| 1. |
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| 2. |
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| 3. |
- Rylander, Thomas, 1972, et al.
(författare)
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Advances in FEM-FDTD hybrid methods
- 2005
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Ingår i: Computational Electrodynamics: The Finite-Difference Time-DomaMethod (3rd edition) -- Allen Taflove and Susan C. Hagness.
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Rylander, Thomas, 1972, et al.
(författare)
-
FEM algorithms for Maxwell's equations
- 1998
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Ingår i: EMB 98 - Electromagnetic Computations for Analysis and Design of Complex Systems.
-
Konferensbidrag (refereegranskat)
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| 5. |
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| 6. |
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| 7. |
- Atalaya, Juan, 1981, et al.
(författare)
-
Design and optimization of coreless components using admittance matrix and efficiently calculated sensitivities
- 2007
-
Ingår i: IEEE Transactions on Magnetics. ; 43, s. 1621-1624
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel technique for designing coreless components (inductors and transformers) based on the admittance matrix at quasi-static approximation. In addition, an optimization method based on continuum sensitivity is applied. Efficiency of the design method is shown for inductors that have axisymmetry and carry azimuthal currents. In order to avoid coupling between closely located inductors, a shielding structure is proposed and shape-optimized to confine the magnetic energy.
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| 8. |
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| 9. |
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| 10. |
- Botha, Matthys M, et al.
(författare)
-
An improved quadrature error estimate for nearly-singular MoM integrals
- 2018
-
Ingår i: 2018 IEEE Antennas and Propagation Society International Symposium and USNC/URSI National Radio Science Meeting, APSURSI 2018 - Proceedings. ; , s. 2431-2432
-
Konferensbidrag (refereegranskat)abstract
- A well-known numerical integration scheme for weakly near-singular integrands on triangle domains, is the Radial-Angular-RI-Sqrt near-singularity cancellation transformation quadrature scheme. Such integrals feature routinely in the method of moments (MoM), for integral equation based numerical electromagnetic field calculations. Recently, a closed-form quadrature error estimate has been proposed for this scheme. In this paper, the estimate is further improved, such that its range of applicability is extended.
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| 11. |
- Botha, Matthys M, et al.
(författare)
-
Analysis and estimation of quadrature errors in weakly singular source integrals of the method of moments
- 2018
-
Ingår i: International Journal of Numerical Modelling: Electronic Networks, Devices and Fields. - : Wiley. - 0894-3370 .- 1099-1204. ; 31:1
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Tidskriftsartikel (refereegranskat)abstract
- The method of moments (MoM) is used for the numerical solution of electromagnetic field integral equations. Weakly singular integrals over surfaces in 3 dimensions (3D) are routinely evaluated for the impedance matrix setup and for post-processing. Available numerical integration schemes range from direct application of Gauss-Legendre product-rule quadrature, to singularity and near-singularity cancellation, coordinate transformation schemes. This paper presents a general, explicit, pole-based, a priori procedure to estimate quadrature errors in the numerical evaluation of weakly singular and near-singular, 3D surface integrals in the MoM. It is based on an error theorem for linear Gaussian quadrature, which involves the analytic extension of the integrand into the complex plane. Errors are linked to poles in the complex plane. New closed-form estimates are presented for direct Gaussian product-rule integration, polar-coordinate integration, and the Radial-Angular-R 1 -Sqrt singularity cancellation scheme, for triangle integration domains. This work can serve as a foundation/template for further, 3D MoM-related work to identify appropriate quadrature schemes according to their error characteristics; for automatic selection of optimal schemes and quadrature orders in a computer implementation of the MoM; and for local and global estimation of MoM quadrature errors. This work can be specialized to the MoM for surfaces in 2D.
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| 12. |
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| 13. |
- Botha, Matthys M, et al.
