Electromagnetic identification system
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United States of America Patent
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Apr 14, 1992
Issued Date -
N/A
app pub date -
Aug 14, 1990
filing date -
Apr 22, 1986
priority date (Note) -
Expired
status (Latency Note)
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Abstract
An electromagnetic identfication system of the kind in which a transmitter generates an electromagnetic interrogation field in a detection zone. At least one passive responder is provided capable of disturbing the interrogation field. A detection circuit detects a disturbance of the interrogation field caused by a responder. The responder is a single receiver circuit which responds to the interrogation field which supplies energy to activate a digital encoding circuit having a binary-code defining circuit. The encoding circuit is arranged, in operation, through a switch to vary the electrical characteristics of the receiver circuit to generate a code signal that is detectable by the detection circuit. The encoding circuit is arranged to control the switch during the pre-determined periods of time for varying the electrical characteristics of the receiver circuit. A programmer is provided to modulate the transitter to generate a modulated interrogation field.
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