What materials can reflect millimeter wave well?

To reflect millimeter waves, the material should have high electrical conductivity or a large refractive index. Here are some materials that reflect mmWave well:

1. Metals: Metals such as aluminum, copper, and silver are excellent reflectors of millimeter waves. They are highly conductive, which allows them to reflect waves effectively. Metals reflect millimeter waves better than most materials because electrons in metals can move freely, providing high conductivity that can reflect waves efficiently.

2. Conductive coatings: Coatings made of conductive materials such as silver or carbon can reflect millimeter waves. These coatings can be applied to non-conductive materials such as plastics or ceramics to make them reflective.

3. Dielectric materials: Some dielectric materials, such as ceramics and plastic composites, can reflect millimeter waves. Reflection is caused by the material having a different refractive index than the surrounding air, and can reflect millimeter waves with low conductivity and low loss, making it suitable for some specific applications, such as waveguides and lenses.

Additionally, the effectiveness of these materials as mmWave reflectors depends on various factors, such as the wavelength of the wave, angle of incidence, and the surface finish of the material.