Lund University Publications
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Lund University Lund University Publications2000-01-01T00:00+00:001dailyPhysical-density integral equation methods for scattering from multi-dielectric cylinders
https://lup.lub.lu.se/search/publication/e68b3ba4-2f22-4a96-b6ec-de3db4e88d53
Helsing, JohanKarlsson, Anders2019An integral equation-based numerical method for scattering from multi-dielectric cylinders is presented. Electromagnetic fields are represented via layer potentials in terms of surface densities with physical interpretations. The existence of null-field representations then adds superior flexibility to the modeling. Local representations are used for fast field evaluation at points away from their sources. Partially global representations, constructed as to reduce the strength of kernel singularities, are used for near-evaluations. A mix of local- and partially global representations is also used to derive the system of integral equations from which the physical densities are solved. Unique solvability is proven for the special case of scattering from a homogeneous cylinder under rather general conditions. High achievable accuracy is demonstrated for several examples found in the literature.http://lup.lub.lu.se/record/e68b3ba4-2f22-4a96-b6ec-de3db4e88d53http://dx.doi.org/10.1016/j.jcp.2019.02.050scopus:85062835234engJournal of Computational Physics; 387, pp 14-29 (2019)ISSN: 0021-9991BeräkningsmatematikAnnan fysikCorner singularityHelmholtz equationMultiple material interfaceScatteringTransmission boundary conditionPhysical-density integral equation methods for scattering from multi-dielectric cylinderscontributiontojournal/articleinfo:eu-repo/semantics/articletextOn a Helmholtz transmission problem in planar domains with corners
https://lup.lub.lu.se/search/publication/cf094989-a190-4b32-bd48-d566bc9f992c
Helsing, JohanKarlsson, Anders2018-10-15A particular mix of integral equations and discretization techniques is suggested for the solution of a planar Helmholtz transmission problem with relevance to the study of surface plasmon waves. The transmission problem describes the scattering of a time-harmonic transverse magnetic wave from an infinite dielectric cylinder with complex permittivity and sharp edges. Numerical examples illustrate that the resulting scheme is capable of obtaining total magnetic and electric fields to very high accuracy in the entire computational domain.http://lup.lub.lu.se/record/cf094989-a190-4b32-bd48-d566bc9f992chttp://dx.doi.org/10.1016/j.jcp.2018.05.044scopus:85048160202engJournal of Computational Physics; 371, pp 315-332 (2018)ISSN: 0021-9991BeräkningsmatematikAnnan fysikCorner singularityHelmholtz equationNyström discretizationScatteringSurface plasmon waveOn a Helmholtz transmission problem in planar domains with cornerscontributiontojournal/articleinfo:eu-repo/semantics/articletextResonances in Axially Symmetric Dielectric Objects
https://lup.lub.lu.se/search/publication/60a52ed0-5cf5-485f-b71a-37393356b612
Helsing, JohanKarlsson, Anders2017-07-01A high-order convergent and robust numerical solver is constructed and used to find complex eigenwavenumbers and electromagnetic eigenfields of dielectric objects with axial symmetry. The solver is based on Fourier-Nyström discretization of combined integral equations for the transmission problem and can be applied to demanding resonance problems at microwave, terahertz, and optical wavelengths. High achievable accuracy, even at very high wavenumbers, makes the solver ideal for benchmarking and for assessing the performance of general-purpose commercial software.http://lup.lub.lu.se/record/60a52ed0-5cf5-485f-b71a-37393356b612http://dx.doi.org/10.1109/TMTT.2017.2653773scopus:85013290067wos:000405006300001engIEEE Transactions on Microwave Theory and Techniques; 65(7), pp 2214-2227 (2017)ISSN: 0018-9480Elektroteknik och elektronikAxial symmetrybody of revolutionboundary integral equation (BIE)dielectric resonatorelectric field integral equation (EFIE)magnetic field integral equation (MFIE)Nyström methodwhispering-gallery mode (WGM)Resonances in Axially Symmetric Dielectric Objectscontributiontojournal/articleinfo:eu-repo/semantics/articletextMedical Implant Communication Systems
https://lup.lub.lu.se/search/publication/4f389d9b-100c-4120-becc-b243ece81fcf
Johansson, Anders JKarlsson, AndersScanlon, WilliamEvans, NoelRahmat-Samii, Yahya2006http://lup.lub.lu.se/record/774828ISBN: 1-58053-493-7scopus:52949100212engElektroteknik och elektronikMedical Implant Communication Systemscontributiontobookanthology/chapterinfo:eu-repo/semantics/bookParttextOn the efficiency and gain of antennas
https://lup.lub.lu.se/search/publication/4e63444d-fe83-457b-a6a7-75101cea5bbe
Karlsson, Anders2013The fundamental limits of the gain and e±ciency of an
antenna are explored. These are very important quantities for, e.g.,
superdirective arrays. The antenna is in this paper con¯ned in a sphere
and all of the currents are assumed to run in a material with a given
conductivity. It is shown that one can ¯nd the current distribution
in the sphere that optimizes the gain, given the frequency and the
radius of the sphere. The results indicate the distribution of antenna
elements in an antenna array in order to maximize gain, or e±ciency.