(författare)
-
Quadrature error estimation for MoM matrix entries
- 2017
-
Ingår i: 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017; Verona; Italy; 11 September 2017 through 15 September 2017. - 9781509044511 ; , s. 973-975
-
Konferensbidrag (refereegranskat)abstract
- This paper is concerned with the method of moments (MoM) for electric field integral equation (EFIE) based numerical electromagnetic analysis of conducting surface structures. Inner (source) and outer (testing) integrals are encountered, when evaluating matrix entries. The well-known Radial-Angular-R1-Sqrt (RA-R1-Sqrt) weak near singularity cancellation transformation quadrature scheme for the inner integrals and standard Gaussian numerical integration for the outer integrals, are considered. It is shown that the quadrature error in the matrix entries, due to inner integral evaluation, can be accurately estimated under certain circumstances. A closed-form quadrature error estimate for the RA-R1-Sqrt scheme is employed.
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| 14. |
- Botha, Matthys, 1976, et al.
(författare)
-
Results in quadrature error estimation for weak near-singular MoM integrals
- 2017
-
Ingår i: 2017 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING. - 1522-3965. - 9781538632840 ; , s. 1555-1556
-
Konferensbidrag (refereegranskat)abstract
- In the method of moments (MoM) for integral equation based numerical electromagnetic field calculation, weakly singular and near-singular surface integrals must be routinely evaluated. Applicable numerical integration schemes are standard Gaussian quadrature or specialized singularity cancellation transformation quadrature. When applying numerical integration, an error is incurred. Qualitative knowledge of the error behaviour and quantitative error estimates are valuable to MoM developers in identifying appropriate quadrature schemes and orders, which lead to increased efficiency and reliability of MoM implementations. An accurate, closed-form error estimate is presented for direct Gaussian product-rule quadrature, as well as for the Radial-Angular-R1-Sqrt transformation scheme.
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| 15. |
- Candefjord, Stefan, 1981, et al.
(författare)
-
Microwave technology for detecting traumatic intracranial bleedings: tests on phantom of subdural hematoma and numerical simulations
- 2017
-
Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 1741-0444 .- 0140-0118. ; 55:8, s. 1177-1188
-
Tidskriftsartikel (refereegranskat)abstract
- Traumatic brain injury is the leading cause of death and severe disability for young people and a major public health problem for elderly. Many patients with intracranial bleeding are treated too late, because they initially show no symptoms of severe injury and are not transported to a trauma center. There is a need for a method to detect intracranial bleedings in the prehospital setting. In this study, we investigate whether broadband microwave technology (MWT) in conjunction with a diagnostic algorithm can detect subdural hematoma (SDH). A human cranium phantom and numerical simulations of SDH are used. Four phantoms with SDH 0, 40, 70 and 110 mL are measured with a MWT instrument. The simulated dataset consists of 1500 observations. Classification accuracy is assessed using fivefold cross-validation, and a validation dataset never used for training. The total accuracy is 100 and 82–96 % for phantom measurements and simulated data, respectively. Sensitivity and specificity for bleeding detection were 100 and 96 %, respectively, for the simulated data. SDH of different sizes is differentiated. The classifier requires training dataset size in order of 150 observations per class to achieve high accuracy. We conclude that the results indicate that MWT can detect and estimate the size of SDH. This is promising for developing MWT to be used for prehospital diagnosis of intracranial bleedings.
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| 16. |
- Candefjord, Stefan, 1981, et al.
(författare)
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Microwave technology for localization of traumatic intracranial bleedings—a numerical simulation study
- 2013
-
Ingår i: Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS. - 1557-170X. - 9781457702167 ; , s. 1948-1951
-
Konferensbidrag (refereegranskat)abstract
- Traumatic brain injury (TBI) is a major public health problem worldwide. Intracranial bleedings represents the most serious complication of TBI and need to be surgically evacuated promptly to save lives and mitigate injury. Microwave technology (MWT) is promising as a complement to computed tomography (CT) to be used in road and air ambulances for early detection of intracranial bleedings. In this study, we perform numerical simulations to investigate if a classification algorithm based on singular value decomposition can distinguish between bleedings at different positions adjacent to the skull bone for a similar but simplified problem. The classification accuracy is 94-100% for all classes, a result that encourages us to pursue our efforts with MWT for more realistic scenarios. This indicates that MWT has potential for localizing a detected bleeding, which would increase the diagnostic value of this technique.
