This study analyzed the modeling and characteristics of parallel-plate capacitors for underwater capacitive wireless power transfer (CWPT) systems. Using finite element method (FEM) simulations, this study investigated the impact of various factors on the simulation results for both capacitance and conductance. A fitting equation is proposed for the coupling capacitance and conductance in a seawater environment. The derived equations were verified by varying the coupler size. For four different sizes, the maximum error percentage for capacitance was 9.18% at a size of 180×100 mm. For conductance, all error percentages were less than 3.49% at a transfer distance of 20 mm. The agreement between the simulated results and those calculated from the derived equations confirms the validity of the derived equations for both capacitance and conductance. Notably, this study also demonstrates a ratio of approximately 295.9 between the real and imaginary parts of the coupling admittance at a frequency of 3 MHz. This finding confirms that conductance, rather than susceptance, dominates the CWPT systems in underwater applications.

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