Electromagnetic modelling of 3D periodic structure containing magnetized or polarized ellipsoids

Coupling matrix and coupling coefficient concepts are applied to the interaction of an incident plane wave with a regular array of small magnetized or polarized ellipsoids, placed in a homogeneous surrounding medium. In general case, the angle of incidence and polarization of the plane wave upon an array of ellipsoids can be arbitrary. In this model, it is assumed that all the ellipsoids are the same, and the direction of their magnetization is also the same. The direction of magnetization is arbitrary with respect to the direction of the propagation of the incident wave and to the boundary plane between the first medium, where the incident wave comes from, and the array material under study. Any magnetized or polarized ellipsoid is represented as a system of three orthogonal elementary magnetic radiators (EMR) and/or three orthogonal elementary electric radiators (EER). Mutual interactions of individual radiators in the array through the incident plane wave and corresponding scattered electromagnetic fields are taken into account. The electrodynamic characteristics — reflection from the surface of the semi-infinite array (in particular, containing uniaxial hexagonal ferrite resonators), transmission through the array, and absorption are analyzed.     

Thickness-shear modes and magnetoelastic waves in a longitudinally magnetized ferromagnetic plate

Magnetoelastic (ME) waves and thickness-shear modes in the ferromagnetic plate are studied. Coupled vibrations of magnetization and shear elastic deformations excited simultaneously by a variable magnetic field propagate in two mutually perpendicular directions: parallel and normal to a surface. For parameters characteristic of isotropic ferromagnet with the sample magnetization and Zeeman field parallel to the surface, resonant frequencies of shear modes are computed and their dispersion law is examined. It is shown that the dependence of dimensional resonances frequencies on wave number k_z of ME wave propagating along saturating field direction occurs. The possibility of excitation of ME waves with different k_z explains multimode character of thickness ME resonances.     

Theory of electromagnetic wave propagation in a longitudinally periodic cylinder

Thinking of photonic crystals, we investigate the theory of electromagnetic wave propagation in a perfectly conducting semi-cylinder endowed with a periodic permittivity along its axis while its circular base is illuminated by an harmonic Bessel beam, symmetric around the cylinder axis. We prove that the Floquet-Bessel expansions of electromagnetic fields whose Floquet parts are solutions of a Mathieu equation. is a suitable tool to handle this kind of problems.     

Simulation of longitudinally magnetized three-dimensional magneto-optical devices by a full-vectorial beam propagation method

A full three-dimensional vector finite-difference beam propagation method is developed and tested. In this scheme, a delicate way to discretize the coupled equations is incorporated. The resulting matrix for the difference equation then has a tri-diagonal structure, which makes the program robust and, computationally, efficient. The transparent boundary condition is also improved so that any exponential growth at a boundary is suppressed. The method is applied to the simulation of magneto-optical devices and the design of a waveguide-based optical switch, with −25 dB isolation, is presented.     

Peculiarities of electric polarization in bi-layered longitudinally magnetized ferrromagnetic film

Electric polarization arising in a vicinity of magnetic inhomogenety in longitudinally magnetized ferromagnetic films has been considered. A variety of polarization transformations induced by external magnetic field have been studied. It has been demonstrated that electric polarization can change continuously or with a jump-like character depending on intrinsic, mainly anisotropic properties of the layers, the direction and the value of external magnetic field.     

Numerical analysis of open circular longitudinally magnetized p-Ge and n-InSb waveguides

By means of coupled modes, there have been studied the dispersion dependencies of the main and three higher modes of open circular -gyrotropic waveguides made of semiconductor materials having electron or hole conductivity. Dispersion dependencies of such waveguides have been studied at various biasing magnetizing field inductions B and concentrations N of charge carriers. Cut-off frequency dependence on concentration N has been computed.     

Optical properties of a superconducting annular periodic multilayer structure

The optical properties of a superconducting annular Bragg reflector (SABR) are theoretically investigated based on the transfer matrix method for the cylindrical waves. For TM wave at an azimuthal mode number, $m\ge 1$, it is found that there exist some novelties compared with the usual superconducting planar Bragg reflector (SPBR). An additional high-reflectance band is seen and some reflection dips near the threshold wavelength of a superconductor are generated as well. These two special results arising from the higher order azimuthal mode of the cylindrical waves are not found in the SPBR. The results suggest that the SABR could be used to design a narrowband transmission filter or an annular resonator without introducing any physical defect layer in the structure.     

磁化等离子体的鞘层结构

采用流体方法数值研究了斜磁场作用下的等离子体鞘层结构.模拟结果显示磁场对鞘层结构有显著的影响,特别是在磁鞘边界附近离子的密度分布产生了明显的变化.分别讨论了离子垂直入射和斜入射两种情况,当离子斜入射进鞘层时,其运动情况要相对复杂一些.在适当的条件下,洛伦兹力的作用使离子在某些区域产生相对聚集,离子密度分布产生波动. 关键词： 鞘层 等离子体 磁场     

纵向极化与磁化叠层复合材料磁电效应理论及计算

基于纵向极化压电材料及纵向磁化磁致伸缩材料的压电和压磁方程与磁电元件运动方程,给出磁电元件开路电压表达式;鉴于压电材料高输出阻抗的特点,考虑测试仪器的有限输入阻抗和传输信号引线电缆电容,通过建立等效电路模型推出了非开路情况下磁电电压计算式,取不同材料参数对磁电电压进行了数值计算.研究表明,材料参数、电路参数对输出电压均产生影响.对磁伸材料两端面受非均匀偏置磁场产生外力的非自由边界磁电效应进行研究发现,恒外力作用使压电元件产生不可检测的稳恒电压. 关键词： 纵向极化 磁电效应 磁电元件 层叠材料     

Electrodynamic properties of a thin-film periodic structure in an external magnetic field

Reflection and transmission of light by a bounded periodically layered structure formed by periodically repeated dielectric and semiconductor layers in a magnetic field are studied. The period of the structure is assumed to be much shorter than the wavelength. The magnetic field vector is parallel to the layer plane, and the wave propagation direction is perpendicular to the magnetic field. Passage to the limit of the thin-layer structure is performed. It is shown that the structure in this case is a biaxial crystal. The properties of the reflection and transmission coefficients are studied.     

