Abstract:
An barcode scanner with a pattern mirror that doubles as a radio frequency identification (RFID) tag reader antenna to provide better overlap between barcode label and RFID tag reader reading zones. The barcode scanner includes at least one of pattern mirror with a conductive coating, and a radio frequency identification tag reader coupled to the conductive coating of the one pattern mirror. The conductive coating of the one pattern mirror functions as an antenna for the radio frequency identification tag reader.

Description:
BACKGROUND 
     Barcode scanners are well known for their usefulness in identifying products. Barcode scanners may be equipped with add-on (internal or external in the checkout stand) radio frequency identification (RFID) tag readers, but barcode label and RFID tag reading zones do not coincide, resulting in operator confusion as to item placement. Further, finding space for a RFID tag reader antenna is a challenge. 
     It would be desirable to better integrate RFID tag readers with barcode scanners and provide better overlap between barcode label and RFID tag reading zones. 
     SUMMARY 
     A barcode scanner with mirror antenna is provided. 
     The barcode scanner includes at least one of pattern mirror with a conductive coating, and a radio frequency identification tag reader coupled to the conductive coating of the one pattern mirror. The conductive coating of the one pattern mirror functions as an antenna for the radio frequency identification tag reader. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example barcode scanner. 
         FIG. 2  illustrates layers of a pattern mirror. 
         FIG. 3  is a perspective view of an example barcode scanner. 
         FIG. 4  is a cross-sectional view of the barcode scanner of  FIG. 3  with a cover portion removed. 
         FIG. 5  is a view of an example pattern mirror including a radio frequency identification (RFID) tag reader antenna. 
         FIG. 6  is a view illustrating a top side of an example resonator. 
         FIG. 7  is a view illustrating an example bottom side of the resonator of  FIG. 6 . 
         FIG. 8  is a view illustrating a back surface of a mirror housing which is aperture side down. 
         FIG. 9  is a view illustrating the back surface of the mirror housing of  FIG. 8 , with a resonator mounted in an example location. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , example barcode scanner  10  includes laser  12 , mirrored spinner  14 , pattern mirrors  16 , collector  18 , detector  20 , scale assembly  22 , weigh plate  24 , and control circuitry  26 . Barcode scanner  10  additionally includes radio frequency identification (RFID) tag reader  28 . 
     Laser  12  generates a laser beam. 
     Mirrored spinner  14  directs the laser beam towards pattern mirrors  16  and directs light reflected from item  30  towards collector  18 . Motor  34  rotates mirrored spinner  14 . 
     Pattern mirrors  16  produce a pattern of scanning light beams for scanning barcode label  42  on item  30 . Pattern mirrors  16  direct the laser beam towards item  30  and direct the light reflected from item  30  towards mirrored spinner  14 . 
     Pattern mirrors  16  include pattern mirror  16   a , which includes RFID tag reader antenna  32 . 
     With reference to  FIG. 2 , pattern mirrors  16  may include front surface mirrors, with a substrate  52  and an aluminum coating  54 . Substrate  52  may be made of glass or plastic, but glass is typically preferred because of its superior flatness. 
     Pattern mirrors  16  may additionally be coated with a passivation layer  56  to prevent oxidation of the aluminum coating  54 . Passivation layer  56  may include silicon oxide (quartz). Both the aluminum and passivation layers  54  and  56  may be applied to a glass substrate  52  by a vacuum deposition process. 
     In accordance with the present invention, the conductive aluminum coating  54  is used as an RFID tag reader antenna  32 . Any of pattern mirrors  16  may serve this purpose, within a certain range of sizes and qualities, where quality depends on the conductivity of the aluminum coating  54  and the dielectric losses in substrate  52 . 
     For a glass pattern mirror  16  to serve as pattern mirror  16   a , the size range should be about four to six inches for the largest dimension. Plastic mirrors would be the larger sizes of the same range. The dielectric constant of most plastics is about 3, while glass can be as high as 10, resulting in smaller sizes for glass than plastic for the same frequency. 
     The suitability of any pattern mirror  16  also depends on dielectric effects of the plastic of mirror housing  72  ( FIGS. 4 ,  9 , and  10 ) and the means for mounting the pattern mirror  16  to mirror housing  72 , such as glue, clips, or snaps. 
     If glue is used, the type of glue (dielectric constant), thickness of the glue, and coverage of the glue (whether it is applied to all of the surface or only partially) all affect the suitability. 
     The shape of a candidate pattern mirror  16  is also important because it determines signal polarization. RFID tags  44  are typically linearly polarized. 
