Parabolic reflector

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Parabolic reflector

A parabolic reflector (or dish or mirror) is a parabola

Parabola

In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface....
-shaped reflective

Mirror

A mirror is an object with one surface polished, which leads to reflection and another opaque. The most familiar type of mirror is the plane mirror, which has a flat surface....
device, used to collect or distribute energy

Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
such as light

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
, sound

Sound

Sound is vibration transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a threshold of hearing to be heard, or the sensation stimulated in organs of hearing by such vibrations....
, or radio wave

Radio Wave

Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s. Parabolic reflectors are used to collect energy from a distant source (for example sound waves or incoming star

Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
light) and bring it to a common focal point

Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
, thus correcting spherical aberration

Spherical aberration

Spherical aberration is an optical effect observed in an optical device that occurs due to the increased refraction of light rays when they strike a lens or a reflection of light rays when they strike a mirror near its edge, in comparison with those that strike nearer the center....
found in simpler spherical reflectors. Since the principles of reflection

Specular reflection

Specular reflection is the perfect, mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected into a single outgoing direction....
are reversible, parabolic reflectors can also be used to project energy of a source at its focus outward in a parallel beam, used in devices such as spotlights

Stage lighting instrument

Stage lighting instruments are used in stage lighting to illuminate theatre productions, rock concerts and other performances taking place in live performance Theater s....
and car headlights.

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

Ray (optics)

In optics, a ray is an idealized narrow beam of light. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of Ray tracing ....
that is parallel to the axis of the dish will be reflected to a central point, or "focus

Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
".

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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

Ray (optics)

Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
". 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

Aberration in optical systems

Aberrations are departures of the performance of an optical system from the predictions of paraxial optics. Aberration leads to blurring of the image produced by an image-forming optical system....
called coma

Coma (optics)

In optics , the coma in an optical system refers to aberration in optical systems inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted....
. This is primarily of interest in telescopes because most other applications do not require sharp resolution off the axis of the parabola.

History

The principle of parabolic reflectors may have been known since classical antiquity

Classical antiquity

Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of Ancient Greece and Ancient Rome....
. Archimedes

Archimedes

Archimedes of Syracuse was a Greek mathematics, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity....
in the third century BC described the mathematics of parabolas and there are claims

Archimedes

Archimedes of Syracuse was a Greek mathematics, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity....
that he even used the principle in the form of some sort of weapon during the Siege of Syracuse

Siege of Syracuse (212 BC)

The Siege of Syracuse by the Roman Republic took place in 214 BC-212 BC, at the end of which the Magna Graecia Hellenistic civilization city of Syracuse, Italy, located on the east coast of Sicily, fell....
. The first century BC Greek

Hellenistic Greece

In the context of Ancient Greek art, architecture, and culture, Hellenistic Greece corresponds to the period between the death of Alexander the Great in 323 BC and the annexation of the Classical Greece heartlands by Roman Republic in 146 BC....
mathematician

Mathematician

A mathematician is a person whose primary area of study and/or research is the field of mathematics....
and geometer Diocles

Diocles (mathematician)

Diocles was a Hellenistic Greece mathematician and geometer....
was thought to have written that burning mirrors shaped like a parabola "burn most strongly". The first written descriptions of parabolic mirrors were by the Arabian physicist

Islamic physics

Islamic physics refers to the study of physics within Islamic science, which flourished during the Islamic Golden Age, variously dated from the 8th century to the 16th century, when experimental physics, mathematical physics and theoretical physics were studied in the Muslim world....
, Ibn Sahl

Ibn Sahl

This article is about the physicist. For the physician, see Ali ibn Sahl Rabban al-Tabari. For the poet, see Ibn Sahl of Sevilla.Ibn Sahl was an Arabian Islamic mathematics, Islamic physics and optics Inventions in the Islamic world of the Islamic Golden Age associated with the Abbasid court of Baghdad....
, in the 10th century. James Gregory

James Gregory (astronomer and mathematician)

James Gregory , was a Scotland mathematician and astronomer. It has been said that "Of the British mathematicians of the seventeenth century, Gregory was only excelled by Isaac Newton."...
, in his 1663 book Optica Promota (1663), pointed out that a reflecting telescope

Reflecting telescope

A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration....
with a mirror that was parabolic would correct spherical aberration

Spherical aberration

Chromatic aberration

In optics, chromatic aberration is the failure of a lens to Focus all colors to the same point. It occurs because lenses have a different refractive index for different wavelengths of light ....
seen in refracting telescope

