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.
How does the metal mesh in a microwave door prevent radiation leakage?
The metal mesh functions as a Faraday cage. When microwaves are generated inside the oven, they are contained by the metal walls and the door. The mesh acts as a barrier because the electrical charges within the metal redistribute themselves to cancel out the electromagnetic field of the microwaves trying to pass through the holes. Since the holes are smaller than the microwave's wavelength, the electromagnetic waves cannot effectively propagate through them. This containment is essential for safety, preventing microwave energy from escaping into the kitchen environment.