Thin Conductive Sheet Research Articles

Particle removal performance of a novel ESP type air cleaning system for indoor air quality in a subway station

A novel electrostatic precipitation type air cleaning technology with near zero ozone emission for indoor air quality of a subway station was developed. To minimize ozone emission and achieve high particle removal performance against ultrafine particulate matters (PMs), a multi-channel charging method using soft ionization by micrometre carbon fibers and a narrow gap collection method using high electric field by thin conductive plastic sheets as a high voltage electrode were used. In this study, the novel electrostatic charging and collection technologies were applied to a real scale air cleaning system in an Air Handling Unit (AHU) with air flow rate of 950 m3/min in Yuseong Oncheon subway station with an area of 3000 m2 in Daejeon, South Korea. The particle removal performance of the demonstration system was evaluated with real suspended particles in the subway station during test period with high PM concentrations in Korea over 40 μg/m3. Particle collection efficiency, pressure drop and ozone emission were evaluated, and compared to those of the a minimum efficiency reporting value (MERV) 10 and 14 filters used in the typical subway stations in Korea. In the field researches, the developed ESP achieved over 80% of the PM collection efficiency higher than those of the filters with MERV-10 and -14, and even 10% higher efficiency against PM1.0, while generating only 10% of pressure drop and also emitting nearly zero ozone. It is concluded that a novel ESP type air cleaning system with near zero ozone emission could be a promising air cleaning method for a large indoor environment such as a subway station where polluted air with ultrafine particles flowed in with a very high flow rate.

Self-Sustained Rigid Fully Metallic Metasurfaces to Enhance Gain of Shortened Horn Antennas

This paper presents mechanically robust, low-cost, lightweight, and polarization-independent metallic metasurfaces (MMs) to enhance the gain and directivity of shortened horn antennas. The MM was designed based on the strategy of correcting the actual phase errors probed on the aperture of the horn using the near-field phase-transformation principle. The fundamental unit cell of the MM is made of a pair of cross slots created in a monolithic thin conductive sheet and is entirely free from high-cost dielectrics. The lack of dielectrics makes MM lightweight, cost-efficient and easy to fabricate the prototype for mass production. The MM has a 2D array of unit cells arranged to increase the gain of the shortened horn by improving aperture efficiency through local phase transformation in a wide frequency band. The concept is demonstrated by designing MMs for shortened horns with different heights and the same physical aperture at the center operating frequency of 12.5 GHz. The maximum gain-bandwidth with MM is achieved for the shortest horn, which is validated by measuring the physical prototype. The results indicate that horn gain with MM increases by 9.2 dB (from 11.1 to 20.3 dBi) and has a 3-dB fractional gain-bandwidth of 10.4%. The weighted density of the fabricated MM is only 0.87 g/cm². Including MM, the total antenna height is around 61% shorter than a conventional air-filled horn having a similar peak gain.

Boundary element method for 3D conductive thin layer in eddy current problems

PurposeThin conducting sheets are used in many electric and electronic devices. Solving numerically the eddy current problems in presence of these thin conductive sheets requires a very fine mesh which leads to a large system of equations, and it becomes more problematic in case of higher frequencies. The purpose of this paper is to show the numerical pertinence of equivalent models for 3D eddy current problems with a conductive thin layer of small thickness e based on the replacement of the thin layer by its mid-surface with equivalent transmission conditions that satisfy the shielding purpose, and by using an efficient discretization using the boundary element method (BEM) to reduce the computational work.Design/methodology/approachThese models are solved numerically using the BEM and some numerical experiments are performed to assess the accuracy of the proposed models. The results are validated by comparison with an analytical solution and a numerical solution by the commercial software Comsol.FindingsThe error between the equivalent models and analytical and numerical solutions confirms the theoretical approach. In addition to this accuracy, the computational work is reduced by considering a discretization method that requires only a surface mesh.Originality/valueBased on a hybrid formulation, the authors present briefly a formal derivation of impedance transmission conditions for 3D thin layers in eddy current problems where non-conductive materials are considered in the interior and the exterior domain of the sheet. BEM is adopted to discretize the problem as there is no need for volume discretization.