Refracting telescope

A refracting or refractor telescope is a Dioptrics telescope that uses a lens as its Objective to form an image. The refracting telescope design was originally used in telescope and astronomical telescopes but is also used in other devices such as binoculars and long or Telephoto lens camera lenses....
s. The design he came up with bears his name: the "Gregorian telescope

Gregorian telescope

The Gregorian telescope is a type of reflecting telescope designed by Scotland mathematician and astronomer, James Gregory in the 17th century and first built in 1673 by Robert Hooke....
"; but according to his own confession, Gregory had no practical skill and he could find no optician capable of actually constructing one. Isaac Newton

Isaac Newton

Sir Isaac Newton, Fellow of the Royal Society was an English people physicist, mathematician, Astronomy, Natural philosophy, Alchemy, and Theology and one of the the 100 in human history....
knew about the properties of parabolic mirrors but chose a spherical shape for his Newtonian telescope

Newtonian telescope

The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton , using a Curved mirror#Concave mirrors and a flat diagonal secondary mirror....
mirror to simplify construction. John Hadley

John Hadley

John Hadley was an England mathematician, inventor of the octant and precursor to the sextant around 1730.In 1717 he became member of the Royal Society of London....
introduced parabolic mirrors into practical astronomy

Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
in 1721 when he used one in his reflecting telescope

Reflecting telescope

Lighthouse

A lighthouse is a tower, building, or framework designed to emit light from a system of lamps and lens or, in older times, from a fire and used as an aid to navigation and to Maritime pilot at sea....
s also commonly used parabolic mirrors to collimate a point of light from a lantern into a beam, before being replaced by more efficient fresnel lens

Fresnel lens

A Fresnel lens is a type of lens invented by France physics Augustin-Jean Fresnel. Originally developed for lighthouses, the design enables the construction of lenses of large aperture and short focal length without the weight and volume of material which would be required in conventional lens design....
es in the 19th century.

Applications

The most common modern applications of the parabolic reflector are in satellite dish

Satellite dish

A satellite dish is a type of parabolic antenna that receives or transmits electromagnetic signals to and from another location typically a satellite....
es, reflecting telescope

Reflecting telescope

Radio telescope

A radio telescope is a form of Directional antennae radio Antenna used in radio astronomy and in tracking and collecting data from satellites and space probes....
s, parabolic microphone

Parabolic microphone

A parabolic microphone is a microphone that uses a parabolic reflector to collect and focus sound waves onto a receiver, in much the same way that a parabolic antenna does with radio waves....
s, and many lighting

Electric light

Most of the industrialized world is lit by electric lights, which are used both at night and to provide additional light during the daytime. These lights are normally powered by the electric grid, but some run on local electrical generators, and emergency generators serve as backups in hospitals and other locations where a loss of power could...
devices such as spotlights

Stage lighting instrument

Parabolic aluminized reflector light

A parabolic aluminized reflector luminare, or PAR light, is a stage lighting fixture widely used in theatre, concerts and motion picture film production when a substantial amount of flat lighting is required for a scene....
and LED housings.

The Olympic Flame

Olympic Flame

The Olympic Flame or Olympic Torch is a symbol of the Olympic Games. Commemorating the theft of fire from the Greek god Zeus by Prometheus, its origins lie in ancient Greece, when a fire was kept burning throughout the celebration of the Ancient Olympic Games....
has been lit using a parabolic reflector concentrating sunlight

Sunlight

Sunlight, in the broad sense, is the total spectroscopy of the electromagnetic radiation given off by the Sun. On Earth, sunlight is Filter ed through the Earth's atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon....
. Parabolic mirrors are one of many shapes for a burning-glass

Burning-glass

A burning-glass is a large Lens #Types of lenses that can concentrate the sun's rays onto a small area, heating up the area and thus resulting in Combustion of the exposed surface....
.

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

Real image

In optics, a real image is a representation of an object in which the perceived location is actually a point of convergence of the ray that make up the image....
(with the magnification

Magnification

Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called magnification....
1) of an object placed on the bottom of it, which gives the optical illusion

Optical illusion

An optical illusion is characterized by visual perception images that differ from objective reality. The information gathered by the eye is processed in the brain to give a percept that does not tally with a physical measurement of the stimulus source....
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.

External links

: Design and make a paraboloid for use as a solar concentrator, sound mirror or microwave antenna.
www.antenna-theory.com

Parabolic reflector

Theory

History

Applications

See also

External links