Abstract:
An RFID device for tires utilizes a wireless antenna. The antenna is formed of conductive rubber having a slot formed therein. The conductive rubber antenna is encapsulated between a pair of non-conductive sheets. A third non-conductive member encircles the conductive rubber antenna and is itself sealed between the first and second sheets of non-conductive material. A microchip is positioned in the slot and conductively attached to the antenna on opposite sides of the slot.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of U.S. Provisional Patent Application No. 61/337,933 filed Feb. 12, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The use of radio frequency identification devices (RFID) in tires is gaining in popularity. See for example my issued U.S. Pat. No. 7,504,947. Other devices, including RFID devices, which may be incorporated on a surface of or within the structure of a tire for monitoring various functions relative to the tire include the following U.S. Pat. Nos. 5,562,787; 5,741,966; 6,062,072; 6,856,245; 6,897,770; 7,009,576; and 7,186,308. The disclosures contained in these patents are incorporated herein by reference. 
         [0003]    U.S. Pat. No. 7,009,576 discloses a tire having a radio frequency antenna embedded therein. Since the rubber in which the radio frequency antenna is embedded is in a mixture of rubber and the conductive dielectric material carbon black, the patent discloses the use of an insulating layer, which is attached to the antenna by an adhesive coating, to insulate the antenna from the conductive dielectric rubber. Although U.S. Pat. No. 7,009,576 does not specifically identify the material from which the antenna is manufactured, typically, the antenna will be a conductive metal wire or a thin sheet of metal foil such as copper as disclosed in U.S. Pat. No. 5,562,787 or 6,147,659. 
         [0004]    RFID devices for use in tires continues to be a goal in order to provide improved quality and traceability. However, the tire industry has been slow to adopt the RFID devices with their copper antennas. The installation foreign material in a tire is a concern. The ability to provide RFID devices in a tire with minimal component size is an important goal. 
       SUMMARY OF THE PRESENT INVENTION 
       [0005]    The RFID device of the present invention utilizes a wireless antenna of conductive rubber along with a computer chip and is embedded in the body of a tire or affixed to the inner surface of the tire. The antenna is formed of electrically conductive green rubber encapsulated in insulation formed by a pair of non-conducting green rubber sheets adhered together. The insulation preferably is a non-conducting green rubber but could be non-conducting rubber or other materials having properties suitable for integration within the rubber tire. Other materials which may be utilized for the insulation include an elastomer or rubber minus the carbon black which is the conductive component. The insulation isolates the antenna from the dielectric rubber of the tire and, thereby, prevents the conductive rubber from dissipating the energy being conducted by the antenna. 
         [0006]    The RFID device of the present invention utilizes a standard computer chip, preferably an EPC1 GEN2 RFID chip of less than one millimeter (1 mm)×one millimeter in size. The RFID chip is coupled with a conductive rubber dipole or slot antenna. Under one embodiment, conductive adhesives and/or other encapsulates maybe utilized to improve the interface between the chip mounting and the rubber antenna thus improving the performance. In this case, cured or vulcanized rubber rather than green rubber could be used for the antenna. If green rubber is used for the antenna, it is not necessary to use adhesive as the natural stickiness of the green rubber will cause it to adhere to the surface of the insulating layer engaged thereto. On the other hand, it is possible to use adhesive with an antenna of green rubber in order to provide a more effective seal. The sub-assembly of the rubber antenna and the computer chip is enclosed in a non-conductive rubber envelope or sheets. The current technology allows for the rubber antenna to be an integral component of the tire with no concerns of destroying the integrity of the tire. 
         [0007]    Preferably the RFID device of the present invention is produced in the uncured state. It is affixed to the inner or outer surface of the tire in the green state. It may also be embedded in the tires, between the plies. Following such affixing or embedding, it is vulcanized along with the rest of the tire. However, it could also be vulcanized and then affixed following vulcanization of the tire or assembled using vulcanized conductive rubber and then affixed to the tire. The installed RFID devices will allow improved quality, sorting of tires on conveyors and tracking of shipments. 
