This article considers an example of eddy current behaviour that has not been described previously in textbooks and physics education journals. This phenomenon involves a sharp rise in the active resistance of a multilayer coil with increasing alternating current frequency. This effect is not explained by the classic skin effect and is not related to losses in a core. The results of measurements of the frequency dependence of the active resistance of multilayer coils obtained by the resonance method and the results of calculating this dependence in the framework of the tape model of a multilayer solenoid are presented. The special case of relatively low frequencies is analysed when the classic skin effect is weak in a solitary wire. However, the active resistance of a multilayer coil is significantly higher than its DC resistance. A schematic model of the observed effect is proposed. The analysed example of eddy currents is easy to realize in an experiment and open to clear physical interpretation. It might be appropriate for students of various specialities to discuss this effect in intermediate or advanced physics laboratories.

中文翻译：

---

多层线圈中的涡流

本文考虑了一个涡流行为的示例，该示例以前在教科书和物理学教育期刊中都没有介绍过。这种现象包括随着交流频率的增加，多层线圈的有源电阻急剧上升。经典的集肤效应无法解释这种效应，并且与核心损耗无关。给出了通过共振方法获得的多层线圈的有源电阻的频率依赖性的测量结果以及在多层螺线管的带模型的框架内计算该依赖性的结果。当传统的趋肤效应在单根导线中较弱时，将分析相对较低频率的特殊情况。但是，多层线圈的有源电阻明显高于其直流电阻。提出了观察到的效果的示意图。所分析的涡流示例易于在实验中实现，并且易于进行清晰的物理解释。各个专业的学生都可以在中级或高级物理实验室中讨论这种效应。