Waveguides in EBG structures formed from cylinders with controlled elements

Uniform EBG structures in the form of 2D lattices in a planar waveguide are analyzed. The structures are formed from metal cylinders with gaps containing controlled capacitors. Eigenmodes of such structures are studied and dependences of the stopband width and position on the structure parameters are investigated. Eigenmodes in a waveguide formed in an EBG structure by changing the capacitor capacitances in an infinite row of the lattice cylinders are analyzed. It is shown that application of cylinders with controlled capacitors allows formation of electrically controlled defects inside a uniform EBG structure such that the set of these defects has properties of waveguides. Quantitative characteristics of such waveguides are studied.     

Liquid-crystal display with electrically controlled birefringence

Applications of electrically controlled birefringence of nematic liquid crystals to display devices are tested with a matrix-type letter-and-number indication system. Such a cell, with 35 × 35 elements, was realised without storage circuits. The display shows bright colours, especially red and green, for low operating voltages (< 20 V). The feasibility of a liquid-crystal matrix display with 100 × 100 points has been demonstrated in the laboratory.     

Theoretical optimization of complete forbidden bands in woodpile-type photonic crystals

Based on the plane-wave method, the optical properties of complete forbidden bands of woodpile structure photonic crystal with an entire Lattice rotation of 45° in the x-y plane were theoretically studied in terms of height-to-pitch ratios, filling factors, and rotation angles. The calculated results show that the gap to mid-gap ratio changes slightly with a filling fraction ranging from 0.25 to 0.30. The optimum height-to-pitch ratio is about 1.3. The gap to mid-gap ratio reaches more than 0.18 when the rotation angle increases from 40° to 50° and the maximum gap to mid-gap ratio of 0.2 remains unchanged for the rotation angle from 42°to 48° with a constant height-to-pitch ratio of 1.3. The gap to mid-gap ratio reaches the maximum value of 0.2 when the height-to-pitch ratio is 1.3. This woodpile-type photonic crystal can provide large band gaps within a wider parameter range, which makes it convenient to manufacture three-dimensional photonic crystals in the laboratory.     

Theoretical optimization of complete forbidden bands in woodpile-type photonic crystals

Based on the plane-wave method,the optical properties of complete forbidden bands of woodpile structure photonic crystal with an entire lattice rotation of 45o in the x-y plane were theoretically studied in terms of height-to-pitch ratios,filling factors,and rotation angles. The calculated results show that the gap to mid-gap ratio changes slightly with a filling fraction ranging from 0.25 to 0.30. The optimum height-to-pitch ratio is about 1.3. The gap to mid-gap ratio reaches more than 0.18 when the rotation angle increases from 40o to 50o and the maximum gap to mid-gap ratio of 0.2 remains unchanged for the rotation angle from 420 to 48o with a constant height-to-pitch ratio of 1.3. The gap to mid-gap ratio reaches the maximum value of 0.2 when the height-to-pitch ratio is 1.3. This woodpile-type photonic crystal can provide large band gaps within a wider parameter range,which makes it convenient to manufacture three-dimensional photonic crystals in the laboratory.     

Resonance features of the allowed and forbidden bands of the microwave photonic crystal with periodicity defects

The resonance features of the allowed and forbidden bands of the microwave waveguide photonic crystals with periodicity defects are theoretically and experimentally analyzed. It is demonstrated that the number of resonances in the allowed band is determined by the number of identical elements whose periodic sequence determines the photonic crystal and the maximum Q factor is reached in the vicinity of the lower and upper boundaries of the allowed band. An increase in the size of the forbidden bands and a decrease in the size of the allowed bands of the microwave photonic crystal due to a decrease in the number of resonances in the allowed band are caused by violations of periodicity of the photonic crystal related to nonidentity of a single element.     

Acoustic Surface Waveguides and Comparisons with Optical Waveguides

An overview is presented first of the various types of waveguides for acoustic surface waves which have been studied theoretically and experimentally. Many of these waveguides resemble certain waveguiding structures proposed recently for use in integrated and fiber optics. The similarities and differences between corresponding waveguiding structures in the two different fields are then discussed from the standpoints of their properties and their mechanisms of operation.     

一种光学状态可由电场控制的液晶复合材料的制备与表征

液晶材料对电、热、磁、光等外界物理量的变化具有不同的响应特性,向其中添加具有一定特性的化合物,可以得到具备一定响应特性的液晶复合材料。利用所制备的液晶复合材料对于电场变化具有响应特性的特点,制备出具有信息记录功能的复合材料。合成手性离子液体,按一定配比将其加入手征向列相液晶(N~*-LC)中,得到反射波段可电控的手征向列相液晶/手性离子液体复合材料。实验结果表明:材料初始状态为光透射状态;对材料施加直流电压40V时,样品表现为光散射状态,透过率低于10%;施加高频交流电压40V时,样品表现为半透明镜面反射,反射范围覆盖400～750nm,透射率为45%左右;撤去电场后,可恢复至初始状态,并且每种状态都具有一定的记忆效应。该种液晶复合材料制备简单,无需紫外辐射工艺,且具有电场响应特性,可以通过电场控制在可见光范围内表现出光透射、强烈光散射、半透明镜面反射3种不同状态,具有记忆效应,操作简单方便。     

Acoustoinjection transistor-a new type of electrically controlled transducer

A new principle of signal amplification is experimentally demonstrated which is based on the effect of modulation of conductivity of a semiconductor due to bunching of electrons by the acoustic wave. For the layered structure LiNbO3-CdSe good agreement between theory and experiment is obtained.     

