Megahertz-range wireless power transfer has become a promising approach for increasing spatial freedom of charging. This article proposes a cylindrical-shaped coil, which can produce the homogeneous magnetic field in a plane. The coil consists of two helical windings, which are wound to guide the current in opposite directions. A single power source is used to excite the transmitter without any current amplitude or phase control circuits. Furthermore, since the parasitic capacitance of the coil is not negligible due to the complexity of the coil shape, we develop a general equivalent model with parasitic capacitance for the analysis of complex coils. The system efficiency of the proposed omnidirectional wireless power transfer device is validated by a practical experiment. The measured dc-to-dc efficiency of approximately 72.4% and the load power of 13 W are demonstrated for the proposed wireless charging system at 6.78-MHz operating frequency. Finally, we verify that the electromagnetic exposure satisfies the safety regulations.

中文翻译：

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用于二维全向无线电力传输的圆柱形发射线圈

兆赫兹范围的无线电力传输已成为增加充电空间自由度的有前途的方法。本文提出了一种圆柱形线圈，可以在平面内产生均匀的磁场。线圈由两个螺旋绕组组成，它们被缠绕以引导相反方向的电流。单个电源用于激励发射器，无需任何电流幅度或相位控制电路。此外，由于线圈形状的复杂性，线圈的寄生电容不可忽略，我们开发了一个具有寄生电容的通用等效模型，用于分析复杂的线圈。通过实际实验验证了所提出的全向无线电力传输装置的系统效率。测得的 DC-DC 效率约为 72。所提出的无线充电系统在 6.78 MHz 的工作频率下展示了 4% 和 13 W 的负载功率。最后，我们验证电磁暴露是否满足安全规定。