Parallel Plate Electrodes Research Articles

High-temperature time domain measurement system for solid and molten materials

A low-cost time domain system for measuring dielectric relaxation in the frequency range of 1 Hz–1 MHz of solid and molten materials at high temperatures is described in detail. A parallel plate electrode sample cell is described that can hold molten material by capillary action. In order to avoid electrical breakdown or a change in electrode distance due to opposite charge buildup, the step voltage can be set to the mV range. At this level interference noise affects the measurements and active filtering is required. The resulting signal is captured using a digital storage oscilloscope. An algorithm for reducing the measured data prior to data processing is discussed. The system is calibration free and its upper temperature is limited only by the construction materials of the furnace and electrodes. Molten NaCl is presented as a test sample.

Controllable Water Droplet for Microsystem Actuators: An Experimental Analysis

Dielectric liquids such as water exhibit significant displacement under a high electric field. Alike smart materials, oscillations of such dielectric liquids can be manipulated using controlled voltage. This study investigates basic actuation property of a water droplet by applying an electrical voltage across two parallel plate electrodes covered by a thin dielectric material. The dynamic characteristics of the water droplet response are evaluated using step input voltage. The sensitivity of the droplet response to a change in the system parameters is also analyzed. The procedure of analysis of variance is adopted to analyze the effectiveness and the combined effect of different parameters on the response. Accordingly, several parameters such as the relative permittivity of the dielectric substrate, thickness of the dielectric substrates, gap between the electrodes, relative permittivity of the dielectric fluid, and applied electric voltage are chosen as control factors. The steady-state response and damping ratio are considered as the output responses. The quadratic regression model associated with the response surface methodology is thereafter used to correlate the output response with the system parameters. It is shown that the gap between the electrodes is the dominant factor affecting the steady-state response whereas the thickness of the dielectric substrate is the dominant factor affecting the damping ratio. In addition, a good consistency is observed between the predicted and experimental responses.

On the Determination of the Initial Ignition Voltage of a Surface Discharge in Air

The experimental and calculated values of the initial ignition voltage of a surface barrier discharge in atmospheric air in a plane–parallel electrode system with a Plexiglas barrier are presented. It is shown that the calculation of the initial voltage based on a simplified procedure, in which the criterion of the discharge initiation is the realization of the Townsend condition, provides the calculated dependence of the initial voltage on the barrier thickness, which coincides with the experimental data.

Design of a Filter-Press Flow Cell with Parallel Plate Electrodes to Guarantee Homogeneous Current Distributions in Turbulent Flow Conditions. the Importance of Mathematical Modeling Coupled to a Printing 3D

The characterization of the reaction environment in continuous electrochemical reactors is necessary to optimize the operational conditions of electrolysis, such as hydrodynamics, current density, residence time, conversion of the electro-active species, among others. In this context the mathematical modeling followed by experimental trials permit to construct models of operation that guarantee the efficiency and yield of the desired reaction. In this work we are interested in the design of a filter-press flow cell to be used in the evaluation of a nickel deposit on a stainless steel cathode. The goal is to minimize the edge effects at the inlet and exit of the cell. To achieve the above, a plastic mesh that avoids the jet flows in the entrance was designed; such design also diminishes the distribution at the beginning of the electrodes. A theoretical analysis of tertiary current distributions was carried out using previous experimental data of nickel deposition in acidic media. Tertiary current distribution analysis was made coupling the RANS equations with the k-epsilon turbulence model and the Launder-Spalding-like equations using wall functions. Different geometric configurations and operational conditions (flow rate, applied current density, etc.) were evaluated founding that the turbulence promotor and flow distributors posses and important role in the performance of the cell. The cell and its components were printed in 3D from the CFD simulations. Close agreement between experimental and theoretical current density distributions were attained. Primary and secondary current distributions were also calculated. The solution of the above mentioned equations was obtained by using a commercial software via finite element method.

