Chaos correlation optical time domain reflectometry

We propose a novel correlation optical time domain reflectometry (C-OTDR) of using broadband chaotic light. This reflectometry has the advantage over the conventional OTDR and the pseudorandom signal C-OTDR in range-independent spatial resolution. We employ a laser diode with feedback from a long fiber ring cavity as the source of chaotic probe light. Experimental and numerical studies show that the chaotic light has broad and flat spectrum, and excellent correlation properties. Using this broadband chaotic...     

Modeling and analysis of radio frequency connector degradation using time domain reflectometry technique

Radio frequency (RF) connectors play an important role in electronic and communication systems. Their reliability behavior directly affects the integrity of transmitted signals and degradation in the contact surface reduces reliability. In this work, a combination of experimental and theoretical analysis was used to investigate the effects of contact interface degradation in RF connectors using time domain reflectometry (TDR), and the TDR analysis technique had been employed to identify the faulty position. A series of experiments was conducted to measure the reflected voltages using a network analyzer for time domain analysis and the position of the degraded contact surface was identified. An equivalent circuit model was developed, and the failure mechanism analyzed. It was found that when the connector initially degrades, the inductive characteristics increase. As further degradation occurs, the inductive characteristic will decrease, and the resistance characteristics will become more significant. The simulation and experimental results show good consistency each other. The contact degradation process of RF connector and TDR variations under different degradation levels were performed from the perspective of the time domain.     

便携式时域反射仪硬件系统设计

介绍了用于土壤参数测量的时域反射仪硬件系统的设计与实现方案,并研制出样机TDR-I。该样机使用DSP做主控板,利用阶跃恢复二极管(SRD)产生140ps上升沿的快沿发射脉冲,采用快慢斜波比较法获得等效采样步进精度为8.7ps的取样脉冲。经过实验数据获取验证,该系统测量效果良好。     

基于相干检测的偏振光时域反射光纤振动传感系统

提出将相干检测技术和偏振光时域反射技术POTDR(Polarization Optical Time Domain Reflectometry)相结合,利用相干检测技术的高探测灵敏度和偏振光时域反射技术中偏振态对外界环境敏感的特点,实现光纤分布式传感,测量微弱振动信号并实现定位功能.首先分别介绍了相干检测技术及其与POTDR相结合的相关原理,分析可行性,然后提出实验测试方案并搭建了测试系统.实验结果表明,基于相干检测技术的POTDR传感系统能成功地实现振动信号的探测和振动点的定位功能,这对于光纤分布式传感系统的进一步发展具有重要意义.     

Finite difference time domain analysis of extended composite right/left‐handed transmission line equations

In this article, a set of differential equations to model the behavior of the extended composite right/left handed transmission line in time domain is proposed. These equations are solved by an explicit finite difference time domain algorithm. To investigate the numerical stability of the proposed algorithm, the amplification matrix is extracted. The results of the proposed algorithm are confirmed by the results of the Agilent ADS commercial software. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:68–76, 2014.     

二维光子晶体传输特性的时域精细积分法

本文研究了二维光子晶体的时域精细积分法,并对其精度、效率、以及稳定性进行分析.从麦克斯韦方程的微分形式出发,利用Yee元胞将空间微分算子近似为差分算子,结合边界条件及激励源的表达式得到一组关于时间的常微分方程.对时间进行精细划分,使用精细积分算法求解常微分方程组.结合通解与激励源的特解得到光子晶体两端的反射场及透射场分布,进而通过傅里叶变换求得二维光子晶体的传输特性.数值算例表明,本文方法具有准确、稳定、高效的特点.     

Feedback sensitivity functions analysis of finite‐time stabilizing control system

This paper presents feedback sensitivity functions analysis of implicit Lyapunov function‐based control system in case of finite‐time stabilization problem. The Gang of Four is chosen as a feedback sensitivity tool. The results can be used for parametric tuning of control algorithms in order to guarantee desired closed‐loop sensitivity specifications. The obtained results are supported by numerical examples. Copyright © 2016 John Wiley & Sons, Ltd.     

Solving time domain microwave imaging for two‐dimensional inhomogeneous dielectric cylinder

This article presents the studies of time domain inverse scattering for a two‐dimensional (2D) inhomogeneous dielectric cylinder buried in a slab medium by the asynchronous particle swarm optimization (APSO) and dynamic differential evolution (DDE) method. The method of finite‐difference time‐domain is employed for the analysis of the forward scattering part, while the inverse scattering problem is transformed into optimization one. The DDE algorithm and the APSO are applied to reconstruct the permittivities distribution of a 2D inhomogeneous dielectric cylinder. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise. Numerical results indicate that the APSO algorithm outperforms the DDE in terms of reconstruction accuracy and convergence speed. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:147–154, 2014.     

