EP0242906A1 — Electromagnetic identification system

Claim 1

Independent Claim 219 words

An electromagnetic identification system comprising a transmitter for generating an electromagnetic interrogation field in a detection zone, at least one passive responder capable of disturbing said interrogation field, and detection means for detecting a disturbance of the interrogation field caused by a responder, the responders comprising a single receiver circuit which in response to an interrogation field, via rectifier means, can supply energy to active digital encoding means comprising a binary-code defining means, said encoding means being arranged, in operation, through a switch means, to vary the electrical characteristics of said receiver circuit in the rhythm of the binary code to generate a code signal that is detectable by said detection means, said encoding means being arranged to control the switch member during pre-determined periods of time for varying the electrical characteristics of said receiver circuit, which pre- determined periods of time alternate with intervals during which the electrical characteristics of the receiver circuit are not affected, characterized in that said encoding means comprise a decoding section which in response to a modulation of the interrogation field can, at least in part, change the binary code defined by said code-defining means, and that there is provided a transmitter comprising a programmer for providingsuchmodulation, said transmitter being arranged, in operation, to generate a modulated interrogation field during said predetermined intervals.

Claim 2

Dependent Claim 219 words

An electromagnetic identification system comprising a transmitter for generating an electromagnetic interrogation field in a detection zone, at least one passive responder capable of disturbing said interrogation field, and detection means for detecting a disturbance of the interrogation field caused by a responder, the responders comprising a single receiver circuit which in response to an interrogation field, via rectifier means, can supply energy to active digital encoding means comprising a binary-code defining means, said encoding means being arranged, in operation, through a switch means, to vary the electrical characteristics of said receiver circuit in the rhythm of the binary code to generate a code signal that is detectable by said detection means, said encoding means being arranged to control the switch member during pre-determined periods of time for varying the electrical characteristics of said receiver circuit, which pre- determined periods of time alternate with intervals during which the electrical characteristics of the receiver circuit are not affected, characterized in that said encoding means comprise a decoding section which in response to a modulation of the interrogation field can, at least in part, change the binary code defined by said code-defining means, and that there is provided a transmitter comprising a programmer for providingsuchmodulation, said transmitter being arranged, in operation, to generate a modulated interrogation field during said predetermined intervals.

Claim 3

Dependent Claim 31 words

An electromagnetic identification system as claimed in claim 1, characterized in that the transmitter comprising a programmer is the same transmitter which normally generates an interrogation field in a detection zone.

Claim 4

Dependent Claim 74 words

An electromagnetic identification system as claimed in claim 1, characterized in that the transmitter comprising the programmer comprises adjusting means for varying the energy transmitted, the responder comprising a Zener diode which limits the supply voltage provided by the rectifier means to a pre-determined threshold value, and the adjusting means being arranged to adjust the energy transmitted to an energy level corresponding to said pre- determined threshold value of the supply voltage during programming.

Claim 5

Dependent Claim 50 words

An electromagnetic identification system as claimed in claim 3, characterized in that the programmer is arranged, starting from the energy level corresponding to the predetermined threshold value of the supply voltage, to effect an amplitude modulation of the interrogation field with a modulation depth not exceeding a pre-determined maximum value.

Claim 6

Dependent Claim 49 words

An electromagnetic identification system as claimed in claim 3 or 4, characterized in that the detection means are arranged, upon variation of the energy transmitted, to detect a sudden change of the amount of energy absorbed by a responder, and to provide a corresponding signal to the adjusting means.

Claim 7

Dependent Claim 22 words

An electromagnetic identification system as claimed in any of the preceding claims, characterized in that the binary-code defining means comprises an EEPROM.

Claim 8

Dependent Claim 42 words

An electromagnetic identification system as claimed in any of the preceding claims, characterized in that the transmitter is arranged to intermittently generate an interrogation field and that the responders are arranged to generate a coded signal after the interrogation field drops out.

Claim 9

Dependent Claim 53 words

An electromagnetic identification system as claimed in claim 7, characterized in that said responders are provided with an amplifier which after the interrogation field drops out, together with the receiver circuit, forms an oscillator attuned to the frequency of the interrogation field and withdrawing energy from an energy buffer provided in said responder.

Claim 10

Dependent Claim 32 words

An electromagnetic identification system as claimed in claim 8, characterized in that said amplifier comprises an inhibit input that is energized so long as the responder withdraws energy from the receiver circuit.

Claim 11

Dependent Claim 16 words

A responder for use in an electromagnetic identification system as claimed in any of claims 1-9.

Claim 12

Independent Claim 203 words

A method of programming the code of a coded responder which forms part of an electromagnetic identification system and is arranged to form supply energy from an interrogation field through rectifier means and a voltage limiter, and in response to an interrogation field to generate a code signal during pre-determined periods of time alternating with time intervals, said code signal being in accordance with a digital code defined by a programmable code defining means forming part of active digital coding means including a decoding section, characterized in that a transmitter by means of which an interrogation field can be generated is provided with a programmer for modulating said interrogation field; that the energy transmitted by the transmitter is varied; that the energy level at which a sudden leap occurs in the energy absorbed by the responder is detected; that at least during the intervals when the responder does not generate a code signal, the transmitter is adjusted to an energy level corresponding to the detected energy level; and that subsequently, during the intervals, the programmer is energized to modulate the interrogation field in accordance with a desired code, which code is decoded by the decoding section and written into the code defining means.

Claim 13

Independent Claim 203 words

A method of programming the code of a coded responder which forms part of an electromagnetic identification system and is arranged to form supply energy from an interrogation field through rectifier means and a voltage limiter, and in response to an interrogation field to generate a code signal during pre-determined periods of time alternating with time intervals, said code signal being in accordance with a digital code defined by a programmable code defining means forming part of active digital coding means including a decoding section, characterized in that a transmitter by means of which an interrogation field can be generated is provided with a programmer for modulating said interrogation field; that the energy transmitted by the transmitter is varied; that the energy level at which a sudden leap occurs in the energy absorbed by the responder is detected; that at least during the intervals when the responder does not generate a code signal, the transmitter is adjusted to an energy level corresponding to the detected energy level; and that subsequently, during the intervals, the programmer is energized to modulate the interrogation field in accordance with a desired code, which code is decoded by the decoding section and written into the code defining means.

Electromagnetic identification system

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