Luneburg lens

Named after the mathematician Rudolf Karl Luneburg lens, also Luneburg lens or rare Luneberg lens is a spherical gradient index. It consists of a massive ball of lossless dielectric material with position-dependent dielectric constant. When their back is mirrored, it throws incident, parallel shafts exactly in the direction of its source back and thus acts as a retroreflector.

Construction

The refractive index in the interior of the ball is designed so that parallel incident beams are focussed at a point opposite to the point of contact of the wave front. This gives it with the distance from the center. He follows ideally the formula

Wherein the radius of the sphere. Now, if the back of the ball is mirrored, the beam returns to exactly and the wave is reflected exactly in the direction of its source. Thus, the arrangement works as a retroreflector.

Luneburg lenses can also be made for all- retro-reflection, for example, as a radar reflector, carry then take the back mirroring a narrow horizontal belt made of a conductive layer. You must always depend exactly perpendicular when used as a radar reflector on boats, so that the horizontal on both sides of the belt entering the ball radio waves are precisely focused onto the reflective metal strips on the back.