arXiv subjects

Michael A. Fiddy

Publications and source records attributed to Michael A. Fiddy.

10 recordsLinked to original sources

arXiv2017

Imaging of buried objects from multi-frequency experimental data using a globally convergent inversion method

This paper is concerned with the numerical solution to a 3D coefficient inverse problem for buried objects with multi-frequency experimental data. The measured data, which are associated with a single direction of an incident plane wave, are backscatter data for targets buried in a sandbox. These raw scattering data were collected using a microwave scattering facility at the University of North Carolina at Charlotte. We develop a data preprocessing procedure and exploit a newly developed globally convergent inversion method for solving the inverse problem with these preprocessed data. It is shown that dielectric constants of the buried targets as well as their locations are reconstructed with a very good accuracy. We also prove a new analytical result which rigorously justifies an important step of the so-called "data propagation" procedure.

math.NA↗

arXiv2016

Numerical Solution of a Coefficient Inverse Problem with Multi-Frequency Experimental Raw Data by a Globally Convergent Algorithm

We analyze in this paper the performance of a newly developed globally convergent numerical method for a coefficient inverse problem for the case of multi-frequency experimental backscatter data associated to a single incident wave. These data were collected using a microwave scattering facility at the University of North Carolina at Charlotte. The challenges for the inverse problem under the consideration are not only from its high nonlinearity and severe ill-posedness but also from the facts that the amount of the measured data is minimal and that these raw data are contaminated by a significant amount of noise, due to a non-ideal experimental setup. This setup is motivated by our target application in detecting and identifying explosives. We show in this paper how the raw data can be preprocessed and successfully inverted using our inversion method. More precisely, we are able to reconstruct the dielectric constants and the locations of the scattering objects with a good accuracy, without using any advanced \emph{a priori} knowledge of their physical and geometrical properties.

math.NA↗

arXiv2016

Apex-angle-dependent resonances in triangular split ring resonators

Along with other frequency selective structures [1] (circles and squares), triangular split-ring resonators (TSRRs) only allow frequencies near the center resonant frequency to propagate. Further, TSRRs are attractive due to their small surface area [2], comparatively, and large quality factors (Q) factors as previously investigated by Gay-Balmaz, et al. [3]. In this work we examine the effects of varying the apex angle on the resonant frequency, the Q factor, and the phase shift imparted by the TSRR element within the GHz frequency regime.

physics.optics↗

arXiv2014

Surface Plasmon Polaritons Excited By Electromagnetic Waves Under General Boundary Conditions

We investigate single interface surface plasmon polaritons (SPPs) excited by electromagnetic waves under general electromagnetic boundary conditions that allow for non-zero surface charge and surface current densities. Incorporating these, we derive general conditions for single interface SPPs and solve both the surface source distributions and the surface electromagnetic waves for such SPPs when excited by electromagnetic waves.

physics.optics↗

arXiv2014

Imaging of buried objects from experimental backscattering time dependent measurements using a globally convergent inverse algorithm

We consider the problem of imaging of objects buried under the ground using backscattering experimental time dependent measurements generated by a single point source or one incident plane wave. In particular, we estimate dielectric constants of those objects using the globally convergent inverse algorithm of Beilina and Klibanov. Our algorithm is tested on experimental data collected using a microwave scattering facility at the University of North Carolina at Charlotte. There are two main challenges working with this type of experimental data: (i) there is a huge misfit between these data and computationally simulated data, and (ii) the signals scattered from the targets may overlap with and be dominated by the reflection from the ground's surface. To overcome these two challenges, we propose new data preprocessing steps to make the experimental data to be approximately the same as the simulated ones, as well as to remove the reflection from the ground's surface. Results of total 25 data sets of both non blind and blind targets indicate a good accuracy.

math-ph↗

arXiv2013

Reconstruction from blind experimental data for an inverse problem for a hyperbolic equation

We consider the problem of reconstruction of dielectrics from blind backscattered experimental data. Experimental data were collected by a device, which was built at University of North Carolina at Charlotte. This device sends electrical pulses into the medium and collects the time resolved backscattered data on a part of a plane. The spatially distributed dielectric constant $\varepsilon_{r}(\mathbf{x}),\mathbf{x}\in \mathbb{R}^{3}$ is the unknown coefficient of a wave-like PDE. This coefficient is reconstructed from those data in blind cases. To do this, a globally convergent numerical method is used.

math-ph↗

arXiv2013

Reconstruction of the refractive index from experimental backscattering data using a globally convergent inverse method

The problem to be studied in this work is within the context of coefficient identification problems for the wave equation. More precisely, we consider the problem of reconstruction of the refractive index (or equivalently, the dielectric constant) of an inhomogeneous medium using one backscattering boundary measurement. The goal of this paper is to analyze the performance of a globally convergent algorithm of Beilina and Klibanov on experimental data acquired in the Microwave Laboratory at University of North Carolina at Charlotte. The main challenge working with experimental data is the the huge misfit between these data and computationally simulated data. We present data pre-processing steps to make the former somehow look similar to the latter. Results of both non-blind and blind targets are shown indicating good reconstructions even for high contrasts between the targets and the background medium.

math-ph↗

arXiv2013

Negative Refraction Does Not Make Perfect Lenses

The widely-accepted theoretical treatment of the electromagnetic boundary problem of evanescent wave transfer at an interface between a normal medium of n=1 and an ideal negative index medium of n=-1 neglects the non-zero induced surface current and charge densities at the interface and is self-inconsistent. We re-solve the electromagnetic boundary problem by taking into account the non-zero induced surface current and charge densities that have been neglected so far by others. We give the exact induced surface current and charge distributions for this special case and solve the refracted and reflected fields analytically using Green's function method. The self-consistent solution yields a transmission coefficient of 1 and reflection coefficient of 0 for all evanescent waves. Accordingly, we found that, on the contrary to the popular belief, negative index of refraction does not make perfect lenses.

physics.optics↗

arXiv2009

Revisiting the Perfect Lens with Loss

We reconsider the refraction of evanescent waves at an interface between air and negative index medium under the assumption that negative index medium is necessarily dispersive and lossy. We show that all evanescent waves in air will be refracted into decaying propagating waves inside a negative index medium, with different spatial frequency components having different propagation directions which are separated both in time and space; hence no refocus of these evanescent waves is possible. Accordingly, all information encoded by evanescent waves will be lost in the image making sub-diffraction-limited imaging impossible.

physics.optics↗

arXiv2008

Revisiting the Perfect Lens

We carefully examine the negative refractive index slab perfect lens theory by Pendry and point out an inconsistency that can be resolved. As a result, we find negative index slabs do not amplify or enhance evanescent waves and therefore they do not make a perfect lens in the sense that was originally suggested.

physics.optics↗