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| 17. |
- Cerullo, Livia, 1982, et al.
(författare)
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Concurrent estimation of space and frequency variation for dielectrics: a microwave tomography system for process sensing applications
- 2011
-
Ingår i: Proceedings of the 9th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, Kansas City, MO USA, May 31 - June 3, 2011. - 9781629934556 ; , s. 177-184
-
Konferensbidrag (refereegranskat)abstract
- In many powder processing operations, the effective complex permittivity of the material under processing yields important information concerning the state of the process. This complex permittivity varies in general with respect to both space and frequency. For an accurate estimation of the process material parameters, it is important to be able to incorporate these dependencies in the estimation algorithm. Here, we present a rather general type of parameterization that is tailored for this type of situation. The parameterization is described in terms of a parameterization mesh, which makes it feasible to refine the computational mesh without influencing the number of degrees of freedom in the estimation problem. A test case demonstrates that our approach can yield accurate reconstructions.
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| 18. |
- Cerullo, Livia, 1982, et al.
(författare)
-
Determination of model order for inverse scattering applications
- 2010
-
Ingår i: Proceedings of the V European Conference on Computational Fluid Dynamics ECCOMAS CFD 2010 J. C. F. Pereira, A. Sequeira and J. M. C. Pereira (Eds) Lisbon, Portugal,14-17 June 2010. - 9789899677814
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Konferensbidrag (refereegranskat)
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| 19. |
- Cerullo, Livia, 1982, et al.
(författare)
-
Inverse scattering for a closed cavity equipped with microwave antenna sensors
- 2012
-
Ingår i: AntennEMB, 5-8 March, Stockholm.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceutical processes are often hosted by completely closed vessels that are difficult of access by means of measurement equipment. In particular, it is challenging to assess the interior or global process state with sensors placed on the vessel enclosing the process. This information about the process would allow for a better process monitoring and control. Here, a novel application of microwave sensing for process tomography is presented.
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| 20. |
- Cerullo, Livia, 1982, et al.
(författare)
-
Microwave measurement system for dispersive dielectric properties of densely packed pellets
- 2017
-
Ingår i: Measurement: Journal of the International Measurement Confederation. - : Elsevier BV. - 0263-2241. ; 106, s. 179-189
-
Tidskriftsartikel (refereegranskat)abstract
- We present a microwave measurement system that is intended for the estimation of the dispersive dielectric properties for densely packed pellets. In particular, we estimate the Debye parameters for the effective permittivity of a mixture of air and densely packed moist microcrystalline cellulose pellets for the frequency band 2.7–5.1 GHz. The Debye parameters are estimated by means of minimizing the misfit between the measured scattering parameters and the corresponding computed response given a model of the measurement system. This minimization is performed by means of a nonlinear iterative optimization procedure, which is supported by continuum sensitivities, and the optimum is found in 10–60 iterations for the cases presented in this article. We find that increasing moisture content yields an increase in the static permittivity and a decrease in the relaxation time.
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| 21. |
- Cerullo, Livia, 1982, et al.
(författare)
-
Microwave Measurements for Metal Vessels
- 2013
-
Ingår i: 7th European Conference on Antennas and Propagation, EuCAP 2013, Gothenburg, Sweden, 8-12 April 2013. - 2164-3342. - 9781467321877 ; , s. 3869 - 3873
-
Konferensbidrag (refereegranskat)abstract
- We present two different measurement techniques intended for closed metal vessels, where the objective is to measure the permittivity inside the metal vessel. This problem is relevant for many applications found in e.g. process industry. The first approach exploits the measurement of resonance frequencies, where the metal vessel is used as a microwave resonator. In the second approach, we let the boundary of the metal vessel be equipped with aperture antennas, where the aperture antennas are implemented in terms of rectangular waveguides. The waveguide apertures loads the cavity significantly and we exploit the scattering matrix parameters for the solution of the inverse problem.
