The coil design of the inductive power transfer (IPT) for a transmitter (Tx) and receiver (Rx) is crucial to determine the performance of the IPT. Considering core loss and copper loss of the Tx and Rx coils, which are major loss terms of the whole IPT system, determination of the winding turns for the Tx and Rx coils becomes a key factor for maximum power transfer design of the IPT coils. In this paper, an optimal turns design of IPT coils for laptop wireless charging applications with a maximum power transfer efficiency is proposed. Under a specific design requirement of IPT, optimal turns of the Tx and Rx coils N1,op and N2,op can be determined by the proposed IPT coil design procedure with a finite-element-method (FEM) based simulation analysis. From the results of the coil design by the proposed IPT coil design methodology, N1,op and N2,op for maximum power efficiency, and input DC voltage Vdc for the target load power can be found by the proposed coil design procedure. The 40W prototypes of the two symmetry and asymmetry IPT coils for laptop wireless charging were fabricated, and verified by simulation and experiments. To separately verify the core and copper loss of the IPT coils, a resistance model and Steinmetz equation-based methods were comparatively evaluated, and it was found that they matched well at a core temperature condition of below 40oC. The results showed that the total weight and the thickness of the Tx and Rx coils as well as the maximum power efficiencies of 95.1% and 96.8% for the symmetry and asymmetry cases were obtained by the proposed IPT coil design procedure, which becomes a practical solution for the laptop wireless charging coil design.
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