An electromagnetic identification system for identifying a plurality of coded responders simultaneously present in an interrogation field.

摘要

An electromagnetic detection and identification system for detecting and identifying a plurality of responders, each containing a unique code, and simultaneously present in one and the same interrogation field generated by a transmitter/receiver. According to the invention the transmitter/receiver is arranged to adjust the frequency of the interrogation field periodically to one of a pre-determined number of pre-determined values, and each responder is arranged to detect the instantaneous frequency of the interrogation field, the arrangement being such that, in a number of selection cycles, each time a number of responders temporarily deactivate themselves in dependence upon the instantaneous frequency until one single responder remains which can generate the appurtenant code without becoming deactivated until the responder has been identified by the transmitter/receiver, whereafter the responder concerned is blocked by a change in field frequency, and the temporarily deactivated responders are reactivated, and the selection procedure is repeated until all responders in the interrogation field have been identified and blocked.