Piezoelectric direct discharge plasma

Last updated

Piezoelectric direct discharge (PDD) plasma is a type of cold non-equilibrium plasma, generated by a direct gas discharge of a high voltage piezoelectric transformer. It can be ignited in air or other gases in a wide range of pressures, including atmospheric. Due to the compactness and the efficiency of the piezoelectric transformer, this method of plasma generation is particularly compact, efficient and cheap. It enables a wide spectrum of industrial, medical and consumer applications.

Contents

Background

Cold non-equilibrium atmospheric-pressure plasmas can be produced by high voltage discharges in the atmospheres of various working gases. The following 3 types of electric discharges found most applications in industrial processes:

All these types of electric discharges require high voltage electronics and high voltage cabling. Those are bulky, expensive, and in the case of AC power can be very inefficient due to dielectric losses. Moreover, industrial applications often require high power of the order 1 kW. This imposes strict safety requirements on the high voltage enclosures with open electrodes. A construction based on multiple low-power high voltage modules might improve safety aspects. Likewise, incorporation of the high voltage generator and the discharge electrode into a single module should reduce dielectric losses in the cables. However, so far no cost-effective solution to the system based on low-power modules was found.

Principles of PDD

Piezoelectric direct discharge uses a piezoelectric transformer as a generator of AC high voltage. The high voltage side of this transformer acts as an electrode generating electric discharges in the air or other working gases producing atmospheric-pressure plasmas. [1] [2] The piezoelectric transformer is very compact and requires only a source of a low power low voltage AC. This allows the whole plasma generator to be made exceptionally compact and cheap, enabling construction of hand-held plasma generators or cost-effective plasma generator arrays.

Piezoelectric transformers of the Rosen type, which can be made of lead zirconate titanate, convert the electric energy in the form of low voltage AC into mechanical oscillations. [3] [4] Consequently, these mechanical oscillations produce high voltage AC at the other end of the transformer. The highest amplitude is achieved at mechanical resonances, which occur at the frequencies typically between 10 kHz and 500 kHz. The dimensions of the piezoelectric crystal define the resonance frequency, while its dielectric environment can cause small shifts of the resonance. The low voltage electronics continuously adjusts the frequency to keep the transformer operating within the resonance. At the resonance, such transformers offer very high voltage conversion factors up to 1000 with voltages of 5 – 15 kV.

Properties of the plasma

Electric discharges produced in the gas from the high voltage side of the piezoelectric transformer have properties found also in the corona discharges and in the dielectric barrier discharges. While the former mode occurs when the high voltage side of the piezoelectric transformer is operated far from the electric grounds, the latter mode occurs when it is operated close to the electric grounds separated by a dielectric. Near the open electric grounds, the piezoelectric transformer produces periodic sparks. Transition to the electric arc does not occur because of the limited power of the transformer. The typical power of such transformers is of the order of 10 W. The efficiency of the plasma generation reaches 90%, while the remaining 10% of the power is lost due to mechanical and dielectric heating of the piezoelectric transformer.

Due to low electric currents, typical for the dielectric barrier and the corona discharges, the piezoelectric direct discharge produces a non-equilibrium plasma. This means that its constituent electrons, ions and the neutral gas particles have different kinetic energy distributions. Temperature of the neutral gas within the plasma volume remains lower than 50 C. At the same time, the electrons and the ions reach energies of 1 – 10 eV. This is 300 – 3000 times higher than the average energy of the neutral gas particles. The densities of the electrons and the ions reach 1016 – 1014 m−3. Since most of the plasma volume consists of the cold neutral gas, the plasma is cold. However, the very energetic electrons and ions excite atoms and molecules producing large amounts of short-lived chemical species, making this plasma chemically very active.

Applications

Properties of the piezoelectric direct discharge plasmas enable a large spectrum of applications in medical technology, microbiology and clinical research. [5] Typical industrial applications include ultra-fine cleaning and plasma activation of metal, ceramic, glass and plastic surfaces. Such plasma processing increases the surface energy improving the surface wettability and adhesion. The latter increases the quality of the subsequent printing or gluing. [6]

Very compact dimensions of the PDD plasma generator further broaden the sphere of possible applications to compact devices for laboratory work, hand-held applications, ozone generators, and even consumer products.

