Editing Inductor (section)

===Ferromagnetic-core inductor===
{{See also|Magnetic core}}
[[Image:Aplikimi i feriteve.png|thumb|A variety of types of ferrite core inductors and transformers]]

Ferromagnetic-core or iron-core inductors use a magnetic core made of a [[ferromagnetic]] or [[ferrimagnetic]] material such as iron or [[Ferrite (magnet)|ferrite]] to increase the inductance. A magnetic core can increase the inductance of a coil by a factor of several thousand, by increasing the magnetic field due to its higher [[magnetic permeability]]. However the magnetic properties of the core material cause several side effects which alter the behavior of the inductor and require special construction:
  {{glossary}}
  {{term|[[Core loss]]es}}{{defn|A time-varying current in a ferromagnetic inductor, which causes a time-varying magnetic field in its core, causes energy losses in the core material that are dissipated as heat, due to two processes:{{glossary}}
  {{term|[[Eddy current]]s}}{{defn|From [[Faraday's law of induction]], the changing magnetic field can induce circulating loops of electric current in the conductive metal core. The energy in these currents is dissipated as heat in the [[electrical resistance|resistance]] of the core material. The amount of energy lost increases with the area inside the loop of current.}}
{{term|[[Hysteresis loop|Hysteresis]]}}{{defn|Changing or reversing the magnetic field in the core also causes losses due to the motion of the tiny [[magnetic domain]]s it is composed of. The energy loss is proportional to the area of the hysteresis loop in the BH graph of the core material. Materials with low [[coercivity]] have narrow hysteresis loops and so low hysteresis losses.}}
  {{glossary end}}
Core loss is non-linear with respect to both frequency of magnetic fluctuation and magnetic flux density. Frequency of magnetic fluctuation is the frequency of AC current in the electric circuit; magnetic flux density corresponds to current in the electric circuit. Magnetic fluctuation gives rise to hysteresis, and magnetic flux density causes eddy currents in the core. These nonlinearities are distinguished from the threshold nonlinearity of saturation. Core loss can be approximately modeled with [[Steinmetz's equation]]. At low frequencies and over limited frequency spans (maybe a factor of 10), core loss may be treated as a linear function of frequency with minimal error. However, even in the audio range, nonlinear effects of magnetic core inductors are noticeable and of concern. }}
{{term|Saturation}}{{defn|If the current through a magnetic core coil is high enough that the core [[Saturation (magnetic)|saturates]], the inductance will fall and current will rise dramatically. This is a nonlinear threshold phenomenon and results in distortion of the signal. For example, [[audio signal]]s can suffer [[intermodulation distortion]] in saturated inductors. To prevent this, in [[linear circuit]]s the current through iron core inductors must be limited below the saturation level. Some laminated cores have a narrow air gap in them for this purpose, and powdered iron cores have a distributed air gap. This allows higher levels of magnetic flux and thus higher currents through the inductor before it saturates.<ref>{{cite web |url=http://www.newark.com/pdfs/techarticles/vishay/Inductors101.pdf |title=Inductors 101 |publisher=vishay |access-date=2010-09-24}}</ref>}}
{{term|Curie point demagnetization}}{{defn|If the temperature of a ferromagnetic or ferrimagnetic core rises to a specified level, the magnetic domains dissociate, and the material becomes paramagnetic, no longer able to support magnetic flux.  The inductance falls and current rises dramatically, similarly to what happens during saturation.  The effect is reversible: When the temperature falls below the Curie point, magnetic flux resulting from current in the electric circuit will realign the magnetic domains of the core and its magnetic flux will be restored.  The Curie point of ferromagnetic materials (iron alloys) is quite high; iron is highest at 770{{nbsp}}°C. However, for some ferrimagnetic materials (ceramic iron compounds – [[ferrite (magnet)|ferrite]]s) the Curie point can be close to ambient temperatures (below 100{{nbsp}}°C).{{citation needed|date=February 2018}} }}
{{glossary end}}

====Laminated-core inductor====
[[Image:Vorschaltdrossel Kvg.jpg|thumb|upright=0.8|Laminated iron core [[ballast (electrical)|ballast]] inductor for a [[metal halide lamp]] ]]
Low-frequency inductors are often made with [[laminated core]]s to prevent eddy currents, using construction similar to [[transformer]]s. The core is made of stacks of thin steel sheets or [[lamination]]s oriented parallel to the field, with an insulating coating on the surface. The insulation prevents eddy currents between the sheets, so any remaining currents must be within the cross sectional area of the individual laminations, reducing the area of the loop and thus reducing the energy losses greatly. The laminations are made of low-conductivity [[silicon steel]] to further reduce eddy current losses.

====Ferrite-core inductor====
{{main|Ferrite core}}
For higher frequencies, inductors are made with cores of ferrite. Ferrite is a ceramic ferrimagnetic material that is nonconductive, so eddy currents cannot flow within it. The formulation of ferrite is xxFe<sub>2</sub>O<sub>4</sub> where xx represents various metals. For inductor cores [[soft ferrite]]s are used, which have low coercivity and thus low hysteresis losses.

====Powdered-iron-core inductor <span class="anchor" id="powdered_iron_anchor"></span>====
{{see also|Carbonyl iron}}
Another material is powdered iron cemented with a binder. [[Medium frequency]] equipment almost exclusively uses powdered iron cores, and inductors and transformers built for the lower [[shortwave]]s are made using either cemented powdered iron or [[Ferrite core|ferrite]]s.{{citation needed|date=September 2022}}

====Toroidal-core inductor====
{{main|Toroidal inductors and transformers}}
[[File:3Com OfficeConnect ADSL Wireless 11g Firewall Router 2012-10-28-0869.jpg|thumb|Toroidal inductor in the power supply of a wireless router]]

In an inductor wound on a straight rod-shaped core, the [[magnetic field lines]] emerging from one end of the core must pass through the air to re-enter the core at the other end. This reduces the field, because much of the magnetic field path is in air rather than the higher permeability core material and is a source of [[electromagnetic interference]]. A higher magnetic field and inductance can be achieved by forming the core in a closed [[magnetic circuit]]. The magnetic field lines form closed loops within the core without leaving the core material. The shape often used is a [[toroid]]al or doughnut-shaped ferrite core. Because of their symmetry, toroidal cores allow a minimum of the magnetic flux to escape outside the core (called ''[[leakage flux]]''), so they radiate less electromagnetic interference than other shapes. Toroidal core coils are manufactured of various materials, primarily ferrite, powdered iron and laminated cores.<ref>{{cite web|url=http://www.vishay.com/docs/34053/definit.pdf |title=Inductor and Magnetic Product Terminology |publisher=Vishay Dale |access-date=2012-09-24}}</ref>