Method and apparatus for RFID communication

Abstract

A plurality of battery-operated transceivers encapsulated by lamination to form a sheet of independent transceivers is tested in a two piece fixture that forms an enclosure surrounding each in-sheet transceiver. Each enclosure has an antenna for transmitting a command signal to the transceiver at a known power level and for receiving a reply message from the transceiver containing a power level measurement made by the transceiver. Test methods using the fixture of the present invention are also described.An RFID tag and interrogator may each include a transmitter and a receiver. The tag and interrogator may communicate with each other at different frequency bands and may communicate in accordance with a wireless communication protocol.

1. A method of testing the RF communication operation of an RF transponder, comprising the steps of:
 providing a sheet characterized by first and second opposite faces and a thickness;   mounting on the sheet an RF transponder that includes a transponder RF antenna;   positioning a first RF shield so as to abut the first face of the sheet;   positioning a second RF shield so as to abut the second face of the sheet, the second RF shield being in the shape of a cup having a mouth abutting said second face, wherein the first and second RF shields are positioned so that the first and second RF shields together form a closed cavity which completely surrounds and encloses the transponder RF antenna except where the thickness of the sheet separates the first RF shield from the mouth of the second RF shield, wherein said thickness is sufficiently small so that the first and second RF shields prevent any RF signals within the cavity from radiating outside the cavity;   positioning a test fixture RF antenna within the cavity;   transmitting an RF signal from the test fixture antenna;   detecting a response by the transponder to the RF signal; and   subsequently removing the transponder from proximity to the first and second shields and the test fixture RF antenna, so that no shielding obstructs the transponder RF antenna from sending and receiving RF radiation at any angle.   
     
     
       2. A method according to  claim 1 , wherein the cavity encloses the entire RF transponder. 
     
     
       3. A method according to  claim 1 , wherein the sheet has no shielding mounted thereon that obstructs RF radiation from the transponder RF antenna. 
     
     
       4. A method according to  claim 1 , wherein:
 the first RF shield is in the shape of a cup having a mouth abutting the first face; and   the step of positioning the second RF shield further comprises aligning the mouth of the second shield with the mouth of the first shield.   
     
     
       5. A method according to  claim 1 , wherein the step of positioning the test fixture RF antenna within the cavity comprises:
 mounting the test fixture RF antenna to a surface of one of the two RF shields;   connecting an RF transmission line to the test fixture RF antenna; and   passing the transmission line through an opening in said one RF shield to extend outside the cavity.   
     
     
       6. A method according to  claim 1 , further comprising the step of:
 fabricating the sheet to include electrically conductive material adjacent the mouth of the second RF shield so as to improve RF shielding of the cavity.   
     
     
       7. A method according to  claim 1 , wherein the RF signal is transmitted at a predetermined wavelength, and wherein the RF shields are dimensioned to improve the gain of the cavity at that wavelength. 
     
     
       8. A method according to  claim 1 , wherein the RF signal is transmitted at a predetermined wavelength, and wherein the RF shields are dimensioned so that the cavity resonates at that wavelength. 
     
     
       9. A method of testing the RF communication operation of a plurality of RF transponders, comprising the steps of:
 providing a sheet characterized by first and second opposite faces and a thickness;   mounting on the sheet a plurality of RF transponders, wherein each transponder includes a transponder RF antenna;   positioning a first test fixture section having a first RF shield so that the first RF shield abuts the first face of the sheet;   positioning a second test fixture section so as to abut the second face of the sheet, wherein:   the second test fixture section includes a plurality of RF shields,
 each RF shield in the second test fixture section is in the shape of a cup having a mouth abutting said second face of the sheet, 
 the first and second test fixture sections so that each RF shield in the second test fixture section encircles a corresponding one of the transponder RF antennas so as to form, in combination with the first RF shield, a closed cavity that completely surrounds and encloses said corresponding transponder RF antenna except where the thickness of the sheet separates the first RF shield from the mouth of said RF shield in the second test fixture section, and 
 said thickness is sufficiently small so that the first and second RF shields prevent any RF signals within the cavity from radiating outside the cavity; 
   positioning within each cavity a corresponding test fixture RF antenna;   transmitting an RF signal from each test fixture antenna;   detecting a response by each transponder to the RF signal transmitted by its corresponding test fixture antenna; and   subsequently removing each transponder from proximity to the first and second test fixture sections and the test fixture RF antennas, so that no shielding obstructs each transponder RF antenna from sending and receiving RF radiation at any angle.   
     
     
       10. A method according to  claim 9 , wherein the each cavity encloses the entire corresponding RF transponder. 
     
     
       11. A method according to  claim 9 , wherein:
 the first RF shield is in the shape of a plurality of cups so that each cup has a mouth abutting the first face of the sheet; and   the step of positioning the second RF shield further comprises aligning each mouth of the second shield with a corresponding mouth of the first shield.   
     
     
       12. A test fixture for testing the RF communication operation of an RF transponder which is mounted on a sheet which extends beyond the perimeter of the transponder, the RF transponder having an antenna for receiving RF signals, comprising:
 first and second RF shields, the second RF shield being in the shape of a cup having a mouth;   an alignment mechanism for positioning the first and second RF shields to abut opposite sides of the sheet so that the mouth encircles the transponder antenna and so that the combination of the first and second RF shields forms a closed cavity completely surrounding and enclosing the transponder antenna except where the sheet separates the two RF shields, wherein the distance by which the sheet separates the two RF shields is small enough to prevent any RF signals within the cavity from radiating outside the cavity; and   a test fixture RF antenna mounted within the cavity.   
     
