A Curved Transmitting-Coil Array for Multidimensional Wireless Power Transfer in 3-D Cylindrical Space

In recent years, high-frequency wireless power transfer (WPT), such as operating at 6.78 MHz (MHz), has attracted increasing attention due to its improved spatial freedom. In applications such as pipeline inspection robots and medical implants, the transmitting (Tx) coils are usually attached to curved surfaces, and the receiving device often undergoes multi-degree-of-freedom rotations during movement (i.e., positional and angular misalignment). Therefore, this article develops a staggered and overlapping curved Tx-coil array design to achieve a uniform magnetic field distribution in three-dimensional (3D) directions in cylindrical space. The staggered layout is periodic and spatially scalable, overcoming the spatial limitations of traditional designs; the overlapping of each individual curved Tx coil also suppresses the cross-coupling inside the coil array in the 3D direction. In addition, Tx input current phase modulation is applied to shape the magnetic field in the cylindrical space. Finally, the concept of the staggered curved coil array is implemented and verified in a 6.78 MHz WPT experimental system. The results show that the design greatly improves the spatial freedom of power transfer in 3D cylindrical space with a static and pre-optimized manner (i.e., no adaptation), especially showing high tolerance to rotations with position and angle misalignment. For instance, when charging a planar receiver with misaligned position and 20$^{\circ }$titled angle, the coefficient of variation of the received output voltage is reduced to 6.5% over a 360$^{\circ }$rotation.