Dielectric barrier discharge
Encyclopedia
Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric
barrier. Originally called silent (inaudible) discharge and also known as ozone
production discharge or partial discharge
, it was first reported by Ernst Werner von Siemens
in 1857.
, ranging from lower RF
to microwave
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. Another technique using a semiconductor layer of Gallium arsenide (GaAs
) to replace the dieletric layer, enables these devices to be driven by a DC voltage between 580V and 740V.
or cylindrical, using coaxial
plates with a dielectric tube between them. In a common coaxial configuration, the dielectric is shaped in the same form as common fluorescent 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 millimeters in ozone generators and up to several centimeters in CO2 lasers.
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 frequency and energy of which corresponds to the type of gas used to fill the discharge gap.
ultraviolet
lamps can produce light with short wavelengths which can be used used to produce ozone
in industrial scales. Ozone is still used extensively in industrial air and water treatment. Early 19th-century attempts at commercial nitric acid and ammonia production used DBDs as several nitrogen-oxygen compounds are generated as discharge products.
surfaces), that can also act as dielectric barrier, or to modify gases.
Since the 19th century, DBDs are known 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, , pollution control and plasma displays panels
. The relatively lower temperature of DBDs makes it an attractive method of generating plasma at atmospheric pressure.
.
gas for removal of bacteria and organic contaminates in drinking water suppplies. Treatment of public swimming Baths, Aquariums and Fish ponds involves the use of Ultraviolet radiation produced when a dieletric mixture of Xenon
gas and glass are used.
An excimer
lamp 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.
Despite the operation with continuous sine waves or square waves, which is mostly used in high power industrial installations, pulsed operation of DBDs may lead to higher discharge efficiencies.
s and Cold cathode fluorescent lamps.
Especially the operation mode and the topologies of circuits for the generation of continuous sine or square waves are similar to those standard drivers. Beneficially, 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 can stay within the circuit and only the real power, that is consumed by the lamp, has to be provided by the power supply. Because mostly multiple ignitions per voltage half-wave are enforced, the Power Factor
of the lamp is quite high.
Differently, drivers for pulsed operation suffer from rather low power factor and in many cases must fully recover the DBD's energy. Basic topologies are Resonant Flyback
and Resonant Half Bridge
. A flexible circuit, that combines the two topologies is given in and and may be used to adaptively drive DBDs with varying capacitance.
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
barrier. Originally called silent (inaudible) discharge and also known as ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
production discharge or partial discharge
Partial discharge
In electrical engineering, partial discharge is a localised dielectric breakdown of a small portion of a solid or fluid electrical insulation system under high voltage stress, which does not bridge the space between two conductors...
, it was first reported by Ernst Werner von Siemens
Ernst Werner von Siemens
Ernst Werner Siemens, von Siemens since 1888, was a German inventor and industrialist. Siemens' name has been adopted as the SI unit of electrical conductance, the siemens...
in 1857.
Process
The process normally uses high voltage alternating currentAlternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
, ranging from lower RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
to microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
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. Another technique using a semiconductor layer of Gallium arsenide (GaAs
Gaas
Gaas is a commune in the Landes department in Aquitaine in south-western France....
) to replace the dieletric layer, enables these devices to be driven by a DC voltage between 580V and 740V.
Construction
DBD devices can be made in many configurations, typically planar, using parallel plates separated by a dielectricDielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
or cylindrical, using coaxial
Coaxial
In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional linear analogue of concentric.Coaxial cable, as a common example, has a wire conductor in the centre a circumferential outer conductor and an insulating medium called the dielectric separating...
plates with a dielectric tube between them. In a common coaxial configuration, the dielectric is shaped in the same form as common fluorescent tubing. It is filled at atmospheric pressure with either a rare gas or rare gas-halide
Halide
A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
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 millimeters in ozone generators and up to several centimeters in CO2 lasers.
Operation
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 (millionths of a second), leading to their reformation elsewhere on the surface. Similar to other electrical discharge methods, the contained plasmaPlasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
is sustained if the continuous energy source provides the required degree of ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
, 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
Paschen's law
Paschen's Law, named after Friedrich Paschen, was first stated in 1889. He studied the breakdown voltage of gas between parallel plates as a function of pressure and gap distance. The voltage necessary to arc across the gap decreased up to a point as the pressure was reduced. It then increased,...
. The discharge process causes the emission of an energetic photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
, the frequency and energy of which corresponds to the type of gas used to fill the discharge gap.
Usage of generated radiation
DBDs can be used to generate optical radiation by the relaxiation of excited species in the plasma. The main application here is the generation of UV-radiation. Those ExcimerExcimer
An excimer is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is...
ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
lamps can produce light with short wavelengths which can be used used to produce ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
in industrial scales. Ozone is still used extensively in industrial air and water treatment. Early 19th-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
The plasma itself is used to modify (clean) surfaces of materials (e.g. Polymers, semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
surfaces), that can also act as dielectric barrier, or to modify gases.
Since the 19th century, DBDs are known 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, , pollution control and plasma displays panels
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
. The relatively lower temperature of DBDs makes it an attractive method of generating plasma at atmospheric pressure.
Medicine
Dielectric barrier discharges were used to generate relatively large volume diffuse plasmas at atmospheric pressure and applied to inactivate bacteria in the mid 1990’s. This eventually led to the development of a new field of applications, the biomedical applications of plasmas. This field is now known as plasma medicinePlasma medicine
Plasma medicine is an innovative and emerging field combining plasma physics, life sciences and clinical medicine to use physical plasma for therapeutic applications. Initial experiments confirm that plasma can be effective in in vivo antiseptics without affecting surrounding tissue and, moreover,...
.
Water treatment
An additional process when using ChlorineChlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
gas for removal of bacteria and organic contaminates in drinking water suppplies. Treatment of public swimming Baths, Aquariums and Fish ponds involves the use of Ultraviolet radiation produced when a dieletric mixture of Xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
gas and glass are used.
Industry
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, improve the absorption of dyes, 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
Excimer
An excimer is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is...
lamp 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.
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
- voltages and currents during discharge event have major influence on discharge behaviour (filamented, homogeneous).
Despite the operation with continuous sine waves or square waves, which 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 mostly contain a transformer for high voltage generation. Drivers resemble the control gear used to operate Compact fluorescent lampCompact fluorescent lamp
A compact fluorescent lamp , also called compact fluorescent light, energy-saving light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent lamp; some types fit into light fixtures formerly used for incandescent lamps...
s and Cold cathode fluorescent lamps.
Especially the operation mode and the topologies of circuits for the generation of continuous sine or square waves are similar to those standard drivers. Beneficially, 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 can stay within the circuit and only the real power, that is consumed by the lamp, has to be provided by the power supply. Because mostly multiple ignitions per voltage half-wave are enforced, the Power Factor
Power factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
of the lamp is quite high.
Differently, drivers for pulsed operation suffer from rather low power factor and in many cases must fully recover the DBD's energy. Basic topologies are Resonant Flyback
Flyback converter
The flyback converter is used in both AC/DC and DC/DC conversion with galvanic isolation between the input and any outputs. More precisely, the flyback converter is a buck-boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional...
and Resonant Half Bridge
Half bridge
Half-Bridge can refer to:* A single-direction configuration of an H-Bridge motor controller* A form of DC to DC converter switched-mode power supply.* One of a pair of devices that connect to perform the Bridging function of a computer network...
. A flexible circuit, that combines the two topologies is given in and and may be used to adaptively drive DBDs with varying capacitance.