Broadband dual-band linear orthogonal polarisation reflectarray

A single-layer dual-band orthogonal polarisation reflectarray antenna composed of a combination of split cross and rectangle rings for one band and double split square rings for the other band is presented. Using these types of cell elements, a wideband, single-layer dualband (12 GHz/14 GHz) orthogonal polarisation reflectarray is designed, fabricated, and tested. Measured results demonstrate radiation efficiency close to 60% for both bands and a 1 dB gain bandwidth of 24% for the lower band and 19% for the upper band.     

介观耦合金属环中的持续电流

在考虑电荷是量子化的基础上，计算了处在外加磁场中的三个有相互耦合作用的介观金属环中的持续电流，分析研究了耦合因素对金属环中持续电流的影响。结果显示，持续电流的幅度不仅受耦合的强度而且还受耦合的相对方向的共同影响．     

一种新型周期永磁聚束系统的设计

本文以传统的轴向相斥排列的周期永磁结构为基础,为了减小各个峰值的波动和降低端峰的磁场梯度,通过延长两端磁环的厚度,对各磁环选用不同性能的磁性材料的方法,经过不断模拟计算和修正,最终得到了峰值波动小,端峰磁场梯度小的周期永磁结构,其ΔBp=5.78%,端峰磁场梯度为0.0849 T/mm。     

强磁场下金属钠蒸气中二次谐波性质的研究

金属蒸气由于具有中心对称性,故在电偶极矩近似下,二次谐波是不存在的或者说是极弱的.近几年来陆续出现了一些金属蒸气中二次谐波的报道.首先是在1977年Matsuoka报道了在横向直流磁场70高斯下钠蒸气4~2D-3~2S的二次谐波.实验是用闪光灯泵浦染料激光器调谐到该跃迁的双光子共振上.1983年Chen报道了在无外磁场下观察到钠蒸气中同一跃迁的二次谐波,并且确认了地磁场的作用.1981年Freeman报道了无外磁场下钠蒸气的二次谐波的存在,并提出了由多光子电离的电场所致.但是我们认为磁场的作用是主要的,在强磁场下二次谐波的强度是否仍然与磁场强度平方成正比,这个问题至今未见报道.我们研究     

Whispering-gallery-like modes in square resonators

The mode frequencies and field distributions of whispering-gallery (WG)-like modes of square resonators are obtained analytically, which agree very well with the numerical results calculated by the FDTD technique and Pade approximation method. In the analysis, a perfect electric wall for the transverse magnetic mode or perfect magnetic wall for the transverse electric mode is assumed at the diagonals of the square resonators, which not only provides the transverse mode confinement, but also requires the longitudinal mode number to be an even integer. The WG-like modes of square resonators are nondegenerate modes with high-quality factors, which make them suitable for fabricating single-mode low-threshold semiconductor microcavity lasers.     

Elliptic Curve Paillier Schemes

This paper is concerned with generalisations of Paillier's probabilistic encryption scheme from the integers modulo a square to elliptic curves over rings. Paillier himself described two public key encryption schemes based on anomalous elliptic curves over rings. It is argued that these schemes are not secure. A more natural generalisation of Paillier's scheme to elliptic curves is given. Received January 2001 and revised June 2001 Online publication 23 November 2001     

Metallic glass ribbon probe for the measurement of the magnetic field, first and second order field gradients

A stress-driven magnetoelastic amorphous metal ribbon probe is presented which demonstrates equivalent noise floors of 18 pT/ square root (Hz) for the magnetic field, 23 pT/cm/ square root (Hz) for the first order field gradient, and 43 pT/cm/sup 2// square root (Hz) for the second order field gradient.<>     

Periodic Arrays of Magnetoelectrically Excited Double and Single Split-Ring Resonators as Artificial Magnetic Conductors

The amplitude and phase of the reflection coefficient of periodic arrays of electrically conducting elements in the form of double and single split rings are determined for two orientations of these rings, corresponding to magnetic (H) and magnetoelectric (HE) excitation. It is shown that, in the case of the HE-excitation of the rings, the arrays possess the properties of an artificial magnetic conductor or a high-impedance surface. The electric and magnetic fields near the arrays are calculated, and the dependence of the impedance on the distance between the array and the plane in which the impedance is determined is obtained. It is shown that the maximum of the impedance is in close vicinity of the array and can amount to tens of thousands of ohms. The feasibility of implementing a modified Salisbury radio absorber of small thickness by means of such arrays is shown theoretically and experimentally. It is also shown that, under illumination of an array of limited dimensions by a closely placed dipole, the screening effect reaches –30 dB with good matching of the dipole to the feed line (the reflection coefficient in the line is less than –20 dB).     

