| 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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Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary Full-Wave Solvers
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:1, s. 830-839
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Tidskriftsartikel (refereegranskat)abstract
- Characteristic modes are formulated using the scattering dyadic, which maps incident plane waves to scattered far fields generated by an object of arbitrary material composition. Numerical construction of the scattering dyadic using arbitrary full-wave electromagnetic solvers is demonstrated in examples involving a variety of dielectric and magnetic materials. Wrapper functions for computing characteristic modes in method-of-moments, finite-difference time domain, and finite element solvers are provided as supplementary material.
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| 3. |
- 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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| 4. |
- Capek, Miloslav, et al.
(författare)
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Fundamental Bounds for Volumetric Structures and Their Feasibility
- 2020
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Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020. - 9788831299008
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Konferensbidrag (refereegranskat)abstract
- Fundamental bounds on antenna and scattering metrics are presented in this paper utilizing volumetric method of moments. This makes it possible to investigate scenarios not solvable with classical surface method of moments which assumes that good conductors as used. One practical example is the study of plasmonic devices whose operation relies on the interaction between material properties and radiation mechanisms. The implementation of the code is briefly summarized, including some implementation hints which allow for fast evaluation of necessary matrix operators. Two optimization problems are introduced and solved for scattering and antenna problems. Feasibility of the bounds will be investigated with topology optimization and the results will be presented during the conference.
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| 5. |
- Capek, Miloslav, et al.
(författare)
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Inversion-Free Evaluation of Nearest Neighbors in Method of Moments
- 2019
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 18:11, s. 2311-2315
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Tidskriftsartikel (refereegranskat)abstract
- A recently introduced technique of topology sensitivity in method of moments is extended by the possibility of adding degrees of freedom (reconstruct) into the underlying structure. The algebraic formulation is inversion-free, suitable for parallelization, and scales favorably with the number of unknowns. The reconstruction completes the nearest neighbors procedure for an evaluation of the smallest shape perturbation. The performance of the method is studied with a greedy search over a Hamming graph representing the structure in which initial positions are chosen from a random set. The method is shown to be an effective data mining tool for machine learning-related applications.
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| 6. |
- Capek, Miloslav, et al.
(författare)
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Inversion-free evaluation of small geometry perturbation in method of moments
- 2019
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Ingår i: 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings. - 9781728106922 ; , s. 1039-1040
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Konferensbidrag (refereegranskat)abstract
- Topology sensitivity is introduced and defined to be utilized within method of moments. It is based on a series of the smallest perturbations of the investigated structure and, thanks to the application of the Woodbury matrix identity, its evaluation is inversion-free, suitable for vectorization and parallelization, and results in a fast and versatile tool for analyzing antenna optimality.
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| 7. |
- Capek, Miloslav, et al.
(författare)
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Numerical Benchmark based on characteristic modes of a spherical shell
- 2017
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Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings. - 9781538632840 ; 2017-January, s. 965-966
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Konferensbidrag (refereegranskat)abstract
- Characteristic modes of a spherical shell are found analytically and compared with numerical solutions acquired from both in-house and commercial packages. These studies led to a proposal of several independent benchmarks, all with analytically known results. Dependence on mesh size, electrical size and other parameters can easily be incorporated. It is observed that all contemporary implementations have limitations.
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| 8. |
- Capek, Miloslav, et al.
(författare)
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Optimal Inverse Design Based on Memetic Algorithms - Part 1 : Theory and Implementation
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:11, s. 8806-8816
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Tidskriftsartikel (refereegranskat)abstract
- A memetic framework for optimal inverse design is proposed by combining a local gradient-based procedure and a robust global scheme. The procedure is based on method-of-moments matrices and does not demand full inversion of a system matrix. Fundamental bounds are evaluated for all optimized metrics in the same manner, providing natural stopping criteria and quality measures for realized devices. Compared to density-based topology optimization, the proposed routine does not require filtering or thresholding. Compared to commonly used heuristics, the technique is significantly faster, still preserving a high level of versatility and robustness. This is a two-part paper in which the first part is devoted to the theoretical background and properties, and the second part applies the method to examples of varying complexity.
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| 9. |
- Capek, Miloslav, et al.
(författare)
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Optimal Inverse Design Based on Memetic Algorithms - Part II : Examples and Properties
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:11, s. 8817-8829
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Tidskriftsartikel (refereegranskat)abstract
- Optimal inverse design, including topology optimization and evaluation of fundamental bounds on performance, which was introduced in Part 1, is applied to various antenna design problems. A memetic scheme for topology optimization combines local and global techniques to accelerate convergence and maintain robustness. Method-of-moments (MoMs) matrices are used to evaluate objective functions and allow determination of fundamental bounds on performance. By applying the Shermann-Morrison-Woodbury identity, the repetitively performed structural update is inversion-free yet full-wave. The technique can easily be combined with additional features often required in practice, e.g., only a part of the structure is controllable, or evaluation of an objective function is required in a subdomain only. The memetic framework supports multifrequency and multiport optimization and offers many other advantages, such as an actual shape being known at every moment of the optimization. The performance of the method is assessed, including its convergence and computational cost.
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| 10. |
- Capek, Miloslav, et al.
(författare)
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Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.
- 2019
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Ingår i: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 61:4, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here, we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on the radiation quality factor (Q-factor) (maximizing single-resonance fractional bandwidth) but are far from reaching the associated physical bounds for efficiency. The relative performance of other canonical antenna designs is comparable in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.
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