What Is a Microwave?

The word “microwave” is a synonym for electromagnetic radiation, which comes in waves or particles with different wavelengths and frequencies, from radio waves and visible light to X-rays. The boundaries between far infrared, terahertz radiation, microwaves, and radio and X-rays are fairly arbitrary; what’s important is that each type of radiation can do different things.

Microwave energy is reflected by metal, passes through glass and paper (and most plastics), and is absorbed by food—which is what makes it useful for cooking. Like most types of electromagnetic radiation, microwaves can be used for communications and radar.

Percy Spencer, an engineer for the Raytheon Corporation, is generally credited with inventing the modern microwave oven after World War II using technology developed for radar. His experiment involved pointing a magnetron tube at such objects as a bag of popcorn and an egg. Both the popcorn and the egg exploded, which he concluded was the result of microwaves being absorbed by these materials.

Unlike lower-frequency radio waves, which can reflect off the ionosphere or be absorbed by buildings and trees (groundwaves), microwaves travel solely through line-of-sight paths. This is why mobile phones need so many transmitter towers and why radar works by sending out bursts of microwaves, detecting the echoes they hit, and using the time it takes for those echoes to come back to determine their distance from the radar receiver.

Despite the proliferation of microwaves, they’re still relatively new, having been introduced for consumer use in 1946. Since then, they’ve become the workhorses of our kitchens, doing everything from reheating leftovers to defrosting frozen foods to making popcorn and baking.