Time-Domain Shielding of a Thin Conductive Sheet in the Presence of Pulsed Vertical Dipoles

The classical problem represented by a planar thin conductive shield in the presence of vertical dipole field sources (electric or magnetic) is solved analytically in the time domain via the Cagniard-de Hoop technique. Comparisons with numerical solutions carried out by means of efficient integration algorithms are provided and discussed.

Modeling Magnetized Graphene in the Finite-Difference Time-Domain Method Using an Anisotropic Surface Boundary Condition

A cost-effective approach to the finite-difference time-domain (FDTD) modeling of magnetized graphene sheets as a dispersive anisotropic conductive surface is proposed. We first introduce a novel method for implementation of anisotropic conductive surface boundary condition in the FDTD method. Then, by applying the surface conductivity matrix of magnetized graphene, we present modeling magnetized graphene as an infinitesimally thin conductive sheet in the FDTD method. The applicability, accuracy, and stability of the method are demonstrated through numerical examples. The proposed approach is validated by comparing the results with existing analytic solution.

DGTD Analysis of Electromagnetic Scattering From Penetrable Conductive Objects With IBC

To avoid straightforward volumetric discretization, a discontinuous Galerkin time-domain (DGTD) method integrated with the impedance boundary condition (IBC) is presented in this paper to analyze the scattering from objects with finite conductivity. Two situations are considered. 1) The skin depth is smaller than the thickness of the conductive volume. 2) The skin depth is larger than the thickness of a thin conductive sheet. For the first situation, a surface impedance boundary condition (SIBC) is employed, wherein the surface impedance usually exhibits a complex relation with the frequency. To incorporate the SIBC into DGTD, the surface impedance is first approximated by rational functions in the Laplace domain using the fast relaxation vector-fitting (FRVF) technique. Via inverse Laplace transform, the time-domain DGTD matrix equations can be obtained conveniently in integral form with respect to time t. For the second situation, a transmission IBC (TIBC) is used to include the transparent effects of the fields. In the TIBC, the tangential magnetic field jump is related with the tangential electric field via the surface conductivity. In this work, a specifically designed DGTD algorithm with TIBC is developed to model the graphene up to the terahertz (THz) band. In order to incorporate the TIBC into DGTD without involving the time-domain convolution, an auxiliary surface polarization current governed by a first-order differential equation is introduced over the graphene. For open-region scattering problems, the DGTD algorithm is further hybridized with the time-domain boundary integral (TDBI) method to rigorously truncate the computational domain. To demonstrate the accuracy and applicability of the proposed algorithm, several representative examples are provided.

Modeling of Magnetized Graphene From Microwave to THz Range by DGTD With a Scalar RBC and an ADE

This paper presents a discontinuous Galerkin time-domain (DGTD) method for the transient analysis of magnetized graphene from the microwave to terahertz (THz) frequencies. By considering the atom thick graphene layer as an infinitely thin conductive sheet with finite surface conductivity, a frequency-dependent anisotropic resistive boundary condition (RBC) is obtained. Based on this RBC, the direct volumetric discretization of graphene layer is avoided. Instead of directly deriving the numerical flux for DGTD considering the presence of this anisotropic and dispersive RBC, an auxiliary surface polarization current governed by a first-order time-dependent partial differential equation (PDE) is introduced over the graphene with the purpose to obtain an isotropic and simultaneously nondispersive RBC. In this way, the new formulated numerical flux expression derived from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Rankine–Hugoniot jump relations</i> is isotropic, and no time-domain convolution is involved in the finalized matrix equations. To verify the applicability and accuracy of the proposed algorithm, the Faraday rotation and the surface plasmon resonance of a plane wave through magnetically biased graphene are investigated. For open-region scattering problems, a hybrid DGTD and time-domain boundary integral (TDBI) method is applied to rigorously truncate the computational domain.

