Design and Optimization of a Novel Double-Layer Helmholtz Coil for Wirelessly Powering a Capsule Robot

Inductively coupled wireless power transfer (IWPT) is promising to power a freely moving capsule robot (CR) continuously. The existing IWPT system for this application normally adopts a single-layer Helmholtz coil (SHC), which can generate a uniform alternating magnetic field (AMF) to cover the CR workspace but leads to low power transfer efficiency (PTE). To improve the PTE, this article proposes a novel double-layer Helmholtz coil (DHC). The DHC is composed of two in-parallel connected SHCs that have identical coil turns and winding directions but different diameters. To design and optimize the DHC, a dedicated analytical model is built and verified. A comparison between the DHC and SHC is also conducted, which shows that the DHC can not only generate a uniform AMF to cover a larger region, but its power consumption is lower when the generated AMF is identical, thus improving the PTE. Finally, the DHC is used to power a 3-D receiving coil, and the achieved PTE is in a range of 7.58%-17.41%, higher than that when using the SHC, which is in a range of 6.74%-14.92%.