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24 DESIGN007 MAGAZINE I JULY 2024 energy from electromagnetic waves. Larger diameters allow for better energy absorption, while smaller diameters limit energy transfer. e wave energy is determined by its ampli- tude. e amplitude of an electromagnetic wave refers to the maximum field strength of its electric and magnetic fields. e energy carried by an electromagnetic wave is directly proportional to the square of its amplitude. In other words, if the amplitude of a wave dou- bles, its energy increases by four times. is relationship holds true for all types of electro- magnetic waves (Figure 1). When electromagnetic waves encounter a conductor (such as a PCB trace and its refer- ence line, typically a ground conductor), they induce oscillating currents in the conductors due to the fluctuating electric and magnetic fields. A pair of associated conductors, usu- ally a signal line and reference line, are used to move energy from point A to point B. ese induced currents themselves emit electromag- netic waves at the same frequency, which can either constructively or detrimentally inter- fere. If the conductor has a small diameter (compared to the wavelength of the incident wave), the induced currents are limited, and the energy absorption is reduced. Conversely, a larger conductor diameter allows for more efficient energy absorption. It's essential to note that the speed of energy/ signal traveling down a conductor is actually the speed of the electromagnetic wave, not the movement of electrons. e signal travels on this electromagnetic carrier wave. e EM wave traveling along (guided by) the copper trace forms a type of waveguide. e propaga- tion of the wave is affected by the interaction with the material(s) in and surrounding the dielectric, caused by the presence of electric charge carriers, interacting with the electric field component, and magnetic dipoles, inter- acting with the magnetic field component. e energy/signal flows overwhelmingly outside the electrical conductor. e purpose of the conductor is thus not to conduct energy, but to guide the energy-carrying wave. e electromagnetic fields do not move through space. It is the electromagnetic energy that moves. e electric field of a conduc- tor extends to the return conductor, which is usually closely coupled to the signal trace. At Figure 1: Energy carried by an EM wave depends on its amplitude. Doubling the E (electric) field and B (magnetic) field quadruples the energy density (u) and the energy flux (uc). (Source: Samuel J. Ling)