Electromagnetic Waves or EM Waves are waves that are created as a result of vibrations between an electric field and a magnetic field. In other words, EM waves are composed of oscillating magnetic and electric fields.
Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are hence known as ‘electromagnetic’ waves. The electric field and magnetic field of an electromagnetic wave are perpendicular (at right angles) to each other. They are also perpendicular to the direction of the EM wave.
EM waves travel with a constant velocity of 3.00 x 108 m/s in vacuum. They are deflected neither by the electric field, nor by the magnetic field. However, they are capable of showing interference or diffraction. An electromagnetic wave can travel through anything – be it air, a solid material or vacuum. It does not need a medium to propagate or travel from one place to another. Mechanical waves (like sound waves or water waves), on the other hand, need a medium to travel. EM waves are ‘transverse’ waves. This means that they are measured by their amplitude (height) and wavelength (distance between the highest/lowest points of two consecutive waves).
The highest point of a wave is known as ‘crest’, whereas the lowest point is known as ‘trough’. Electromagnetic waves can be split into a range of frequencies. This is known as the electromagnetic spectrum. Examples of EM waves are radio waves, microwaves, infrared waves, X-rays, gamma rays, etc.
Every interconnect in an electronic system has some impedance, but what is the physical reason for this impedance? This is not a contrived notion—it reflects how signals really travel across an interconnect and through real media. Signals travel through PCBs as electromagnetic waves, and the propagation behavior is determined in part by the wave impedance. This term is normally used to reference waveguides, but it is a universal term that applies to any PCB trace and is used to derive analytical expressions for trace impedance.