N.v. Nederlandsche Apparatenfabriek Nedap

N.v. Netherlandsche Apparatenfabriek Nedap

Willem H Venema

Jan Cornelis Stekelenburg

Harm J Kip

Arjan H Scholten

Marius L Tervoert

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. According to the invention, the transmitter/receiver is arranged to adjust the frequency of the interrogation field periodically to one of a predetermined number of predetermined 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 an 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.

Electromagnetic identification system for identifying a plurality of

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. The control device has two inputs for the supply of clock signals and data signals and includes level detectors cooperating with the inputs and arranged to allow the passage of an input signal voltage exceeding a pre-determined value as a valid input signal pulse. The coil is connected to the inputs through a two-branch voltage divider so that the voltage at the clock signal input is higher than that at the data signal input.

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Enschede, Netherlands

Willem H Venema