Abstract: A method for enabling authenticated access of an individual (10) to a security area (12) by means of a transponder (14) carried by the individual which on receiving an interrogation signal outputs an ID code group, and a control unit (18) located in the security area (12) which generates the interrogation signal and checks the ID code group output by the transponder (14) for enabling access of the individual (10) to the security area (12) only when right of access is authenticated, is characterized in that the interrogation signal is relayed by capactive coupling from the control unit (18) via the individual (10) to the transponder (14).

Abstract: An improved inductor/antenna (100)improves the selectivity of a recognition system (10) by ensuring that only the transponder (14) closest to the inductor/antenna (100) of an interrogator (12) receives therefrom, and reacts to, an interrogation signal (S1). The improved inductor/antenna (100) also receives the resulting recognition signal (S2) from the transponder (14) for analysis by the interrogator (12). The inductor/antenna (100) includes two or more coils (102, 104; 124, 126, 128, 130; 132, 134) which may be wound on ferromagnetic cores (108), spaced around a metal mass (46, 48) such as a lock cylinder (46) of an ignition switch (24). The shape, number, location and relative winding sense of the coils are selected to shape and locate the energy field (F; 118, 122) radiated by the inductor/antenna (100) so that only the transponder (14) in a key (26) which is inserted into or operating the ignition switch (24) responds to the interrogation signal (S1) radiated by the inductor/antenna (100).

Abstract: An alternative resonant circuit configuration reduces the amount of RF current that is switched by the power-stage transistors of a T/R unit and thereby also significantly reduces the reliability risk. A parallel resonant antenna configuration of coils and capacitors reduces the RF current through the output stage push-pull transistor configuration to a small fraction of the RF current experienced by typical series resonant circuits. This circuit offers advantages of low cost, reliable impedance matching while reducing the volume necessary to perform the function.

Abstract: An improved inductor/antenna (100)improves the selectivity of a recognition system (10) by ensuring that only the transponder (14) closest to the inductor/antenna (100) of an interrogator (12) receives therefrom, and reacts to, an interrogation signal (S1). The improved inductor/antenna (100) also receives the resulting recognition signal (S2) from the transponder (14)for analysis by the interrogator (12). The inductor/antenna (100) includes two or more coils (102,104; 124,126,128,130; 132,134) which may be wound on ferromagnetic cores (108), spaced around a metal mass (46,48) such as a lock cylinder (46) of an ignition switch (24). The shape, number, location and relative winding sense of the coils are selected to shape and locate the energy field (F; 118,122) radiated by the inductor/antenna (100) so that only the transponder (14) in a key (26) which is inserted into or operating the ignition switch (24) responds to the interrogation signal (S1) radiated by the inductor/antenna (100).