- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
UPML-ABC of dispersive materials for the unconditionally stable 2-D WLP-FDTD method
摘要： In this paper, uniaxial anisotropic perfectly matched layer (UPML) absorbing boundary condition (ABC) of dispersive materials is presented for 2-D finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLP). Taking advantage of the auxiliary differential equation (ADE) technique, our proposed algorithm avoids not only the complicated formulations but also the convolution integral. Using ADE scheme, the relationship between field components and auxiliary differential variables is derived in Laguerre domain. Substituting auxiliary differential variables into UPML-ABC, the electric field E of order q can be expressed directly by magnetic field H in Laguerre domain. Inserting magnetic field H of order q into electric field, and using central difference scheme, the formulations of uniaxial anisotropic dispersive media PML are obtained. One numerical example of wave propagation in 2-D dispersive materials is simulated. Numerical results validate the efficiency of the presented method.
关键词： finite-difference time-domain (FDTD),weighted laguerre polynomials (WLP),uniaxial anisotropic dispersive materials,perfectly matched layer (PML),Auxiliary differential equation (ADE)
更新于2025-09-23 15:23:52
-
Magnetoelectric uniaxial metamaterials as wide-angle polarization-insensitive matching layers
摘要： Antire?ection or impedance matching is a topic that has been extensively researched by the optical and microwave communities over the past century and until today. However, due to the diverging wave impedances of TE (s) and TM (p) polarizations with increasing incident angle, it is impossible to achieve perfect matching simultaneously for both polarizations at varying incidence angles with a single conventional isotropic matching layer. To achieve polarization-insensitive matching at an arbitrary incident angle, we propose a magnetoelectric uniaxial metamaterial layer (MEUML) that is inspired by the perfectly matched layer (PML) concept in computational electromagnetics. Similar to the PML, the MEUML requires speci?c uniaxial permittivity and permeability tensors. However, to simultaneously control both the transversal and longitudinal material parameters is not an easy task. To date, a true PML has not been realized with metamaterials. In this paper, we employ a simple and yet special metamaterial unit cell to achieve such control and synthesize a physical MEUML. The unit cell comprises two parallel metallic rings separated by a holey substrate. The transversal electric and magnetic dipole moments, and the longitudinal capacitive and diamagnetic coupling between the rings are judiciously controlled to achieve the required permittivity and permeability tensors. To aid the MEUML synthesis, we also introduce a technique that can extract the material parameter tensors at any incident angle. We ?rst demonstrate this concept by achieving polarization-insensitive matching of a high-index substrate at 45? with a single subwavelength-thick MEUML. We further adapt the concept to the microwave regime by developing a MEUML-based radome. Exceptional matching performance was obtained both in the simulations and measurements. The re?ectance remains below 5% from normal incidence (0?) to near grazing angle (85?) for both polarizations and over a wide bandwidth. With this unprecedented control of the material parameter tensors, the MEUML concept not only can be applied to impedance matching, but also can be utilized in many exotic applications that require extreme control of the material properties.
关键词： wide-angle,impedance matching,polarization-insensitive,radome,magnetoelectric uniaxial metamaterials
更新于2025-09-23 15:21:21
-
Dielectric Anisotropy Sensor Using Coupled Resonators
摘要： In this article, a new approach is proposed for the measurement of the uniaxial anisotropic dielectric constant of different planar samples by means of a single sensor. The sensor is based on a couple of straight-line coupled resonators in microstrip technology that can be excited in odd and even propagation modes. This sensor is designed on an isotropic substrate at the design frequency. Due to the electric field configuration specific for each mode, it is possible to relate these modes to the dielectric constant in two different directions (parallel and perpendicular) of a dielectric material placed on top of the sensor. This technique is used for the successful characterization of the dielectric constant anisotropic of anisotropic dielectrics (FR4, Rogers 4350B, and Arlon Diclad 880), and the isotropic material PTFE.
关键词： FR4,Anisotropic,dielectric constant,printed circuit board (PCB),uniaxial,anisotropy,sample under test (SUT)
更新于2025-09-16 10:30:52
-
[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Tuning the electron band structure of graphene for optoelectronics
摘要： Graphene, a conjugated sp2 carbon sheet arranged in a two-dimensional honeycomb-like lattice, shows the unique electronic structure in which conical shaped π-electron conduction and valence bands meet at the Dirac point. The properties of graphene are largely controlled by the Fermi level and the density of π-electron states, which can be used for tuning graphene to specific optoelectronic and electrochemical applications. We report a computational study of the electron states and electrochemical response towards I?/I3 redox mediator used in dye sensitized solar cells. We consider the influence of lattice deformations and magnetic field combined with covalently bonded moieties and charged ions on the heterogeneous electron transfer kinetics.
关键词： uniaxial strain,density of electron states,graphene,heterogeneous electron transfer,Landau levels
更新于2025-09-12 10:27:22
-
CONTROLLED MORPHOLOGICAL EVOLUTIONS OF SILVER FILMS ON COMPLIANT SUBSTRATES BY TUNING MECHANICAL STRAIN
摘要： Controlled surface morphologies of sti? ˉlms on compliant substrates possess a variety of applications, ranging from stretchable electronics, surface engineering to biomimics. Here, we report on the morphological evolutions of silver ˉlms deposited on prestretched compliant PDMS substrates by tuning the ˉlm strain in unloading, reloading and further stretching processes. It is found that the silver ˉlms generate transverse (perpendicular to the loading direction) wrinkles and longitudinal (parallel to the loading direction) cracks during the unloading process. On the contrary, longitudinal wrinkles and transverse cracks can be observed during the further stretching process. The morphological characteristics, evolution behaviors and mechanical mechanisms of the crack and wrinkle patterns are investigated in detail. The report in this work could promote a better understanding of the morphological evolutions of sti? ˉlms on compliant substrates by tuning the mechanical strain.
