Development of the mathematical theory by James Clerk Maxwell (1831−1879) was a major breakthrough, which led to the discovery of the electromagnetic radiation. An exact description of electromagnetic radiation and its behavior requires a knowledge of Maxwell’s electromagnetic ﬁeld equations that describe the temporal and spatial dependence of electromagnetic ﬁelds and provide good agreement with observed phenomena over a wide range of frequencies in the spectrum. The spectrum is the variation of the intensity of the radiation as a function of the frequency or wavelength. Around 1864, Maxwell predicted the existence of electromagnetic waves that travel through space at the speed of light. Heinrich Rudolf Hertz (1847−1894) proved Maxwell’s laws in the late 1880s when he produced electromagnetic waves using an oscillating current generated by the spark of an induction coil.