基于二维零位光栅的高精度平面定位系统

随着微电子工业和纳米加工技术的快速发展，对超高精度的定位基准的要求也越来越高．提出一种基于特殊编码的非周期性二维零位光栅的平面定位传感器，采用在二维方向上的非周期性编码产生一个表征绝对零位的最大输出峰．当两块二维零位光栅的相互位置完全对准时，透过的光强达到峰值，峰值的半宽仅为一个光栅栅格尺寸；当两块二维零位光栅的相互位置稍有移动时，透过光强急剧衰减．用光电接受器件接受透射光强信号，经过电路处理，反馈给定位驱动装置，可以在平面内同时实现X和Y方向高精度的定位要求．采用栅格常数为5μm的光栅做实验，可以达到优于20nm的定位精度．实验表明，该平面定位系统可以满足高精度平面定位的要求，有着广泛的应用空间．     

零位光栅的计算机设计与性能评定

圆光栅传感器采用零位光栅提供绝对零位信号,以防止掉电时数据丢失.在零位光栅设计过程中,通过设置阈值,将计算机产生的随机序列转换成布尔值序列,并利用两条经验结论作为判断条件,计算、比较后得到满足要求的栅线序列.分析零位光栅刻线序列的特点,得出了一些对于零位光栅刻划具有指导意义的结论.     

IQ不平衡OFDM系统两种逼近最大似然性能的亚最大似然补偿算法

针对在同相正交IQ不平衡的正交频分复用(OFDM)系统中用传统的最大似然(ML)补偿算法需要二维复向量的搜索,从而导致计算复杂度较高的问题,提出了两种逼近ML算法性能的补偿算法,即一维实向量迭代搜索算法和二维实向量迭代搜索算法,它们通过在空间中迭代搜索一维或二维实向量来降低计算复杂度.仿真结果表明,上述改进的亚ML补偿算法的性能优于现有的频域和时域最小二乘补偿方法,逼近ML算法,其计算复杂度明显低于传统的ML算法,误比特性能与ML算法相当.     

一种简单的计算机零位光栅设计方法

光栅扭矩传感器采用零位光栅提供绝对零位信号，以防止掉电时数据出错。在零位光栅设计过程中，采用了阈值法，即采用计算机随机产生栅线序列，经计算通过阈值判断以获得所需要的零位栅线序列。该方法可以大大减小编程的复杂性及难度，减小编程量，同时保证设计结果具有光通量大和对比度高的特点，并能满足实际应用的需要。     

基于小波计算的平面物体射影不变性的识别

利用非均匀有理B样条从单幅图像中提取平面物体在射影变换下的几何不变特征,建立经典框架.讨论用小波计算框架的一维和二维特征不变矩的方法以减少计算量.实验结果表明所选取的特征不变量和算法有较小的计算量,对二维平面物体的识别有很好的性能,特别是允许景物中有部分的遮挡物存在.     

基于小波计算的平面物体射影不变性的识别

利用非均匀有理B样条从单幅图像中提取平面物体在射影变换下的几何不变特征,建立经典框架.讨论用小波计算框架的一维和二维特征不变矩的方法以减少计算量.实验结果表明所选取的特征不变量和算法有较小的计算量,对二维平面物体的识别有很好的性能,特别是允许景物中有部分的遮挡物存在.     

基于小波计算的平面物体射影不变性的识别

利用非均匀有理B样条从单幅图像中提取平面物体在射影变换下的几何不变特征,建立经典框架。讨沦用小波计算框架的一维和二维特征不变矩的方法以减少计算量。实验结果表明所选取的特征不变量和算法有较小的计算量,对二维平面物体的识别有很好的性能,特别是允许景物中有部分的遮挡物存在。     

同轴腔高功率多注速调管注-波互作用系统的模拟设计

以同轴腔高功率多注速调管为研究对象,以大信号程序KLY及PIC粒子模拟软件对其多电子注-波互作用系统开展了一维初始设计、二维等效设计及全三维模拟设计.通过采用二次谐波腔技术及参数优化,使同轴腔注-波互作用系统达到了70％以上的计算效率.与传统长漂移管方案注-波互作用系统相比,二次谐波腔方案不仅可以获得较高的注-波互作用效率,并且其系统长度可比传统方案缩短35％,有利于器件小型化.文中给出了以单通道圆柱腔代替多通道同轴腔的注-波互作用系统二维等效快速计算方法,与一维及三维计算结果的对比表明,这种方法具有较高的计算精度.     