A Resistive Boundary Condition Enhanced DGTD Scheme for the Transient Analysis of Graphene

In this paper, the electromagnetic (EM) features of graphene are characterized by a discontinuous Galerkin time-domain (DGTD) algorithm with a resistive boundary condition (RBC). The atomically thick graphene is equivalently modeled using an RBC by regarding the graphene as an infinitesimally thin conductive sheet. To incorporate RBC into the DGTD analysis, the surface conductivity of the graphene composed of contributions from both intraband and interband terms is first approximated by rational basis functions using the fast-relaxation vector-fitting (FRVF) method in the Laplace domain. Next, through the inverse Laplace transform, the corresponding time-domain matrix equations in integral can be obtained. Finally, these matrix equations are solved by time-domain finite integral technique (FIT). For elements not touching the graphene sheet, however, the well-known Runge-Kutta (RK) method is employed to solve the two first-order time-derivative Maxwell’s equations. The application of the surface boundary condition significantly alleviates the memory consuming and the limitation of time step size required by Courant–Friedrichs–Lewy (CFL) condition. To validate the proposed algorithm, various numerical examples are presented and compared with available references.

Scalable and high-yield production of exfoliated graphene sheets in water and its application to an all-solid-state supercapacitor

One of the most critical issues in graphite exfoliation is realizing efficient, low-cost, eco-friendly, and scalable production of graphene for energy storage applications. The most promising strategies for exfoliating graphite to single-layer graphene sheets in scalable quantities with nearly non-oxidized content is the exfoliation of graphite by using an environmentally friendly solution. Herein, we demonstrate a universal exfoliation principle that uses imidazole, which has an anionic nature and π-conjugated heterocyclic coplanar structure, as the exfoliant for the successful production of large quantities of graphene suspensions in water. The exfoliant interacts with both surfaces of the exfoliated graphene sheets and the aqueous solution, significantly improving graphene dispersion (1mg/mL) in water. Exfoliation in aqueous solutions produced graphene in high yield (>90%, ⩽3 layers), with a large lateral size (μm) and high quality (ID/IG ratio≈0.1). The electrical conductivity of the graphene paper is 131.7S/cm, which is superior to the values reported from exfoliated graphene prepared using solution processes. An all-solid-state supercapacitor with a new design fabricated using the atomically thin and flat conductive exfoliated graphene sheets delivered an ultrahigh area capacitance (∼71.9mF/cm2). Therefore, imidazole -assisted exfoliation has great potential for scalable preparation of graphene suspensions for supercapacitor applications.

High order transmission conditions for thin conductive sheets in magneto-quasistatics

We propose transmission conditions of order 1, 2 and 3 approximating the shielding behaviour of thin conducting curved sheets for the magneto-quasistatic eddy current model in 2D. This model reduction applies to sheets whose thicknesses $\eps$ are essentially smaller or at the order of the skin depth. The sheet has itself not to be resolved, only its midline is represented by an interface. The computation is directly in one step with almost no additional cost. We prove the well-posedness w.r.t.~to the small parameter $\eps$ and obtain optimal bound for the modelling error outside the sheet of order $\eps^{N+1}$ for the condition of order N. Numerical experiments with high order finite elements for sheets with varying curvature verify the theoretical findings.

The transient electromagnetic response of a resistive sheet: straightforward but not trivial

Thin conductive sheets are often used to model base metal deposits for mineral exploration. In a similar manner, thin resistive sheets can be used as the building blocks of oil, gas or gas hydrate reservoir models. One would expect that the calculation of the electromagnetic response of a resistive sheet using an integral equation method should follow trivially from the well-studied solution methods for a conductive sheet. The only physical difference between the two situations is the fact that the conductive solution relies on the continuity of the electric field tangential to the sheet surface whereas the resistive solution requires continuity of the normal current density. The authors started to develop the building blocks for a practical tool which would be useful in marine controlled-source electromagnetic projects. However, progress proved slow. It was eventually realized that the style of the approximations used in the conductive calculation resulted in solutions in the resistive case that failed surprisingly to converge. It turns out that the resistive problem is far more subtle than one might expect, not only for the full 3-D case, but also for the simplified 2-D version. This paper derives and examines the quasi-analytical solution for the response of a 2-D resistive sheet buried in a double half-space and excited by a 2-D inline dipole—dipole system. Non-trivial differences between the resistive and conductive solution techniques are illuminated, and a deeper understanding of the underlying physics behind the resulting response is gained. Results show that a large resistive sheet of finite transverse impedance behaves in the same way as a layer with corresponding thickness and resistivity, a well-known result in the resistivity method. The response of a finite sheet shows characteristics similar to those observed in full numerical modelling.

