Microwave doors block radiation using a metal mesh with holes smaller than the wavelength of microwaves, but larger than visible light waves.
The metal mesh in a microwave door acts as a Faraday cage for microwave radiation. Microwaves have a relatively long wavelength, typically around 12 cm. The holes in the mesh are significantly smaller than this wavelength, preventing the microwaves from passing through and escaping the oven. However, visible light has a much shorter wavelength, on the order of nanometers, allowing it to easily pass through the same holes, which is why you can see inside the microwave.
While microwave doors are designed to contain radiation, it's always wise to ensure your appliance is in good condition and not damaged.
What are the safety standards for microwave oven doors?
Microwave oven doors must meet strict safety standards to ensure they effectively contain microwave radiation. In the United States, the FDA sets these standards under the Radiation Control for Health and Safety Act. These regulations limit the amount of microwave energy that can leak from any microwave oven, including through the door, to a very low level (typically no more than 5 milliwatts per square centimeter at any point 5 cm or more from the oven surface). The door and its sealing mechanism are crucial components in meeting these safety requirements.