Patent Name: Method of Treating Foodstuffs
Patent Number: 2,495,429
Patent Date: 24 January 1950
Inventor: Percy L. Spencer, of West Newton, Massachusetts
What It Does: Cooks food quickly by microwave radiation.
Background: In 1946, Percy Spencer, a self-taught electronics wizard who never graduated grammar school, received U.S. patent 2,408,235 for the development of a high-efficiency magnetron. Magnetron tubes employ heated cathodes to generate electrons that are affected by electro-magnetic energy and reduced microwave radiation. Microwave radiation is used both in radar and in the "method of treating foodstuffs" that Spencer invented and patented four years later.
While working for the Raytheon Manufacturing Company, Spencer was running tests on one of the new magnetron tubes when he noticed the candy bar in his pocket began to melt. In playing his natural inventor instincts, he decided to play some uncooked popcorn in front of the magnetron tube. To his delight, the Colonels began popping. (This is still a favorite application of microwave technology.)
Engineers at Raytheon went to work on Spencer's discovery. The first commercial microwave oven was introduced in 1947. It was 750 pounds and 5 1/2 feet tall. Twenty years in many modifications later, the first countertop, domestic microwave oven hit the market. By 1975, microwaves were selling faster than conventional gas range ovens.
In the Inventor's Words
"Such energy has been used before for this purpose, but the frequencies implied have been relatively low, for example, not over 50 mega-cycles area I have found that at frequencies of this order of magnitude, the energy necessarily expended in order to generate sufficient heat satisfactorily cook the foodstuff is much too high to permit the practical use of the process. I have further found, however, that this disadvantage may be eliminated by implying wavelengths falling in the microwave region of the electromagnetic spectrum, for example, wavelengths of the order of 10 centimeters or less. By doing so, the wavelength of the energy becomes comparable to the average dimension of the foodstuff to be cooked, and as a result, the heat generated in the foodstuff becomes intense, the energy expended becomes a minimum, and the entire process becomes efficient and commercially feasible."
The microwave oven did not come about as a result of someone trying to find a better, faster way to cook. During World War II, two scientists invented the magnetron, a tube that produces microwaves. Installing magnetrons in Britain’s radar system, the microwaves were able to spot Nazi warplanes on their way to bomb the British Isles. By accident, several years later, it was discovered that microwaves also cook food. Called the Radar Range, the first microwave oven to go on the market was roughly as large and heavy as a refrigerator.
The idea of using microwave energy to cook food was accidentally discovered by Percy LeBaron Spencer of the Raytheon Company when he found that radar waves had melted a candy bar in his pocket. Experiments showed that microwave heating could raise the internal temperature of many foods far more rapidly than a conventional oven. The first Raytheon commercial microwave oven was the 1161 Radarange, which was marketed in 1954. Rated at 1600 watts, it was so large and expensive that it was practical only for restaurant and institutional use. In 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven, marking the beginning of the use of microwave ovens in home kitchens. Although sales were slow during the first few years, partially due to the oven’s relatively expensive price tag, the concept of quick microwave cooking had arrived. In succeeding years, Litton and a number of other companies joined the countertop microwave oven market. By the end of 1971, the price of countertop units began to decrease and their capabilities were expanded.
All electromagnetic energy can be characterized as waves with a specific wavelength and frequency distributed over a continuous range known as the electromagnetic spectrum. For example, some radio waves have a wavelength of 6 feet (2 meters) and a frequency of 50 million hertz (Hz-cycles per second). Visible light waves have a wavelength of 400 to 700 millimicrons, and typical X-rays have a length of 0.01 millimicrons and a frequency of 30 x 1012 millions. Microwaves (short waves or high frequency radio waves) are the shortest of radio waves, with a length of 0.1 millimeter and a frequency of 3 x 101 Hz. They are found in the non-ionizing portion of the energy spectrum, between radio waves and visible light. "Non-ionizing" means that microwaves do not detach charged particles and produce atoms with an unbalanced plus or minus charge. Microwaves can therefore safely produce heat and not cause food to become radioactive. Microwaves are reflected from most metals but they produce inductive resonance's in the atoms of many other substances. It was the discovery of their reaction to metals that led to the invention of radar. It was their ability to produce resonant coupling that led to the invention of the microwave oven.
source: http://www.ideafinder.com/history/inventions/story068.htm 12may2005
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