平面阵波束形成算法效率比较

二维平面阵声呐系统所采用的阵元个数、形成波束的数量都较一维线阵声呐系统高一个数量级,数据处理量巨大,对信号处理机的实时处理能力要求非常高。如何提高二维波束形成算法的效率是工程实现二维平面阵声呐系统的关键,本文讨论了三种二维平面阵波束形成算法,并对这三种算法进行了计算效率和波束性能的对比。     

快速反射镜系统用光栅测微仪

为了精确控制FSM系统中平面反射镜的偏转角度,研制了专用型光栅测微仪对其进行位置测量,以实现系统的闭环控制.在明确了FSM系统对测微仪应用需求的基础上,根据其技术原理,对光栅测微仪的小型滑轨、标尺光栅图案、指示光栅图案、绝对零位编码、指示光栅移相以及接触探头分别进行了设计与选择.经精密加工、装配、调试后,所得光栅测微仪...     

Comparison of antireflection surfaces based on two-dimensional binary gratings and thin-film coatings

A comparison of antireflection surfaces based on the two-dimensional binary gratings and thin-film coatings is presented. First, a two-dimensional hybrid binary grating is proposed and analyzed by use of a vector-based implementation of the rigorous coupled-wave analysis method. The optimum parameters of the structure are determined and the effects that changing them have on spectral characteristics of the structure are studied. Then this structure is compared with multilayer thin-film antireflection filters. These filters are designed by genetic algorithm and needle methods, which are powerful methods for multilayer filter design. The comparison results show that the sensitivity of the grating to changes in the incident wavelength is high. However, a reflectance of the order of 10(-3)% at the design wavelength can be achieved. The sensitivity of designed antireflection thin-film filters to wavelength changes is lower, however, and the minimum achievable reflectance is higher.     

Rate allocation for serial concatenated convolutional codes

The paper proposes an analytical method to solve the rate allocation problem in serial concatenated convolutional codes (SCCCs). The goal is to find the best rate allocation between the inner and the outer constituent convolutional codes of an SCCC for constant overall code rate, interleaver size and complexity. Simulation results are shown in the paper to demonstrate the optimum and superior design criteria. In addition, the `density evolution' model is shown to verify the proposed rate allocation method, while indicating that a high rate inner code should not be used for SCCCs. Finally, it is also shown that the upper bounds on BER of ML decoded SCCCs do not provide good design criteria for allocating the rate in iteratively decoded SCCCs     

Bandwidth-efficient code design for coordinate interleaved coded cooperation

A two-user coordinate interleaved coded cooperation scheme is proposed for quasi-static Rayleigh fading channels, where cooperative and modulation diversity techniques are properly combined to take their full advantage. Two selective cooperation schemes are considered related to whether users know the cooperation case or not. Pairwise error probability (PEP) analysis is performed for all cooperation cases and code design criteria are derived from the PEP upper bounds. Bandwidth-efficient 4-, 8- and 16-state rate 2/4 cooperative quadrature phase shift keying (QPSK) trellis codes are obtained based on these criteria by means of exhaustive computer search. The error performances of the new codes evaluated by computer simulations show their superiority compared to the corresponding best space-time codes used in cooperation with coordinate interleaving. The simulation results are supported by an upper bound on the bit error probability developed using union bounding technique.     

Control of the freezing interface motion in two-dimensional solidification processes using the adjoint method

The aim of this work is to calculate the optimum history of boundary cooling conditions that, in two-dimensional conduction driven solidification processes, results in a desired history of the freezing interface location/motion. The freezing front velocity and heat flux on the solid side of the front, define the obtained solidification microstructure that can be selected such that desired macroscopic mechanical properties and soundness of the final cast product are achieved. The so-called two-dimensional inverse Stefan design problem is formulated as an infinite-dimensional minimization problem. The adjoint method is developed in conjunction with the conjugate gradient method for the solution of this minimization problem. The sensitivity and adjoint equations are derived in a moving domain. The gradient of the cost functional is obtained by solving the adjoint equations backward in time. The sensitivity equations are solved forward in time to compute the optimal step size for the gradient method. Two-dimensional numerical examples are analysed to demonstrate the performance of the present method.     