弱磁场中向列相液晶TEB30A薄膜自衍射现象研究

采用1.5 mW低功率的He-Ne激光(632.8 nm)正入射向列相液晶TEB30A薄膜,研究向列相液晶TEB30A薄膜在不同强度的弱磁场(0、0.4649、0.5062和0.5185 T)中的远场衍射特性。实验结果表明,向列相液晶TEB30A薄膜在4种不同强度的弱磁场(0,0.4649,0.5062和0.5185 T)中都能产生远场衍射。衍射图样会随磁场强度的增加而发生明显的变化。衍射环的数目增加,衍射环宽度变宽,衍射场向外拓展。当磁场强度为0.5062 T时,衍射环上出现了近似相互平行的干涉直条纹。当磁场强度达到0.5185 T时,干涉直条纹更加明显的趋于平行。在弱磁场的作用下,激光束在远场的散度变得明显。基于Kirchhoff-Fraunhofer衍射积分原理的理论模拟结果表明,当激光通过处在弱磁场中的向列相液晶TEB30A薄膜时,横向非线性相移会增大。随着弱磁场强度由0 T增加到0.5185 T,非线性相移也由4 π增加到20 π。弱磁场引起样品非线性相移增大,导致其远场衍射图样发生了变化。远场衍射光强图样的变化也是透射光能量分布的改变,因此,可将弱磁场调控向列相液晶这一技术应用于磁控光开关及光限幅等领域。     

基于磁共振压力显微系统的量子保真度

在不同的初始态条件下,基于磁共振压力显微系统探讨两原子的量子态保真度随时间的变化。结果表明：在不同的初态条件下,保真度随时间的演化曲线不同。悬臂偏移量引起的磁场偏差以及自旋与射频磁场的相互作用使得保真度的周期大大的缩短,从而可以在更短的时间间隔内使量子信息恢复到最原始的初态。同时射频磁场可以使得量子信息在传播过程中接近理想状态。这为探测样品中的原子状态以及提高量子信息在传递过程中的准确率提供了一定的保证。     

Backscatter RCS for TE and TM excitations of dielectric-filledcavity-backed apertures in two-dimensional bodies

Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section     

Energy spectrum in a concentric double quantum ring of GaAs–(Ga,Al)As under applied magnetic fields

The energy spectrum of an electron in a two-dimensional concentric double quantum ring is exactly calculated in the presence of an axial magnetic field using linear combinations of confluent hypergeometric functions. The influence of the geometric confinement on the energy spectrum is analyzed as a function of the inner and outer ring radii. The applied magnetic field modifies the electron energy spectrum and we discuss the appearance of the well-known Aharonov–Bohm oscillations. Interesting behavior of the probability amplitude of the electron state was found reflecting the competition between geometric and magnetic confinements. Electronic tunneling between the coupled rings may be reinforced or suppressed by conveniently modulating the barrier size separating the two rings, leading to drastic change in the electronic charge distribution through the nanostructure.     

SiGe quantum rings on the Si(100) surface

Results of experimental studies of forming SiGe nanometer-size rings on the Si(100) surface by the molecular-beam epitaxy method are presented. Detailed shapes and size distributions of the grown nanorings are studied by the atomic-force microscopy method. The elemental composition is determined by the Raman scattering method. The average germanium content in the nanorings was 37% for a forming temperature of 680°C. The obtained data on the geometry and composition of the produced nanostructures were used for calculations by the 6-band k × p-method of the energy spectrum and charge density distribution of hole states, localized on the SiGe quantum rings embedded in the Si-matrix. It is shown that the heterostructures with quantum SiGe rings are promising objects for creating devices that are capable of detecting electromagnetic radiation in terahertz and infrared wavelength ranges.     

New Optically Controlled Frequency-Agile Microstrip Antenna

A novel class of microstrip antennas composed of organic semiconductor polymer [poly(3-hexylthiophene) (P3HT)] is proposed for frequency sweeping applications. The permittivity of the P3HT film is measured using the reflective coaxial method for illuminated and nonilluminated states. Resonant frequencies of the proposed antennas instantly change on changing the optical illumination intensity from an adjustable white-light source. Two different antenna configurations (square and square ring) are designed and tested experimentally. The square ring antenna is able to sweep a broader frequency band (1.5 GHz). The gain and radiation efficiency of the proposed square antenna are compared with the corresponding copper microstrip antenna. The proposed antennas have acceptable resonant and radiation characteristics, albeit with modest radiation efficiency.     

