Abstract: An identification system is provided for identifying a plurality of randomly aligned object-based transponders (18, 20, 22) passing through a predetermined reading volume. A reader (10) includes multiple transmitting and receiving antenna arrays (12, 14, 16) which are arranged sequentially to transmit interrogating and energizing fields (29) into the reading volume, with each energizing field having a different polarisation. Each transponder (12, 14, 16) is arranged to be powered by at least one of the interrogating and energizing fields, and includes a short term memory module (30) which is arranged to record the successful transmission or otherwise of the identification signal of the transponder (20) and to retain the record in the absence of a power supply to the transponder. The short term memory module has a retention time longer than any predicted interruption of power supply to the transponder via one of the energizing fields within the reading volume.

Abstract: A radio frequency transponder assembly comprises a passive transponder and an antenna with a matching circuit comprising an inductor and a capacitor which are formed integrally with the antenna components. The antenna is a dipole with legs formed from wire or foil strips, in which case the inductor and capacitor are formed from same material as the antenna legs. The values of the inductor and capacitor are calculated to match the antenna impedance to the equivalent load of the transponder circuit as seen via the power rectification circuits of the transponder.

Abstract: An identification system is provided for identifying a plurality of object-based transponders (14, 16, 18, 20) using an interrogator (10). The interrogator (10) includes a transmitter for transmitting an interrogation signal to the transponders, a receiver for receiving identification signals from the transponders, and processor means (21) for determining the individual and correct receipt of an identification signal. The transponders operate on the basis of backscatter modulation, and include a detector for detecting the presence of an interrupt signal from the interrogator. Control logic responsive to the detector is arranged to cease signal transmission from the transponder if the transponder completes transmission of the identification signal without receiving an interrupt signal during such transmission.