Microwave oven is an appliance that uses short, high-frequency waves of electromagnetic energy to heat and cook food. These waves, called microwaves, are absorbed primarily by the water molecules in food. The waves cause the molecules to vibrate rapidly. This vibration results in friction between the molecules, which in turn produces the heat that cooks the food.
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Microwaves are generated in a microwave oven by an electron tube called a magnetron. An antenna on the magnetron transmits the waves into a waveguide, a metal enclosure that channels the energy into the oven’s cooking cavity. The waves bounce off the metal walls, flooring, and door, and penetrate the food. In most microwave ovens, a revolving metal fan called a stirrer reflects the waves, scattering them throughout the cavity for more even cooking. In some ovens, a rotating antenna also distributes the microwaves. In many, a rotating tray moves the food through the waves of energy.
Microwave cooking generally takes much less time than cooking with electric or gas ovens. Regular ovens cook food gradually, from the outside in, but microwave ovens produce heat directly inside the food. A food’s volume and density affect the depth to which microwaves will penetrate it. When microwaves cannot penetrate food completely, they heat and cook the outside layers, while the inner portion cooks from the outside in. Microwaves pass through glass, paper, plastic, and most ceramics. Most containers made of these materials may be used to hold food in microwave ovens. Metal cookware should be avoided because metal reflects the microwaves, preventing them from reaching the food, and often causes sparking. But a microwave oven’s metal accessories, such as racks, are designed to work in harmony with its energy pattern.
Microwave ovens are made with door seals that virtually eliminate microwave leakage. Ovens with poorly fitting or damaged doors should never be used because they may leak hazardous levels of microwave energy.
Manufacturers introduced microwave ovens for home use in the 1950’s. Sales of these appliances have grown rapidly since the mid-1970’s.
See also Spencer, Percy LeBaron .
