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Litz wires consist of many individual, isolated conductor strands. Certain litz wires are fabricated by simply twisting the bundle of strands, hence a wire pitch is realized. In this paper, the ac resistance of coils made of such twisted litz wire are calculated by combining two-dimensional finite element simulation and circuit laws. In so doing, the inherently three-dimensional problem can be solved at much lower computational cost. Results are presented for the current distribution, and for the alternating current resistance of coils, validated against measured data. [ABSTRACT FROM AUTHOR]

A nonlocal generalization of the IBC (impedance boundary condition) concept is introduced in this work for modeling the coil wires in resonant WPT (wireless power transfer) links. Such NLIBCs (nonlocal IBCs) can accurately account for the skin and proximity effects in the wires for all frequencies relevant to resonant WPT systems and can be utilized in both finite-element and surface-integral-equation numerical frameworks. The NLIBCs have run-time performance close to that of the IBC because the NLIBCs take advantage of the quasi-2D nature of the electromagnetic field inside the wires. The results for a typical WPT configuration illustrate the performance. [ABSTRACT FROM AUTHOR]