Electro-thermo-convective flow of a dielectric liquid due to nonautonomous injection of charge by an elliptical electrode

Electro-thermo-hydrodynamic (ETHD) flow induced by the simultaneous Coulomb and buoyancy forces in a dielectric medium is studied using the lattice Boltzmann method. Nonautonomous charge injection from a high temperature inner elliptical electrode to two cold parallel-plate electrodes is considered. Systematical simulations are conducted for ETHD problems with different injection models and non-dimensional parameters, including electric Rayleigh number T, Rayleigh number Ra and the ellipticity e of the elliptical electrode. It is found that the charge transport process, flow instability and heat transfer enhancement are significant affected by nonautonomous injection, especially in the Coulomb force dominant flow regime and the large ellipticity cases. Quantitatively, for dielectric liquid M = 10, e = 2 and Pr = 10 under strong injection C = 10, when compared to the autonomous charge injection assumption, nonautonomous injection shown an average of 16.4% increases in the mean Nusselt number within the range of driving parameters explored (103 ≤ Ra ≤ 107, 300 ≤ T ≤ 1800).

Multilayer piezoelectric MEMS energy harvester based on longitudinal effect

Piezoelectric MEMS energy harvesters based on multilayer (ML) Pb(Zr,Ti)O3 (PZT) thin films with interdigitated electrodes (IDE) as their internal and top electrodes are proposed and designed. Thick PZT thin films with good piezoelectric characteristics can be deposited by using multilayer deposition technique. Furthermore, IDE is adopted to the harvester design in order to take advantage of the longitudinal piezoelectric effect, which typically has twice piezoelectric constant as large as transverse effect. The energy harvesters with two electrode configurations, parallel plate electrodes (PPE) and IDE, are designed and estimate these output power. According to the result of finite element analysis, the output power per gravitational acceleration is about 124 μW for the PPE configuration. On the other hand, the output power per gravitational acceleration for the IDE configuration is about three times as large as that for PPE. Moreover, the influence of IDE patterns and the number of PZT layers were investigated. The larger number of layers results in the larger output power.

Electrohydrodynamics of confined two-dimensional liquid droplets in uniform electric field

In this study, the electrohydrodynamics of viscous droplets in a confined domain under the action of a uniform electric field is investigated numerically. Considering both the phases to be perfect dielectric or leaky dielectric, two-dimensional numerical simulations are performed to obtain the shape deformation of droplets placed between two parallel plate electrodes. The aim of this study is to show the effect of domain confinement on the droplet morphology and temporal droplet deformation. Perfect dielectric systems always deform into a prolate shape, and the magnitude of deformation is augmented or reduced in a confined domain depending on the electrical permittivity ratio. For leaky dielectric systems, the electrical conductivity ratio comes into play and the droplet can attain an oblate or prolate shape depending on the size of the droplet relative to the channel height. A regime diagram is constructed to show the impact of domain confinement on the droplet shape. Additionally, the steady-state deformation parameter undergoes some non-monotonic variation with domain confinement for the leaky dielectric systems. The domain confinement can significantly decrease the droplet deformation and thereby suppress the droplet breakup phenomenon for few leaky dielectric systems. The domain confinement markedly affects the temporal evolution of the droplet deformation. The temporal evolution of the droplet shape shows that the droplet deforms more sluggishly toward its final steady configuration in a confined domain when the inertial effects are negligible. The oscillations in droplet deformation at the finite inertial regime are also suppressed in a confined domain. Finally, the interaction of two droplets is also studied, which shows that coalescence and detachment of the droplet pairs take place at a slower rate in a confined domain with respect to an unbounded domain. Thus, the present study shows the possibility of modulating the droplet morphology by tuning the domain confinement, which can be of potential use in designing droplet-based microfluidic devices.

