Radiation Characteristics of Traveling-Wave Antennas Excited by Nonsinusoidal Currents

In this paper, the idea about traveling-wave antennas excited by nonsinusoidal currents for high-resolution exploration is advanced. First the analytic expressions of the radiation waveforms in the far zone produced by a single transient of current traveling along a straight wire are derived in time domain. Then the radiation characteristics of traveling-wave antennas excited by nonsinusoidal current, such as the mean-power pattern functions and the directivity, are given, and the space waveform control and radiation efficiency are discussed. Based on previous results, the radiation waveforms of dipole antennas excited by pulse current are obtained from time- domain analysis. In a practical example, comparing these waveforms with corresponding waveforms obtained from frequency-domain analysis and measured data in [4] and [13], good agreements are obtained in various radiation directions. Some errors in [14] are also pointed out and corrected.     

Suboptimal approximation/identification of transient waveforms from electromagnetic systems by pencil-of-function method

A noniterative method for approximating signals by a linear combination of exponentials is presented. Although the technique results in a suboptimal approximation, the continuous dependence of the suboptimal exponentssim{s}_{i}on the integral square errorepsilonis such that lim(epsilon = 0) sim{s}_{i} rightarrow {s}_{i}, the best least squares exponents. The method is also useful for system identification, where the system is modeled by a black box and one has access only to the input and output terminals. A technique is demonstrated for finding the multiple poles of a system along with the residues at the poles when the system output to a known input is given. Advantages of the method are natural insensitivity to noise in the data and a capability for approximately determining signal order. Representative computations are made of the poles from the transient response of a conducting pipe tested at the ATHAMAS-I EMP simulator.     

The singularity expansion method and its application to targetidentification

The singularity expansion method (SEM) for quantifying the transient electromagnetic (EM) scattering from targets illuminated by pulsed EM radiation is reviewed. SEM representations for both induced currents and scattered fields are presented. Natural-resonance-based target identification schemes, based upon the SEM, are described. Various techniques for the extraction of natural-resonance modes from measured transient response waveforms are reviewed. Particular attention is given to the aspect-independent (extinction) E-pulse and (single-mode) S-pulse discriminant waveforms which, when convolved with the late-time pulse response of a matched target, produce null or mono-mode responses, respectively, through natural-mode annihilation. Extensive experiment results for practical target models are included to validate the E-pulse target discrimination technique. Finally, anticipated future extensions and areas requiring additional research are identified     

A wavefront interpretation of the singularity expansion method

The singularity expansion method (SEM) represents transient scattering by superposition of damped oscillatory fields corresponding to the complex resonant frequencies of the scatterer. The series of these global wave fields, which encompass the scattering object as a whole, is slowly convergent at early observation times and even deficient at very early times when portions of the object are as yet unexcited. Thus, the resonance series representation must generally be augmented by an entire function in the complex frequency domain. The choice of the entire function is relatively arbitrary but affects the excitation coefficients, called coupling coefficients, of individual resonances and also the "turn-on" and "switch-on" times of the SEM series. Moreover, it contains essential (intrinsic) and nonessential (removable) portions which have been subjected to various interpretations. By formulating the transient problem in terms of traveling (progressing) incident, reflected and diffracted wavefronts, these constructs in the SEM can be interpreted in a precise and physical manner. Furthermore, the analysis clarifies the evolution of resonances as collective summations of multiple wavefront fields which are caused by successive reflections or diffractions at the surfaces and scattering centers comprising the object. By combining wavefronts and resonances self-consistently, one may construct a hybrid field that avoids the difficulties at early times in the SEM formulation. The systematic exploration of the interplay between wavefronts and resonances is facilitated through use of a flow diagram, as introduced in system theory. These concepts are developed in broad generality and are illustrated for two-dimensional scattering by various special configurations.     

