A parallel FFT accelerated transient field-circuit simulator

A novel fast electromagnetic field-circuit simulator that permits the full-wave modeling of transients in nonlinear microwave circuits is proposed. This time-domain simulator is composed of two components: 1) a full-wave solver that models interactions of electromagnetic fields with conducting surfaces and finite dielectric volumes by solving time-domain surface and volume electric field integral equations, respectively, and 2) a circuit solver that models field interactions with lumped circuits, which are potentially active and nonlinear, by solving Kirchoff's equations through modified nodal analysis. These field and circuit analysis components are consistently interfaced and the resulting coupled set of nonlinear equations is evolved in time by a multidimensional Newton-Raphson scheme. The solution procedure is accelerated by allocating field- and circuit-related computations across the processors of a distributed-memory cluster, which communicate using the message-passing interface standard. Furthermore, the electromagnetic field solver, whose demand for computational resources far outpaces that of the circuit solver, is accelerated by a fast Fourier transform (FFT)-based algorithm, viz. the time-domain adaptive integral method. The resulting parallel FFT accelerated transient field-circuit simulator is applied to the analysis of various active and nonlinear microwave circuits, including power-combining arrays.     

A unified discrete-time state-space model for switching converters

A unified nonlinear state-space model for arbitrary switching converters is presented, which uses discrete-time modeling of switches. Although its compact and powerful notation is valid for all types of switching circuits, perhaps its main application field is power electronics. The proposed model is valid for any electric circuit composed of ideal switches (externally or internally controlled), RLC elements and energy sources. Therefore, the model is general considering semiconductor devices as ideal switches, which are dealt with as discrete-time dynamic systems. Thus the developed model may be either a hybrid continuous-discrete-time one or a full discrete-time one. Moreover, this model is valid as a circuit simulator     

金属接触非线性引起的无源互调效应的数值分析

针对时域物理光学方法求解无源互调问题的局限性,提出基于"场路结合"的数值分析方法,建立非线性金属结的等效电路模型并将其引入到全波方法中,通过全波方法与等效电路相结合的方式来分析系统的无源互调干扰.计算实例表明,该方法可以精确地计算由于金属接触非线性引起的无源互调及其作为二次辐射源所激发的电磁场,避免了时域方法在电大尺寸问题上计算的积累误差以及只能对处于远场区的简单微波结构的无源互调效应进行求解的问题.本文提出的场路结合数值分析方法为微波部件无源互调效应的研究提供了新的思路与方法.     

A rate distortion theory lower bound on desired function filtering error (Corresp.)

A discrete-time nonlinear filtering lower bound algorithm is given for evaluating the error in a desired function of the state vector. The algorithm is based on a rate distortion bound derived previously by the author. The problem is formulated in terms of Monte Carlo analysis. The theory of backward Markovian models is used to evaluate the conditional expectation appearing in the Bucy representation for the ease of Gauss-Markov signal models. An approximation procedure is given for the case of nonlinear signal models. In comparison with the author's previous bound the bound algorithm obtained here is tighter and does not require the difficult computation of the entropy of the state vector.     

On the electromagnetic radiation of printed-circuit-board interconnections

Large ground and supply layers on interconnected boards represent a radiating antenna structure which may be efficiently excited at its resonances by small high-frequency potential differences. Such potential differences between the boards mainly originate from the inevitable inductive impedance of the signal-current return path in the connector, usually provided by ground pins. The presented modeling approach is based on an antenna transfer function for the global interconnecting structure and a partial-inductance equivalent circuit for the connector. As shown by the example of a motherboard-daughterboard structure, the model enables a systematic study of the radiation mechanism, depending on signal/ground-pin configuration, as well as geometrical and electrical parameters. In conjunction with SPICE simulations of the connector equivalent circuit, the signal driver and receiver dynamic characteristic can also be properly included. Validation is provided by full-wave simulation and measurement results.     

A Discrete-Time Model of Electrcally Stimulated Muscle

A model describing the input/output properties of electrically stimulated isometric muscle is developed and experimentally tested. A discrete-time model gives the force output at the times of stimulation during pulse width modulation of recruitment at fixed stimulus amplitudes and periods. Two elements are necessary in the model: a static nonlinear element followed by a linear dynamic element. The static nonlinearity describes the relationship between pulse width and steady-state force. The dynamic properties are described with less than 10 percent error by a second-order discrete-time deterministic autoregressive moving average (DARMA) model. Exponentially weighted recursive least squares methods allow efficient parameter estimation. Model parameters are found to vary systematically with muscle length and stimulus frequency. Tests comparing actual and simulated feedback control of electrically stimulated muscle indicate that the model is adequate for digital controller design for applications in functional electrical stimulation.     