Study on Inactivation of <italic>Escherichia Coli</italic> by Double Dielectric Barrier Discharge

A dielectric barrier discharge reactor with plane-parallel electrode was utilized to disinfect the bacterium Escherichia coli ( $E. coli$ ) to figure out the efficiency and mechanism of inactivation. During the treatment, a satisfactory potential for inactivation was observed. The inactivation rate reached 100% without any gases ventilated after 15 min of treatment and 100% with 0.6 L/min air after 9 min of treatment. The plasma was generated by a high-voltage alternating current regulator. The output power was around 33.8 W per cycle and the power utilization efficiency was 57.6%. The atmospheric sources of sole nitrogen or sole oxygen were not favorable for the bacterial inactivation, while air plasma presented better inactivation results. It indicates that the presence of active species containing nitrogen and oxygen, generated from the air plasma, or other active species derived from NO $x$ , such as ONOOH, which is produced by NO2 and OH, plays a more important role on bacterial inactivation. The ventilation result is different from others’ studies. Moreover, scanning electron microscopy was used to observe the $E.~coli$ cell topography alternation. After discharge, $E.~coli$ seemed to be more shrunken and blurred. Cells finally collapsed and part of them got stuck to each other.

Demulsifier assisted film thinning and coalescence in crude oil emulsions under DC electric fields

Electrocoalescence has been considered a most efficient method of crude oil dewatering; however, just electric fields are not enough when dealing with heavy crude oils. In this work we studied effect of asphaltene flocculation and effectiveness of variety of chemical demulsifiers in electrocoalescence of water-in-crude oil emulsions. A parallel plate electrode cell was used to apply linearly rising uniform DC electric field to a thin layer of emulsion and the current running through the emulsion was monitored as an indicator of progress in the coalescence. In the first part of the study, model crude oils were used to investigate the roles of flocculated asphaltenes and flocculation inhibitor in electrocoalescence process. It was observed that the asphaltene flocculation adversely affects the rate of electrocoalescence. Second part compares effectiveness of different chemical demulsifiers in breaking water-in-crude oil emulsions under electric field. The experimental observations suggest that there exist a threshold demulsifier concentration limit and further increasing the concentration does not improve electrocoalescence rate. Also the addition of a demulsifier before dispersion of water results into faster separation as compared to the electrocoalescence in emulsion where the demulsifier was added later. Further, we devised a model for qualitative prediction of film drainage between two demulsifier-laden water–crude oil interfaces under a constant DC electric field. The film thinning rates predicted by the model are consistent with the experimentally measured critical electric field values.

Secondary electron emission influenced by oxidation on the aluminum surface: the roles of the chemisorbed oxygen and the oxide layer

A relationship between the apparent secondary electron yield () and the oxygen coverage/oxide layer thickness on an aluminum cathode is obtained in an experiment under a controlled environment. The apparent secondary electron yield () is deduced from the breakdown voltage between two parallel plate electrodes in a 360 mTorr argon environment using a simple Townsend breakdown model with the assumption that the variation of the apparent secondary electron yield is dominated by the variation of the argon ion induced processes. The oxygen coverage/oxide layer thickness on the aluminum cathode is measured by a semi in situ x-ray photoemission spectroscopy equipment which is directly attached to the discharge chamber. It is found that three phases exist: (1) in the monomonolayer regime, as the oxygen coverage increases from 0 to 0.3, decreases by nearly , (2) as the oxygen coverage increases from 0.3 to 1, keeps nearly constant, (3) as the oxide layer thickness increases from about 0.3 nm to about 1.1 nm, increases by . We propose that, in the submonolayer regime, the chemisorbed oxygen on the aluminum surface causes the decrease of by creating a local potential barrier, which reduces the Auger neutralization rate and the energy gained by the Auger electrons. In the multilayer regime, as the oxide layer grows in thickness, there are three proposed mechanisms which cause the increase of : (1) the work function decreases; (2) resonance neutralization and Auger de-excitation may exist. This is served as another channel for secondary electron production; (3) the kinetic energy of Auger electrons is increased on average, leading to a higher probability for electrons to overcome the surface potential barrier.

Direct Printing of Stretchable Elastomers for Highly Sensitive Capillary Pressure Sensors.

