Weakly ionized plasmas as tunable elements for radio-frequency systems *

Weakly ionized electric-discharge plasmas have unique properties making them promising as tunable elements in radio-frequency (RF) electronics, especially in high-power applications. Plasma discharges can combine resistive, capacitive, and inductive properties and all three can be tuned over very wide ranges. In recent breakthrough experimental studies, capacitively coupled radio-frequency (CCRF) discharges were driven by variable-frequency and/or variable-power sources so that the discharge impedance experienced by a much higher frequency weak probing signal was tuned widely, including change from capacitive to inductive behavior. Tunable plasma antennas are also of great interest, but their gain was, until recently, expected to be poor compared with that of conventional metallic antennas. However, recent experiments demonstrated that plasma antennas can have a gain comparable with that of metallic antennas despite the fact that the electrical conductivity of the plasma is orders of magnitude lower than that of metals.