Plasma ignition in a quarter-wavelength microwave slot resonator

Abstract

A new microwave plasma source concept, particularly for use in the atmospheric pressure region, is presented where impedance matching is realized by a quarter-wavelength waveguide resonator structure. The waveguide is formed by a slot of 100 µm width machined into a copper sheet of 50 mm × 10 mm with a thickness of 200 µm. The slot length for a resonance frequency of 2 GHz is approximately 37.5 mm. This allows generating voltages high enough for ignition of an atmospheric plasma by this very small, simple and easy-to-fabricate structure. After ignition, the plasma extends over approximately 12 mm length of the slot, so a high electrode lifetime can be expected. Furthermore, the planar geometry of this source facilitates up-scaling to array configurations, which allows realization of a distributed source for treating large areas. Basic ignition parameters are investigated. Statistics for multiple ignitions are presented and the resulting Paschen characteristics are shown in the pressure region from 100 Pa to atmospheric pressure.

Microplasmas ignited and sustained by microwaves

“…Any reflected wave from the plasma discontinuity is primarily recycled by reflection from the grounded end of the microstrip line. A quarter-wave resonator is illustrated, but half-wave [21][22][23] and 3/4-wave resonators [24,25] behave in a similar fashion. A third microwave coupling strategy is sketched in figure 1(c).…”

Microwave-excited atmospheric-pressure microplasmas based on a coaxial transmission line resonator

“…A number of plasma sources with various electrode configurations have been developed [1]. Sources operating with dc [2,3], low-frequency (kHz) [4], rf [5][6][7], microwave [8][9][10] and pulsed [11] power have been reported. Microwave-induced atmospheric-pressure plasmas have been used for analytical purposes [10], surface modification and biomedical applications such as cell treatment, sterilization [12] and decontamination of toxic agents [13][14][15].…”

“…In this paper, a new portable microplasma source based on a coaxial transmission line resonator (CTLR) is described. The design and performance of the device is parallel to that of microstrip based devices [8,9,16] but this device has a pen-like shape that makes it more convenient for hand-held applications and parallel operation, or both. Unlike the coaxial device reported in [10], the device presented in this paper operates at resonance, resulting in an efficient plasma source.…”

Observation of microwave volume plasma ignition in ambient air

“…One of them is MW microplasmas. They can be realized in a number of ways and only some of them are mentioned here: split-ring [14,15] or slot [16] resonators, compact re-entrant cavity applicators [10], planar transmission line configuration corresponding to linear resonators [17] or microstripline applicators [18,19], end of coaxial line [20] or in small torches [21,22]. Small dimensions and low consumed power (1-100 W) allow avoidance of high thermal load, and spontaneous ignitions can be observed in high-quality resonators.…”

“…A resonance structure amplifies the electric field quite strongly in comparison with the metallic nozzle used in torches [11,12,23,24] or tungsten needle applied in high power discharges [6,7]. The ignition pin provokes plasmas with relatively large volume and consumes higher power in contrast to microplasmas [10,[14][15][16][17][18][19][20][21][22]. The principal difference from resonant cavities [3,4] is that the volume discharge is maintained outside the resonator.…”