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| 22. |
- Christie, Michael, 1946, et al.
(författare)
-
Some issues in online assessment
- 2005
-
Ingår i: IPSI Conference, Pescara, Italy 27-31 July 2005.
-
Konferensbidrag (refereegranskat)
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| 23. |
|
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| 24. |
|
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| 25. |
- DEGERFELDT, DAVID, 1979, et al.
(författare)
-
A higher-order finite element method with an explicit higher-order time integration scheme
- 2007
-
Ingår i: EMB07 Computational Electromagnetics Methods and Applications, Lund, Sweden, Oct 18-19, 2007. ; , s. 91-98
-
Konferensbidrag (refereegranskat)abstract
- We formulate and analyze a FEM that exploits higher-order approximations of the fields for both space and time. An explicit leap-frog type scheme is used to update Faraday's and Ampére's law, and we present a stability and error analysis for this time-stepping scheme. Our formulation exploits a matrix free representation of Maxwell's equations, which reduces the memory requirementssignificantly. The scheme is tested by solving eigenvalueproblems in a cubic cavity with metal walls. The tests demonstrate that the method yields exponential convergence with respect to spatial order p and polynomial convergence, h2p, with respect to the cell size h. Analogous convergence is achieved for the time-stepping scheme. The method reduces to the standard FDTD method for lowest order of approximation with respect to space and time. The technique presented is useful for computational studies of reverberation chambers and similar applications.
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| 26. |
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| 27. |
- DEGERFELDT, DAVID, 1979, et al.
(författare)
-
Scattering Analysis by a Stable Hybridization of the Finite Element Method and the Finite-Difference Time-Domain Scheme with a Brick-Tetrahedron Interface
- 2008
-
Ingår i: Electromagnetics. - : Informa UK Limited. - 0272-6343 .- 1532-527X. ; 28:1-2, s. 3-17
-
Tidskriftsartikel (refereegranskat)abstract
- We present scattering computations performed with a newly developed stable hybridization of the finite element method (FEM) and the finite-difference time-domain (FDTD) scheme, which is based on Nitsche's method. This hybrid has not been tested on scattering problems previously, and here we compute the radar cross-section (RCS) for three different targets: (i) the perfect electric conducting (PEC) sphere, (ii) the NASA almond, and (iii) a generic aircraft called RUND. In order to assess the discretization errors associated with the hybrid, we provide comparisons with established results and techniques: (i) the Mie-series for the PEC sphere, (ii) the method of moments (MoM) implemented in the commercial code FEKO, and (iii) a stable FEM-FDTD hybrid that exploits pyramids and a curl-conforming representation of the electric field. The bistatic RCS for the PEC sphere shows second order convergence towards the analytical solution and a relative error of 2% is achieved for about 20 points per wavelength. The NASA almond has a low monostatic RCS in its horizontal plane, which makes it a good benchmark problem for scattering computations. It features a sharp tip and, as a consequence, the order of convergence for the RCS is lowered. Given a careful convergence study for the NASA almond, we achieve a highly accurate monostatic RCS by means of extrapolation and this result is state-of-the-art in the open literature.
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| 28. |
- Dommisse, William R., et al.
