edVirtus Reference

What Are Electromagnetic Waves?

How Do Electric and Magnetic Fields Carry Energy Through Space?

An electromagnetic wave is a propagating disturbance made up of changing electric and magnetic fields. Electromagnetic waves carry energy and momentum from a source through space and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

Changing electric and magnetic fields are linked by Maxwell's Equations. A changing electric field is associated with a magnetic field, and a changing magnetic field is associated with an electric field. Under suitable conditions these coupled fields detach from their source and propagate outward as an electromagnetic wave.

Unlike a sound wave, an electromagnetic wave does not require air, water, or another material medium. In a vacuum it travels at the speed of light, exactly 299,792,458 meters per second. It can also travel through material media, although its speed, wavelength, attenuation, and direction may change.

An ideal plane wave in free space is transverse: the electric field and magnetic field are perpendicular to one another and to the direction of travel. The direction of the electric field defines the wave's polarization. In the far field, the electric and magnetic components have a predictable relationship and are commonly considered together.

Fields close to an antenna or another RF source can be more complicated. Reactive energy may remain stored near the source, field components need not have the simple far-field relationship, and the electric or magnetic field may dominate locally. This is why near-field exposure assessment may require separate measurements of both components.

Frequency describes how rapidly the fields oscillate, while wavelength is the distance over which the wave repeats. Amplitude describes field strength. Phase and polarization describe other aspects of the wave, and modulation varies one or more properties so that the wave can carry information.

When an electromagnetic wave encounters matter, it may be reflected, transmitted, refracted, diffracted, scattered, or absorbed. Absorbed energy can be converted into heat or contribute to other interactions whose nature depends on frequency, field strength, material properties, and exposure conditions.

In RF safety, electromagnetic-wave behavior connects the transmitting source to the exposure environment. Propagation, antenna direction, distance, reflections, and absorption determine where energy travels and how much may reach or be absorbed by a person.