We demonstrate the successful fabrication of highly sensitive capillary pressure sensors using an innovative 3D printing method. Unlike conventional capacitive pressure sensors where the capacitance changes were due to the pressure-induced interspace variations between the parallel plate electrodes, in our capillary sensors the capacitance was determined by the extrusion and extraction of liquid medium and consequent changes of dielectric constants. Significant pressure sensitivity advances up to 547.9 KPa−1 were achieved. Moreover, we suggest that our innovative capillary pressure sensors can adopt a wide range of liquid mediums, such as ethanol, deionized water, and their mixtures. The devices also showed stable performances upon repeated pressing cycles. The direct and versatile printing method combined with the significant performance advances are expected to find important applications in future stretchable and wearable electronics.

Effective ionization coefficient of C5 perfluorinated ketone and its mixtures with air

C5 perfluorinated ketone (C5 PFK with UIPAC chemical name 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)-2-butanone and sold by 3M as Novec™ 5110) has a high dielectric strength and a low global warming potential, which makes it interesting as an insulating gas in medium and high-voltage applications. The study was carried out to determine the effective Townsend ionization coefficient αeff as a function of electric field strength and gas density for C5 PFK and for its mixtures with air. The non-self-sustained Townsend discharge between parallel plate electrodes was initiated by illuminating the cathode by UV radiation. The discharge current, I, was measured as a function of inter-electrode distance, d, at different gas densities, N, and electric field strengths, E. The effective ionization coefficient αeff was determined from the semi-logarithmic plots of I/I0 against d. For each tested gas mixture, the density normalized effective ionization coefficient αeff/N was found to be a unique function of reduced electric field strength E/N. The measurements were carried out in the absolute pressure range of 0.05–1.3 bar and E/N range of 150–1200 Td. The increasing fraction of C5 PFK in air resulted in the decrease of effective ionization coefficient. The limiting electric field strength (E/N)lim where the effective ionization coefficient αeff became zero was 770 Td (190 kV cm−1 at 1 bar) for pure C5 PFK and decreased to 225 Td (78 kV cm−1 at 1.4 bar) for 7.6% C5 PFK/air mixture. The latter value of (E/N)lim is still more than two times higher than the (E/N)lim value of synthetic air and about two-thirds of the value corresponding to pure SF6. The investigated gas mixtures have the potential to become an alternative to SF6 in numerous high- and medium-voltage applications.

Homogeneous dielectric barrier discharges in atmospheric air and its influencing factor

The stable homogeneous dielectric barrier discharge (DBD) is obtained in atmospheric 2–3 mm air gap. It is generated using center frequency 1 kHz high voltage power supply between two plane parallel electrodes with specific alumina ceramic plates as the dielectric barriers. The discharge characteristics are studied by a measurement of its electrical discharge parameters and observation of its light emission phenomena. The results show that a large single current pulse of about 200 μs duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two electrodes. The homogeneous discharge generated is a Townsend discharge during discharge. The influences of applied barrier, its thickness, and surface roughness on the transition of discharge modes are studied. The results show that it is difficult to produce a homogeneous discharge using smooth plates or alumina plate surface roughness Ra < 100 nm even at a 1 mm air gap. If the alumina plate is too thin, the discharge also transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. With the increase of air gap distance and applied voltage, the discharge can also transit from a homogeneous mode to a filamentary mode. In order to generate stable and homogeneous DBD at a larger air gap, proper dielectric material, dielectric thickness, and dielectric surface roughness should be used, and proper applied voltage amplitude and frequency should also be used.

Effect of parallel magnetic field on repetitively unipolar nanosecond pulsed dielectric barrier discharge under different pulse repetition frequencies

A magnetic field, with the direction parallel to the electric field, is applied to the repetitively unipolar positive nanosecond pulsed dielectric barrier discharge. The effect of the parallel magnetic field on the plasma generated between two parallel-plate electrodes in quiescent air is experimentally studied under different pulse repetition frequencies (PRFs). It is indicated that only the current pulse in the rising front of the voltage pulse occurs, and the value of the current is increased by the parallel magnetic field under different PRFs. The discharge uniformity is improved with the decrease in PRF, and this phenomenon is also observed in the discharge with the parallel magnetic field. By using the line-ratio technique of optical emission spectra, it is found that the average electron density and electron temperature under the considered PRFs are both increased when the parallel magnetic field is applied. The incremental degree of average electron density is basically the same under the considered PRFs, while the incremental degree of electron temperature under the higher-PRFs is larger than that under the lower-PRFs. All the above phenomena are explained by the effect of parallel magnetic field on diffusion and dissipation of electrons.

