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 can I check my microwave door for safety issues?
You can perform a simple visual inspection of your microwave door. Check the metal mesh for any signs of damage such as tears, punctures, or significant dents. Also, examine the door seal around the perimeter for any cracks, warping, or gaps, as a compromised seal can allow radiation to escape. If the door doesn't close properly or feels loose, it's a potential safety concern. For a more thorough check, you can use a microwave leak detector tool, though professional servicing is the most reliable method for detecting actual radiation leakage.