Piezoelectric direct discharge plasma

Piezoelectric direct discharge is a type of a cold (nonequilibrium) plasma generation method that can efficiently ionize different process gases including air in a wide pressure range.

Background

The majority of industrial plasma processing is conducted with glow discharges at pressures below 10 torr. It has long been recognized that glow discharges would play a much larger industrial role if they could be generated at normal pressure, and in ambient air. In this context the Paschen’s law describes the physical limits of plasma ignition depending on pressure and electrode gap.

For atmospheric plasma sources used in technology, low frequency and DC power supplies are always connected with high current electric arcs and the formation of thermal equilibrium plasma where the temperature is relatively homogeneous throughout the atoms, molecules, ions and electrons and can quickly exceed several thousand Kelvin.

Nonequilibrium plasma (cold plasma) can be generated under atmospheric conditions at very high frequencies or using short duration microdischarges created by dielectric breakdown between two electrodes separated by an insulating dielectric barrier. The so-called “cold discharge” or dielectric barrier discharge (DBD) is used in many applications where high temperatures have to be avoided.

Principle of piezoelectric direct discharge (PDD)

The basic concept of the piezoelectric direct discharge technology (PDD) is to use a piezoelectric transformer (PT) as an integral part of the plasma source. Thus, all high voltage problems of traditional atmospheric plasma sources can be avoided. Both plasma microjets and surface discharge plasma devices of the corona type can be built.

Technology

Piezoelectric transformers made of PZT electroceramics generate high voltage, by electro-mechanical energy conversion based on the piezoelectric effect. The oscillating surface potential can cause excitation and ionization of atoms and molecules resulting in the generation of piezoelectric direct discharge plasma (PDD). The discharge structure shows the characteristic filament micro pattern of short duration (microseconds and below) typical for dielectric barrier discharges (DBD). PDD is applicable for ozone generation, excimer lamps, chemical microreactors and surface treatment.

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