Atmospheric pressure plasmas: A review

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

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Plasma-liquid interactions: A review and roadmap

Summary: Low temperature, high pressure, non-equilibrium plasmas are now routinely used in several material processing applications, and in some cases are competing with low pressure plasmas in areas where these have historically been dominant. Etching and deposition are examples of such applications. Amongst the novel applications of non-equilibrium plasmas, biomedical applications such as electrosurgery, surface modification of biocompatible materials, and the sterilization of heat-sensitive medical tools are particularly interesting. In this paper, first a brief overview of recent research on reduced-pressure plasma-based sterilization/decontamination methods is given. Then a detailed review and discussion on the effects of atmospheric pressure non-equilibrium plasmas on the cells of bacteria is presented. This includes the evaluation of the inactivation kinetics and the roles of the various plasma agents in the inactivation process. Measurements of the plasma temperature, the UV emission, and concentrations of various reactive species for the case of air plasma are presented. Plasma sub-lethal effects are also briefly discussed, and the prospects of the use of “cold” plasmas in the biomedical field are outlined.

Low Temperature Plasma-Based Sterilization: Overview and State-of-the-Art

Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

Evaluation of the roles of reactive species, heat, and UV radiation in the inactivation of bacterial cells by air plasmas at atmospheric pressure

The atmospheric pressure plasma jet (APPJ) [A. Schutze et al., IEEE Trans. Plasma Sci. 26, 1685 (1998)] is a nonthermal, high pressure, uniform glow plasma discharge that produces a high velocity effluent stream of highly reactive chemical species. The discharge operates on a feedstock gas (e.g., He/O2/H2O), which flows between an outer, grounded, cylindrical electrode and an inner, coaxial electrode powered at 13.56 MHz rf. While passing through the plasma, the feedgas becomes excited, dissociated or ionized by electron impact. Once the gas exits the discharge volume, ions and electrons are rapidly lost by recombination, but the fast-flowing effluent still contains neutral metastable species (e.g., O2*, He*) and radicals (e.g., O, OH). This reactive effluent has been shown to be an effective neutralizer of surrogates for anthrax spores and mustard blister agent. Unlike conventional wet decontamination methods, the plasma effluent does not cause corrosion and it does not destroy wiring, electronics, or mo...

Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ)

Discharge phenomena of a nonthermal atmospheric pressure plasma source have been studied. An atmospheric pressure plasma jet (APPJ) operates using rf power and produces a stable homogeneous discharge at atmospheric pressure. After breakdown, the APPJ operation is divided into two regimes, a “normal” operating mode when the discharge is stable and homogeneous, and a “failure” mode when the discharge converts into a filamentary arc. Current and voltage (I–V) characteristics and spatially resolved emission intensity profiles have been measured during the normal operating mode. These measurements show that the APPJ produces an alpha (α) mode rf capacitive discharge. Based upon a dimensional analysis using the observed I–V characteristics, a rough estimate is made for plasma density of 3×1011 cm−3 and an electron temperature of 2 eV. In addition, the gas temperature of 120 °C has been spectroscopically measured inside the discharge. These plasma parameters indicate that the APPJ shows promise for various mater...

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Discharge phenomena of an atmospheric pressure radio-frequency capacitive plasma source

Gas breakdown is studied in an atmospheric pressure rf capacitive plasma source developed for materials applications. At a rf frequency of 13.56 MHz, breakdown voltage is largely a function of the product of the pressure and the discharge gap spacing, approximating the Paschen curve. However, breakdown voltage varies substantially with rf frequency due to a change in the electron loss mechanism. A large increase in breakdown voltage is observed when argon, oxygen, or nitrogen is added to helium despite their lower ionization potential. Discussion is given for optimal breakdown conditions at atmospheric pressure.

Gas Breakdown in an Atmospheric Pressure Radio-Frequency Capacitive Plasma Source

Neutral bremsstrahlung emission spectrum is measured in an atmospheric-pressure radio frequency (rf) capacitive discharge for a gas mixture of helium (99.5%) and oxygen (0.5%) using a high resolution triple monochromator between 450 and 1000 nm. Good agreement is obtained for spectral variation and absolute intensity between the observed neutral bremsstrahlung and theoretical emissivity calculated using electron–neutral momentum cross sections. Based on a theoretical fitting, the discharge is characterized by a time averaged electron density of 2.9×1011 cm−3 and an electron temperature of 1.9 eV for an input power density of 28 W/cm3.

Neutral bremsstrahlung measurement in an atmospheric-pressure radio frequency discharge

As touch based input becomes more popular in mobile devices, there is an increasing need for haptic feedback on key-less input surface. Four experiments were conducted to design and evaluate identifiable emulated key-click signals using a piezoelectric actuator. Experiments I and II assessed the information transmission capacity for the amplitude, frequency, and number of cycles of raised cosine waveforms used to drive the piezo actuators under fixed- and roving-background conditions, respectively. Experiment III estimated the total information transfer for all three parameters. The results were used to reduce the number of stimulus alternatives in the key-click signal set with the goal to achieve perfect identification performance. Experiment IV verified that up to 5 to 6 identifiable key-click signals could be achieved with the experimental setup. The present study outlines an information theoretic approach to conducting identification experiments to guide the design of and to evaluate a perfectly identifiable stimulus set. The methodology can be applied to other applications in need of perceptually identifiable stimulation patterns.

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Jaeyoung Park

Papers

Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ)

Discharge phenomena of an atmospheric pressure radio-frequency capacitive plasma source

Gas Breakdown in an Atmospheric Pressure Radio-Frequency Capacitive Plasma Source

Neutral bremsstrahlung measurement in an atmospheric-pressure radio frequency discharge

Design and Evaluation of Identifiable Key-Click Signals for Mobile Devices