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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date Sept. 2000

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Displaying Results 1 - 25 of 28
  • A note from the editor

    Publication Year: 2000 , Page(s): 1277
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  • James R. Wait - Remarkable scientist

    Publication Year: 2000 , Page(s): 1278 - 1286
    Cited by:  Papers (1)
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  • Introduction to special issue

    Publication Year: 2000 , Page(s): 1287 - 1288
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  • Low-grazing angle scattering from rough surfaces in a duct formed by a linear-square refractive index profile

    Publication Year: 2000 , Page(s): 1461 - 1474
    Cited by:  Papers (5)
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    The problem of rough surface scattering and propagation over rough terrain in a ducting environment has been receiving considerable attention in the literature. One popular method of modeling this problem is the parabolic wave equation (PWE) method. An alternative method is the boundary integral equation (BIE) method. The implementation of the BIE in inhomogeneous media (ducting environments) is not straightforward, however, since the Green's function for such a medium is not usually known. In this paper, a closed-form approximation of the Green's function for a two-dimensional (2-D) ducting environment formed by a linear-square refractive index profile is derived using asymptotic techniques. This Green's function greatly facilitates the use of the BIE approach to study low-grazing angle (LGA) rough surface scattering and propagation over rough surfaces in the aforementioned ducting environment. This paper demonstrates how the BIE method can model the combined effects of surface roughness and medium inhomogeneity in a very rigorous fashion. Furthermore, it illustrates its capability of accurately predicting scattering in all directions including backscattering. The boundary integral equation of interest is solved via the method of ordered multiple interactions (MOMI), which eliminates the requirements of matrix storage and inversion and, hence, allows the application of the BIE method to very long rough surfaces View full abstract»

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  • Radio wave propagation characteristics in lossy circular waveguides such as tunnels, mine shafts, and boreholes

    Publication Year: 2000 , Page(s): 1354 - 1366
    Cited by:  Papers (24)
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    We present the characteristics of radio propagation in a circular lossy waveguide whose walls are composed of earth soil materials with frequency-dependent properties. This type of structure is used to represent a radio link for an underground wireless communication channel such as a tunnel, mine shaft, or borehole. We present calculated results of the attenuation constant for various propagation modes in the soil waveguide structure for various soil constituents and moisture levels. Transverse field plots of the various modes for different soil types are also presented. Finally, it is shown that for small |k2a| (where k2 is the wavenumber in the soil and a is the radius of the waveguide) some modes in the waveguide disappear and a discussion of this behavior and how it relates to excitation problems is given View full abstract»

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  • Ray-density normalization for ray-optical wave propagation modeling in arbitrarily shaped tunnels

    Publication Year: 2000 , Page(s): 1316 - 1325
    Cited by:  Papers (27)
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    This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characteristics in highway or railway tunnels in the ultrahigh-frequency (UHF) range and above (>300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method requires multiple representatives of each physical EM wave at a time. The contribution of each ray to the total field at the receiver is determined by the proposed ray-density normalization (RBN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure at caustics. In contrast to existing techniques, the new approach does not use ray tubes or adaptive reception spheres. Consequently, it does not suffer their restrictions to planar geometries. Therefore, it allows one to predict the propagation of high-frequency EM waves in confined spaces with curved boundaries, like tunnels, with an adequate precision. The approach is verified theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models View full abstract»

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  • Laboratory models used in the investigation of radio wave propagation in irregular structures

    Publication Year: 2000 , Page(s): 1367 - 1375
    Cited by:  Papers (2)
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    A laboratory model first conceived by Wait (see IEEE Antennas Propagat. Mag., vol.40, p.7-24, 1998) to investigate radio wave propagation in the perturbed environment of the Earth-ionosphere waveguide is described. The construction of the laboratory model involves the exploitation of the following fundamental invariant properties of Maxwell's equations and the ability to physically simulate the appropriate boundary conditions including the Earth's curvature: (1) invariance of Maxwell's equations to size-wavelength transformations permits the scaling down in size of the Earth-ionosphere waveguide; (2) duality relationships between the electric and magnetic fields permits the representation of the azimuthally independent TMn,0 modes excited by vertical dipoles in the Earth ionosphere waveguide by the TE n,0 modes in rectangular waveguides; (3) a perfectly conducting magnetic wall (where the tangential component of the magnetic field vanishes) is simulated through the use of imaging techniques; (4) to account for dissipation in the ionosphere, an equivalent surface impedance boundary is simulated using a wall loading material with a specific thickness and complex permittivity; and (5) to simulate the Earth's curvature in the rectangular waveguide, an especially fabricated dielectric material with a prescribed permittivity height profile is used as the medium of propagation in the interior of the waveguide. All five of the above artifices have been employed in order to construct a scaled model of the Earth-ionosphere waveguide. However, one or a combination of them can be employed by researchers today to construct laboratory models from which controlled experimental data can be obtained to validate analytical and numerical solutions as well as to provide insights for novel approaches to solve difficult propagation problems View full abstract»