A General Analytical Formulation for the Motional Parameters of Piezoelectric MEMS Resonators.

This paper reports on a general analytical expression for the motional resistance ( ) of an arbitrary mode in a piezoelectric microelectromechanical system resonator with parallel plate electrode geometry. After applying simplifying assumptions and using analytical modes shapes, expressions for the of modes with out-of-plane flexure as the primary displacement are presented. These modes include free-free transverse beam flexure (TBF), unclamped disk flexure resonators (DFRs), and antisymmetric Lamb modes. For verification, is extracted from resonators fabricated in a lead zirconate titanate on silicon process. Predicted of TBF and DFR modes is validated using on-wafer extracted constants, analytical modal properties, and independently measured material properties.

A semi-analytical analysis of electro-thermo-hydrodynamic stability in dielectric nanofluids using Buongiorno’s mathematical model together with more realistic boundary conditions

Abstract The main aim of the present analysis is to examine the electroconvection phenomenon that takes place in a dielectric nanofluid under the influence of a perpendicularly applied alternating electric field. In this investigation, we assume that the nanofluid has a Newtonian rheological behavior and verifies the Buongiorno’s mathematical model, in which the effects of thermophoretic and Brownian diffusions are incorporated explicitly in the governing equations. Moreover, the nanofluid layer is taken to be confined horizontally between two parallel plate electrodes, heated from below and cooled from above. In a fast pulse electric field, the onset of electroconvection is due principally to the buoyancy forces and the dielectrophoretic forces. Within the framework of the Oberbeck-Boussinesq approximation and the linear stability theory, the governing stability equations are solved semi-analytically by means of the power series method for isothermal, no-slip and non-penetrability conditions. In addition, the computational implementation with the impermeability condition implies that there exists no nanoparticles mass flux on the electrodes. On the other hand, the obtained analytical solutions are validated by comparing them to those available in the literature for the limiting case of dielectric fluids. In order to check the accuracy of our semi-analytical results obtained for the case of dielectric nanofluids, we perform further numerical and semi-analytical computations by means of the Runge-Kutta-Fehlberg method, the Chebyshev-Gauss-Lobatto spectral method, the Galerkin weighted residuals technique, the polynomial collocation method and the Wakif-Galerkin weighted residuals technique. In this analysis, the electro-thermo-hydrodynamic stability of the studied nanofluid is controlled through the critical AC electric Rayleigh number R ec , whose value depends on several physical parameters. Furthermore, the effects of various pertinent parameters on the electro-thermo-hydrodynamic stability of the nanofluidic system are discussed in more detail through graphical and tabular illustrations.

Experimental investigation on the repetitively nanosecond pulsed dielectric barrier discharge with the parallel magnetic field

The effects of a parallel magnetic field on the unipolar positive nanosecond pulsed dielectric barrier discharge are experimentally investigated through electrical and spectral measurements. The discharge is produced between two parallel-plate electrodes in the ambient air with a parallel magnetic field of 1.4 T. Experimental results show that both the discharge intensity and uniformity are improved in the discharge with the parallel magnetic field. The intensity ratio of the spectrum at 371.1 nm and 380.5 nm, which describes the average electron density, is increased by the parallel magnetic field. Meanwhile, the intensity ratio of the spectrum at 391.4 nm and 337.1 nm, which describes the electron temperature, is also increased. It is speculated that both the average electron density and the electron temperature are increased by the parallel magnetic field. The aforementioned phenomena have been explained by the confinement effect of the parallel magnetic field on the electrons.

