Apparatus and method for simultaneously reading out of passive inductive transponders

• US 6,824,054 B2
• Filed: 10/27/2003
• Issued: 11/30/2004
• Est. Priority Date: 12/20/2000
• Status: Expired due to Fees

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Hammerschmidt, Dirk, Vom Boegel, Gerd, Christoffers, Niels, Niederholz, Juergen
• Primary Examiner(s): TREMBLAY, MARK STEPHEN
• Application Number:
  US10/451,009
• Publication Number:
  US 20040065735A1
• Time in Patent Office: 400 Days
• Field of Search: 235/449, 235/451
• US Class Current: 235/451
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: G06K 19/07796 arrangements on the record carrier to allow stacking of a plurality of similar record carriers, e.g. to avoid interference between the non-contact communication of the plurality of record carriers
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10029 the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot

Abstract

The present invention relates to a transponder reading device for reading out a plurality of inductive passive transponders having a resonant circuit. A transmitter is provided to create an alternating magnetic field having an operating frequency f_B, in which the number of transponders may be placed such that same are magnetically coupled to each other. A retuning means is further provided which is arranged in the alternating magnetic field and has such a frequency-dependent impedance that a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f_B.

Claims

1. Transponder reading device for reading out a plurality of inductive passive transponders having a resonant circuit, the device comprising:

a transmitter coil for generating an alternating magnetic field having an operating frequency f_B, in which the plurality of transponders may be placed such that they are magnetically coupled to each other; and

a retuning circuit arranged in the alternating magnetic field and having such a frequency-dependent impedance that a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f_B.

2. Transponder reading device as claimed in claim 1, wherein the retuning circuit comprises a coil.

3. Transponder reading device as claimed in claim 2, wherein the retuning circuit further comprises at least one further network element which is connected to the coil and is selected from the group consisting of capacitors, resistors, and coils.

4. Transponder reading device as claimed in claim 1, wherein the retuning circuit comprises a resonant circuit.

5. Transponder reading device as claimed in claim 1, wherein the frequency-dependent impedance of the retuning circuit is variable.

6. Transponder reading device as claimed in claim 5, wherein the resonant circuit of the retuning circuit comprises a coil and a capacitor, the inductance of the coil and/or the capacitance of the capacitor of the resonant circuit of the retuning circuit being variable.

7. Transponder reading device as claimed in claim 5, which further comprises a controller for varying the impedance of the retuning circuit until a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f_B.

8. Method for reading out a plurality of inductive passive transponders having a resonant circuit, the method comprising:

generating an alternating magnetic field having an operating frequency f_B;

placing the plurality of transponders in the alternating magnetic field such that the transponders are magnetically coupled to each other;

placing a retuning circuit in the alternating magnetic field, the retuning circuit having such a frequency-dependent impedance that a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f_B; and

receiving data created by the transponders in response to the voltage induced.

9. Method as claimed in claim 8, wherein the step of placing the retuning circuit includes the step of varying the impedance of the retuning circuit until the voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f_B.

10. Transponder having a resonant circuit consisting of a transponder coil and a tuning capacitor, the resonant circuit being tuned such that a lower minimum cut-off frequency f_u,min is in the range of a preset operating frequency f_B of an alternating magnetic field, the lower minimum cut-off frequency f_u,min being the frequency approached by the lowest-frequency maximum of the voltage induced in the transponder resonant circuit by the alternating magnetic field of the operating frequency f_B if a theoretically unlimited number of transponders are arranged in the alternating magnetic field.