Numerical modeling of an enhanced very early time electromagnetic(VETEM) prototype system

In this paper, two numerical models are presented to simulate an enhanced very early time electromagnetic (VETEM) prototype system, which is used for buried-object detection and environmental problems. Usually, the VETEM system contains a transmitting loop antenna and a receiving loop antenna, which run on lossy ground to detect buried objects. In the first numerical model, the loop antennas are accurately analyzed using the method of moments (MoM) for wire antennas above or buried in lossy ground. Then, the conjugate gradient (CG) methods, with the use of the fast Fourier transform (FFT) or MoM, are applied to investigate the scattering from buried objects. Reflected and scattered magnetic fields are evaluated at the receiving loop to calculate the output electric current. However, the working frequency for the VETEM system is usually low and, hence, two magnetic dipoles are used to replace the transmitter and receiver in the second numerical model. Comparing these two models, the second one is simple, but only valid for low frequency or small loops, while the first modeling is more general. In this paper, all computations are performed in the frequency domain, and the FFT is used to obtain the time-domain responses. Numerical examples show that simulation results from these two models fit very well when the frequency ranges from 10 kHz to 10 MHz, and both results are close to the measured data     

An addendum to “Numerical modeling of an enhanced very earlytime electromagnetic (VETEM) prototype system”

For original paper see Cui et al. (IEEE Antennas and Propagation Magazine, vol.42, no.2, p.17-27, 2000 April). Cui et al. proposed two numerical models to simulate an enhanced very early time electromagnetic (VETEM) prototype system, used for buried-object detection and environmental problems. In the first model, the transmitting and receiving loop antennas were accurately analyzed using the method of moments (MoM), and then conjugate gradient (CG) methods with the fast Fourier transform (FFT) were utilized to investigate the scattering from buried conducting plates. In the second model, two magnetic dipoles were used to replace the transmitter and receiver, because the working frequency for the VETEM system is usually low. Both the theory and formulation were correct, and the simulation results for the primary magnetic field and the reflected magnetic field were accurate. We have compared the simulation results for the magnetic field reflected by a wire-conductor mesh on the ground with measured data. They fit very well. However, the scattered magnetic fields in the simulation results were inaccurate, because we did not use a sufficient number of iterations in the CG-FFT algorithm when the frequency was very low     

3-D imaging of large scale buried structure by 1-D inversion ofvery early time electromagnetic (VETEM) data

A simple and efficient method for large scale three-dimensional (3D) subsurface imaging of inhomogeneous background is presented. One-dimensional (1D) multifrequency distorted Born iterative method (DBIM) is employed in the inversion. Simulation results utilizing synthetic scattering data are given. Calibration of the very early time electromagnetic (VETEM) experimental waveforms is detailed along with major problems encountered in practice and their solutions. This discussion is followed by the results of a large scale application of the method to the experimental data provided by the VETEM system of the U.S. Geological Survey. The method is shown to have a computational complexity that is promising for on-site inversion     

Time-domain sensing of targets buried under a rough air-groundinterface

We consider plane wave time-domain scattering from a fixed target in the presence of a rough (random) surface with application to ground penetrating radar. The time-domain scattering data are computed via a two-dimensional (2-D) finite-difference time-domain (FDTD) algorithm. In addition to examining the statistics of the time-domain fields scattered from such a surface, we investigate subsurface target detection by employing a (commonly used) matched-filter detector. The results of such a detector are characterized by their receiver operating characteristic (ROC), which quantifies the probability of detection and probability of false alarm. Such ROC studies allow us to investigate fundamental assumptions in the matched-filter detector: that the target response is deterministic and the clutter signal stochastic, with the two signals treated as additive and independent     

InGaAsP planar buried heterostructure laser diode (PBH-LD) with very low threshold current

Using a new LPE growth technique, an InGaAsP/InP planar buried heterostructure laser diode (PBH-LD) has been realised in 1.3 and 1.5 ?m wavelength regions. As a result of the effective carrier confinement, CW threshold currents as low as 8.5 mA and 13 mA have been obtained in 1.3 and 1.5 ?m PHB-LDs, respectively, at room temperature.     