Terahertz free‐space dielectric property measurements using time‐ and frequency‐domain setups

Based on a simple and effective calculation method, two free‐space measurement setups are employed to investigate the dielectric properties of various materials at terahertz (THz) frequencies. One setup involves THZ time‐domain spectroscopy (THz‐TDS) at a frequency range of 0.4 to 1 THz. The other setup comprises a vector network analyzer (VNA) with pairs of VAN extenders (VNAXs) and diagonal standard gain horns (SGHs) at a frequency range of 0.22 to 1.1 THz. The calculation method is verified for the THz‐TDS system and employed in the VNA system for the first time. Dielectric properties, including refractive indices, power absorption coefficients, relative permittivities, and loss tangents, are calculated from measured transmission data. Several materials, including printed circuit boards and 3D printing materials, are characterized to verify the calculation method and compare the measurement setups.     

Regional stabilisation of polynomial non-linear systems using rational Lyapunov functions

In this article, we propose a new non-linear stabilisation approach based on the popular linear parameter-varying control techniques. The regional state-feedback control problem of polynomial non-linear systems will be studied using rational Lyapunov functions of states. By bounding the variation rates of each state, the domain of attraction will be embedded in the region specified by the non-linear vector field. As a result, the state-feedback stabilisation conditions will be formulated as a set of polynomial matrix inequalities and can be solved efficiently by sum-of-squares programming. The resulting Lyapunov matrix and state-feedback gains are typically state-dependent rational matrix functions. This approach is also extended to a class of output-dependent non-linear systems where the stabilising output-feedback controller can be synthesised using rational Lyapunov functions of outputs. Finally, several examples will be used to demonstrate the proposed stabilisation approach and clarify the effect of various choices of Lyapunov function forms and state constraints.     

Continuous‐time stable and unstable system modelling with orthonormal basis functions

In this paper, model sets for linear time‐invariant continuous‐time systems which are spanned by fixed‐pole orthonormal bases are investigated. The obtained model sets are shown to be complete in the Lebesque spaces L_p (1<p<∞) and in C, the space of complex‐valued functions that are continuous on the extended imaginary axis. The L_p norm error bounds for estimating systems in L_p by the partial sums of the Fourier series formed by the orthonormal functions are computed for the case 1<p<∞. Some inequalities on the 𝓁_p means of the Fourier coefficients are also derived. These results have application in estimation and model reduction of stable and unstable continuous‐time linear time‐invariant systems. A numerical example illustrates the use of the basis functions for the approximation of unstable infinite‐dimensional dynamics. Copyright © 2000 John Wiley & Sons, Ltd.     

Finite‐time stability of switched nonlinear time‐varying systems via indefinite Lyapunov functions

This note considers the problem of finite‐time stability (FTS) for switched nonlinear time‐varying systems. First, a relaxed condition is proposed to verify the FTS of nonlinear time‐varying systems by using an indefinite Lyapunov function. Then, the result obtained is extended to study the FTS of switched nonlinear time‐varying systems. Several relaxed conditions are given by using a common indefinite Lyapunov function and multiple indefinite Lyapunov functions. Moreover, the corresponding estimates on convergence regions and times of systems are also given. Comparing with the existing results, the conditions obtained allow the time derivative of Lyapunov functions of subsystems (or systems) to be indefinite and all subsystems to be not finite‐time stable or even unstable. Finally, a numerical example is given to illustrate the theoretical results.     

Fault estimation observer design for discrete‐time systems in finite‐frequency domain

This paper proposes a framework of fault estimation observer design in finite‐frequency domain for discrete‐time systems. First, under the multiconstrained idea, a full‐order fault estimation observer in finite‐frequency domain is designed to achieve fault estimation by using the generalized Kalman–Yakubovich–Popov lemma to reduce conservatism generated by the entire frequency domain. Then, a reduced‐order fault estimation observer is constructed, which results in a new fault estimator to realize fault estimation using current output information. Furthermore, by introducing slack variables, improved results on full‐order fault estimation observer and reduced‐order fault estimation observer design with finite‐frequency specifications are obtained such that different Lyapunov matrices can be separately designed for each constraint. Simulation results are presented to illustrate the advantages of the theoretic results obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Recursive state estimation for discrete‐time nonlinear systems with event‐triggered data transmission,norm‐bounded uncertainties and multiple missing measurements

In this paper, we consider the recursive state estimation problem for a class of discrete‐time nonlinear systems with event‐triggered data transmission, norm‐bounded uncertainties, and multiple missing measurements. The phenomenon of event‐triggered communication mechanism occurs only when the specified event‐triggering condition is violated, which leads to a reduction in the number of excessive signal transmissions in a network. A sequence of independent Bernoulli random variables is employed to model the multiple measurements missing in the transmission. The norm‐bounded uncertainties that could be considered as external disturbances which lie in a bounded set. The purpose of the addressed filtering problem is to obtain an optimal robust recursive filter in the minimum‐variance sense such that with the simultaneous presence of event‐triggered data transmission, norm‐bounded uncertainties, and multiple missing measurements; the filtering error is minimized at each sampling time. By solving two Riccati‐like difference equations, the filter gain is calculated recursively. Based on the stochastic analysis theory, it is proved that the estimation error is bounded under certain conditions. Finally, two numerical examples are presented to demonstrate the effectiveness of the proposed algorithm. Copyright © 2016 John Wiley & Sons, Ltd.     

