Uses of Radio Waves, Microwaves and Infrared

Choosing a wave for a job

Radio waves, microwaves and infrared are all electromagnetic radiation. They can transfer energy without needing a material to carry them. They can also carry information: a transmitter varies a wave to represent a message, and a receiver detects it. Different uses depend on whether the radiation can travel along the required path and what happens when a material absorbs it.

Radio waves: broadcasting and communication

A broadcasting transmitter sends radio waves carrying sound or television information. A receiver, such as a radio or television aerial, picks up the waves so the information can be reproduced. Radio waves also carry signals in other wireless communications, including transmissions involving satellites. For a satellite link, the chosen waves must be able to travel between Earth and the satellite through the atmosphere.

Microwaves: communication or cooking

Microwaves can carry information between communication equipment on Earth and satellites, as well as in other wireless links. Frequencies suitable for these links are chosen so that the waves can pass through the atmosphere with relatively little absorption. A satellite receives a signal and sends one onwards, allowing communication across large distances.

A microwave oven puts a different interaction to use. Microwaves are absorbed by water in food, transferring energy to it. The warmed parts of the food then transfer energy to neighbouring parts, cooking the food. The microwave frequencies used for communication are chosen for transmission through the atmosphere, whereas those used in ovens are useful because food absorbs them.

Infrared: heating, seeing heat and sending signals

Warm objects emit infrared radiation. When food absorbs infrared from a hot grill or toaster element, its temperature rises: this is one way infrared is used in cooking. A thermal imaging camera works in the other direction. It detects infrared emitted by objects and converts differences in the detected radiation into a visible image. This can reveal a warm person against cooler surroundings.

Infrared can carry information too. A television remote sends coded pulses of infrared to a receiver on the television. This is short-range communication and normally needs a clear path between the two devices. Infrared signals can also carry data along optical fibres: thin glass or plastic strands that guide the radiation around bends by repeated total internal reflection. Infrared security systems may detect the radiation associated with a warm person to trigger an alarm or light; other systems use an infrared beam and detect when it is interrupted. In each case, the equipment uses an infrared signal or a change in detected infrared to respond.

Radio waves

Broadcasting and other wireless communications use radio waves to carry information to receivers. Radio waves are also used in satellite transmissions.

Microwaves

Microwaves carry communication signals, including signals to and from satellites; suitable frequencies pass through the atmosphere with little absorption. In ovens, microwaves are absorbed by water in food and transfer energy for cooking.

Infrared

Infrared absorbed by food provides heating for cooking. Infrared emitted by objects is detected in thermal imaging. Coded infrared pulses provide short-range communication, including TV remotes; infrared can also carry data through . Security systems can detect infrared from warm objects or interruptions to an infrared beam.