Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive resonant circuit

Abstract

The invention relates to a method of reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit during reading. The method is distinguished in that the passive antenna of the resonant circuit is associated with at least one transponder antenna, and the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association corresponds to one of the frequencies of the emission side bands of the transponder to be read. The invention also relates to the system corresponding to the method, a transponder structure and an object containing the transponder, in particular a travel document.

1 . A method for reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit during reading,
 wherein the passive antenna of the resonant circuit is associated with at least one transponder antenna, and the passive resonant circuit is tuned in such a way that the resonance frequency resulting from the association corresponds to one of the frequencies of the emission side bands of the transponder to be read.   
   
   
       2 . A method according to  claim 1 , wherein the association of the passive antenna of the passive resonant circuit with at least one transponder antenna is made negligible and the passive resonant circuit is tuned to a resonance frequency corresponding to one of the frequencies of the emission side bands of the transponder to be read. 
   
   
       3 . A reading method according to  claim 2 , wherein the method further includes a step during which:
 the transponders are so configured as to be negligible in the association with the passive resonant circuit, by each drawing less magnetic field and/or by interfering less with the other antennas of the transponder.   
   
   
       4 . A reading method according to  claim 3 ,
 wherein at least one antenna format and one response from a transponder having a behavior corresponding to such format are determined, and   the passive resonant circuit is so configured as to obtain a behavior corresponding to such a format for each transponder.   
   
   
       5 . A reading method according to  claim 4 , wherein the passive antenna is defined between two rectangles respectively 81 mm×49 mm, and 64 mm×34 mm. 
   
   
       6 . A reading method according to  claim 1 , wherein the side bands are respectively selected approximately at 13.56 MHz±847 Khz or respectively 12.71 and 14.4 MHz, the interrogation frequency being 13.56 MHz rated at 847 Khz. 
   
   
       7 . A reading method according to  claim 5 , wherein the antenna of the passive resonant circuit includes between 3 and 6 turns. 
   
   
       8 . A reading method according to  claim 1 , wherein the passive resonant circuit has a quality factor with a value of less than 30. 
   
   
       9 . A reading method according to  claim 1 , wherein the transponder has a reduced format and has an antenna, the surface inside the outer turn of which is greater than a 15×15 mm surface and smaller than a surface of approximately 30×30 mm. 
   
   
       10 . A reading method according to  claim 9 , wherein the transponder antenna includes 13 to 18 turns. 
   
   
       11 . A reading method according to  claim 10 , wherein the tuning frequency is between 15 and 18 MHz. 
   
   
       12 . A reading method according to  claim 11 , wherein the transponder has a quality factor above 30. 
   
   
       13 . A reading method according to  claim 12 , wherein each transponder is positioned in a support in a random position, with the support allowing several positions of the transponder which are shifted with respect to each other. 
   
   
       14 . A reading system with at least one RF transponder, with said system including
 one reader able to emit an interrogation field on at least one transponder and to collect a response from the transponder,   a passive resonant circuit to perform a magnetic coupling with at least one transponder during the reading,   wherein the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association M of the resonant circuit with at least one transponder corresponds to one of the frequencies of the emission side bands of the transponder to be read.   
   
   
       15 . A supporting object containing at least one main transponder, one secondary transponder and an associated passive resonant circuit associated with at least the main transponder,
 wherein the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association of the resonant circuit with at least the main transponder corresponds with one of the frequencies of the emission side bands of the secondary transponder.   
   
   
       16 . A supporting object containing at least one transponder and one passive resonant circuit associated with at least one transponder,
 wherein the passive resonant circuit is tuned to a resonance frequency corresponding to one of the frequencies of the emission side bands of the transponder.   
   
   
       17 . A transponder including a flat antenna on a support defining an outer turn, wherein:
 the surface inside the outer turn is greater than a 15×15 mm surface and smaller than or equal to a surface of approximately 30×30 mm,   the antenna includes about 13 to 18 turns,   the tuning frequency is between 15 and 18 MHz,   a quality factor is above 30.   
   
   
       18 . A travel document including several pages between two covers and a plurality of transponders between the pages, each transponder being contained in a plane support separate from the pages or covers but having substantially the format of a page, wherein the transponders are configured as in  claim 17 . 
   
   
       19 . A travel document according to  claim 18 , wherein the transponders are positioned in the supports in various positions. 
   
   
       20 . An assembly of transponders according to  claim 17 , with each transponder being positioned in a sheet having a greater format than the latter, wherein the transponders are positioned in the supports in various positions from one sheet to another.