Most households these days have a microwave, a device that uses microwave signals to cook food rapidly and efficiently. As a result, most people are familiar with the term microwaves. However, many people do not fully understand what these signals are, or how often they are used in modern society.
All electromagnetic waves oscillate in a wave pattern; if you imagine it as a wavy line drawn on a piece of paper, the wavelength is the length of the part that repeats over and over. Short wavelengths create higher frequency waves, and long wavelengths create lower frequency waves.
By definition, a microwave is any type of electromagnetic wave where the wavelength is less than one meter. Microwave signals are similar to radio broadcasting signals, with the primary difference being that radio waves are longer than a meter. This means that they are of a higher frequency than radio signals.
Although microwave signals are technically defined as radiation, they are not to be thought of as the same type of radiation that is dangerous to living creatures, such as the ionizing radiation caused by a nuclear weapon. They simply "radiate" from their source.
Microwave signals have the advantage of being more focused, and more resistant to interference than radio waves. As a result, they have been used more a variety of communication purposes. In the 1940s and 1950s, long distance phone calls were carried from tower to tower using these signals. Today, some cell phone networks and wireless devices such as Bluetooth® use low frequency, or longer-length, microwave signals.
Besides telecommunication, these signals are used in many technologies that we use every day. For instance, they're often used by regular television broadcast stations and wireless Internet connections. Likewise, low frequency microwave signals are present in the cables that provide cable TV and high speed Internet access.
Microwave signals are also being used in other forms of technology. For example, satellites orbiting above Earth utilize microwave communications. Although they are not lethal, they are used in a weapon known as the Active Denial System, which uses microwave-induced heat to control crowds and prevent targets from approaching.