Parallel Plate Electrodes Research Articles

Defining Plasma Polymerization: New Insight Into What We Should Be Measuring

External parameters (RF power and precursor flow rate) are typically quoted to define plasma polymerization experiments. Utilizing a parallel-plate electrode reactor with variable geometry, it is shown that these parameters cannot be transferred to reactors with different geometries in order to reproduce plasma polymer films using four precursors. Measurements of ion flux and power coupling efficiency confirm that intrinsic plasma properties vary greatly with reactor geometry at constant applied RF power. It is further demonstrated that controlling intrinsic parameters, in this case the ion flux, offers a more widely applicable method of defining plasma polymerization processes, particularly for saturated and allylic precursors.

Ionization coefficients for argon in a micro-discharge

Ionization coefficients are measured for electrons in a dc micro-discharge in argon from optical emission profiles. The micro-discharge is operated in the Townsend regime between two parallel-plate electrodes. Axial profiles of emission are obtained with sufficient resolution to provide spatial ionization coefficients. The measured coefficients agree very well with the data obtained from other sources, indicating the operation of the discharge in the Townsend regime and also that Townsend mechanisms do not need extension to describe such discharges.

Pull-in experiments on electrostatically actuated microfabricated meso scale beams

We report on the results of characterization and modeling of electrostatically actuated meso scale beams. The beams with clamped ends were 5000μm long, 150μm thick and 10, 12 and 15μm wide and were operated by a parallel plate electrode located at the distance of 20μm from the beam. The devices were fabricated using deep reactive ion etching (DRIE) from a silicon on insulator (SOI) wafer with 150μm thick device layer. The beams were operated in ambient air conditions and the voltage–displacement dependence was built using image processing. In addition, pull-in behavior of the beams was modeled using several approaches, starting from geometrically nonlinear shallow Euler–Bernoulli beam model and up to fully coupled nonlinear large deflection three-dimensional anisotropic elasticity finite elements simulations. Excellent agreement between the results provided by the models and the experimental data was observed. The results of the work demonstrate an ability to achieve large displacements in simple meso scale beam structures and provide a reliable experimental reference for double clamped beams actuated by a parallel-plate electrode.

Microbial inactivation utilizing impulse waveform

Inactivation of Escherichia coli has been successfully performed by the utilization of impulse voltage waveform. The process involves in microbial inactivation is pulsed electric field (PEF) treatment. PEF utilizes short-duration high-voltage pulses for microbial inactivation by the process of electroporation. Inactivation rate was measured against peak electric field, number of applied pulses, and energy input to unit volume of liquid. Two different electrode configuration spherical–spherical and parallel-plate electrode systems were used. The results indicate that parallel-plate electrode system results in better inactivation rate than spherical electrode system. With applied electric field of 24 kV/cm and 20 pulses, six log reductions were achieved in parallel-plate electrode system indicating that inactivation rate is strongly dependent on electrode configuration, peak electric field, and applied pulses.

Propylene Carbonate Based Compact Fiber Mach–Zehnder Interferometric Electric Field Sensor

We demonstrate a compact fiber Mach-Zehnder (MZ) interferometric electric field sensor by splicing a short section of single mode fiber between two sections of single mode fibers with a large lateral offset of 62.5 μm, where the propylene carbonate is filled into the open arm of the interferometer. Based on the Kerr electro-optic effect of propylene carbonate, the applied intensive transient electric field can change the refractive index of propylene carbonate, which shifts the interferometric fringe. The electrical field intensity could be demodulated by monitoring the fringe shift. In the experiment, high voltages from 10.67 kV to 23.3 kV are applied to our sensor through parallel-plate electrodes. More than 150 kV/cm electrical field intensity in the middle place of the parallel-plate electrodes is measured when the voltage is 23.3 kV, and the sensitivity is ~ 0.1 w (v/m). Such kind of safe sensor has good stability, high reproducibility, compact size, lightweight and easy fabrication, making it attractive for applications in measuring different kinds of electric field, especially when the measurement space is limited or closed.

