自校准法测量波片相位延迟

在旋转补偿器椭偏仪(RCE)的基础上,提出了一种自校准的波片相位延迟测量方法。该方法将补偿器的相位延迟作为未知参数,根据Mueller矩阵理论建立了4个非线性方程,求解得到待测波片的相位延迟;实现了补偿器相位延迟的自校准,消除了其定标不准确带来的系统误差,尤其适用于多个波长的波片延迟测量。在此基础上建立了一套波片延迟测量系统,并分析和模拟了各种主要的误差源对系统测量精度的影响。结果表明,对于任意延迟的波片,测量系统最大的系统误差和随机误差分别为0.036°和0.040°。此外,使用该方法分别测量了λ/4波片、λ/2波片、127°波片和空气(不放入任何样品)在波长517.3、525.0、532.4nm处的相位延迟以评估测量系统的性能,其中空气的相位延迟代表测量系统的测量精度,与模拟结果基本一致。     

利用消光式椭偏仪精确测量波片相位延迟量

采用消光式椭偏仪精确测量波片的相位延迟量。从理论上分析了椭偏仪测量波片相位延迟量的可行性,重点讨论了标准1／4波片及待测波片的相位延迟量误差对测量精度的影响,并给出相应的实验验证。实验表明：该方法测量过程简单,方便,易受光强波动的影响,测量相位延迟量重复性精度达0．02°,相对误差为0．02％,是一种实用及有效的波片相位延迟量测量的方法。     

波片相位延迟的精确测量及影响因素分析

提出一种精确测量波片相位延迟的方法。将待测波片置于起偏器和检偏器之间,转动待测波片和检偏器至不同的位置并探测输出的光强,得到波片的相位延迟。采用光源调制技术和解调技术,抑制了连续光所无法克服的背景光干扰和电子噪声的干扰;将光路分为测量光路和参考光路,采用软件除法技术,消除了光源波动的影响,从而实现波片相位延迟的精确测量。详细分析了影响测量精度的误差因素,主要有光源波长变化、温度变化、入射角倾斜、转台转角误差和光源波动,计算了1064 nm波长时厚度为0.52 mm的λ/4多级结晶石英波片产生的相位延迟误差,其中光源波动的影响在作除法后有显著的改善,各误差因素的总测量误差为±1.58°。实际测量了该λ/4结晶石英波片的相位延迟为91.06°±1.78°,与理论分析相符。该测量和误差分析方法同样适合其他的波片。     

光纤电流互感器λ/4波片温度特性及其影响研究

λ/4波片是通过截取适当长度的保偏光纤制作的,它的相位延迟会随温度的变化而改 变。利用这一特性,可以补偿由于λ/4波片相位延迟变化造成的互感器尺度因子变化,同时也可以测量光纤电流互感器传感头的温度,补偿维尔德(Verdet)常数的温度影响,提高光纤电流互感器的测量精度。     

晶体相位延迟测量的λ/4波片法及理论研究

通过两束平面偏振光的合成推导出椭偏测量的理论基础,并由此得出用λ/4波片测晶体的相位延迟时器件的设置及方法。     

影响相位延迟器Jones矩阵的因素

为了研究相位延迟器的Jones矩阵,采用理论推导和分析的方法,得到了统一的Jones矩阵表达式,并对一些文献中的Jones矩阵做了修正及说明。对λ/n波片,采用理论分析和实验验证的方法,分析验证了相位延迟量对延迟器Jones矩阵的影响。结果表明,对λ/n波片,波片厚度与材料光性对偏振光产生的物理影响等效;但对Jones矩阵的影响则不同,取快轴与x轴成θ角时,波片厚度对Jones矩阵有影响,材料光性对Jones矩阵无影响。     

半阴法测量λ／4波片的相位延迟

本文介绍了测量λ／４波片的半阴方法，并利用透过波片的透射光强度导出待测波片相位延迟到计算公式，分析了起偏器最佳位置的确定方法。     

测量云母双折射率的波长调制补偿方法

根据云母折射率的色散关系和相位延迟随波长变化关系,给出了一种测量双折射率比较精确的方法.通过测量云母材料的厚度和相应厚度情况下作为λ/4波片使用所对应的波长,利用相位延迟与波长及厚度函数关系式直接求得云母的双折射率.该方法简便,测量精度达到10-5量级.     

