Learn More
—An electromagnetic feasible adjoint sensitivity technique (EM-FAST) has been proposed recently for use with frequency domain solvers. It makes the implementation of the ad-joint variable approach to design sensitivity analysis straightforward while preserving the accuracy at a level comparable to that of the exact sensitivities. The overhead computations(More)
In a causally dispersive medium the signal arrival appears in the dynamical field evolution as an increase in the field amplitude from that of the precursor fields to that of the steady-state signal. The interrelated effects of phase dispersion and frequency dependent attenuation and/or amplification alter the pulse in such a fundamental way that results in(More)
Superluminal group velocities, defined as group velocities exceeding the speed of light in vacuum, c, have been theoretically predicted and experimentally observed in various types of dispersive media, such as passive and active Lorentzian media, one-dimensional photonic crystals, and undersized waveguides. Though superluminal group velocities have been(More)
In this paper, the finite difference time domain (FDTD) technique is combined with time-frequency analysis, to provide a versatile approach for the modeling of precursor fields in dispersive media. Previous analytical studies, based on asymptotic analysis, are restricted to simple media, while the proposed approach can address spatially complex and(More)
In wireless communication systems, transmitted signals are corrupted by fading as well as noise. The receiver can benefit from the estimates of fading channels to detect the transmitted symbols. However, in practical wireless systems channel information cannot be estimated perfectly at the receiver. Therefore, it is crucial to examine the effect of channel(More)
—Time reversal techniques are based on the time reversal invariance of the wave equation. They use time-reversed fields recollected by an array antenna to perform imaging and focusing on the source of received signals. Two widely used time reversal techniques are DORT and time reversal MUSIC which are based on eigenvalue decomposition of the time reversal(More)
This paper presents a solution to one of the most troublesome sections of Newton algorithm for solving harmonic balance nonlinear system of equations which is choosing an appropriate initial condition. A good initial condition guaranties the convergence of the algorithm. Here, we have used Volterra series analysis to calculate the appropriate initial(More)
The appearance of precursor fields in a causally dispersive dielectric is due to the interrelated effects of phase dispersion and frequency dependent attenuation of the medium. Until now, rigorous studies of these transient fields have been performed showing the evolution of the precursors and their unique penetrating features that can be used in imaging(More)
—Imaging techniques based on time reversal method are particularly suitable for detection of targets embedded in a strongly scattering media. Generally in time reversal imaging technique we need to know the Green's function of the medium and the exact locations of the transmitter and receiver antennas. We introduce a target imaging method in which imaging(More)