Coil

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For other uses, see Coil (disambiguation).
"Winding" redirects here. For other uses, see Winding (disambiguation).
A coil is a series of loops. A coiled coil is a structure where the coil itself is in turn also looping.
Contents
1 General applications
2 Electromagnetic coils
2.1 Analysis
2.2 Coil examples
3 Chemistry, biology and medicine
4 In Ceramics (Fine Arts)
5 External links
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General applications

A helical spring.
A coil is made up of materials, usually rigid, which can be fashioned into a spiral or helical shape. Flexible materials like wire, roe, hose, cable or paper can also be coiled into empty loops, or wound around a central drum or spindle. Some common applications of coils include:
A coil spring is the most common type of spring.
A spiral staircase, a stairway fashioned in a coil shape.
A Slinky is a coil-shaped toy.
Evaporator coils are used in air conditioning and other refrigeration cycles.
A boiler coil is an element in a water heater.
An Alpine coil, one of several coil knots, is a method for carrying a rope.
Quilling coils use shaped paper to create artistic designs.
Coils are also used electrically.
Electromagnetic coils
Main article: Electromagnetic coil

Diagram of typical transformer configurations
An electromagnetic coil (or simply a "coil") is formed when a conductor (usually a solid copper wire) is wound around a core or form to create an inductor or electromagnet. One loop of wire is usually referred to as a turn, and a coil consists of one or more turns. For use in an electronic circuit, electrical connection terminals called taps are often connected to a coil. Coils are often coated with varnish and/or wrapped with insulating tape to provide additional insulation and secure them in place. A completed coil assembly with taps etc. is often called a winding. A transformer is an electromagnetic device that has a primary winding and a secondary winding that transfers energy from one electrical circuit to another by magnetic coupling without moving parts. The term tickler coil usually refers to a third coil placed in relation to a primary coil and secondary coil A coil tap is a wiring feature found on some electrical transformers, inductors and coil pickups, all of which are sets of wire coils. The coil tap(s) are points in a wire coil where a conductive patch has been exposed (usually on a loop of wire that extends out of the main coil body). As self induction is larger for larger coil diameter the current in a thick wire tries to flow on the inside. The ideal use of copper is achieved by foils. Sometimes this means that a spiral is a better alternative. Multilayer coils have the problem of interlayer capacitance, so when multiple layers are needed the shape needs to be radically changed to a short coil with many layers so that the voltage between consecutive layers is smaller (making them more spiral like).
Analysis
The inductance of single-layer air-cored coils can be calculated to a reasonable degree of accuracy with the simplified formula
where ?H (microhenries) are units of inductance, R is the coil radius (measured in inches to the center of the conductor), N is the number of turns, and L is the length of the coil in inches. The online Coil Inductance Calculator calculates the inductance of any coil using this formula. Higher accuracy estimates of coil inductance require calculations of considerably greater complexity. A layperson's translation is:
Note that if the coil has a ferrite core, or one made of another metallic material, it's inductance cannot be calculated with this formula.In calculating the distances, one centimeter is equal to 0.393700787 inches and one inch is equal to 2.54 centimeters. The inductance formula uses inches. The relationship between the radius and the circumference of a coil is , with r as the radius, c as the circumference, and ? (the Greek letter pi) as the constant 3.141. The circumference of a coil can be calculated by , with d as the diameter of the coil and ? as 3.141.
Coil examples

Nikola Tesla's flat spiral coil.
Some common electromagnetic coils include:
A bifilar coil is a coil that employs two parallel windings.
A Barker coil is used in low field NMR imaging.
A Balun is set of transformer coils for transmission lines.
A Braunbeck coil is used in geomagnetic research.
A degaussing coil is used in the process of removing permanent magnetism (magnetic hysteresis) from an object.
A choke coil (or choking coil) is low-resistance inductor used to block alternating current while passing direct current.
A Flat coil is used in thin electric motor.
A Garrett coil is used in metal detectors.
A Helmholtz coil is a device for producing a...(and so on)

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