Gain scheduled control for discrete‐time systems depending on bounded rate parameters

In this paper we consider a linear, discrete‐time system depending multi‐affinely on uncertain, real time‐varying parameters. A new sufficient condition for the stability of this class of systems, in terms of a feasibility problem involving linear matrix inequalities (LMIs), is obtained under the hypothesis that a bound on the rate of variation of the parameters is known. This condition, obtained by the aid of parameter dependent Lyapunov functions, obviously turns out to be less restrictive than that one obtained via the classical quadratic stability (QS) approach, which guarantees stability in presence of arbitrary time‐varying parameters. An important point is that the methodology proposed in this paper may result in being less conservative than the classical QS approach even in the absence of an explicit bound on the parameters rate of variation. Concerning the synthesis context, the design of a gain scheduled compensator based on the above approach is also proposed. It is shown that, if a suitable LMI problem is feasible, the solution of such problem allows to design an output feedback gain scheduled dynamic compensator in a controller‐observer form stabilizing the class of systems which is dealt with. The stability conditions are then extended to take into account L₂ performance requirements. Some numerical examples are carried out to show the effectiveness and to investigate the computational burden required by the proposed approach. Copyright © 2005 John Wiley & Sons, Ltd.     

Parametric modeling of microwave filter using combined MLS‐SVR and pole‐residue‐based transfer functions

In this article, an advanced technique is developed to combine multi‐output least‐squares support vector regression (MLS‐SVR) and pole‐residue‐based transfer function models for microwave filter parametric modeling. MLS‐SVR is trained to learn the relationship between the length of tuning screws and the pole/residues of the transfer function, where MLS‐SVR is an effective method to cope with the multi‐output case unlike the traditional approach. Traditional approach treats the different outputs separately in the multi‐output case and it cannot model the relation between different outputs. Another important element for modeling is feature parameters. Extracted feature parameters have an important influence on the accuracy of modeling. For the purpose of establishing a more accurate model, the complex system poles and residues from Y‐parameters are chosen as the outputs of modeling, which are obtained by vector fitting (VF). Then we give a solution to obtaining pole/residues extracted by VF when the filter is in high detuned. After the proposed modeling process, trained model can be used to provide an accurate and fast prediction of the behavior of microwave filter with the length of tuning screws as variables, and model the electromagnetic simulation (or actual) microwave filter tuning. The methodology is applied to a narrow band coaxial‐resonator filter modeling, and more accurate results are achieved compared with the other methods. An example is presented to illustrate the efficiency of the proposed method.     

Robust simulation of continuous‐time systems with rational dynamics

This paper concerns the simulation of a class of nonlinear continuous‐time systems under a set of initial conditions described by an ellipsoid. By getting inspiration from Lyapunov theory, we show that it is possible to derive a procedure allowing the computation of a bounding ellipsoidal envelope, which will enclose all the states that can be reached from the set of initial conditions. This numerical procedure is based on convex optimization, and it makes it possible to set a guaranteed hard bound on the evolution of the state of the system for all the possible initial conditions. At the end of the paper, we show an application of the method through an academic example. Copyright © 2016 John Wiley & Sons, Ltd.     

用MATLAB求取线性系统的时域性能指标

采用MATLAB编程求取线性系统的时域性能指标,用户只需从键盘上输入线性系统的传递函数的分子,分母多项式系数,就可以获得该系统的时域性能指标和阶跃响应图,使得时域性能指标的求取变得简单、容易、准确、应用实例验证了所设计的程序的有效性,该程序可用于线性系统的分析和设计。     

A new multilevels Huygens sub‐gridding finite difference time domain based on a tree structure and object oriented programming

In this article, an efficient sub‐gridding finite‐difference time‐domain is developed for the simulation of multiscaled electromagnetic problems. The proposed technique is based on using the Huygens surfaces for interfacing electromagnetic fields between different grids. The use of the Object Oriented Programming for modeling FDTD simulations facilitates the imbrication of multiple sub‐grids. That heightens the spatial ratio without affecting the accuracy and stability of the sub‐gridding technique. Spatiotemporal interpolation is used to evaluate the electromagnetic fields in Huygens surface location among the coarse grid. Results of numerical experiments prove that the use of imbricated sub‐grids and spatiotemporal interpolation in the Huygens sub‐gridding is more efficient than the use of a single sub‐grid with only spatial interpolation.