Electric-field Equation Research Articles

Thermo-Electrical Field Analysis for the Treatment of Tumors in the Liver Using Low-Frequency Joule Heating

Hepatic tumors occur in liver tissue due to the growth of malignant cells. Low-frequency Joule heating (LFJH) is one of the cancer treatment methods that show tremendous potential to treat hepatic cancer without causing excessive side effects or patient discomfort as other cancer treatments such as chemotherapy. In this localized thermal treatment method, the tumor in liver tissue is heated to a critical temperature range using radiofrequency (RF) energy designed to damage malignant cells. An electrode is introduced over the tumor and electric current is passed through it to induce Joule heating. The volume heat generation due to the Joule heating raises local temperature in tumor cells and causes complete destruction or damage. In this study, a computational simulation model is created based on coupled solution of bio heat equation and electrical field equation and considering a composite region of malignant tumor embedded in liver tissue region. The electrical and thermal fields that can cause damage to the malignant cells without affecting the surrounding tissue are determined and optimized by changing various controlling parameters such as electrode design, frequency, and amplitude of the RF energy

Selective imaging of the terahertz electric field of the phonon-polariton in LiNbO3

Coherent phonon-polaritons have attracted a considerable amount of interest owing to their relevance to nonlinear optics and terahertz (THz)-wave emissions. Therefore, it is important to analyze the THz electric-fields of phonon-polaritons. However, in the majority of previous measurements, only a single component of the THz electric field was detected. In this paper, we demonstrate that pump-probe electro-optical imaging measurements using the Stokes parameters of probe polarization enable the phase-resolved selective detection of THz electric-field components that are associated with the phonon-polariton. We experimentally distinguish the mode profiles of ordinary and extraordinary phonon-polaritons, and clarify the excitation mechanism as optical rectification. These results are explained by numerical calculations of Maxwell equations for the THz electric field. The technique of selectively observing the THz electric field components may be useful for designing efficient THz-wave emitters.

Switchable broadband metamaterial absorber/reflector based on vanadium dioxide rings.

A new broadband tunable metamaterial absorber based on different radii of vanadium dioxide (VO2) rings loaded on the dielectric layer is designed. According to the insulator-to-metal phase transition characteristics of VO2 under thermal excitation, the dynamic adjustment of the absorption by the external temperature is achieved. The simulation results demonstrate that when VO2 is in its metal phase at high temperature, an absorption greater than 90% in the bandwidth range of 2.64-7 THz can be obtained and its relative bandwidth is reached to 90.5%. However, the absorption rate in the same frequency range is always lower than 2.3% when VO2 is in the insulator phase at low temperature, which means that the absorber can be used as a perfect reflector. The maximum tunable range of the proposed absorber can be realized from below 2.3% to nearly 100%. We further analyze and discuss the equivalent impedance and electric field distribution of the absorber and clarify the adjustment mechanism of the absorption performance of the VO2 ring. In addition, a multireflection interference theory is also investigated to quantitatively explain the physical absorption mechanism. Such a tunable broadband absorber based on temperature control has great potential to be applied to sensors, thermophotovoltaics, and wireless communication.

Simulations of a weakly conducting droplet under the influence of an alternating electric field.

We investigate the electrohydrodynamics of an initially spherical droplet under the influence of an external alternating electric field by conducting axisymmetric numerical simulations using a charge-conservative volume-of-fluid based finite volume flow solver. The mean amplitude of shape oscillations of a droplet subjected to an alternating electric field for leaky dielectric fluids is similar to the steady-state deformation under an equivalent root mean squared direct electric field for all possible electrical conductivity ratio and permittivity ratio of the droplet to the surrounding fluid. In contrast, our simulations for weakly conducting media show that this equivalence between alternating and direct electric fields does not hold for . Moreover, for a range of parameters, the deformation obtained using the alternating and direct electric fields is qualitatively different, that is, for low and high , the droplet becomes prolate under alternating electric field but deforms to an oblate shape in the case of the equivalent direct electric field. A parametric study is conducted by varying the time period of the applied alternating electric field, the permittivity and the electrical conductivity ratios. It is observed that while increasing has a negligible effect on the deformation dynamics of the droplet for , it enhances the deformation of the droplet when for both alternating and direct electric fields. We believe that our results may be of immense consequence in explaining the morphological evolution of droplets in a plethora of scenarios ranging from nature tobiology.