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  • A viable model for power focusing in a lossy cylinder

    Publication Year: 2000 , Page(s): 1485 - 1488
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    In this paper, we are interested in controlling the power dissipation within a homogeneous lossy cylinder of finite length when a field is applied to the surface of the cylinder. The fields are assumed to be independent of the azimuthal angle. To begin, a field which satisfies the required dissipation inside the cylinder is assumed on the axis of the lossy cylinder. An analytical evaluation of the continuous source on the surface of the cylinder can then be carried out. This is an inverse problem where the response is known and the source is to be determined. A realization of the continuous source (surface field) in terms of a discrete array is also given. Results are presented that show an excellent agreement between the actual continuous sources and the discrete array in producing the field on the axis of the lossy cylinder. In fact, a small number of slots (fifteen or less) produce accurate agreement for the required field on the axis of the cylinder. Bioelectromagnetics and hyperthermia treatment of cancer in cylindrical objects such as limbs and torsos is one potential application. Nondestructive testing of manufactured cylindrical products is another one where the energy is focused in a given region in the cylinder View full abstract»

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  • Prof. James R. Wait and mining production technology-an appreciation

    Publication Year: 2000 , Page(s): 1438 - 1441
    Cited by:  Papers (2)
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    Prof. James R. Wait (1951, 1953, 1967) examined electromagnetic (EM) wave propagation in many situations of interest to mining production, including propagation in tunnels, propagation along extended conductors such as cables and drill stems, and propagation in coal seams. This work remains relevant, both to the mining engineer interested in the EM environment of an operating mine and to the electrical engineer interested in verifying new computational techniques and in extending the scope of EM technology in mining production. Late work in EM focussing in a geological environment is relevant to “next generation” geophysical monitoring equipment View full abstract»

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  • On the convergence of a perturbation series solution for reflection from periodic rough surfaces

    Publication Year: 2000 , Page(s): 1489 - 1495
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    In 1977, Rosich and Wait (see Radio Science, vol.12, no.5, p.719-29, Sept./Oct. 1977) presented a general expression for a perturbation series solution to electromagnetic (EM) reflection from an imperfectly conducting periodic rough surface. This is the first known publication of such a general result. Although this expression was shown to be consistent with earlier published results, all questions concerning the convergence of the series were deferred. This paper takes a first step in addressing this oversight View full abstract»

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  • Modeling electromagnetic propagation in the Earth-ionosphere waveguide

    Publication Year: 2000 , Page(s): 1420 - 1429
    Cited by:  Papers (66)
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    The ionosphere plays a role in radio propagation that varies strongly with frequency. At extremely low frequency (ELF: 3-3000 Hz) and very low frequency (VLF: 3-30 kHz), the ground and the ionosphere are good electrical conductors and form a spherical Earth-ionosphere waveguide. Many giants of the electromagnetics (EMs) community studied ELF-VLF propagation in the Earth-ionosphere waveguide, a topic which was critically important for long-range communication and navigation systems. James R. Wait was undoubtedly the most prolific publisher in this field, starting in the 1950s and continuing well into the 1990s. Although it is an old problem, there are new scientific and practical applications that rely on accurate modeling of ELF-VLF propagation, including ionospheric remote sensing, lightning remote sensing, global climate monitoring, and even earthquake precursor detection. The theory of ELF-VLP propagation in the Earth-ionosphere waveguide is mature, but there remain many ways of actually performing propagation calculations. Most techniques are based on waveguide mode theory with either numerical or approximate analytical formulations, but direct finite-difference time-domain (FDTD) modeling is now also feasible. Furthermore, in either mode theory or FDTD, the ionospheric upper boundary can be treated with varying degrees of approximation. While these approximations are understood in a qualitative sense, it is difficult to assess in advance their applicability to a given propagation problem. With a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide, we investigate the accuracy of these approximations. We also show that fields from post-discharge ionospheric currents and from evanescent modes become important at lower ELF (≲500 Hz) over short distances (≲500 km). These fields are not easily modeled with mode theory, but are inherent in the FDTD formulation of the problem. In this way, the FDTD solution bridges the gap between analytical solutions for fields close to and far from the source View full abstract»

