Effective Medium Approximation Method Research Articles

Functionalization of Graphene by Interfacial Engineering in Thermally Conductive Nanofibrillated Cellulose Films.

Flexible nanocomposites incorporating nanofibrillated cellulose (NFC) hold significant promise for thermal management applications. However, their heat dissipation performance is primarily constrained by the interfacial thermal resistance (Rbd). In this work, 1-pyrenemethylamine hydrochloride (PyNH2) noncovalent functionalized graphene subsequently self-assembled with NFC through a vacuum-assisted filtration technique. PyNH2 could not only stabilize graphene with π-π conjugation but also interact with NFC via hydrogen bonding. The prepared layered-structure nanocomposites achieve a thermal conductivity of 11.32 W·m-1·K-1 with a low filler content of just 5 wt %. Utilizing the effective medium approximation (EMA) method and two-dimensional X-ray scattering techniques, we know that this satisfactory thermal conductivity is mainly attributed to pyrene functionalization of graphene by interfacial engineering-induced low Rbd and high orientation degree of graphene. Undoubtedly, this study provides experimental and theoretical guide for fabrication of thermal conductive nanocomposites in the near future.

Effective medium approximation for the electromagnetic properties of rocks with surface conductivity

We present an approach to calculate the complex dielectric permittivity of a microheterogeneous rock composed of non-conductive solid grains with surface conductivity and a conductive liquid.We have calculated the effective electrical properties of a rock using the model that consider the complex structure of the conducting double layer between a solid grain and the electrolyte in the pores. The influence of two parts of double layer: the Stern (inner) layer on the solid surface and the diffuse (outer) layer was considered.Previously, the Differential Effective Medium (DEM) scheme was used to calculate the effective conductivity and dielectric permittivity. In contrast, we have adopted the Effective Medium Approximation (EMA) method for calculation of the effective electromagnetic properties of a rock with high inclusion concentration. This method allows one to describe both elastic and electromagnetic properties of the rock based on the unified model of the pore space.The calculations were performed both for the rock model with a fixed grain size and for the model with a fractal distribution of grain sizes.Our calculations have shown that the value of the dielectric permittivity in the low frequency range depends on the concentration and dimension of solid grains. However, the frequency-dispersion behavior is a function of the inclusion size only and it does not relate to the inclusion concentration in the porosity range typical for sedimentary rocks. This effect confirms the feasibility of the determination of the inclusion concentration and dimension by using the dielectric permeability and electrical conductivity dispersion curves.

Study of optical properties of porous silicon by DFT, comparison to experimental and effective medium approximation methods

Study of optical properties of porous silicon by DFT, comparison to experimental and effective medium approximation methods

Absorption properties by irregularly shaped particles with inclusions at visible and near-infrared wavelength regions

The absorption properties of snow and ice particles containing impurities such as black carbon (BC) and mineral dust (DS) were investigated using the geometrical optics approximation method (GOM). This study focuses on analyzing the single scattering co-albedo (SSCA) characteristics of non-spherical particles, aiming to enhance the interpretation of radiation observations in snow and ice regions. Particle sizes were varied (rva=50,200 and 500μm) and two types of inclusions (1 ppmw of BC and 100 ppmw DS) were considered. Significant differences in SSCA, ranging from one to two orders of magnitude were observed at λ=0.5μm between the “homogeneous model” with effective medium approximation method (EMA) and the “inhomogeneous model” with 50 BC inclusions. Similarly, differences of a factor of 2 to 4 were found for DS with 100 ppmw at λ=0.5μm and BC with 1 ppmw at λ=0.875μm. To bridge intermediate SSCA values between these models, we propose an “inhomogeneous model with EMA”, introducing two parameters to account for impurity concentration and inclusion aggregation. Our findings highlight the importance of selecting appropriate single scattering calculation methods in the analysis of observation data, particularly when dealing with BC impurity with significant absorption characteristics. This research contributes to a deeper understanding of solar radiation absorption in snow and ice regions, with potential implications for the optical remote sensing of snow and ice and climate modeling studies.

Dynamic behavior description and three-dimensional cutting simulation of SiCp/Al composites with high volume fraction

According to the dynamic behavior characteristics of SiCp/Al composites, the constitutive equation of high volume fraction composites is established by SHPB dynamic compression test, shear lag model and effective medium approximation method, and the calculation results are in good agreement with the experiments. The established constitutive equation is then imported into Abaqus to establish a three-dimensional cutting simulation model, which is combined with cutting experiments to analyze the dynamic removal mechanism of material during the cutting process and the cutting surface formation process. The results show that the formation and propagation of holes and cracks play an important role in the formation of chips. The failure removal mode of SiC particles is an important factor affecting the cutting surface morphology. The research results provide an important theoretical basis and research means for the study of cutting mechanism of SiCp/Al composites with high volume fraction.

