Devoted to the problem of sound wave scattering by elastic cylindrical objects in a plain acoustic waveguide. The Multi-Modal Integral Method is proposed. It is shown that the implementation of the method requires few computer resources for good accuracy of the solution.

Acoustic propagation in the ocean can be strongly affected by small random variations in ocean properties, including rough surfaces and volume fluctuations in the ocean or seabed. Such inhomogeneities scatter part of the incident acoustic field, stripping energy from the coherent part of the field. This scattered energy, or reverberation, propagates further in the modes of the ocean waveguide. The distribution of energy among modes is changed and the coherence of the acoustic field is reduced. This thesis introduces several models which describe scattering of low-frequency sound. First, the rough surface scattering theory of Kuperman and Schmidt is reformulated in terms of normal modes. Scattering from rough fluid-fluid interfaces and rough elastic halfspaces is modeled, and statistics of the acoustic field are calculated. Numerical results show the modal formulation agrees well with Kuperman and Schmidt's model, while reducing computation times by several orders of magnitude for the scenarios considered. Next, a perturbation theory describing scattering from sound speed and density fluctuations in acoustic media is developed. The theory is used to find the scattered field generated by volume fluctuations in sediment bottoms. Modal attenuations due to sediment volume scattering are calculated, and agreement is demonstrated with previous work. The surface and volume scattering theories are implemented in a unified modal reverberation code and used to study bottom scattering in shallow water. Numerical examples are used to demonstrate the relationship between volume and surface scattering. Energy distribution among scattered field modes is found to be a complicated function of the scattering mechanism, the scatterer statistics, and the acoustic environment. In particular, the bottom properties strongly influence the coherence of the acoustic field. Examples show that excitation of fluid-elastic interface waves is a potentially important scattering path. Cross-modal coherences are calculated and used to study the loss of signal coherence with range. Finally, earlier work on scattering from the Arctic ice sheet is extended. Simulations of long-range transmissions are compared with data from the April 1994 trans-Arctic propagation test. The results show modal attenuations and group speeds can be predicted reasonably well, indicating that acoustic monitoring of Arctic climate is feasible.

Single mode equivalent network representations have been a key tool for the industrial design and development of a large variety of microwave systems. The reduced dimensions and increased complexity of modern microwave equipment, however, makes the inclusion of the higher order mode interactions essential for the correct industrial design and optimization of all microwave hardware. In this context, the analytical techniques originally exploited to develop single mode networks have recently been extended to produce multi-mode algorithms that can form the basis of fast and accurate Computer Aided Design tools. Furthermore, alternative multi-modal techniques, involving resonant rather than guided modes, have recently been developed for the design of waveguide components of arbitrary shape. This book describes in detail a number of modern multi-modal techniques for the analysis and design of passive microwave components. The authors comprehensively cover modal analysis of waveguides and cavities; discuss several multi-mode procedures for the study of both basic and arbitrarily shaped waveguide junctions and, finally, describe specific applications such as inductively coupled filters, waveguide couplers, metal insert and dual-mode filters. The book will be of interest to professional engineers and researchers in the microwave engineering field as well as students engaged in research at an advanced level. Distinctive features of this book include: * detailed explanation of several multi-mode analysis techniques for the analysis of waveguide components based on both canonical and arbitrary waveguide profiles * measured versus simulated results for a number of specific application examples * accompanying software that allows the reader to input their own data thereby demonstrating how the techniques described can be effectively used to develop fast and accurate CAD tools.

The inverse scattering problem is central to many areas of science and technology such as radar, sonar, medical imaging, geophysical exploration and nondestructive testing. This book is devoted to the mathematical and numerical analysis of the inverse scattering problem for acoustic and electromagnetic waves. In this fourth edition, a number of significant additions have been made including a new chapter on transmission eigenvalues and a new section on the impedance boundary condition where particular attention has been made to the generalized impedance boundary condition and to nonlocal impedance boundary conditions. Brief discussions on the generalized linear sampling method, the method of recursive linearization, anisotropic media and the use of target signatures in inverse scattering theory have also been added.

The Fourier transform technique has been widely used in electrical engineer ing, which covers signal processing, communication, system control, electro magnetics, and optics. The Fourier transform-technique is particularly useful in electromagnetics and optics since it provides a convenient mathematical representation for wave scattering, diffraction, and propagation. Thus the Fourier transform technique has been long applied to the wave scattering problems that are often encountered in microwave antenna, radiation, diffrac tion, and electromagnetic interference. In order to u~derstand wave scattering in general, it is necessary to solve the wave equation subject to the prescribed boundary conditions. The purpose of this monograph is to present rigorous so lutions to the boundary-value problems by solving the wave equation based on the Fourier transform. In this monograph the technique of separation of vari ables is used to solve the wave equation for canonical scattering geometries such as conducting waveguide structures and rectangular/circular apertures. The Fourier transform, mode-matching, and residue calculus techniques are applied to obtain simple, analytic, and rapidly-convergent series solutions. The residue calculus technique is particularly instrumental in converting the solutions into series representations that are efficient and amenable to nu merical analysis. We next summarize the steps of analysis method for the scattering problems considered in this book. 1. Divide the scattering domain into closed and open regions. 2. Represent the scattered fields in the closed and open regions in terms of the Fourier series and transform, respectively. 3.