A Robust Method to Accurately Treat Arbitrarily Curved 3-D Thin Conductive Sheets in FDTD

In this paper, we propose a novel method to treat thin conductive (TC) sheets of arbitrary three-dimensional (3-D) shape and curvature with the electromagnetic (EM) finite-difference time-domain (FDTD) algorithm without the need to resolve the sheet thickness spatially. We show that the physical properties of TC sheets enable us to do so without introducing additional field components to the conventional Yee scheme. Due to this noninvasive approach, in addition to the preserved stability of the FDTD algorithm, the method can be directly applied to any existing FDTD kernel, such as parallelized or hardware accelerated versions. The method has been developed within the framework of a professional EM FDTD software package and tested on real-world problems.

Analysis of the Equiangular Spiral Antenna on a Dielectric Substrate

While the first equiangular spiral antennas were slots cut from a thin conductive sheet, the widespread availability of cheap photoetching fabrication has made it more common for the spiral to be printed on a dielectric substrate. This paper examines the effects of the substrate on the spiral's performance. The finite-difference time-domain (FDTD) technique is used to model the spiral over a range of configurations. The results are used to construct a design graph that shows that the substrate significantly affects the impedance of the antenna. The results also show that the substrate can negatively impact the bore-sight gain and radiation patterns. Measurements from two spirals are used to verify the accuracy of the numerical model.

Transient field solution for a layer of finite thickness on a resistive basement

A closed‐form asymptotic solution is derived for the magnetic field of the currents induced by a transient airborne magnetic source in a conductive layer of finite thickness. The conductive layer rests on top of a resistive half‐space. Like the well‐known solution found by J. C. Maxwell for a thin conductive sheet surrounded by an insulator, the secondary magnetic field is expressed in terms of an image source receding from the layer. However, the new solution also accounts for the layer thickness h and the conductivity of the half‐space. One of the conclusions from the new solution is that the mirror plane that specifies the position of the image is located below the upper interface of the conductive layer at depth h/3. This indicates the correct position at which the equivalent thin sheet should be placed when Maxwell's solution is applied to a layer of finite thickness. If the basement that underlies the layer is highly resistive, Maxwell's solution becomes accurate when induced currents are almost uniformly spread across the layer. It remains accurate as long as currents induced in the basement can be neglected. Eventually, the secondary magnetic field of these currents will prevail over the field of currents in the layer. Maxwell's solution loses its accuracy long before this occurs. Depending on parameters of the model, the validity time range of Maxwell's solution may be narrow or even nonexistent. The generalized image solution is applicable in the time range h/vs &lt; t &lt; (σs/σb)(h/vs), where vs is the image recession speed, and σs and σb are the layer and basement conductivities, respectively. This range is significantly wider than that of Maxwell's solution. At early times, the secondary magnetic field is controlled by the position of the nearest interface of the conductive layer. Accounting for this observation, a simple modification of the new solution may be used to extend the applicability range towards even earlier times. The generalized solution is faster by several orders of magnitude than a numeric solution based on successive wavenumber‐to‐space and frequency‐to‐time domain fast Hankel transforms.

Integral methods for analysis and design of low-frequency conductive shields

This paper presents and compares two different approaches to the analysis and design of nonferrous shields for extremely low-frequency magnetic fields. The first method is based on a circuital approach where the shield is modeled by a set of conductors coupled with each other by a matrix of self and mutual inductances. The second technique is based on an algebraic formulation of electromagnetic fields and adapted by means of integral equations to the analysis of thin conductive sheets. The paper shows the accuracy of the two methods for calculating induced current density inside the shield and for evaluating magnetic flux density in the shielded region.

