Design, Modeling, and Optimization of a Coaxial Cable-Embedded Flexible Inductor for Wearable Applications

Flexible and bendable inductors have attracted increasing attention because of their broad application prospects in power supplies for wearable devices. This paper proposes a coaxial flexible inductor that consists of a cable-embedded bendable magnetic core and a copper conductor. The inductor's design, modeling, and optimization procedure are presented in detail. This flexible inductor can eliminate the rigid block of a discrete inductor from the wearable device, making it more comfortable to wear. Also, because its heat distribution is more uniform, the surface temperature of the inductor can be greatly reduced. The inductor's inductance, losses, and flexibility have been modeled using geometric parameters, the current waveform, and material characteristics of ferrite sheets. These derived models can be used to optimize the inductor. A case study of a 1-μH inductor used in a 3.3-5-V 5-W boost converter has been performed to exemplify this procedure. Finally, based on the optimization results, a prototype has been fabricated and experimentally tested. The results verify the good performance of the cable-embedded inductor and the effectiveness of the optimization method.