[[Image:F-Stecker und Kabel.jpg|thumb|Radio-frequency electrical currents are usually carried by specially-designed [[transmission line]] such as [[coaxial cable]], as ordinary [[electrical cable]]s would have high power loss.]]
'''Radio frequency''' ('''RF''') is the [[oscillation]] rate of an [[Alternating current|alternating electric current]] or [[voltage]] or of a [[Magnetic field|magnetic]], electric or [[electromagnetic field]] or mechanical system in the [[frequency]]<ref name="Scarpati">{{cite web |author=Jessica Scarpati |title=What is radio frequency (RF, rf)? |url=https://searchnetworking.techtarget.com/definition/radio-frequency |website=SearchNetworking |access-date=29 January 2021 |language=en}}</ref> range from around {{val|20|ul=kHz}} to around {{val|300|ul=GHz}}. This is roughly between the upper limit of [[audio frequencies]] that humans can hear (though these are not electromagnetic) and the lower limit of [[infrared]] frequencies, and also encompasses the [[microwave]] range. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as [[radio wave]]s, so they are used in [[radio]] technology, among other uses. Different sources specify different upper and lower bounds for the frequency range.
'''Radio frequency''' ('''RF''') is the [[oscillation]] rate of an [[Alternating current|alternating electric current]] or [[voltage]] or of a [[Magnetic field|magnetic]], electric or [[electromagnetic field]] or mechanical system in the [[frequency]]<ref name="Scarpati">{{cite web |author=Jessica Scarpati |title=What is radio frequency (RF, rf)? |url=https://searchnetworking.techtarget.com/definition/radio-frequency |website=SearchNetworking |access-date=29 January 2021 |language=en}}</ref> range from around {{val|20|ul=kHz}} to around {{val|300|ul=GHz}}. This is roughly between the upper limit of [[audio frequencies]] that humans can hear (though these are not electromagnetic) and the lower limit of [[infrared]] frequencies, and also encompasses the [[microwave]] range. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as [[radio wave]]s, so they are used in [[radio]] technology, among other uses. Different sources specify different upper and lower bounds for the frequency range.
== Electric current {{anchor|Current}} ==
== Electric current {{anchor|Current}} ==
[[Image:Energy is among us.jpg|thumb|Boy allowing the arc from a [[Tesla coil]] to strike his hand. Coming in contact with radio frequency arcs as shown here is extremely dangerous and can result in electrocution.]]
[[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 Hz current used in [[electrical power distribution]].
[[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 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.
* 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.
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* 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.
* 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.
* 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.
{{see also|Applications of radio|Radio spectrum#Applications}}
Radio has many practical applications, which include broadcasting, voice communication, data communication, radar, radiolocation, medical treatments, and remote control.
===Communications===
Radio frequencies are used in communication devices such as [[transmitters]], [[radio receiver|receivers]], [[computers]], [[televisions]], and [[mobile phones]], to name a few.<ref name="Scarpati"/> Radio frequencies are also applied in [[carrier current]] systems including [[telephony]] and control circuits. The [[MOS integrated circuit]] is the technology behind the current proliferation of radio frequency [[wireless]] [[telecommunications]] devices such as [[cellphones]].
