Abstract: An electromagnetic detection and identification system for detecting and identifying a plurality of responders (improved transponders), each containing a unique code, and simultaneously present in one and the same interrogation field generated by a transmitter/receiver.

Abstract: A system for the contactless exchange of data between a transceiver and a passive data carrier is described. A prior data carrier comprises at least one digital memory and at least one digital control device for the memory. In it, the data carrier has a single-coil receiver circuit connected to a controllable switch device. In operation, the data carrier provides, in response to an electromagnetic a.c. field generated by a transceiver, via at least one rectifier, supply power for active components of the data carrier and clock signals for the control of digital components of the data carrier. According to the present invention, in order to provide for the possibility of bi-directional data exchange between a transceiver and a passsive data carrier, and in general, to provide a universally applicable data exchange system of the contactless kind, the transceiver is equipped with a modulator for amplitude modulating the a.c. field.