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Freeze-drying assisted fabrication of highly homogenized reduced graphene oxide/alumina metacomposites with negative permittivity
摘要： Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al2O3) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al2O3 and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al2O3 metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al2O3 metacomposites were investigated by ?eld emission scanning electron microscopy, X-ray di?raction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan δ), alternating current conductivity (σac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σac was observed when the content of RGO increased from 13.50 to 15.38 wt%, and the percolation threshold ?tted by the power law was 14.31 wt%, which appeared earlier than the reported GR/Al2O3 and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50 wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO13.50/Al2O3 and RGO15.38/Al2O3 metacomposites realized the ε′ transition from negative to positive at 501 and 299 MHz, corresponding to the capacitive-inductive conversion.
关键词： Freeze-drying,Negative permittivity,Highly homogenization,Metacomposites
更新于2025-09-23 15:23:52
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Applicability of near infrared spectroscopy for real-time soil detection during automatic dishwashing
摘要： The purpose of this study was to utilize NIR spectrometry to develop a novel method to detect and determine concentrations of different soils in dishwashing liquor during automatic dishwashing in real-time. If it is possible to differentiate between soils, this could be an opportunity to react specifically to them (e.g. by increasing the water temperature if fat components are not sufficiently emulsifying). The possibility of an automatic adaptation of the dishwashing process to different soils and soil levels could lead to a shorter, more environmentally friendly and cost-reducing process. In a first approach, an emulsion containing three soil types (oatmeal, egg-yolk and butterfat), water and detergent were used to develop NIR spectrometry prediction models. Transmittance spectra obtained with an Fourier transform near infrared (FT-NIR) spectrometer of testing standards of 76 automatic dishwashing cycles with seven samples per cycle were taken at various times during the main washing process for calibration (and validation) of the NIR spectrometry prediction models. The spectra were pretreated to develop NIR spectrometry prediction models for each type of soil using the partial least squares regression method with cross-validation. Overall, the coefficients of determination in cross-validation are R2 > 0.92 for all NIR spectrometry prediction models developed. The results of the prediction models developed show that NIR spectrometry technology is a promising method to predict different levels of predefined soils in dishwashing liquor. The NIR spectrometry models were applied to an automatic dishwashing process with soiled dishes instead of emulsions containing soils to test their applicability. The resulting dishwashing process could be tracked in real-time by the dissolved soil concentrations, observed in the dishwashing liquor.
关键词： dishwasher,validation,sensor,emulsion,calibration,homogenization,soil,Near infrared spectroscopy
更新于2025-09-23 15:22:29
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Hierarchically structured metamaterials with simultaneously negative mass density and Young’s modulus by using dynamic homogenization
摘要： We propose one-dimensional hierarchical metamaterials (HMMs) that have simultaneously negative mass density and Young’s modulus in the sense of effective properties. Frequency-dependent effective properties of the HMMs are evaluated by using a dynamic homogenization theory. By considering three necessary conditions for dynamic homogenizability, we verify that our proposed HMMs can have physically meaningful double negativity, whereas the conventional periodic structures cannot. In addition, HMMs yield the broader ranges of the frequency and the effective properties for double negativity due to the large number of geometrical parameters. By exploring all the possible effective properties of HMMs, we discuss whether we can design metamaterials with the opposite sign of material properties in nature, ultimately aiming at perfect impedance matching.
关键词： dynamic homogenization,double negativity,impedance matching,hierarchical metamaterials
更新于2025-09-23 15:21:21
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Effective Parameters for 1D Photonic Crystals with Isotropic and Anisotropic Magnetic Inclusions: Coherent Wave Homogenization Theory
摘要： A homogenization theory that can go beyond the regime of long wavelengths is proposed, namely, a theory that is still valid for vectors of waves near the edge of the first zone of Brillouin. In this paper, we consider that the displacement vector and the magnetic induction fields have averages in the volume of the cell associated with the values of the electric and magnetic fields in the edges of the cell, so they satisfy Maxwell’s equations. Applying Fourier formalism, explicit expressions were obtained for the case of a photonic crystal with arbitrary periodicity. In the case of one-dimensional (1D) photonic crystals, the expressions for the tensor of the effective bianisotropic response (effective permittivity, permeability and crossed magneto-electric tensors) are remarkably simplified. Specifically, the effective permittivity and permeability tensors are calculated for the case of 1D photonic crystals with isotropic and anisotropic magnetic inclusions. Through a numerical calculation, the dependence of these effective tensors upon the filling fraction of the magnetic inclusion is shown and analyzed. Our results show good correspondence with the approach solution of Rytov’s effective medium. The derived formulas can be very useful for the design of anisotropic systems with specific optical properties that exhibit metamaterial behavior.
关键词： metamaterial,homogenization theory,effective parameters,photonic crystal
更新于2025-09-23 15:21:01
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Homogenization of time-harmonic Maxwella??s equations in nonhomogeneous plasmonic structures
摘要： We carry out the homogenization of time-harmonic Maxwell’s equations in a periodic, layered structure made of two-dimensional (2D) metallic sheets immersed in a heterogeneous and in principle anisotropic dielectric medium. In this setting, the tangential magnetic field exhibits a jump across each sheet. Our goal is the rigorous derivation of the effective dielectric permittivity of the system from the solution of a local cell problem via suitable averages. Each sheet has a fine-scale, inhomogeneous and possibly anisotropic surface conductivity that scales linearly with the microstructure scale, d. Starting with the weak formulation of the requisite boundary value problem, we prove the convergence of its solution to a homogenization limit as d approaches zero. The effective permittivity and cell problem express a bulk average from the host dielectric and a surface average germane to the 2D material (metallic layer). We discuss implications of this analysis in the modeling of plasmonic crystals.
