An algorithm for successive identification of reflections

A new algorithm for successive identification of seismic reflections is proposed. Generally, the algorithm can be viewed as a curve matching method for images with specific structure. However, in the paper, the algorithm works on seismic signals assembled to constitute an image in which the investigated reflections produce curves. In numerical examples, the authors work on signals assembled in CMP gathers. The key idea of the algorithm is to estimate the reflection curve parameters and the reflection coefficients along these curves by combining the multipulse technique and the generalized Radon transform. The multipulse technique is used for wavelet identification in each trace, and the generalized Radon transform is used to coordinate the wavelet identification between the individual traces. Furthermore, a stop criterion and a reflection validation procedure are presented. The stop criterion stops the reflection estimation when the actual estimated reflection is insignificant. The reflection validation procedure ensures that the estimated reflections follow the shape of the investigated reflection curves. The algorithm is successfully used in two numerical examples. One is based on a synthetic CMP gather, whereas the other is based on a real recorded CMP gather. Initially, the algorithm requires an estimate of the wavelet that can be performed by any wavelet estimation method.     

Parameter extraction and correction for transmission lines anddiscontinuities using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is useful for performing broadband characterization of uniform transmission lines and discontinuities. Modeling a geometry often requires the implementation of an absorbing boundary condition (ABC). When this is the case, numerical reflections from the ABC's will add significant error to the calculated transmission line or scattering (S) parameters. This paper introduces a simple post-processing algorithm for extracting these parameters and correcting for numerical reflection error. Furthermore, this method is shown to have a unique relationship to Prony's method. Practical application and limitations of this technique are also discussed. Finally, the impedance and propagation constant of a microstrip line are calculated using this method     

Determination of reflection coefficient due to a parallel admittance across a matched transmission line using an unmatched line

A simple and straightforward method of determining reflection coefficient and VSWR due to a parallel admittance across a matched transmission line using an unmatched realistic line is introduced. This approach also predicts reflections and VSWR of the unmatched line when the shunt admittance is removed completely.     

Reflection of pulses in a nonlinear random medium with strong fluctuations

The reflection of delta pulses from a strongly fluctuating nonlinear random medium is studied. With the use of the equation of a backscattered field obtained by the invariant imbedding method, a numerical algorithm is developed for solving the one-dimensional direct and inverse problems of wave reflection in time representation. The solutions obtained can be used for investigation of the fluctuation-related features of reflections occurring in nonlinear random media and in the design of remote sensing methods. The conditions that give rise to wave stochastic resonance and dynamic effects in nonlinear random reflections are considered.     

有限周期频率选择面的电磁特性分析

从工程测量技术出发提出了一种有限尺寸频率选择表面反射系数和透射系数的数值计算方式,同时使用矩量法及多层快速多极子方法进行了数值仿真.仿真结果表明这一计算方式是可行并可靠的.     

A novel propagation modeling for microcellular communications inurban environments

A novel method for microcellular communications to predict propagation characteristics is presented in this paper. It takes into account multiple reflections among walls, ground, vehicles, as well as the transmission/reflection due to groups of trees. Although these are three-dimensional (3-D) problems, we can combine two-dimensional (2-D) ray tracing and simple 3-D geometric considerations to solve them in a very efficient way. We have investigated the propagation loss versus size, number, and locations of vehicles and groups of trees on a safe island. Our results show that the radio wave propagation exhibits severe fast fading, attenuation, and blockage due to reflection, transmission, and shadowing, respectively     

An efficient solution for the response of electrical well loggingtools in a complex environment

A symmetrical form of the solution for an electrical source in a multibed well-logging environment is derived. The method uses local reflection and transmission operators of a single-bed boundary and a general recursive algorithm to derive generalized reflection and transmission operators. Using this method, the computation time scales linearly as N, where N is the number of beds in the environment. A computer program was developed to implement the solution. The program is robust and generates accurate results from 20 kHz to 25 MHz     

Permittivity determination using amplitudes of transmission andreflection coefficients at microwave frequency