Identification of pulsating flow effects with CNT nanoparticles on the performance enhancements of thermoelectric generator (TEG) module in renewable energy applications

In this study, performance assessment of a thermoelectric generator module located in between two channels where carbon-nanotube/water nanofluid streams flow is studied with combined effects of nanoparticle inclusion and flow pulsations. The finite element method is used to solve the 3D unsteady coupled fluid flow, heat transfer and electric field equations. Different pertinent parameters effects such as Reynolds number (between 250 and 1000), nanoparticle volume fraction (between 0 and 0.04), pulsating flow frequency (Strouhal number between 0.01 and 0.1) and amplitude (between 0.25 and 0.95) on the power generation are examined. It is observed that flow pulsation changes the dynamic features of thermoelectric power generated in the device. Higher power values are obtained when Reynolds number, flow pulsation amplitude and nanoparticle solid volume fraction rise. However, the effect is reverse for higher pulsation frequencies. Including nano sized particles further enhances the performance of the device with flow pulsation. It is also observed that 24.4 % enhancement in the power are achieved for nanofluid with flow pulsation when lowest and highest pulsation amplitudes are compared. At lowest pulsation frequency and highest amplitude 14.2 % enhancement in power is obtained for water as compared to steady flow case while this amount rises to 31 % for carbon nanotube nanofluid at the highest solid volume fraction. System identification method is used to obtain dynamic lower order model of the system for different pulsation amplitudes to predict the time dependent power generated in the thermoelectric generator device. • TEG module performance with flow pulsation and nanofluid is examined. • Higher amplitudes, ϕ, Re number and lower frequency resulted in higher powers. • When amplitudes are varied, 24.4% power enhancement is obtained with pulsation. • As compared to steady case, 31% enhancement is seen with nanofluid and pulsation. • System identification is used to construct dynamic model of the TEG module.

Performance assessment of a thermoelectric module by using rotating circular cylinders and nanofluids in the channel flow for renewable energy applications

In the present study, a novel thermal flow system configuration is offered with rotating cylinders and nanofluids in channel to increase the powers generated in the TEG module mounted between the channels. The 3D coupled heat transfer, fluid flow and electric field equations are solved with finite element method. The numerical study is performed for different Reynolds number (between 350 and 1000), rotational Reynolds number (between −4000 and 4000), number (between 1 and 5), size (between 0 and 0.2H), location of the circular cylinders and solid CNT nanoparticle volume fraction (between 0 and 0.02). It is observed that as the cylinders are used in the channel with rotation, power enhancements of TEG module are achieved. When reference case of no-cylinder is compared, power increments of 56.5% and 27.5% are achieved for rotational Reynolds number of −3000 at Reynolds number of 350 and 1000. Higher number of cylinders provide higher power enhancements in the module and with five cylinders rotating at the highest speed, increments up to 47% are obtained at Reynolds number of 1000. Size and location of the cylinders are also found o be effective in altering the power features of the TEG module. Inclusion of nanoparticle is found to be efficient in the TEG power enhancement when performance of the system is low. Thus, slight improvement is achieved with nanoparticles when system with five cylinder at the highest speed and highest Reynolds number is considered. A reduced order model which is based on proper orthogonal decomposition methods is used to predict the temperature variations in the coupled domains and to effectively calculate the power generated in the TEG module.

Modelling and analysis of chirped long-period grating inscribed in a planer optical waveguide structure for sensing applications

Abstract A chirped long-period grating inscribed in a planer optical waveguide sensor is demonstrated. The distribution of electric field within the structure has been obtained using boundary condition for the electric field equations at different dielectric boundaries. The transmission spectrum of the proposed sensor is obtained by transfer-matrix method. Further, the sensitivity for ambient refractive index and temperature has been analysed by observing the shift in resonance wavelengths. The presence of two dips in the transmission spectrum effectively doubles the sensitivity in comparison to the single resonance structure. We have achieved refractive index sensitivity of 5600 nm/RIU and temperature sensitivity of 0.8 nm/ °C, respectively.

Parallel-Channel Electrotaxis and Neuron Screening of Caenorhabditis elegans.

