Editing Inductive coupling (section)

{{Short description|Electrical circuit coupling using induction}}
{{Refimprove|date=December 2009}}
[[File:Lamp powered by induction 1910.jpg|thumb|Example of inductive coupling, 1910. The bottom coil is connected to AC power. The alternating magnetic field through the top coil induces current in it which lights the lamp.]]

In [[electrical engineering]], two [[electrical_conductor|conductors]] are said to be '''inductively coupled''' or '''magnetically coupled'''<ref>{{cite book |last=Zverev |first=A.I. |title=Handbook of filter synthesis |publisher=Wiley |orig-year=1967 |date=2005 |isbn=9780471749424}}</ref> when they are configured in a way such that change in current through one wire [[Faraday's law of induction|induces]] a voltage across the ends of the other wire through [[electromagnetic induction]].  A changing current through the first wire creates a changing [[magnetic field]] around it by [[Ampere's circuital law]].  The changing magnetic field induces an [[electromotive force]] (EMF) [[voltage]] in the second wire by [[Faraday's law of induction]].  The amount of inductive coupling between two conductors is measured by their [[mutual inductance]].  

The coupling between two wires can be increased by winding them into [[electromagnetic coil|coils]] and placing them close together on a common axis, so the magnetic field of one coil passes through the other coil.  Coupling can also be increased by a [[magnetic core]] of a [[ferromagnetic]] material like iron or [[ferrite (magnet)|ferrite]] in the coils, which increases the magnetic flux.   The two coils may be physically contained in a single unit, as in the primary and secondary windings of a [[Transformer types#Interstage and coupling transformer|transformer]], or may be separated.  Coupling may be intentional or unintentional. Unintentional inductive coupling can cause signals from one circuit to be induced into a nearby circuit, this is called [[crosstalk|cross-talk]], and is a form of [[electromagnetic interference]].

[[File: Coupling Coefficient.gif|thumb|300px|k is the [[Inductance#Coupling coefficient|coupling coefficient]], Le1 and Le2 is the [[leakage inductance]], M1 (M2) is the mutual inductance]]

An inductively coupled [[transponder]] consists of a solid state [[transceiver]] chip connected to a large coil that functions as an [[antenna (radio)|antenna]].  When brought within the oscillating magnetic field of a reader unit, the transceiver is powered up by energy inductively coupled into its antenna and transfers data back to the reader unit inductively.  

Magnetic coupling between two [[magnet]]s can also be used to mechanically transfer power without contact, as in the [[magnetic gear]].<ref>{{cite web |url=http://machinedesign.com/motorsdrives/could-magnetic-gears-make-wind-turbines-say-goodbye-mechanical-gearboxes|title= Could Magnetic Gears Make Wind Turbines Say Goodbye to Mechanical Gearboxes? |date= 19 June 2014 |publisher=machinedesign.com}}</ref>