Dielectric barrier discharge

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Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier. Originally called silent discharge, and also known as ozone production discharge,^[1] or partial discharge,^[2] it was first reported by Ernst Werner von Siemens in 1857.^[3]

The process uses high voltage alternating current, often at lower RF frequencies but recently even at microwave levels. DBD devices can be made in many configurations, typically planar, using parallel plates separated by a dielectric, or cylindrical, using coaxial plates with a dielectric tube between them.^[4] In a common coaxial configuration, the dielectric is shaped in the same form as common fluorescent tubing, filled at atmospheric pressure with either a rare gas or rare gas-halide mix, with the glass walls acting as the dielectric barrier. Due to the atmospheric pressure level, such processes require high energy levels to sustain. Common dielectric materials include glass, quartz, ceramics and polymers. The gap distance between electrodes varies considerably, from 0.1 mm in plasma displays, 1 mm in ozone generators, or several cm in CO₂ lasers.

A multitude of random arcs form between the two electrodes during operation. As the charges collect on the surface of the dielectric, they discharge in microseconds, leading to their reformation elsewhere on the surface. Similar to other electrical discharge methods, the contained plasma is sustained if the continuous energy source provides the required degree of ionization, overcoming the recombination process leading to the extinction of the discharge. Such recombinations are directly proportional to the collisions between the molecules, and in turn to the pressure of the gas, as explained by Paschen's Law. The discharge process causes the emission of an energetic photon, the energy of which corresponds to the type of gas used to fill the discharge gap.

[edit] Applications

Original applications for the use of DBDs centered around their production of ozone, and this is still used extensively in industrial air and water treatment.^[4] Early 19th-century attempts at commercial nitric acid and ammonia production used DBDs,^[5] as several nitrogen-oxygen compounds are generated as discharge products.^[3] DBDs were also noted since the 19th century for their decomposition of different gaseous compounds, such as NH₃, H₂S and CO₂. Other modern applications include semiconductor manufacturing, germicidal processes, polymer surface treatment, high-power CO₂ lasers typically used for welding and metal cutting, excimer ultraviolet lamps, pollution control, and plasma displays panels. The relatively lower temperature of DBDs makes it an attractive method of generating plasma at atmospheric pressure.

[edit] References