The Microwave Oven By JennaNodine 1920 Vacuum tube radio transmitters developed 1933 First demonstration of food cooking with shortwave transmitter at Chicago World's Fair 1937 Application is patented in U.S. by Bell Laboratories 1945 Specific heating effect of a high-powered microwave accidentally discovered 1947 First microwave oven comercially available, costing $5,000 1986 25% of U.S. housholds have a microwave 1997 90% of U.S. households have a microwave