![DBD](https://upload.wikimedia.org/wikipedia/commons/e/e6/DBD.png)
Dielectric-barrier discharge (DBD) is the
electrical discharge
An electric discharge is the release and transmission of electricity in an applied electric field through a medium such as a gas (ie., an outgoing flow of electric current through a non-metal medium).American Geophysical Union, National Research ...
between two
electrodes
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials dep ...
separated by an insulating
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
barrier. Originally called silent (inaudible) discharge and also known as
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
production discharge or
partial discharge
In electrical engineering, partial discharge (PD) is a localized dielectric breakdown (DB) (which does not completely bridge the space between the two conductors) of a small portion of a solid or fluid electrical insulation (EI) system under hig ...
, it was first reported by
Ernst Werner von Siemens
Ernst Werner Siemens (von Siemens from 1888; ; ; 13 December 1816 – 6 December 1892) was a German electrical engineer, inventor and industrialist. Siemens's name has been adopted as the SI unit of electrical conductance, the siemens. He foun ...
in 1857.
[Kogelschatz, Ulrich, Baldur Eliasson, and Walter Egli]
From ozone generators to flat television screens: history and future potential of dielectric-barrier discharges
Pure Applied Chemistry, Vol. 71, No. 10, pp. 1819-1828, 1999. Retrieved on 2007-08-05.
Process
The process normally uses high voltage
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
, ranging from lower
RF to
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
frequencies. However, other methods were developed to extend the frequency range all the way down to the DC. One method was to use a high resistivity layer to cover one of the electrodes. This is known as the resistive barrier discharge.
[M. Laroussi, I. Alexeff, J. P. Richardson, and F. F. Dyer " The Resistive Barrier Discharge", IEEE Trans. Plasma Sci. 30, 158 (2002)] Another technique using a semiconductor layer of gallium arsenide (
GaAs
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circ ...
) to replace the dielectric layer, enables these devices to be driven by a DC voltage between 580 V and 740 V.
Construction
DBD devices can be made in many configurations, typically planar, using parallel plates separated by a
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
or cylindrical, using
coaxial
In geometry, coaxial means that several three-dimensional linear or planar forms share a common axis. The two-dimensional analog is ''concentric''.
Common examples:
A coaxial cable is a three-dimensional linear structure. It has a wire condu ...
plates with a dielectric tube between them.
[Kraus, Martin, Baldur Eliasson, Ulrich Kogelschatzb, and Alexander Wokauna]
CO2 reforming of methane by the combination of dielectric-barrier discharges and catalysis
Physical Chemistry Chemical Physics, 2001, 3, 294-300. Retrieved on 2007-08-05. In a common coaxial configuration, the dielectric is shaped in the same form as common
fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...
tubing. It is 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 less than 0.1 mm in plasma displays, several millimetres in ozone generators and up to several centimetres in CO
2 lasers.
Depending on the geometry, DBD can be generated in a volume (VDBD) or on a surface (SDBD). For VDBD the plasma is generated between two electrodes, for example between two parallel plates with a dielectric in between.
At SDBD the microdischarges are generated on the surface of a dielectric, which results in a more homogeneous plasma than can be achieved using the VDBD configuration At SDBD the microdischarges are limited to the surface, therefore their density is higher compared to the VDBD. The plasma is generated on top of the surface of an SDBD plate. To easily ignite VDBD and obtain a uniformly distributed discharge in the gap, a pre-ionization DBD can be used.
A particular compact and economic DBD plasma generator can be built based on the principles of the
piezoelectric direct discharge. In this technique, the high voltage is generated with a piezo-transformer, the secondary circuit of which acts also as the high voltage electrode. Since the transformer material is a dielectric, the produced electric discharge resembles properties of the dielectric barrier discharge.
Operation
A multitude of random arcs form in operation gap exceeding 1.5 mm between the two electrodes during discharges in gases at the atmospheric pressure . As the charges collect on the surface of the dielectric, they discharge in microseconds (millionths of a second), 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
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
, overcoming the recombination process leading to the extinction of the discharge plasma. 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
Paschen's law is an equation that gives the breakdown voltage, that is, the voltage necessary to start a discharge or electric arc, between two electrodes in a gas as a function of pressure and gap length. It is named after Friedrich Paschen who ...
. The discharge process causes the emission of an energetic
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...
, the frequency and energy of which corresponds to the type of gas used to fill the discharge gap.
Applications
Usage of generated radiation
DBDs can be used to generate optical radiation by the relaxation of excited species in the plasma. The main application here is the generation of UV-radiation. Such
excimer ultraviolet lamps can produce light with short wavelengths which can be used to produce
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
in industrial scales. Ozone is still used extensively in industrial air and water treatment.
Early 20th-century attempts at commercial nitric acid and ammonia production used DBDs as several nitrogen-oxygen compounds are generated as discharge products.
Usage of the generated plasma
Since the 19th century, DBDs were known for their decomposition of different gaseous compounds, such as NH
3, H
2S and CO
2. Other modern applications include semiconductor manufacturing, germicidal processes, polymer surface treatment, high-power CO
2 lasers typically used for welding and metal cutting, pollution control and
plasma displays panels,
aerodynamic
Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
flow control... The relatively lower temperature of DBDs makes it an attractive method of generating plasma at atmospheric pressure.
