US20050092838A1 - System and Method for Selective Communication with RFID Transponders - Google Patents

Abstract

A system having an RFID transceiver is adapted to communicate exclusively with a single RFID transponder located in a predetermined confined transponder target area. The system includes a magnetic coupling device comprising a magnetic flux generator responsive to a radio frequency input signal and a magnetic field pattern former. The pattern former is configured to collect flux produced by the flux generator and to form a field pattern in the location of the transponder target area. The system establishes, at predetermined transceiver power levels, a mutual magnetic coupling which is selective exclusively for a single transponder located in the transponder target area.

Description

BACKGROUND OF INVENTION
• 1. Field of the Invention
• The invention relates to RFID communication systems which are selective for an individual transponder located in a predetermined target area, to the exclusion of other transponders, and to printers and other larger systems having such RFID communication systems.
• 2. Description of Related Art
• Inductively coupled radio frequency identification (RFID) technology allows data acquisition and or transmission from and or to active (battery powered) or passive RFID transponders using RF magnetic induction. To read or write from and or to an RFID transponder, the RFID transponder is exposed to an RF magnetic field that couples with and energizes the RFID transponder through magnetic induction and transfers commands and data using a predefined “air interface” RF signaling protocol.
• When multiple RFID transponders are within the range of the same RF 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 RFID transponder. Anti-collision management technologies exist to allow near simultaneous reading and writing to numerous RFIDs in a common RF magnetic field. However, anti-collision management increases system complexity and cost. Further, anti-collision management is blind. It cannot recognize where a responding transponder is located in the RF magnetic field.
• One way to prevent errors during reading and writing to RFID transponders without using anti-collision management is to isolate each RFID transponder from nearby RFID transponders. Previously, isolation of RFID transponders has used RF shielded housings and or anechoic chambers through which the RFID transponders are individually passed for isolated exposure to the interrogating RF magnetic field. This requires that the individual transponders have cumbersome shielding or a significant physical separation.
• When RFID transponders are supplied attached to a carrier substrate, for example in RFID-mounted labels, tickets, tags or other media supplied in bulk rolls, Z-folded stacks or other format, an extra portion of the carrier substrate is required to allow one RFID transponder on the carrier substrate to exit the isolated field area before the next RFID transponder in line enters it. The extra carrier substrate increases materials costs and the required volume of the RFID media bulk supply for a given number of RFID transponders. Having increased spacing between RFID transponders may also slow overall throughput.
• When the size or form factor of the utilized RFID transponder is changed, the RF shielding and or anechoic chamber configuration may also require reconfiguration, adding cost and complexity and reducing overall productivity.
• There exists applications wherein it is desired to print on transponder-mounting media in the same target space in which the transponder is being read from or written to. This may be very difficult to accomplish if the transponder must be interrogated in a shielded housing or chamber.
• Printers have been developed which are capable of on-demand printing on labels, tickets, tags, cards or other media with which is associated an RFID transponder. These printers have an RFID transceiver for on-demand communicating with the RFID transponder on the individual media. 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 transducers exacerbates the task of serially communicating with each individual transponder without concurrently communicating with transponders on neighboring media. This selective communication exclusively with individual transponders is further exacerbated in printers designed to print on the media in the same space as the transponder is positioned when being interrogated.
• Competition in the market for such “integrated” printer-transceiver systems and selective RFID interrogation systems has focused attention on minimization of overall costs, including reduction of the costs of individual RFID transponders, bulk RFID label and or tag supply carrier substrates, printers and or interrogators.
• Therefore, it is an object of the invention to provide a system and method which overcomes deficiencies in such prior art.
BRIEF DESCRIPTION OF DRAWINGS
• 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 side schematic view of a media printer according to one embodiment of the invention having an improved RFID interrogation system.
• FIG. 2 is a top view of a magnetic coupling device embodying principles of the present invention.
• FIG. 3 is a bottom view of the magnetic coupling device ofFIG. 2.
• FIG. 4 is a top view of the magnetic coupling device ofFIG. 2, with a magnetic field pattern former applied.
• FIG. 5 is a bottom view of the magnetic coupling device ofFIG. 4.