The face‐current concept and its application to survey design in electrical exploration

This paper presents a new method to identify the regions over a 3D geoelectrical structure that produce major contributions to the electrical potential established in response to a dc source at the ground surface. The measured potential is represented by a sum of a known primary potential (due to a homogeneous half space) plus an unknown potential caused by conductivity inhomogeneities. Because the primary potential is continuous everywhere, the interfaces with a conductivity contrast act as sources or sinks of currents in order to maintain the continuity of the current density related to the primary flux. These disturbing face currents are responsible for the generation of the secondary potential, and mapping them over a given structure allows us to assess the regions where the secondary potential is generated. In general, the face currents vanish away from the source according to the decay of the primary electric field. For this reason, deeper investigations can be expected when using pole sources because its primary field decays with the inverse of the squared distance, instead of the cubed distance as for dipole sources. For thin sheets, the polarization decay with distance is one order higher than that for large 3D bodies, which makes the detection of a sheet yet more difficult. The quantification of the total face current over the structure for different positions along a profile helps one choose the proper electrode array and determine its optimum length. This is done in two steps: (1) identification of the offset where the dc source provides the highest polarization (face current) on the targeted structure, and (2) determination of the array length by locating the potential electrodes closest to the region with the highest polarization. This second criterion came from an analogy between the face‐current and artificial current sources, where it is intuitively seen that the resulting potential is highest close to the source. The proposed survey design technique is applied to three models commonly used in electrical exploration: a shallow conductive heterogeneity, a buried contact, and a thin conductive sheet.

Numerical simulation using ADI-FDTD method to estimate shielding effectiveness of thin conductive enclosures

Numerical simulations were run using the alternating-direction implicit-finite-difference time-domain (ADI-FDTD) method to calculate the shielding effectiveness of various enclosures. The enclosures were composed of very thin conductive sheets, which are generally fabricated using conductive paints or electroless plating techniques on plastic surfaces. In this case, very fine cells must be used for finite-difference time-domain (FDTD) modeling. In the conventional FDTD method, fine cells reduce the time-step size because of the Courant-Friedrich-Levy (CFL) stability condition, which results in an increase in computational effort, such as the central processing unit (CPU) time. In the ADT-FDTD method, on the other hand, a larger time-step size than allowed by the CFL stability condition limitation can be set because the algorithm of this method is unconditionally stable. Consequently, an increase in computational efforts caused by fine cells can be prevented. The results from the ADI-FDTD method were compared with results from the conventional FDTD method, analytical solutions, and experimental data. These results clearly agree quite well, and the required CPU time for the ADI-FDTD method can be much shorter than that for the FDTD method.

A Finite Difference Scheme for Elliptic Equations with Rough Coefficients Using a Cartesian Grid Nonconforming to Interfaces

We consider the problem of calculating a potential function in a two-dimensional inhomogeneous medium which varies locally in only one direction. We propose a staggered finite difference scheme on a regular Cartesian grid with a special cell averaging. This averaging allows for the change in conductivity to be in any direction with respect to the grid and does not require the grid to be small compared to the layering. We give a convergence result and numerical experiments which suggest that the new averaging works as well as the standard homogenization with thin conductive nonconformal sheets and exhibits better accuracy for resistive sheets.

3-D modeling of thin conductive sheets for magnetic field shielding: calculations and measurements

Summary form only as given. This paper presents a new technique for calculating the magnetic field shielding effectiveness of thin conductive sheets of materials. The sheets are modeled as meshes of passive shielding wire filaments. Using this technique, complex three dimensional sources and shield configurations can be easily modeled. A computer program was developed to perform the calculations, and a comprehensive set of experiments was performed to verify the technique. Calculations and measurements are compared in the paper. The calculation method provides a numerical and experimentally verified technique for evaluating the shielding effectiveness of thin conductive sheets for power system magnetic field shielding applications. A predictive method such as this is becoming increasingly important as conductive materials are increasingly becoming accepted as effective shielding materials.

FE calculation of transient eddy currents in thin conductive sheets using dynamic boundary conditions

FE calculation of transient eddy currents in thin conductive sheets using dynamic boundary conditions