T-S fuzzy controllers for nonlinear interconnected systems with multiple time delays

This paper investigates the effectiveness of a passive tuned mass damper (TMD) and fuzzy controller in reducing the structural responses subject to the external force. In general, TMD is good for linear systems. We proposed here an approach of Takagi-Sugeno (T-S) fuzzy controller to deal with the nonlinear system. To overcome the effect of modeling error between nonlinear multiple time-delay systems and T-S fuzzy models, a robustness design of fuzzy control via model-based approach is proposed in this paper. A stability criterion in terms of Lyapunov's direct method is derived to guarantee the stability of nonlinear multiple time-delay interconnected systems. Based on the decentralized control scheme and this criterion, a set of model-based fuzzy controllers is then synthesized via the technique of parallel distributed compensation (PDC) to stabilize the nonlinear multiple time-delay interconnected system and the H/sup /spl infin// control performance is achieved at the same time. Finally, the proposed methodology is illustrated by an example of a nonlinear TMD system.     

EMC-oriented full-wave modelling of passive MMIC structures for wireless applications

A class of full-wave models useful to tackle emc problems in passive mmic structures, as well as in conventional electronic circuitry, employed in wireless technology applications is presented. Upon using the appropriate dyadic Green’s function, the prediction of undesired emi effects, a widely addressed problem in high package-density modules, is performed by accounting for both electromagnetic coupling and surface/volume wave excitation. Particular efforts have been devoted to the simulation of circuits in realistic exciting/loading situations through the derivation of equivalent network representations. The resulting full-wave models allow an accurate prediction of possible emc problems in mmics already during the design stage, thus paving the way to low-cost solutions for emi reduction.     

On the quasi-TEM and full-wave approaches applied to coplanarmultistrip on lossy dielectric layered media

The characteristic parameters of coplanar multistrip lines embedded in multilayered lossless/lossy substrates are commonly computed by using either quasi-TEM or full-wave model. Several methods are provided in the literature to deal with this type of structure. A comparative study of quasi-TEM and rigorous solutions is carried out in order to establish criteria for the validity of the quasi-TEM approach. Reliable quasi-TEM and full-wave numerical data have been properly generated by applying an enhanced spectral domain analysis. The authors conclude that the quasi-TEM model yields satisfactory results for many MIC and MMIC practical cases. However, significant errors arise when high conductivity substrates are involved in MMIC applications. A discussion about the computation of the dynamic modal characteristic impedance is also reported, showing how the insertion of the modal orthogonality can save computational effort in a lossy multiport system     

Decentralized variable structure control of interconnected multi-input/ multi-output nonlinear systems

For a broad class of interconnected nonlinear systems, this paper develops a complete design methodology for decentralized variable structure control. Specifically, the paper sets forth design schemes for local switching surfaces and the related local switched feedback gains which together force the original nonlinear interconnected system to behave as a reduced order interconnected equivalent system having a desired response such as stability, tracking, or prespecified eigenvalues. Also developed is a numerical algorithm for constructing the switched local feedback gains. A simple nonlinear example illustrates the control strategy.     

Synchronization and input recovery in digital nonlinear systems

This paper is devoted to the simultaneous synchronization and input reconstruction in nonlinear discrete-time models. To deal with these, we propose an observer-based approach for two classes of dynamical systems that describe a large wide of nonlinear models. First, we consider the general case of nonlinear dynamics where the inputs to be reconstructed introduce nonlinearly into the model. The second class of systems considered here is composed of linear and nonlinear parts. Sufficient conditions for asymptotic convergence are derived from useful regular transformations. High performances, easiness of implementation, and robustness against disturbances will be shown through simulation results of some well-known nonlinear chaotic models.     

A full-wave modal analysis of arbitrarily shaped waveguidediscontinuities using the finite plane-wave series expansion

A full-wave electromagnetic model for analyzing waveguide discontinuities of arbitrarily shaped piecewise planar boundaries is presented. The analysis is facilitated by using the finite plane-wave series expansion of circular cylindrical modal functions. Since electromagnetic fields on each of the planar boundary surfaces of the inhomogeneous region are expressed in terms of plane-wave modal functions, the complete solution is carried out analytically without any numerical integration. To verify the formulation, a number of practical waveguide components are analyzed. The calculated results are compared with other full-wave electromagnetic models. Excellent agreement is obtained for all the cases     

Reliable $$H_{\infty }$$ Stabilization of Fuzzy Systems with Random Delay Via Nonlinear Retarded Control

In this paper, the robust reliable \(H_\infty \) control problem has been investigated for a class of nonlinear discrete-time TS fuzzy systems with random delay. In particular, the proposed fuzzy system consists of local nonlinear models with set of fuzzy rules, but the conventional TS fuzzy systems has local linear models. Our attention is focused on the design of a feedback reliable nonlinear retarded control law to ensure the robust asymptotic stability for nonlinear discrete-time TS fuzzy system with admissible uncertainties as well as actuator failure cases and random delay. In particular, by using an input delay approach, the random delay with stochastic parameters in the system matrices is introduced in the system model. Based on the Lyapunov approach, firstly, a sufficient condition for asymptotic stability is proposed for TS fuzzy systems in the presence of actuator failures. Then, a robust reliable \(H_\infty \) control is designed for the uncertain TS fuzzy system by solving a strict linear matrix inequalities using the available numerical software. Finally, a numerical example based on real-time ball and beam system is provided to validate the effectiveness of the proposed design technique.     

