You’ve probably never heard of Percy Spencer, but you’ve certainly used one of his most famous inventions—probably to make popcorn.
The microwave was invented in 1947 and soon became an American household staple. The devices sped up the heating and reheating process in the kitchen, and flew off store shelves and onto countertops by the millions in the 1970s, ’80s, and ’90s. But in recent years, sales have started to stagnate and decline. In part, that’s because the convenience they offer comes with the cost of uneven cooking. In the late 2010s, the microwave needs a technological makeover to improve the way they generate heat, while remaining smaller and faster than traditional ovens.
Spencer, an engineer during the first and second World Wars in the US, stumbled upon the physics that power the microwave. He worked at the Raytheon Manufacturing Company, which to this day produces missiles and other warfare technology. After World War II, he began a project working with magnetrons, which produce electromagnetic wave pulses that can be used like radar. George “Rod” Spencer, Percy’s grandson, told Popular Mechanics that his grandfather always kept peanut clusters—like a nutty snack bar—in his pockets to feed animals outside the plant in Cambridge, Massachusetts. While testing a magnetron designed to improve plane radar, Percy slipped his hand into his pocket and discovered that the peanut clusters had melted.
Spencer had discovered that magnetrons can be used to create microwaves, which are a form of electromagnetic radiation with waves shorter than radio waves but longer than anything we can see. When electricity runs through a metal filament, negatively charged electrons rush to positive end. Magnetrons keep these electrons going in a loop created by a magnet. As electrons whiz around, they create electromagnetic microwaves that radiate outward.
These waves hijack the water molecules in food. When exposed to microwaves, water molecules will start wiggling around rapidly. All microwave ovens have metal mesh lining, which reflect these waves, so they bounce around in a closed setting about 2.5 billion times per second. Water molecules get tugged back and forth so fast they create friction that heats food from within.
The first consumer microwave from 1947 was the size of a coat closet and had to be hooked up to a plumbing system to be cooled down with water. Over the next 20 years, technology got smaller and cheaper. In 1967,…