| Radio Frequency Identification (RFID) technology is a kind of non-contact automatic identification technology which transmits information by coupling of radio signal and identifies objects by the information it transmitted. The advantage of RFID technology is that it can identify tags faster, has larger storage space, can simultaneously identify multiple tags and adapt to complex surrounding environment. RFID technology has been developed for more than 50 years. It is becoming mature both in theory and application, and has been widely used in logistics, public transportation, retail sales, industrial production control, medical and many other fields.Left-Handed Metamaterial (LHM) is an artificial medium in which both the permittivity and permeability are simultaneously negative. Because the group velocity and phase velocity of electromagnetic waves are in the opposite directions in LHMs, they have many strange properties, such as negative refraction, reversed Doppler shift, reversed Cherenkov radiation, perfect lens and so on. The discovery of left-handed material has been regarded as one of the ten most significant discoveries in science community in 2003.Based on the application of RFID system, UHF band RFID near-field reader antenna is designed and fabricated. The resonant rings which have left-handed properties are used in the design of RFID antenna. Finally the effect of SRR structure and left-handed materials on micro-strip antenna is studied and discussed.First, the basic principle of left-handed metamaterials and split resonant rings (SRRs) which are part of LHMs is analyzed theoretically. The composition, working principle and classification of typical RFID system are introduced. The basic antenna parameters are introduced briefly as well as the basic analyzing methods of micro-strip antenna. Followed by that is detailed information on near-field coupling theory. Finally the algorithm of electromagnetic field calculation and simulation software is introduced.Second, because traditional UHF RFID system is based on far-field back scatting of radio signals and it can be affected by surrounding environment, it is a big challenge to develop a near-field coupled UHF RFID system. A structure of small size, low cost near-field coupled UHF RFID reader antenna is designed and fabricated. The structure of this antenna is ring-shape. The measurement results and the simulation results match very well.Third, comparing with some common ring-shape resonant structures, the dimension of SRR is the smallest. Then the characteristic of electromagnetic resonance in SRRs is studied seriously. The UHF band RFID reader antenna is simulated and fabricated in which the SRRs are used as radiation unit. The impedance and radiation property of this antenna is good. On H-plane this antenna is omni-directional and the gain of this antenna is large. Finally this antenna is fabricated and the result of measurement is presented.At last, the effect of LHMs on the performance of antenna is discussed and summarized briefly. The effect of SRRs on RFID reader antennas is simulated, analyzed and verified using different reader antennas. The result is that if the board of SRR is placed above the radiation plane of antennas, the resonant frequency of antennas is reduced as well as the dimension of them. The impedance and the omnidirectional characteriscs of antennas are both improved. |
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