• FIG. 6A is a cut-away side view of a magnetic coupling device as shown inFIGS. 4 and 5, illustrating schematically a mutual magnetic coupling selectively with a single RFID transponder supplied in-line with other RFID transponders on a carrier substrate.
• FIG. 6B is a view similar toFIG. 6A of an alternative embodiment of an aspect of the invention.
• FIG. 7 is a partial cut-away top schematic view of the magnetic coupling device and carrier substrate mounted RFID transponders ofFIG. 6A; a printhead and platen roller have been omitted for clarity.
• FIG. 8A is a test chart showing relative power levels delivered for activation by a magnetic coupling device of the invention of several different types of RFID transponders, in “landscape” orientation, as a function of location of the transponder along a feed path of a hypothetical media printer.
• FIG. 8B is a test chart similar to that ofFIG. 8A but with the transponders in a “portrait” orientation.
• FIG. 9 is a test chart showing successful RFID transponder writes with respect to the position of an RFID transponder along a feed path of a label printer containing a magnetic coupling device according to one embodiment of the invention having a constant magnetic coupling device power level.
• FIG. 10 is a chart showing a range of acceptable RFID transponder locations and substrate dimensions for use with a magnetic coupling device according to one embodiment of the invention.
DETAILED DESCRIPTION
• 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 RFID transponder when one or more other transponders are in close proximity, without the need for physical isolation or cumbersome shielded housings or chambers.
• The invention is useful in the loading or reading of 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 on 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 communication 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 other type of printer 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 general space occupied by the transponder when it is being interrogated (sometimes herein termed the “transponder target area”).
• FIG. 1 illustrates by way of example only an implementation of the invention in a thermaltransfer label printer12 in which both printing and transponder communication are accomplished, but at different locations in the printer.
• As shown inFIG. 1, theprinter12 includes aprinthead sub-assembly15 comprising a conventionalthermal printhead14 andplaten roller16, as in a direct thermal printer for printing on thermally-sensitive media. Aweb24 of media, such as labels, tickets, tags or cards, is directed along afeed path26 to theprinthead14 where theprinthead14 applies on demand text and/or graphics under control of a computer or microprocessor (not shown). After being printed, the media may be peeled off theunderlying carrier substrate20 at atear bar32 and follows amedia exit path34. The liner orcarrier substrate20 for the media is guided out of theprinter12 by aroller36 where it exits the printer along anexit path38.
• When a thermal printer is configured for use as a thermal transfer printer, aribbon supply roll18 delivers a thermal transfer ribbon (not shown for clarity) betweenprinthead14 and the media onweb24. After use, the spent ribbon is collected on a take-up reel22.
• In accordance with an aspect of the present invention, the printer includes atransceiver42 and amagnetic coupling device1 located proximate themedia feed path26. As will be explained and illustrated in detail hereinafter, the system (includingtransceiver42 and magnetic coupling device1) forms a magnetic flux field pattern in the location of a transponder target area44 (seeFIG. 6A). The system is configured to establish at predetermined transceiver power levels a mutual magnetic coupling which is selective exclusively for a single transponder located in the transponder target area44.
• As labels or other media with embedded transponders move along themedia feed path26, through target area44, data may be read from and or written totransponder10. Information indicia then may be printed upon an external surface of the media as the media passes between theplaten roller16 and theprinthead14 by selective excitation of the heating elements in theprinthead14, as is well known in the art. When thethermal printer12 is configured as a direct thermal printer, the heating elements form image dots by thermochromic color change in the heat sensitive media; when thethermal printer12 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 betweenprinthead14 and the media onweb24 fromsupply roll18. Patters of printed dots thus form the desired information indicia on the media, such as text, barcodes or graphics.
• Media conveyance is well known in the art. Therefore themedia conveyance25 portion of the printer that drives the media with transponders along themedia feed path26 is not described in detail.
• Themagnetic coupling device1 and its manner of operation will now be described with reference toFIGS. 2-7. One embodiment of themagnetic coupling device1 is configured for use, for example, with 13.56MHz RFID transponders10.Transponders10 are bulk supplied on acarrier substrate20 in label, ticket, card or tag form with aprintable facestock30.
