Radio frequency(RF) is theoscillationrate of analternating electric currentorvoltageor of amagnetic,electric orelectromagnetic fieldor mechanical system in thefrequency[1]range from around20kHzto around300GHz.This is roughly between the upper limit ofaudio frequenciesand the lower limit ofinfraredfrequencies, and also encompasses themicrowaverange. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space asradio waves,so they are used inradiotechnology, among other uses. Different sources specify different upper and lower bounds for the frequency range.
Electric current
editElectric currentsthat oscillate at radio frequencies (RF currents) have special properties not shared bydirect currentor loweraudio frequencyalternating current,such as the 50 or 60 Hz current used inelectrical power distribution.
- Energy from RF currents in conductors can radiate into space aselectromagnetic waves(radio waves).[2]This is the basis ofradiotechnology.
- RF current does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as theskin effect.
- RF currents applied to the body often do not cause the painful sensation and muscular contraction ofelectric shockthat lower frequency currents produce.[3][4]This is because the current changes direction too quickly to triggerdepolarizationof nerve membranes. However, this does not mean RF currents are harmless; they can cause internal injury as well as serious superficial burns calledRF burns.
- RF current canionizeair, creating a conductive path through it. This property is exploited by "high frequency" units used in electricarc 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 thedielectricinsulator of acapacitor.This is becausecapacitive reactancein 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 theinductive reactanceof 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 calledstanding waves.RF current may be carried efficiently overtransmission linessuch ascoaxial cables.
Frequency bands
editTheradio spectrumof frequencies is divided into bands with conventional names designated by theInternational Telecommunication Union(ITU):
Frequency
rangeWavelength
rangeITUdesignation IEEE bands[5] Full name Abbreviation[6] Below 3 Hz >105km — 3–30 Hz 105–104km Extremely low frequency ELF — 30–300 Hz 104–103km Super low frequency SLF — 300–3000 Hz 103–100 km Ultra low frequency ULF — 3–30 kHz 100–10 km Very low frequency VLF — 30–300 kHz 10–1 km Low frequency LF — 300 kHz – 3 MHz 1 km – 100 m Medium frequency MF — 3–30 MHz 100–10 m High frequency HF HF 30–300 MHz 10–1 m Very high frequency VHF VHF 300 MHz – 3 GHz 1 m – 100 mm Ultra high frequency UHF UHF,L,S 3–30 GHz 100–10 mm Super high frequency SHF S,C,X,Ku,K,Ka 30–300 GHz 10–1 mm Extremely high frequency EHF Ka,V,W,mm 300 GHz – 3 THz 1 mm – 0.1 mm Tremendously high frequency THF —
Frequencies of 1 GHz and above are conventionally calledmicrowave,[7]while frequencies of 30 GHz and above are designatedmillimeter wave. More detailedband designationsare given by the standardIEEEletter- band frequency designations[5]and the EU/NATO frequency designations.[8]
Applications
editCommunications
editRadio frequencies are used in communication devices such astransmitters,receivers,computers,televisions,andmobile phones,to name a few.[1]Radio frequencies are also applied incarrier currentsystems includingtelephonyand control circuits. TheMOS integrated circuitis the technology behind the current proliferation of radio frequencywirelesstelecommunicationsdevices such ascellphones.
Medicine
editMedical applications of radio frequency (RF) energy, in the form ofelectromagnetic waves(radio waves) or electrical currents, have existed for over 125 years,[9]and now includediathermy,hyperthermytreatment of cancer,electrosurgeryscalpels used to cut and cauterize in operations, andradiofrequency ablation.[10]Magnetic resonance imaging(MRI) uses radio frequency fields to generate images of the human body.[11]
Non-surgical weight loss equipment
editRadio Frequency or RF energy is also being used in devices that are being advertised for weight loss and fat removal. The possible effects RF might have on the body and whether RF can lead to fat reduction needs further study. Currently, there are devices such astrusculpt ID,Venus Bliss and many others utilizing this type of energy alongside heat to target fat pockets in certain areas of the body. That being said, there is limited studies on how effective these devices are.
Measurement
editTest 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.[12][citation needed] [13]
Mechanical oscillations
editWhile RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: seemechanical filterandRF MEMS.
See also
editReferences
edit- ^abJessica Scarpati."What is radio frequency (RF, rf)?".SearchNetworking.Retrieved29 January2021.
- ^Service, United States Flight Standards (1976).Airframe and Powerplant Mechanics: Airframe Handbook.Department of Transportation, Federal Aviation Administration, Flight Standards Service. p. 520.
- ^
Curtis, Thomas Stanley (1916).High Frequency Apparatus: Its construction and practical application.US: Everyday Mechanics Company. pp.6.
electric shock pain.
- ^ Mieny, C.J. (2005).Principles of Surgical Patient Care(2nd ed.). New Africa Books. p. 136.ISBN9781869280055.
- ^abIEEE Std 521-2002Standard Letter Designations for Radar-Frequency Bands,Institute of Electrical and Electronics Engineers,2002. (Convenience copyat National Academies Press.)
- ^Jeffrey S. Beasley; Gary M. Miller (2008).Modern Electronic Communication(9th ed.). pp. 4–5.ISBN978-0132251136.
- ^Kumar, Sanjay; Shukla, Saurabh (2014).Concepts and Applications of Microwave Engineering.PHI Learning Pvt. Ltd. p. 3.ISBN978-8120349353.
- ^Leonid A. Belov; Sergey M. Smolskiy; Victor N. Kochemasov (2012).Handbook of RF, Microwave, and Millimeter-Wave Components.Artech House. pp. 27–28.ISBN978-1-60807-209-5.
- ^Ruey J. Sung & Michael R. Lauer (2000).Fundamental approaches to the management of cardiac arrhythmias.Springer. p. 153.ISBN978-0-7923-6559-4.Archivedfrom the original on 2015-09-05.
- ^Melvin A. Shiffman; Sid J. Mirrafati; Samuel M. Lam; Chelso G. Cueteaux (2007).Simplified Facial Rejuvenation.Springer. p. 157.ISBN978-3-540-71096-7.
- ^Bethge, K. (2004-04-27).Medical Applications of Nuclear Physics.Springer Science & Business Media.ISBN9783540208051.Archivedfrom the original on 2018-05-01.
- ^"RF Radio Frequency Signal Generator » Electronics Notes".www.electronics-notes.com.Retrieved29 January2021.
- ^Siamack Ghadimi (2021),Measure a DUT's input power using a directional coupler and power sensor,EDN
External links
edit- Analog, RF and EMC Considerations in Printed Wiring Board (PWB) Design
- Definition of frequency bands (VLF, ELF... etc.) IK1QFK Home Page (vlf.it)
- Radio, light, and sound waves, conversion between wavelength and frequencyArchived2012-03-11 at theWayback Machine
- RF Terms GlossaryArchived2008-08-20 at theWayback Machine