A microwave oven heats food very quickly by absorbing ELECTROMAGNETIC WAVES. The waves can be reflected off metal and glass, pass through plastics and paper, and are absorbed by food molecules. The energy from the waves is absorbed uniformly throughout the item to cook it evenly. This is unlike conventional ovens which rely on conduction to slowly transfer heat from the outside to the inside.
Microwaves are electromagnetic waves with wavelengths between about one meter and a millimeter, or 300 MHz and 300 GHz. The prefix “micro” is used because the waves have shorter wavelengths than radio waves or infrared radiation, and are much smaller than the waves used in radar (300 GHz is about 3 cm).
Jagadish Chandra Bose in 1894 invented spark oscillators to generate millimeter-wave frequencies, but he did not use the term “microwave”. The first experimental microwave transmitters were built at Westinghouse laboratories in 1933 and transmitted voice, telegraph and facsimile data over 3.3 GHz bidirectional beams at the focus of 10-foot (3 m) metal dishes. The technology was rapidly exploited after World War II because of its ability to transmit information very long distances.
The high frequency of microwaves allows signals to be focused into narrower beams than for lower frequencies and also allows much higher data transmission rates. In the 1960s microwave relay networks were constructed across the US and Europe to transmit telephone, television and telegraph data between cities. Today microwaves are used extensively for point-to-point telecommunications, to provide voice, video and data services as well as supervisory control and data acquisition (SCADA) for remote machinery, switches, valves and signals.