See also

Related Research Articles

In physics, the term dielectric strength has the following meanings:

<span class="mw-page-title-main">Van de Graaff generator</span> Electrostatic particle accelerator operating on the triboelectric effect

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials. It produces very high voltage direct current (DC) electricity at low current levels. It was invented by American physicist Robert J. Van de Graaff in 1929. The potential difference achieved by modern Van de Graaff generators can be as much as 5 megavolts. A tabletop version can produce on the order of 100 kV and can store enough energy to produce visible electric sparks. Small Van de Graaff machines are produced for entertainment, and for physics education to teach electrostatics; larger ones are displayed in some science museums.

<span class="mw-page-title-main">Spark gap</span> Two conducting electrodes separated in order to allow an electric spark to pass between

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light, and heat.

<span class="mw-page-title-main">Corona discharge</span> Ionization of air around a high-voltage conductor

A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. It represents a local region where the air has undergone electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air. A corona discharge occurs at locations where the strength of the electric field around a conductor exceeds the dielectric strength of the air. It is often seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages, and emits light by the same mechanism as a gas discharge lamp. Corona discharges can also happen in weather, such as thunderstorms, where objects like ship masts or airplane wings have a charge significantly different from the air around them.

<span class="mw-page-title-main">Flashtube</span> Incoherent light source

A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when triggered, ionizes and conducts a high-voltage pulse to make light. Flashtubes are used most in photography; they also are used in science, medicine, industry, and entertainment.

<span class="mw-page-title-main">Neutron generator</span> Source of neutrons from linear particle accelerators

Neutron generators are neutron source devices which contain compact linear particle accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains deuterium, tritium or a mixture of these isotopes. Fusion of deuterium atoms results in the formation of a helium-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom results in the formation of a helium-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV. Neutron generators have applications in medicine, security, and materials analysis.

<span class="mw-page-title-main">Electrical breakdown</span> Conduction of electricity through an insulator under sufficiently high voltage

In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material, subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material's dielectric strength. The voltage at which a given insulating object becomes conductive is called its breakdown voltage and, in addition to its dielectric strength, depends on its size and shape, and the location on the object at which the voltage is applied. Under sufficient voltage, electrical breakdown can occur within solids, liquids, or gases. However, the specific breakdown mechanisms are different for each kind of dielectric medium.

<span class="mw-page-title-main">Plasma globe</span> Decorative electrical device

A plasma ball, plasma globe, or plasma lamp is a clear glass container filled with noble gases, usually a mixture of neon, krypton, and xenon, that has a high-voltage electrode in the center of the container. When voltage is applied, a plasma is formed within the container. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light. Plasma balls were popular as novelty items in the 1980s.

<span class="mw-page-title-main">Electric arc</span> Electrical breakdown of a gas that results in an ongoing electrical discharge

An electric arc is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma, which may produce visible light. An arc discharge is initiated either by thermionic emission or by field emission. After initiation, the arc relies on thermionic emission of electrons from the electrodes supporting the arc. An arc discharge is characterized by a lower voltage than a glow discharge. An archaic term is voltaic arc, as used in the phrase "voltaic arc lamp".

<span class="mw-page-title-main">Induction lamp</span> Gas-discharge lamp using electric and magnetic fields to transfer energy to the gas inside

The induction lamp, electrodeless lamp, or electrodeless induction lamp is a gas-discharge lamp in which an electric or magnetic field transfers the power required to generate light from outside the lamp envelope to the gas inside. This is in contrast to a typical gas discharge lamp that uses internal electrodes connected to the power supply by conductors that pass through the lamp envelope. Eliminating the internal electrodes provides two advantages:

An electron avalanche is a process in which a number of free electrons in a transmission medium are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them. This releases additional electrons which accelerate and collide with further atoms, releasing more electrons—a chain reaction. In a gas, this causes the affected region to become an electrically conductive plasma.

