Most of us take our microwave ovens for granted. Yet these little workhorses of the kitchen are actually high-tech marvels that use powerful electromagnetic waves to heat up food quickly and easily.

It may seem like a holdout against the solid-state world, but the vacuum-tube magnetron is still at the heart of every consumer microwave oven and many commercial ones used for cooking or drying.

In 1967, Amana Corporation introduced the first tabletop-sized microwave oven for consumer use. Since then, the microwave has become an indispensable small appliance in virtually every home in the ...