Parallel-plate Configuration Research Articles

Ion-diffusion losses and j/p2-scaling of hollow-cathode effect in DC discharges with parallel-plate cathode configuration

Ion-diffusion losses and j/p2-scaling of hollow-cathode effect in DC discharges with parallel-plate cathode configuration

Tailor-Made Design of Three-Dimensional Batteries Using a Simple, Accurate Geometry Optimization Scheme.

In the rapidly evolving Internet of Things (IoT) society, the demand for microbatteries with high areal energy density is surging. As a promising strategy to enhance areal energy density, three-dimensional (3D) batteries have attracted attention. The feature of 3D batteries is the decoupling of the electrode thickness from the ion-transport distance through the modification of the spatial arrangement of the positive and negative electrodes beyond the conventional parallel plates configuration. This allows for the accommodation of a larger amount of active materials without increasing internal resistance. However, identifying the optimal 3D geometry is a complex task, as it depends on printable materials, the resolution of the fabrication equipment, as well as battery usage, which constitutes a multiobjective optimization problem. To overcome this challenge, we propose a novel approach to determine the optimal 3D microbattery geometry. Our innovative method involves a 3D battery optimization system, which integrates an automatic geometry generator with a quick and accurate performance simulator. This approach allows, for the first time, the discovery of material- and discharge-current-dependent optimal geometries. We successfully apply this optimization scheme to two standard electrode pairs (LiFePO4/Li4Ti5O12 and LiNi0.5Mn0.3Co0.2O2/graphite), demonstrating a significant increase in energy density (30%-40% greater than the current state-of-the-art geometry), particularly under high current conditions. These findings underscore the importance of tailor-made batteries for diverse IoT applications and showcase the potential of our approach in realizing such designs.

A Generalized Townsend's Theory for Paschen Curves in Planar, Cylindrical, and Spherical Geometries in Planetary Atmospheres

AbstractIn this work, we focus on plasma discharges produced between two electrodes with a high potential difference, resulting in the ionization of the neutral particles supporting a current in a gaseous medium. At low currents and low temperatures, this process can create luminescent emissions: glow and corona discharges. The parallel plate geometry used in Townsend's theory lets us develop a theoretical formalism, with explicit solutions for the critical voltage effectively reproducing experimental Paschen curves. However, most discharge processes occur in non‐parallel plate geometries, such as discharges between particles in multiphase systems and between cylindrical conductors. Here, we propose a generalization of the classic parallel plate configurations to concentric spherical and coaxial cylindrical geometries in Earth, Mars, Titan, and Venus atmospheres. In a spherical case, a small radius effectively represents a sharp tip rod, while larger, centimeter‐scale radii represent blunted tips. In cylindrical geometries, small radii resemble thin wires. We solve continuity equations in the gap and estimate a critical radius and minimum breakdown voltage that allows the formation of a glow discharge. We show that glow coronæ form more easily in Mars's low‐pressure, CO2‐rich atmosphere than in Earth's high‐pressure, N2‐rich atmosphere. Additionally, we present breakdown criteria for Titan and Venus, two planets where discharge processes have been postulated. We further demonstrate that critical voltage minima occur at 0.5 cm⋅Torr for all three investigated geometries, suggesting easier initiation around millimeter‐size particles in dust and water clouds. This approach could be readily extended to examine other multiphase flows with inertial particles.

Photofabricated channel-digital microfluidics (pCDMF): A promising lab-on-a-chip platform for fully integrated digital PCR

Microfluidics-based digital PCR (dPCR) is a potent technique capable of absolute quantification of nucleic acids with ultrahigh sensitivity. However, an indispensable process, nucleic acid extraction (NAE) remains hard to be integrated with dPCR into a monolithic device, because both of them involve complicated processes and exquisite fluid manipulation. An ideal solution to this issue is to integrate the two main microfluidic platforms, channel-based microfluidics (CMF) and digital microfluidics (DMF), which, however, remains very challenging. To address these challenges, we herein develop a photofabricated channel-digital microfluidic chip (pCDMF) with significant advantages including: the fabrication of pCDMF is very convenient due to the flexible material choices of photocuring, without tedious process of hydrophobic coating; a parallel-plate configuration can be easily formed, enabling all basic functions of DMF; various channels and microstructures can be freely designed, allowing for fluidic functions of CMF. It is therefore the first example of full integration of DMF and CMF as a monolithic device, with capabilities to precisely handle both discrete droplets and continuous fluids. Finally, an all-in-one device for sample-to-answer digital PCR has been successfully demonstrated. We also envisioned that the pCDMF may open an alternative route toward the fully integrated lab-on-a-chip for various biological applications.

