Patent ID: 7106174
Filing Date: 2006-09-12
Classification: G06K

Abstract:
1. A radio frequency tag identification system comprising a plurality of tags and a transceiver for sending information to and receiving information from the tags, wherein each tag is allocated an identification word comprising a predetermined number of bits, the tags comprising means for selectively modulating a signal received from the transceiver and transmitting the modulated signals back to the transceiver, and the transceiver comprising means for sending an interrogation signal comprising a plurality of portions, wherein each portion of the interrogation signal has two possible signal formats, in the form of pulses having different durations, and the format used for a given interrogation signal portion is determined by the transceiver in dependence on modulated responses received from the tags during the transmission of the said given interrogation signal any previous portion, wherein each portion is associated with a predetermined bit, or bit sequence, of the identification words and is used to simultaneously interrogate the tags to identify, in response to modulated signals provided by the tags in response to the predetermined bit or bit sequence, the presence of a tag or tags having a given value of the identification word at the predetermined bit or bit sequence, wherein each tag is deactivated when not having said given value of the identification word at the predetermined bit or bit sequence.