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1 SPATIALLY SELECTIVE UHF NEAR FIELD MICROSTRIP COUPLER DEVICE AND RFID SYSTEMS USING DEVICE
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 12/133,801, filed Jun. 5, 2008, which is a divisional of U.S. application Ser. No. 10/604,996, filed Aug. 29, 2003, which is hereby incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to RFID systems, operable with a variety of different dimensioned electro-magnetically coupled transponders, working at close proximity, to an RF transceiver antenna that is spatially selective for an individual transponder located in a predetermined transponder operating region to the exclusion of other adjacent transponders, and its application to printers-encoders or other systems utilizing such in UHF RFID systems.
2. Description of Related Art
UHF radio frequency identification (RFID) technology allows wireless data acquisition and or transmission from and or to active (battery powered) or passive transponders using a backscatter technique. To communicate with, i.e., “read” from and or “write” commands and/or data to a transponder, the transponder is exposed to an RF electro-magnetic field by the transceiver that couples with and energizes (if passive) the transponder through electro -magnetic induction and transfers commands and data using a predefined “air interface” RF signaling protocol.
When multiple passive transponders are within the range of the same RF transceiver electro-magnetic field they will each be energized and attempt to communicate with the transceiver, potentially causing errors in “reading” and or “writing” to a specific transponder in the reader field. Anti-collision management techniques exist to allow near simultaneous reading and writing to numerous closely grouped transponders in a common RF electro-magnetic field. However, anticollision management increases system complexity, cost and delay response. Furthermore, anti-collision management is “blind” in that it cannot recognize where a specific transponder being processed is physically located in the RF electromagnetic field, for example, which transponder is located proximate the print head of a printer-encoder.
One way to prevent errors during reading and writing to transponders without using anti-collision management is to electrically isolate a specific transponder of interest from nearby transponders. Previously, isolation of transponders has used RF-shielded housings and/or anechoic chambers through which the transponders are individually passed for personalized exposure to the interrogating RF field. This requires that the individual transponders have cumbersome shielding or a significant spatial separation.
RFID printers-encoders have been developed which are capable of on-demand printing on labels, tickets, tags, cards or other media with which a transponder is attached or embedded. These printer-encoders have a transceiver for ondemand communicating with the transponder on the individual media to read and/or store data into the attached transponder. For the reasons given, it is highly desirable in many applications to present the media on rolls or other format in which the transponders are closely spaced. However, close
spacing of the transponders exacerbates the task of serially communicating with each individual transponder without concurrently communicating with neighboring transponders on the media. This selective communication exclusively with an individual transponder is further exacerbated in printersencoders designed to print on the media in or near the same space as the transponder is positioned when being interrogated.
When transponders are supplied attached to a carrier substrate, for example in RFID-attached labels, tickets, tags or other media supplied in bulk rolls, Z-folded stacks or other format, an extra length of the carrier substrate is required to allow one transponder on the carrier substrate to exit the isolated field area before the next transponder in line enters it. The extra carrier substrate increases materials costs and the required volume of the transponder media bulk supply for a given number of transponders. Having increased spacing between transponders may also slow overall printer-encoder throughput.
When transponders of different sizes and form factors are processed, the RF shielding and or anechoic chamber configuration will also require reconfiguration, adding cost, complexity and reducing overall productivity. In certain printerencoders it is desired to print on transponder-mounting media in the same transponder operating region in which the transponder is being read from or written to. This may be very diflicult to accomplish if the transponder also must be isolated in a shielded housing or chamber.
UHF transponders may operate in, for example, the 902928 MHz band in the United States and other ISM bands designated in different parts of the world. For example, in FIG. 1 a conventional one-half wavelength “Forward Wave” microstrip prior art coupler 3 consisting of a, for example, rectangular conductive strip 5 upon a printed circuit board 7 having a separate ground plane 9 layer configured for these frequencies. One end of the conductive strip 5 is connected to transceiver 42 and the other end is connected through tenninating resistor 8 to ground plane 9. The conductive strip 5 as shown in FIG. 1 has a significant width due to RF design requirements imposed by the need to create acceptable frequency response characteristics. This type of prior art coupler 3 has been used with UHF transponders that are relatively large compared to the extent of prior art coupler 3.
As shown by FIGS. 2a and 2b, recently developed transponders 1, designed for operation at UHF frequencies, have one dimension so significantly reduced, here for example a few millimeters wide, that they will be activated upon pas sage proximate the larger prior art coupler 3 by electro-magnetic power leakage 10 concentrated at either side edge of the conductive strip 5 of prior art coupler 3. In FIG. 2A, the two leakage regions “A” and “B” defined by electro-magnetic power leakage 10 are small and relatively far apart, increasing system logical overhead and media conveyance positioning accuracy requirements. If the transponders 1 were placed close together, then multiple transponders 1 might be activated by the physically extensive one-half wavelength “Forward Wave” microstrip prior art coupler 3.
Thus the minimum required spacing of these transponders 1 to isolate them, and thus the minimum size of media 11 (assuming that they are embedded one per label or media 11 on carrier substrate 13) must be large relative to the size of the microstrip coupler 3. This creates issues for media suppliers by limiting the available space on the media 11 for transponder 1 placement and significantly increasing the necessary accuracy of the transponder 1 placement within and or under the printable media 11 and along the liner or carrier substrate 13. This also reduces the cost advantages of using the narrow
dimensioned transponder(s) 1 Within media 11, as the media 11 must be much larger than the transponder 1 to achieve adequate RF isolation.