Irreversibility analysis of Magnetohydrodynamic (MHD) mixed convection flow of viscoelastic hybrid nanofluid flow in a channel

This manuscript delves into the analysis of irreversibility in Magnetohydrodynamic (MHD) mixed convection flow of a viscoelastic hybrid nanofluid within a vertical channel. The study adopts a parallel plate configuration and employs Aluminum oxide (Al2O3) and Titanium oxide (TiO2) nanoparticles dispersed in a Carboxymethyl cellulose (CMC)-water base fluid. Utilizing similarity transformations, the governing partial differential equations (PDEs) are converted into a set of ordinary differential equations (ODEs), streamlining the mathematical model. These ODEs are then solved using the homotopy analysis method via Mathematica software for various governing parameter values. Key parameters including the Brinkman number, volume fractions of nanoparticles, magnetic effects, and wall temperature parameter are systematically investigated. Noteworthy insights include that volume fraction and magnetic parameter augments velocity at the left wall and slows down it toward the right wall; Brinkman number and wall temperature parameters significant in elevating temperature; Entropy and Bejan number respond differently to variations in the Brinkman number. Entropy escalates with increasing magnetic parameter, while the Bejan number declines. Illustrated through graphs, these findings enrich the comprehension of MHD mixed convection flow and heat transfer in viscoelastic hybrid nanofluids, elucidating irreversibility aspects tied to such systems.

Electrokinetic Thin-Film Model for Electrowetting: The Role of Bulk Charges.

The electrowetting behavior of a charge-carrying sessile droplet is relevant to applications such as point-of-care diagnostics. Often biomedical assays involve droplets that contain charged molecules such as dissolved ions, proteins, and DNA. In this work, we develop a reduced-order electrokinetic model for electrowetting of such a charge-carrying droplet under a parallel-plate electrode configuration. An inertial-lubrication model based on the weighted residual integral boundary layer (WRIBL) technique is used to obtain evolution equations that describe the spatiotemporal evolution of the fluid-air interface and the depth-integrated flow rate. The solutions to the evolution equations are obtained numerically by using the spectral collocation method. We investigate the role of domain and surface charges, characterized by the Debye length, on droplet wetting. Under low relaxation timescales, both droplet deformation and wetting alteration under an AC field are shown to be equivalent to that under a root-mean-square (RMS) DC field. We show that an electrolytic sessile droplet can exhibit a larger deformation in comparison to the two asymptotic limits of a perfect conductor and a perfect dielectric droplet, corresponding, respectively, to very low and high Debye lengths. The effects of several other parameters such as the inherent equilibrium wettability, permittivity ratio, and electric field strength are also investigated.

Numerical study of the self-pulsing of DC discharge: from corona to parallel-plate configurations

We present here an investigation of the self-pulsing phenomenon of negative corona and parallel-plate discharge in argon within one frame of a one-dimensional fluid model in cylinder–cylinder electrode geometry. The transition from corona to parallel-plate discharge is obtained by changing the inner and outer radii of the electrodes. The model reproduces the self-pulsing waveform well and provides the spatiotemporal behaviors of the charged particles and electric field during the pulse. The self-pulsing shows a common feature that occurs in various configurations and that does not depend on a specific electrode structure. The self-pulsing is the transformation between a weak-current Townsend mode and a large-current normal glow mode. The behavior of the positive ions is the dominant factor in the formation of the pulse.

Design of Electrical Characterization Method for Electroporation-Treated Biological Tissues

The design of a method to evaluate the efficacy of electroporation-treated (with several pulses) tissues is proposed. This method is based on the application of both the standard and a non-standard electrical characterization of biological tissues, on a platform, containing the samples under test, adopted to have minimal invasive contact measurements. Standard direct current electrical characterization was performed for comparison. For the electroporated tissues (using eight pulses), the electrical behavior of the tissue in working condition, governed by high intensity and short duration square wave stimuli, typically used in electrochemotherapy treatments, is utilized. Both electroporation stimuli application and direct current testing were performed using the same electrodes in parallel plate configuration on the parallelepiped shaped samples. The electrodes were not removed during the designed procedure to reduce the interaction with the tissue under test and the effect of different contact resistances. A finite element analysis-based numerical evaluation of the test cell used in the procedure was also performed, both with a constant and an electric field-dependent electrical conductivity, showing its robustness. The method is tested on potato samples, as an example of a biomaterial, whose electrical conductivity is electric field-dependent. The samples were subjected to a high intensity square wave pulse voltage of 100μs long, in order to evaluate the effect of multiple pulses, as a single protocol parameter. Results indicate the dependency of the electrical conductivity on the electric field strength applied using multiple pulses, and the method is easily scalable and usable as a starting point for evaluating the effect of other protocol parameters.