(författare)
-
Macro Basis Functions for Efficient Analysis of Thick Wires in the MoM
- 2024
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents a macro basis function (MBF) formulation for efficient method of moments (MoM) modelling of conducting wires with appreciable thickness. General surface formulations are prohibitively inefficient for electrically thin wires, while the typical exact-kernel, rooftop-basis, thin-wire MoM becomes wholly inaccurate for electrically thick cylinders. The MBF formulation bridges the gap between thin-wire MoM, and general conducting surface MoM formulations, by introducing circumferential variations and components beyond the standard rooftop basis functions. The MBFs are constructed upon a full-order, divergence-conforming, triangle element MoM discretization. Comprehensive junction and end-cap treatment, and tapered wire support, are natural features of the formulation. As with thin-wire MoM, degrees of freedom (DoFs) are purely proportional to the electrical length of the wire. Results demonstrate that the intermediate range of “thick wires” is analyzed with practically the same accuracy as general surface MoM, with significantly reduced DoFs.
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| 29. |
- Du Plessis, Jacques T., et al.
(författare)
-
Scattering Analysis of Thick Wires with the MoM using Macro Basis Functions
- 2022
-
Ingår i: 2022 International Conference on Electromagnetics in Advanced Applications, ICEAA 2022. ; , s. 340-342
-
Konferensbidrag (refereegranskat)abstract
- This work is concerned with the analysis of scattering by conducting wires connected to conducting structures, using the method of moments (MoM). Based on thin-wire assumptions, low numbers of degrees of freedom (DoFs) are required by typical exact-kernel thin-wire MoM solvers, for accurate analysis. However, the thin-wire assumptions break down when the wire diameter becomes appreciably large in terms of the wavelength. An approach based on macro basis functions (MBFs) for wire current representation is outlined, aimed at extending the wire thickness range of accurate analysis, while maintaining a low number of DoFs similar to that of thin-wire formulations. Preliminary results demonstrate the effectiveness of the MBF approach.
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| 30. |
- Ericsson, David, 1979, et al.
(författare)
-
A quasi-planar incident wave excitation for time-domain scattering analysis of periodic structures
- 2005
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a quasi-planar incident wave excitation for time-domain scattering analysis of periodic structures. It uses a particular superposition of plane waves that yields an incident wave with the same periodicity as the periodic structure itself. The duration of the incident wave is controlled by means of its frequency spectrum or equivalently the angular spread in its constituting plane waves. Accuracy and convergence properties of the method are demonstrated by scattering computations for a planar dielectric half-space. Equipped with the proposed source a time-domain solver based on linear elements yields an error of roughly 1 percent for a resolution of 20 points per wavelength and second order convergence is achieved for smooth scatterers. Computations of the scattering characteristics for a sinusoidal surface and a random rough surface show similar performance.
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| 31. |
- Ericsson, David, 1979, et al.
(författare)
-
Optimization of Frequency Selective Surfaces
- 2005
-
Ingår i: RVK05 - Radiovetenskap och Kommunikation.
-
Konferensbidrag (refereegranskat)abstract
- Frequency selective surfaces are important in many electromagnetic applications since they transmit electromagnetic energy for some frequencies and reflect for others. There is a variety of tools available for the design of the interior structure of frequency selective surfaces. Here, we propose to use gradient-based optimization techniques in combination with a time-domain hybrid Finite Element Method (FEM) and Finite-Difference Time-Domain (FDTD) scheme for the design of frequency selective surfaces. The sensitivity of the goal function is computed cheaply from the solution of an adjoint field problem, which yields the steepest descent direction with respect to all design parameters.
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| 32. |
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| 33. |
- Halleröd, Tomas, 1978, et al.