In this paper, we report a novel microfluidic method to conduct a Caenorhabditis elegans electrotaxis movement assay and neuronal imaging on up to 16 worms in parallel. C. elegans is a model organism for neurodegenerative disease and movement disorders such as Parkinson’s disease (PD), and for screening chemicals that alleviate protein aggregation, neuronal death, and movement impairment in PD. Electrotaxis of C. elegans in microfluidic channels has led to the development of neurobehavioral screening platforms, but enhancing the throughput of the electrotactic behavioral assay has remained a challenge. Our device consisted of a hierarchy of tree-like channels for worm loading into 16 parallel electrotaxis screening channels with equivalent electric fields. Tapered channels at the ends of electrotaxis channels were used for worm immobilization and fluorescent imaging of neurons. Parallel electrotaxis of worms was first validated against established single-worm electrotaxis phenotypes. Then, mutant screening was demonstrated using the NL5901 strain, carrying human -synuclein in the muscle cells, by showing the associated electrotaxis defects in the average speed, body bend frequency (BBF), and electrotaxis time index (ETI). Moreover, chemical screening of a PD worm model was shown by exposing the BZ555 strain, expressing green fluorescence protein (GFP) in the dopaminergic neurons (DNs), to 6-hydroxydopamine neurotoxin. The neurotoxin-treated worms exhibited a reduction in electrotaxis swimming speed, BBF, ETI, and DNs fluorescence intensity. We envision our technique to be used widely in C. elegans-based movement disorder assays to accelerate behavioral and cellular phenotypic investigations.

Ultrahigh energy density and thermal stability in sandwich-structured nanocomposites with dopamine@Ag@BaTiO3

The progress in advanced dielectrics by tremendously enhancing the discharge energy densities is of great importance for the current electronic power systems. Herein, we report heterogeneous sandwich-structured nanocomposites with low nanofillers content, which offered the ultrahigh discharge energy density (Ue) of 21.03 ​J/cm3 at 592.1 ​MV/m. This energy density is the highest reported until now, with similar nanoparticle content and equivalent electric field. We used linear-type polyetherimide as the outer two layers, which offered insulation of charge injection from electrodes, reduced polymer free-volume, improved breakdown strength, and enhanced the overall thermo-mechanical stability. Besides, dopamine@Ag@BaTiO3 nanoparticles (DA@Ag@BT NPs)-modified ferroelectric-type polyvinylidene fluoride is employed as the middle layer for rendering higher polarizability and additionally increased breakdown strength due to well-known Coulomb blockade effect. Finite element simulations showed reduced local electric field in the outer, as well as middle layer matrixes, indicating higher breakdown strength and consequently higher energy storage prospects of heterogeneous sandwich-structured nanocomposites. The energy storage results at high temperatures demonstrated its significant thermal stability until 170 ​°C. Overall, this contribution not only paves the new way for developing industrially viable low nanofillers-concentrated flexible dielectric films but also provides the insight of polarization mechanism and electric breakdown in heterogeneous sandwich-structured dielectric materials.

Numerical investigation on pressure-driven electro osmatic flow and mixing in a constricted micro channel by triangular obstacle

Purpose The characteristics of fluid motions in micro-channel are strong fluid-wall surface interactions, high surface to volume ratio, extremely low Reynolds number laminar flow, surface roughness and wall surface or zeta potential. Due to zeta potential, an electrical double layer (EDL) is formed in the vicinity of the wall surface, namely, the stern layer (layer of immobile ions) and diffuse layer (layer of mobile ions). Hence, its competent designs demand more efficient micro-scale mixing mechanisms. This paper aims to therefore carry out numerical investigations of electro osmotic flow and mixing in a constricted microchannel by modifying the existing immersed boundary method. Design/methodology/approach The numerical solution of electro-osmotic flow is obtained by linking Navier–Stokes equation with Poisson and Nernst–Planck equation for electric field and transportation of ion, respectively. Fluids with different concentrations enter the microchannel and its mixing along its way is simulated by solving the governing equation specified for the concentration field. Both the electro-osmotic effects and channel constriction constitute a hybrid mixing technique, a combination of passive and active methods. In microchannels, the chief factors affecting the mixing efficiency were studied efficiently from results obtained numerically. Findings The results indicate that the mixing efficiency is influenced with a change in zeta potential (ζ), number of triangular obstacles, EDL thickness (λ). Mixing efficiency decreases with an increment in external electric field strength (Ex), Peclet number (Pe) and Reynolds number (Re). Mixing efficiency is increased from 28.2 to 50.2% with an increase in the number of triangular obstacles from 1 to 5. As the value of Re and Pe is decreased, the overall percentage increase in the mixing efficiency is 56.4% for the case of a mixing micro-channel constricted with five triangular obstacles. It is also vivid that as the EDL overlaps in the micro-channel, the mixing efficiency is 52.7% for the given zeta potential, Re and Pe values. The findings of this study may be useful in biomedical, biotechnological, drug delivery applications, cooling of microchips and deoxyribonucleic acid hybridization. Originality/value The process of mixing in microchannels is widely studied due to its application in various microfluidic devices like micro electromechanical systems and lab-on-a-chip devices. Hence, its competent designs demand more efficient micro-scale mixing mechanisms. The present study carries out numerical investigations by modifying the existing immersed boundary method, on pressure-driven electro osmotic flow and mixing in a constricted microchannel using the varied number of triangular obstacles by using a modified immersed boundary method. In microchannels, the theory of EDL combined with pressure-driven flow elucidates the electro-osmotic flow.

