Analytical computation of distributed capacitance for NFC coil antenna

Abstract

A new method for formulating the equivalent distributed capacitance of NFC coil antenna is proposed. This method is based on an analytical approach by conformal mapping for quantifying the capacitance per unit length and then applied the capacitance network method for calculating the equivalent distributed capacitance. The results of this method are verified with simulated and measured results of two different types of antenna and the agreement is >91%. It is also tested that the capacitance between nonadjacent turns cannot be ignored in the equivalent distributed capacitance computation. Furthermore, the effects of the coil width and gap between the two adjacent coils are predicted in calculating the equivalent distributed capacitance for a specific coil antenna. The proposed method will be useful for designing NFC coil antennas with a better accuracy of capacitance.