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Parametric resonances in a temporal photonic crystal slab
摘要： We have studied resonances in a dynamic slab whose permittivity and/or permeability are periodic functions of time, namely, a temporal photonic crystal. We find strong and narrow resonances for frequencies that are equal to 1/2 or 3/2, etc. of the modulation frequency provided that a certain geometric parameter (proportional to the slab thickness and to the modulation frequency) assumes values such that the electric field in the slab is either symmetric or antisymmetric with respect to the slab center. These resonances turn out to be absent whenever the electric and magnetic modulations are in phase and have equal strengths, that is, when there are no band gaps between k bands. The resonance peaks appear for all the modulation harmonics and are superimposed on Fabry-Pérot–like background oscillations. For not very strong modulations, the resonances can be described in terms of the relative impedance of the slab and a parameter that expresses the modulation strength.
关键词： modulation frequency,dynamic slab,Fabry-Pérot–like oscillations,parametric resonances,permittivity,temporal photonic crystal,permeability
更新于2025-09-09 09:28:46
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Peculiarities of band structure of one-dimensional photonic crystals
摘要： In this paper, the peculiarities of the band structure of one-dimensional photonic crystals are studied, when the periodic (quasiperiodic) medium is inhomogeneous in relation to both the dielectric and magnetic properties. It is shown that the photonic band gap does not appear at small angles of incidence, in the case when the modulation depths of the dielectric permittivity and magnetic permeability coincide. The possibilities of obtaining photonic bandgaps in the terahertz radiation region are considered. The features of the band structure of photonic crystal with different spatial periods of the dielectric permittivity and magnetic permeability are investigated. It is shown that in this case, four PBGs appear in each diffraction reflection order.
关键词： Dielectric permittivity,Band structure,Magnetic permeability,Photonic crystals,Terahertz radiation
更新于2025-09-09 09:28:46
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[IEEE 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Erlagol (Altai Republic), Russia (2018.6.29-2018.7.3)] 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Analysis of the Technological Parameters Influence on the Reproducibility of the Active Dielectrics Properties
摘要： An analytical description of the process parameters and various industry sorts of external factors influence (heat, electrical, magnetic, mechanical) on active dielectrics properties (relative permittivity, polarization) that govern the materials use in functional electronics elements is presented. The article proves expediency of x-rays use to improve the reproducibility of dielectric properties of hydrogen-containing ferroelectrics (for example, triglycine sulfate). Higher reproducibility of parameters is due to the presence of flat areas in dependence of the relative permittivity on the electric field (cid:304)(E) during (cid:534)-radiation exposure, and therefore the additional errors of dialectic properties measurement are reduced significantly due to the impossibility of fixing the exact values of process parameters. For example, when the radiation dose D = 50 kR extra measurement error (cid:304) is reduced not less than 2.5 times.
关键词： properties reproducibility,radiation,Active dielectric,dielectric permeability,electric field strength
更新于2025-09-09 09:28:46
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A NOVEL DNG MEDIUM FORMED BY FERROMAGNETIC MICROWIRE GRID
摘要： Effective permittivity and permeability of a medium consisting of an infinite number of ferromagnetic microwires are evaluated in this paper. Analysis is carried out with the help of local and average fields inside a unit cell. In the literature, effective permittivity of the microwire grid is obtained by assuming the grid as an impedance loaded surface. The analysis is applicable only for the case of T Mz polarized normally incident wave. Proposed analysis enable us to evaluate all the three diagonal components of effective permittivity and permeability for arbitrarily incident uniform plane wave having arbitrary polarization angle. Numerical results are obtained through MATLAB, and a comparison is done with the results available in the literature for validation. Numerical results have shown a DNG like behaviour of the medium for a T Mz polarized incident wave.
关键词： effective permittivity,ferromagnetic microwires,T Mz polarization,DNG medium,arbitrary polarization,effective permeability,T Ez polarization
更新于2025-09-04 15:30:14
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LOW-LOSS COMPLEX PERMITTIVITY AND PERMEABILITY DETERMINATION IN TRANSMISSION/REFLECTION MEASUREMENTS WITH TIME-DOMAIN SMOOTHING
摘要： An approach is proposed for determination of the complex permittivity and permeability of low-loss materials, eliminating half-wavelength resonances occurring in transmission/re?ection (T/R) measurements. To this end, we apply time-domain smoothing for removing resonant artifacts from the wave impedance obtained with the conventional T/R method, assuming that we do not have such artifacts in the refractive index. Accordingly, the permittivity and permeability are found from the smoothed wave impedance and conventional refractive index. Our method is validated by measurements for two di?erent low-loss materials, nylon and lithium ferrite, and those results are discussed. Further, results from the present approach are compared to those from the approximate approach derived in our previous work.
