Defining the mutual coupling of capacitive power transfer for wireless power transfer

Capacitive power transfer (CPT) based on electric field coupling has been proposed recently as an alternative technology for wireless power transfer, and a good understanding of the capacitive coupling is of great importance in the design and evaluation of CPT systems. A new term named capacitive coupling coefficient k_E is introduced to provide a quantitative measure of the coupling condition between the coupling plates. The term is derived by modelling the capacitive coupling plates based on electric charge balance, and its physical meaning is explained clearly in relation to the equivalent primary/secondary and mutual capacitances, which is also experimentally demonstrated by comparing two CPT systems with different cross-coupling configurations.