Patent ID: 7808389
Filing Date: 2010-10-05
Classification: G06K,H01Q

Abstract:
1. Method for transmitting data and/or energy between a reading device and a transponder unit, comprising the steps of: generating a magnetic field by means of a first antenna coil of a reading device, said first antenna coil being supplied with a first current; generating a second magnetic field by means of a second antenna coil supplied with a second current such that when a transponder unit is brought within a communication range of said reading device, current imbalances caused by impedances are induced between said first and second antenna coils; and deriving the second current from the first current by using a current mirror to prevent said current imbalances caused by impedances induced in said coils when said transponder unit is brought within said communication range of said reading device, said second magnetic field being generated by the second antenna coil so that in a near field of the reading device its absolute value is smaller than that of the first magnetic field and outside the near field has approximately the same absolute value with opposite sign to cause said magnetic fields to cancel outside said near field and thereby prevent tapping of a communication between said reading device and said transponder from outside of said communication range.