Wireless Power Transfer System Using High-Quality Factor Superconducting Transmitting Coil for Biomedical Capsule Endoscopy

We experimentally investigated the power transfer efficiency (PTE) of a wireless power transfer (WPT) system for capsule endoscopy that uses a high-temperature superconducting (HTS) transmitting (Tx) coil and a small Cu receiving (Rx) coil. A high-quality factor Tx coil is needed to maximize the PTE of a WPT system. A previously developed high-quality factor coil using double-sided HTS coated conductor wire was used as the Tx coil to improve the PTE. The diameter of the coil was 235 mm. The Rx coil was φ10 × 20 mm. The measured quality factors of the coils were 13,007 and 105, respectively. That of the Tx coil was about 13 times that of a Cu one. We measured the PTE of the WPT system in the facing direction, axial misalignment, and angular misalignment. The measured PTEs of two systems, one with an HTS Tx coil and one with a Cu Tx coil, in the facing direction at a transfer distance of 15 cm were 48.6% and 15.3%, respectively. The PTE of the system with a HTS Tx coil under axial misalignment, and angular misalignment conditions showed sufficiently high robustness compared with a system with a Cu Tx coil. The measured quality factors of the HTS and Cu Tx coils with a liquid phantom were 1,350 and 382, respectively. That of the Tx coil was about 3.5 times that of the Cu one.