Glucose sensor modeling based on Fano resonance excitation in titania nanotube photonic crystal coated by titanium nitride as a plasmonic material.

The brilliant optical properties of plasmonic metal nitrides improve many applications. Modeling of light-confining Fano resonance based on a titanium nitride (TiN)-coated titanium oxide one-dimensional photonic crystal is investigated as a glucose sensor. There is a cavity layer filled with a glucose solution between the TiN thin layer and photonic crystals. The reflection spectrum is calculated numerically by using Bruggeman's effective medium approximation and transfer matrix method. The effect of plasmonic layer thickness, cavity layer thickness, and the thicknesses of the titanium oxide nanotube layers are optimized to achieve a high performance sensor. The result shows that the Fano resonances shift to higher wavelengths with increasing glucose concentration. The best sensitivity of the optimized biosensor is about 3798.32 nm/RIU. Also, the sensor performance parameters such as the limit of detection, figure of merit, and quality factor are discussed. The proposed sensor can be of potential interest due to its easy fabrication and higher performance than many previous reported sensors in the sensing field.

Seismic surface wave attenuation by resonant metasurfaces on stratified soil

AbstractThis study aims to theoretically and numerically investigate the dispersion relations of Rayleigh waves propagating through vertical oscillators periodically distributed on stratified media. The classical elastodynamics theory and an effective medium approximation method are adopted to describe the dynamic behavior of metasurfaces and hybridization between the local oscillators and the foundational surface wave modes. The Abo‐zena algorithm and delta‐matrix method are combined to simplify the Eigen equation to overcome the accuracy problem in solving the closed‐form dispersion laws and improve the computational efficiency. Subsequently, plane‐strain finite element (FE) models with three configurations are developed to confirm the analytical predictions and obtain further insight into the resonator‐Rayleigh wave coupling mechanism. The numerical results are in good agreement with the analytical solutions, revealing that only the foundational mode is strongly coupled with the vertical resonators at resonance, while the surface wave band gap reported in homogeneous media is crossed by the remaining higher‐order surface modes. The attenuation performance and mechanical behavior of a finite‐length metasurface are investigated, and it is demonstrated that the output surface ground motion can be significantly reduced in a narrow frequency band near resonance. Moreover, a graded resonant metasurface with decreasing frequency is simulated to assess the feasibility of broadband attenuation. In summary, the aforementioned analytical framework and numerical simulation results show that the vertical oscillators placed atop a stratified soil system can be designed as resonant metasurfaces for shielding seismic surface waves to protect multiple large infrastructures or special structures from earthquake hazards.

Functional characterization of nano-porous silicate-polymer composite for bovine serum albumin immobilization

The paper dwells upon the elaboration of a simple and energy-efficient approach for the “bottom-up” fabrication of porous polymeric film, which possesses unique surface, structural and bulk properties, followed by its comprehensive study through various characterization techniques. The fabricated film is multi-layered methyl silsesquioxane and suitably modified with the help of several treatments making the film compatible for biosensing applications. Film characterization reports the self- organized topography of the film deposited over the substrate and confirms the successful bonding between the polymers. The influence of the concentration of polypropylene glycol, which itself acts as thermally labile dendrimer, is studied by observing its bond formation ensuring polymer mixing by using FTIR. Energy dispersive x-ray analysis has been performed for the confirmation of elements. In addition to this, the nanoporous film is also studied with the help of variable angle spectroscopic ellipsometry for the determination of film porosity and refractive index. In this analysis, Cauchy model and graded-index model were chosen for data analysis and the Bruggeman effective medium approximation method was used for evaluating the optical constant. The surface of the porous film has been treated with different silane surfaces, characterized with the help of FTIR, UV-VIS, and AFM and envisioned for protein immobilization.