Three Dimensional Bacteria Concentration by Negative Dielectrophoresis

Thispaper reports a novel method to concentrate bacteria in three-dimension by negative dielectrophoretic (n-DEP) force in a microchannel. This was achieved by placing a thin dielectric layer on one of a pair of parallel plate electrodes. The dielectric layer having a home-plate like pentagonal shape, forms a gradient of electric field causing n-DEP. A three-dimensional numerical simulation of bacteria trajectory predicts that bacteria flowing a microchannel were three-dimensionally concentrated beneath the tip of the pentagonal dielectric thin layer. The trajectory and concentration of bacteria under n-DEP force were also experimentally confirmed using Escherichia coli cells. Bacteria moved along edges of the dielectric layer and were pushed to the opposite electrode, resulting in their concentration in three-dimension. The proposed device might be applicable to selective concentration of bacteria depending on their dielectric properties.

Simulation of spatial characteristics of very high frequency hydrogen plasma produced by a balanced power feeding

The effects of a balanced power feeding (BPF) method on a very high frequency hydrogen plasma produced with narrow-gap parallel plate electrodes are studied by 2-dimensional simulation. It was found that the electron density increases inside the electrodes and decreases outside the electrodes. The input power was effectively absorbed into the intermediate region of the electrodes. In addition, the electron density outside the electrodes decreased with increasing the gas pressure, and the electron density inside the electrodes peaked at a certain pressure. The property of the power absorption was improved and the electron temperature decreased for the higher gas pressure in the BPF model.

Fabrication of a Large-Scale Conductive Composite Film Containing Electrically Aligned Carbon Nanotubes

Application of high electric field is effective for the alignment of carbon nanotubes (CNTs) in a nanocomposite film. The conventionally used one pair of parallel plate electrode is not applicable to large-sized nanocomposite fabrication due to limited output voltage of high voltage source. We have proposed a new method using parallel array electrode system to prepare large-scale conductive composite film containing aligned CNTs. In the electrode system, the electric field generated by an array of interdigitated parallel wire electrodes was applied to the CNTs by using an electric field averaging scheme. The array electrode system made a large-scale (15 × 15 cm2) composite film containing uniformly aligned CNTs. In this study, we investigated the relationship between weight fraction of the CNTs and electrical conductivity of the composite film. Measurement of the surface electric potential of the composite film after corona discharge exposure revealed that the film with an electrical conductivity increased by electric field-induced CNTs alignment could serve as an antistatic film.

Low-voltage pulsed plasma discharges inside water using a bubble self-generating parallel plate electrode with a porous ceramic

Characteristics of pulsed bubbles discharges in water were investigated using parallel punched plate electrodes with a porous thin ceramic plate inserted between two metal plates. The micro-bubbles were generated just beneath the porous ceramic plate by flowing gas through it. The transition from spiky dielectric barrier discharges to pulsed glow discharges enables efficient bubble discharges at a relatively low voltage of 1.8 ∼ 4.0 kV of the 5 kHz square-waves with a pulse-width of about 750 ns. With 80% Ar and 20% O2 mixture gas at 4.0 kV, the 50 mg/l Indigo Carmine aqueous solution was efficiently decolorized within about 3 min.

Mass-transfer studies in an electrochemical reactor with a small interelectrode gap

This paper reports the distribution of the local mass-transfer coefficient along the electrode length for an electrochemical reactor with parallel-plate electrodes and narrow interelectrode gaps of 1 and 2.2mm, using the reduction of ferricyanide as a test reaction. The studies were performed at different flow rates, Reynolds numbers ranging from 370 to 3700, with the empty reactor and also the interelectrode gap was filled with two types of expanded plastics and a woven plastic mesh as turbulence promoters. The effect of both the interelectrode gap and the partial placing of the turbulence promoter along the electrode length on the mass-transfer behaviour was also analyzed. In all cases the pressure drop across the reactor was measured. A more uniform distribution of the local mass-transfer coefficient, ±15% related to its mean value, and an important increase of the mean mass-transfer coefficient, enhancement factor ranging from 2 to 8, were observed, depending on the type of turbulence promoter, the volumetric flow rate, and the interelectrode gap.

