A coil is a series of loops.

General applications

A coil is made of materials, usually rigid, which can be fashioned into a spiral or helical shape. Flexible materials like wire, rope, hose, or cable 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 set of stairs fashioned in a coil shape, which are called spiral staircases.
• 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.
• A Alpine coil, one of several coil knots, is a method for carrying a rope.

Electromagnetic

In electrical engineering, an electromagnetic coil is formed when a metallic or conductive wire is looped around a core to create an electronic inductor or electromagnet. One loop of wire is usually referred to as one turn. 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).

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 Garrett coil is used in metal detectors.
• A Helmholtz coil is a device for producing a region of nearly uniform magnetic field.
• A hybrid coil (or bridge transformer) is a single transformer that effectively has three windings.
• An induction coil (or ignition coil) is an electrical device in common use as the ignition system (ignition coil or spark coil) of internal-combustion engines.
• A loading coil is, in electronics, a coil (inductor) inserted in a circuit to increase its inductance. Archaically called Pupin coils.
• A multiple coil magnet is an electromagnet that has several coils of wire connected in parallel.
• A Maxwell coil is a device for producing almost a constant magnetic field.
• A Oudin coil is a disruptive discharge coil.
• The polyphase coils are connected together in a polyphase system such as a generator or motor.
• A relay coil is the copper winding part of a relay that produces a magnetic field that actuates the mechanism.
• A Repeating coil is a voice-frequency transformer.
• A Rogowski coil is an electrical device for measuring alternating current.
• A single coil is a type of pickup for the electric guitar.
• A solenoid is a mechanical device, based around a coil of wire, that converts energy into linear motion.
• A Tesla coil is category of disruptive discharge coils, usually denoting a resonant transformer that generates very high voltages at radio frequencies.
• A voice coil which is mounted to the moving cone of a loudspeaker.

A coilgun is a type of cannon that uses a series of electromagnetic coils to accelerate a magnetic shell to very high velocities.

Further reading

• Querfurth, William, "Coil winding; a description of coil winding procedures, winding machines and associated equipment for the electronic industry" (2d ed.). Chicago, G. Stevens Mfg. Co., 1958.
• Weymouth, F. Marten, "Drum armatures and commutators (theory and practice) : a complete treatise on the theory and construction of drum winding, and of commutators for closed-coil armatures, together with a full résumé of some of the principal points involved in their design; and an exposition of armature reactions and sparking". London, "The Electrician" Printing and Publishing Co., 1893.
• "Coil winding proceedings". International Coil Winding Association.
• Chandler, R. H., "Coil coating review, 1970-76". Braintree, R. H. Chandler Ltd, 1977.

External articles

• R. Clarke, "Producing wound components". Surrey.ac.uk, 2005 October 9th.

Chemistry, biology and medicine

A chemistry coil is a tube of spiral form, used commonly to cool originating steam of the distillation and thus to condense them in liquid form. In the study of how molecules interact with each other, there are a few specific references to organic coils. During self-assembly, organic elements organize to form this structural pattern. Molecular self-assembly assembles the molecules, without guidance or management from an outside source, into these shapes.

Examples of these structural patterns include:

• A coiled coil is a structural motif found in many proteins.
• The DNA coil is a nucleic acid structure that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses).
• A random coil is a polymer conformation where the monomers are arranged at random.
• The RNA coil is a nucleic acid structure consisting of a string of covalently-bound nucleotides.

As an acronym, COIL denotes the Chemical Oxygen Iodine Laser.

In medicine, the Guglielmi Detachable Coil is a platinum coil commonly used in intracranial non-invasive surgery, for the occlusion of brain aneurysms.

External links

• For the definition of Coil and words related to it, see Wiktionary.