• Themagnetic coupling device1 comprises a magnetic flux generator and a magnetic field pattern former, as will be described. The magnetic flux generator may comprise one or more coils responsive to RF signals supplied by thetransceiver42. The coils may take the form of a planar elongated coil created, for example, by conductor(s) coupled with a coil support structure. The conductors and coil support structure may comprise, for example, a coil trace(s)50 on and or within a multi-layered printed circuit board (PCB)60. Coil trace(s)50 may be formed without sharp corners to minimize creation of impedance discontinuities.
• Because the wavelength at 13.56 MHz is approximately 22 meters, design of a small, low-cost antenna for coupling to an RFID transponder using electromagnetic radiation is difficult. Therefore, themagnetic coupling device1 is configured to mutually couple to RFID transponder(s) operating at frequencies with long wavelengths using only magnetic induction coupling. As will be described hereinafter, electric fields emitted bycoil trace50 are suppressed by a groundedE-field suppressor shield90.
• The dimensions of themagnetic coupling device1 and the number of turns, for example three to five turns, used in the coil(s) are determined in part by the intended range from and longitudinal dimensions of theRFID transponder10 which the magnetic field of the magnetic coupling device will selectively mutually inductively couple with.Capacitors80, for example surface mounted to thePCB60 local to the coils trace(s)50, may be used for impedance matching (for example, 50 ohm) and tuning of themagnetic coupling device1, to zero the imaginary component of impedance at a desired resonant frequency. Other impedance matching and or magnetic coupling device tuning components that may be applied include matching transformers, inductors and a tap of the magnetic coupling device coil. one or more resistor(s)85 may be used to adjust a Q-factor of the magnetic coupling device.
• TheE-field suppressor shield90 may be created, for example, by forming another conductive layer on one or both sides of thePCB60 containingcoil trace50, as shown inFIGS. 2, 3,4 and6A and6B. TheE-field suppressor shield90 may be formed as a gapped loop that covers the magnetic coupling device radiating coil trace(s)50 completely with the exception of a smallopen circuit100, as shown inFIGS. 1 and 2. The purpose of theopen circuit100 is to prevent Eddy current flow in theE-field suppressor shield90 which would cause signal losses.
• Without more, the coil trace(s) of themagnetic coupling device1 may be expected to emit magnetic flux lines in a generally omnidirectional toroid pattern about the coil trace(s)50. A transponder-selective magnetic field pattern former110 is provided to collect flux produced by the flux generator (coil trace(s)50 in the illustrated embodiment) and to form afield pattern70 in the location of a predetermined transponder target area44.
• FIG. 6A illustrates an arrangement wherein atransceiver42 andmagnetic coupling device1 are located in a printer having aprinthead14 and associatedplaten roller16 which are located proximate the transponder target area44. With theprinthead14 within or near the transponder target area44, a label or other media carrying a transponder can be interrogated (read and or write) and the carrying media can be printed in essentially the same space. This is important in on demand systems, particularly portable or compact systems, where it would be impractical to have a print station located remotely from the transponder interrogation station.
• The field pattern former110 increases the amount of magnetic flux by inserting into the field space a material of higher magnetic flux permeability than free space. The field pattern former110 has agap112 within and adjacent to which the field pattern is formed. Thegap112 is defined as areas of themagnetic coupling device1, and in the present embodiment particularly coverage of thecoil trace50, which are not covered by the field pattern former110. The resulting field pattern is therefore positioned and influenced by the configuration and position of thegap112. In theFIG. 6A embodiment, thegap112 may be, for example, approximately the width of one side of the coil traces50 or may be about 50% of the top surface area of the PCB60 (if thecoil trace50 is centered on the PCB60) and is located at the end of themagnetic coupling device1 nearest theprinthead14. Configurations that cover more or less of the coil traces50 and or, for example, all edges of thePCB50 are also usable to create amagnetic field pattern70 that matches a desired transponder target area44. A top view of the arrangement shown inFIG. 6A is illustrated inFIG. 7.
• Alternatively, a simplified RFID transponder read and or write system may be formed without printing capabilities by positioning amagnetic coupling device1 coupled to atransceiver42 proximate a media conveyance moving sequential RFID transponders through a target area44 of themagnetic coupling device1.
• Such an alternative embodiment is shown inFIG. 6B wherein thegap112 in coverage by a field pattern former110 is disposed intermediate the ends ofmagnetic coupling device1. TheFIG. 6B embodiment is configured for applications wherein an associated printing function in the same physical space is not necessary. TheFIG. 6B embodiment contemplates that any printing or other function to be performed is accomplished at another station. Theprinter12 illustrated inFIG. 1 and described above is an example of an execution of the invention wherein the interrogation of the transponders is accomplished at a distance from theprinthead14.
