Patent Publication Number: US-2006012387-A1

Title: Systems and methods for testing radio frequency identification tags

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of U.S. Provisional Application No. 60/583,402, filed Jun. 29, 2004 (Atty. Dkt. No. 1689.0630000), which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to radio frequency identification tags, and more specifically to testing of radio frequency identification tags.  
      2. Background Art  
      Currently, radio frequency identification (RFID) tags manufactured in high volume are difficult to test. For example, in the presence of a large number of tags, such as in a tag assembly line, it may be difficult to isolate an individual tag for testing. In other words, a standard read signal used to test a tag in a population of tags not only powers the tag under test, but the other tags in range. Thus, the effectiveness of the tag test may be diminished by the possibility of responses from the other tags in range.  
      Spatial isolation of a particular tag under test is difficult to accomplish. In some test systems, near field cavity coupling (evanescent coupling) is used to spatially isolate the radio frequency signal/field used to test a tag to sub-wavelength dimensions. However, this is complex, expensive, and often does not work sufficiently to read one and only one tag.  
      Thus, what is needed is a method, system, and apparatus for improved testing of individual RFID tags.  
     BRIEF SUMMARY OF THE INVENTION  
      Methods, systems, and apparatuses are described for the testing of radio frequency identification (RFID) tags alone or in the presence of other tags.  
      In an aspect of the present invention, methods and systems for testing tags in volume are described. According to a first embodiment, an array of radiation sources is present. Each radiation source in the array corresponds to a tag in a plurality of tags. A plurality of radiation sources in the array controllably emit radiation to their corresponding tag to inhibit operation of an integrated circuit of their corresponding tag. A first radiation source in the array does not emit radiation to its corresponding tag. The tag corresponding to the first radiation source is tested, as its operation is not inhibited by radiation. Thus, the tag may be reliably tested in an isolated manner, even in the presence of other tags.  
      Each tag in the array may be tested in this manner, by stopping the emission of radiation to the tag by the corresponding radiation source during testing of the tag.  
      According to a second embodiment, an array of blocking elements is present. Each blocking element in the array corresponds to a tag in a plurality of tags. A blocking element in the array controllably inhibits radiation emitted by a radiation source to allow operation of an integrated circuit of its corresponding tag. A first blocking element in the array inhibits radiation from being incident upon its corresponding tag. The tag corresponding to the first blocking element is tested, as its operation is not inhibited by radiation. Thus, the tag may be reliably tested in an isolated manner, even in the presence of other tags.  
      Each tag in the array may be tested in this manner, by inhibiting radiation from being incident upon the tag by the corresponding blocking element during testing of the tag.  
      These and other objects, advantages and features will become readily apparent in view of the following detailed description of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES  
      The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.  
       FIG. 1  shows a plan view of an example radio frequency identification (RFID) tag.  
       FIG. 2  shows an example web of tag substrates that is a continuous roll type.  
       FIG. 3  shows an addressable lighting system for radiating tags under test, according to an example embodiment of the present invention.  
       FIG. 4  shows a tag testing system including an addressable lighting system, according to an example embodiment of the present invention.  
       FIGS. 5 and 6  show an addressable lighting system that includes radiation sources for testing of a row of tags in a web, according to an example embodiment of the present invention.  
       FIG. 7  shows an addressable blocking system for inhibiting radiation from being incident upon tags under test, according to an example embodiment of the present invention.  
       FIG. 8  shows a tag testing system including an addressable blocking system, according to an example embodiment of the present invention.  
       FIGS. 9 and 10  show an addressable blocking system that includes blocking elements for testing of a row of tags in a web, according to an example embodiment of the present invention.  
       FIG. 11  shows a tag testing system in which an addressable lighting system and an addressable blocking system are controlled by a common controller, according to an example embodiment of the present invention.  
       FIG. 12  shows a tag testing system in which an addressable lighting system and an addressable blocking system are controlled by different controllers, according to an example embodiment of the present invention.  
    
    
      The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.  
     DETAILED DESCRIPTION OF THE INVENTION  
      I. Overview  
      The present invention relates to the testing of individual RFID tags located in a group of RFID tags. Embodiments of the present invention use radiation sources to inhibit operation of tags. A single tag (or multiple tags, depending on the type of test) is not radiated, and thus its operation is not inhibited. This “isolated” tag is then tested, by any desired technique, for proper operation. For example, in an embodiment, the isolated tag may be tested by a reader that transmits a communication signal directed to the isolated tag, including “near-field” read or “far-field” read configurations.  