Space charge dynamics investigation based on Kerr electro-optic measurements and processing of CCD images

The Kerr electro-optic technique is used to investigate electric field and space charge effects using large Kerr constant propylene carbonate as the dielectric liquid with Kerr constant B≈1.22×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> m/V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . However, improved accuracy of this technique to measure space charge distributions remains an important goal. This paper describes inversion algorithm research on obtaining accurate space charge distributions from Kerr measurements. The original charge-coupled device (CCD) image of light intensity was converted into grayscale values for improved calculation. The grayscale CCD image was transformed into the frequency domain through a two-dimensional Fourier transformation. Butterworth filtering techniques were employed for edge enhancement algorithms. The most important parameter for calculation of space charge distributions are the integer fringe numbers n in the sequence of light and dark fringes measured by the CCD camera. Comparison of the improved algorithm and traditional methods for calculating electric field and space charge distributions between a pair of stainless steel parallel plate electrodes was investigated. The space charge dynamics were also calculated after processing the CCD images with some improvements. The results showed the electric field was essentially uniform at early times of pulsed high voltages. This uniformity indicated the absence of space charge during the early transient interval, while a bipolar charge injection was found in the central region between electrodes at later times. For longer times the electric field and space charge distributions slowly became uniform again. Grayscale processing and Butterworth filtering played an important role in the improvement of the algorithm for better image quality and edge enhancement.

Integration of microplasma with transmission electron microscopy: Real-time observation of gold sputtering and island formation

An in situ platform for characterizing plasma-materials interactions at the nanoscale in the transmission electron microscope (TEM) has been demonstrated. Integrating a DC microplasma device, having plane-parallel electrodes with a 25 nm thick Au film on both the cathode and anode and operating in 760 Torr of Ar, within a TEM provides real-time observation of Au sputtering and island formation with a spatial resolution of < 100 nm. Analyses of TEM and atomic force microscopy images show the growth of Au islands to proceed by a Stranski-Krastanov process at a rate that varies linearly with the discharge power and is approximately a factor of 3 larger than the predictions of a DC plasma sputtering model. The experiments reported here extend in situ TEM diagnostics to plasma-solid and plasma-liquid interactions.

Plasma polymerization in a microcapillary using an atmospheric pressure dielectric barrier discharge

Atmospheric pressure plasma deposition is a beneficial technology due to its low cost and flexibility in terms of its operation and integration for in-line processing. This paper presents the use of an atmospheric pressure dielectric barrier discharge (DBD) to deposit an amine functional polymer film onto the inner surface of a glass microcapillary. A micro discharge was generated in a DBD chip made from a rectangular borosilicate glass capillary using externally attached parallel plate electrodes. A new microplasma configuration which consists of a perforated high voltage electrode and a ground electrode with large surface area is implemented to sustain a stable glow discharge at atmospheric pressure and a temperature of 35°C. Polymerization was performed using a laboratory made plasma source working at a frequency of 8kHz with 50% duty ratio of the inverter. The monomer precursors allylamine and ethylenediamine were selected to optimize the polymerization conditions at atmospheric pressure. The hydrophobicity and philicity of the deposited surface were controlled as functions of plasma power. The atmospheric pressure plasma polymerized (APPP) films were characterized using Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), plasma emission spectroscopy, contact angle measurements and growth rate analysis. An average growth rate of 1.18μgs−1 for plasma polymerized ethylenediamine (PPEDA) and 1.91μgs−1 for plasma polymerized allylamine (PPAA) was obtained at a discharge power of 15W and 10sccm of monomer flow rate. The film thickness of 0.9μm for PPEDA and 2.1μm for PPAA was determined using AFM for deposition time of 10min. Polymerization results showed that the properties of APPP films can be controlled through optimization of parameters such as discharge power, treatment time and flow rates of the main gas and monomer vapors.