Tunable far-infrared hyperbolic metamaterial based on graphene-polar dielectric

Abstract In this work, we propose a tunable hyperbolic graphene-polar dielectric metamaterial in the far-infrared range. Here, we employ LiF as a strongly dispersive photonic material which can support surface plasmon polariton within its polaritonic gap. The proposed metamaterial has been analyzed using effective medium approximation (EMA) and transfer matrix method (TMM). It is found that the characterization of the hyperbolic behavior and reflection coefficient of the proposed metamaterial can be effectively controlled by Fermi energy, number of graphene layers and thickness of LiF. According to the results, the hyperbolic bandwidth broadening is possible by increasing Fermi energy, number of graphene layers and decreasing LiF thickness. Furthermore, we have shown fully controllable reflective filtering property of the proposed metamaterial using EMA and TMM. It can be clearly visualized that for thick LiF, effective medium approximation results in complete validation in calculation of the reflection coefficient. This is demonstrating by comparison between the reflection coefficient of the proposed metamaterial calculated using EMA and TMM. We believe that the proposed graphene-polar dielectric metamaterial offers a potential strategy for fine tunning the hybridized surface plasmon phonon polariton in the far-infrared region towards high performance, tunable and active metamaterials.

Effects of Snow Grain Shape and Mixing State of Snow Impurity on Retrieval of Snow Physical Parameters From Ground‐Based Optical Instrument

AbstractWe proposed new snow grain model and snow impurity mixture models for the purpose of accurate retrievals of snow grain size and concentration of light‐absorbing particles (LAP) in snow from the optical remote sensing data. Two kinds of ice crystal models, irregularly shaped Voronoi columns, and Voronoi aggregates were employed. LAP can be captured by the snow through two processes: dry and wet deposition. Two different snow impurity mixture models were proposed. One is an external mixture model. We employed a coated sphere model in which soot were hydrophilic particles to represent a hygroscopic property of aerosol and assumed the hydrophilic soot particles to be externally mixed with snow particles. The other is an internal mixture model. We employed a dynamic effective medium approximation method in which soot particles were randomly located within snow particle with any size distribution and number concentration. Validation of these models is conducted using a ground‐based spectral radiometer system with in situ measurement data. For snow grain size retrievals, a Voronoi mixture model seamlessly representing a geometrical shape and an optical properties of various snow types can provide accurate retrievals. For the retrieval of LAP concentration in snow, employing different mixing state models depending on season and measurement site gives accurate results. We also discussed the uncertainty of retrieved snow parameters on the surface slope involved in the retrieval accuracy. These models are expected to be useful for advanced airborne/satellite remote sensing and climate studies via radiative transfer modeling in the atmosphere‐snow system.

Investigation of optical properties of hybrid ZnO/Graphene-based photodetectors

The problem of ozone depletion lies behind the importance of developing a photodetector device, which is used as a preliminary detection step against the risk of solar radiation. At present, hybrid photodetectors are a major concern because they have detection and operational advantages over conventional photodetectors. In this study, we investigated the optical properties and photoresponse of hybrid ZnO/graphene (HZG) systems, of which ZnO nanorod (ZnO NR) was used in the system. Investigations were carried out using spectroscopic ellipsometry (SE) and solar simulators. The results of SE fittings with the effective medium approximation (EMA) method confirmed that the length of ZnO NR was 27.81, 42.67, and 220.46 nm respectively. We note that increasing the size of ZnO NR promotes light absorption to increase significantly. Furthermore, the relationship between light absorption and HZG photoresponse was discussed using a comprehensive analysis.

Application and validity of the effective medium approximation to the optical properties of nano-textured silicon coated with a dielectric layer.

The emergence of nanotextures in photovoltaics has resulted in challenges associated with optical modelling. Whilst rigorous methods exist to accurately solve these textures, the computational effort required limits the scope of modeling applications. The effective medium approximation (EMA) is a potential alternative to provide rapid modeling results which can be easily integrated with ray tracing of large complex structures. However, the validity of this technique is strongly dependent on the size of features relative to the wavelength of interest, making the application of EMA ambiguous for many situations. This paper aims to address this issue by comparing the simulated results between EMA and finite element methods for three randomly distributed silicon textures with and without a dielectric layer. Criteria for which the EMA approach is valid are proposed and generalized using ratios between root-mean-square roughness, correlation length and incident wavelength, making these limits broadly applicable, beyond that of just the nanotexture under specific solar spectrum regimes. The results in this work apply to random, isotropic textures under normally incident light. Based on the proposed criteria, the validity of different optical simulation techniques for a set of industrial photovoltaic textures is discussed. This analysis reveals a region within which neither geometric optics nor EMA are adequate for calculating the reflectivity of a textured surface, and hence FDTD or other new approaches are required.