      According to embodiments of the present invention, individual RFID tags located in a group of tags may be isolated and tested that are much less than a wavelength of the communication signal away from each other.  
      The present invention is applicable to any type of RFID tag.  FIG. 1  shows a plan view of an example radio frequency identification (RFID) tag  100 . Tag  100  includes a substrate  102 , an antenna  104 , and an integrated circuit (IC)  106 . Antenna  104  is formed on a surface of substrate  102 . IC  106  includes one or more integrated circuit chips/dies and/or other electronic circuitry. IC  106  is attached to substrate  102 , and is coupled to antenna  104 . IC  106  may be attached to substrate  102  in a recessed and/or non-recessed location. IC  106  controls operation of tag  100 , and transmits signals to, and receives signals from RFID readers using antenna  104 . The present invention is applicable to tag  100 , and to other types of tags.  
      Volume production of RFID tags, such as tag  100 , is typically accomplished on a printing web based system. For example, the tags are assembled in a web of substrates, which may be a sheet of substrates, a continuous roll of substrates, or other group of substrates. For example,  FIG. 2  shows a plan view of an example web  200  that is a continuous roll type. For example, web  200  may extend further in the directions indicated by arrows  210  and  220 . As shown in  FIG. 2 , web  200  includes a plurality of tags  100   a - p.  In the example of  FIG. 2 , the plurality of tags  100   a - p  in web  200  is arranged in a plurality of rows and columns. The present invention is applicable to any number of rows and columns of tags, and to other arrangements of tags.  
      On a web, such as web  200 , RFID tags are typically assembled/placed as close to each other as possible to maximize throughput, thus making the process of reading and testing individual tags difficult. Inline testing of tags at the location of tag manufacture is key to reducing the cost of tags. For example, a problem in reading one tag in a dense array of tags is a problem of sub-wavelength imaging. In a manufacturing web, tags may be printed and assembled in a grid where the tag-to-tag spacing is much less that the wavelength of the radio waves used to excite the tags. Because of the close spacing, it is very difficult to localize a reader field to excite only one tag.  
      A shorter wavelength electromagnetic signal, that can be relatively easily localized to just one tag, can be used to read a tag under test. For example, in an embodiment, tags are stimulated with a shorter wavelength radio frequency signal. However, while the tag integrated circuits can potentially use and decode a wide band of RF frequencies, the tag antenna that couples to this signal will typically operate well at only the relatively long wavelength for which they were designed.  
      In another embodiment, a photosensitivity of the integrated circuit of the tag, which may be a silicon die or chip for example, is used. Integrated circuits are naturally sensitive to light. Photons from infrared frequencies through X-ray frequencies are able to generate photo-induced charge carriers (electrons-hole pairs). If the flux of light is high enough, these rogue photoelectrons and holes can inhibit the operation of the tag. This phenomenon can be exploited in the manufacturing process, such as in testing of tags.  
      In tag testing embodiments, a transmitter, such as a reader, can transmit a long wavelength RF read signal to the tags on the manufacturing web. In doing so, the tag under test will be activated (assuming it is operational) and many of its neighbors will also be activated. However, to ensure that only the tag under test is activated and read, in an embodiment of the present invention, all tags except for the tag under test are illuminated with a radiation source, such as a light source. Like radio waves, light is an electromagnetic wave, but has a wavelength of hundreds of nanometers, rather than tens of inches in wavelength for RF signals typically used to read tags. Because the wavelength of light is relatively short, focusing and directing light on a single tag is less complicated.  
      According to embodiments of the present invention, a photosensitivity property of a tag electrical circuit, such as IC  106 , is used to enable testing of individual tags. In an embodiment, radiation is directed onto a tag to inhibit tag operation. For example, light may be directed onto the tags. Directing light onto the tag can inhibit tag operation despite the fact that the tag may be receiving sufficient RF power to operate.  
      II. Addressable Lighting System  
       FIG. 3  shows a plan view of an addressable lighting system  300 , according to an example embodiment of the present invention. System  300  can be used to inhibit tags in a plurality of tags (such as the plurality of tags  100   a - p  in web  200  shown in  FIG. 2 ) from responding to read requests, except for a tag under test. For example, system  300  shows a four-by-four array of radiation sources  302   a - p  (e.g., light sources) that corresponds to the plurality of tags  100   a - p  shown in  FIG. 2 . Radiation sources  302  are attached to a radiation source mount  304 . The array of radiation sources  302  of  FIG. 3  may extend further in the directions of arrows  210  and  220  (i.e., “up” and “down” web) as needed to cover additional tags of web  200 . Furthermore, system  300  can have any width of radiation sources  302  to cover webs  200  that are wider (i.e., “cross-web”) (e.g., have additional columns of tags) or are less wide (e.g., have fewer columns of tags). Furthermore, the pitch of radiation sources  302  (e.g., the distance between centers of adjacent radiation sources  302 ) can be adjusted for denser or less dense arrays of tags in web  200 . Any number of radiation sources  302  may be present as needed, including ones, tens, hundreds, thousands, and more.  
