Microwaves

Microwaves, short, high-frequency radio waves lying between infrared waves, which have higher frequency, and conventional radio waves (see Electromagnetic Radiation). Microwaves thus range in length from about 1 mm to 30 cm (0.04 to 12 in). They are generated in special electron tubes, such as the klystron and the magnetron, with built-in resonators to control the frequency (see Electronics) or by special oscillators or solid-state devices. Microwaves have many applications: in radio and television, radar, meteorology, satellite communications, distance measuring, research into the properties of matter, and cooking.

Microwave ovens operate by agitating the water molecules in the food, causing them to vibrate, which produces heat. The microwaves enter through openings in the top of the cooking cavity, where a stirrer scatters them evenly throughout the oven. They are unable to enter a metal container to heat food, but they can pass through non-metal containers.

Microwaves can be detected by an instrument consisting of a silicon-diode rectifier (see Rectification) connected to an amplifier, and a recording or display device. Exposure to microwaves is dangerous mainly when high densities of microwave radiation are involved, as with masers. They can cause burns, cataracts, damage to the nervous system, and sterility. The possible danger of long-term exposure to low-level microwaves is not yet well known. Nevertheless, governments generally limit the level of exposure to microwaves.