Estimation of electron temperature in atmospheric pressure dielectric barrier discharge using line intensity ratio method

Dielectric Barrier Discharge was produced by applying high voltage AC source of frequency (10-30 KHz) and potential difference of (0-20) kV across two parallel plate electrodes with glass as dielectric barrier. Optical emission spectroscopy was used for the characterization of the discharge produced at atmospheric pressure. The emission spectra in the range of 200 nm to 850 nm have been analyzed to estimate the electron temperature by line intensity ratio method. The results showed that the electron temperature is about 0.9 eV. Kathmandu University Journal of Science, Engineering and Technology Vol. 8, No. II, December, 2012, 37-42 DOI: http://dx.doi.org/10.3126/kuset.v8i2.7323

Effect of apparent density of sliced food particles on the efficiency of pulsed electric field treatment

Abstract This work discusses the effects of pulsed electric field (PEF) (electric field strength, E , 100–1000 V; pulse duration, t p , 100 μs) on disintegration of potato slices treated between parallel plate electrodes by using a laboratory compression chamber equipped with a PEF-treatment system. The apparent density of slices (bed of particles), ρ , was varied within 0.313 g/cm 3 and 1 g/cm 3 . The electrical conductivity σ ( ρ ) of the packing of slices versus volume fraction of particles ϕ was approximated by the percolation law σ ∝ ( φ − φ c ) t , where ϕ c ≈ 0.290, t = t i ≈ 0.46 and t = t d ≈ 1.39 for the intact and completely damaged tissues, respectively. The impact of electric field strength and apparent density of slices on PEF-induced damage kinetics was studied. The more accelerated kinetics of damage was observed for more dense packing of slices. The approximated relation between the applied, E , and effective, E e , electric field strengths accounting for the σ ( ρ ) dependence was derived. Industrial relevance The practical applications of PEF treatment (e.g., pressing, drying, extraction, etc.) demand operations with slices of food particles. In this study, research towards the electroporation efficiency of PEF applied to the porous packing of sliced food particles is provided.

High-Speed Imaging of EDM Gap Phenomena using Transparent Electrodes

In electrical discharge machining (EDM), discharge occurs with a high frequency in a narrow gap space between parallel plane electrodes filled with a dielectric fluid thus making direct observation of electrical discharge phenomena extremely difficult. On the other hand, SiC single crystals are electrica lly conductive and optically transparent. This paper describes observation of the EDM gap phenomena through the transparent electrode from the direction normal to the discharge surface using a high speed camera. In consecutive pulse discharges, distribution of discharge locations and volume fraction of bubbles in the working gap were clarified.

Capacitance Sensor for Nondestructive Determination of Total Oil Content in Peanut Kernels

In this work, attempts were made to estimate the total oil content (TOC) in single peanut kernels, using the CI meter (Chari’s Impedance meter, described below). Mature peanut kernels of selected varieties with a range of oil contents from 47% to 61% were placed one at a time, between the parallel-plate electrodes of the CI meter, and the impedance (Z) and phase angle (q) of the system were measured, and capacitance, C was computed at 1, 5 and 9 MHz. After the measurements, the TOC of each kernel was determined by Soxhlet method. Using the known TOC values, and the corresponding C, Z and q values, initially on a calibration group of kernels, calibration equations were developed. Using the model coefficients from the calibration, the TOCs of kernel samples of 31 diverse peanut genotypes grown in different environments in Australia were determined. The method predicted the TOC values of peanut kernels of 31 peanut genotypes, within 2% of the Soxhlet values, with an R2 of 0.87 (P 0.001).