      During test, all but one of radiation sources  302   a - p  emit radiation (e.g., light) that inhibits operation of all of the plurality of tags  100   a - p  of web  200 , except for one. The one tag of tags  100   a - p  that does not receive radiation can be tested, as its operation is not inhibited. If that tag is found to be defective it can be subsequently sorted out in the production line. For example, a defective tag can be marked (e.g., inked), or its location can be stored (such as in storage of a computer system), for later locating of the defective tag and disposal or recycling.  
       FIG. 4  shows a tag testing system  400 , according to an example embodiment of the present invention. In  FIG. 4 , system  400  includes addressable lighting system  300 , a controller  402 , and a reader  404 .  FIG. 4  shows a side view of addressable lighting system  300  and web  200 . Controller  402  controls addressable lighting system  300 , sending a signal or signals to addressable lighting system  300  to direct addressable lighting system  300  to emit radiation to inhibit operation of dies  106  of tags  100  in web  200 , except for a particular tag  100  under test. Reader  404  includes an antenna  406 , and is used to read or interrogate the particular tag  100  under test. Antenna  406  broadcasts a read signal  408  which is received by the particular tag  100 , and receives a proper response from the particular tag  100 , if the particular tag  100  is properly operational. Controller  402  controls addressable lighting system  300  to cycle through testing of all tags  100  in web  200  that are desired to be tested.  
      Reader  404  can test tags  100  according to any communications protocol/algorithm, as required by the particular application. For example, reader  404  can communicate with tags  100  according to a binary algorithm, a tree traversal algorithm, or a slotted aloha algorithm. Reader  404  can communicate with tags  100  according to a standard protocol, such as Class 0, Class 1, Gen 2, and any other known or future developed RFID communications protocol/algorithm.  
      In an example embodiment, by default, all radiation sources  302  emit light, thus shutting down all the tags. A command sent from controller  402  (which may be a computer, processor, logic, or other device, for example) shuts off one of the radiation sources  302 , thus allowing the corresponding tag to be read and tested. By sequentially instructing different ones of radiation sources  302  to shut off, all the tags can be individually tested.  
       FIG. 5  shows an example addressable lighting system  500  that includes radiation sources  302   a - d  for testing of a row of tags  100   a - d  in web  200 , according to an example embodiment of the present invention. Addressable lighting system  500  may include further rows of radiation sources  302  corresponding to further rows of tags  100  in web  200 , to inhibit operation of selected tags  100 . As shown in  FIG. 5 , in a first iteration of a tag test algorithm, radiation sources  302   b - d  are emitting radiation to inhibit operation of ICs  106   b - d  of tags  100   b - d,  under the direction of controller  402 . Thus, tag  100   a  may be tested, as radiation source  302   a  is not emitting radiation, and therefore operation of IC  106   a  tag  100   a  is not inhibited.  
      In a next iteration of a tag test algorithm, as shown in  FIG. 6 , radiation sources  302   a,    302   c,  and  302   d  are emitting radiation to inhibit operation of ICs  106   a,    106   c,  and  106   d  of tags  100   a,    100   c,  and  100   d,  respectively, under the direction of controller  402 . Thus, tag  100   b  may be tested, as radiation source  302   b  is not emitting radiation, and therefore operation of IC  106   b  of tag  100   b  is not inhibited. This algorithm may be continued to test tags  100   c  and  100   d,  and further tags  100  in additional rows of web  200 , if present.  
      Any type of radiation source can be used for radiation source  302 . For example, silicon ICs are sensitive to light from infrared frequencies and greater frequencies. Thus, radiation sources  302  can be used that emit radiation/light somewhere in these frequencies. For example, radiation sources  302  that emit light in a band from infrared (˜800 nm) to red (˜600 nm), or emit light at short wave ultraviolet (&gt;350 nm) may be used. For example, a radiation source can be a light emitting diode (LED), a liquid crystal display (LCD), a laser, or any other applicable type of radiation source.  
