用假设弱透镜焦距表达式是一个幂级数中的第一项的方法，可以导出相当准确且便于实用的电磁电子透镜物镜焦距公式。
By assuming the weak lens focal length expression to be the first term in a power series a simple and accurate formula can be derived for the objective focal length of a magnetic electron lens.
无刷直流永磁电机的电源虽是直流电，但其内部绕组中的电流仍是交流电，其旋转部分犹如同步电机的磁极转子，其结构及电磁原理与同步电机相似。
With the power being DC, the current of inner winding of the magneto is AC, and the rotating part is just similar to the magnetic rotor of synchronous dynamo.
本文讨论了电磁场逆问题的求解方法，系统地进行了随机类优化算法的改进研究以及轮毂式永磁电机优化设计的应用研究。
This paper mainly presents the method of solving inverse electromagnetic problems, the improvement of the stochastic optimization algorithm and the optimal designing of outer-rotor permanent motor.
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