Effective Medium Model of Periodic Nanolayered Transparent Shields

An innovative effective medium model based on the transfer matrix method is proposed for the simulation of 1D-periodic subwavelength metal–dielectric laminated structures excited by TM- or TE-polarized plane wave with oblique incidence angles. The homogeneous medium of each period is characterized by TM or TE complex effective permeability and conductivity. The resulting effective single layer (ESL), having the same total thickness of the multilayer laminate, is represented by a transfer matrix given by the product of the transmission matrices of the periods composing the structure. Notice that this model allows the homogenization of n -layer periods, while the effective medium approximation method is formulated for only two-layer periods. The ESL is used to compute the transmission and reflection coefficients and the shielding effectiveness of 1D-periodic nanolayered transparent coatings made by alternating layers of silver, zinc oxide, or titanium dioxide films, in the frequency range from 100 MHz up to 10 THz. The propagating wave performances of the ESL are compared with the ones given by the rigorous multilayer model. Finally, two different screens made of transparent coatings over glass are proposed and analyzed.

Gas transport in shale matrix coupling multilayer adsorption and pore confinement effect

Accurate prediction of gas transport in shale formations mainly consisting of micro- and nano-scale pores is a great challenge since most existing models only consider monolayer adsorption and the underlying multi-physics are either partially or completely overlooked. In this work, we have proposed a comprehensive single-component gas transport model integrating multilayer adsorption, surface diffusion, real gas effect, and pore confinement effect. The new analytical model is developed based on Bravo layer-sequence-model and then upscaled using an Effective Medium Approximation (EMA) method, where the generalized Brunauer-Emmett-Teller (BET) model, the modified Peng-Robinson equation of state (EoS) model, and the Sutton’s viscosity model are innovatively incorporated. The newly developed model has been successfully validated against simulation and experimental results with the assistance of an efficient iterative ensemble smoother (ES) algorithm. It is observed that the pore confinement effect is of importance when the pore size is smaller than 50 nm. The increase of gas viscosity due to the real gas effect is significant under reservoir conditions. The apparent permeability is found to increase greatly as the adsorption layer number increases, implying that the application of Langmuir model in existing gas transport models may substantially underestimate it. Given inorganic nanopores, the viscous flow is important at any pore sizes and the Knudsen diffusion plays a role in the pores that are less than 5 nm under reservoir conditions. As for organic nanopores, the contribution of surface diffusion is tangible when the pore size is below 150 nm and the Knudsen diffusion is negligible under high pressures.

Effect of anisotropy on the spectral characteristics of one-dimensional porous silicon photonic crystal microcavity for optical sensing applications

We present a numerical study of the effect of anisotropy on the spectral characteristics of one-dimensional porous silicon microcavity (1D-PSMC) with single defect layer. These structures have strong potential applications in optical sensing of chemicals and bioanalytes. Bruggeman’s effective medium approximation (BEMA) and (4 × 4) general transfer matrix method are used for theoretical modeling of spectral response of anisotropic 1D-PSMC. The potential of this structure as a sensing material is illustrated by analyzing wavelength shift in the defect mode induced by infiltration of biochemical analytes of different refractive indices inside the pores. Observed wavelength shift is found to be linearly dependent on the refractive index of analytes. We propose two 1D-PSMC-based sensors with a microcavity wavelength around 800 and 1200 nm. An anisotropic sensor with an operating wavelength around 800 nm shows a maximum sensitivity of 190 while an isotropic sensor with the same design parameters displays a maximum sensitivity of 150. In the case of an anisotropic sensor designed around 1200 nm, the maximum sensitivity is 260; for the isotropic sensor with similar structure, maximum sensitivity of 210 is obtained. Increased sensitivity is observed in anisotropic structures as compared to the isotropic ones. Design parameters play an integral role to obtain desired sensitivity in 1D-PSMC structure for sensor applications. These sensors can be used for high precision optical sensing of chemical-analytes, bioanalytes, gases, and environmental pollutants.

Numerical analysis of electromagnetic interactions by a cell during the mitosis phases.

In this work, a numerical study of the interaction of an electromagnetic field with a biological cell in the different phases of mitosis is presented. In particular, the validity of the single-shell model during mitosis from a geometrical viewpoint has been considered. We consider the Jurkat cell for our analysis and model the content of the cell, composed by the nucleus and different organelles immersed in cytoplasm and delimited by the cell membrane, as a single material with appropriate electromagnetic properties derived by making use of effective medium approximation methods, i.e., we used a quasistatic approach to deal with the cell. To validate the model, a comparison between the original and 2 approximated geometry models is made and the results are in very good accordance. Subsequently, an analysis of the scattered field indicates that the most sensitive component to the mitosis phase is the one parallel to the segment joining the centers of the cells.