• The field pattern former110 may be formed using a material preferably having a magnetic relative permeability of 20 or more. The material may be, for example, a ferrite composition. Ferrite is a general name for a class of materials having a powdered, compressed, and sintered magnetic material having high resistivity, consisting chiefly of ferric oxide combined with one or more other metals. The high resistance of ferrite compositions makes eddy-current losses extremely low at high frequencies. Examples of ferrite compositions include nickel ferrite, nickel-cobalt ferrite, manganese-magnesium ferrite and yttrium-ion garnet. The field pattern former110 may be a rubberized flexible ferrite, ferrite polymer film or stennite material. Flex Suppressor (trademark) material available from Tokin EMC is also a suitable material. The selected field pattern former110 may be connected to thePCB60, for example, with an adhesive. Alternatively, the field pattern former110 may be applied in a liquid or semi liquid form, upon the desired areas of thePCB60 or other coil support structure and solidified and or cured to leave, for example, only a desiredgap112 uncovered by the material comprising the field pattern former110.
• The embodiment shown inFIGS. 4-7 may have a field pattern former110 of flexible ferrite. For example, for the embodiment shown inFIGS. 4, 5,6A and7, the field pattern former110 covers themagnetic coupling device1 area of the bottom side of thePCB60 and extends, wrapped about thePCB60 in a single portion to cover approximately one half of the top side of the coil traces50, resulting in the concentration of flux and the formation of amagnetic field pattern70 within and adjacent thegap112.
• In accordance with an aspect of the present invention, the system is configured to establish at predetermined transceiver power levels a mutual magnetic coupling which is selective exclusively for a single transponder located in the predetermined transponder target area44. As will become evident from the description ofFIGS. 8A and 8B, the mutual coupling will vary depending upon the mechanical and electrical characteristics of the coupled transponder, the applied power levels of thetransceiver42, the size and other properties of anymedia20 which supports the transponder, the characteristics of the pattern former, and other factors.
• Obviously, at some exaggerated transceiver power level transponders outside the transponder target area44 may be excited. However, by this invention, at power levels in the range of normal transceiver operations, and, for example, allowing for a 3 dB or greater tolerance margin, the mutual coupling created will be highly selective for thetransponder10 in the transponder target area44.
• The compact size of themagnetic coupling device1 and the lack of any other shielding requirements allows the economical addition of sequentially spaced multiple RFID transponder format read and or write capability to a range of sequential RFID transponder transport devices, for example label printers, to form a selective transponder communication module.
• Because themagnetic coupling device1 may be configured to be selective exclusively for a single transponder located in the transponder target area44, it is now possible by this invention to use a web of media having transponders which are closely spaced on the web, as shown in the figures of this application. Prior to this invention it was extremely difficult to communicate with just one transponder in a closely spaced series of transponders without simultaneously activating adjacent transponders.
• FIGS. 8A and 8B are test charts showing relative power levels delivered for activation by a magnetic coupling device according to the invention of several different types of rectangular transponders as a function of location along thefeed path26 ofprinter12, and the orientation of these transponders along theweb24.FIG. 8A shows data for selected transponders in the “landscape” orientation similar toFIG. 7.FIG. 8B shows data for selected transponders in the “portrait” orientation, in which the long axis of the transponder is alongfeed path26. TheFIGS. 8A and 8B charts reveal how highly sensitive the system of the invention is for a transponder located in the transponder target area44, and how highly non-sensitive the system is for any transponder outside the target area44.
• The different curves in theFIGS. 8A and 8B charts are associated with different commercially available 13.56 MHz RFID transponders, as labeled. Here, the RFID integrated types, antenna geometries and/or manufacturers of the selected transponders are not in themselves important, as they are used only as examples to demonstrate the effect of the invention. The curves themselves reflect how the mutual coupling with the various selected transponders results in different position sensitivity to excitation within the transponder target area44.
• The different curves shown in the charts ofFIGS. 8A and 8B are not magnetic field distributions, but rather estimates of the available power margin over the reading threshold for each type of transponder as a function of orientation and position relative the target area44. This measurement is made by applying a constant-power RF signal to themagnetic coupling device1 through a variable RF attenuator; then increasing the attenuation in decibels until the reading of data fromtransponder10 stops; and finally recording the attenuation value as a function of position and orientation on the appropriate chart inFIG. 8A or8B. These charts are used to select an optimal location within the labels, tickets, tags or cards for embedding the transponders, and determine the minimum allowable spacing between transponders along theweb24.