Two-dimensional PIC simulation of the ion-extraction process in an electrostatic field using different electrode configurations

The ion-extraction process from a finite-size photoplasma is simulated by using a two-dimensional electrostatic particle-in-cell code. To investigate the impact of different electrode configurations on the ion extraction process the parallel plate, wire-type, II-type, and M-type electrode configurations are used. The present study compares the ion extraction time of these electrodes and provides a quantitative audit of the photoions. Through this, it is observed that the M-type electrode configuration extracts more ions in less time than the other electrode configurations. Subsequently, this study quantifies the ion collection on different electrodes, which can be further utilized to design the electrode configuration. Moreover, it gives a systematic study of the ion extraction process in an electrostatic field with different electrode configurations.

An Investigation into the Effects of Electric Field Uniformity on Electrospun TPU Fiber Nano-Scale Morphology.

ANSYS Maxwell was used to replicate the conditions of two potential electrospinning configurations: a needle-plate and a parallel-plate configuration. Simulations showed that the electric field generated within the parallel-plate configuration was much more uniform than that within the needle-plate configuration. Both configurations were assembled and used electrospin fibers at three different spinning distances (10 cm, 12 cm, and 15 cm), at a consistent electric field strength of 1.7 kV/cm. Scanning electron microscopy was used to compare the morphologies of the fibers produced in both configurations in order to confirm whether a more uniform electric field yielded thinner fibers. The results show that the needle-plate configuration produced finer fibers than the parallel-plate configuration at all three spinning distances. However, there was no difference in the fiber diameters produced at the 12 and 15 cm spinning distances within the needle-plate configuration, implying thinning may only occur up to a certain distance in this configuration.

In-Operando Optical Spectroscopy of Field-Effect-Gated Al-Doped ZnO

Transparent conductive oxides (TCO) have the unique characteristics of combining optical transparency with high electrical conductivity; such a property makes them uniquely alluring for applications in visible and infrared photonics. One of their most interesting features is the large sensitivity of their optical response to the doping level. We performed the active electrical manipulation of the dielectric properties of aluminum-doped ZnO (AZO), a TCO-based on Earth-abundant elements. We actively tuned the optical and electric performances of AZO films by means of an applied voltage in a parallel-plate capacitor configuration, with SrTiO3 as the dielectric, and monitored the effect of charge injection/depletion by means of in-operando spectroscopic ellipsometry. Calculations of the optical response of the gated system allowed us to extract the spatially resolved variations in the dielectric function of the TCO and infer the injected/depleted charge profile at the interface.

Modeling and Simulation of PGGP Electrode Configuration for Ion-Extraction Process Using 2.5D-PIC Code

The ion extraction from laser-induced photoplasma in an electrostatic field is investigated by a 2.5-D-electrostatic particle-in-cell (PIC) code. The external electrostatic field is applied by a plate–grid–grid–plate (PGGP) electrode configuration. In this configuration, two additional grids are introduced in a parallel plate electrode configuration. Basically, these grids are kept at more negative potential than the cathode, and therefore, the grid extracts the ion, whereas plates collect the ions. Through such biasing, the sputtering of the already collected ions on the collecting plate can be avoided. The present investigation emphasizes on spatiotemporal evolution of photoplasma in the PGGP electrode configuration. Subsequently, investigate the performance of this electrode configuration with different biasing of electric potential. Finally, it compares the performance of PGGP with parallel plate and M-type electrode configurations. Based on this comparative analysis, an improved design of the PGGP electrode configuration is suggested. In addition, it also explains modeling aspects of different electrode geometries using 2.5-D-PIC, which includes the boundary conditions for Poisson’s equation, particle boundary conditions, and grid designing.