=== Medicine ===
{{main|Medical applications of radio frequency}}
Medical applications of radio frequency (RF) energy, in the form of [[electromagnetic wave]]s ([[radio wave]]s) or electrical currents, have existed for over 125 years,<ref>{{cite book
|title = Fundamental approaches to the management of cardiac arrhythmias
}}</ref> and now include [[diathermy]], [[hyperthermy]] treatment of cancer, [[electrosurgery]] scalpels used to cut and cauterize in operations, and [[radiofrequency ablation]].<ref>{{cite book
| title = Simplified Facial Rejuvenation
|author1=Melvin A. Shiffman |author2=Sid J. Mirrafati |author3=Samuel M. Lam |author4=Chelso G. Cueteaux | publisher = Springer
}}</ref> [[Magnetic resonance imaging]] (MRI) uses radio frequency fields to generate images of the human body.<ref>{{Cite book|url=https://books.google.com/books?id=EAVYCfcQCxEC&q=%C2%A0+Magnetic+resonance+imaging+%28MRI%29+uses+radio+frequency+waves+to+generate+images+of+the+human+body.&pg=PA101|title=Medical Applications of Nuclear Physics|last=Bethge|first=K.|date=2004-04-27|publisher=Springer Science & Business Media|isbn=9783540208051|language=en|url-status=live|archive-url=https://web.archive.org/web/20180501015943/https://books.google.com/books?id=EAVYCfcQCxEC&pg=PA101&dq=%C2%A0+Magnetic+resonance+imaging+(MRI)+uses+radio+frequency+waves+to+generate+images+of+the+human+body.&hl=en&sa=X&ved=0ahUKEwjlrrL-mKfVAhVMy1QKHUc9D5UQ6AEIJjAA#v=onepage&q=%C2%A0%20Magnetic%20resonance%20imaging%20(MRI)%20uses%20radio%20frequency%20waves%20to%20generate%20images%20of%20the%20human%20body.&f=false|archive-date=2018-05-01}}</ref>
==Measurement==
==Measurement==
Test apparatus for radio frequencies can include standard instruments at the lower end of the range, but at higher frequencies, the test equipment becomes more specialized.<ref>{{cite web |title=RF Radio Frequency Signal Generator » Electronics Notes |url=https://www.electronics-notes.com/articles/test-methods/signal-generators/rf-radio-frequency-signal-generator.php |website=www.electronics-notes.com |access-date=29 January 2021}}</ref>{{citation needed|date=July 2017}}
Test apparatus for radio frequencies can include standard instruments at the lower end of the range, but at higher frequencies, the test equipment becomes more specialized.<ref>{{cite web |title=RF Radio Frequency Signal Generator » Electronics Notes |url=https://www.electronics-notes.com/articles/test-methods/signal-generators/rf-radio-frequency-signal-generator.php |website=www.electronics-notes.com |access-date=29 January 2021}}</ref>{{citation needed|date=July 2017}}<ref>{{Citation |title=Measure a DUT's input power using a directional coupler and power sensor |author1=Siamack Ghadimi|publisher=EDN|date=2021}}</ref>
<ref>{{Citation |title=Measure a DUT's input power using a directional coupler and power sensor |author1=Siamack Ghadimi|publisher=EDN|date=2021}}</ref>
==Mechanical oscillations==
==Mechanical oscillations==
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* [[Radio astronomy]]
* [[Radio astronomy]]
* [[Spectrum management]]
* [[Spectrum management]]
* [[Waveguide (radio frequency)]]
{{div col end}}
{{div col end}}
Latest revision as of 07:37, 11 November 2025
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Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency[1] range from around Template:Val to around Template:Val. This is roughly between the upper limit of audio frequencies that humans can hear (though these are not electromagnetic) and the lower limit of infrared frequencies, and also encompasses the microwave range. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves, so they are used in radio technology, among other uses. Different sources specify different upper and lower bounds for the frequency range.
Electric current Script error: No such module "anchor".
File:Energy is among us.jpgBoy allowing the arc from a Tesla coil to strike his hand. Coming in contact with radio frequency arcs as shown here is extremely dangerous and can result in electrocution.
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.[3][4] 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 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 waves. RF current may be carried efficiently over transmission lines such as coaxial cables.
Frequency bands
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Frequencies of 1 GHz and above are conventionally called microwave,[7] while frequencies of 30 GHz and above are designated millimeter wave.
More detailed band designations are given by the standard IEEE letter- band frequency designations[5] and the EU/NATO frequency designations.[8]
Applications
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Radio has many practical applications, which include broadcasting, voice communication, data communication, radar, radiolocation, medical treatments, and remote control.
Measurement
Test apparatus for radio frequencies can include standard instruments at the lower end of the range, but at higher frequencies, the test equipment becomes more specialized.[9]Script error: No such module "Unsubst".[10]
Mechanical oscillations
While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see mechanical filter and RF MEMS.
