Radio frequency

Radio frequency (RF) is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist (see mechanical filter and RF MEMS).

Special properties of RF current

Electric currents that oscillate at radio frequencies have special properties not shared by direct current or alternating current of lower frequencies. The energy in an RF current can radiate off a conductor into space as electromagnetic waves (radio waves); this is the basis of radio technology. RF current does not penetrate deeply into electrical conductors but flows along their surfaces; this is known as the skin effect. For this reason, when the human body comes in contact with high power RF currents it can cause superficial but serious 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. 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, so RF current must be carried by specialized types of cable called transmission line.

Radio communication

In order to receive radio signals an antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune in to a particular frequency (or frequency range).1 This is typically done via a resonator – in its simplest form, a circuit with a capacitor and an inductor forming a tuned circuit. The resonator amplifies oscillations within a particular frequency band, while reducing oscillations at other frequencies outside the band.

Frequencies

Frequency Wavelength Designation Abbreviation2

3 - 30 Hz 10^5km-10^4km Extremely low frequency ELF

30 - 300 Hz 10^4km-10^3km Super low frequency SLF

300 - 3000 Hz 10^3km-100km Ultra low frequency ULF

3 - 30 kHz 100km-10km Very low frequency VLF

30 - 300 kHz 10km-1km Low frequency LF

300 kHz - 3 MHz 1km-100m Medium frequency MF

3 - 30 MHz 100m-10m High frequency HF

30 - 300 MHz 10m-1m Very top frequency VHF

300 MHz - 3 GHz 1m-10cm Ultra top frequency UHF

3 - 30 GHz 10cm-1cm Super top frequency SHF

30 - 300 GHz 1cm-1mm Extremely top frequency EHF

In medicine

Radio frequency (RF) energy has been used in medical treatments for over 75 years,3 generally for minimally invasive surgeries, using radiofrequency ablation and cryoablation, including the treatment of sleep apnea.4 Magnetic resonance imaging (MRI) uses radio frequency waves to generate images of the human body.

RF as a synonym for wireless

Although radio frequency is a rate of oscillation, the term "radio frequency" or its acronym "RF" are also used as a synonym for radio – i.e. to describe the use of wireless communication, as opposed to communication via an electrical connector. Examples include:
Radio-frequency identification
ISO/IEC 14443-2 Radio frequency power and signal interface5