Detection of buried targets via active selection of labeled data: application to sensing subsurface UXO

When sensing subsurface targets, such as landmines and unexploded ordnance (UXO), the target signatures are typically a strong function of environmental and historical circumstances. Consequently, it is difficult to constitute a universal training set for design of detection or classification algorithms. In this paper, we develop an efficient procedure by which information-theoretic concepts are used to design the basis functions and training set, directly from the site-specific measured data. Specifically, assume that measured data (e.g., induction and/or magnetometer) are available from a given site, unlabeled in the sense that it is not known a priori whether a given signature is associated with a target or clutter. For N signatures, the data may be expressed as {x/sub i/,y/sub i/}/sub i=1,N/, where x/sub i/ is the measured data for buried object i, and y/sub i/ is the associated unknown binary label (target/nontarget). Let the N x/sub i/ define the set X. The algorithm works in four steps: 1) the Fisher information matrix is used to select a set of basis functions for the kernel-based algorithm, this step defining a set of n signatures B/sub n//spl sube/X that are most informative in characterizing the signature distribution of the site; 2) the Fisher information matrix is used again to define a small subset X/sub s//spl sube/X, composed of those x/sub i/ for which knowledge of the associated labels y/sub i/ would be most informative in defining the weights for the basis functions in B/sub n/; 3) the buried objects associated with the signatures in X/sub s/ are excavated, yielding the associated labels y/sub i/, represented by the set Y/sub s/; and 4) using B/sub n/,X/sub s/, and Y/sub s/, a kernel-based classifier is designed for use in classifying all remaining buried objects. This framework is discussed in detail, with example results presented for an actual buried-UXO site.     

上升段高超声速目标预警系统需求分析

为了应对日益增长的临近空间高超声速目标（Near Space Hypersonic Target,NSHT）威胁,急需建立相应的NSHT预警系统。从NSHT的特点出发分析防御上升段NSHT的优势及挑战,然后建立空基拦截模型,在充分考虑拦截武器杀伤距离、机动过载、飞行速度的限制下,分析上升段拦截NSHT对预警系统的需求。     

Ku-band long distance site-diversity (SD) Characteristics using new measuring system

This paper deals with the short (10 km) and long distance (300-1400 km) site-diversity (SD) characteristics by using a newly developed measuring system. In the proposed measuring system, six earth stations transmit 14-GHz band QPSK signals, and one measuring earth station receives 12-GHz band signals and processes them to determine SD characteristics. As a result, easy operation and maintenance, low-cost measuring system construction and highly accurate data have been obtained. By comparing those measured results with the SD joint probability approximation equation in ITU-R Rec.P.618-7, a good agreement can be obtained. Furthermore, the effect of typhoons on SD characteristics were measured.     

Detection of nonmetallic buried objects by a step frequency radar

An attempt was made to detect nonmetallic buried objects by means of a stepped frequency radar which uses the phase information of the returned UHF signal. After a brief discussion concerning the attenuation of the signal in the soil and the principle of operation it was demonstrated that the two 3-in ABS plastic drain pipes buried 35 cm deep in soil can be detected. The horizontal and vertical resolutions are 7 cm and 12.5 cm, respectively. The penetration is 70-90 cm.     

Characteristics of a new isolated p-well structure using thinepitaxy over the buried layer and trench isolation

An isolated p-well structure for deep-submicrometer BiCMOS LSIs is proposed. The structure consists of a retrograde p-well in an n-type thin epitaxial layer over an n⁺ buried layer, and trench isolation. Latchup characteristics in this CMOS structure and breakdown characteristics of the shallow p-well are studied on test devices. Excellent latchup immunity and sufficient voltage tolerance are obtained with a thin 1-μm epitaxial layer. A CMOS 1/8 dynamic-type frequency divider using this well structure functions properly up to 3.2 GHz at a 2-V supply voltage     

Design verification and testing of power supply system by using virtual prototype

This paper proposes a simulation approach to verify and test power supply system by using a virtual prototype before the hardware prototyping in a single simulation environment. By applying the proposed methodology, the designer can use the virtual prototype effectively by keeping a short simulation CPU time as well as catching most of the design problems.     

利用KPCA特征提取的Adaboost红外目标检测

针对传统红外目标检测算法中存在的不足,提出了一种基于核主成分分析(KPCA)特征提取的Adaboost分类器红外目标检测算法.首先,采用KPCA对目标训练样本进行特征提取,将背景训练样本和待检测样本在概率核空间中向目标样本特征量投影作为它们的特征量;然后,用目标和背景样本特征来训练Adaboost分类器;最后,用此分类...     