Expansion of a finite-size photoplasma in an electrostatic field with M-type electrode configuration using a novel adaptive mesh 2D-PIC code

A two-dimensional electrostatic particle-in-cell code is developed with an adaptive mesh feature to investigate the dynamics of photoplasma in M-type electrode configurations. This adaptive mesh is designed by using a one-dimensional pseudo mesh, where at the starting of each pseudo cell the quasineutrality and density of charged particles are checked, which decides the coarseness of the actual computational mesh. Through this developed particle-in-cell code, the ion extraction process from a finite-size photoplasma is simulated for parallel plate and M-type electrode configurations. Subsequently, the ion extraction time from the photoplasma is investigated by using the different potential waveforms, i.e. constant and two-step potential. On the basis of this numerical hypothesis, it is observed that the efficacy of M-type configuration is better than the parallel plate electrode configuration. Moreover, ion collection efficiency is also improved using a two-step potential waveform.

Current Collector-Free Interdigitated Nb2O5//LiFePO4 Micro-Batteries Prepared by a Simple Laser-Writing Process

The recent development of the internet of things (IoT) raises new needs in energy storage micro-devices to power implantable and wearable applications. Conventional battery components, including electrode materials and current collectors, have to be miniaturized and integrated onto flexible substrates while keeping their electrochemical performance. Although numerous micro-fabrication processes were successfully adapted to prepare lithium-ion micro-batteries (Li-ion μBs), they often rely on wet processing routes such as electrochemical deposition, which does not allow the preparation of energy micro-sources at a large scale. Laser-writing processes are among the most practical and versatile methods to deposit active materials as thin films on flexible substrates. Here, we report about the integration of positive LiFePO4 (LFP)-based and negative pseudocapacitive niobium pentoxide (Nb2O5)-based electrodes onto flexible current collector-free polyimide foils, through laser-writing of a mixture of HAuCl4, cellulose acetate, and active material coated on polyimide. The influence of the laser energy during the laser-writing step on the electrochemical performance of the as-prepared electrodes was studied. Laser-scribed (LS) Nb2O5 flexible electrodes exhibit a typical pseudocapacitive behavior, and deliver up to 114 μAh.cm−2 (205 mF.cm−2), while 76 μAh.cm−2 were recorded for LS-LiFePO4 battery electrodes prepared with the optimized laser parameters. Nb2O5//LiFePO4 micro-devices were assembled in a parallel-plate configuration, providing a 32 μAh.cm−2 areal capacity, despite the absence of any underlying current collectors. Finally, interdigitated planar micro-batteries were realized by this simple laser-writing procedure, thus paving the path towards the facile fabrication of micro-batteries at a large scale.

Investigation and correlation between surface modifications and field emission properties of laser-induced silicon plasma ion irradiated stainless steel

Laser-induced silicon (Si) plasma has been used as a source of ion irradiation for modifications in surface, structural and field emission properties of Stainless Steel (SS). Nd:YAG (532 nm, 10 ns) laser at irradiance of 15 GW/cm2 was used to generate Si-plasma ions which were detected by solid-state nuclear track detector (CR-39) and Faraday Cup (FC). Both the energy and fluence of Si ions were measured by FCs. In response to a stepwise increase in the number of laser pulses from 3000 to 12000, the ion fluence varies from 4.6 × 1014 to 18.3 × 1014 ions/cm2 with constant energy of 30 keV. Fourier Transformation Infrared (FTIR) spectroscopy analysis revealed that irradiated silicon makes the stretch band with oxygen Si–O–Si. X-Ray Diffraction (XRD) analysis confirmed the identification of new phase of Si (111) with an anomalous trend in crystallite size, dislocation line density and induced stresses in response to the irradiation with various Si ion fluences. Optical microscopy analysis showed the formation of pits, voids and tracks. Scanning electron microscope (SEM) analysis revealed the formation of nanoscale surface features including pores, craters, embedded particulates and protruded disk-like structures with multiple ablative layers at the fluence of 4.6 × 1014 to 13.7 × 1014 ions/cm2. At the highest ion fluence of 18.3 × 1014 ions/cm2, the flake/flower-like morphology is observed. Field emission (FE) properties were studied under ultra-high vacuum condition in a parallel plate configuration using planar virgin SS as an anode and structured SS as a cathode. The Fowler–Nordheim plots were obtained from I–V characteristics to evaluate the turn-on field, field enhancement factor β and a maximum current density ranging 1.5–4.5 V/µm, 5008–12807 and 96–454 nA/cm2, respectively. The variation in the FE properties is attributed to the different morphological features at varying silicon ion fluences.

