Optimization Design Of RFID Tag Antenna

Radio Frequency Identification (RFID) is a type of non-contact automatic identification technology using radio waves to uniquely identify an object, animal, or a person. Bearing features of great capacity, long term of service life, non-contact data reading and writing, high speed moving object recognition and multi-target recognition, RFID has become a hot research field of automatic identification, regarded as one of the ten major technologies in the 21st century. RFID has found applications in various areas such as toll collection, asset identification, retail item management, access control, animal tracking and vehicle security and so on.RFID antennas normally contain reader antennas and tag antennas. The tag antennas have been given increasing attentions due to their limitations by the size, price, working condition and so on. The rapid development of RFID technology poses new challenges on tag antenna design. Firstly, the impedance of an IC chip may be an arbitrary value and always a complex value which makes the impedance matching more difficult. Secondly, a broader bandwidth may be needed with the extended RFID applications in higher frequency range. Thirdly, the objects near the tags may cause bad effects, such as resonant frequency shift, modified radiation pattern, low radiation efficiency and so on. Then tag antennas that features small size,low cost,wide-bandwidth and high efficiency will be needed.This thesis contributes to the optimization design of the RFID fragment-type tag antenna, using genetic algorithms (GA) and Finite Difference Time Domain (FDTD) method. In the first, we review the RFID history and summarize some important problems the tag antenna designers face. Then FDTD method is introduced and applied to the impedance and radiation characteristic calculation. GA is used for the whole optimization and several antennas are obtained. Last, we also study the effects of the objects the tag antennas attached to.The main work of this thesis includes two parts. Firstly, a new FDTD method for the impedance calculation of the ftagment-type antenna was obtained. And the selections of the GA strategies and parameters are discussed. Secondly, several antennas are obtained including several UHF tag antennas and 2.45GHz tag antenna. One 2.45GHz tag antenna was fabricated and measured. There is good agreement between the simulation and the measurement.