(författare)
-
Electric and magnetic losses modeled by a stable hybrid with explicit-implicit time-stepping for Maxwell's equations
- 2008
-
Ingår i: Journal of Computational Physics. - : Elsevier BV. - 1090-2716 .- 0021-9991. ; 227:9, s. 4499-4511
-
Tidskriftsartikel (refereegranskat)abstract
- A stable hybridization of the finite-element method (FEM) and the finite-difference time-domain (FDTD) scheme for Maxwell's equations that allows for electric and magnetic losses is presented for two-dimensional problems. It combines the flexibility of the FEM withthe efficiency of the FDTD scheme. The electric and magnetic losses are treated by the FEM on an unstructured mesh, which allows for local mesh refinement in order to resolve rapid variations in the materialparameters and/or the electromagnetic field. The hybrid method is based directly on Ampère's and Faraday's law and it is stable up to the Courant stability limit of the FDTD method. The hybrid method shows second order convergence for smooth scatterers. The bistatic radar cross section (RCS) for a circular metal cylinder with a lossycoating converges to the analytical solution and an accuracy of 2% is achieved for about 20 points per wavelength. The monostatic RCS for an airfoil that features sharp corners yields a lower order of convergence and it is found to agree well with what can be expectedfor singular fields at the sharp corners. A careful convergence study with resolutions from 20 to 140 points per wavelength provides accurate extrapolated results for this non-trivial test case, which makes it possible to use as a reference problem for scattering codesthat model both electric and magnetic losses.
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| 34. |
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| 35. |
|
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| 36. |
- Halleröd, Tomas, 1978, et al.
(författare)
-
Shape and materials optimization to reduce RCS for antenna mounted on airfoil
- 2005
-
Ingår i: Proceedings of RadioVetenskap och Kommunikation. - 9170561230
-
Konferensbidrag (refereegranskat)abstract
- We investigate a new way of using Bézier curves to parameterize boundaries in optimization problems. Combined with a continuum design sensitivity formulation, this parameterization is used in two different test cases with the aim of reducing the monostatic RCS of an airfoil. The parameterization is shown to be flexible when setting up new optimization problems. The designs can be described using a few number of design variables, without loosing detail. The parameterization in combination with a gradient based method is robust and reliable, and the optimum can be found in a few number of iterations.
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| 37. |
- Hamnerius, Yngve, 1950, et al.
(författare)
-
Design of Safe Wireless Power Transfer Systems for Electric Vehicles
- 2018
-
Ingår i: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018. - 9789082598735
-
Konferensbidrag (refereegranskat)abstract
- Wireless charging of electric vehicles is convenient but in order to make it safe the exposure of humans to electromagnetic fields must be below acceptable limits. We have designed a prototype system that transmits 3 kW with an efficiency of 85% where the magnetic fields around and inside the vehicle are below the EU council recommendation of 6.25μT at 85 kHz.
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| 38. |
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| 39. |
- Hansbo, Peter F G, 1959, et al.
(författare)
-
A linear nonconforming finite element method for Maxwell's equations in two dimensions. Part I: Frequency domain
- 2010
-
Ingår i: Journal of Computational Physics. - : Elsevier BV. - 0021-9991 .- 1090-2716. ; 229:18, s. 6534-6547
-
Tidskriftsartikel (refereegranskat)abstract
- We suggest a linear nonconforming triangular element for Maxwell’s equations and test it in the context of the vector Helmholtz equation. The element uses discontinuous normal fields and tangential fields with continuity at the midpoint of the element sides, an approximation related to the Crouzeix–Raviart element for Stokes. The element is stabilized using the jump of the tangential fields, giving us a free parameter to decide. We give dispersion relations for different stability parameters and give some numerical examples, where the results converge quadratically with the mesh size for problems with smooth boundaries. The proposed element is free from spurious solutions and, for cavity eigenvalue problems, the eigenfrequencies that correspond to well-resolved eigenmodes are reproduced with the correct multiplicity.
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| 40. |
- Hashemzadeh, Parham, 1976, et al.
(författare)
-
Analysis of 3-D shape estimation using bistatic multi-channel radar systems
- 2008
-
Ingår i: SAM 2008 - 5th IEEE Sensor Array and Multichannel Signal Processing Workshop; Darmstadt; Germany; 21 July 2008 through 23 July 2008. - 9781424422418 ; , s. 463-467
-
Konferensbidrag (refereegranskat)abstract
- We estimate the radius of a perfect electric conductor (PEC) half-sphere placed on a ground plane, given six bi-conical antennas that suffer from manufacturing errors. The results are complemented by an analytical model of the sensor system and the scatterer. The analytical model includes the front-end electronics in combination with the antenna radiation impedance and the radiation field function.