Stability of an incompressible plasma–vacuum interface with displacement current in vacuum

We study the free boundary problem for a plasma–vacuum interface in ideal incompressible magnetohydrodynamics. Unlike the classical statement when the vacuum magnetic field obeys the div‐curl system of pre‐Maxwell dynamics, to better understand the influence of the electric field in vacuum, we do not neglect the displacement current in the vacuum region and consider the Maxwell equations for electric and magnetic fields. Under the necessary and sufficient stability condition for a planar interface found earlier by Trakhinin, we prove an energy a priori estimate for the linearized constant coefficient problem. The process of derivation of this estimate is based on various methods, including a secondary symmetrization of the vacuum Maxwell equations, the derivation of a hyperbolic evolutionary equation for the interface function, and the construction of a degenerate Kreiss‐type symmetrizer for an elliptic‐hyperbolic problem for the total pressure.

Influence of slip velocity at the core of a diffuse soft particle and ion partition effects on mobility.

Nonlinear effects on the electrophoresis of a soft particle, consisting of a rigid hydrophobic core coated with a diffuse polymer layer (PEL) suspended in an electrolyte medium, are studied. The impact of the ion partitioning effect arising due to the Born energy difference between the PEL and the electrolyte is approximated based on the equilibrium Boltzmann equation, with which the ion distribution and hence, the charge density is modified. The equations describing the electrokinetic transport comprising the Darcy-Brinkman extended Navier-Stokes equations which includes the ion partitioning effect coupled with the modified Nernst-Planck equations and Poisson equations for electric field are solved numerically. The present numerical model for the soft particle compares well with the existing theoretical solutions and experimental results in the limiting cases. A deviation from existing simplified models based on the Boltzmann distribution of ions occurs when the Debye layer polarization, relaxation and the electroosmosis induced by the PEL immobile charge become significant. The hydrophobicity of the inner core strongly influences the nonlinear electrokinetic effects by modifying the Debye layer, electroosmotic flow in the PEL and surface conduction. The results indicate that the ion partitioning can significantly increase the electrophoretic mobility of the soft particle by attenuating the shielding effect. When the Debye layer is in the order of the particle size the hydrophobicity of the core surface and the ion partitioning effect manifest the surface conduction, which implies that the Boltzmann distribution of ions is no longer valid. The core hydrophobicity and ion partitioning effect have influence on the condensation of the PEL immobile charge, which creates a significant impact on the mobility.

Compact and low-frequency broadband microwave metamaterial absorber based on meander wire structure loaded resistors

In this paper, a compact and low-frequency broadband microwave metamaterial absorber (MMA) based on meander wire structure loaded with lumped resistor has been proposed and investigated numerically and experimentally. Compared with the single meander wire structure, the bandwidth and absorption level of the proposed MMA loaded with lumped resistors can be improved extremely. The retrieved equivalent constitutive parameters and simulated electric and magnetic fields distributions have been demonstrated to illustrate the mechanism underlying observed absorption. The simulated results exhibit that the proposed MMA can keep a good stability in a wide angular range for both transverse electric (TE) and transverse magnetic (TM) waves under normal and oblique incidence. Further simulated results indicate that the performance of the MMA can be adjusted by changing parameters of unit-cell structure and lumped resistors. Finally, we have fabricated a modified MMA sample practically, composing of meander wire structure loaded with lumped resistors, FR-4(loss), foam and continuous metal film. The modified MMA yields absorbance of over 85% from 1.84 GHz to 5.96 GHz in the experiment, and the relative bandwidth is about 105.6%, which is agreement reasonable with simulation.

An electron temperature model of the nMOSFETs

With the development of IC manufacturing process, the device dimensions have been on the nanoscale, while the device performance, such as the electron velocity, mobility and thermal noise, is significantly affected by the hot carrier effect. This paper proposes an electron temperature model to accurately predict the hot carrier effect. The channel transverse electric field is firstly derived by using the channel electric potential equation, taking into account the boundary conditions of the electric field. Based on the electric field equation, the energy balance equation is solved involving the impact of the temperature gradient and then the electron temperature model is established. The impact of the electron temperature on the channel mobility and of temperature gradient on the electron velocity has also been investigated. The results show that when the device enters the nanoscale, the electron mobility is more susceptible to the influence of the electric field and the electron temperature, and the impact of the temperature gradient on the velocity becomes obviously greater. The electron temperature model proposed in this paper can be applied to the performance analysis and modeling of nanosized MOSFETs.

