Structural Un-uniformity and Electrical Anisotropy of μc-Si:H Films

Structural un-uniformity and electrical anisotropy of μc-Si∶H film are investigated in this paper. It is found that the structure of μc-Si∶H film along the direction perpendicular to the substrate is not uniform, which is modulated by film thickness. In addition, there is a dark conductivity anisotropy along the direction parallel(σ∥) and perpendicular(σ⊥)to the substrate in μc-Si∶H film. The reasons for such an property of μc-Si∶H film and the effect of oxygen contamination are analyzed.     

Parameter reconstruction of materials with off-diagonal anisotropy using the state transition matrix method

An effective non-iterative method is developed for determination electromagnetic parameters of complex materials with anisotropy. Unlike the existing methods, the proposed method can extract the electromagnetic tensor parameters of materials with off-diagonal anisotropy using co- and cross-polarized reflection and transmission without using iterative procedures. Useful analytical expressions are derived for extracting the medium parameters of materials with off-diagonal anisotropy. The advantage of the method is that it uses state transition matrix and its properties in order to avoid nonlinearity and complexity of the problem. The method can work very well for dispersive materials since it is based on frequency-by-frequency extraction. The proposed method is validated by extraction of the complex permittivity and permeability tensors of two typical anisotropic materials.     

Petrophysics of magnetic dipole fields in an anisotropic earth

Measurement-while-drilling (MWD) resistivity log data are often acquired in highly deviated or horizontal holes. The loop sensors are located on the drill collar and are approximated as magnetic dipoles. The conductivity of the earth in the vertical direction σ_v and horizontal direction σ_h are almost always different. When an MWD resistivity tool enters a new bed, the response is compared with the precomputed logs to aid in the determination of the location of the drill bit. The MWD tool response, however, is sensitive to resistivity anisotropy. An alternative method is used to derive analytical expressions for the Sommerfeld-type integrals. Numerical results give typical MWD tool response as a function of the inclination angle &thetas; the tool makes with respect to the axes of anisotropy and also as a function of the anisotropy index κ=(σ_h/σ_v)^1/2     

Space Surface Parameters Determined from Fourier Transforms in Atomic Force Microscopy

A tabular analytic method for calculating space surface parameters of different materials is suggested. It uses Fourier transforms obtained with an atomic force microscope. Examples of calculation are given for periodic space structures and surfaces with different degrees of anisotropy and periodicity. It is shown that space parameters, namely, texture direction and texture direction index and also radial wavelength and radial wavelength index, allow anisotropy characterization and periodicity determination at a nanometer scale.     

Optimization of Anisotropic Magnetic Shielding

The concept of anisotropy is introduced in a laminar structure of magnetic sheet and the condition for minimum volume and maximum effectiveness of the magnetic shield of a spherical shell is investigated. The advantage of this structure over the conventional layered structure is shown. Figures and tables of this condition for typical shielding factor and permeability values are given.     

The magnetic field associated with a plane wave front propagating through cardiac tissue

An action potential propagating through a two-dimensional sheet of cardiac tissue produces a magnetic field. In the direction of propagation, the intracellular and extracellular current densities are equal and opposite, so the net current is zero. However, because of the unequal anisotropy ratios in the intracellular and extracellular spaces, the component of the current density perpendicular to the direction of propagation does not, in general, vanish. This line of current produces the magnetic field. The amplitude of the magnetic field is zero only if the action potential propagates parallel to or perpendicular to the fiber direction, or if the tissue has equal anisotropy ratios.     