关键词： Jump condition on hypersurface,Time-harmonic Maxwell’s equations,Layered structures,Two-scale convergence,Homogenization
更新于2025-09-23 15:21:01
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Multi-scale process simulation for additive manufacturing through particle filled vat photopolymerization
摘要： The majority of research into vat photopolymerization (VP), has been focused on experimental investigations of the influence of process and material parameters. In a specific application of the VP technique, where the resin is filled with particles, this empirical approach has its limitations. In order to fully understand the relation between process parameters and the material properties a detailed numerical analysis is needed. In this paper we present a multi-scale and multi-physical simulation approach to unravel such relations in the complex production process. Using a homogenization approach, the influence of the filler particles, in this case alumina, on the light scattering, conversion characteristics and resulting effective thermal and mechanical properties is determined. The effective composite material and scattering properties are then used as input in a process simulation framework. This enables prediction of key filled-VP characteristics at a structural level. A mesh sensitivity analysis at the component scale reveals that adequate predictions may be obtained with a rather course discretization, facilitating multi-physics VP part simulations.
关键词： Homogenization framework,Multi-physical modeling,Process simulation,Ceramics,Additive manufacturing,Vat photopolymerization,Multi-scale modeling
更新于2025-09-23 15:19:57
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Fabrication of Random Microlens Array for Laser Beam Homogenization with High Efficiency
摘要： The miniaturized and integrated microlens array (MLA) can effectively achieve the beam homogenization, compactness and miniaturization of laser systems. When the high-coherence laser beam is homogenized by means of using the MLA, interference fringes will occur in the homogenized light spot due to the periodicity of the MLA, which seriously affects the uniformity of the homogenized light spot. To solve this problem, a novel random microlens array (rMLA) structure was proposed for the purpose of achieving beam homogenization. The coherence in the homogenization process is suppressed by means of breaking the periodicity of the MLA. The homogenized light spot with a high energy utilization is then obtained accordingly. In the fabrication process, a clever method of combining chemical etching with lithography technology is performed to fabricate a honeycomb rMLA and a rectangular rMLA. The experimental results show that the energy utilization rate of the two types of the rMLAs is about 90%, and the uniformity of the homogenized light spots generated by the honeycomb rMLA and the rectangular rMLA are more than 80% and 85%, respectively. Meanwhile, fully cost-effective fabrication is possible to be realized.
关键词： random microlens array,beam homogenization,laser,chemical etching
更新于2025-09-23 15:19:57
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Mie Scattering in the Macroscopic Response and the Photonic Bands of Metamaterials
摘要： Herein, a general approach for the numerical calculation of the effective dielectric tensor of metamaterials is presented, and it is shown that the formalism may be used to study metamaterials beyond the long-wavelength limit. A system composed of high-refractive-index cylindrical inclusions is considered, and it is shown that the method reproduces the Mie resonant features and photonic band structure obtained from a multiple scattering approach, hence opening the possibility to study arbitrarily complex geometries for the design of resonance-based negative refractive metamaterials at optical wavelengths.
关键词： Mie resonances,nonlocal optics,metamaterials,homogenization
更新于2025-09-23 15:19:57
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Retrieving effective material parameters of metamaterials characterized by nonlocal constitutive relations
摘要： The parameter retrieval is a procedure in which effective material properties are assigned to a given metamaterial. A widely used technique bases on the inversion of reflection and transmission from a metamaterial slab. Thus far, local constitutive relations have been frequently considered in this retrieval procedure to describe the metamaterial at the effective level. This, however, is insufficient. The retrieved local material properties frequently fail to predict reliably the optical response from the slab in situations that deviate from those that have been considered in the retrieval, e.g., when illuminating the slab at a different incidence angle. To significantly improve the situation, we describe here a parameter retrieval, also based on the inversion of reflection and transmission from a slab, that describes the metamaterial at the effective level with nonlocal constitutive relations. We retrieve the effective material parameters at the example of a basic metamaterial, namely, dielectric spheres on a cubic lattice but also on a more advanced, anisotropic metamaterial of current interest, i.e., the fishnet metamaterial. We demonstrate that the nonlocal constitutive relation can describe the optical response much better than local constitutive relation would do. Our approach is widely applicable to a large class of metamaterials.
关键词： nonlocal constitutive relations,spatial dispersion,parameter retrieval,metamaterials,homogenization
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Laser Beam Homogenization Technology and its Application in High Speed Photography
摘要： We proposed a method of laser beam homogenization based on different optical components. Applications in various experiments the homogenization system significantly reduces the focal spot non-uniformity in high-speed photolithography. By virtue of the advantages such as high efficiency, high brightness and high reliability, laser is widely applied in various applications. The homogenization system of the laser beam normally presents non-uniformity in high speed photolithography. Therefore, in order to achieve uniform flat-top beam distribution, the laser beam homogenization technology emerges. In this component, we used different optical to homogenize laser beam, Conducted experiments and verified the feasibility of the method. The experiments were performed on SII light speed device. We used framing camera to photograph the process of the laser beam homogenization and processed the image with non-uniformity reduction algorithm. The results show that the homogenization system significantly reduces the focal spot non-uniformity in high-speed photolithography.
关键词： laser beam homogenization,non-uniformity reduction,high-speed photolithography,optical components
更新于2025-09-12 10:27:22