波片延迟误差校正的理论与技术

从几何光学的理论出发,研究波片延迟误差的校正方法。通过研究晶体延迟器件光线入射方向与其延迟量变化的关系,从理论上导出了光线斜入射到波片时波片相位延迟量变化的计算公式,从而证明了可以通过绕与波片光轴平行的轴向或绕垂直于波片光轴的轴向转动波片进行波片延迟误差的校正。用消光法和最小光强法分别对λ/2波片和λ/4波片进行了延迟误差的校正。结果表明,波片的延迟误差可以通过转动波片的方法来消除。     

利用迈克耳孙干涉仪测量波片相位延迟量和快轴方向

分析了基于偏振光分量强度测量来确定波片参数的方法,指出这类方法在任意波片的测量上存在的不确定性。分析表明,波片相位延迟量与光强测量值之间存在多值函数关系,因而无法仅由线偏振分量光强测量值来确定波片相位延迟量的真正值,包括无法得到波片的级次及快轴方向。提出了把迈克耳孙干涉仪白光干涉的特征性彩虹条纹作为零光程差的定位参考标志,从而可以对光程差进行绝对测量,可以确切测量波片真正的相位延迟量和快轴方向。利用此方法对商用1/4波片进行了测量,实验结果表明所提出的迈克耳孙干涉仪零光程差法是行之有效的。最后还初步分析了色散对测量的影响,讨论了本方法适用的波片范围。     

孔隙结构金属板电磁屏蔽效能的实验研究

探究机箱金属板表面孔隙特性对于电磁屏蔽效能的影响是解决不同电子系统之间电磁干扰问题的关键所在。本文依托HFSS电磁仿真软件,采用矩形波导测试方法,通过大量对比实验研究了含不同特性孔隙金属板的电磁泄漏情况,从而得出提高金属板电磁屏蔽效能的方法。实验结果显示,改变孔隙形状、缩小孔隙开口尺寸以及增大孔隙深度都可以有效地改善金属板电磁屏蔽特性,从而减小电磁干扰的危害。     

On the implementation of the conjugate gradient Fourier transformmethod for scattering by planar plates

The accuracy of two conjugate gradient fast Fourier transform formulations for computing the electromagnetic scattering by resistive plates of an arbitrary periphery is discussed. One of the formulations is based on a discretization of the integral equations prior to the introduction of the Fourier transform, whereas the other is based on a similar discretization after the introduction of the Fourier transform. The efficiency and accuracy of these formulations are examined by comparison with measured data for rectangular and nonrectangular plates. The latter method is found to provide a more accurate computation of the plate scattering by eliminating aliasing errors (other than those due to undersampling). It is also found to be substantially more efficient. Its greatest advantage is realized when solving large systems generated by convolutional operators not yielding Toeplitz matrices, as is the case with plates having nonuniform resistivity     

A Semi-Infinite Array of Parallel Metallic Plates of Finite Thickness for Microwave Systems

An array of parallel metallic plates of finite thickness are useful in microwave lenses. The effect of finite thickness in the idealized situation of a semi-infinite array of perfect conductivity, is treated theoretically and experimentally for normal incidence of a uniform plane wave on the plane interface separating the medium from free space. The theoretical discussion involves the approximate variational method and a procedure is given for estimating the order of magnitude of the error in the final result. It is shown that it can be advantageous to use plates of finite thickness since the reflection from the interface can be reduced from that existing for infinitely thin plates.     

Wave penetration through slits on stacked thick plates

Wave penetration through slits on single and stacked metal plates of finite thickness is studied by using the Galerkin method. The limiting case of slits on infinitesimally thin plates are also formulated to compare the shielding effectiveness of metal plates with slits against incident plane waves. It is observed that the wave penetrating through slits on stacked plates with a proper separation is much less than that through a single slit on a plate with twice the thickness     

The Exciting Mechanism of the Parallel-Plate EMP Simulator

It is said that the parallel-plate electromagnetic-pulse (EMP) simulator is essentially a parallel-plate waveguide. This is not true. An analysis of the subpulses emitted from subregions of the sloping triangular and parallel rectangular plates shows that, when the length b of the parallel-plate section is close to the height h between the two parallel plates (which is true in most practical cases), the simulator is essentially a cone-plate radiator rather than a parallel-plate waveguide. The EMP in the working volume is contributed by the current pulses on the triangular plate near the pulse generator, so that the parallel plate actually plays a rather small role in forming the EMP in the working volume.     