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| 41. |
- Holmberg, Carl, 1992, et al.
(författare)
-
Accurate and Efficient Crosstalk Analysis by Full-wave Computations and System Identification
- 2020
-
Ingår i: Proceedings of the 2020 International Symposium on Electromagnetic Compatibility - EMC EUROPE, EMC EUROPE 2020.
-
Konferensbidrag (refereegranskat)abstract
- We present a system-identification procedure applied to a crosstalk problem, which can be accurately analyzed by an in-house full-wave solver based on the method of moments (MoM). Given a relatively few frequency-samples of the crosstalk current, we demonstrate that it is feasible to estimate a reduced-order model of the continuous frequency dependence, where the frequency band of interest corresponds to an electrical size of the system that ranges roughly from 0.005 to 2.7 wavelengths. The estimated low-order model of the frequency response takes the form of a Padé approximant and it yields an accurate representation when compared to the reference frequency-response, as it is computed directly by the MoM solver. In addition, the low-order model can be evaluated at an extremely low computational cost and it provides useful information such as resonance frequencies and their quality factors. For the system analysis of a real-world device, the low-order model can serve as a computationally powerful and accurate representation of the electromagnetic response for a subsystem that features full-wave phenomena that otherwise could be too challenging to describe at a system level.
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| 42. |
- Holmberg, Carl, 1992, et al.
(författare)
-
System Identification of Electromagnetic Devices Based on Full-Wave Computations
- 2021
-
Ingår i: 2021 Joint IEEE International Symposium on Electromagnetic Compatibility Signal and Power Integrity, and EMC Europe, EMC/SI/PI/EMC Europe 2021. ; , s. 952-957
-
Konferensbidrag (refereegranskat)abstract
- We present a framework that allows for the estimation of port-to-port characteristics of electromagnetic devices, which are linear and passive. Our approach is based on system identification (SI) techniques applied to the numerically computed admittance or impedance matrices of the electromagnetic device. The SI procedure yields a low-order model expressed in terms of a Padé approximant, which is represented as the ratio of two polynomials with respect to frequency. In this article, we demonstrate that the admittance and impedance matrices computed at a rather small number of frequency points can yield a highly accurate low-order model that describes the system response as a continuous function throughout the frequency band used for estimation of the model. The computational cost to store and evaluate the low-order model is basically negligible in comparison to the computational cost required by the numerical full-wave solver. The derived port-to-port model allows for the individual and independent analysis of subsystems that do not couple electromagnetically, where such subsystems can be combined later to form a complete system and this allows for great flexibility in a virtual design-process. We test our approach on two different crosstalk problems.
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| 43. |
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| 44. |
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| 45. |
- Jacobsson, Per, 1977, et al.
(författare)
-
A Finite Element Method Approach to the Finite-Difference Time-Domain Scheme with Cut Cells
- 2010
-
Ingår i: Electromagnetics. - : Informa UK Limited. - 0272-6343 .- 1532-527X. ; 30:1--2, s. 82 - 93
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, a finite element method approach to the finite-difference time-domain scheme with cut cells for Maxwell's equations in two dimensions is presented and tested. The method is based on a structured Cartesian grid of square elements, where cut cells are introduced for curved or oblique boundaries. The field is approximated by piecewise bilinear basis functions, and it is allowed to be discontinuous at interfaces modeled by cut cells, where continuity is enforced in the weak sense by means of Nitsche's method. Trapezoidal quadrature on the uncut elements recovers the finite-difference approximation that features a diagonal mass matrix. The time-domain formulation of this method is based on a hybrid explicit-implicit time-stepping method, which reduces to the leap-frog scheme for the uncut elements and the unconditionally stable Newmark method for the cut elements. The global time step is bounded by the Courant condition of the finite-difference time-domain scheme. For problems with regular solutions, the method yields a discretization error that is proportional to the square of the cell size. The method is tested on square cavities in two dimensions, where the first test problem involves homogeneous material parameters, and the second problem features a dielectric region in a vacuum cavity.
