Abstract:
An RFID device for tires includes first and second sheets non-conducting insulation material having positioned therebetween a semi-conductor chip and a wireless antenna formed of electrically conducting ink printed on one of said sheets.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of U.S. Provisional Application No. 61/270,079 filed Jul. 2, 2009. 
     
    
     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. 
       SUMMARY OF THE PRESENT INVENTION 
       [0004]    The present invention utilizes an antenna which is embedded along with a computer chip in the body of a tire or affixed to the inner surface of the tire. The antenna is formed of an electrically conductive ink having a formulation which includes carbon and silver and is encapsulated in insulation formed by a pair of non-conducting rubber sheets adhered together. The insulation preferably is a non-conducting rubber but could be 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. 
     
    
     
       IN THE DRAWINGS 
         [0005]      FIG. 1  is a sectional view of a tire showing an RFID device with the antenna of the present invention encapsulated therein. 
           [0006]      FIG. 2  is a plan view showing one form of antenna with a computer chip encapsulated between two layers of insulation material. 
           [0007]      FIG. 3  is a sectional view of the assembly shown in  FIG. 2 . 
           [0008]      FIG. 4  is a view showing various configurations of antennae formed using electrically conductive ink. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    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 . 
         [0010]    Referring to  FIGS. 2 and 3 , the RFID device includes a pair of insulation members  22  and an antenna  24  encapsulated therebetween. A semiconductor microchip  26  such as one manufactured by NXP as its item SL3S1001FTT is attached to tabs  28  of the antenna  24 . 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. 
         [0011]    As can be seen in  FIG. 3 , the edges  23  of the opposing insulation members  22  are sealed together completely around the periphery of the assembly at edges  23  to thereby encapsulate the antenna  24  and the chip  26 . Preferably, the insulation members are formed non-conductive green (non-vulcanized) rubber. When manufactured of green rubber, the edges  23  of the opposed insulation members  22  will adhere together without the necessity of providing any adhesive therebetween. When green rubber is used for the insulation, the insulation members  22  can be sealed together simply by pressing together the edges of the opposed members  22 . If the insulation members  22  are formed of a material other than green rubber the edges can be heat sealed or adhesively joined together. 
         [0012]    The conductive ink is printed directly on one of the insulation members  22  which is then cured for 8 to 12 minutes at a temperature of 90° to 130° C. and preferably for 10 minutes at 100 degrees C., thus curing the ink. The chip  26  is then installed and the other insulation member  22  is affixed thereto over the antenna  24  and chip  26  and the edges  23  of such joined insulation members  22 ,  22  are sealed together thereby encapsulating the antenna  24  and chip  26  there between. 
         [0013]    The thickness of the ink is in the range of 0.0006 to 0.34 mm. with a preferred average thickness of about 0.011 mm. The conductive ink is formulated on a custom basis as set forth herein using conductive inks of the type manufactured and distributed by Engineered Conductive Materials, LLC (ECM), Delaware, Ohio. Among the inks used in formulating the ink for the antenna  24  of the present invention are ECM&#39;s product numbers Cl-1036 silver/proprietary resin, Cl-2001 carbon/vinyl and Cl-2014 carbon/vinyl. 
         [0014]    Inks of the above type are mixed to provide a solution having a preferred range of about 80% silver resin to about 20% carbon/vinyl. An antenna suitable for the intended purpose of the present invention could have 100% silver resin and 0 carbon. However, from the standpoint of economics, it is preferred to have lower amounts of silver resin because the cost of silver resin is significantly higher than the cost of carbon/vinyl ink. From a practical standpoint in providing in ink on an economical basis with suitable properties for the tire antenna of the present invention, the silver resin of the ink formulation should be at least 75% with no more than 25% carbon/vinyl. The higher the percentage of concentration of silver resin in the solution forming the ink, the more conductive will be the antenna. 
         [0015]    Even with an ink formulation having a very high percentage of silver resin, the cost of producing an RFID device utilizing the ink antenna of the present invention is significantly less than the cost of manufacturing a conventional RFID device with copper or other metal for the antenna. Thus, the cost of a conventional RFID devices copper antenna could be approximately twenty cents per device. This compares with the cost of an RFID device manufactured using the antenna as set forth in the present invention of approximately one to two cents per device. 
         [0016]    In preparing the RFID device using the antenna  24  of the present invention, after formulating, the ink formulated as set forth above is printed onto a surface of one of the insulation members  22  in the thickness range set forth above. The semiconductor microchip  26  is then positioned between the tabs  28  of the antenna  24  and a second insulation member  22  is engaged to the first insulation member  22  with the antenna  24  and semi-conductor microchip  26  therebetween. The assembly is then cured for 5-10 minutes by heating to approximately 110° C. Such curing causes the second insulation member  22  and its edges  23  to become adhered to the first insulation member  22  and its edges  23  thereby encapsulating the antenna  24  and semi-conductor microchip  26  therebetween.  FIG. 2  shows one possible configuration of an antenna  24 . 
         [0017]      FIG. 4  is a view showing various configurations of antennae formed with one of the ink formulations disclosed herein. Thus, in  FIG. 4 , each of the configurations of antenna shown in the right column has a higher resistance than antenna having configurations shown in the left column. In the right column, the resistance of the respective antenna is higher the further down the column it is located, however some of that variation may due to differences in the formulation and/or the thickness of the applied ink forming the antenna. Those antenna in the bottom row generally have a resistance higher than those in the left row by lower than those shown in the right column. 
         [0018]    For the antennae shapes shown in  FIG. 4  produced from ink of 100% silver resin the resistance was less than 1 ohm for those shapes shown in the left column to slightly over 2 ohms for those shapes shown in the right column. For antenna shapes shown in  FIG. 4  produced with ink of 75% silver, there is also a variation of resistance. 
         [0019]    It can be readily seen from the foregoing, that it is possible to vary the ohms of resistance for the various shapes of antennae by varying the amount of silver used in the solution used for forming the antenna of the RFID device of the present invention and by varying the shape. The various antenna shapes include a pair of tabs  28  each of which is engaged to the chip  26  and each of which has extending therefrom linear and/or arcuate sections. 
         [0020]    For the RFID device of the present invention it is preferred that the antenna have a resistance in the range of 200-300 ohms; however, it could have a range as great as 1 ohm to 500 ohms. 
         [0021]    Antennae that have lower resistances and match the impendence of the RFID chip provide a long range of transmission. 
         [0022]    The RFID device of the present invention is one which is economical to manufacture and can be provided with an antenna ink formulation and configuration to provide one of a number of levels of resistance tailored to the specific requirements of the device.