Numerical analysis of electro-convection in dielectric liquids with residual conductivity

Injection-induced electro-convection (EC) of dielectric liquids is a fundamental problem in electrohydrodynamics. However, most previous studies with this type of EC assume that the liquid is perfectly insulating. By perfectly insulating, we mean an ideal liquid with zero conductivity, and in this situation, the free charges in the bulk liquid originate entirely from the injection of ions. In this study, we perform a numerical analysis with the EC of dielectric liquids with a certain residual conductivity based on a dissociation–injection model. The spatiotemporal distributions of the flow field, electric field, and positive/negative charge density in the parallel plate configuration are solved utilizing the finite volume method. It is found that the residual conductivity inhibits the onset of EC flow, as well as the strength of the flow field. The flow features and bifurcations are studied in various scenarios with three different injection strengths in the strong, medium, and weak regimes. Three distinct bifurcation sequences with abundant features are observed by continually increasing or decreasing the electric Reynolds number. The present study shows that the residual conductivity significantly affects the bifurcation process and the corresponding critical point of EC flows.

Constitutive modeling of an electro-magneto-rheological fluid

The present article deals with a continuum mechanics-based method to model an electro-magneto-rheological (EMR) fluid deformation subjected to an electromagnetic field. The proposed method follows the fundamental laws of physics, including the principles of thermodynamics. We start with the general balance laws for mass, linear momentum, angular momentum, energy, and the second law of thermodynamics in the form of Clausius–Duhem inequality with Maxwell’s equations. Then, we formulated a generalized constitutive model for EMR fluids following the representation theorem. Later, we validate the model with the results of an EMR rheometer and ER fluid valve system-based configurations. At last, the possible simulation-based velocity profiles are also discussed for parallel plate configuration. As a result, we succeed in providing more physics-based analytical findings than the existing studies in the literature.

An electrostatic finite element analysis of the electrospinning process of bilayer constructs using a parallel-plate collector

Fundamental knowledge of the deposition process of electrospun fibers is of paramount importance to the fabrication of constructs with fibers oriented in specific directions, depending on the mandrel geometry. This paper presents an electrostatic finite element analysis of a parallel-plate electrospinning configuration that reveals the effects of the electric potential intensity and directionality on the deposition of aligned and randomly oriented fibers, resulting in the formation of a fibrous bilayer construct. Simulations demonstrate that polymer deposition between the collector plates yields a local effect on the electric field. This study provides a computational methodology for investigating other collector configurations and guidance for designing electrospinning setups capable of producing microfibrous constructs with tailored morphologies.

Active tuning of the optical response of field-effect-gated transparent conductive oxides

Transparent Conductive Oxides (TCOs) are a class of materials with high optical transparency and electrical conductivity. This combination makes them extremely appealing for solar cells, optoelectronics and infrared-plasmonics applications. In this work, we report the active tuning of the optical response of aluminium-doped ZnO (AZO) films upon electrical gating within a parallel-plate capacitor configuration. We investigated the electrical-bias-dependent optical response of thin AZO films fabricated by pulsed laser deposition by means of spectroscopic ellipsometry (SE). Calculations based on an exponentially-decaying spatial distribution of injected/depleted charge density in the AZO film are in accordance with experimental observations, allowing the extraction of the Debye length.

An Analytical Multiphase Model for Membraneless Alkaline Water Electrolyzers

Membranes in electrolyzers add cost, ohmic resistance and increase degradation. Membraneless electrolyzers offer the potential to make hydrogen production more economically viable by removing the membrane. In the absence of a membrane, it is critical to avoid product crossover to ensure safety and high product purity. Therefore, it is essential to understand the multiphase flow in a membraneless electrolyzer.This work aims to further the understanding of multiphase flow in a membraneless electrolyzer using a parallel plate configuration. We model the two-phase hydrodynamics for laminar flow in the electrochemical cell using the mixture model formulation. Using the mixture model equations1 and assuming an exponentially decreasing gas fraction, we derive accurate analytical expressions for the velocity profile and the relation between pressure drop and average superficial electrolyte velocity. We verify these analytical expressions against the numerical solutions obtained using COMSOL and experimental data from the literature2. Fig. 1 shows reasonable agreement between the analytical results, the numerical solution obtained using COMSOL, and the experimental data2. The analytical model assumes the same gas fraction on both electrodes; hence the asymmetry is not captured. In this work, we discuss how our analytical expressions can guide the design of a membraneless electrolyzer. Figure 1 : Comparison of the present analytical and COMSOL model with the experimental data from the literature2 for a buoyancy-driven membraneless electrolyzer. The above profiles are for a current density of 1000A/m2 at a height of 35mm from the bottom of the electrode.