the embodiments of  FIGS. 4 and 5  can also be configured as multi-frequency resonant structures via the inclusion of further slots appropriately constructed so as to allow the structure to resonate at the desired frequencies. 
         [0047]    It will be understood that other slot dimensions, locations, spacing, interconnectedness, etc., are possible and will depend on the requirements of a particular implementation. Similarly, the position of the strap comprising the chip and connectors can vary as required by a particular implementation. Accordingly, the specific implementations illustrated herein should not be seen as limiting the embodiments disclosed to any particular configuration. 
         [0048]    It will also be understood that the impedance of the resulting antenna structure in the above embodiments will need to be matched to that of the chip. This can impact the slot dimensions, etc. It can also require additional circuit elements, i.e., the inclusion of a matching circuit. 
         [0049]    A retro-reflective film can be used to cover the front surface of the license plate. Such a film can make the license plate modification invisible from front view; and can also makes the license plate viewable in dark lighting. If the retro-reflective film contains metal materials, e.g., a metallized polymer film, then a selective metal removal process can be applied such that the film area covering the open area in the license plate is de-metallized. Such a de-metallization is described in detail in co-owned U.S. Pat. No. 7,034,688, as well as Co-owned patent application Ser. No. 10/485,863, each of which are incorporated herein by reference as if set forth in full. In other embodiments, the antenna structure can actually be formed on a retro-reflective layer that is then applied to a non-metallic, or metallic, license plate. 
         [0050]    While certain embodiments of the inventions have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the inventions should not be limited based on the described embodiments. Rather, the scope of the inventions described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.