关键词： complex permittivity,transmission/re?ection measurements,permeability,low-loss materials,time-domain smoothing
更新于2025-09-04 15:30:14
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Contact Lenses || Contact Lens Materials
摘要： The chapter provides an overview of contact lens materials, focusing on their development, properties, and the ocular response they elicit. It discusses the evolution from glass and PMMA to silicone hydrogels, highlighting the importance of oxygen permeability, wettability, and mechanical properties in lens design. The chapter also explores the challenges in achieving biocompatibility and comfort, the impact of lens materials on ocular health, and the future directions in materials development to address issues like dry eye and the ageing ocular surface.
关键词： Oxygen Permeability,Dry Eye,Ocular Response,Ageing Anterior Eye,Silicone Hydrogels,Contact Lens Materials,Biocompatibility
更新于2025-09-04 15:30:14
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Simulation of the wave-absorbing model of a carbonyl iron?/?silver-coated core–shell structure
摘要： The microwave-absorbing performances of carbonyl iron powder/silver core–shell composite particles are studied on the basis of the electromagnetic scattering theory and the energy conservation law. In addition, a calculation method for re?ection loss of the carbonyl iron powder/silver core–shell composite particles with microwave is proposed. The calculated re?ection loss of the carbonyl iron powder/silver core–shell composite particles is compared with the experimental results. The ?ndings show that the trend of re?ection loss of the carbonyl iron powder/silver composite particles can be predicted which can subsequently provide a relevant reference for future experiment and calculation of the absorbing mechanism of electromagnetic wave-microscopic carbonyl iron powder/silver core–shell composite particles.
关键词： magnetic permeability,Carbonyl iron powder/silver nucleus,wave loss
更新于2025-09-04 15:30:14
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Synthesis of type-II based (1-x)Ba <sub/>0.6</sub> (Ca <sub/>1/2</sub> Sr <sub/>1/2</sub> ) <sub/>0.4</sub> Ti <sub/>0.5</sub> Fe <sub/>0.5</sub> O <sub/>3</sub> +(x)Ni <sub/>0.40</sub> Zn <sub/>0.45</sub> Cu <sub/>0.15</sub> Fe <sub/>1.9</sub> Eu <sub/>0.1</sub> O <sub/>4</sub> composites via standard solid state reaction method and investigation of multiferroic properties
摘要： A series of multiferroic composites, (1-x)Ba0.6(Ca1/2Sr1/2)0.4Ti0.5Fe0.5O3+(x)Ni0.4Zn0.45Cu0.15Fe1.9Eu0.1O4 ((1-x)BCSTFO+(x)NZCFEO) where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0 have been synthesized by standard double sintering ceramic method sintered for 3 hours at 1200?C in air. The X-ray diffraction patterns reveal that the multiferroics and the parent ceramic samples crystallize in simple cubic structure with a slightly distored lattice parameter. The X-ray and bulk density increase with the increasing ferrite content. Consequently, the porosity decreases indicating better crystallization. A decreasing trend in dielectric constant is observed while the relative quality factor (RQF) increases signi?cantly with the increasing ferromagnetic NZCFEO. At the same time, M–H hysteresis loops reveal that ferromagnetic property enhances with the addition of Ni0.40Zn0.45Cu0.15Fe1.9Eu0.1O4 (NZCFEO). The highest values of coercive ?eld ～ 92 O and saturation magnetization ～1.37 emu/g are observed for x = 10% and x = 50% compositions respectively. Additionally, the permeability enhances up-to x = 30% but decreases with further doping. The room temperature resistivity rises due to the decrease in hopping mechanism. The samples exhibit a decreasing trend for resistivity with the increase of temperature. The dopant concentration has also shown an impressive impact on the activation energy. As a result, the multiferroic properties of (1-x)BCSTFO+(x)NZCFEO have been signi?cantly improved considering the measured magnetic and ferroelectric properties.
关键词： multiferroic composites,resistivity,dielectric constant,permeability,ferromagnetic property
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - A Scatterometer Operating at Millimetre and SubMillimetre Wave Wavelengths
摘要： A scatterometer operating in the bands from 50 to 750 GHz has been designed and fabricated. Operation in the different bands is achieved by using a Network Analyser with appropriate frequency extenders and corrugated horns. The beam is propagated using reflective quasi-optics on two levels with the sample being mounted on the lower level. The two levels are connected by a rotating periscope which collects the scattered radiation from the sample and transfers it to the upper level where the phase and amplitude are measured by the Network Analyser. The scatterometer can measure in both reflection and transmission and in VV, HH, VH and HV polarisations. During a measurement the Network Analyser heads and associated cables remain static to prevent drift. Rough reference samples have been developed for testing the scatterometer and preliminary results are reported in the 50 - 75 GHz band.
关键词： scattering,permeability,permittivity,materials,propagation,antenna,measurement
更新于2025-09-04 15:30:14