Rings as elements for frequency selective surfaces

Arrays of simple rings on close packed square or triangular lattices are useful frequency selective surfaces for reflector antennas. Reflection bandwidths of about 26 per cent and transmission/reflection band ratios of 3:1 are readily attainable for angles of incidence of up to 45° at least. Experimental transmission coefficients are compared with the results of modal computations.     

Multilayer Microwires: Tailoring Magnetic Behavior by Sputtering and Electroplating

A novel technique for preparing multilayer microwires with controlled magnetic behavior has been developed. This technique involves combining sputtering and electroplating procedures to deposit (magnetic or non‐magnetic) metallic nano‐ and microlayers onto glass‐coated amorphous magnetic microwires. A suitable choice of magnetostrictive amorphous metallic nucleus, together with the specific stresses induced by the deposited layers, allows the tailoring of specific magnetic behavior. In this way, the preparation of multilayer microwires characterized either by square‐shaped hysteretic loops (typical of magnetically bistable microwires with longitudinal easy axes), or by nearly non‐hysteretic loops (for those microwires with a circumferential magnetization easy axes), can be achieved.     

双注电子枪中最小二乘法拟合磁场的研究

用粒子仿真软件EGUN和MAGIC仿真电子枪时,需设置一组线圈来拟合磁控注入电子枪的磁场.为了提高设计效率,采用最小二乘法计算线圈参数,拟合电子枪磁场,计算结果用于34GHz双注磁控注入电子枪的仿真中,仿真结果表明:最小二乘法能够直接计算出拟合磁场的线圈组合,提高设计电子枪的效率;仿真的双注磁控注入电子枪电子速度零散小,横纵速度比适中,满足回旋管对电子枪的要求.     

A genuine circular contact grid pattern for solar cells

A model was developed for a genuine circular contact grid, based on the same principles that led to previously reported models for other contact grid types. The circular grid differs from the regular (radial) grid often applied to round solar cells, in that it has considerably less radial lines and many more concentric rings, to the effect that the rings now take on the role of fingers, while the lines serve as busbars. For a 16 mm² n‐on‐p GaAs cell and irradiances ranging from 1 to 1000 suns, optimised grids of this new circular design were compared to equivalent radial, square and inverted square grids. Furthermore, in order to allow for a fair comparison of the different grid types, the previously reported radial grid model was modified to obtain additional freedom in design that is comparable to that of the other grid configurations. The circular grid turned out to suffer less power loss than a comparable radial grid up to a concentration ratio of 30. At higher concentration ratios, cells with a radial grid performed better, while comparable square and inverted square grids perform better over the entire range of concentration ratios. For GaAs cells serving as the bottom cell in a mechanical tandem, the effects of secondary shadowing were calculated for a range of translational and rotational misalignments, for the four patterns optimised for the case where the GaAs cell is effectively subjected to a concentration ratio of 500. The effects of translational misalignment varied little between the grids, but the rotational misalignment effects demonstrated the strength of the circular grid, since its shadowing loss hardly increases with increasing rotational misalignment angle, while those of the other three grid types quickly approach a doubling. When these secondary shadowing effects are taken into account, the circular grid can be the preferred pattern for the constituent cells of a mechanical stack, depending on the accuracy with which those cells can be rotationally aligned. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of large area nano-rings for MRAM application

We have developed lateral etch techniques to fabricate large area high density nano-scale magnetic ring arrays by deep ultraviolet lithography. Both centered and de-centered rings have been obtained. The width of the rings are controlled by the lateral etch time, and the inner ring diameter was scaled down below the lithography resolution limit. For de-centered rings, the shift between the center of inner and outer circles was easily adjustable. The characteristics of the ring arrays were characterized by SEM, AFM and SQUID.     

Resonant magnetotunnelling spectroscopy of a quantum loop

We report on tunnelling transport through a novel quantum device consisting of a double barrier structure fabricated as a submicron square loop in the plane of growth. We find two kinds of quantum confinement coexist in such a device: near the current onset, tunelling starts through zero-dimensional states located in the four corners of the loop, whereas at higher bias the resonant current exhibits kinks due to one-dimensional confinement in the arms of the loop. The use of a high magnetic field permits us to measure the binding energy of the dot ground state to the first one-dimensional subband in the connecting wires. This value is then compared to existing theory. Moreover, we show that the different kinds of lateral confinement are not only evidenced in the resonant structure, but also in the scattering assisted replica peaks.