Editing Radio frequency (section)

== Electric current {{anchor|Current}} ==
[[Electric current]]s that oscillate at radio frequencies ('''RF currents''') have special properties not shared by [[direct current]] or lower [[audio frequency]] [[alternating current]], such as the 50 or 60&nbsp;Hz current used in [[electrical power distribution]].
* Energy from RF currents in conductors can radiate into space as [[electromagnetic wave]]s ([[radio wave]]s).<ref>{{cite book |last1=Service |first1=United States Flight Standards |title=Airframe and Powerplant Mechanics: Airframe Handbook |date=1976 |publisher=Department of Transportation, Federal Aviation Administration, Flight Standards Service |page=520 |url=https://books.google.com/books?id=CqZTAAAAMAAJ |language=en}}</ref>  This is the basis of [[radio]] technology.
* RF current does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as the [[skin effect]].
* RF currents applied to the body often do not cause the painful sensation and muscular contraction of [[electric shock]] that lower frequency currents produce.<ref name="Curtis">
{{cite book
  | last = Curtis  | first = Thomas Stanley
  | year = 1916
  | title = High Frequency Apparatus: Its construction and practical application
  | publisher = Everyday Mechanics Company
  | location = US
  | pages = [https://archive.org/details/highfrequencyap00curtgoog/page/n27 6]
  | url = https://archive.org/details/highfrequencyap00curtgoog
  | quote = electric shock pain.
}}
</ref><ref name="Mieny">
{{cite book
  | last = Mieny  | first = C.J.
  | year = 2005
  | title = Principles of Surgical Patient Care
  | edition = 2nd
  | pages = 136
  | publisher = New Africa Books
  | isbn = 9781869280055
  | url = https://books.google.com/books?id=TSxQ6ZzovgkC&q=%22electric+shock%22+pain+%22high+frequency&pg=PA136
}}
</ref> This is because the current changes direction too quickly to trigger [[depolarization]] of nerve membranes. However, this does not mean RF currents are harmless; they can cause internal injury as well as serious superficial burns called [[Radiation burn|RF burns]].
* RF current can [[ionize]] air, creating a conductive path through it. This property is exploited by "high frequency" units used in electric [[arc welding]], which use currents at higher frequencies than power distribution uses.
* Another property is the ability to appear to flow through paths that contain insulating material, like the [[dielectric]] insulator of a [[capacitor]]. This is because [[capacitive reactance]] in a circuit decreases with increasing frequency.
* In contrast, RF current can be blocked by a coil of wire, or even a single turn or bend in a wire. This is because the [[inductive reactance]] of a circuit increases with increasing frequency.
* When conducted by an ordinary electric cable, RF current has a tendency to reflect from discontinuities in the cable, such as connectors, and travel back down the cable toward the source, causing a condition called [[standing wave]]s. RF current may be carried efficiently over [[transmission line]]s such as [[coaxial cable]]s.