Parabolic reflector
From Wikipedia, the free encyclopedia
A parabolic reflector, known as a parabolic dish or a parabolic mirror, is a reflective device, commonly formed in the shape of a paraboloid of revolution. Parabolic reflectors can either collect or distribute energy such as light, sound, or radio waves.
The parabolic reflector functions due to the geometric properties of the paraboloid shape: if the angle of incidence to the inner surface of the collector equals the angle of reflection, then any incoming ray that is parallel to the axis of the dish will be reflected to a central point, or "focus". Because many types of energy can be reflected in this way, parabolic reflectors can be used to collect and concentrate energy entering the reflector at a particular angle. Similarly, energy radiating from the "focus" to the dish can be transmitted outward in a beam that is parallel to the axis of the dish.
John Hadley introduced parabolic mirrors into practical astronomy in 1721 when he used one to build a reflecting telescope with very little spherical aberration. Before that, telescopes used spherical mirrors. Lighthouses also commonly used parabolic mirrors to collimate a point of light from a lantern into a beam, before being replaced by more efficient fresnel lenses in the 19th century.
The most common modern applications of the parabolic reflector are in satellite dishes, telescopes (including radio telescopes), parabolic microphones, and many lighting devices such as spotlights, car headlights, PAR Cans and LED housings.
Parabolic reflectors suffer from an aberration called coma. This is primarily of interest in telescopes because most other applications do not require sharp resolution off the axis of the parabola.
The Olympic Flame is lit using a parabolic reflector concentrating sunlight.
A parabolic reflector pointing upward can be formed by rotating a reflective liquid, like mercury, around a vertical axis. This makes the liquid mirror telescope possible.
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[edit] Mirage bowl
A mirage bowl or parabolic mirror wok is a toy consisting of two parabolic mirrors that are put together like a wok pan and a lid with a hole in it. The device gives the optical illusion that something is on the lid, but actually it is at the bottom of the pan below.
[edit] Parabolic reflectors for WiFi
Parabolic reflectors are a popular alternative for increasing wireless signal strength. Users have reported 3 dBi or more gains. [1]
[edit] See also
[edit] External links
- Java demonstration of a parabolic reflector
- Solar Energy Blog: See and discuss how concentrating solar energy is going to power our world in the not too distant future.