Numerical Simulation of the Plane Electromagnetic Wave Transient Propagation in Lossy Medium

In the field of geophysical exploration, it is of great value to study the transient propagation characteristics of electromagnetic waves in lossy medium. The equations of electric field and magnetic field are derived. The absorbing boundary conditions and numerical stability conditions are analyzed. The two-layer medium model is established to simulate the propagation characteristics of plane waves. The simulation results show that the transient analysis of electromagnetic wave propagation can reflect the time fluctuation characteristics of electromagnetic field in multilayer media, and provide the indication of the boundary position.

Bistatic High-Frequency Radar Cross-Section of the Ocean Surface with Arbitrary Wave Heights

The scattering theory developed in the past decades for high-frequency radio oceanography has been restricted to surfaces with small heights and small slopes. In the present work, the scattering theory for bistatic high-frequency radars is extended to ocean surfaces with arbitrary wave heights. Based on recent theoretical developments in the scattering theory for ocean surfaces with arbitrary heights for monostatic radars, the electric field equations for bistatic high-frequency radars in high sea states are developed. This results in an additional term related to the first-order electric field, which is only present when the small-height approximation is removed. Then, the radar cross-section for the additional term is derived and simulated, and its impact on the total radar cross-section at different radar configurations, dominant wave directions, and sea states is assessed. The proposed term is shown to impact the total radar cross-section at high sea states, dependent on radar configuration and dominant wave direction. The present work can contribute to the remote sensing of targets on the ocean surface, as well as the determination of the dominant wave direction of the ocean surface at high sea states.

Modelling of the Temperature Changes Induced by Transcutaneous Spinal Direct Current Stimulation (tsDCS)

Transcutaneous spinal direct current stimulation is a neuromodulation technique recently exploited to regulate the activity and enhance plasticity of spinal neural structure. Despite the few side-effects reported by clinical studies, the assessment of potential localized temperature increases in tissues is still not solved. In this study, the temperature increase induced by a 3 mA stimulation in the tissue target (i.e., the spinal cord), in its surrounding tissues and in other tissues possibly more vulnerable to temperature increase were assessed through a computational approach. That solves Laplace equation and BioHeat equation for electric field and temperature distribution, respectively, on six whole body high resolution anatomical models, including three models of pregnant women at different gestational ages. Results show that temperature increase distribution in those targets is guided by a complex interaction between different mechanism in which electric stimulation plays a secondary role, in particular when blood perfusion is active. The very low heating assessed (below 1.5 m °C) is not consistent with the hypothesis that the induced temperature increase would critically activate metabolic changes in the target tissues here considered or would contribute to the few side effect that the applications of spinal direct current stimulation protocols have shown.

Geometric phase in Brillouin flows

A geometric phase is found to arise from the cyclic adiabatic variation of the crossed magnetic and electric fields which sustain the Brillouin rotation of a plasma column. The expression of the gauge field associated with this geometric phase accumulation is detailed. The physical origin of this phase is shown to be the uncompensated inductive electric field drift that stems from magnetic field cyclic variations. Building on this result, the effect of a weak, periodic and adiabatic modulation of the axial magnetic field on the particle guiding center drift motion is demonstrated to be equivalent to that of a perpendicular electric field, allowing the study of the gauge induced Brillouin flow through a geometrically equivalent linear radial electric field. This finding opens new perspectives to drive plasma rotation and hints at possible applications of this basic effect.

Parity–Time Symmetry in Bidirectionally Coupled Semiconductor Lasers

We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a configuration that leads to features reminiscent of parity–time symmetry. Starting from the rate equations for the intracavity electric fields of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 × 2 effective Hamiltonian that is identical to that of a typical parity–time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.

Asymptotic Behavior of Solutions of the Bipolar Quantum Drift-Diffusion Model in the Quarter Plane

In this study, we consider the one-dimensional bipolar quantum drift-diffusion model, which consists of the coupled nonlinear fourth-order parabolic equation and the electric field equation. We first show the global existence of the strong solution of the initial boundary value problem in the quarter plane. Moreover, we show the self-similarity property of the strong solution of the bipolar quantum drift-diffusion model in the large time. Namely, we show the unique global strong solution with strictly positive density to the initial boundary value problem of the quantum drift-diffusion model, which in large time, tends to have a self-similar wave at an algebraic time-decay rate. We prove them in an energy method.