Photo: The "cooking cavity" of a typical microwave oven. This strong metal box stops harmful microwaves from escaping. The microwaves are generated by a device called a magnetron, which is behind the perforated metal grid on the right hand side (just behind the lamp that illuminates the oven inside). read more
For decades, ovens achieved “defrost” or any low-power setting simply by turning the magnetron on and off, so that it would generate full-power microwaves for only part of the total cooking time—a cycle that is clearly audible. read more