<span class="mw-page-title-main">Corona treatment</span>

Corona treatment is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of high voltage to an electrode that has a sharp tip. The plasma forms at the tip. A linear array of electrodes is often used to create a curtain of corona plasma. Materials such as plastics, cloth, or paper may be passed through the corona plasma curtain in order to change the surface energy of the material. All materials have an inherent surface energy. Surface treatment systems are available for virtually any surface format including dimensional objects, sheets and roll goods that are handled in a web format. Corona treatment is a widely used surface treatment method in the plastic film, extrusion, and converting industries.

<span class="mw-page-title-main">Brush discharge</span>

A brush discharge is an electrical disruptive discharge similar to a corona discharge that takes place at an electrode with a high voltage applied to it, embedded in a nonconducting fluid, usually air. It is characterized by numerous luminous writhing sparks, plasma streamers composed of ionized air molecules, which repeatedly strike out from the electrode into the air, often with a crackling sound. The streamers spread out in a fan shape, giving it the appearance of a "brush".

Plasma activation is a method of surface modification employing plasma processing, which improves surface adhesion properties of many materials including metals, glass, ceramics, a broad range of polymers and textiles and even natural materials such as wood and seeds. Plasma functionalization also refers to the introduction of functional groups on the surface of exposed materials. It is widely used in industrial processes to prepare surfaces for bonding, gluing, coating and painting. Plasma processing achieves this effect through a combination of reduction of metal oxides, ultra-fine surface cleaning from organic contaminants, modification of the surface topography and deposition of functional chemical groups. Importantly, the plasma activation can be performed at atmospheric pressure using air or typical industrial gases including hydrogen, nitrogen and oxygen. Thus, the surface functionalization is achieved without expensive vacuum equipment or wet chemistry, which positively affects its costs, safety and environmental impact. Fast processing speeds further facilitate numerous industrial applications.

<span class="mw-page-title-main">Plasma-enhanced chemical vapor deposition</span> Method of depositing thin films onto a substrate

Plasma-enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases. The plasma is generally created by radio frequency (RF) frequency or direct current (DC) discharge between two electrodes, the space between which is filled with the reacting gases.

<span class="mw-page-title-main">Dielectric barrier discharge</span> Electrical discharge between two electrodes separated by an insulating dielectric barrier

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.

A microplasma is a plasma of small dimensions, ranging from tens to thousands of micrometers. Microplasmas can be generated at a variety of temperatures and pressures, existing as either thermal or non-thermal plasmas. Non-thermal microplasmas that can maintain their state at standard temperatures and pressures are readily available and accessible to scientists as they can be easily sustained and manipulated under standard conditions. Therefore, they can be employed for commercial, industrial, and medical applications, giving rise to the evolving field of microplasmas.

<span class="mw-page-title-main">Plasma (physics)</span> State of matter

Plasma is one of four fundamental states of matter, characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars, but also dominating the rarefied intracluster medium and intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field.

Plasma-activated bonding is a derivative, directed to lower processing temperatures for direct bonding with hydrophilic surfaces. The main requirements for lowering temperatures of direct bonding are the use of materials melting at low temperatures and with different coefficients of thermal expansion (CTE).

<span class="mw-page-title-main">Streamer discharge</span> Type of transient electric discharge

In electromagnetism, a streamer discharge, also known as filamentary discharge, is a type of transient electric discharge which forms at the surface of a conductive electrode carrying a high voltage in an insulating medium such as air. Streamers are luminous writhing branching sparks, plasma channels composed of ionized air molecules, which repeatedly strike out from the electrode into the air.

References

  1. ↑ M. Teschke and J. Engemann, Contrib. Plasma Phys. 49, 614 (2009)
  2. ↑ M. Teschke and J. Engemann, US020090122941A1, U.S. Patent application
  3. ↑ C.A. Rosen, K.A. Fish, H.C.Rothenberg, U.S. Patent No. 2,830,274 (April 1958)
  4. ↑ C.A. Rosen, in Solid State Magnetic and Dielectric Devices, edited by H. W. Katz (John Wiley & Sons, Inc., London, 1959) pp. 170–197
  5. ↑ A. Fridman, G. Friedman, "Plasma Medicine", Wiley; 1 edition (February 11, 2013)
  6. ↑ M. A. Lieberman, Al. J. Lichtenberg "Principles of Plasma Discharges and Materials Processing", Wiley-Interscience; 2 edition (April 14, 2005)
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.