Capture and Reductive Transformation of Halogenated Pesticides by an Activated Carbon-Based Electrolysis System for Treatment of Runoff.

This study evaluates an electrochemical system to treat the halogenated pesticides, fipronil, permethrin, and bifenthrin, in urban runoff. Compared to the poor sorption capacity of metal-based electrodes, granular activated carbon (GAC)-based electrodes could sorb halogenated pesticides, permitting electrochemical degradation to occur over longer timescales than reactor hydraulic residence times. In a dual-cell configuration, a cathode constructed of loose GAC containing sorbed pesticides was separated from the anode by an ion-exchange membrane to prevent chloride transport and oxidation to chlorine at the anode. When -1 V was applied to the cathode, fipronil concentrations declined by 92% over 15 h, releasing molar equivalents of chloride (2) and fluoride (6), suggesting complete dehalogenation of fipronil. An electrode constructed of crushed GAC particles attached to a carbon cloth current distributor achieved >90% degradation of fipronil, permethrin, and bifenthrin within 2 h under the same conditions. To evaluate a simpler single-cell configuration suitable for scale-up, two of the carbon cloth-based electrodes were placed in parallel without an ion-exchange membrane. For -1 V applied to the cathode, fipronil degradation was >95% over 2 h, and energy consumption declined with closer electrode spacing. However, chloride oxidation at the anode produced chlorine, and the anode degraded. Application of an alternating potential (-1 to +1 V at 0.0125 Hz) to the parallel-plate electrodes achieved >90% degradation of fipronil, bifenthrin, and permethrin over 4 h, releasing chloride at 50-70% of that expected for complete dechlorination. No loss of performance or formation of chlorine or halogenated byproducts was observed over 5 cycles of treating fipronil-spiked surface water.

Numerical study on discharge characteristics influenced by secondary electron emission in capacitive RF argon glow discharges by fluid modeling**Project supported by the National Natural Science Foundation of China (Grant No. 51172101).

A one-dimensional (1D) fluid model of capacitive RF argon glow discharges between two parallel-plate electrodes at low pressure is employed. The influence of the secondary electron emission on the plasma characteristics in the discharges is investigated numerically by the model. The results show that as the secondary electron emission coefficient increases, the cycle-averaged electric field has almost no change; the cycle-averaged electron temperature in the bulk plasma almost does not change, but it increases in the two sheath regions; the cycle-averaged ionization rate, electron density, electron current density, ion current density, and total current density all increase. Also, the cycle-averaged secondary electron fluxes on the surfaces of the electrodes increase as the secondary electron emission coefficient increases. The evolutions of the electron flux, the secondary electron flux and the ion flux on the powered electrode increase as the secondary electron emission coefficient increases. The cycle-averaged electron pressure heating, electron Ohmic heating, electron heating, and ion heating in the two sheath regions increase as the secondary electron emission coefficient increases. The cycle-averaged electron energy loss increases with increasing secondary electron emission coefficient.

Experimental and computational study of optically-driven electrothermal vortex

Optically-driven electrothermal vortex flow is one of the most effective ways to induce convection in microscale domains. In this work, side view microscopic imaging is used for qualitative flow visualisation as well as quantitative µPIV measurements of the vortex pattern in microfluidic chips between simple parallel-plate electrodes. The uniform electric field is generated from parallel-plate, indium tin oxide (ITO) electrodes separated by 400 µm. Alternating current (AC) electric fields at a range of frequencies (9-100 kHz) and voltages (5-40 V) are applied to the electrodes to drive the flow. Simultaneously, a near-infrared (1064 nm) laser beam at various intensities is focused on the bottom electrode surface of the microchannel. Strong electrothermal vortices are observed in the flow visualisation experiments and measured by µPIV. A realistic computational model featuring a laser heat source and an applied electrical field is constructed. Computational simulations are performed under the same conditions as the experiments. The simulations and the experiments show the same qualitative behaviours and also agree quantitatively when comparing the maximum velocities.