         [0008]    The prior art RFID devices for tires utilize a wire wound antenna. The wire wound antenna comes into direct contact with the rubber. The carbon black used in the tire rubber causes the rubber to be somewhat conductive. Unless properly insulated, the conductive characteristics of the tire rubber will de-tune the antenna of the RFID device which greatly reduces its effective range. 
         [0009]    The antenna of the RFID device of the present invention has a conductive rubber compound which has been developed for its conductivity to get into the range of 20 ohms to 400 ohms per inch of rubber. Resistances in the range of 40-100 ohms per inch are suitable for use as an antenna. The non-conductive rubber is utilized as an electrical insulator which isolates the antenna from the rubber of the tire. The encapsulation in the non-conductive rubber causes the antenna to stay in tune with the RFID microchip, which allows for the long range read characteristics. 
     
    
     
       IN THE DRAWINGS 
         [0010]      FIG. 1  is a sectional view of a tire showing an RFID device with the antenna of the present invention encapsulated therein or affixed to the interior sidewall. 
           [0011]      FIG. 2  is a plan view showing one form of RFID device with a microchip and antenna encapsulated in and between layers of insulation material. 
           [0012]      FIG. 3  is a sectional view along line  3 - 3  of  FIG. 2 . 
           [0013]      FIG. 4  is an exploded perspective view of the RFID device of the present invention utilizing the wireless antenna of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 1  there is shown a tire T having a crown  10  with external treads  12  and grooves  14 . In cross-section the tire T has the crown  10  extending radially outwardly along an arcuate path to a pair of oppositely disposed sidewalls  16  which define the maximum radial extent of the tire T. The sidewalls  16  curve inwardly from such maximum radial extent to a narrower area terminating at a pair of oppositely disposed beads  18 . As shown in  FIG. 1  there is provided an RFID device  20  of the present invention which is permanently embedded either in the crown  10  or in one of the sidewalls  16 . It may also be adhered to the inner surface of the tire in the area of the crown  10  or the sidewall  16 . 
         [0015]    Referring to  FIGS. 2 ,  3  and  4 , the RFID device includes a pair of insulation members  22  and an antenna  24  encapsulated therebetween. A RFID microchip  26  such as EPC1 GEN has tabs  28  attached to the antenna  24 . The antenna  24 , which may be one of a number of shapes, is shown as a rectangle having a length defined by long upper and lower (as viewed in  FIGS. 2 and 4 ) edges  24 A, short side edges  24 B and curved or arcuate corners  24 C. 
         [0016]    The antenna  24  has a slot  32  extending downwardly (as viewed in  FIGS. 2 and 4 ) from the upper edge  24 A which follows a path which provides suitable tuning characteristics for the specific RFID microchip  26  utilized. 
         [0017]    The slot  32  as shown in  FIG. 2  follows a downward path toward the lower edge  24 A followed by one curving into a perpendicular segment extending toward the side edge  24 B on the right followed by another segment extending toward the lower edge  24 A and finally one extending toward the side edge  24 B on the left. The slot  32  could also have segments disposed at acute angles to the edges  24 A and  24 B as well as curved segments depending on the shape most suitable for tuning for the specific RFID microchip utilized. Depending upon the characteristics of the microchip, it could also be straight and could extend completely between the upper edge  24 A and the lower edge  24 A thereby resulting in the antenna  24  being two pieces separated by the slot  32 . 
         [0018]    As may be seen most clearly in  FIGS. 2 and 4 , a stamped or otherwise shaped central insulation member  36  formed of non-conductive green rubber is also positioned between the two insulation members  22 . The stamped insulation member  36  has an enlarged opening  38  sized to snugly receive therein the antenna  24 . Thus, the internal edge  38 A of the opening  38  is substantially the same size as the peripheral edge of the antenna  24  as represented by the numerals  24 A,  24 B, and  24 C. With this construction, the antenna  24 , including its edges is completely encapsulated in non-conducting insulation members  22 ,  36  and  22 . 