Competition in the market for such “integrated” printerencoder systems as Well as other RFID interrogation systems has focused attention on the ability to interrogate With high spatial selectivity any transponder from a Wide range of available transponders having different sizes, shapes and coupling characteristics as Well as minimization of overall system, media size, and transponder costs.
Therefore, it is an object of the invention to provide a device, systems, and methods that overcome deficiencies in such prior art.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
The accompanying draWings, Which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together With a general description of the invention given above, and the detailed description of the embodiments given beloW, serve to explain the principles of the invention.
FIG. 1 is a top vieW of a prior art microstrip forWard Wave coupler.
FIG. 2a is a simplified cut-aWay side vieW of a transpondercoupler structure using a prior art forWard Wave coupler as shoWn in FIG. 1, illustrating schematically locations Where coupling With a narroW dimensioned transponder supplied in-line With other transponders on a carrier substrate may occur.
FIG. 2b is a partial cut-aWay top schematic vieW of the prior art forWard Wave coupler and carrier substrate With embedded transponders of FIG. 2a.
FIG. 3 is a side schematic vieW of a media printer according to one embodiment of the invention having an improved RFID interrogation system.
FIG. 4a is a top vieW of a coupler according to one embodiment of the invention.
FIG. 4b is a top vieW of a coupler according to another embodiment of the invention.
FIG. 5a is a simplified cut-aWay side vieW of a transpondercoupler structure using a coupler according to the invention, illustrating schematically the spaced apart areas Where coupling With a narroW dimensioned transponder supplied in-line With other transponders on a carrier substrate may occur.
FIG. 5b is a partial cut-aWay top schematic vieW of the coupler according to the invention and carrier substrate With embedded transponders of FIG. 5a.
DETAILED DESCRIPTION OF THE INVENTION
The present invention concerns apparatus and method Which enables an RFID transceiver (sometimes termed herein an “interrogator”) to communicate selectively and exclusively With a single UHF transponder 1 When one or more other similar transponders are in close proximity, Without the need for physical isolation or cumbersome shielded housings or chambers.
The invention is useful in the reading and or data loading of UHF transponders, for example on an assembly line, in distribution centers or Warehouses Where on-demand RFID labeling is required, and in a variety of other applications. In many applications a transponder or a number of transponders are mounted or embedded on or in a label, ticket, tag, card or other media carried on a liner or carrier. It is often desirable to be able to print on the media before, after, or during commu
nication With a transponder. Although this invention is disclosed here in a specific embodiment for use With a direct thermal or thermal transfer printer, it may also be used With any type of spatially selective RFID interrogation device or other types of printers using other printing technologies, including inkjet, dot-matrix, and electro-photographic methods.
In some applications a print station may be at a distance from the RFID transceiver; in others it may be necessary to accomplish the print function in the same target space occupied by the transponder When it is being interrogated.
FIG. 3 illustrates by Way of example only an implementation of the invention in a thermal transfer media printer 16 in Which both printing and transponder communication are accomplished, but at different locations in the media printer 16. The media printer 16 includes a printhead sub-assembly comprising a conventional thermal printhead 18 and platen roller 19, as in a direct thermal printer for printing on thermally-sensitive media. A Web 24 of media 11, such as labels, tickets, tags or cards, is directed along a feedpath 26 under the printhead 18 Where on-demand printing of text, bar codes and/or graphics takes place under control of a computer or microprocessor (not shoWn). After being printed, the media 11 folloWs a media exit path 34 and may be peeled off the underlying carrier substrate 13 at a peeler bar 32. The liner or carrier substrate 13 for the media is guided out of the media printer 16 by a roller 36 Where it exits the printer along a carrier exit path 38.
When a thermal printer is configured for use as a thermal transfer printer, a ribbon supply roll 28 delivers a thermal transfer ribbon (not shoWn for clarity) betWeen printhead 14 and the media on Web 24. After use, the spent ribbon is collected on a take-up reel 22.
In accordance With an aspect of the present invention, the media printer 16 includes a transceiver 42 for generating RF communication signals that are fed to a frequency and spatially selective microstrip near field coupler 30 located proximate the media feed path 26. As Will be explained and illustrated in detail hereinafter, the system (including transceiver 42 and near field coupler 30) forms a near field pattern in the location of a transponder operating region C (see FIG. 5A). The system is configured to establish at predetermined transceiver poWer levels a mutual coupling Which exclusively activates and communicates With a single transponder 1 located in the transponder operating region C.
As labels or other media 11 With embedded transponders 1 move along the media feed path 26 through transponder operating region “C”, data may be read from and or Written to each transponder 1. Information indicia then may be printed upon an external surface of the media 11 as the media passes betWeen the platen roller 19 and the printhead 18 by selective excitation of the heating elements in the printhead 18, as is Well knoWn in the art. When the media printer 16 is configured as a direct thermal printer, the heating elements form image dots by therrnochromic color change in the heat sensitive media; When the media printer 16 is configured as a thermal transfer printer, then ink dots are formed by melting ink from the thermal transfer ribbon (not shoWn for clarity) delivered betWeen printhead 18 and the media on Web 24 from ribbon supply roll 28. Patterns of printed dots thus form the desired information indicia on the media 11, such as text, bar codes or graphics.
Media conveyance is Well knoWn in the art. Therefore the media conveyance 25 portion of the printer that drives the media With transponders along the media feed path 26 is not described in detail.