• To better understand theFIGS. 8A and 8B charts, an explanation with respect to one of the curves, identified as describing the characteristics of a “Lintec I*CODE 16×47 mm” RFID transponder, will be made in detail. In the example shown inFIG. 8A, the curve begins at a first position where the front edge of the coil of thetransponder10 is located in the target area44 at a distance of 16 mm from a reference “0” line defined by the sharp corner edge of thetear bar32. At this point, the leading edge of thetransponder10 antenna coil is also located 2 mm back of a second reference line labeled “print line” ofprinthead14. The print line is analogous to the print line inFIG. 6A where theprinthead14 engages a media to be printed. The Lintec I*CODE 16×47 mm transponder curve shows that, at the designated transceiver test power level, the transponder cannot be activated.
• In this printer configuration, moving the transponder back only 2 mm to aposition 18 mm from the reference “0” line and 4 mm behind the “print line”, the transponder is responsive until the test transceiver power level is suppressed 6 dB. If the transponder is moved back another 4 mm, to aposition 8 mm behind the “print line” the transceiver test power level must be attenuated a full 13 dB before the transponder will not respond normally.
• The back side of the Lintec I*CODE 16×47 mm curve is equally steep. With the transponder moved back only 14 mm from the print line; the transponder responds normally with the test transceiver power level suppressed up to 12 dB. However, with the transponder moved back just 20 mm from the print line, the transponder will not respond to the transceiver delivering the test power level.
• The transponder is 16 mm wide and 47 mm long. In a landscape orientation with respect to the direction of media travel, as soon as the leading edge of the transponder coil clears either side of a roughly 17 mm target area, it is unable to be activated. The other curves demonstrate responses of a range of different RFIDs using the same test configuration. Allowing for the possible use of all the different transponders with the same magnetic coupling device configuration provides a usable target area of 25 mm or less. With this degree of selectivity provided by the present invention, transceiver power levels can be raised to provide a comfortable safety margin without concern for energizing adjacent transponders even when the transponders are closely spaced. Conversely, the target area is wide enough that pinpoint positioning of the transducer is not necessary for reliable communication.
• Results in the portrait orientation shown inFIG. 8B are less closely defined. When the longer dimension of the RFID transponder is along thefeed path26, themagnetic coupling device1 may inductively couple along any portion of the extended length ofRFID transponder10, even if a majority of the transponder area is outside the target area44.
• Another way to measure the system performance is shown inFIG. 9.FIG. 9 is a test chart demonstrating the number of successful write operations out of ten attempts as a typical Phillips I*Code (trademark) 13.56 MHz RFID transponder with a 12×38 mm antenna coil is moved across the print media path of a Zebra Technologies, Inc. model R402 label printer/RFID programmer, equipped with amagnetic coupling device1 according to the present invention. The RFID transponder location for each test series is shown relative to either side of the printer's tear bar (representing “0” on the tag position axis), along the print media path. Results of three different test series taken with 13.56 MHz RF excitation and themagnetic coupling device1 resonant at frequencies 13.31, 13.56, and 13.81 MHz respectively are shown for each location at 1 mm increments.FIG. 9 demonstrates that the focusedmagnetic field pattern70 generated by the present invention may be configured to cause successful inductive coupling with an RFID transponder only within a very closely defined target area, permitting the RFID transponders to be closely sequentially spaced together without causing read and or write collisions through accidental activation of multiple transponders.
• FIG. 10 shows an RFID transponder placement map, also for I*Code 12×38 mm RFID transponders, derived from testing on the model R402 similar to that shown inFIGS. 8 and 9 for a plurality of different transponder locations. Labels having a width “a” of at least 21 mm; a length “b” of between 29 and 102 mm; a lead edge distance “y” of between 8 and 22 mm; and a label spacing “s” of a minimum of 1 mm are possible. From this form of testing, specific to each RFID transponder, a minimum periodicity “P” for a specific RFID transponder may be calculated as P=a+s. The value of “P” then becomes the same as the minimum RFID transponder spacing, leading edge to leading edge (as well as the minimum label repeat distance along the web) required to ensure that read and or write collisions do not occur for the selected RFID transponder andmagnetic coupling device1 combination.
• The magnetic field pattern former110 may be easily adjusted for different desired magnetic field directions and or shapes during manufacture by varying the size, configuration and or location of the magnetic field pattern former110 applied to thePCB60 or other coil support structure.

