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An identification system for wireless electronic identification and data transmission, comprises a reading unit and at least one electronic label including a resonant circuit and carrying data stored in a memory device of the label, which data can be read wirelessly when the label is introduced into

An identification system for wireless electronic identification and data transmission, comprises a reading unit and at least one electronic label including a resonant circuit and carrying data stored in a memory device of the label, which data can be read wirelessly when the label is introduced into a high-frequency interrogation field formed by a transmitter of the reading unit. The reading unit includes a control device which, in operation, periodically switches the interrogation field on and off and in the time intervals when the field is switched off switches on a receiver capable of detecting a signal transmitted by a label. The at least one label includes a modulator which in the time intervals when the field is switched off can modulate the quality factor Q of the resonant circuit in dependence on the data stored in the memory device.

대표청구항 ▼

1. In an identification system for wireless electronic identification and data transmission, comprising a reading unit and at least one electronic label, each electronic label comprising a resonant circuit and carrying data stored in a memory device of label and capable of being read wirelessly when

1. In an identification system for wireless electronic identification and data transmission, comprising a reading unit and at least one electronic label, each electronic label comprising a resonant circuit and carrying data stored in a memory device of label and capable of being read wirelessly when the label is introduced into a high-frequency interrogation field formed by a transmitter of the reading unit, the improvement wherein: said reading unit comprises a control device which, in operation, periodically switches the interrogation field on and off and in the time intervals when the field is switched off switches on a receiver capable of detecting a signal transmitted by a label; and said at least one label each comprises a modulator in which in the time intervals when the field is switched off modulates the quality factor Q of the resonant circuit in dependence on the data stored in the memory device. 2. An identification system as claimed in claim 1, wherein the modulator includes a switch means controlled by output signals from the memory device in the time intervals when the interrogation field is switched off. 3. An identification system as claimed in claim 2, wherein the switch means when energized at least partly short-circuits the resonant circuit. 4. An identification system as claimed in claim 1, wherein said at least one label each comprises a clock circuit receiving from said resonant circuit a high frequency voltage generated in use in said resonant circuit by said high frequency interrogation field, and having an amplitude level and wherein said clock circuit detects said amplitude level and generates clock signals from variations in said amplitude level. 5. An identification system as claimed in claim 4, wherein the clock circuit includes a rectifier and a smoothing capacitor, and further a level detector providing a high output signal when the voltage across the smoothing capacitor exceeds a pre-determined level, and providing a low output signal when the voltage across the smoothing capacitor decreases below a pre-determined level; and that the output signal of the level detector forms the clock signal. 6. An identification system as claimed in claim 4, wherein the output of the clock circuit is connected to a monostable multivibrator and to an address counter which, in turn, is connected to the memory device, the output of the memory device and the monostable multivibrator each being connected to an input of an AND gate circuit whose output is connected to the switch means. 7. An identification system as claimed in claim 1, wherein said at least one label each comprises a means connected to the resonant circuit and a smoothing capacitor for forming supply voltage for active circuits of the label. 8. An identification system as claimed in claim 1, wherein the reading unit comprises at least coil and a switch controlled by said control device to connect said at least one antenna coil alternately with the output of the transmitter and the input of the receiver. 9. An identification system as claimed in claim 8, wherein when switching off the interrogation field, the switch connects the antenna to a suitable damping resistor before connecting the antenna coil to the receiver. 10. An identification system as claimed in claim 1 wherein said at least one label each comprises at least one sensor capable of affecting the contents of the memory device. 11. A label for use in an identification system for wireless electronic identification and data transmission, said system comprising at least one electronic label, and a reading unit including a transmitter for generating a high-frequency interrogation field, wherein the reading unit comprises a control device which, in operation, periodically switches the interrogation field on and off and in the time intervals when the field is switched off switches on a receiver capable of detecting a signal transmitted by a label, and said at least one label each comprises a resonant circuit, a memory device sorting data, and a modulator which in the time intervals when the interrogation field is switched off modulates the quality factor Q of the resonant circuit in dependence on the data stored in the memory device. 12. A label as claimed in claim 11, wherein the modulator includes a switch means controlled by output signals from the memory device in the time intervals when the interrogation field is switched off. 13. A label as claimed in claim 12, wherein the switch means when energized at least partly short-circuits the resonant circuit. 14. A label as claimed in claim 11 and further comprising a clock circuit forming clock signals generated by said switching of said interrogation field. 15. A label as claimed in claim 14, wherein the clock circuit comprises a rectifier and a smoothing capacitor, and further a level detector providing a high output signal when the voltage across the smoothing capacitor exceeds a pre-determined level, and providing a lower output signal when the voltage across the smoothing capacitor decreases below a pre-determined level, and the output signal of the level detector forms the clock signal. 16. A label as claimed in claim 14, wherein the output of the clock circuit is connected to a monostable multivibrator and to an address counter which, in turn, is connected to the memory device, the output of the memory device and the monostable multivibrator each being connected to an input of an AND gate circuit whose output is connected to the switch means. 17. A label as claimed in claim 11 and further comprising rectifier means connected to the resonant circuit and a smoothing capacitor for forming supply voltage for active circuits of the label. 18. A label as claimed in claim 11 and further comprising at least one sensor capable of affecting the contents of the memory device.