A Novel Multi-loop Tag for Near Field Communication in UHF Band

In this paper, we propose a new loop tag for near field communication in UHF band. The proposed loop tag is composed of a loop structure for coupling to reader and a microchip for modulation. Specially, the suggested loop tag differs from a general single loop tag in that there are a number of linked loops as a antenna body to enhance the near magnetic field. To understand impedance matching principle of the tag, we equalize the loop tag as a parallel circuit combined a series LC circuit of a loop antenna with a parallel RC circuit of a microchip. We project a total impedance of a loop antenna and a microchip on Smith chart and confirm that a tag operates as a resonator with a RLC circuit at operating frequency. Next, to verify a superior readability of the proposed tag, we interpret a near magnetic field distribution when a source antenna as a reader radiates to the tag. Comparing with a general single loop tag, we confirm that the near magnetic field around the suggested loop tag is about 10 dB higher than a general single loop tag. Also, the results assure that the multi-loop antenna can be read well than a single loop tag in a various application required perfectly readability using near field communication in UHF band.