  Table ofParts

  1	magnetic coupling device
  10	transponder
  12	printer
  14	printhead
  15	printhead sub-assembly
  16	platen roller
  18	supply roll
  20	carrier substrate
  22	take upreel
  24	web
  25	media conveyance
  26	feed path
  30	facestock
  32	tear bar
  34	label exit path
  36	roller
  38	carrier exit path
  42	transceiver
  44	target area
  50	coil trace
  60	printedcircuit board
  70	field pattern
  80	capacitors
  85	resistor
  90	E-field suppressor shield
  100	open circuit
  110	field pattern former
  112	gap

• Where in the foregoing description reference has been made to ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.
• While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant's general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.

Claims (38)

1. A method of establishing communication between a transceiver and a single RFID transponder located in a predetermined confined transponder target area, comprising:

generating a magnetic flux field which varies in response to a radio frequency input signal; and

collecting and forming said magnetic field pattern in the location of said transponder target area; and

establishing at predetermined power levels of the transceiver a mutual magnetic coupling which is selective exclusively for a single transponder located in said transponder target area.

2. The method defined byclaim 1 including locating in said magnetic flux field a ferrite structure having a gap, said field pattern being formed within and adjacent to said gap.

3. The method defined byclaim 1 including transporting a web of labels through said target area, at least some of which labels have an RFID transponder, and wherein said method includes printing on said labels.

4. The method defined byclaim 1 including suppressing electric fields associated with said generating of said magnetic flux field, which fields would otherwise reach said target area.

5. A magnetic coupling device, comprising:

a coil having a first side and a second side;

a magnetic field pattern former; and

the magnetic field pattern former covering the first side of the coil and at least a portion of the second side of the coil.

6. The magnetic coupling device ofclaim 5, wherein the coil is formed as at least a first trace on a printed circuit board.

7. The magnetic coupling device ofclaim 5, wherein the magnetic field pattern former has a magnetic permeability of at least 20.

8. The magnetic coupling device ofclaim 5, wherein the magnetic field pattern former is ferrite.

9. The magnetic coupling device ofclaim 8, wherein the ferrite is flexible and the ferrite is applied to cover the first side of the coil, around at least a first edge and at least a portion of a second side of the coil.

10. The magnetic coupling device ofclaim 9, wherein the portion of the second side of the coil that is covered by the ferrite is at least 30 percent.

