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Identification system and method with passive tag

  • US 5,491,468 A
  • Filed: 06/24/1993
  • Issued: 02/13/1996
  • Est. Priority Date: 06/24/1993
  • Status: Expired due to Term
First Claim
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1. An identification system, comprisinga reading device including means for receiving and processing coded information received via a magnetic coupling from at least one portable tag and for radiating a continuous wave alternating magnetic field, the reading device includinga first conductive coil,a transmission circuit coupled to the first conductive coil for generating the continuous wave alternating magnetic field of a predetermined frequency;

  • andat least one portable tag for transmitting the coded information via the magnetic coupling in response to the reception of the continuous wave alternating magnetic field radiated by the reading device, each portable tag includingmeans for storing the coded information to be transmitted,a second conductive coil for receiving and collecting energy of the radiated magnetic field,a reception circuit including a storage capacitor electrically coupled to the second conductive coil for charging the storage capacitor throughout a first time duration,the reception circuit including a circuit switch electrically coupled to the storage capacitor for discharging the capacitor after the charge on the capacitor has attained a predetermined threshold level, the discharging occurring during a second time duration less than the first time duration, said circuit switch being activated in direct response to the voltage across the capacitor having attained the predetermined threshold level and independent of the amplitude of the received radiated magnetic field, andcoded information transmission means responsive to the activation of the switch, allowing discharging of the storage capacitor, and operable to transmit the stored coded information to the reading device by means of the magnetic coupling, during the second time duration.

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