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  • The failure of “classic” perturbation theory at a rough Neumann boundary near grazing

    Publication Year: 2000 , Page(s): 1452 - 1460
    Cited by:  Papers (2)  |  Patents (1)
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    Rice's (1951) “classic” perturbation theory predicts an erroneous limit at grazing for vertically polarized plane wave scatter from an infinite perfectly conducting rough surface; likewise, the attendant result for the specularly reflected mode also fails at grazing. We show where and why in the system of perturbational equations this difficulty occurs. We then reformulate the perturbational approach to handle the low-incidence angle region for a one-dimensionally (1-D) rough Neumann boundary (vertical polarization from a perfectly conducting surface). The result for scattered fields vanishes in direct proportion to the incidence angle above grazing and the result for the normalized roughness-modified surface impedance becomes constant with angle near grazing. For completeness and comparison, we give results for the horizontal polarization at a Dirichlet boundary, where perturbation results encounter no difficulties. Scatter dependence on grazing angle is explained in terms of the “classic” perturbation result multiplied by a propagation factor to the cell. The latter includes the sum of the direct and specularly reflected waves at the surface. This quantity can be replaced by the appropriate surface-wave propagation factor for radiation from dipole antennas, thereby explaining the strong observed vertically polarized sea scatter at high frequency (HF) on and below the horizon View full abstract»

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  • Scattering from an ionized column in the Earth-ionosphere space

    Publication Year: 2000 , Page(s): 1496 - 1497
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    An extension of an earlier paper (see ibid., vol.39, p.1051-4, July 1991) on this subject is hereby developed to allow for the generalization of the Born approximation to account for eddy currents in the column. Also, the relevance to VLF sprites is pointed out; these are ionized columns extending from the cloud tops to the low ionosphere View full abstract»

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  • Petrophysics of magnetic dipole fields in an anisotropic earth

    Publication Year: 2000 , Page(s): 1376 - 1383
    Cited by:  Papers (5)
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    Measurement-while-drilling (MWD) resistivity log data are often acquired in highly deviated or horizontal holes. The loop sensors are located on the drill collar and are approximated as magnetic dipoles. The conductivity of the earth in the vertical direction σv and horizontal direction σh are almost always different. When an MWD resistivity tool enters a new bed, the response is compared with the precomputed logs to aid in the determination of the location of the drill bit. The MWD tool response, however, is sensitive to resistivity anisotropy. An alternative method is used to derive analytical expressions for the Sommerfeld-type integrals. Numerical results give typical MWD tool response as a function of the inclination angle θ the tool makes with respect to the axes of anisotropy and also as a function of the anisotropy index κ=(σhv)1/2 View full abstract»

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  • Modeling radio wave propagation in tunnels with a vectorial parabolic equation

    Publication Year: 2000 , Page(s): 1403 - 1412
    Cited by:  Papers (15)
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    To study radio wave propagation in tunnels, we present a vectorial parabolic equation (PE) taking into account the cross-section shape, wall impedances, slowly varying curvature, and torsion of the tunnel axis. For rectangular cross section, two polarizations are decoupled and two families of adiabatic modes can be found explicitly, giving a generalization of the known results for a uniform tunnel. In the general case, a boundary value problem arises to be solved by using finite-difference/finite-element (FD/FE) techniques. Numerical examples demonstrate the computational efficiency of the proposed method View full abstract»

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  • Enhancement of reflected waves in single-hole polarimetric borehole radar measurement

    Publication Year: 2000 , Page(s): 1430 - 1437
    Cited by:  Papers (8)
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    A polarimetric approach is presented to extract information of reflected waves that is masked by the transmitter-receiver directly coupled wave in a single-hole borehole radar measurement. Radar polarimetry theory is expanded to an omnidirectional radar system with electric and magnetic dipoles arranged on the same axis. First, we formulate the transfer functions directly coupled between the antennas for cross-hole and single-hole arrangements in copolarized channels. We found that the theoretical scattering matrices of the direct-wave coupling is identical to the scattering matrix from a dihedral corner reflector. Second, we also consider signals in polarimetric channel of a wave reflected from a plane scatter in single-hole arrangements. As advanced reflection borehole radar measurement, we demonstrate a technique for both reduction of the directly coupled wave and enhancement of the reflected waves from a plane fracture with measured data in dipole-dipole and slot-slot antenna combinations. For quantitative determination of the scattering matrix, we use a technique to compensate the antenna transfer functions by the time derivative of the directly coupled signals in single-hole measurement. Also, we propose a technique to reduce the directly coupled component by adding vertical (VV) and horizontal (HH) signals and we showed that the directly coupled wave is effectively reduced and reflected waves are enhanced with experimental data. Finally, we show that this technique is more useful for near-range reflector detection than a conventional subtraction technique with moving average of the measured waveforms View full abstract»

