High-temperature superconducting (HTS) tapes are mainly used in cables and motors at relatively low frequencies below 1 kHz, and it has been reported that the AC loss of superconducting tapes in this range increases proportionally to the frequency because the hysteresis loss is dominant. In contrast, the recently developed wireless power transmission system is expected to be applied at 10 kHz or higher when using high-temperature superconducting tapes, and the AC loss in the superconducting tape is generally expected to increase with the square of the frequency due to the eddy current loss in the protective layer as well as the hysteresis loss in the superconducting layer. There are two types of HTS tapes: REBCO tapes and BISCCO tapes. BISCCO tape is buried in a protective layer of silver, which is expected to have large eddy current losses and cannot be used for high frequency applications, while REBCO tape has protective layers such as Hastelloy substrate and silver layer, which cause eddy current losses in this area.

In order to investigate these characteristics of AC loss, this study employed the finite element method (FEM) for the purpose of analyzing the electromagnetic field, with the objective of deriving the AC loss in each layer of the REBCO tape. In the context of wireless power transmission, given the reports of the potential for achieving very high Q-values at low power at high frequencies, this study investigated the AC losses under such conditions. As direct estimation of AC losses at low currents is challenging due to the necessity for a fine mesh, this study initially derived the losses in each layer for the REBCO tape with a critical current of 400 A and energized at 100 to 300 A. The findings demonstrated that the AC losses were found to be affected by each layer. Consequently, it was confirmed that the AC losses in each layer affect each other. Based on these results, equations for fitting up to 0.1A in each layer were proposed. The results demonstrate that eddy current losses in the Hastelloy layer account for the majority of the losses at high frequencies in the low current region.