| 1. |
- Capek, Miloslav, et al.
(författare)
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Characteristic Mode Decomposition of Scattering Dyadic
- 2022
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Ingår i: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, AP-S/URSI 2022 - Proceedings. - 9781665496582 ; , s. 283-284
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Konferensbidrag (refereegranskat)abstract
- This abstract describes the decomposition of a matrix representing a scattering dyadic into characteristic modes. Scattering dyadic, as compared to conventionally used impedance matrices, are independent of numerical method used to compute them and the same characteristic mode formulation can be used for decomposition of composite and inhomogeneous materials. The utilization of scattering dyadic makes it possible to synthesize characteristic modes which are orthogonal over prescribed portions of the far-field sphere, or ex-post decomposition of measured data. The theory is demonstrated on a simple example and its features are discussed.
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| 2. |
- Capek, Miloslav, et al.
(författare)
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Cloaking Synthesis Based on Exact Re-analysis
- 2022
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Ingår i: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, AP-S/URSI 2022 - Proceedings. - 9781665496582 ; , s. 293-294
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Konferensbidrag (refereegranskat)abstract
- A novel synthesizing procedure is introduced and employed to extract locally-optimal cloaking devices. Their performance is compared with fundamental bounds found using a convex optimization approach. The optimization method is based on a method-of-moments paradigm utilizing rank-1 updates of the structure iteratively performed based on a greedy algorithm. This approach produces locally optimal shapes and its incorporation into a global search strategy is described and applied. As compared to classical topology optimization schemes, no post-processing is required. Two canonical problems are solved and presented.
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| 3. |
- Gustafsson, Mats, et al.
(författare)
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Unified Theory of Characteristic Modes : Part I: Fundamentals
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; , s. 11801-11813
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Tidskriftsartikel (refereegranskat)abstract
- A unification of characteristic mode decomposition for all method-of-moment formulations of field integral equations describing free-space scattering is derived. The work is based on an algebraic link between impedance and transition matrices, the latter of which was used in early definitions of characteristic modes and is uniquely defined for all scattering scenarios. This also makes it possible to extend the known application domain of characteristic mode decomposition to any other frequency-domain solver capable of generating transition matrices, such as finite difference or finite element methods. The formulation of characteristic modes using a transition matrix allows for the decomposition of induced currents and scattered fields from arbitrarily shaped objects, providing high numerical dynamics and increased stability, removing the issue of spurious modes, and offering good control of convergence. This first part of a two-part paper introduces the entire theory, extensively discusses its properties and offers its basic numerical validation.
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| 4. |
- Gustafsson, Mats, et al.
(författare)
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Unified Theory of Characteristic Modes : Part II - Tracking, Losses, and FEM Evaluation
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 70:12, s. 11814-11824
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Tidskriftsartikel (refereegranskat)abstract
- This is the second component of a two-part paper dealing with a unification of characteristic mode decomposition. This second part addresses modal tracking, interpolation, the role of ohmic losses, and presents several numerical examples for surface-based method-of-moment formulations. A new tracking algorithm based on algebraic properties of the transition matrix is developed, achieving excellent precision and requiring a very low number of frequency samples as compared to procedures previously reported in the literature. The transition matrix is further utilized to show that characteristic mode decomposition of lossy objects fails to deliver orthogonal far fields and to demonstrate how characteristic modes can be evaluated using the finite element method.
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| 5. |
- Losenicky, Vit, et al.
(författare)
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Method of Moments and T-Matrix Hybrid
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 70:5, s. 3560-3574
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid computational schemes combining the advantages of a method of moments formulation of a field integral equation and T-matrix method are developed in this article. The hybrid methods are particularly efficient when describing the interaction of electrically small complex objects and electrically large objects of canonical shapes such as spherical multilayered bodies where the T-matrix method is reduced to the Mie series making the method an interesting alternative in the design of implantable antennas or exposure evaluations. Method performance is tested on a spherical multilayer model of the human head. Along with the hybrid method, an evaluation of the transition matrix of an arbitrarily shaped object is presented and the characteristic mode decomposition is performed, exhibiting fourfold numerical precision compared to conventional approaches.
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| 6. |
- Schab, Kurt, et al.
(författare)
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Upper bounds on focusing efficiency
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:25, s. 45705-45723
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Tidskriftsartikel (refereegranskat)abstract
- Upper bounds on the focusing efficiency of aperture fields and lens systems are formulated using integral equation representations of Maxwell’s equations and Lagrangian duality. Two forms of focusing efficiency are considered based on lens exit plane fields and optimal polarization currents within lens design regions of prescribed shape and available materials. Bounds are compared against the performance of classical prescriptions of ideal lens aperture fields, hyperbolic lens designs, and lenses produced by inverse design. Results demonstrate that, without regularization, focusing efficiency based solely on lens exit plane fields is unbounded, similar to the problem of unbounded antenna directivity. Additionally, results considering extruded two-dimensional dielectric geometries driven by out-of-plane electric fields for the calculation of bounds and inverse design demonstrate that aperture fields based on time-reversal do not necessarily yield optimal lens focusing efficiency, particularly in the case of near-field (high numerical aperture) focusing.
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