Design and Analysis of Millimeter-Wave Marchand Balun with Interconnected Transmission Line

This paper presents the design and analysis of general baluns of Marchand-type with a transmission line connected between two sections. A series of new expressions of S-parameters are derived for such type of Marchand balun. The relations between the length of interconnected transmission line and the imbalance of Marchand balun are discussed. By using analytical method, a millimeter-wave Marchand balun was designed and simulated by the full-wave electromagnetic software HFSS, and fabricated in 0.15 μm pHEMT GaAs process. The measurement results show that the balun achieves low insertion loss and good balance in the band of 24–40 GHz. The results are in good agreement with the simulated ones. The theoretical analysis is verified.     

Full wave physical models of nonspecular scattering in irregularstratified media

A physical interpretation is given of each term in the full-wave expansion of the vertically or horizontally polarized electromagnetic fields scattered by irregular stratified media. These solutions provide a basis for the construction of physical models of nonspecular scatter in complex, irregular, layered structures. The full wave solutions involve a pair of nonspecular reflection scattering coefficients and a pair of nonspecular transmission scattering coefficients that reduce to the familiar Fresnel reflection and transmission coefficients for the specular case. The full-wave solutions are shown to satisfy the reciprocity and duality relationships in electromagnetic theory, and they are invariant to coordinate transformations. The relationships between the full-wave solution, the high-frequency physical optics solution, and the low-frequency perturbation solution are demonstrated. The analysis is relevant to problems of communication in irregular stratified media and to problems of remote sensing     

Digital interval modeling and hybrid control of uncertain systems

This paper addresses two issues: (1) converting a continuous-time uncertain system to an equivalent discrete-time interval model; and (2) constructing a robust digital control law from a robust analogue control law for hybrid control of sampled-data uncertain systems. The system matrices characterizing the state-space representation of the original continuous-time uncertain systems are assumed to be interval matrices. The Pade approximation method together with a geometric-series approximation method is employed to obtain the generalized enclosing discrete-time interval models. The generalized enclosing interval models are able to tightly enclose the exact discrete-time uncertain model, and can be utilized for digital simulation and digital design of continuous-time uncertain systems. A new family of digitally redesigned interval controllers is constructed from a continuous-time robust controller for robust digital control of continuous-time uncertain systems. Using the newly digitally redesigned interval controllers, the dynamic states of the digitally controlled sampled-data uncertain systems are able to closely match those of the original analogously controlled continuous-time uncertain systems for a relatively longer sampling period     

Orthogonal approaches to time-series analysis and systemidentification

Some recent, efficient approaches to nonlinear system identification, ARMA modeling, and time-series analysis are described and illustrated. Sufficient detail and references are furnished to enable ready implementation, and examples are provided to demonstrate superiority over established classical techniques. The ARMA identification algorithm presented does not require a priori knowledge of, or assumptions about, the order of the system to be identified or signal to be modeled. A suboptimal, recursive, pairwise search of the orthogonal candidate data records is conducted, until a given least-squares criterion is satisfied. In the case of nonlinear systems modeling, discrete-time Volterra series is stressed, or rather a more efficient parallel-cascade approach. The model is constructed by adding parallel paths (each consisting of the cascade of dynamic linear and static nonlinear systems). In the case of time-series analysis, a non-Fourier sinusoidal series approach is stressed. The relevant frequencies are estimated by an orthogonal search procedure. A search of the candidate sinusoids is conducted until a given mean-square criterion is satisfied     

Calculation and stability investigation of periodic steady states of the voltage controlled Buck DC-DC converter

A new method for investigating the complex dc-dc converters dynamics is suggested in this paper. The method is based on the formulation of a nonlinear difference equation with respect to the duty cycle. This equation embodies the nonlinear and discrete-time characteristics of dc-dc converters and allows both the calculation of normal and subharmonic steady states and their local stability analysis. The method is presented through the analysis of a voltage controlled Buck dc-dc converter.     

Characterization of strip-fed cavity-backed slots

The use of strip-fed cavity-backed slots is an attractive approach for compact conformal antenna arrays. This configuration also offers greater potential than traditional designs for additional antenna functions demanded by high-performance system requirements. As with previous approaches, it is desirable to avoid costly, time-consuming empirical design techniques, which in turn requires highly accurate analytic/numerical models. A full-wave integral equation analysis is presented, which by using the dyadic Green's functions for multilayered substrates, models this array element with a high degree of accuracy. Using a previously presented Green's function for a grounded slab, the analysis also accounts for dielectric-covered slots. Comparisons are made with measurements to validate the results