System for communicating identification information and the like

Claim 1

A data transfer system comprising: an external interrogator device (10,31) comprising: a wave generator (12,26) for generating an electric wave (11,28) and emitting the same from said interrogator device (10,31) externally, and a comparator (13,27,30) for receiving external reflections (14,29) of said electric wave (11,28) emitted from said wave generator (12,26); and a plurality of portable responder devices, each comprising: an antenna (4a,4b) for reflecting said electric wave (11,28) emitted from said interrogator device (10,21), a data generator (9) for generating data (ID) from a memory means (7,FF₁-FF n ) within the responder device to be sent from said responder device to said interrogator device (10,31), and means (8) for changing with time the impedance of said antenna (4a,4b) in accordance with said data (ID) generated by said data generator (9), whereby said electric wave reflected by said antenna means (4a,4b) is modulated with said data generated by said data generating means (9); wherein said comparator (13,27,30) receives electric waves (14,29) reflected by said antennae (4a,4b) and compares the same with said electric wave (11,28) from said wave generator (26) so that said data (ID) can be derived from a result of the comparison; characterised in that the interrogator device is operative to vary the frequency J of said electric wave periodically as a function of time t , the function being J=ω₀+Δω₀t where ω₀ and Δω₀ are constants; and in that said comparator includes demodulating means (30) for discriminating between simultaneously received reflected waves modulated by individual ones of the responder devices according to reflected frequency.

Claim 5

A system according to any one of the preceding claims, wherein said impedance changing means (8) comprises switching means (8) having a control electrode, a first main electrode and a second main electrode, said control electrode being connected to said data generating means (9), said first main electrode being connected to said antenna means (4a) and said second main electrode being connected to ground.

Claim 6

A system according to any one of the preceding claims wherein said comparator (27, 30) is arranged to detect the frequency difference between said electric wave reflected by said antenna and the electric wave from said wave generator to detect the distance between said portable devices and said interrogator device.

Claim 7

A system according to any one of the preceding claims wherein each portable device further comprises: generating means (107a) for generating synchronising data; transmitting means (114, 104) for transmitting said synchronising data to said external device, receiving means (104) for receiving information data supplied from said external device, detecting means (110) for detecting control data supplied from said external device; and controlling means (113) for controlling read and write operations of said memory means (107b); wherein said information data is supplied in synchronism with said synchronising data and is rewritten in said memory means (107b) when a controlling signal from said controlling means is detected and otherwise said information data is read from said memory means (107b) and transmitted to said external device through said transmitting means.