     For a linearly polarized RFID tag reader antenna  32 , the direction of the polarization of RFID tag reader antenna  32  must match that of the antenna in RFID tag  44  to achieve maximum read range. If the polarizations are crossed (horizontal-vertical), RFID tag reader  28  will not likely read RFID tag  44 . 
     For a circularly polarized RFID tag reader antenna  32 , the orientation of the tag antenna relative to RFID tag reader antenna  32  is not so critical. The maximum reception distance is less than that of a properly oriented linearly polarized RFID tag reader antenna  32 , and the efficiency is reduced by 3 dB. The loss of efficiency associated with using a circularly polarized RFID tag reader antenna  32  is not significant as most commercial RFID tag readers  28  have powers and ranges which far exceed the range required to read an RFID tag  44  on an item  30  within the barcode scanning zone of scanner  10 . In fact, the power of RFID label reader  28  may have to be reduced to prevent reading of RFID tags  44  outside the barcode scanning zone of scanner  10  (in shopping carts and adjacent checkout lanes). 
     Returning to  FIG. 1 , collector  18  directs the light reflected from item  30  towards detector  20 . 
     Detector  20  converts the light reflected from item  30  into electrical signals. 
     Scale assembly  22  produces electrical signals based upon the weight of produce items. Scale assembly  22  may include a load cell or other weight measuring device and a weigh plate. 
     Item  30  may be labeled only with barcode label  42 , only with RFID tag  44 , or both. 
     RFID tag reader  28  wirelessly interrogates RFID tag  44  on item  30 . RFID tag reader  28  operates in the Industrial, Scientific, and Medical (ISM) band (860 MHz in Europe, 902-928 MHz in the United States). RFID tag reader  28  couples to RFID tag reader antenna  32  through a wired or wireless connection. 
     Control circuitry  26  controls operation of barcode scanner  10 . Control circuitry  26  receives electrical signals from detector  20  and determines item identification information stored within barcode label  42 . Control circuitry  26  receives weight signals from scale assembly  22 . Control circuitry  26  receives item identification information stored within RFID tag  44  from RFID tag reader  28 . Control circuitry  26  sends weight information and item identification information to point-of-sale (POS) terminal  50 . 
     POS terminal  50  determines a price of item  30  based upon the item identification information. POS terminal  50  also determines prices of produce items based upon the weight information and produce identification information entered into POS terminal  50  by an operator. 
     With reference to  FIG. 3 , an example barcode scanner  10  is illustrated. Example barcode scanner  10  is a dual-aperture barcode scanner. 
     Example barcode scanner  10  includes a first housing portion  60  and a second housing portion  66 . Pattern mirrors  16  are located in both first housing portion  60  and second housing portion  66  for scanning an item from a plurality of different directions. 
     Housing portion  60  includes substantially horizontal aperture  62 . Substantially horizontal aperture  62  may be located in a scale weigh plate  64 . 
     Housing portion  66  includes substantially vertical aperture  68 . Cover portion  70 , when removed, exposes a mirror housing  72  ( FIG. 3 ). 
     Example barcode scanner  10  directs scanning light beams from laser  12  through substantially horizontal and vertical apertures  62  and  68  for illuminating item  30  from a plurality of different sides and angles. In this way, example barcode scanner  10  has a high probability of reading barcode label  42  during a first pass of item  30  over scanner  10 . 
     With reference to  FIGS. 4-5 , one choice for pattern mirror  16   a  is a large pattern mirror  74  ( FIG. 5 ). Pattern mirror  74  is mounted to an inside surface  78  of mirror housing  72  within housing portion  66 . Mirror housing  72  is made of plastic. Pattern mirror  74  functions to direct the scanning light beams in a diagonal downward direction towards a top surface of item  30 . 
     Pattern mirror  74  is a good choice for pattern mirror  16   a . Pattern mirror  74  is one of the largest pattern mirrors  16  in scanner  10 . Pattern mirror  74  also has a trapezoidal shape that is close enough to a square shape to provide RFID tag reader antenna  32  with a polarization that is close to circular. Pattern mirror  74  has the correct size to achieve a correct resonating frequency for an antenna operating with the range of RFID frequencies. Also, pattern mirror  74  is located such that it faces the center of the intended RFID scan zone, over substantially horizontal aperture  62  of weigh plate  64  and in front of substantially vertical aperture  68  of second housing portion  66 . 
