Radio frequency

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 range from around 20 kHz to around 300 GHz. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies;[1][2] these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.

This article is about the generic oscillation. For the radiation, see radio wave. For the spectrum, see radio spectrum. For the electronics, see radio-frequency engineering.
"RF" redirects here. For other uses, see RF (disambiguation).

Electric current

Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or alternating current of lower frequencies.

  • Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). 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.[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 easily 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
Main article: Radio spectrum

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

Frequency
range		Wavelength
range		ITU designationIEEE bands[5]
Full name Abbreviation[6]
Below 3 Hz >105 kmTremendously low frequency[7]TLFN/A
3–30 Hz 105–104 kmExtremely low frequencyELFN/A
30–300 Hz 104–103 kmSuper low frequencySLFN/A
300–3000 Hz 103–100 kmUltra low frequencyULFN/A
3–30 kHz 100–10 kmVery low frequencyVLFN/A
30–300 kHz 10–1 kmLow frequencyLFN/A
300 kHz – 3 MHz 1 km – 100 mMedium frequencyMFN/A
3–30 MHz 100–10 mHigh frequencyHFHF
30–300 MHz 10–1 mVery high frequencyVHFVHF
300 MHz – 3 GHz 1 m – 10 cmUltra high frequencyUHFUHF, L, S
3–30 GHz 10–1 cmSuper high frequencySHFS, C, X, Ku, K, Ka
30–300 GHz 1 cm – 1 mmExtremely high frequencyEHFKa, V, W, mm
300 GHz – 3 THz 1 mm – 0.1 mmTremendously high frequencyTHFN/A

Frequencies of 1 GHz and above are conventionally called microwave,[8] 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.[9]

Applications

Communications

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.

Medicine
Main article: Medical applications of radio frequency

Radio frequency (RF) energy, in the form of radiating waves or electrical currents, has been used in medical treatments for over 75 years,[10] generally for minimally invasive surgeries using radiofrequency ablation including the treatment of sleep apnea.[11]

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.

Mechanical oscillations

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

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See also

References
  1. J. A. Fleming, The Principles of Electric Wave Telegraphy and Telephony, London: Longmans, Green & Co., 1919, p. 364
  2. A. A. Ghirardi, Radio Physics Course, 2nd ed. New York: Rinehart Books, 1932, p. 249
  3. Curtis, Thomas Stanley (1916). High Frequency Apparatus: Its Construction and Practical Application. USA: Everyday Mechanics Company. pp. 6. electric shock pain.
  4. Mieny, C. J. (2005). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055.
  5. IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands Archived 2013-12-21 at the Wayback Machine, Institute of Electrical and Electronics Engineers, 2002. (Convenience copy at National Academies Press.)
  6. Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136.
  7. Tremendously low frequency (TLF) (electromagnetic radiation, frequency below 3 Hz)
  8. Kumar, Sanjay; Shukla, Saurabh (2014). Concepts and Applications of Microwave Engineering. PHI Learning Pvt. Ltd. p. 3. ISBN 978-8120349353.
  9. Leonid A. Belov; Sergey M. Smolskiy; Victor N. Kochemasov (2012). Handbook of RF, Microwave, and Millimeter-Wave Components. Artech House. pp. 27–28. ISBN 978-1-60807-209-5.
  10. Ruey J. Sung & Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN 978-0-7923-6559-4. Archived from the original on 2015-09-05.
  11. Melvin A. Shiffman; Sid J. Mirrafati; Samuel M. Lam; Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN 978-3-540-71096-7.
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