This tutorial provides an intuitive and concrete description of the phenomena of electromagnetic nonreciprocity that will be useful for readers with engineering or physics backgrounds. The notion of time reversal and its different definitions are discussed with special emphasis on its relationship with the reciprocity concept. Starting from the Onsager reciprocal relations that are generally applicable to many physical processes, we present the derivation of the Lorentz theorem and discuss other implications of reciprocity for electromagnetic systems. Next, we identify all possible routes toward engineering nonreciprocal devices and analyze three of them in detail, based on external bias and on nonlinear and time-variant systems. The principles of the operation of different nonreciprocal devices are explained. We address the similarity and fundamental difference between nonreciprocal effects and asymmetric transmission in reciprocal systems. In addition to the tutorial description of the topic, this article also contains the original findings. In particular, the general classification of reciprocal and nonreciprocal phenomena in linear bianisotropic media based on the space- and time-reversal symmetries is presented. This classification serves as a powerful tool for drawing analogies between seemingly distinct effects having the same physical origin and can be used for predicting novel electromagnetic phenomena. Furthermore, electromagnetic reciprocity theorem for time-varying systems is derived, and its applicability is discussed.

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电磁非互易性及其起源教程

本教程对电磁非互易性现象进行了直观而具体的描述，对具有工程或物理背景的读者很有用。讨论了时间反转的概念及其不同的定义，特别强调了它与互惠概念的关系。从普遍适用于许多物理过程的昂萨格互易关系开始，我们介绍了洛伦兹定理的推导，并讨论了互易性对电磁系统的其他影响。接下来，我们确定了设计非互易设备的所有可能途径，并基于外部偏差以及非线性和时变系统详细分析了其中的三个。解释了不同非互易设备的操作原理。我们解决了互惠系统中非互惠效应和非对称传输之间的相似性和根本区别。除了该主题的教程描述外，本文还包含原始发现。特别是，提出了基于空间和时间反转对称性的线性双各向异性介质中互易和非互易现象的一般分类。这种分类是在具有相同物理起源的看似不同的效应之间进行类比的强大工具，可用于预测新的电磁现象。此外，推导了时变系统的电磁互易定理，并讨论了其适用性。除了该主题的教程描述外，本文还包含原始发现。特别是，提出了基于空间和时间反转对称性的线性双各向异性介质中互易和非互易现象的一般分类。这种分类是在具有相同物理起源的看似不同的效应之间进行类比的强大工具，可用于预测新的电磁现象。此外，推导了时变系统的电磁互易定理，并讨论了其适用性。除了该主题的教程描述外，本文还包含原始发现。特别是，提出了基于空间和时间反转对称性的线性双各向异性介质中互易和非互易现象的一般分类。这种分类是在具有相同物理起源的看似不同的效应之间进行类比的强大工具，可用于预测新的电磁现象。此外，推导了时变系统的电磁互易定理，并讨论了其适用性。这种分类是在具有相同物理起源的看似不同的效应之间进行类比的强大工具，可用于预测新的电磁现象。此外，推导了时变系统的电磁互易定理，并讨论了其适用性。这种分类是在具有相同物理起源的看似不同的效应之间进行类比的强大工具，可用于预测新的电磁现象。此外，推导了时变系统的电磁互易定理，并讨论了其适用性。