Transient radiation from a linear antenna with nonreflecting resistive loading

The transient waveforms radiated by step voltage or Gaussian pulse excited resistively loaded linear antennas are investigated by numerical means. Current distributions on the harmonically excited antenna are obtained as functions of frequency and for different values of the loading. The transfer functions of the antenna and the spectral densities of the radiated waveforms are obtained as functions of frequency and the loading and for different directions in space. The time dependent radiated waveforms produced by the antenna are obtained by using the fast Fourier inversion technique. The effects of the various antenna parameters on the radiated waveforms are also investigated. Some of the results are compared with available approximate analytical results.     

Modeling the positive-feedback regenerative process of CMOS latchupby a positive transient pole method. I. theoretical derivation

A novel method to characterize the mechanism of positive-feedback regeneration in a p-n-p-n structure during CMOS latchup transition is developed. It is based on the derived time-varying transient poles in large-signal base-emitter voltages of the lumped equivalent circuit of a p-n-p-n structure. Through calculating the time-varying transient poles during CMOS latchup transition, if is found that there exists a transient pole to change from negative to positive and then this pole changes to negative again. A p-n-p-n structure, which has a stronger positive-feedback regeneration during turn-on transition, will lead to a larger positive transient pole. The time when the positive transient pole occurs during CMOS latchup transition is the time when the positive-feedback regeneration starts. By this positive transient pole, the positive-feedback regenerative process of CMOS latchup can be quantitatively characterized     

Deconvolution of the impulse response of a conducting sphere by the conjugate gradient method

An experimental technique for determining the impulse response of a conducting sphere has been presented. A method of exciting and recording transient waveforms scattered from conducting spheres of various sizes has been described and extensively tested. A modified conjugate-gradient method has been applied to the transient waveforms to determine the impulse response of the objects. It is shown that by proper weighting in computing the residual in the conjugate-gradient method the oscillation due to noise could be reduced. A recently developed data-processing technique has been applied to these impulse responses to obtain their spectra, which yield adequately the resonant frequencies of the objects.     

Shuttle Imaging Radar (SIR-B) Investigations of the Canadian Shield: Initial Report

Two of the 43 Shuttle Imaging Radar (SIR-B) experiments carried out from the 41-G shuttle mission in 1984 involved a 2600-km swath across the Canadian Shield, with the objectives of studying the structure of province boundaries and developing techniques for the geologic use of orbital radar. Despite degraded single incidence angle imagery resulting from system problems, valuable experience has been obtained with data over a test site near Bancroft, Ontario. It has been found that even subdued glaciated topography can be effectively imaged, variations in backscatter being caused by variations in local incidence angle rather than shadowing. It has been demonstrated that small incidence angles are more sensitive to topography than large angles. Backscatter is extremely sensitive to look direction, topographic features nearly normal to the illumination being highlighted, and those nearly parallel to it being suppressed. It is concluded that orbital radar can provide a valuable tool for geologic studies of the Canadian Shield and similar areas, if suitable look angles and at least two look directions can be utilized for each area.     

The analysis of multiple signal data

This paper discusses the automatic processing of data containing multiple signals. In particular, filters which modify their structures in order to recognize initially unknown waveforms in Gaussian noise and an unknown signal environment are investigated experimentally. The general structure, derived from decision theory, processes the data in nonlinear fashion and effectively sets up a narrow decision region about the estimate of the signal. The results demonstrate the possibility of using filters of the new type for automatically processing data although the relevant waveforms may be unknown {em a priori}.     