Inactivation of Salmonella enterica serovar Typhimurium and Escherichia coli O157:H7 in peanut butter cracker sandwiches by radio-frequency heating

A multistate outbreak of Salmonella enterica serovar Typhimurium recently occurred in the USA, which was traced back to various food products made with contaminated peanut butter. This study was conducted to investigate the efficacy of radio-frequency (RF) heating to inactivate S. Typhimurium and Escherichia coli O157:H7 in peanut butter cracker sandwiches using creamy and chunky commercial peanut butter and to determine the effect on quality by measuring color changes and sensory evaluation. Samples were treated for a maximum time of 90 s in a 27.12 MHz RF heating system. Samples were prepared in the form of peanut butter cracker sandwiches and placed in the middle of two parallel-plate electrodes. After 90 s of RF treatment, the log reductions of S. Typhimurium and E. coli O157:H7 were 4.29 and 4.39 log CFU/g, respectively, in creamy peanut butter. RF treatment of chunky peanut butter for 90 s also significantly (P < 0.05) reduced levels of S. Typhimurium and E. coli O157:H7 by 4.55 log CFU/g and 5.32 log CFU/g. Color values and sensory characteristics of the RF treated peanut butter and crackers were not significantly (P > 0.05) different from the control. These results suggest that RF heating can be applied to control pathogens in peanut butter products without affecting quality.

Characterization and antimicrobial efficacy against E. coli of a helium/air plasma at atmospheric pressure created in a plastic package

A plasma source, sustained by the application of a floating high voltage (±15 kV) to parallel-plate electrodes at 50 Hz, has been achieved in a helium/air mixture at atmospheric pressure (P = 105 Pa) contained in a zip-locked plastic package placed in the electrode gap. Some of the physical and antimicrobial properties of this apparatus were established with a view to ascertain its performance as a prototype for the disinfection of fresh produce. The current–voltage (I–V) and charge–voltage (Q–V) characteristics of the system were measured as a function of gap distance d, in the range (3 × 103 ⩽ Pd ⩽ 1.0 × 104 Pa m). The electrical measurements showed this plasma source to exhibit the characteristic behaviour of a dielectric barrier discharge in the filamentary mode and its properties could be accurately interpreted by the two-capacitance in series model. The power consumed by the discharge and the reduced field strength were found to decrease quadratically from 12.0 W to 4.5 W and linearly from 140 Td to 50 Td, respectively, in the range studied. Emission spectra of the discharge were recorded on a relative intensity scale and the dominant spectral features could be assigned to strong vibrational bands in the 2+ and 1− systems of N2 and , respectively, with other weak signatures from the NO and OH radicals and the N+, He and O atomic species. Absolute spectral intensities were also recorded and interpreted by comparison with the non-equilibrium synthetic spectra generated by the computer code SPECAIR. At an inter-electrode gap of 0.04 m, this comparison yielded typical values for the electron, vibrational and translational (gas) temperatures of (4980 ± 100) K, (2700 ± 200) K and (300 ± 100) K, respectively and an electron density of 1.0 × 1017 m−3. A Boltzmann plot also provided a value of (3200 ± 200 K) for the vibrational temperature. The antimicrobial efficacy was assessed by studying the resistance of both Escherichia coli K12 its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK selected to identify possible cellular responses and targets related with 5 min exposure to the active gas in proximity of, but not directly in, the path of the discharge filaments. Both the parent strain and mutants populations were significantly reduced by more than 1.5 log cycles in these conditions, showing the potential of the system. Post-treatment storage studies showed that some transcription regulators and specific genes related to oxidative stress play an important role in the E. coli repair mechanism and that plasma exposure affects specific cell regulator systems.

The role of the field emission effect in direct-current argon discharges for the gaps ranging from 1 to 100 µm

This paper contains results of experimental and simulation studies of the direct-current breakdown voltage curves in argon discharges with parallel-plane electrodes separated from 1 to 100 µm. The negative slope of the Fowler–Nordheim plot indicates that the current flow is due to field-emitted electrons. Based on the breakdown voltage curves, the effective yield has been estimated. The secondary electron emission in microgaps depends primarily on the electric field E rather than reduced electric field E/N, leading directly to the violation of Paschen's law. The obtained results provide better insight into the role of the enhancement of the secondary electron emission due to high electric field generated in microgaps. Due to the lack of experimental data in microgaps, there are only a few values for the effective yield and no value for argon. By fitting presented experimental data, realistic values of the effective yield in microgaps are obtained and used for the calculations of the breakdown voltages representing basic design data of high-voltage equipment.