A new method is proposed in this paper to determine the permittivity of materials. The general consideration is to use only the amplitudes of the transmission and reflection coefficients to do the permittivity determination. According to the analysis, the permittivity can be uniquely determined by measuring these two amplitudes when a sample is prepared with large enough attenuation that the multiple reflections between the two surfaces of the sample can be neglected. The validity of the method was proven by experiments. Using the method, the instantaneous and noncontacting measurements of the amplitudes can be realized. Thus, the dynamic measurement of the permittivity becomes possible     

电路设计中的信号完整性分析和研究

随着半导体技术的不断发展,集成电路工作频率的提高,信号完整性问题变得无处不在,对电路稳定性影响巨大。文章详细阐述了信号完整性问题的三个部分:反射、串扰和电源系统完整性产生原理,并总结出了相应的设计规则。对传输线反射、串扰问题产生机理和减小反射、串扰设计方法进行了仿真。结果表明在高速电路设计中采用基于信号完整性的规则是可行的,也是必要的。     

适于多种反射现象的光照估计方法

增强现实技术是将虚拟物体叠加到真实环境中,为了使虚拟物体更逼真地融入到环境,就需要估计场景中的真实光照。文中针对同时存在漫反射和镜面反射的场景或只存在漫反射的场景,提出了一种适于多种反射现象的光照估计方法。该方法使用相机拍摄多幅视角图像,通过检测每幅视角图像的镜面高光点来识别场景中是否存在镜面反射。若不存在镜面反射,则采用单张漫反射图像估计光照算法进行多幅视角图像光照估计。反之,若存在镜面反射则以镜面反射提供的信息为先验知识,再结合漫反射光照估计方法得到最终的光照估计结果。实验结果表明,文中方法提高了多种反射现象的光照估计的准确性。     

A new driver circuit for chip-to-chip signal transmission in Josephson packaging

A new driver circuit is developed for chip-to-chip logic signal transmission in Josephson computers. Multiple reflection noises between driver and connector impedance discontinuities may cause false logic operations in the driver and receiver circuits. Based on this factor, the driver is designed to match the impedance between the driver and transmission line in order to reduce multiple reflections. Since the noises due to the first reflections remain in this driver system, its use is limited to special cases. When used in these cases, however, the driver provides a shorter transmission path delay than Klein's driver. Experimentation shows that the driver has perfect impedance matching effects within a wide bias current margin (±26 percent).     

透射光谱法测光栅参数的可行性

利用透射光谱,结合正单纯形法来反演折射率调制光栅参数,首先利用光栅衍射傅里叶模式理论及RTCM算法得出在200nm~900nm波长范围内的透射光谱曲线,从上取5个点,作为理论计算值; 其次,在上述曲线上加入偏差不同的高斯噪声,以模拟透射光谱的测量曲线,再从每条曲线上各取5个对应点,获取模拟测量值;然后,假定光栅参数的初始值,代入评价函数,用正单纯形法不断进行迭代反演,得到光栅参数的计算模拟结果。此方法简单、快速、精确。     

Reflection of VLF radio waves at a junction in the Earth-ionospherewaveguide

The conditions for the neglect of reflection of VLF modes incident on a junction between the daytime and nighttime Earth-ionosphere waveguides are considered. It is shown that reflections are indeed small but some interesting and possibly significant exceptions may occur at highly oblique incidence. In fact, total reflection may take place for night-to-day transmission at angles within several degrees of grazing. The same analytical model is also relevant to oblique transmission across a flat lying coast line     

A Microwave Method for Noniterative Constitutive Parameters Determination of Thin Low-Loss or Lossy Materials

A noniterative transmission-reflection method is proposed for instant measurement of constitutive parameters of thin samples attached to a sample holder. It uses reflection-only measurements for constitutive parameters determination thanks to the asymmetric nature of the structure (holder sample). In addition, the method can also measure the complex permittivity of the sample holder from transmission and reflection measurements. The disadvantage of the method, however, is that it requires different reflection-only measurements, and hence, a suitable selection of holder thickness and permittivity combination. In case similar reflection properties of the structure are measured, the noniteratively measured constitutive parameters by the proposed method can be utilized as an initial guess in a search algorithm, which uses transmission and reflection measurements. In this way, the proposed method provides a suitable initial guess for electrical properties of materials under test with no prior information.      