     Use of pattern mirror  74  results in an antenna pattern that is hemispherical and centered over the weigh plate  64 . The antenna pattern is influenced by the metallic parts of scanner  10 , such as weigh plate  64 , a metal chassis within first housing portion  60 , metal components in second housing portion  66 , and electronic article surveillance (EAS) coils, if installed, around one or both of apertures  62  and  68 . This metal in the vicinity of pattern mirror  74  limits the RFID tag reading zone to approximately the barcode scanning zone, such that RFID tags on items  30  in shopping carts or over scanners  10  in adjacent lanes are not read by RFID tag reader  28  in a present lane. 
     The large size of pattern mirror  74  facilitates wireless coupling of an RF signal from RFID tag reader  28  to RFID tag reader antenna  32  through mirror housing  72  without a need for major changes to mirror housing  72 , such as drilling holes for connectors and cables that would pass from the backside surface  76  to the inside surface  78  of mirror housing  72 . 
     Excitation of RFID tag reader antenna  32  may be provided by a resonator  80 . Resonator  80  may include an additional antenna or ground-plane on backside surface  76  of mirror housing  72 , opposite mirror  74 . Resonator  80  may take the form of a conductive coating on backside surface  76  or a sheet of metal (preferably copper or aluminum) attached to backside surface  76  ( FIGS. 8 and 9 ). In an example configuration, backside surface  76  includes a recess  77  which accommodates placement of resonator  80 . 
     With reference to  FIGS. 6-7 , an example resonator  80  is illustrated. In this example, resonator  80  includes a top layer  82  and a bottom layer  84 . Top layer  82  includes a drive circuit  88  including a transmission line  89  on a printed circuit board  86 , such as a standard FR4 printed circuit board. 
     An example second layer  84  ( FIG. 7 ) includes a ground plane  94  with slot  96  in the center. Transmission line  89  crosses over slot  96 . Slot  96  is an interruption in ground plane  94  which force the current of the wave traveling in transmission line  89  to “disconnect” from the wave, resulting in radiation off the back of ground plane  94 . 
     A linear slot  96  would be the simplest structure. However, if the amount of coupling desired would require a linear slot  96  that starts approaching half a wavelength in length, then the linear slot  96  may start acting as an antenna and radiate both off the front and back of ground plane  94 . 
     To counteract this, the shape can be changed such that the current still travels a large distance but the overall dimensions of slot  96  stay well below half a wavelength. An “X” or “H” shaped slot  96  can be used for that purpose. 
     The slot size, the position where transmission line  89  crosses slot  96 , as well as the length of transmission line  89  beyond slot  96 , are all parameters that affect impedance. These parameters can be varied to achieve an antenna input impedance as close as possible to match the impedance of transmission line  89 , and thus maximize the energy coupled to and from (receiving) RFID tag reader antenna  32 . 
     Ground plane  94  should be larger than RFID tag reader antenna  32  in order to avoid backside radiation of energy away from the barcode label reading zone by RFID tag reader antenna  32  that would degrade performance of RFID tag reader antenna 
     Drive circuit  88  includes coaxial coupling  92 , which couples an RF signal wire in coaxial cable  90  to transmission line  89  and a ground sheath to ground plane  94  in an unbalanced configuration. A balanced configuration drive circuit with two coaxial couplings (positive and negative signals) on opposite ends of transmission line  89  is also envisioned. 
     Resonator  80  is mounted either with fasteners into stand-offs or snaps on the backside surface  76  of mirror housing  72 . Resonator  80  is mounted with ground plane  94  facing downward towards pattern mirror  16   a.    
     For small pattern mirrors  16   a  (about four inches long), ground plane  94  should be within about 0.25 mm of the backside of the small pattern mirror  16   a  to operate at the desired frequency range of 902 to 928 MHz. For large pattern mirrors  16   a  (about five to six inches), the ground plane should be within about five to ten millimeters of the backside of the large pattern mirror  16   a  to operate at the desired frequency range of 902 to 928 MHz. 
     In operation, an RF signal from RFID tag reader  28  travels over coaxial cable  90  and through coupling  92  to transmission line  89 . Ground plane  90  radiates the energy of the RF signal to pattern mirror  16   a . The aluminum coating  54  re-radiates the energy into the barcode label reading zone of scanner  10 , with the RFID tag reading zone and the barcode label reading zone substantially overlapping. Pattern mirror  16   a  receives a return RF signal from RFID tag  44  and radiates the energy in the return RF signal to resonator  80  and transmission line  89 . Transmission line  89  sends the return signal to RFID tag reader  28  over coaxial cable  90 . 
     Although particular reference has been made to certain embodiments, variations and modifications are also envisioned within the spirit and scope of the following claims.