11. The magnetic coupling device ofclaim 5, further including a first RF shield covering a first side of the coil.

12. The magnetic coupling device ofclaim 11, wherein the first RF shield has a loop shape with an open circuit.

13. The magnetic coupling device ofclaim 11, wherein the first RF shield is coupled to an electrical ground.

14. The magnetic coupling device ofclaim 11, further including a second RF shield covering a second side of the coil.

15. The magnetic coupling device ofclaim 6, further including a first RF shield covering the first trace; the first RF shield formed as a second trace on the printed circuit board.

16. The magnetic coupling device ofclaim 5, further including:

at least one capacitor in one of series with the coil for series resonance and across the coil for parallel resonance.

17. A planar coil printed circuit board magnetic coupling device, comprising:

a first trace on the printed circuit board forming the planar coil;

a first RF shield, the first RF shield insulated from and covering a first side of the first trace;

a second RF shield, the second RF shield insulated from and covering a second side of the first trace; and

a magnetic field pattern former covering a first side of the printed circuit board area covered by the first trace and at least a portion of a second side of the printed circuit board area covered by the first trace.

18. The magnetic coupling device ofclaim 17, wherein:

the first RF shield is a second trace on the printed circuit board.

19. The magnetic coupling device ofclaim 17, wherein:

the first RF shield has an open circuit.

20. The magnetic coupling device ofclaim 17, wherein:

the magnetic field pattern former has a magnetic permeability of at least 20.

21. The magnetic coupling device ofclaim 20, wherein:

the magnetic field pattern former is flexible ferrite.

22. A method for increasing planar selectivity of a magnetic coupling device, comprising the steps of:

covering an area of the magnetic coupling device where a magnetic field emanation is not desired with a magnetic field pattern former.

23. The method ofclaim 22, wherein the magnetic field pattern former has a magnetic permeability of at least 20.

24. The method ofclaim 22, wherein the magnetic field pattern former is flexible ferrite.

25. The method ofclaim 24, wherein the flexible ferrite is arranged to cover a first side of the magnetic coupling device, a first edge of the magnetic coupling device and at least a portion of a second side of the magnetic coupling device.

26. A transponder communication selective module, comprising:

a magnetic coupling device partially covered by a magnetic field pattern former; located proximate a media feed path;

the media feed path arranged to carry a plurality of transponders sequentially past the magnetic coupling device.

27. The apparatus ofclaim 26, further including a printhead arranged to apply indicia upon an outer surface of the transponders.

28. The apparatus ofclaim 26, wherein the outer surface is a label.

29. The apparatus ofclaim 26 wherein, the magnetic coupling device is formed as at least a first trace on a printed circuit board.

30. The apparatus ofclaim 26, wherein the magnetic field pattern former has a magnetic permeability of at least 20.

31. The apparatus ofclaim 26, wherein the magnetic field pattern former is ferrite.

32. The apparatus ofclaim 31, wherein the ferrite is flexible and the ferrite is applied to cover the first side of the magnetic coupling device, around at least a first edge and at least a portion of a second side of the magnetic coupling device.

33. The apparatus ofclaim 32, wherein the portion of the second side of the magnetic coupling device that is covered by the ferrite is at least 30 percent.

34. The apparatus ofclaim 26, further including a first RF shield covering a first side of the magnetic coupling device.

35. The apparatus ofclaim 34, wherein the first RF shield has a loop shape with an open circuit.

36. A system for sequentially communicating with a plurality of RFID transponders, comprising:

a magnetic coupling device located proximate a media supply path arranged to transport RFID transponders sequentially past the magnetic coupling device;

the magnetic coupling device having a magnetic field pattern former arranged to minimize magnetic flux emanation away from the magnetic coupling device, except through a gap; and

the gap dimensioned to enable inductive coupling with only a single RFID transponder at a time.

37. A method for selectively communicating with a desired RFID transponder among a plurality of RFID transponders, comprising the steps of:

energizing a magnetic coupling device; and

passing the desired RFID transponder through a magnetic flux field generated by the magnetic coupling device;

the magnetic coupling device covered on a first side and at least a portion of a second side by a magnetic field pattern former whereby a magnetic flux field generated by the magnetic coupling device is in an area small enough so that only the desired RFID transponder is energized.

38. The method ofclaim 37, wherein the magnetic field pattern former is formed from a flexible ferrite material.

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