Wireless Power in Passive RFID

Abstract

Radio-frequency Identification (RFID) technology has many applications in various fields. Compared to a traditional Auto-ID system, the RFID technology has many advantages. Firstly, the identification of tags is more accurate and the distance is more flexible. Secondly, the maximum memory capacity of RFID tags can be several megabytes which is much more than that of the traditional Auto-ID’s. Thirdly, RFID has better performance in anti-pollution, because the data is saved in a chip wrapped by the tag. Finally, RFID tag is rewritable. We can add, modify and delete the data stored in the tag repeatedly.

There are three types of RFID tags: passive tag, semi-passive tag, and active tag. Since there are no batteries in the passive tag, it has to get power from the reader to drive the chip inside. How is the power transported from readers to tags? How does the tag turn the high frequency AC to DC? How does the tag use this power to send signals back? These are the questions I concentrated on in this thesis. Finding out the ansewers to these questions can help users to implement a RFID system.