ACTIVE, PASSIVE AND SEMIPASSIVE RFID SYSTEMS

Abstract

There was presented the essence of RFID system and its components. The systems are divided into the inductively coupled and radiatively coupled ones. There was explained the method of data transmission between transponders and reader by backward modulation of the magnetic field or by modulation of the reflected electromagnetic wave. The simplified block diagram of a transponder was depicted. It was explained how passive transponders may be powered from magnetic or electromagnetic field created by the reader. In this respect there were discussed three kinds of transponders: active, passive and semi-passive ones. There are given some figures referring to the issue of the powering of transponders. The attention was paid to semi-passive transponders comprising in their structure a circuit for energy harvesting from ambient, especially from electromagnetic fields created by mobile telephony base stations. Simple calculations were performed that indicated the extent to that such harvesting may be efficient. The results were that the usage of semi-passive transponders (and whole semi-passive RFID systems) is possible within several tens to one hundred meters from GSM base stations. Such result may be made better by the transponders improvements aimed for decreasing their required supply power.