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| 46. |
|
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| 47. |
- Jacobsson, Per, 1977, et al.
(författare)
-
Gradient-based shape optimisation of conformal array antennas
- 2010
-
Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:2, s. 200-209
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Tidskriftsartikel (refereegranskat)abstract
- We present and test a gradient-based shape optimisation method for the minimisation of the active reflection coefficient for conformal array antennas. The goal function is an average of the active reflection coefficient with respect to all antenna elements, a prespecified frequency interval, and a set of excitation modes. The sensitivity of the goal function with respect to changes of the antenna's shape is based on the continuum form of Maxwell's equations, which provides good flexibility for the choice of field solver. The sensitivity is formulated in terms of the field solution of the original antenna problem and a similar adjoint field problem, which gives the sensitivity for an arbitrary number of design parameters given the solution of Maxwell's equations. We test the optimisation method in two dimensions for array antennas that conform to a circular cylinder, where both uniform arrays and arrays that occupy a part of the cylinder's circumference are considered. For some cases, we find that it is feasible to reduce the active reflection coefficient for arrays that partially cover the circumference of the cylinder by means of end elements that differ from the bulk elements of the array. In general, substantial reductions in the active reflection coefficient can be achieved by relatively small shape changes of the antenna elements. For the test cases considered in this article, the optimisation method typically converges to an optimised design within 5-15 iterations.
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| 48. |
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| 49. |
- Jacobsson, Per, 1977, et al.
(författare)
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Shape Optimization of Conformal Array Antennas
- 2009
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Ingår i: European Conference on Antennas and Propagation. ; , s. 2713-2717, s. 2713-2717
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Konferensbidrag (refereegranskat)abstract
- We present a shape optimization method for the minimization of the activereflection coefficient for conformal array antennas. Our formulation is based onthe continuum form of Maxwell's equations, where the gradient of the goalfunction is expressed in terms of the solution to the original field problem andthe solution to an adjoint field problem. The computational work for the goalfunction and its gradient amounts to the computation of the scattering matrix,which makes our method independent of the number of degrees of freedom used toparameterize the geometry. In addition, the field solver is decoupled from theoptimization process, which offers great freedom in the choice of field solver.The method is tested in two dimensions for an array antenna that conforms to acircular cylinder. An optimum is found in approximately 10 iterations when fourdegrees of freedoms are used to describe the antenna geometry and inapproximately 30 iterations when 40 degrees of freedoms are used.
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| 50. |
- Jacobsson, Per, 1977, et al.
(författare)
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Shape optimization of the total scattering cross section for cylindrical scatterers
- 2009
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 44:4
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Tidskriftsartikel (refereegranskat)abstract
- We propose and test a gradient-based shape optimization algorithm for the total scattering cross section of infinitely long cylinders, by means of changing the shape of the cylinder's cross section. On the basis of the optical theorem, we derive sensitivity expressions for both dielectric and metal cylinders given an incident plane wave, where the wave vector is perpendicular to the cylinder axis. Both the transverse electric (TE) case and the transverse magnetic case are considered. The sensitivity expressions are based on the continuum form of Maxwell's equations, and they provide the sensitivity with respect to an arbitrary number of shape parameters in terms of the field solution of the original scattering problem and an adjoint scattering problem. These results are used to construct a gradient-based optimization algorithm that we exploit for the reduction of the total scattering cross section in the TE case for metal cylinders, e.g., struts used in reflector antennas. We present optimized cross sections that are oblong in the direction of the incident wave vector, and some of these designs feature corrugations that are parallel to the cylinder axis. We show designs with asymmetric cross sections that yield a low monostatic scattering cross section for certain directions in combination with a low total scattering cross section, which can be used to reduce the noise temperature contributions from the upper strut in an inverted Y tripod reflector antenna.
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