Detection of multiple articles

An identification system comprising an interrogator and a plurality of transponders, wherein:

• the interrogator comprises transmitter means for transmitting at least two independent interrogation signals to the transponders, receiver means for receiving response signals from the transponders responsive to at least one of the interrogation signals transmitted by said transmitter means, and processor means for identifying the transponders from data in the response signals;
• each transponder comprises receiving means, a code generator, and transmitting means connected to the code generator, so that on receipt of at least one of the interrogation signals transmitted by said transmitter means the transponder transmits a response signal containing data which identifies the transponder;
• and
• the transmitter means of the interrogator transmits the at least two interrogation signals intermittently, with an interval between successive interrogation signals which is less than a minimum period within which transponders which have been disabled by a disable instruction in an interrogation signal reset themselves automatically.

An identification system comprising an interrogator and a plurality of transponders, wherein:

• the interrogator comprises transmitter means for transmitting at least two independent interrogation signals to the transponders, receiver means for receiving response signals from the transponders responsive to at least one of the interrogation signals transmitted by said transmitter means, and processor means for identifying the transponders from data in the response signals;
• the transmitting means of the interrogator comprises a transmitting antenna, at least first and second transmitters for generating interrogation signals at respective different frequencies, and switch means for switching the outputs of the transmitters alternatively to the transmitting antenna;
• the receiver means and the processor means of the interrogator distinguish response signals from transponders in response to interrogation signals transmitted at the respective different frequencies of the at least first and second transmitters;
• each transponder comprises receiving means, a code generator, and transmitting means connected to the code generator, so that on receipt of at least one of the interrogation signals transmitted by said transmitter means the transponder transmits a response signal containing data which identifies the transponder;
• and
• the processor means detects duplicate transponder response signals transmitted on two or more of the respective different frequencies and disregards them.

An identification system comprising an interrogator and a plurality of transponders, wherein:

• the interrogator comprises transmitter means for transmitting an interrogation signal and an inhibiting signal having respective different frequencies to the transponders, receiver means for receiving response signals from the transponders responsive to the interrogation signal transmitted by said transmitter means, and processor means for identifying the transponders from data in the response signals;
• and
• each transponder comprises receiving means for receiving the interrogation signal and the inhibiting signal transmitted by said transmitter means, a code generator, and transmitting means connected to the code generator,
• the respective different frequencies of the interrogation signal and the inhibiting signal being selected to fall within the reception bandwidth of the receiving means of the transponder,
• the transponder being adapted to transmit a response signal containing data which identifies the transponder on receipt of the interrogation signal, to be disabled by a turn-off instruction in the interrogation signal on successful identification of the transponder, and to remain disabled while it continues to receive the inhibiting signal.

An interrogator for identifying at least one transponder of a plurality of transponders, the interrogator comprising:

• transmitter means for simultaneously transmitting at least two independent interrogation signals to the transponders, each independent interrogation signal being adapted to independently activate any one or more transponders receiving said signal;
• receiver means for receiving at least one response signal from any of the transponders in response to any one or more of the independent interrogation signals transmitted by said transmitter means, each response signal including data identifying a respective transponder;
• and
• processor means for identifying the respective transponder from data contained in the at least one response signal.

An interrogator for identifying at least one transponder of a plurality of transponders, the interrogator comprising:

• transmitter means for transmitting at least two independent interrogation signals to the plurality of transponders;
• receiver means for receiving at least one response signal from any of the transponders in response to any one or more of the independent interrogation signals transmitted by said transmitter means, each response signal including data identifying a respective transponder;
• and
• processor means for identifying the respective transponder from data contained in the at least one response signal,
• wherein the transmitter means transmits the at least two interrogation signals intermittently, with an interval between successive interrogation signals which is less than a minimum period within which transponders which have been disabled by a disable instruction in an interrogation signal reset themselves automatically.

An interrogator for identifying at least one transponder of a plurality of transponders, the interrogator comprising:

• transmitter means for transmitting at least two independent interrogation signals to the plurality of transponders, wherein the transmitter means comprises a transmitting antenna, at least first and second transmitters for generating interrogation signals at respective different frequencies, and switch means for switching the outputs of the transmitters alternatively to the transmitting antenna;
• receiver means for receiving at least one response signal from any of the transponders in response to any one or more of the independent interrogation signals transmitted by said transmitter means, each response signal including data identifying a respective transponder;
• and
• processor means for identifying the respective transponder from data contained in the at least one response signal, wherein:
• the receiver means and the processor means distinguish response signals from transponders in response to interrogation signals transmitted at the respective different frequencies of the at least first and second transmitters, and
• the processor means detects duplicate transponder response signals transmitted on two or more of the respective different frequencies to disregard them.