Radio frequency

Lore & Background

Radio frequency currents have properties distinct from direct current or lower-frequency alternating current, such as the 50 or 60 Hz current used in power distribution. Energy from RF currents in conductors can radiate into space as electromagnetic waves, which is the basis of radio technology. RF current does not penetrate deeply into conductors but tends to flow along their surfaces, a phenomenon known as the skin effect.

When applied to the body, RF currents often do not cause the painful sensation and muscular contraction of electric shock that lower frequencies produce, because the current changes direction too quickly to trigger depolarization of nerve membranes. However, RF currents can cause internal injury and serious superficial burns called RF burns. RF current can also ionize air, creating a conductive path, a property exploited in electric arc welding units that use higher frequencies than power distribution.

RF current can appear to flow through paths containing insulating material, such as the dielectric insulator of a capacitor, because capacitive reactance decreases with increasing frequency. Conversely, RF current can be blocked by a coil of wire or even a single turn or bend in a wire, as inductive reactance increases with frequency. When conducted by an ordinary electric cable, RF current tends to reflect from discontinuities like connectors, causing standing waves; it is carried efficiently over transmission lines such as coaxial cables.

Reader's Guide

Radio frequency is central to a wide range of practical applications, including broadcasting, voice communication, data communication, radar, radiolocation, medical treatments, and remote control. The radio spectrum is divided into frequency bands with conventional names designated by the International Telecommunication Union (ITU). 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 standard IEEE letter-band frequency designations and EU/NATO frequency designations.

Test apparatus for radio frequencies includes standard instruments at the lower end of the range, but at higher frequencies, the test equipment becomes more specialized. Radio-frequency signal generators are commonly used as sources in RF testing and calibration setups, providing controlled oscillating signals over wide frequency ranges. Several manufacturers and engineering organizations publish technical documentation and design guides describing practical implementations of RF generators and high-frequency power systems. While RF usually refers to electrical oscillations, mechanical RF systems also exist, as seen in mechanical filters and RF MEMS.

Did You Know?

• RF currents applied to the body often do not cause the painful sensation of electric shock because the current changes direction too quickly to trigger nerve depolarization.
• RF current can ionize air, creating a conductive path, a property used in electric arc welding.
• RF current can be blocked by a coil of wire because inductive reactance increases with frequency.