Alicia Garcia-Lopez - IEEE Xplore Author Profile

Showing 1-25 of 36 results

Filter Results

Show

Results

We develop a modal approach for analyzing multiple-input-multiple-output (MIMO) wireless channel propagation in a tunnel with lossy walls. We use parametric methods to study the effects of the number of modes and of the separation among antennas. We evaluate the performance of the MIMO channel in terms of capacity as a function of range and tunnel size.Show More
We review recent research work on wireless communication in straight and curved tunnels. Modal theory of fields in a circular tunnel excited by a linear source is given in detail. Closed form expressions for the propagation parameters of the dominant modes in circular and rectangular straight tunnels in the high frequencies are derived. We present field measurements in tunnels and interpret them i...Show More
In this article, we give a presentation of wireless electromagnetic propagation in tunnels. We discuss in depth the characteristics of multimodal propagation. We show analytical models whereby we are able to study electromagnetic fields in tunnels. To complement the analysis, we give an account of experiments performed in the Channel Tunnel between France and England, and the Massif Central in sou...Show More
We study models for propagation in circular tunnels. The excitation is a fundamental electric current source. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We perform an asymptotic analysis of the complex wavenumbers for use as initial estimates in a complex root finder. We then produce the modes in the lossy structure by contour integration techniq...Show More
First Page of the Article
Show More
Wireless communication channels in large tunnels at microwave frequencies involve an interaction among many guided wave modes. It has been reported that spatial records of field strength versus axial distance in straight tunnels can be divided into two zones. Close to the transmitting source (near zone), the field consists of many modes interacting in such it way as to produce rapid decay and stro...Show More
Wireless communication channels in large tunnels at microwave frequencies involve a large number of guided wave modes. It has been reported that spatial records of field strength versus axial distance in such tunnels can be divided into two zones. Close to the transmitting source, the field consists of many modes interacting in such a way as to produce rapid decay and strong local variations. For ...Show More
We study models for propagation in circular tunnels. The excitation is either a circular magnetic or circular electric current loop. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We then produce the modes in the lossy structure by contour integration techniques. We include numerical results for the field intensity both as a function of axial distanc...Show More
We present a model for propagation in lossy circular tunnels. Our study has potential application to wireless communication in highway and railroad tunnels where the cross-sectional geometry is often circular except for the roadbed. In addition, the circular tunnel model has relevance to wireless communication in underground nuclear waste storage facilities, such as that planned for Yucca Mountain...Show More
We re-examine one model in the classic paper by Mahmoud and Wait (for original paper see Rad. Sci., vol. 9, p. 1147-1158 (1974)) on rectangular tunnels. The model consists of two perfectly conducting and two imperfectly conducting walls. We have verified and reproduced the results in Mahmoud and Wait for both their modal and ray-optic solutions. The x-component of the electric field obtained in Ma...Show More
Dudley and Johnson (see ibid., vol.50, p.XX XX, Nov. 2002) comments that Li, Leong, Kooi and Yeo (see ibid., vol.49, p.645-659, April 2001) formulate in detail the dyadic Green's functions for the dielectric spheroid stating that one result of their derivations, the singularity of the electric Green's dyadics is extracted. They also comment that there is nothing formally wrong with extracting the ...Show More
Convergence proofs and measures of accuracy in solutions to integral equations by the method of moments (MoM) remain important issues thirty five years after R. F. Harrington's pioneering work. We discuss the present state of affairs, both in general and specifically applied to surfaces using the computer code EIGER.Show More
We present a general framework to study the solution of first-kind integral equations. The integral operator is assumed to be compact and nonself-adjoint and the integral equation can possess a nonempty null space. An approach is presented for adding contributions from the null space to the minimum-energy solution of the integral equation through the introduction of weighted Hilbert spaces. Stabil...Show More
Summary form only given. In the study of linear inverse problems, integral equations of the first kind play an important role. In many applications, the inversion of these integral equations is widely used to produce estimates of media parameters and geometries in areas as diverse as geophysical prospecting, medical imaging, and nondestructive evaluation. The authors interests an in wave motion an...Show More
For original paper see Peterson et al. (IEEE Trans. Antennas Propag. vol.27, p.241-2, April 1996). Peterson et al. compared moment method solutions by Galerkin and non-Galerkin procedures. They point out that their results are at odds with some commonly held beliefs in the superiority of the Galerkin method. The purpose of the present comments is twofold: 1) to add support to their position and 2)...Show More
Diffusion approximations are often used to study the interaction of transient electromagnetic waves with the Earth. If a frequency-independent conductivity and permittivity are assumed, then neglecting the displacement currents in the Earth reduces the wave equation to the diffusion equation, which sometimes can be solved analytically using elementary special functions. We study the validity of th...Show More
We develop a method for the analytical evaluation of the inverse Laplace transform representations for transient transverse magnetic (TM) plane wave obliquely incident on a conductive half-space. We assume that the permittivity and conductivity of the dispersive half-space are independent of frequency. The time-domain expressions for the reflected and transmitted waves are first represented as inv...Show More
A method which allows for the analytical evaluation of the inverse Laplace transform representations for a transient TE plane wave, obliquely incident on a conductive half-space, is discussed. We assume that the permittivity and conductivity of the dispersive half-space are independent of frequency. Starting with the equations for the transmitted wave in the Laplace domain, the corresponding time-...Show More
A new approximation and a new measurable constraint for slab profile inversion is introduced. A comparison is given between the Born, the exact, and the new approximation. The new approximation and constraint can be utilized along with other methods such as the integral equation, the iterative or perturbed Born, and the alternating projection approaches. The latter is considered. The results obtai...
First Page of the Article
Show More
In the above paper (see ibid., vol.37, p.192, 1995) the authors went to great lengths to derive an explicit solution in terms of incomplete Lipschitz-Hankel integrals (ILHI's) to the propagation problem of a double exponential pulse in a homogeneous medium. Technically, He has no doubt on the correctness of their ILHI representation. However, He doubts their claim about the computational efficienc...Show More
We develop an efficient method for the analysis of ultra-wide-band (UWB) electromagnetic pulses (e.g., double-exponential pulse) propagating through a waveguide or cold plasma (i.e., the ionosphere). First we show that the inverse Fourier-transform representations for the electric and magnetic fields satisfy second order, nonhomogeneous, ordinary, differential equations. These differential equatio...Show More
A pulsed-NMR (nuclear magnetic resonance) apparatus has been developed for petrophysical evaluation of earth formations. The instrument is deployed in boreholes drilled in the ground that are typically 20 cm in diameter and 0.5-5 km deep. The NMR measurement yields the volume fraction of the pores in the rock and the distribution of the pore sizes. A vital component of borehole NMR instruments is ...Show More
For transient excitation, it is well known that the ray optic solution is useful for early time descriptions but is not, in general, suitable for late time. On the other hand, the singularity expansion method (SEM) is a late time technique that is not in general suitable for early time. Perfectly conducting circular cylinder studies have shown that it is possible to obtain two hybrid formulations ...Show More
The problem of a wire penetrating a circular aperture in an infinite conducting screen and entering a circular cylindrical cavity is considered. An approximate method is developed for evaluating the fields outside the cavity for observation points located far from the aperture. Results are presented in the frequency domain which compare this far-field approximation to the method of moments solutio...Show More