Like all other radio communication applications, mobile telephony uses radio waves to carry the information, like voice, text and images, through the air. Radio waves are a kind of electromagnetic fields (EMF) that are also called radio frequency fields or radio frequency energy.

Radio waves travel with the speed of light. They consist of an electric and a magnetic component, which vary periodically in time. The number of oscillations per second is called the frequency. Different types of electromagnetic fields have different frequencies. Visible light, for instance, has higher frequencies than radio waves, but lower than ultraviolet light.

Electromagnetic waves with frequencies higher than ultraviolet light are called ionizing radiation, which has sufficient energy to break molecular bonds and thereby the potential to cause damage to biological tissue. X-rays and gamma rays are examples of ionizing radiation. Radio waves belong to the lower frequency part of the electromagnetic spectrum, which is called non-ionizing radiation. Here the electromagnetic energy is too low to break molecular bonds.