Editing Skin effect (section)

== Mitigation ==<!-- This section is linked from [[Transformer]] -->

A type of cable called litz wire (from the German ''Litzendraht'', braided wire) is used to mitigate skin effect for frequencies of a few kilohertz to about one megahertz.  It consists of a number of insulated wire strands woven together in a carefully designed pattern, so that the overall magnetic field acts equally on all the wires and causes the total current to be distributed equally among them. With skin effect having little effect on each of the thin strands, the bundle does not suffer the same increase in AC resistance that a solid conductor of the same cross-sectional area would due to skin effect.<ref>{{harvnb|Xi Nan|Sullivan|2005}}</ref>

Litz wire is often used in the windings of high-frequency [[transformer]]s to increase their efficiency by mitigating both skin effect and proximity effect.
Large power transformers are wound with stranded conductors of similar construction to litz wire, but employing a larger cross-section corresponding to the larger skin depth at mains frequencies.<ref name="cegb_1982">{{cite book
| author = Central Electricity Generating Board
| title = Modern Power Station Practice
| year = 1982
|publisher = Pergamon Press}}</ref>
Conductive threads composed of [[carbon nanotube]]s<ref>{{cite web|url=https://www.sciencedaily.com/releases/2009/03/090309121941.htm |title=Spinning Carbon Nanotubes Spawns New Wireless Applications |publisher=Sciencedaily.com |date=2009-03-09 |access-date=2011-11-08}}</ref> have been demonstrated as conductors for antennas from medium wave to microwave frequencies. Unlike standard antenna conductors, the nanotubes are much smaller than the skin depth, allowing full use of the thread's cross-section resulting in an extremely light antenna.

High-voltage, high-current [[overhead power line]]s often use [[Aluminium Conductor Steel Reinforced|aluminum cable with a steel reinforcing core]]; the higher resistance of the steel core is of no consequence since it is located far below the skin depth where essentially no AC current flows.

In applications where high currents (up to thousands of amperes) flow, solid conductors are usually replaced by tubes, eliminating the inner portion of the conductor where little current flows. This hardly affects the AC resistance, but considerably reduces the weight of the conductor. The high strength but low weight of tubes substantially increases span capability. Tubular conductors are typical in electric power switchyards where the distance between supporting insulators may be several meters. Long spans generally exhibit physical sag but this does not affect electrical performance. To avoid losses, the conductivity of the tube material must be high.

In high current situations where conductors (round or flat [[busbar]]) may be between 5 and 50&nbsp;mm thick skin effect also occurs at sharp bends where the metal is compressed inside the bend and stretched outside the bend. The shorter path at the inner surface results in a lower resistance, which causes most of the current to be concentrated close to the inner bend surface. This causes an increase in temperature at that region compared with the straight (unbent) area of the same conductor. A similar skin effect occurs at the corners of rectangular conductors (viewed in cross-section), where the magnetic field is more concentrated at the corners than in the sides. This results in superior performance (i.e. higher current with lower temperature rise) from wide thin conductors (for example, ''ribbon'' conductors) in which the effects from corners are effectively eliminated.

It follows that a transformer with a round core will be more efficient than an equivalent-rated transformer having a square or rectangular core of the same material.

Solid or tubular conductors may be silver-[[Electroplating|plated]] to take advantage of silver's higher conductivity. This technique is particularly used at [[VHF]] to [[microwave]] frequencies where the small skin depth requires only a very thin layer of silver, making the improvement in conductivity very cost effective. Silver plating is similarly used on the surface of waveguides used for transmission of microwaves. This reduces attenuation of the propagating wave due to resistive losses affecting the accompanying eddy currents; skin effect confines such eddy currents to a very thin surface layer of the waveguide structure. Skin effect itself is not actually combatted in these cases, but the distribution of currents near the conductor's surface makes the use of precious metals (having a lower resistivity) practical. Although it has a lower conductivity than copper and silver, gold plating is also used, because unlike copper and silver, it does not corrode. A thin oxidized layer of copper or silver would have a low conductivity, and so would cause large power losses as the majority of the current would still flow through this layer.

Recently, a method of layering non-magnetic and ferromagnetic materials with nanometer scale thicknesses has been shown to mitigate the increased resistance from skin effect for very high-frequency applications.<ref name=Rahimi-Yoon-2016/> A working theory is that the behavior of ferromagnetic materials in high frequencies results in fields and/or currents that oppose those generated by relatively nonmagnetic materials, but more work is needed to verify the exact mechanisms.{{Citation needed|date=June 2020}} As experiments have shown, this has potential to greatly improve the efficiency of conductors operating in tens of GHz or higher. This has strong ramifications for [[5G]] communications.<ref name=Rahimi-Yoon-2016>{{cite journal |first1=A. |last1=Rahimi |first2=Y.-K. |last2=Yoon |date=2016-03-16 |title=Study on Cu/Ni nano superlattice conductors for reduced RF loss |journal=IEEE Microwave and Wireless Components Letters |volume=26 |issue=4 |pages=258–260 |issn=1531-1309  |doi=10.1109/LMWC.2016.2537780 |s2cid=30187468 |url=https://www.researchgate.net/publication/298797532 |via=ResearchGate |access-date=2020-12-22 <!-- prior link, equivalent to DOI, https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7434554 -- replaced with free-access Research Gate link --> }}</ref>