      III. Addressable Blocking System  
       FIG. 7  shows a plan view of an addressable blocking system  700 , according to an example embodiment of the present invention. System  700  can be provided between a radiation source (such as the radiation sources  302   a - p  shown in  FIG. 3 ) and a plurality of tags (such as the plurality of tags  100   a - p  in web  200  shown in  FIG. 2 ) to selectively block radiation that is emitted from the radiation source. For example, system  700  shows a four-by-four array of blocking elements  702   a - p  that corresponds to the plurality of tags  100   a - p  shown in  FIG. 2 . The array of blocking elements  702  of  FIG. 7  may extend further in the directions of arrows  210  and  220  (i.e., “up” and “down” web) as needed to cover additional tags of web  200 . Furthermore, system  700  can have any width of blocking elements  702  to cover webs  200  that are wider (i.e., “cross-web”) (e.g., have additional columns of tags) or are less wide (e.g., have fewer columns of tags). Furthermore, the pitch of blocking elements  702  (e.g., the distance between centers of adjacent blocking elements  702 ) can be adjusted for denser or less dense arrays of tags in web  200 . Any number of blocking elements  702  may be present as needed, including ones, tens, hundreds, thousands, and more.  
      During test, all but one of blocking elements  702   a - p  allow radiation (e.g., light) to inhibit operation of all of the plurality of tags  100   a - p  of web  200 , except for one. The one tag of tags  100   a - p  that does not receive radiation can be tested, as its operation is not inhibited. If that tag is found to be defective it can be subsequently sorted out in the production line. For example, a defective tag can be marked (e.g., inked), or its location can be stored, for later locating of the defective tag and disposal or recycling.  
      A blocking element  702  may block light in any of a variety of ways. According to an embodiment, a blocking element  702  blocks light based on the polarity of the blocking element  702 . For example, the polarity of blocking elements  702  at steady state may be such that blocking elements  702  allow light to pass therethrough. The polarity of a blocking element  702  may be changed by a stimulus (e.g., an electrical, magnetic, or chemical stimulus). The stimulus may be applied to all but one of blocking elements  702 , causing all of the blocking element  702  to block light, except for one. In another example, the polarity of blocking elements  702  at steady state may be such that blocking elements  702  block light. A stimulus may be applied to a blocking element  702 , causing that blocking element to allow light to pass therethrough.  
       FIG. 8  shows tag testing system  400 , according to another example embodiment of the present invention. In  FIG. 8 , system  400  includes lighting system  800 , addressable blocking system  700 , controller  402 , and reader  404 .  FIG. 8  shows a side view of lighting system  800 , addressable blocking system  700 , and web  200 . Lighting system  800  may include a single radiation source  802 , as shown in  FIG. 8 , or any other suitable number of radiation sources.  
      Controller  402  controls addressable blocking system  700 , sending a signal or signals to addressable blocking system  700  to direct addressable blocking system  700  to block radiation from being incident upon a particular tag  100  under test. For instance, addressable blocking system  700  may prevent radiation emitted from radiation source  802  from being incident upon the particular tag  100 , while allowing the radiation to be incident upon other tags in web  200 . Addressable blocking system  700  prevents radiation emitted from radiation source  802  from inhibiting operation of the particular tag  100 .  
      Reader  404  includes an antenna  406 , and is used to read or interrogate the particular tag  100  under test. Antenna  406  broadcasts a read signal  408  which is received by the particular tag  100 , and receives a proper response from the particular tag  100 , if the particular tag  100  is properly operational. Controller  402  controls addressable blocking system  700  to cycle through testing of all tags  100  in web  200  that are desired to be tested.  
       FIG. 9  shows an example addressable blocking system  900  that includes blocking elements  702   a - d  for testing of a row of tags  100   a - d  in web  200 , according to an example embodiment of the present invention. Addressable blocking system  900  may include further rows of blocking elements  702  corresponding to further rows of tags  100  in web  200 , to inhibit operation of selected tags  100 . As shown in  FIG. 9 , in a first iteration of a tag test algorithm, blocking elements  702   b - d  are allowing radiation to inhibit operation of ICs  106   b - d  of tags  100   b - d,  under the direction of controller  402 . Thus, tag  100   a  may be tested, as blocking element  702   a  is blocking radiation, and therefore operation of IC  106   a  tag  100   a  is not inhibited.  
