| 1. |
- Andersson, Michael, et al.
(författare)
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Stabilization of evanescent wave propagation operators
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The reflection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the reflection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented.
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| 2. |
- Andersson, Michael, et al.
(författare)
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Stabilization of Evanescent Wave Propagation Operators
- 2023
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Ingår i: Progress In Electromagnetics Research B. - 1937-6472. ; 101, s. 17-44
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The re ection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the re ection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented.
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| 3. |
- Cheney, Margaret, et al.
(författare)
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Resonance Enhancement in Noise
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This document compares two approaches to finding resonance peaks from asingle sensor: 1) averaging multiple measurements of the transfer function orfrequency-domain scattering matrix, versus 2) using the iterative time-reversalprocess, which involves iteratively re-transmitting a time-reversed version ofthe scattered field at the previous iterations. The averaging method has theadvantage of handling arbitrarily much noise if sufficiently many averages areused. On the other hand, up to a certain level of noise, the time-reversalmethod has dramatic advantages over the averaging method; but it also requires more complex equipment. This document discusses the tradeoffs involved, with the goal of providing information that may be useful in the system design process.
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| 4. |
- Gower, Artur, et al.
(författare)
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A simple model to validate effective waves in random particulate media: radial symmetry
- 2023
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Ingår i: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - 1364-5021. ; 479:2279
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Tidskriftsartikel (refereegranskat)abstract
- There has not been a satisfying numerical validation of the theory of effective waves in random particulate materials. Validation has been challenging because the theoretical methods for effective waves have been limited to random particulate media in infinite slabs or half-spaces, which require a very large number of particles to perform accurate numerical simulations. This paper offers a solution by providing, from first principles, a method to calculate effective waves for a sphere filled with particles for a spherically symmetric incident wave. We show that this case can excite exactly the same effective wavenumbers, which are the most important feature to validate for effective waves. To check correctness, we also deduce an integral equation method which does not assume the effective wave solution. Our methods are, in principal, valid for any frequency, particle volume fraction and disordered pair-correlation. With the methods we provide, it is now possible to validate, with a heavier Monte Carlo simulation, the predictions from effective wave theory.
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| 5. |
- Gower, Artur, et al.
(författare)
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Effective Waves for Random Three-dimensional Particulate Materials
- 2020
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- How do you take a reliable measurement of a material whose microstructure is random? When using wave scattering, the answer is often to take an ensemble average (average over time or space). By ensemble averaging we can calculate the average scattered wave and the effective wavenumber. To date, the literature has focused on calculating the effective wavenumber for a plate filled with particles. One clear unanswered question was how to extend this approach to a material of any geometry and for any source. For example, does the effective wavenumber depend on only the microstructure, or also on the material geometry? In this work, we demonstrate that the effective wavenumbers depend on only microstructure and not the geometry, though beyond the long wavelength limit there are multiple effective wavenumbers. We show how to calculate the average wave scattered from a random particulate material of any shape, and for broad frequency ranges. As an example, we show how to calculate the average wave scattered from a sphere filled with particles.
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| 6. |
- Gower, Artur, et al.
(författare)
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Effective waves for random three-dimensional particulate materials
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- How do you take a reliable measurement of a material whose microstructure is random? When using wave scattering, the answer is often to take an ensemble average (average over time or space). By ensemble averaging we can calculate the average scattered wave and the effective wavenumber. To date, the literature has focused on calculating the effective wavenumber for a plate filled with particles. One clear unanswered question was how to extend this approach to a material of any geometry and for any source. For example, does the effective wavenumber depend on only the microstructure, or also on the material geometry? In this work, we demonstrate that the effective wavenumbers depend on only microstructure, though beyond the long wavelength limit there are multiple effective wavenumbers for one fixed incident frequency. We show how to calculate the average wave scattered from a random particulate material of any shape, and for broad frequency ranges. As an example, we show how to calculate the average wave scattered from a sphere filled with particles.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Kristensson, Gerhard, et al.
(författare)
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Multiple scattering by a collection of randomly located obstacles distributed in a dielectric slab
- 2020
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Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 621-651
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Bokkapitel (refereegranskat)abstract
- Multiple scattering of electromagnetic waves by a discrete collection of scatterers is a well-studied subject, and many excellent treatments are found in the literature. The deterministic analysis of the scattering problem in this chapter is an extension of the problems treated previosly. Moreover, the present analysis generalizes the established results in two previous papers to a geometry with a more general background material, which is practical for a controlled experimental verification of the final result. The transmitted and reflected intensities are conveniently represented as a sum of two terms-the coherent and the incoherent contribution. In this chapter, we focus on the analysis of the coherent term. The chapter is organized as follows. In Section 25.2, the geometry of the multiple electromagnetic scattering problem is given, and in Section 25.3, the main tool to solve the problem-the integral representation-is introduced. The integral representations are exploited in the various homogeneous regions of the problem in Section 25.4, and the appropriate expansions of the surface fields are introduced in Section 25.5. The final goal of the chapter is to calculate the transmitted and reflected coherent fields of the problem.
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