Time domain analysis of transient propagation in inhomogeneous magnetized plasma using Z-transforms

The electromagnetic propagation through an inhomogeneous magnetized plasma slab is studied using the Z-transform formulation of the Finite-Difference Time-Domain（FDTD） method. The direction of electromagnetic propagation is parallel to the biasing magnetic filed. To validate the Z-transform algorithm, the reflection and transmission coefficients for the right-hand circularly polarized wave of the homogeneous magnetized plasma slab are computed by means of discrete Fourier transform. The comparison between the reflection and transmission coefficients of the homogeneous plasma slab and analytical values indicates that Z-transform algorithm is very accurate. When the plasma frequency varies according to the square root and parabolic relations, the reflection and transmission coefficients of the inhomogeneous magnetized plasma slab are computed.     

C2动态相位估计的偏差补偿算法——雷达低空目标俯仰角测量提取的研究与应用

由于多径回波信号的干扰,极大地影响了雷达对低空目标俯仰角的测量,且对低空目标俯仰角的闭环跟踪测量实现极为困难,通常采用偏轴跟踪技术。通过对多路径反射环境模型分析,同时考虑镜面反射和漫反射的干扰,得出了岸、海基单脉冲雷达低空目标跟踪时俯仰角测量误差的产生原因,将传统的多目标分辨算法(C~2算法)与偏差补偿技术相结合应用于低角多径环境下偏轴跟踪目标俯仰角的测量,由C~2算法代替偏差补偿算法的航迹滤波并且动态估计直射和反射路径的相位差,然后对单脉冲比进行补偿,弥补两种算法各自的不足。在给定的测量环境下对不同高度目标进行了仿真,得到良好的仿真结果,表明C~2动态相位估计的偏差补偿算法,可较大地提高低空目标偏轴跟踪俯仰角的测量精度。并将其应用于某次试验中对掠海巡航飞行目标俯仰角的事后提取,与雷达实时输出的俯仰角测量数据相对比,验证了该算法的有效性和可实施性。     

Reflection properties of multimode interference devices

We report on the reflection properties of multimode interference (MMI) devices: we distinguish between reflection back into the input waveguides and internal resonance modes due to the occurrence of simultaneous self-images. Because of self-imaging, reflection can be extremely efficient, even in the case of MMI devices with optimized transmission. This conclusion is confirmed by the observed spectral behavior of InP-based ring lasers incorporating MMI 3 dB couplers and MMI power splitters. Several techniques are proposed to minimize the influence of these reflections     

An optimization approach to the frequency-domain inverse problemfor a nonuniform LCRG transmission line

The inverse problem for a nonuniform LCRG transmission line is considered in the frequency domain. Imbedding equations for the reflection and transmission coefficients are derived through the concept of wave-splitting. An optimization approach is applied to reconstruct the line parameters as functions of the position using band-limited reflection and/or transmission data. Exact and explicit expressions for the gradients are derived, and the reconstruction algorithm (based upon a conjugate gradient method) is tested with both clean and noisy data, The problem of the nonuniqueness is also discussed     

粒子群优化算法用于光纤布拉格光栅综合问题的研究

提出了一种新的光纤光栅综合技术,将光纤光栅的传输矩阵法与粒子群优化算法(PSO)结合起来,得到了一种光纤光栅综合问题的全新方法。通过调整粒子群优化算法的相关参数,我们可以得到适合需要的反射谱。与其它光栅综合算法相比,该方法具有简单,收敛速度快等优点,同时该技术具有普遍性,还可以用于其它类似的综合问题。     

行波折反射法在信号完整性的研究中的应用

近年来随着高速数字电子系统运行速度的不断增加,研究有损传输线的暂态过程已成为高速电路信号完整性分析的重要内容。行波折反射理论已被成功用于分析理想无损均匀传输线,如何运用该方法分析有损传输线有待进一步研究。本文将衰减因子引入行波折反射理论,分析有损均匀传输线暂态过程,计算结果准确,因此该方法是有效的。