Heating food by microwave was discovered accidentally in 1945 by self-taught American engineer Percy Spencer. Spencer was working with the American company Raytheon on active radar sets when he noticed his Mr. Goodbar chocolate bar melting in his pocket.
Spencer experimented with the idea by microwaving popcorn, and and eggs. He created a high density electromagnetic field by feeding microwave power from a magnetron 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 quickly.
Raytheon filed for a US patent for the microwave cooking process in 1945, and an oven was placed in a Boston restaurant for testing. In 1947, the company built the “Radarange”, the first commercial microwave oven. It was almost 1.8 metres (5 ft 11 in) tall, weighed 340 kilograms (750 lb) and cost about US$5000. An early commercial model introduced in 1954 used 1.6 kilowatts and sold for US$2000 to US$3000. Raytheon licensed its technology to the Tappan Stove company in Ohio in 1952. Their attempts to market a large, 220 volt, wall unit as a home microwave oven in 1955 for US$1295, were unsuccessful. In 1965 Raytheon acquired Amana Corporation and in 1967 they introduced the first popular home model, the countertop Radarange at a price of US$495. (Wikipedia)