Conductivity measurements at the interface between the sinteredconductor and dielectric substrate at microwave frequencies

A novel measuring technique of the effective conductivity at microwave frequencies for both the sintered conductor surface and the interface between conductor and dielectric materials was developed. In the measurement, a dielectric rod resonator is placed between two dielectric plates, one side of which is coated with a sintered conductor. For measuring the surface conductivity, the dielectric rod is sandwiched by the conductor side of the plates. On the other hand, for measuring the interface conductivity, the dielectric rod is sandwiched by the dielectric side of the plates. By the configuration, only interface conductivity contributes to the conducting loss of the resonator, thus allowing the measurement of the interface conductivity. Using the new technique, the frequency dependence of both the surface and interface conductivity of a sintered copper, formed on a glass ceramic substrate by the co-firing technique, was investigated in the frequency range from 11 to 34 GHz. It was confirmed that the values of interface conductivity of the sintered copper were smaller than the values of the surface conductivity     

Microwave Measurement of Dielectric Properties of Low-Loss Materials by the Dielectric Rod Resonator Method

Improvements both in accuracy and speed are described for the technique of measuring the microwave dielectric properties of low-loss materials by using a dielectric rod resonator short-circuited at both ends by two parallel conducting plates. A technique for measuring the effective surface resistance R/sub s/ of the conducting plates is proposed to allow the accurate measurement of the loss tangent tan delta. By means of the first-order approximation, the expressions are analytically derived for estimating the errors of the measured values of relative permittivity epsilon/sub r/, tan delta, and R/sub r/, for measuring the temperature coefficient of epsilon/sub r/, and for determining the required size of the conducting plates. Computer-aided measurements are realized by using these expressions. It is shown that the temperature dependence of R/sub s/, should be considered in the tan delta measurement. The copper plates used in this experiment have the relative conductivity of 91.0+-2.7 percent at 20°C, estimated from the measured R/sub s/ value. For a 99.9-percent alumina ceramic rod sample, the results measured at 7.69 GHz and 25°C show that epsilon/sub r/,= 9.687+-0.003 and tan delta = (1.6+-0.2)x 10/sup -5/. The temperature coefficients measured between 25 and 100°C are 112x10/sup -6//°C for epsilon/sub r/, and 23x10/sup -4//°C for tan delta.     

Silicon that moves-towards the smart sensor

The author describes an electronic accelerometer based on capacitive measurement. It is based on the simple parallel-plate capacitor: one plate is fixed, while the other moves relative to it under acceleration, which causes the capacitance to change. One example of this approach is the Analog Devices ADXL-50, manufactured by surface micromachining. The ADXL 50 consists of a variable differential air capacitor whose plates are etched from a single 2 μm piece of silicon. The fixed plates are simple cantilever beams, supported 1 μm above the chip in free space by polysilicon anchors that form a molecular bond with the chip. The thicker central mass is free to move in a plane perpendicular to the tethers. A series of regular fine elements project from the central mass, each acting as a parallel-plate capacitor. As capacitance is inversely proportional to the distance between the plates, the device has been designed to have the finest gap possible using photolithographic machines, to give the largest possible signal. The operation of the device is briefly discussed     

Accelerated life time testing and optical degradation of remote phosphor plates

In this investigation the thermal stability and life time of remote phosphor encapsulant plates, made from bisphenol-A polycarbonate (BPA-PC), are studied. Remote phosphor plates, combined with a blue-light LED source, could be used to produce white light with a correlated colour temperature (CCT) of 4000 K. Spectral power distribution (SPD) and photometric parameters of thermally-aged phosphor plates were measured by Integrated-Sphere. Results show that thermal ageing leads to a significant decrease in the luminous flux and chromatic properties of plates. The photometric properties of thermally-aged plates, monitored during the stress thermal ageing tests, showed a significant change both in the correlated colour temperature (CCT) and in the chromaticity coordinates (CIE x, y). It is also observed that there is a significant decay both in the phosphor yellow emission and in the blue peak intensity. The decrease in the luminous flux is strongly correlated to the deterioration of the chromatic properties of the phosphor plates. The results also show a significant decay of CCT, postulating that the degradation of the remote phosphor plates affects the efficiency of light and the colour of emitted light as well. The decrease of CCT takes place with almost the same kinetics as the lumen depreciation.     

On the application of the Wiener-Hopf technique to electrostaticfield problems in interdigital transducers

The Wiener-Hopf technique is used to compute the electrostatic field distribution in an interdigital transducer at the plane interface between two dielectric media sandwiched between two grounded metallic plates, with two grounded semi-infinite neighboring plates at the interface on each side of the transducer. To this end, the associated Green's function, which already satisfies the boundary conditions at all the grounded plates, is computed. The Green's function is used to derive the elements of the charge-potential-interrelation matrix for various basis and testing functions for a method-of-moments application. Examples demonstrate that the method has considerable advantages with respect to accuracy and computer-memory requirements