Radio frequency#Current

Electric currents 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 waves (radio waves).{{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}} 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.

{{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.

}}

{{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

}}

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.

{{main|Radio spectrum}}

The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunication Union (ITU):

:

Frequencies of 1 GHz and above are conventionally called microwave,{{cite book

| last1 = Kumar

| first1 = Sanjay

| last2 = Shukla

| first2 = Saurabh

| title = Concepts and Applications of Microwave Engineering

| publisher = PHI Learning Pvt. Ltd

| date = 2014

| pages = 3

| url = https://books.google.com/books?id=GY9eBAAAQBAJ&q=microwave&pg=PA3

| isbn = 978-8120349353

}} 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[https://standards.ieee.org/ieee/521/768/ IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands], Institute of Electrical and Electronics Engineers, 2002. ([https://www.nap.edu/read/21774/chapter/10#235 Convenience copy] at National Academies Press.) and the EU/NATO frequency designations.{{cite book|author1=Leonid A. Belov|author2=Sergey M. Smolskiy|author3=Victor N. Kochemasov|title=Handbook of RF, Microwave, and Millimeter-Wave Components|url=https://books.google.com/books?id=bHhYjINB6KMC&pg=PA28|year=2012|publisher=Artech House|isbn=978-1-60807-209-5|pages=27–28}}

{{see also|Radio#Applications|Radio spectrum#Applications}}

Radio frequencies are used in communication devices such as transmitters, receivers, computers, televisions, and mobile phones, to name a few. 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.

{{main|Medical applications of radio frequency}}

Medical applications of radio frequency (RF) energy, in the form of electromagnetic waves (radio waves) or electrical currents, have existed for over 125 years,{{cite book

|title = Fundamental approaches to the management of cardiac arrhythmias

|author1 = Ruey J. Sung

|author2 = Michael R. Lauer

|name-list-style = amp

|publisher = Springer

|year = 2000

|isbn = 978-0-7923-6559-4

|page = 153

|url = https://books.google.com/books?id=S1fWhl2c5zIC&q=rf+coagulation+75-years&pg=PA153

|url-status = live

|archive-url = https://web.archive.org/web/20150905205035/https://books.google.com/books?id=S1fWhl2c5zIC&pg=PA153&dq=rf+coagulation+75-years&lr=&as_brr=3&ei=IIhuSpfBJ6aqlQT-n7nmDg

|archive-date = 2015-09-05

}} and now include diathermy, hyperthermy treatment of cancer, electrosurgery scalpels used to cut and cauterize in operations, and radiofrequency ablation.{{cite book

| title = Simplified Facial Rejuvenation

|author1=Melvin A. Shiffman |author2=Sid J. Mirrafati |author3=Samuel M. Lam |author4=Chelso G. Cueteaux | publisher = Springer

| year = 2007

| isbn = 978-3-540-71096-7

| page = 157

| url = https://books.google.com/books?id=w1fQK21WK28C&q=rf+coagulation+sleep-apnea&pg=RA1-PA157

}} Magnetic resonance imaging (MRI) uses radio frequency fields to generate images of the human body.{{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}}

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.{{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}}{{citation needed|date=July 2017}}

{{Citation |title=Measure a DUT's input power using a directional coupler and power sensor |author1=Siamack Ghadimi|publisher=EDN|date=2021}}

While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see mechanical filter and RF MEMS.

{{div col begin|colwidth=15em}}

• Amplitude modulation (AM)
• Bandwidth (signal processing)
• Electromagnetic interference
• Electromagnetic radiation
• Electromagnetic spectrum
• EMF measurement
• Frequency allocation
• Frequency modulation (FM)
• Plastic welding
• Pulsed electromagnetic field therapy
• Radio astronomy
• Spectrum management

{{div col end}}

{{reflist}}

• [https://ieee.li/pdf/viewgraphs/analog-rf-emc-considerations-pwb-design.pdf Analog, RF and EMC Considerations in Printed Wiring Board (PWB) Design]
• [http://www.vlf.it/frequency/bands.html Definition of frequency bands (VLF, ELF ... etc.) IK1QFK Home Page (vlf.it)]
• [http://www.sengpielaudio.com/calculator-wavelength.htm Radio, light, and sound waves, conversion between wavelength and frequency] {{Webarchive|url=https://web.archive.org/web/20120311050010/http://www.sengpielaudio.com/calculator-wavelength.htm |date=2012-03-11 }}
• [http://www.sunmantechnology.com/resources_gls_rfts.html RF Terms Glossary] {{Webarchive|url=https://web.archive.org/web/20080820005518/http://www.sunmantechnology.com/resources_gls_rfts.html |date=2008-08-20 }}

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Category:Radio spectrum

Radio waves

Radio waves

Category:Television terminology