Analysis of the Transient State in a Series Circuit of the Class $$RL_{\beta }C_{\alpha }$$

Results of analysis of transient states in a series circuit of the class \({RL}_{\beta }{C}_{\alpha }\), supplied by an ideal voltage source, have been described in the paper. This circuit consists of a coil \({L}_{\beta }\) and a supercapacitor \({C}_{\alpha }\) described by fractional-order differential equations. A method for determining the current and voltage waveforms in the analyzed circuit, based on the decomposition of rational functions into partial fractions, has been described. This method allows to determine transient waveform shapes in the system for any kind of voltage excitation. Two cases of the problem solutions have been considered. The first case concerns a situation where poles of rational functions are real, and the second where rational functions have complex poles. Effective relations enabling the determination of transient waveforms in a closed form have been given. Analytical formulae describing transient state waveforms in the system for different types of voltage excitations: constant, monoharmonic, periodic and arbitrary being an element of a Hilbert space, have been determined, too. The obtained results have been illustrated by an example.     

Problems and solutions associated with Prony's method for processing transient data

Three difficulties associated with Prony's method are studied. These are the extension of the method to allow multiple poles, the development of techniques for determining the number of poles contained in the transient data, and the effects of noise in the data on the numerical procedures. Solutions to these difficulties are studied, and numerical samples are presented.     

Transient coupling analysis using the singularity expansion method

The problem of electromagnetic coupling between objects has been extensively studied within the context of continuous-wave (CW) signals. The problem of coupling between objects for transient excitation has not received as much attention. This paper addresses the problem of transient coupling using the singularity expansion method (SEM). Specifically, the proper physical interpretation of the SEM modes of a system of objects is discussed within the context of observed transient surface currents and scattered fields. It is seen that the SEM modes of the system of objects are global quantities and hence have no clear physical interpretation prior to times when global modes can be established. It is also apparent that the early-time response of the system can be expressed using the SEM modes of the individual objects for some time periods. These observations are important for the effective use of target identification schemes based on natural resonance phenomena in multiple target situations as well as the proper use of SEM in EMC coupling analyses     

Transient and frequency responses of systems with time delays

For systems containing time delays, root locus methods can locate any Laplace transform closed-loop poles. L'H?pital's rule is shown to give exact residue values for any of the infinity of closed-loop poles. The transient or frequency response can then be estimated from dominant poles and their residues.     

Multiple signal extraction by multiple interference attenuation in the presence of random noise in seismic array data

A vector of digital filters is derived for the multichannel processing of the signals acquired by an array of sensors with the objective of extracting multiple desired signals by the attenuation of multiple interferences and random noise. The signals and interferences are assumed to have arbitrary waveforms with no a priori knowledge of these waveforms. The time duration of the recorded array data is assumed to be long enough to incorporate all time delayed propagated waveforms at the sensors of the array. The derivation is for the general case of an arbitrary array geometric configuration and is not confined to the special case of a linear array of equispaced sensors. The rationale adopted in the derivation of the filters is to give first priority at each discrete frequency to passing the signals, a second priority to canceling the interferences, and a third priority to attenuating the random noise. This rationale well suits the case of seismic data that are dominantly corrupted by strong interferences rather than random noise. Solving a constrained minimization problem derives the vector of array filters. The computation of this vector requires the application of a powerful matrix decomposition technique for the detection of any redundant and/or inconsistent constraints at each discrete frequency. The simulation results demonstrate the extraction ability of the derived filters in both the multiple input single output and the multiple input multiple output processing schemes.     

Finding the site of origin and velocity of propagation in a short one-dimensional strand from two extracellular waveforms

In cardiac muscle times of excitation, the site of origin of excitation and propagation velocity usually are determined from the intrinsic deflections of a collection of extracellular waveforms. Separate waveforms are measured from each site for which an excitation time is to be found. Most of the information in each measured waveshape is discarded, even though waveshape features have been shown to be closely related to propagation characteristics. The objective of this paper is to examine the possibility of more fully utilizing all of the information in the extracellular waveform. Would a small number of measured waveforms, used more completely, be sufficient to find the site of origin, propagation velocity, and excitation times? A computer simulation of intra-and extracellular excitation along a one-dimensional cylindrical cardiac strand provided the framework for the evaluation. The dimensions and the-conductivity of the strand and the action potential shape were assumed known. Extracellular waveforms were simulated at 2 of 51 points on the strand and thereafter taken to be "measurements.?" The objectives were to calculate, from the "measured" waveforms, the site of origin of excitation (possibly anywhere along the strand), the speed of propagation, and the times of excitaion at all 51 points. Propagation speed was assumed constant, but of unknown magnitude, in both directions away from the site of excitation. Notable results of the study include correctly differentiating among different sequences of excitation having identical time differences between the intrinsic deflections of the two known extracellular waveforms.     

