Transverse electromagnetic standing waves with E∥B

This article examines the conditions under which transverse electromagnetic (TEM) waves exist in a sourceless medium. It shows that TEM waves can be classified according to whether their Poynting vector is identically zero or nonzero. The former are nonpropagating TEM standing waves with E∥B and the latter are TEM traveling and standing waves with E⊥B and E∥/B. The general condition under which TEM standing waves with E∥B exist is derived. Mathematical examples of these standing waves are given. An experimental configuration to realize one of these examples is proposed. The behavior of these waves under Lorentz transformations is discussed and it is shown that these waves are lightlike and that their fields lead to well‐defined Lorentz invariants. It is hoped that this article will encourage electrodynamics course instructors to include a discussion of E∥B TEM standing waves.