      In a next iteration of a tag test algorithm, as shown in  FIG. 10 , blocking elements  702   a,    702   c,  and  702   d  are allowing radiation to inhibit operation of ICs  106   a,    106   c,  and  106   d  of tags  100   a,    100   c,  and  100   d,  respectively, under the direction of controller  402 . Thus, tag  100   b  may be tested, as blocking element  702   b  is blocking radiation, and therefore operation of IC  106   b  of tag  100   b  is not inhibited. This algorithm may be continued to test tags  100   c  and  100   d,  and further tags  100  in additional rows of web  200 , if present.  
      Any type of blocking element can be used for blocking element  702 . For example, an opaque or translucent object may be inserted between radiation source  802  and a tag  100  to inhibit radiation emitted from radiation source  802  from being incident upon the tag  100 . The opaque or translucent object may be removed to allow radiation to inhibit operation of the tag  100 .  
      According to an example embodiment, blocking element  702  is a material whose opacity is controllable, such as a polarized glass, according to an electrical or magnetic stimulus. In another example embodiment, blocking element  702  is a mechanical structure, such as a lever, that moves in and out of the radiation.  
      IV. Other Embodiments  
       FIGS. 11 and 12  show that addressable lighting system  300  and addressable blocking system  700  may be included in the same tag testing system  400 . In the example embodiment of  FIG. 11 , addressable lighting system  300  and addressable blocking system  700  are controlled by a common controller  402 . Controller  402  controls addressable lighting system  300 , sending a signal or signals to addressable lighting system  300  to direct addressable lighting system  300  to emit radiation to inhibit operation of dies  106  of tags  100  in web  200 , except for a particular tag  100  under test. Controller  402  controls addressable blocking system  700  to direct addressable blocking system  700  to block radiation from being incident upon the particular tag  100  under test. For instance, addressable blocking system  700  may prevent radiation emitted from neighboring radiation sources  302  from inhibiting operation of the tag  100  under test. Addressable blocking system  700  may prevent radiation inadvertently emitted (e.g., leaking) from the radiation source  302  corresponding to the tag  100  under test from being incident upon the tag  100  under test.  
      As depicted in  FIG. 11 , controller  402  may use the same control signal to control addressable lighting system  300  and addressable blocking system  700 . However, the scope of the present invention is not limited in this respect. According to an embodiment, addressable lighting system  300  receives a signal from controller  402  that is inverted as compared to the signal received by addressable blocking system  700 . In another embodiment, addressable lighting system  300  serves as a backup system to addressable blocking system  700 , or vice versa. For example, controller  402  may enable the addressable functionality of lighting system  300  or blocking system  700  and disable the addressable functionality of the other. If controller  402  disables the addressable functionality of lighting system  300 , then radiation sources  302   a - p  are not selectively controlled. Instead, controller  402  controls radiation sources  302   a - p  using a common control signal. If controller  402  disables the addressable functionality of blocking system  700 , then blocking elements  702   a - p  are not selectively controlled. Instead, controller  402  controls blocking elements  702  using a common control signal.  
      In an example embodiment, by default, all radiation sources  302  emit light and all blocking elements  702  allow light to pass therethrough, thus shutting down all the tags. A command sent from controller  402  shuts off one of the radiation sources  302  and/or instructs one of the blocking elements  702  to block light, thus allowing a corresponding tag to be read and tested. By sequentially instructing different ones of radiation sources  302  to shut off and/or different ones of blocking elements  702  to block light, all the tags can be individually tested.  
      In the example embodiment of  FIG. 12 , addressable lighting system  300  and addressable blocking system  700  are controlled by respective controllers  402   a  and  402   b.  For example, controllers  402   a  and  402   b  may operate independently of each other. In another example, controllers  402   a  and  402   b  may operate in synchronicity.  
      According to an embodiment, addressable lighting system  300  serves as a backup system to addressable blocking system  700 , or vice versa. For example, first controller  402   a,  which controls addressable lighting system  300 , and second controller  402   b,  which controls addressable blocking system  700 , may be communicatively coupled. If first controller  402   a  detects an error associated with addressable lighting system  300 , then first controller  402   a  may transmit an error signal to second controller  402   b.  Second controller  402   b  may then turn on the addressable functionality of addressable blocking system  700  or verify that the addressable functionality of addressable blocking system  700  is enabled. If second controller  402   b  detects an error associated with addressable blocking system  700 , then second controller  402   b  may transmit an error signal to first controller  402   a.  First controller  402   a  may then turn on the addressable functionality of addressable lighting system  300  or verify that the addressable functionality of addressable lighting system  300  is enabled.  
      V. Conclusion  
      While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.