激光激发板状材料中超声导波的有限元数值模拟

材料表面吸收激光辐照的能量后，产生瞬态温度场，引起表面层的局部热膨胀，产生超声波沿不同方向传播。激光超声具有非接触、宽频带、多模态的特点，提供了材料的弹性性质和材料无损检测的有效手段。考虑激光作用过程中材料热物理参数随温度变化的特性，用有限元方法数值模拟激光在板状材料中激发瞬态温度场，建立热弹机制下超声导波的产生和传播的有限元模型。数值模拟的结果表明：材料中瞬态温度场分布在材料的表面层的非常小的区域，温升区域是产生超声的体源。分析近场和远场接收的超声导波的表面波形的传播特征，讨论激光输入参数和激光产生超声波特征之间的关系，为热弹条件下材料性能的激光超声检测提供了定量的基础。     

基于矩阵束方法的传输线系统瞬态响应分析

带有频变负载的传输线系统的瞬态响应分析是电磁兼容领域的一个重要内容,特别是对于频变负载网络较为复杂或内部结构不清晰的情况,其瞬态响应的分析较为困难。本文首先在采样频率点处对频变负载端口导纳进行测量或计算得到相应的采样导纳,并采用有理函数逼近的方式对端口导纳进行等效;之后采用矩阵束(MPM)方法求解出有理逼近函数所需的极点和留数,并将其代入到分段线性递归卷积(PLRC)技术中,实现传输线和频变负载连接点处电压的分段线性递归卷积表达;最后,结合传输线方程实现带有频变负载的传输线系统的瞬态响应分析,并通过2个算例对所提方法的性能进行验证。结果表明,所提方法在计算精确度上具有明显的优势。     

Estimation of the aortic pressure waveform and beat-to-beat relative cardiac output changes from multiple peripheral artery pressure waveforms

We introduce a patient- and time-specific technique to estimate the clinically more relevant aortic pressure (AP) waveform and beat-to-beat relative changes in cardiac output (CO) from multiple peripheral artery pressure (PAP) waveforms distorted by wave reflections. The basic idea of the technique is to first estimate the AP waveform by applying a new multichannel blind system identification method that we have developed (rather than the conventional generalized transfer function) to the PAP waveforms and then estimate the beat-to-beat proportional CO by fitting a Windkessel model to the estimated waveform in which wave distortion should be attenuated. We present an evaluation of the technique with respect to four swine datasets including simultaneous measurements of two peripheral AP waveforms, a reference AP waveform, and reference aortic flow probe CO during diverse hemodynamic interventions. Our results show an overall AP waveform error of 3.5 mmHg and an overall beat-to-beat CO error of 12.9% (after a single CO calibration in each animal). These estimation errors represent substantial improvements compared to those obtained with several alternative PAP waveform analysis techniques. With further successful testing, the new technique may ultimately be employed for automated and less invasive monitoring of central hemodynamics in various cardiovascular patients.     

Determination of the natural frequencies for conducting rectangularboxes

When the problem of the transient electromagnetic scattering from an object is researched by using the singularity expansion method (SEM), the natural frequencies (poles in complex s-plane) of the object are a very important parameter. It is very difficult to calculate the natural frequencies of three-dimensional scatterers. The natural frequencies of conducting rectangular boxes are determined originally and verified by other works. The degeneracy phenomenon of the poles due to the geometrical symmetry of the rectangular boxes and the distribution property of the pole in the complex s-plane are discussed