In low-frequency RFID, the reader communicates with the tag through inductive coupling between the transducer's loop and the tag's loop. In this example circuit, such coupling is represented by a non-ideal transformer with the coupling coefficient smaller than 1. The part of the circuit connected to the primary coil models the reader. The part connected to secondary coil models the tag. The tag rectifies the signal picked up by its loop in order to get the dc power to operate. It then transmits data by periodically commuting its own loop with a switch. In this circuit, the tag is modeled by a diode rectifier and a sensitive relay. The reader's part is modeled by a peak detector and a D-trigger. The tag transmits 1 bit of data. Enjoy!
