Six Degrees of Freedom Wide-Range Ubiquitous IPT for IoT by DQ Magnetic Field

Abstract

Direct and quadrature (DQ) rotating magnetic-field-based transmitting (Tx) coils for wireless charging of multiple internet of things (IoT), which are broadly distributed over three-dimensional (3D) spaces, are newly proposed in this paper. The proposed Tx coils provide a uniformly distributed DQ magnetic field environment so that numerous IoT, such as active radio frequency identification (RFID) tag, electric shelf label (ESL), appliances, and various sensors connected to internet, are charged with 3-D omnidirectional wireless charging. By virtue of the generated DQ magnetic field, six degrees of freedom (6-DoF), regardless of their three-axes positions and directions, are achieved by the proposed Tx coils with plane receiving (Rx) coils, which is essential for the proposed ubiquitous wireless power environment. Therefore, the proposed wide-range ubiquitous inductive power transfer (IPT) is highly recommended for adoption in practical applications, where volumetric structures with large size of core are not allowed. The optimum distance between the DQ lines of the proposed Tx coils $d_{w}$ was found by magnetic field analysis to deliver maximum magnetic field $B_{t}$ at a target distance of $z_{{1}}$ . To generate DQ currents and guarantee zero-voltage-switching operation of the main switches, detailed static analysis of the proposed DQ Class D inverter based on an imaginary gyrator model is presented. The effective area ratio of an Rx coil having a ferrite core is derived and experimentally found in this evenly distributed magnetic field condition. 1:20 and 1:1 scaled-prototypes for $d_{l}\,= \,{\text{10}}\;\text{m}$ and 5 m DQ line cases, respectively, were installed on the ceiling and experimentally verified for the uniformity of magnetic field and the highest wireless power delivery freedom. Experimental results showed that the proposed IPT has 78% of uniformity for magnetic field and Rx coils are freely charged with a 6-DoF characteristic. Two hundred of Rx coils, which are arbitrarily distributed over 3-D space, can be simultaneously charged with 16.2 W of total received load power and 9.3% of power efficiency.