         [0019]    The stamped insulation member  36  has an internal extension  36 A sized and shaped to fit in the slot  32 . The internal extension  36 A substantially fills the slot  32 . If the slot  32  was not filled with the insulation of the internal extension  36 A, the green rubber of the antenna  24  would flow into the slot  32  during vulcanization of the tire or during vulcanization of the RFID device  20  if done prior to its assembly in the tire T. 
         [0020]    As previously discussed, the length and shape of the slot  32  are designed to tune the antenna to be at substantially the same frequency of the RFID microchip  26 . 
         [0021]    In preparation for assembly of the insulation members  22 , the antenna  24  and the stamped insulation member  36 , the RFID microchip  26  may be mounted on either the stamped insulation member  36  (as shown in  FIG. 4 ) or on the antenna  24 . In either event, the tabs  28  of the microchip must be engaged to the antenna  24  on opposite sides of the slot  32  when the components are assembled to form the RFID device  20 . The location of the chip may be adjusted to improve performance of the RFID device  20 . 
         [0022]    The insulation members  22  may be formed of any of a number of non-conductive or low conductive materials such as those specified above and having a dielectric constant of about 4 or less. The insulation members  22  have a thickness in the range of 0.05 mm to 3 mm, where mm is millimeters. The thickness of the antenna  24  and the central insulation member  36  are also in the range of 0.05 mm to 3 mm. Although the central insulation member  36  and the antenna  24  should be the same thickness, it is not necessary that they be the same thickness as the other insulation members  22 ,  22 . They could be thinner or thicker than such other insulation members  22 ,  22 . Additionally, it is possible that one on the outer insulation members  22  be thicker than the other outer insulation member  22 . 
         [0023]    The amount of carbon black and/or other ingredients providing conductivity to the antenna  24  is such as to give it a resistance in the range of 20 ohms to 400 ohms and preferably in the range of 40 ohms to 100 ohms. 
         [0024]    As can be seen in  FIG. 3 , the opposing insulation members  22 ,  22  are sealed to the central insulation member  36  completely around the periphery to thereby encapsulate the antenna  24  and the RFID chip  26 . As previously discussed, the internal edge  38 A of the enlarged opening  38  seals the edges  24 A,  24 B and  24 C of the antenna  24 . Preferably, the insulation members  22 ,  22  and  36  are formed non-conductive green (non-vulcanized) rubber. When manufactured of green rubber, the edges of the opposed insulation members  22  will adhere to the central insulation member  36  without the necessity of providing any adhesive therebetween. The insulation members  22 ,  36 ,  22  will also adhere to the antenna  24  without the use of adhesive provided all of such members are green rubber. When green rubber is used for the insulation and the antenna  24 , the insulation members  22 ,  22  and the central insulation member  36  can be sealed together and to the antenna  24  simply by pressing together. If the insulation members  22  and/or central insulation member  36  and/or antenna  24  are formed of a material other than green rubber, they can be heat sealed or adhesively joined together. 
         [0025]    The completed assembly of the insulation members  22 ,  22  central insulation member  36 , antenna  24  and RFID microchip  26  forming the RFID device  20  may be positioned in the tire T between the various plies thereof or on its inner surface as previously discussed. Following positioning in the tire T or in its inner surface, it will be included in the vulcanization of the tire thereby providing a completed tire and RFID device with a wireless antenna. 
         [0026]    If desired, the RFID device of the present invention could be packaged while the insulation layers  22 ,  22  and  36  and the antenna  24  layer are in the green state and then shipped another manufacturing facility for installation in tires during manufacturing. Additionally, the RFID device of the present invention could itself be vulcanized prior to incorporation in a tire. 
         [0027]    The RFID device of the present invention is one which is economical to manufacture and can be provided with a configuration to provide one of a number of levels of resistance tailored to the specific requirements of the device. 
         [0028]    Many modifications will be readily apparent to those skilled in the art. Accordingly, the scope of the present invention should be determined by the scope of the claims appended hereto.