     
       13. A test fixture according to  claim 12 , further comprising:
 a test fixture RF transmitter having an output connected to the test fixture RF antenna so that the RF antenna radiates RF signals to the transponder RF antenna; and   a test fixture RF receiver having an input connected to the test fixture RF antenna so that the RF receiver receives any responses transmitted by the RF transponder in response to said RF signals.   
     
     
       14. A test fixture according to  claim 12 , wherein the cavity encloses the entire transponder. 
     
     
       15. A test fixture according to  claim 12 , wherein:
 the first RF shield is in the shape of a cup having a mouth abutting the first face; and   the alignment mechanism aligns the mouth of the second shield with the mouth of the first shield.   
     
     
       16. A method according to  claim 12 , further comprising:
 an RF transmission line connected to the test fixture RF antenna;   wherein the transmission line extends through an opening in one of the RF shields so as to extend outside the cavity.   
     
     
       17. A test fixture according to  claim 12 , further comprising a test fixture RF transmitter for providing to the transponder antenna RF test signals having a predetermined wavelength, wherein the first and second RF shields are dimensioned to improve the gain of the cavity at that wavelength. 
     
     
       18. A test fixture according to  claim 12 , further comprising a test fixture RF transmitter for providing to the transponder antenna RF test signals having a predetermined wavelength, wherein the first and second RF shields are dimensioned so that the cavity resonates at that wavelength. 
     
     
       19. A test fixture for testing the RF communication operation of a plurality of RF transponders mounted on a sheet, each RF transponder having an RF antenna, comprising:
 a first test fixture section including a first RF shield;   a second test fixture section including a plurality of RF shields each of which is in the shape of a cup having a mouth;   an alignment mechanism for positioning the first and second test fixture sections to abut opposite sides of the sheet so that each RF shield in the second test fixture section encircles a corresponding one of the transponder antennas so as to form, in combination with the first RF shield, a closed cavity that completely surrounds and encloses said corresponding transponder RF antenna except where the sheet separates the first RF shield from the mouth of said RF shield in the second test fixture section, wherein the distance by which the sheet separates the first RF shield from each RF shield of the second test fixture section is small enough to prevent any RF signals within each cavity from radiating outside that cavity; and   a test fixture RF antenna mounted within each cavity.   
     
     
       20. A test fixture according to  claim 19 , wherein:
 the first RF shield is in the shape of a plurality of cups so that each cup has a mouth abutting the sheet; and   the alignment mechanism aligns each mouth of the second shield with a corresponding mouth of the first shield.   
     
     
       21. An interrogator for performing radio frequency communications, the interrogator comprising:
 one or more antennas,   a transmitter communicatively coupled to the one or more antennas and configured to transmit one or more messages and RE energy to power a radio frequency identification (RFID) tag:   a receiver communicatively coupled to the one or more antennas and configured to receive one or more responses;   a processing unit communicatively coupled to the transmitter to transmit a first command to set an inventory flag on the RFID tag to a first state and to transmit a second command to set the inventory flag on the RFID tag to second state, the RFID tag being identified by one or more random numbers received by the processing unit via the receiver and the one or more antennas.   
     
     
       22. The interrogator of claim 21, wherein the processing unit is further configured to cause the transmitter to transmit at a radio frequency in accordance with a frequency-hopping algorithm. 
     
     
       23. The interrogator of claim 21, wherein the first command and the second command includes the same random number generated by the RFID tag. 
     
     
       24. A method of performing radio frequency communications, the method comprising:
 generating by a radio frequency identification (RFID) tag a random number, the random number having a plurality of bits:   determining by an interrogator a first radio frequency band to transmit messages to the RFID tag
 transmitting by the interrogator a first command at the first radio frequency band; transmitting by the interrogator RF enemy to power the RFID tag; receiving by the RFID tag the first command at the first radio frequency band: 
   setting an inventoried flag in the RFID tag to a first state,   the setting being performed in response to the receiving the first command   communicating by the RFID tag a response to the first command at a second radio frequency band;   receiving one or more additional commands from the interrogator on the first radio frequency band; and   in response to at least one of the additional commands, setting the inventoried flag in the RFID tag to a second state, wherein the first command, the response, and the one or more additional commands include at least a part of one or more random numbers generated by the RFID tag.   
     
     
       25. The method of claim 24, wherein the determining a first radio frequency band comprises:
 selecting the first radio frequency band in accordance with a frequency-hopping algorithm.   
     
     
       26. The method of claim 24, further comprising communicating by the RFID tag data associated with one or more memory locations contained on the RFID tag. 
     
     
       27. The method of claim 24, wherein the interrogator identifies the first RFID tag in subsequent communications using at least one random number provided to the interrogator by the RFID tag. 
     
     
       28. A system for performing radio frequency communications, the system comprising:
 one or more antennas;   one or more interrogators communicatively coupled to the one or more antennas and configured to transmit a first message and a second message via the one or more antennas; and   a radio frequency identification (RFID) tag having a dipole antenna coupled to one or more items to be tracked and configured to set an inventory flag to a first state upon receipt of the first command and to a second state upon receipt of the second command, the first command including at least one random number generated by the RFID tag and the second command including at least one random number generated by the RFID tag.   
     
     
       29. The system of claim 28, wherein the interrogator is further configured to select a first radio frequency to transmit at in accordance with a frequency-hopping algorithm.