Design of capacitive coupling structure for position-insensitive wireless charging

Abstract

The Internet of Things (IoT) connects billions of smart devices through wireless sensor networks (WSNs). However, to ensure the power supply for numerous passive devices in a WSN, it is necessary to replace batteries periodically, which will undoubtedly increase maintenance costs. This study proposes a capacitive coupling structure that is different from the previous capacitive power transfer (CPT) structures. The proposed structure can allow the positional variation of the receiver, and multiple receivers to be charged at the same time. Both theoretical and experimental results demonstrate that the power transmission is less affected by the positional variation of the pickup plates in the vertical and horizontal directions. In this study, all coupling capacitors between the plates are considered and the equivalent circuit model is derived. Further output characteristics of the circuit are derived and analysed. The dimensions of the structure are designed and simulated by using the EM full wave simulation. A prototype is designed to verify that a battery can be charged based on capacitive coupling. A 60 mAh rechargeable lithium-ion button battery is fully charged in 250 min, and the output power is ∼36 mW during charging.