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In either inductive or strongly coupled magnetic resonance type wireless power transfer, the uniformity of magnetic field distribution near the transmitting coil is urgent needed as it would affect the stability of transfer efficiency when the receiving coil is moving. In this article, we proposed a new coil structure to achieve uniform magnetic field based on the relationship between the magnetic field distribution and current distribution of a coil structure. The coil is constructed of three or more spiral coils in series, where each spiral coil has a different current through a novel winding structure. The design procedure is presented, and the improved performance is verified by experiment. Compared with previous literatures, this proposed coil can generate a better uniform magnetic field distribution. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:424–427, 2015

In this paper, an antenna which can generate large, strong, and uniform magnetic field distribution is proposed for the near field magnetic coupling UHF RFID system. The antenna is composed of two elements and a feeding network. By feeding the two elements at different phases, their dead zones can be compensated by each other. Consequently, a uniform magnetic field distribution is achieved, which will be helpful in designing item level RFID system. And the perimeter of the interrogation zone is up to 5.4λ at 920MHz.Index Terms -Near-field RFID, UHF, Uniform magnetic field distribution.

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