 If electromagnetic waves travelling through one material meet another material, having a different dielectric constant or diamagnetic constant from the first,
the waves will reflect or scatter from the boundary between the materials.This means that a solid object in air or in a vacuum, or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves from its surface.This is particularly true for electrically conductive materials such as metal and carbon fibre, making radar well-suited to the detection of aircraft and ships.