电引发HF激光器的参数特性

本文报导输出能量1焦耳的电引发HF激光器,对其输出特性和工作参数的依赖关系进行了实验研究。     

Linear controlled amnesic immittance elements and networks

Construction of linear voltage-controlled resistors and conductors using i.e. multipliers is demonstrated. Experimental results from a network of such elements corroborates the realisation of nonlinear amnesic driving-point and transfer curves by systematic synthesis. Applicability of linear network sensitivity calculations to such networks is experimentally verified.     

Radiation characteristics of microstrip arrays with parasitic elements

The radiation characteristics of microstrip antennas consisting of one centre-fed patch and several identical parasitic patches are studied experimentally. The configurations investigated include a five-element cross and three- and seven-element linear arrays. A significant increase in gain is obtained by using close interelement spacing, with no degradation in pattern characteristics.     

Radiation characteristics of helix antenna with parasitic elements

An antenna system consisting of a driven balanced helix and two parasitic helices is compared with a continuously wound balanced helix with the same total turns. The similarity in the radiation pattern, axial ratio and directive gain are found by theoretical investigation.     

Reflection of light by a slab containing electrically small dielectric spheres

Theoriginal and theenhanced Maxwell-Garnett estimates for the permittivity of a particulate medium are applied to the reflection of light by a composite dielectric slab. The reflection coefficients for incident s and p polarizations are calculated and some curves are plotted and discussed.     

The characteristics of electrically short, umbrella top-loaded antennas

Experimental measurements of the electrical characteristics of umbrella top-loaded, electrically short antennas have been performed. Electrically short antennas can be represented by a series RLC circuit with good accuracy up to and including their first series resonant frequency. Electrically short antennas generally have very high Q's and, consequently, narrow bandwidths. Top-loading, such as umbrella top-loading of electrically short monopole antennas, leads to antennas which have lower Q's and larger bandwidths. The experimental measurements were made using a scale model facility. The antennas measured on the scale model facility were one-hundredth scale models of the anticipated full scale antennas. The equivalent inductance, capacitance, resistance, and effective height of these scale model antennas were determined and compared with values of static capacitance, static effective height, and static resistance obtained from a computer calculation [1], [2] and good correlation was obtained. Additionally, the dynamic characteristics of the antennas were determined from the model studies. The dynamic parameters determined were the antenna inductance, the dynamic radiation resistance, and the dynamic effective height. The measured data obtained from the model study are summarized in graphs and tables and compared with other reported experimental results as well as with computer calculations. Nomograms summarizing the computed data have been constructed and are presented.     

电寻址空间光调制器相位调制特性的研究

利用光在液晶中的双折射效应和泰曼－格林干涉原理,提出了一种测量电寻址液晶空间光调制器相位特性,即相移量与驱动电压（灰度）之间关系的新方法。该方法抗干扰能力强,实验精度高。通过测试Boulder Nonlinear Systems(BNS)公司的256×256像素反射式液晶空间光调制器,得到了其在一定电压范围内的相位调制特性具有良好的线性关系,而且在线性调制范围内器件稳定,有效孔径内各个点的平均调制误差约为0.032?姿,与理论值相吻合,从而验证了该实验方法的有效性。     

Symbolic analysis of circuits containing active elements

A simple modification to Percival's two-graph method is described which allows circuits containing four-terminal infinite-gain voltage amplifiers to be analysed symbolically. The modified method is of more general application than the standard two-graph method which requires that the active devices be represented by voltage-controlled current sources.     

Square and Rectangular Waveguides with Rounded Corners

Eigenfunctions, eigenvalues, and attenuation constants in waveguides are determined for the square with rounded corners, and for the cigar-shaped rectangle with rounded ends. These cross sections allow, by continuous variation of a parameter, the investigation of the deformation of the modes and attenuation curves of a circular waveguide. Particular attention is given to the H/sub01/ mode and its remarkable attenuation curve.     

微机控制帧同步系统的设计方法

帧同步是数字通信的关键,本文设计了一个微机控制的帧同步系统.该系统经过一定的改进,已经用于扩频通信中.文章详细分析了系统的设计方法,给出了系统的实现框图及流程图,最后建立了这种设计方法性能的马尔可夫链模型.     

近红外波段气溶胶的消光特性研究

在已知大气气溶胶折射率和气溶胶谱分布的基础上,对近红外波段的气溶胶消光特性进行了研究。利用Mie散射理论计算并讨论了气溶胶的消光、散射、吸收效率因子随尺度参数的变化和消光系数随半径和波长的变化,并且在MATLAB中对各种变化情况进行了仿真。结果表明,三种气溶胶粒子的消光和散射能力依次为沙尘性粒子,水溶性粒子,烟煤。消光系数在粒子半径和入射波长相近时达到最大,并且粒子半径对消光、散射、吸收系数的影响比入射波长更明显。这些结论可以为红外辐射在大气中的衰减计算和分析提供依据。