Performance evaluation of carbon nanotube yarn-based inductors for ISM-frequency band soft-switching converters

With the advancement of carbon material science, there have been attempts to apply carbon nanotubes in various engineering fields. In power electronics, application research has been conducted on using carbon nanotube (CNT) yarn in inductors, transformers, and motor windings, because CNT yarns show promising mechanical and electrical characteristics when compared with conventional conduction materials. This paper evaluates the feasibility of CNT yarn-based inductor applications with respect to higher-frequency power converter circuits, especially focusing on the ISM (Industry–Science–Medical) frequency range. Inductors are fabricated using two kinds of CNT yarns with different conductivity values. These inductors are compared with copper and lead coiled inductors, since they have a relatively high conductivity with respect to CNT yarns, and due to their popularity in the industry. The small-signal impedance data of each inductor according to the frequency variation are measured using a network analyzer, and the measurements were compared with a COMSOL simulation. One of the main results of this research is that the CNT yarn-based inductors were shown to have a better normalized AC resistance characteristic than the conventional conductor inductors, which have higher conductivity. It was found that CNT inductors have a similar AC resistance when compared to that of metallic conductors with nearly 1.85 times higher conductivity. A 100 W differential class-E resonant converter is implemented to test the inductors and to verify the small-signal measurement results. Efficiencies and thermal images are obtained at 6.78-MHz and 13.56-MHz ISM frequencies.