In 1946, engineer Percy Spencer, who worked for the Raytheon Corporation, experimented with a magnetron tube. And suddenly he saw that the candy in his pocket had melted! This surprised him and he continued to experiment with products by placing the magnetron in a metal box. Electromagnetic waves of small length (12 cm) cannot pass through metal and are absorbed by products, causing the latter to heat up.
Interesting fact, the first commercial microwave oven was released in 1947, it cost $ 5000 and was about 2 meters in size.
Microwave ovens have enjoyed great success in countries that have little gas, such as Japan.