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MICROWAVE OVENS

A microwave oven, or simply a microwave, is a kitchen appliance that heats food by dielectric heating. This is accomplished by using microwave radiation to heat polarized molecules within the food. This excitation is fairly uniform, leading to food being more evenly heated throughout (except in dense objects) than generally occurs in other cooking techniques.

The first personal microwave was introduced in 1967 by the Amana Corporation.

Basic microwave ovens heat foods quickly and efficiently, but, unlike conventional ovens, do not brown or bake food. This makes them unsuitable for cooking certain foods, or to achieve certain culinary effects. Additional kinds of heat sources can be added to microwave packaging, or into combination microwave ovens, to add these additional effects.

The use of high-frequency electric fields for heating dielectric materials had been proposed in 1934, for example US patent 2,147,689 (application by Bell Telephone Laboratories, dated 1937) states "This invention relates to heating systems for dielectric materials and the object of the invention is to heat such materials uniformly and substantially simultaneously throughout their mass. ... It has been proposed therefore to heat such materials simultaneously throughout their mass by means of the dielectric loss produced in them when they are subjected to a high voltage, high frequency field."

The heating effect of microwaves was discovered accidentally in 1945. Percy Spencer, an American self-taught engineer from Howland, Maine, was building magnetrons for radar sets with the American company Raytheon. He was working on an active radar set when he noticed that a peanut chocolate bar he had in his pocket started to melt. The radar had melted his chocolate bar with microwaves. The first food to be deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.[1][2] To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly.

On October 8, 1945[3] Raytheon filed a US patent for Spencer's microwave cooking process and an oven that heated food using microwave energy was placed in a Boston restaurant for testing. In 1947, the company built the Radarange, the first commercial microwave oven in the world.[4] It was almost 1.8 metres (5 ft 11 in) tall, weighed 340 kilograms (750 lb) and cost about US$5000 each. It consumed 3 kilowatts, about three times as much as today's microwave ovens, and was water-cooled. The first Radarange was installed (and it's still there) in the galley of the NS Savannah nuclear-powered passenger/cargo ship. An early commercial model introduced in 1954 consumed 1.6 kilowatts and sold for US$2000 to US$3000. Raytheon licensed its technology to the Tappan Stove company of Mansfield, Ohio in 1952.[5] They tried to market a large, 220 volt, wall unit as a home microwave oven in 1955 for a price of US$1295, but it did not sell well. In 1965 Raytheon acquired Amana. In 1967 they introduced the first popular home model, the countertop Radarange, at a price of US$495.

In the 1960s, Litton bought Studebaker's Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Litton then developed a new configuration of the microwave, the short, wide shape that is now common. The magnetron feed was also unique. This resulted in an oven that could survive a no-load condition, or an empty microwave oven where there is no object to absorb the microwaves, indefinitely. The new oven was shown at a trade show in Chicago, and helped begin a rapid growth of the market for home microwave ovens. Sales volume of 40,000 units for the US industry in 1970 grew to one million by 1975. Market penetration was faster in Japan, due to a re-engineered magnetron allowing for less expensive units.

Several other companies joined in the market, and for a time most systems were built by defense contractors, who were most familiar with the magnetron. Litton was particularly well known in the restaurant business. By the late 1970s the technology had improved to the point where prices were falling rapidly. Often called "electronic ovens" in the 1960s, the name "microwave ovens" later became standardized, often now referred to informally as simply "microwaves." Formerly found only in large industrial applications, microwave ovens were increasingly becoming a standard fixture of most kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use.[citation needed] By 1986, roughly 25% of households in the U.S. owned a microwave oven, up from only about 1% in 1971.[6] Current estimates hold that over 90% of American households own a microwave oven.

 

 

 

 


 

 

 

 

 

 

 

 

 

 
 
 
 
 
 
             
 
             
 
             
 
 
 
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