Industry
The plasma itself is used to modify or clean (
plasma cleaning
Plasma cleaning is the removal of impurities and contaminants from surfaces through the use of an energetic plasma or dielectric barrier discharge (DBD) plasma created from gaseous species. Gases such as argon and oxygen, as well as mixtures such ...
) surfaces of materials (e.g.
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s,
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
surfaces), that can also act as dielectric barrier, or to modify gases
applied further to "soft"
plasma cleaning
Plasma cleaning is the removal of impurities and contaminants from surfaces through the use of an energetic plasma or dielectric barrier discharge (DBD) plasma created from gaseous species. Gases such as argon and oxygen, as well as mixtures such ...
and increasing
adhesion
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
The forces that cause adhesion and cohesion can b ...
of surfaces prepared for coating or gluing (
flat panel display
A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment.
Flat-panel displays are thin, lightweight, provide better l ...
technologies).
A dielectric barrier discharge is one method of plasma treatment of textiles at atmospheric pressure and room temperature. The treatment can be used to modify the surface properties of the textile to improve
wettability
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with ...
, improve the
absorption of dyes and
adhesion
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
The forces that cause adhesion and cohesion can b ...
, and for
sterilization. DBD plasma provides a dry treatment that doesn't generate waste water or require drying of the fabric after treatment. For textile treatment, a DBD system requires a few kilovolts of alternating current, at between 1 and 100 kilohertz. Voltage is applied to insulated electrodes with a millimetre-size gap through which the textile passes.
An
excimer lamp
An excimer lamp (or excilamp) is a source of ultraviolet light based on spontaneous emission of excimer (exciplex) molecules.
Introduction
Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the ult ...
can be used as a powerful source of short-wavelength ultraviolet light, useful in chemical processes such as surface cleaning of semiconductor wafers. The lamp relies on a dielectric barrier discharge in an atmosphere of xenon and other gases to produce the excimers.
Water treatment
An additional process when using
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
gas for removal of bacteria and organic contaminates in drinking water supplies. Treatment of public swimming baths, aquariums and fish ponds involves the use of
ultraviolet radiation
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
produced when a dielectric mixture of
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
gas and glass are used.
Surface modification of materials
An application where DBDs can be successfully used is to modify the characteristics of a material surface. The modification can target a change in its hydrophilicity, the surface activation, the introduction of functional groups, and so on. Polymeric surfaces are easy to be processed using DBDs which, in some cases, offer a high processing area.
Medicine
Dielectric barrier discharges were used to generate relatively large volume diffuse plasmas at atmospheric pressure and applied to inactivate bacteria in the mid 1990s.
[M. Laroussi, "Sterilization of contaminated matter with an atmospheric pressure plasma", IEEE Trans. Plasma Sci. 24, 1188 (1996)] This eventually led to the development of a new field of applications, the biomedical applications of plasmas. In the field of biomedical application, three main approaches have emerged: direct therapy,
surface modification, and plasma polymer deposition. Plasma polymers can control and steer biological–biomaterial interactions (i.e. adhesion, proliferation, and differentiation) or inhibition of bacteria adhesion.
Aeronautics
Interest in
plasma actuator
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pl ...
s as active
flow control devices is growing rapidly due to their lack of mechanical parts, light weight and high response frequency.
Properties
Due to their nature, these devices have the following properties:
* capacitive electric load: low
power factor in range of 0.1 to 0.3
* high ignition voltage 1–10 kV
* huge amount of energy stored in electric field – requirement of energy recovery if DBD is not driven continuously
* voltages and currents during discharge event have major influence on discharge behaviour (filamented, homogeneous).
Operation with continuous sine waves or square waves is mostly used in high power industrial installations. Pulsed operation of DBDs may lead to higher discharge efficiencies.
Driving circuits
Drivers for this type of electric load are power HF-generators that in many cases contain a transformer for high voltage generation. They resemble the control gear used to operate
compact fluorescent lamp
A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for inca ...
s or
cold cathode fluorescent lamp
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet, ul ...
s. The operation mode and the topologies of circuits to operate
BDlamps with continuous sine or square waves are similar to those standard drivers. In these cases, the energy that is stored in the DBD's capacitance does not have to be recovered to the intermediate supply after each ignition. Instead, it stays within the circuit (oscillates between the
BDs capacitance and at least one inductive component of the circuit) and only the
real power, that is consumed by the lamp, has to be provided by the power supply. Differently, drivers for pulsed operation suffer from rather low power factor and in many cases must fully recover the DBD's energy. Since pulsed operation of
BDlamps can lead to increased lamp efficiency, international research led to suiting circuit concepts. Basic topologies are resonant
flyback and resonant
half bridge. A flexible circuit, that combines the two topologies is given in two patent applications, and may be used to adaptively drive DBDs with varying capacitance.
An overview of different circuit concepts for the pulsed operation of DBD optical radiation sources is given in "Resonant Behaviour of Pulse Generators for the Efficient Drive of Optical Radiation Sources Based on Dielectric Barrier Discharges".
References
{{Reflist
Electrical phenomena
Electricity
Electrostatics