Detection of buried dielectric cavities using the finite-differencetime-domain method in conjunction with signal processing techniques

We address the problem of detecting low-dielectric contrast cavities buried deep in a lossy ground by using the finite-difference time-domain (FDTD) method in conjunction with signal processing techniques for extrapolation and object identification. It is well known that very low frequency probing is needed for deep penetration into the lossy ground, owing to a rapid decay of electromagnetic (EM) waves at higher frequencies. It is also recognized that numerical modeling using the FDTD method becomes very difficult, if not impossible, when the operating frequency becomes as low as 1 Hz. To circumvent this difficulty, we propose a hybrid approach in this paper that combines the FDTD method with signal processing techniques, e.g., rational function approximation and neural networks (NNs). Apart from the forward problem of modeling buried cavities, we also study the inverse scattering problem-that of estimating the depth of a buried object from the measured field values at the surface of the Earth or above. Numerical results for a buried prism are given to illustrate the application of the proposed technique     

Time-domain sensing of targets buried under a Gaussian,exponential, or fractal rough interface

The authors numerically examine subsurface sensing via an ultrawideband ground penetrating radar (GPR) system. The target is assumed to reside under a randomly rough air-ground interface and is illuminated by a pulsed plane wave. The underlying wave physics is addressed through application of the multiresolution time-domain (MRTD) algorithm. The scattered time-domain fields are parametrized as a random process and an optimal detection scheme is formulated, accounting for the clutter and target signature statistics. Detector performance is evaluated via receiver operating characteristics (ROCs) for variable sensor parameters (polarization and incident angle) and for several rough-surface statistical models     

Self-timed logic using Current-Sensing Completion Detection (CSCD)

This article proposes a completion-detection method for efficiently implementing Boolean functions as self-timed logic structures. Current-Sensing Completion Detection, CSCD, allows self-timed circuits to be designed using single-rail variable encoding (one signal wire per logic variable) and implemented in about the same silicon area as an equivalent synchronous implementation. Compared to dual-rail encoding methods, CSCD can reduce the number of signal wires and transistors used by approximately 50%. CSCD implementations improved performance over equivalent dual-rail designs because of: (1) reduced parasitic capacitance, (2) removal of spacer tokens in the data stream, and (3) computation state similarity of consecutive data variables. Several CSCD configurations are described and evaluated and transistor-level implementations are provided for comparison.     

Detection of mobile targets on the plane and in space using heterogeneous sensor networks

Detection of targets moving within a field of interest is a fundamental service Wireless Sensor Network (WSN) service. The WSN’s target detection performance is directly related to the placement of the sensors within the field of interest. In this paper, we address the problem of deterministic sensor deployment on the plane and in space, for the purpose of detecting mobile targets. We map the target detection problem to a line-set intersection problem and derive analytic expressions for the probability of detecting mobile targets. Compared to previous works, our mapping allows us to consider sensors with heterogeneous sensing capabilities, thus analyzing sensor networks that employ multiple sensing modalities. We show that the complexity of evaluating the target detection probability grows exponentially with the network size and, hence, derive appropriate lower and upper bounds. We also show that maximizing the lower bound on the probability for target detection on the plane and in space, is analogous to the problem of minimizing the average symbol error probability in two-dimensional and three-dimensional digital modulation schemes, respectively, over additive white Gaussian noise. These problems can be addressed using the circle packing problem for the plane, and the sphere packing problem for space. Using the analogy to digital modulation schemes, we derive sensor constellations from well known signal constellations with low average symbol error probability.

Application of a microgenetic algorithm (MGA) to the design ofbroadband microwave absorbers using multiple frequency selective surfacescreens buried in dielectrics

Over the years, frequency selective surfaces (FSSs) have found frequent use as radomes and spatial filters in both commercial and military applications. In the literature, the problem of synthesizing broadband microwave absorbers using multilayered dielectrics through the application of genetic algorithms (GAs) have been dealt with successfully. Spatial filters employing multiple, freestanding, FSS screens have been successfully designed by utilizing a domain-decomposed GA. We present a procedure for synthesizing broadband microwave absorbers by using multiple FSS screens buried in a dielectric composite. A binary coded microgenetic algorithm (MGA) is applied to optimize various parameters, viz., the thickness and relative permittivity of each dielectric layer; the FSS screen designs and materials; their x- and y-periodicities; and their placement within the dielectric composite. The result is a multilayer composite that provides maximum absorption of both transverse electric (TE) and transverse magnetic (TM) waves simultaneously for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite. While a single FSS screen is analyzed using the electric field integral equation (EFIE), multiple FSS screens are analyzed using the scattering matrix technique