关键词： wrinkle,uniaxial loading,Thin ˉlm,compliant substrate,crack
更新于2025-09-12 10:27:22
-
Effect of the electric field induced birefringence on the slab waveguide evanescent-wave sensor sensitivity
摘要： We have investigated the potential of using the E-field induced birefringence for improving the sensitivity of uniaxial anisotropic slab waveguide sensor based on evanescent wave interactions. LiNbO3 waveguide core was used as an example. We have calculated the sensor sensitivity formulas for the two kinds of modes propagating simultaneously in the waveguide sensor. In our study, we have distinguished between two different cases. The first case when the electric field is applied along the optic axis (+c) of the LiNbO3 wave guiding film (positive electric field); the second case when the electric field is applied opposite to the optic axis (?c) of such uniaxial crystal (negative electric field). The obtained results showed that, for positive electric field, increasing the electric field induces an increasing of the total anisotropy which causes decreasing on sensor sensitivity. However, for negative electric field, the increase of absolute values of negative electric field induces a decrease of the total anisotropy, the latter increases the sensor sensitivity. On the other hand, the study of the physical parameters on the sensor sensitivity showed that, to maximize the sensor sensitivity, it is advisable to use isotropic substrate that has a refractive index as closer as possible to the measurand index.
关键词： Evanescent wave,Uniaxial anisotropy,Planar waveguide sensor,Induced birefringence,Sensor sensitivity
更新于2025-09-12 10:27:22
-
Phase shift formulas in electro-optical crystals with an arbitrary incident direction
摘要： The calculation of the phase shift in electro-optical crystals is related to an extensive range of optical devices. A set of analytical phase shift formulas at arbitrary incidence angle and azimuth angle for a plane-parallel electro-optical crystal plate is derived. This enables us to analyze the phase shift induced by an electro-optical crystal with an arbitrary incident direction. As an example, the derived formulas are used to investigate the influence of incidence angle and azimuth angle on the phase shift in a lithium niobate crystal plate. For the field-free lithium niobate crystal, the phase shift depends only on the incidence angle. In contrast, when an external electric field is applied to the crystal, the phase shift is not only strongly influenced by the incidence angle, but also periodically changes with the azimuth angle. In order to validate the correctness of the derived formulas, the experiments are also conducted. The theoretical results are proved to be in good agreement with the experimental results.
关键词： Electro-optical crystal,Phase shift,Biaxial crystal,Birefringent,Uniaxial crystal
更新于2025-09-11 14:15:04
-
Formation of uniaxial strained Ge via control of dislocation alignment in Si/Ge heterostructures
摘要： Uniaxially strained Ge/SiGe heterostructures are fabricated by selective ion implantation technique, where dislocation alignments are highly controlled by the local defect introduction. Firstly, ion-implantation-defects are selectively induced into a Ge substrate, followed by the growth of a SiGe buffer layer. As a result, the SiGe on the implanted region is largely strain-relaxed due to the defects acting as dislocation sources. In contrast, it is demonstrated that anisotropic strain relaxation takes place in the SiGe on the unimplanted region, leading to the uniaxial strained SiGe. A strained Ge layer is pseudomorphically grown on the SiGe buffer and the same strain states are observed for the Ge layer. It is found that mis?t dislocations generated at the interface between the SiGe layer and the Ge substrate are aligned along only one direction. These one-directional dislocations are an origin of the uniaxial strain relaxation. Moreover, effects of ion-implantation stripe-pattern widths on the strain states are investigated. With the implanted line width increasing, the anisotropy of the strain in the unimplanted region is enhanced. From these results, it can be said that this technique opens a route to engineer dislocation alignments and anisotropic strain in semiconductor hetero structures toward high performance novel devices.
关键词： dislocation alignment,uniaxial strained Ge,Si/Ge heterostructures,selective ion implantation,anisotropic strain relaxation
更新于2025-09-10 09:29:36
-
Hydrostatic and uniaxial effects in InGaN/GaN quantum wells
摘要： We calculate strains, polarizations, and electric fields in InGaN/GaN quantum wells (lattice matched to GaN) under the influence of hydrostatic and uniaxial (along the c-axis) pressure. We calculate the confinement energies for electrons and holes, and we derive simple expressions for the transition energies and their pressure derivatives. We include the changes of the dielectric constant with pressure. The results seem compatible with the experimental data.
关键词： confinement energies,transition energies,uniaxial pressure,electric fields,strain,InGaN/GaN quantum wells,polarization,hydrostatic pressure
更新于2025-09-10 09:29:36
-
Effect of Poling Electric Field and Temperature Change on the Dielectric Anomalies of Relaxor Ferroelectric Strontium-Barium-Niobate Single Crystals
摘要： The dielectric properties of the uniaxial relaxor ferroelectric SrxBa1?xNb2O6 with x = 0.75 were investigated along the polar [001] direction as a function of temperature. The capacitance maximum showed the frequency dispersion commonly observed in relaxors. Additional weak dielectric anomalies were observed in the paraelectric phase; they were only seen during the heating process and disappeared upon subsequent cooling. These were attributed to the existence of large polar clusters strongly pinned at defects and/or to random ?elds and their metastable characters. Aligning the ferroelectric domains along the polar axis at room temperature removed the high-temperature dielectric anomalies. The dependences of the capacitance and the dielectric maximum temperature on the magnitude of the poling ?eld were investigated.
关键词： Uniaxial,Dielectric,Relaxor,SBN,Random ?eld
更新于2025-09-09 09:28:46