Morphological Origin of Charge Transport Anisotropy in Aligned Polythiophene Thin Films

The morphological origin of anisotropic charge transport in uniaxially strain aligned poly(3‐hexylthiophene) (P3HT) films is investigated. The macroscale field effect mobility anisotropy is measured in an organic thin film transistor (OTFT) configuration and compared to the local aggregate P3HT mobility anisotropy determined using time‐resolved microwave conductivity (TRMC) measurements. The field effect mobility anisotropy in highly aligned P3HT films is substantially higher than the local mobility anisotropy in the aggregate P3HT. This difference is attributed to preferentially aligned polymer tie‐chains at grain boundaries that contribute to macroscale charge transport anisotropy but not the local anisotropy. The formation of sharp grains between oriented crystalline P3HT, through tie chain removal by thermal annealing the strained aligned films, results in an order of magnitude drop in the measured field effect mobility for charge transport parallel to the strain direction. The field effect mobility anisotropy is cut in half while the local mobility anisotropy remains relatively constant. The local mobility anisotropy is found to be surprisingly low in the aligned films, suggesting that the π?π stacking direction supports charge carrier mobility on the same order of magnitude as that in the intrachain direction, possibly due to poor intrachain mobility through chain torsion.     

关于各向异性基本电子元件欧姆定律的两种形式

由于各向异性电阻元件的导电各向异性，使电流密度方向和电场强度方向不一致，从而欧姆定律表现为两种形式：电流密度方向的欧姆定律和电场强度方向的欧姆定律。相应地存在一个二阶电阻张量和一个二阶电导张量。并给出了它们的计算公式。分析表明各向异性电阻元件的欧姆定律具有近似性。     

磁各向异性对(In,Ga)As衬底(Ga,Mn)As的影响

在(In,Ga)As缓冲层中生长的Ga<,0.95>Mn<,0.05>As薄膜的磁光圆二向色性(MCD)扫描磁场的测量中发现异常现象,这一现象出现在外磁场把样品的磁化矢量扭转到与入射光方向一致或远离入射光方向之时.通过磁各向异性的平均场理论,我们认为这实际上是磁各向异性对带-带跃迁影响的表现,是由于空穴带劈裂和E-k色...     

Design of microfabricated inductors

Possible configurations for microfabricated inductors are considered. Inductance can be set by adjusting permeability through control of anisotropy of a permalloy core or via a patterned quasi-distributed gap. A design methodology based on a simple model is proposed. A more accurate model and a numerical optimization are also developed. Design examples for 5- and 10-MHz buck converters and 2.5-MHz resonant converter applications are presented     

Anisotropy magnitude dispersion in thin films

The estimation of the effect of angular and magnitude dispersion of anisotropy on the behaviour of thin magnetic films is, in general, a problem of considerable difficulty, owing to the complexity of the magnetostatic interactions in the film. We note that the magnetostatic problem has a straight-forward solution for the case when angular dispersion is zero and amplitude dispersion is periodic along the hard direction. The calculations, although for a highly artificial type of anisotropy dispersion, are of interest, since, in this case, film behaviour can be predicted with due allowance for magnetostatic effects in the film.     

Tunable Optical Mode Ferromagnetic Resonance in FeCoB/Ru/FeCoB Synthetic Antiferromagnetic Trilayers under Uniaxial Magnetic Anisotropy

Ferromagnetic resonance (FMR) is one of the most important characteristics of soft magnetic materials, which practically sets the maximum operation speed of these materials. There are two FMR modes in exchange coupled ferromagnet/nonmagnet/ferromagnet sandwich films. The acoustic mode has relatively lower frequency and is widely used in radio‐frequency/microwave devices, while the optical mode is largely neglected due to its tiny permeability even though it supports much higher frequency. Here, a realistic method is reported to enhance the permeability in the optical mode to an applicable level. FeCoB/Ru/FeCoB trilayers are carefully engineered with both uniaxial magnetic anisotropy and antiferromagnetic interlayer exchange coupling. This special magnetic structure exhibits a high optical mode frequency up to 11.28 GHz and a maximum permeability of 200 at resonance. An abnormally low inverse switch field (<200 Oe, less than 1/5 of the single layer) is observed which can effectively switch the system from optical mode with higher frequency into acoustic mode with lower frequency. The optical mode frequency and inverse switch field can be controlled by tailoring the interlayer coupling strengths and the uniaxial anisotropy fields, respectively. The tunable optical mode resonance thus can increase operation frequency while reduce operation field overhead in FMR based devices.     

