Electronic identification system

An interrogator for use with an electronic identification system also comprising a plurality of transponders, the interrogator comprising:

• transmitter means for transmitting an interrogation signal to the plurality of transponders;
• receiver means for receiving response signals originating from the plurality of transponders, each response signal comprising a signature that is a characteristic of a respective transponder from which the signature originates;
• and
• a controller for processing at least one of the response signals received and for causing an acknowledgement signal comprising the signature to be transmitted.

A transponder comprising:

• receiver means for receiving an interrogation signal;
• signature generating means for generating a signature characteristic of the transponder;
• transmitter means for transmitting in response to the interrogation signal a response signal comprising the signature characteristic of the transponder;
• and
• a controller for causing the transponder to switch from one mode of operation to another, if an acknowledgement signal comprising the signature is received.

A method of operating an electronic identification system comprising an interrogator and a plurality of transponders, the method comprising the steps of:

• transmitting from the interrogator an interrogating signal to the transponders;
• causing the transponders to receive the interrogation signal and each intermittently to respond with a response signal comprising a signature characteristic of the respective transponder,
• causing the interrogator to receive the response signals and to process a response signal from at least one of the transponders;
• causing the interrogator to transmit an acknowledgement signal comprising the signature of the at least one of the transponders;
• and
• causing the at least one of the transponders upon reception of the acknowledgement signal to switch from one mode of operation to another mode of operation.