A periodic surface structure with extreme acoustic properties

Several variational problems of sound absorption and scattering are solved using an impedance-based approach. Analytical expressions are derived for the surface impedances of the best absorber and a perfectly transparent body. A discrete surface structure (coating) is proposed for implementing their acoustic properties. Results of computer simulation are presented.     

Depinning dynamics of two-dimensional magnetized colloids on a substrate with periodic pinning centers

We study, by Langevin simulations, the depinning dynamics of two-dimensional magnetized colloids on a substrate with periodic pinning centers. When the number ratios of pinnings to colloids are 1:1 matching and at finite temperature, we find for the first time crossovers from plastic flow through elastic smectic flow to elastic crystal flow near the depinning with increasing the pinning strength. There exists a power-law scaling relationship between the average velocity of colloids and the external driving force for all the three types of flows. It is found that the critical driving force and the power-law scaling exponent as well as the average intensity of Bragg peaks are invariant basically in the region of elastic smectic flow. We also examine the temperature effect and it reveals that the above dynamic moving phases and their transitions could be attributed to the interplay between thermal fluctuation and pinning potential. At sufficiently low temperature, the thermal fluctuation could be neglected and the colloids near the depinning move in the elastic crystal flow no matter what the pinning strength. In addition, the number of pinning centers is changed and when it is close to the number of colloids, there appears a peak in the critical driving force and a dip in the power-law scaling exponent, respectively. The peak and dip are more pronounced for higher pinning strength.     

Spectral properties of electroacoustic waves in a ferroelectric with a moving periodic domain structure

The propagation of shear waves in a tetragonal ferroelectric with a moving superlattice of 180° domain walls (DW) is considered in a quasistatic approximation. It is found that the spectrum of shear waves consists of alternating allowed and forbidden bands in both cases of static and moving superlattices. It is shown that, due to the Doppler shift in the wave eigenfrequencies, the motion of the DW superlattice causes the degenerate roots of the dispersion equation to split and the splitting increases with the vibration mode number. The acoustic nonreciprocity induced by the moving DW superlattice in the ferroelectric is discussed.     

Dielectric properties of a magnetized electron gas in a nanotube

A quantum expression is derived for the longitudinal permittivity of a magnetized electron gas in a quantum cylinder. The asymptotics of the dispersion law are calculated for longitudinal plasma waves in a degenerate electron gas. The approximations of the weak and strong spatial dispersions are considered. It is shown that the longitudinal permittivity is an oscillating function of the magnetic flux through the cross section of the nanotube.     

Focusing of a diverging ultrasonic beam by a 2D periodic structure into two foci

A preliminarily focused (spherically diverging) ultrasonic beam was directed to a structure of metal rods having two-dimensional periodicity and bounded by reflecting surfaces in a dimension in which this periodicity was absent. For the ultrasound frequency taken at the upper boundary of the “transmission” band of the structure, the splitting of the acoustic image of the focus object into two maxima arranged in the sample homogeneity direction is obtained.     

Optical nutation in a magnetized semiconductor quantum well structure

Using the semiclassical coherent radiation—semiconductor interaction model, optical nutation has been analysed in aGaAs / Al_xGa_1 − xAs quantum well structure (QWS) assumed to be immersed in a moderately strong magnetic field and irradiated by a not-too-strong near band gap resonant femtosecond pulsed Ti–sapphire laser. The finite potential well depth of the QWS and the Wannier–Mott excitonic structure of the crystal absorption edge is taken into account. The excitation intensity is assumed to be below the Mott transition where the various many-body effects have been neglected with adequate reasoning. Numerical analysis made for a GaAs quantum well of thickness  ∼  100 Åand the confining layers ofAl_xGa_1 − xAs withx =  0.3 at intensity I ≤  5  ×  10⁶Wcm ^− 2reveals that the real and imaginary parts of the transient complex-induced polarization are enhanced with an increase in the magnetic field and their ringing behaviour confirms the occurrence of optical nutation in the QWS.     

一维磁化套筒惯性聚变模拟程序的设计与校验

在调研跟踪国外磁化套筒惯性聚变(MagLIF)研究领域最新进展的基础上,以一维磁流体力学方程为基础,结合氘氚燃料能量交换方程,建立一维磁化套筒惯性聚变物理模型,并使用Fortran语言编写完成一维数值模拟程序MagLIF-1D;通过与圣地亚实验室LASNEX,HYDRA等程序计算结果对比展示,完成程序校验工作,讨论后认为程序计算结果存在差异的主要原因可能来自不同程序对于材料状态方程库的选择;通过计算,MagLIF-1D程序可以直接获得内爆速度、燃料压力、燃料密度、聚变产额等关键物理量,这为后续更好地开展磁化套筒惯性聚变实验设计提供了有力工具。