I. Introduction
High-frequency inductors have been widely used in various fields (e.g., wireless power transfer, induction heating, high-speed electrically powered propulsion, and high-frequency transformers). In these high-frequency systems, eddy currents on conductors are inevitable due to stray alternating magnetic fields. The induced currents lead to excessive losses, which degrade efficiency and cause thermal problems in inductors. To prevent this adverse effect, stranded wires have been generally applied to design high-frequency inductors. At the same time, it is necessary to estimate the exact losses of stranded wires in a wide range of frequencies.