Polarization characteristics of 850-nm vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal oxide current aperture

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [\(\overline 1 \) 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.     

Finite-difference time-domain analysis of gyrotropic media. I.Magnetized plasma

When subjected to a constant magnetic field, both plasmas and ferrites exhibit anisotropic constitutive parameters. For electronic plasmas this anisotropy must be described by using a permittivity tensor in place of the usual scalar permittivity. Each member of this tensor is also very frequency dependent. A finite-difference time-domain formulation which incorporates both anisotropy and frequency dispersion, enabling the wideband transient analysis of magnetoactive plasma, is described. Results are shown for the reflection and transmission through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. A comparison to frequency-domain analytic results is included     

Magnetostatic wave propagation in YIG double layers

Calculations are presented for the magnetostatic surface wave propagation characteristics in single-crystal yttrium-iron-garnet (YIG) double layers with arbitrary direction of magnetization. The induced uniaxial magnetic anisotropy field is assumed to be different in the two layers; hence, the magnetization in one layer is aligned at an angle with respect to the magnetization direction in the other layer. The magnetostatic field interactions between layers depend on the angle between the two magnetization directions and on the separation between the two YIG layers. The wave propagation directions and time delays in each layer can be strongly affected by the use of an applied magnetic field and the magnetostatic coupling between the two layers, as well as by the uniaxial anisotropy energy in each layer     

超热电子能谱分布各向异性的实验研究

报道了100 TW超短脉冲钛宝石激光装置上飞秒激光-固体靶相互作用中超热电子的能谱测量,获得了各向异性分布的超热电子能谱.靶前激光反射方向超热电子能谱和靶前法线方向超热电子能谱类似,呈单温类Maxwell分布;而靶后激光传播方向超热电子能谱出现高能尾部;靶前法线方向超热电子的产额比靶后激光传播方向和靶前激光反射方向要高得多.对以上形成的原因进行了分析.     

Ferrites with Planar Anisotropy at Microwave Frequencies

Materials with an easy plane of magnetization (planar anisotropy) have recently been discovered. The large anisotropy field that tends to keep the magnetization in the easy plane reduces the field required to cause ferromagnetic resonance, which makes the material promising for microwave applications. Equations are derived for the susceptibility, taking into account losses and a finite medium. Propagation in a longitudinal and transverse static field is considered. The location of a slab in a rectangular waveguide for minimum loss in the forward direction, and the use of the material as a phase shifter, are discussed. Experimental microwave data on some materials are given, and also data on an isolator and phase shifter incorporating these materials.     

基于有限元方法的超声波仿真研究

针对超声波传播的瞬态问题,提出了一种基于多物理场耦合仿真方法。分别对超声波在流体、各向同性材料、各向异性材料中传播的问题以及压电材料作为声源的问题进行了仿真,并与理论结果进行了对比,结果表明该方法能够较好的仿真超声波传播的问题;在各向异性材料中,不同传播方向的波速不同,某一传播方向纵波速度高,则该方向横波传播速度低,反之亦然;压电材料作为声源时,激励电信号频率与压电材料谐振频率相同或接近时,产生的超声波杂波较少,因此激励电信号频率的选择应该以压电材料的谐振频率为参考。     

Design of thin-film tape heads

In this paper tools to handle the magnetostatic aspects of thin-film tape head design are reviewed. Some illustrative results from transmission-line calculations on inductive write heads and yoke-type magnetoresistive read heads are shown. New is the application to nonlinear saturation effects in write heads. The design of an emboss head for writing servo tracks on tape is described. Finally, a new type of read head is discussed that utilizes anisotropy of the permeability instead of structuring of the fluxguides for obtaining very small track widths.