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  • Ultrawide-band synthetic aperture radar for detection of unexploded ordnance: modeling and measurements

    Publication Year: 2000 , Page(s): 1306 - 1315
    Cited by:  Papers (21)  |  Patents (2)
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    Electromagnetic (EM) scattering from subsurface unexploded ordnance (UXO) is investigated both theoretically and experimentally. Three EM models are considered: the multilevel fast multipole algorithm (MLFMA), the method of moments (MoM), and physical optics (PO). The relative accuracy of these models is compared for several scattering scenarios. Moreover, the model results are compared to data measured by an experimental synthetic aperture radar (SAR) system, SAR images have been generated for subsurface UXO targets, in particular 155-mm shells. We compare SAR images from the measured data with theoretical images produced by the MoM and PO simulations, using a standard back-projection imaging technique. In addition to such comparisons with measurement, we consider additional buried-UXO scattering scenarios to better understand the underlying wave phenomenology View full abstract»

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  • Natural wave propagation in mine environments

    Publication Year: 2000 , Page(s): 1326 - 1339
    Cited by:  Papers (43)
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    Theoretical and experimental aspects of the natural propagation of high-frequency waves in mines are presented. A narrow-band and a wide-band analysis have been carried out to determine the most important characteristics of the channel such as the longitudinal attenuation, the coherence bandwidth, and the delay spread of the impulse response in the various areas of an underground mine. The basic principle of a localization of a mobile has also been checked by determining the direction of arrival of the waves View full abstract»

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  • Sommerfeld and Zenneck wave propagation for a finitely conducting one-dimensional rough surface

    Publication Year: 2000 , Page(s): 1475 - 1484
    Cited by:  Papers (10)
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    Starting with Zenneck and Sommerfeld wave propagation over a flat finitely conducting surface has been extensively studied by Wait (see IEEE Antennas Propagat. Mag., vol.40, p.7-24, 1998) and many other authors. We examine propagation over a finitely conducting rough surface, also studied by many people including Feinberg (1944), Bass and Fuks (1979), and Barrick (see Radio Sci., vol.6, p.517-26, and vol.6., p.527-33). This paper extends the multiple scattering theories based on Dyson and Bethe-Salpeter equations and their smoothing approximations. The theory developed here applies to rough surfaces with small root-mean-square (RMS) heights (σ<0.1λ). We limit ourselves to the one-dimensional (1-D) rough surface with finite conductivity excited by a magnetic line source, which is equivalent to the Sommerfeld dipole problem in two dimensions (x-z plane). With the presence of finite roughness, the total field decomposes into the coherent field and the incoherent field. The coherent (average) field is obtained by using Dyson's equation, a fundamental integral equation based on the modified perturbation method. Once the coherent field has been obtained, we determine the Sommerfeld pole, the effective surface impedance, and the Zenneck wave for rough surfaces of small RMS heights. The coherent field is written in terms of the Fourier transform, which is equivalent to the Sommerfeld integral. Numerical examples of the attenuation function are compared to Monte Carlo simulations and are shown to contrast the flat and rough surface cases. Next, we obtain the general expression for the incoherent mutual coherence functions and scattering cross section for rough conducting surfaces View full abstract»

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  • On the design of NMR sensor for well-logging applications