Nondestructive evaluation of delaminations in fresco plaster using transient infrared thermography

A transient method of thermal nondestructive testing is applied to detect subsurface delaminations in fresco plaster as a part of restoration work that is being conducted in Italy. A two-dimensional cylindrical model is used to estimate temperature distribution in materials with defects of various sizes and depths. The possibility of testing plaster with thickness up to 30 mm is illustrated. The choice of heating technique, which is supposed to be really nondestructive to ancient frescoes and powerful enough to create reasonable temperatures signals, is considered. Test duration and optimum sampling interval are discussed also. The structural noise of plaster and the influence of surface painting are investigated.     

两点沿曲面最短路径的遗传算法研究

求两点沿曲面最小距离的关键是正确选择两点间沿曲面的最短路径。遗传算法是一种全局性概率搜索算法。它在整个问题空间实施搜索,可得到问题的全局最优解,本文应用了遗传算法的理论与方法。首先,将整个曲面作为搜索空间,路径长度作为目标函数,设定了路径优化问题。其次,建立了椭圆坐标系,满足了遗传编码完备性的要求,实现了二维实数编码。运用排序选择方法,单一交叉和最小变异操作,完成了遗传算法,同时获得了最短路径。该方法适用于各种形式的曲面。     

Numerical analysis of two-dimensional compressible turbulent flows in a turbine stage

A numerical analysis based on the compressible Reynolds-averaged Navier-Stokes equation has been developed for the analysis of two-dimensional compressible turbulent flows in a turbine stage (nozzle and bucket). In the present flow analysis, governing equations are solved by the use of a time dependent explicit method and a two-equation model of turbulence is employed to estimate turbulence effects. To calculate nozzle and bucket flow fields simultaneously, a steady interaction between these flows is assumed. For spatial discretization of the governing equations, a control volume method combined with a body-fitted curvilinear coordinate system is developed to calculate the flows in arbitrarily shaped cascades. In order to assure the effectiveness of the present method, computations are carried out for a two-dimensional section at a blade midspan in a turbine stage. The method gives satisfactory results about boundary layers on blade surfaces, nozzle wake profiles and pitchwise averaged turbine design parameters at each blade exit.     

Design and performance analysis of code families for multi-dimensional optical CDMA

A code design algorithm for application in multi-dimensional optical code division multiple access (MD-OCDMA) for asynchronous optical fibre communication is proposed. Two-dimensional (2D) wavelength-time or space-time OCDMA and three-dimensional (3D) space-wavelength-time OCDMA are subsets of MD-OCDMA. Some applications and the performance analysis of the algorithm in 2D multipulse per row codes and 3D multipulse per plane codes are shown. In the applications discussed, this design ensures a maximum cross-correlation of '1' between any two codes. The performance metrics studied are the probability of error due to multiple-access interference for different numbers of active users and optimum temporal length for different values of cardinality. The performance analysis shows that the proposed 2D design offers very low probability of error due to multiple-access interference at lower cardinality when compared with other 2D designs using equivalent code dimension. A comparison of the proposed 3D design with an existing 3D design shows better performance at lower cardinality. The 3D designs show better performance when compared with the 2D designs.     

Shape design sensitivity analysis and optimization of two-dimensional periodic thermal problems using BEM

 A general procedure to perform shape design sensitivity analysis for two-dimensional periodic thermal diffusion problems is developed using boundary integral equation formulation. The material derivative concept to describe shape variation is used. The temperature is decomposed into a steady state component and a perturbation component. The adjoint variable method is used by utilizing integral identities for each component. The primal and adjoint systems are solved by boundary element method. The sensitivity results compared with those by finite difference show good accuracy. The shape optimal design problem of a plunger model for the panel of a television bulb, which operates periodically, is solved as an example. Different objectives and amounts of heat flux allowed are studied. Corresponding optimum shapes of the cooling boundary of the plunger are obtained and discussed. Received 15 August 2001 / Accepted 28 February 2002     

Beam implementation in a nonorthogonal coordinate system: application to the scattering from random rough surfaces

The C method is known to be one of the most efficient and versatile tools established for modeling diffraction gratings. Its main advantage is the use of a coordinate system in which the boundary conditions apply naturally and are, ipso facto, greatly simplified. In the context of scattering from random rough surfaces, we propose an extension of this method in order to treat the problem of diffraction of an arbitrary incident beam from a perfectly conducting (PEC) rough surface. For that, we were led to revisit some numerical aspects that simplify the implementation and improve the resulting codes.