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; 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.
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.
Main article: Radio spectrum
The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunication Union (ITU):
|ITU designation||IEEE bands|
|Below 3 Hz||>105 km||Tremendously low frequency||TLF||—|
|3–30 Hz||105–104 km||Extremely low frequency||ELF||—|
|30–300 Hz||104–103 km||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 called microwave, 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 and the EU/NATO frequency designations.
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 article: 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, and now include diathermy, hyperthermy treatment of cancer, electrosurgery scalpels used to cut and cauterize in operations, and radiofrequency ablation. Magnetic resonance imaging (MRI) uses radio frequency waves to generate images of the human body.
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. 
While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see mechanical filter and RF MEMS.
electric shock pain.