    Publication Year: 2000 , Page(s): 1393 - 1402
    Cited by:  Papers (4)
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    The magnetic fields of antenna and magnet used in inside-out nuclear magnetic resonance (NMR) well-logging tool are computed using a finite-element method (FEM). A typical operating frequency of such tools is 2 MHz, at which the skin depth is about 47 μm for copper conductor. A direct application of FEM to evaluate power loss at such frequency, therefore, requires very fine discretization of the conductors, which, in turn, makes the problem numerically ill-conditioned. A perturbation technique along with FEM is used to evaluate the power loss in conductors that avoids the need for small discretization steps along the conductor thickness. The design of the magnet, on the other hand, is complicated by the fact that the model is nonlinear in nature because of the presence of ferrites and steel materials surrounding the magnet and because the size of the problem is usually quite large; quarter of a million unknowns is fairly common. A typical nonlinear FEM model requires about 35 h of central processing unit (CPU) time on a Sun Ultra 60 296 MHz workstation with one gigabyte of RAM. The magnet is built by stacking several magnet segments along the axial direction and the objective of the design is to magnetize these segments in such a way so as to produce a desired field profile in front of the magnet. It generally requires many executions of the nonlinear FEM model. An optimal control technique is used in conjunction with the FEM to speed up the design process. Very good agreement between the measured and computed antenna efficiency and magnetic field is obtained thus validating the numerical model View full abstract»

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  • Electromagnetic induction and surface impedance in a half-space from an overhead moving current system

    Publication Year: 2000 , Page(s): 1301 - 1305
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    How does an overhead current system having a velocity v influence the electromagnetic (EM) fields and the surface impedance as measured on the ground? We attempt to answer this question in this paper. A formulation is given for the fields produced by a current system having a uniform translational velocity. The numerical results that reflect the influence of velocity on the surface impedance at the air/earth boundary are presented. The relativity effect is not considered View full abstract»

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  • Electromagnetic wave propagation on a thin wire above earth

    Publication Year: 2000 , Page(s): 1413 - 1419
    Cited by:  Papers (16)
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    The electromagnetic properties of a current on a thin horizontal wire above a flat lossy earth is reviewed. Attention is given to the historical development of the topic, starting with the seminal work of Carson. Particularly, the importance of Professor Wait's contribution to the initial understanding of the modal and radiative behaviors of the current, as described in his influential paper (see Radio Sci., vol.7, p.675, 1972), is discussed in detail. A description of Wait's full wave analysis is provided to show how that analysis justified many of the assumptions embedded in Carson's result and how that same analysis later led to a fuller understanding of the current's spatial spectrum. Although no rigorous proof is known to exist with respect to the completeness of this spectrum, a necessary condition for completeness is offered; the basis of this condition is the measurable input conductance of the wire. The paper concludes with a short discussion on the various extensions of Wait's classic work that have been provided over the last two decades View full abstract»

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  • Rise times of impulsive high-current processes in cloud-to-ground lightning

    Publication Year: 2000 , Page(s): 1442 - 1451
    Cited by:  Papers (10)
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    Measurements are presented of electric-field derivative (dE/dt) waveforms that were radiated by first and subsequent return strokes, stepped, and dart-stepped-leader steps just before return strokes and “characteristic pulses” in normal (negative) cloud-to-ground lightning under conditions of minimal distortion due to ground-wave propagation. The main dE/dt peaks produced by the fast-rising portions of all of these processes are found to have similar durations [mean full-width at half-maximum (FWHM) ranging from 79±20 ns for subsequent strokes to 54±17 ns for stepped-leader steps], although widely differing absolute magnitudes (spanning nearly a factor of four). Field-change (E) signatures of first strokes are examined in greater detail after eliminating the 39% of events with multiple dE/dt peaks during their fast-rising portions. The “slow fronts” beginning these waveforms had durations of 3.7±1.2 μs and amplitudes 50%±10% of peak E. The latter ratio was uncorrelated with either peak E or peak dE/dt. The range-normalized peak magnitudes of the remaining fast-rising portions of these field changes were well correlated with those of the corresponding dE/dt signatures, whereas the values of FWHM of dE/dt were uncorrelated with peak dE/dt and only poorly correlated with peak E View full abstract»

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  • Ground wave of an idealized lightning return stroke

    Publication Year: 2000 , Page(s): 1349 - 1353
    Cited by:  Papers (2)
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    We model a lightning return stroke by a vertical traveling wave of current with a complex propagation constant. The Sommerfeld-integral analysis is similar to that of a vertical electric dipole over a lossy earth except that the source is distributed in height. When the integration over the source current is performed analytically, an extra term appears in addition to the classical Sommerfeld attenuation function. This term is a result of the height-gain function of the distributed source due to an effective elevated height of the source dipole moment. In most eases of interest, the extra term is small and the height-gain function is not much larger than one. The results have application to remote sensing of lightning from a ground-based observer View full abstract»

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

    Publication Year: 2000 , Page(s): 1289 - 1294
    Cited by:  Papers (6)
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    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 View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung