Patent ID: 8249502

Claim:
A radio-frequency communication device comprising: an inductive antenna comprising a first winding and a second winding such that when in the presence of (i) a primary magnetic field, which is substantially homogeneous on the scale of the antenna, and (ii) a secondary magnetic field produced by a transponder located in the vicinity of the antenna, the secondary magnetic field induces a relatively larger electromotive force in the first winding than in the second winding preventing a cancellation of the relatively larger electromotive force while the primary magnetic field continues to induce mutually cancelling electromotive forces in the first winding and the second winding; and a transponder interrogation circuit comprising: sampling and processing means for sampling and processing a signal on antenna terminals to produce a reference signal as a function of said signal; modulation means for modulating the reference signal to create a modulated signal; and application means for applying the modulated signal to the antenna terminals.