Parabolic reflector
From Wikipedia, the free encyclopedia
 |
This article does not cite any references or sources. (January 2008) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. |
A parabolic reflector (or dish or mirror) is a Parabola-shaped reflective device, used to collect or distribute energy such as light, sound, or radio waves.
Contents |
[edit] Theory
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. 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.
[edit] History
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[citation needed]. 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.
[edit] Applications
The most common modern applications of the parabolic reflector are in satellite dishes, reflecting telescopes, radio telescopes, parabolic microphones, and many lighting devices such as spotlights, car headlights, PAR Cans and LED housings.
The Olympic Flame has been lit using a parabolic reflector concentrating sunlight. Parabolic mirrors are one of many shapes for a burning-glass.
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.
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 produces upright real image (with the magnification 1) of an object placed on the bottom of it, which gives the optical illusion that something is in the hole of the lid (while actually it is at the bottom of the pan below).
Parabolic reflectors are a popular alternative for increasing wireless signal strength. Even with simple ones, users have reported 3 dB or more gains.[1]
[edit] See also
- Parabola
- Parabolic antenna
- Parabolic trough
- Paraboloid
- Spherical reflector
- Toroidal reflector
- Solar furnace
[edit] External links
- Java demonstration of a parabolic reflector
- Algorithm and spreadsheet for making a simple paraboloid: Design and make a paraboloid for use as a solar concentrator, sound mirror or microwave antenna.
