Detection of multiple articles

A method of identifying a plurality of transponders, comprising:

• transmitting an interrogation signal to the transponders, each transponder receiving the interrogation and transmitting a response signal in response;
• receiving the response signals from the transponders;
• identifying a particular transponder from the response signals;
• and
• disabling the particular transponder;
• wherein at least two intermittent interrogation signals are transmitted, with an interval between successive interrogation signals which is less than a minimum period within which transponders which have been disabled reset themselves automatically.

An identification system comprising:

• an interrogator;
• and
• a plurality of transponders;
• the interrogator comprising:
• transmitter means for transmitting an interrogation signal to the transponders,
• receiver means for receiving response signals from the transponders, and
• means for identifying the transponders from the response signals;
• each of the plurality of transponders comprising:
• receiving means, and
• transmitting means,
• whereby, on receipt of the transmitted interrogation signal, the transponder transmits a response signal;
• wherein the interrogator transmitter transmits a plurality of simultanteous interrogation signals at a plurality of frequencies, each transponder transmiting a response signal on receipt of at least one of whichever of the interrogation signals, and the interrogator identifying response signals from the same transponder which are transmitted at some or all of the frequencies.

An interrogator for identifying a plurality of transponders, the interrogator comprising:

• transmitter means for transmitting an interrogation signal to the transponders;
• receiver means for receiving response signals from the transponders;
• and
• means for identifying transponders from the response signals;
• wherein the interrogator transmitter transmits a plurality of simultaneous interrogation signals at a respective plurality of frequencies, and the interrogator identifies a plurality of respectively distinguishable response signals from the same transponder which are transmitted at some or all of the frequencies.

An interrogator for identifying a plurality of transponders, comprising:

• transmitter means for transmitting an interrogation signal to the transponders;
• receiver means for receiving response signals from the transponders;
• and
• means for identifying the transponders from the response signals;
• the interrogator being capable of disabling any transponder;
• and
• the interrogator transmitter transmiting at least two intermittent interrogation signals, with an interval between successive interrogation signals which is less than a minimum period within which transponders which have been disabled reset themselves automatically.

A method of identifying a plurality of transponders, comprising:

• transmitting an interrogation signal to the plurality of transponders, each of the plurality of transponders receiving the interrogation signal and transmitting a signal in response;
• receiving the response signals from the transponders;
• and
• identifying transponders from the response signals;
• wherein a plurality of simultanteous interrogation signals at a plurality of frequencies are transmitted, a response signal is transmitted by each transmitter on receipt of at least one of whichever of the interrogation signals, and response signals from the same transponder which are transmitted at some or all of the frequencies are identified.

A method of identifying a plurality of transponders, comprising:

• transmitting an interrogation signal to the plurality of transponders, each of the plurality of transponders receiving the interrogation signal;
• and
• disabling any one of the plurality of transponders;
• whereby the interrogation signal and an inhibiting signal are transmitted;
• and
• a disabled transponder remains disabled while the disabled transponder continues receiving the inhibiting signal.

A transponder comprising:

• receiving means for receiving an interrogation signal;
• a code generator;
• and
• transmitting means connected to the code generator, the transponder transmitting a response signal which identifies the transponder on receipt of the interrogation signal, and being disabled by an instruction in the interrogation signal;
• the transponder receiving the interrogation signal and an inhibiting signal;
• and
• a disabled transponder remaining disabled while the disabled transponder continues receiving the inhibiting signal.

A method for identifying one of a plurality of transponders, the method comprising:

• transmitting two independent interrogation signals to the transponders, each independent interrogation signal being adapted to independently activate any one or more of the transponders;
• activating one of the transponders in response to whichever of the two independent interrogation signals the one transponder receives, such that the one transponder transmits a response signal containing code data which identifies the transponder and at least some signal energy from whichever of the two independent interrogation signals the one transponder receives;
• receiving the response signal from the one transponder;
• and
• identifying the one transponder from the code data in the response signal.

An identification system comprising:

• an interrogator;
• and
• a plurality of transponders;
• the interrogator comprising:
• transmitter means for transmitting an interrogation signal to the transponders,
• receiver means for receiving response signals from the transponders, and
• means for identifying the transponders from the response signals;
• each of the plurality of transponders comprising:
• receiving means responsive to a disabling instruction from the interrogator;
• the interrogator transmiting the interrogation signal and an inhibiting signal;
• and
• a disabled transponder remains disabled while the disabled transponder continues receiving the inhibiting signal.

An interrogator for identifying a plurality of transponders, the interrogator comprising:

• transmitter means for transmitting an interrogation signal to the plurality of transponders, wherein, transponders which identified themselves from the interrogation signal are capable of being disabled by an instruction in the interrogation signal;
• receiver means for receiving response signals from the plurality of transponders;
• and
• means for identifying the plurality of transponders from the response signals;
• the interrogator transmitting the interrogation signal and an inhibiting signal, wherein a disabled transponder remains disabled while the disabled transponder continued receiving the inhibiting signal.