Loosely-bound low-loss surface plasmons in hyperbolic metamaterial

Surface plasmons (SPs) carry electromagnetic energy in the form of collective oscillation of electrons at metal surface and commonly demonstrate two important features: strong lateral confinement and short propagation lengths. In this work we have investigated the trade-off relationship existing between propagation length and lateral confinement of SP fields in a hyperbolic metamaterial system, and explored loosening of lateral confinement as a means of increasing propagation length. By performing finite-difference time-domain analysis of Ag/SiO2 thin-film stacked structure we demonstrate long range (~ 100 mm) propagation of SPs at 1.3 µm wavelength. In designing low-loss loosely-bound SPs, our approach is to maximally deplete electric fields (both tangential and normal components to the interface) inside metal layers and to support SP fields primarily in the dielectric layers part of metamaterial. Such highly-localized field distributions are attained in a hyperbolic metamaterial structure, whose dielectric tensor is designed to be highly anisotropic, that is, low-loss dielectric (Re(ε) > 0; Im(ε) ~ 0) along the transverse direction (i.e., normal to the interface) and metallic (large negative Re(ε)) along the longitudinal direction, and by closely matching external dielectric to the normal component of metamaterial’s dielectric tensor. Suppressing the tangential component of electric field is shown to naturally result in weakly-confined SPs with penetration depths in the range of 3–10 µm. An effective-medium approximation method is used in designing the metamaterial waveguide structure, and we have tested its validity in applying to a minimally structured core-layer case (i.e., composed of one or two metal layers). Low-loss loosely-bound SPs may find alternative applications in far-field evanescent-wave sensing and optics.

Ellipsometric study of optical properties of Sm-doped ZnO thin films Co-deposited by RF-Magnetron sputtering

Non-volatile, rewritable and ultra-high-density optical memory necessitates photoreduction of valence state change of rare Earth elements. However, the sensitization of a nanoscale ultra-high storage medium possessing high optical transmission is a challenge. Herein, we studied the optical properties of Sm deposited in ZnO thin film by Radio Frequency (RF) sputtering deposition method. The Sm3+ content, optical properties, and crystal structure were investigated via X-ray fluorescence (XRF), variable angle spectroscopic ellipsometry (VASE) and X-ray diffraction (XRD), respectively. X-Ray fluorescence (XRF) upheld the presence of Sm grains and verified its percentage increase with the deposition power. VASE data were fitted using effective medium approximation method (EMA) to determine the Sm3+ volume fraction and mass thickness (MT). XRD study verified the Wurtzite hexagonal structure stability of ZnO and no crystal structure or phase distortion occurred. The band energy gap of the composite decreased with Sm: ZnO content. The roughness and thickness uniformity of the thin films were determined by the VASE study and were confirmed using field emission scanning electron microscopy (FESEM) and atomic force microscope (AFM). The optimum Sm ions content of high transmittance has been determined.

Inherent heating instability of direct microwave sintering process: Sample analysis for porous 3Y-ZrO2

Direct microwave heating of 3Y-ZrO2 is studied at frequency of 2.45GHz. Different conditions of input power, sample position and size are tested. For the first time, the experimentally known instability of microwave sintering is explained coupling the effective medium approximation and finite-element method. We show how the material dielectric permittivity imaginary part which increases with temperature and relative density encourages high hot spot phenomena. It is shown that the sample location has a great impact on the temperature distribution and decreasing the sample size promotes temperature homogenization thereby assisting the overall sintering stabilization.

Interfacial conduction mechanism of cesium hydrogen phosphate and silicon pyrophosphate composite electrolytes for intermediate-temperature fuel cells

As an electrolyte for intermediate-temperature fuel cells (ITFCs), which are operative at 200°C to 300°C, a composite electrolyte CsH5(PO4)2/SiP2O7 has been investigated. The CsH5(PO4)2/SiP2O7 composite is reported to exhibit higher conductivity than pure CsH5(PO4)2, possibly by forming a highly-conductive new phase at the interface between CsH5(PO4)2 and SiP2O7. In this study, we have prepared several SiP2O7 matrices of different surface properties, and studied the effect of the surface properties on the total conductivity as well as on the formation mechanism of the interfacial conductive phase. An effective medium approximation method was applied to the measured conductivity to analyze the interfacial conductive phase. Several SiP2O7 matrices of different acid properties and crystalline properties were fabricated, and the conductivity of the CsH5(PO4)2/SiP2O7 composite electrolyte was measured by AC impedance method. The acidity and crystallinity of the SiP2O7 matrices were found to be important properties for the formation of the interfacial conductive phase. The highest conductivity of the interfacial conductive phase was estimated to be 500mScm−1, which is almost three times larger than that of the pure CsH5(PO4)2, 160mScm−1.