The analysis is based on the expansion of the electromagnetic ¯elds
in terms of vector spherical harmonics. Explicit expressions for the
limits of gain and e±ciency, and the corresponding current densities,
are derived for di®erent types of antennas.http://lup.lub.lu.se/record/3406242http://dx.doi.org/10.2528/PIER12110504wos:000314747900027scopus:84873359929engProgress in Electromagnetics Research-Pier; 136, pp 479-494 (2013)ISSN: 1070-4698Elektroteknik och elektronikOn the efficiency and gain of antennascontributiontojournal/articleinfo:eu-repo/semantics/articletextNumerical simulations of light scattering by red blood cells
https://lup.lub.lu.se/search/publication/bc3e9c23-f124-434e-8c08-0f43ae7f275b
Karlsson, AndersHe, JiangpingSwartling, JohannesAndersson-Engels, Stefan2005Scattering of electromagnetic waves from a red blood cell is simulated using the finite-difference time-domain method (FDTD), the Rytov approximation and the discrete dipole approximation (DDA). Both FDTD and DDA are full wave methods that give accurate results in a wide range of wavelengths. The Rytov approximation is a much simpler method that is limited to scattering angles within 30/spl deg/ from the forward direction. The investigation comprehends different wavelengths and different orientations of the cell. It shows that the shape, volume, and orientation of the cell have a large influence on the forward scattering.application/pdfhttp://lup.lub.lu.se/record/144358http://dx.doi.org/10.1109/TBME.2004.839634http://lup.lub.lu.se/search/ws/files/4842723/624996.pdfpmid:15651560wos:000225843700003scopus:11244267005enginfo:eu-repo/semantics/openAccessIEEE Transactions on Biomedical Engineering; 52(1), pp 13-18 (2005)ISSN: 0018-9294MedicinteknikNumerical simulations of light scattering by red blood cellscontributiontojournal/articleinfo:eu-repo/semantics/articletextDetermination of normalized magnetic eigenfields in microwave cavities
https://lup.lub.lu.se/search/publication/ea1fb785-44c1-401b-9fff-d7830c2bcf60
Helsing, JohanKarlsson, Anders2015The magnetic field integral equation for axially symmetric cavities
with perfectly conducting surfaces is discretized according to a
high-order convergent Fourier--Nyström scheme. The resulting solver
is used to determine eigenwavenumbers and normalized magnetic
eigenfields to very high accuracy in the entire computational
domain.application/pdfhttp://lup.lub.lu.se/record/5149700http://dx.doi.org/10.1109/TMTT.2015.2408334http://lup.lub.lu.se/search/ws/files/4065366/7442455.pdfwos:000354365900002scopus:85027958774enginfo:eu-repo/semantics/openAccessIEEE Transactions on Microwave Theory and Techniques; 63(5), pp 1457-1467 (2015)ISSN: 0018-9480Elektroteknik och elektronikbody of revolution (BOR)axial symmetryMFIERF-cavityNyström methodwhispering-gallery mode (WGM)toroidal harmonicswakefield.Determination of normalized magnetic eigenfields in microwave cavitiescontributiontojournal/articleinfo:eu-repo/semantics/articletextElevated liver enzymes in Turner syndrome during a 5-year follow-up study
https://lup.lub.lu.se/search/publication/5c581dac-6614-411c-b13a-8e9a87408e74
El-Mansoury, MostafaBerntorp, KerstinBryman, IngerHanson, CharlesInnala, EvaKarlsson, AndersLandin-Wilhelmsen, Kerstin2008Objectives To study the prevalence and incidence of elevated liver enzymes and their relationship with body weight, metabolic factors and other diseases in Turner syndrome (TS). Design Five-year follow-up. Patients Women with TS (n = 218, mean age 33 +/- 13, range 16-71 years) from outpatient clinics at university hospitals in Sweden. Measurements Fasting blood samples for aspartate (AST) and alanine aminotransferase (ALT), bilirubin, alkaline phosphatase (ALP), gamma-glutamyl transferase (GT), viral hepatitis serology and hepatic auto-antibodies, vitamin B12, blood glucose, lipids and hormones. Results Seventy-nine subjects (36%) had one or more liver enzyme levels higher than the reference level, the most prevalent being GT. Karyotype 45,X was present in 51% of all TS women and in 48% of those with elevated liver enzymes. Body weight, body mass index (BMI), total cholesterol, triglycerides, and apolipoproteins A and B at start were higher in TS women with elevated liver enzymes than in TS women with normal levels. At 5 years, AST, ALT and GT were increased and another 23% of patients had developed elevated liver enzymes, that is, 59% in total (36% + 23%), while in 6%, the elevated liver enzymes had been normalized and all 6% also had lowered cholesterol levels. Multivariate analysis showed that GT was correlated with total cholesterol; P = 0.0032 at start and P = 0.0005 at 5 years, independently of other factors. Liver biopsy in six TS women showed one cholangitis, one hepatitis C, two steatosis and two normal biopsies. Withdrawal of oestrogen substitution did not influence the liver enzymes. Conclusions Pathological liver enzymes were common in TS women, with a prevalence of 36% at 33 years of age, an annual incidence over 5 years of 3.4%. There was no relation to karyotype, alcohol, viral hepatitis, E-2 or autoimmunity, but a connection with total serum cholesterol.http://lup.lub.lu.se/record/1196928http://dx.doi.org/10.1111/j.1365-2265.2007.03166.xwos:000253251400024scopus:39149141050engClinical Endocrinology; 68(3), pp 485-490 (2008)ISSN: 1365-2265Endokrinologi och diabetesElevated liver enzymes in Turner syndrome during a 5-year follow-up studycontributiontojournal/articleinfo:eu-repo/semantics/articletextThick screens perforated with a periodic array of apertures with arbitrary cross-section
https://lup.lub.lu.se/search/publication/19119166-24ca-4d7a-bf25-d598b5e40a90
Widenberg, BjörnPoulsen, SörenKarlsson, Anders2000A plane wave impinges on a perfectly conducting thick screen perforated with a periodic array of apertures with arbitrary cross-section. The transmission and reflection coefficients are determined by a mode matching technique, earlier used by other authors for the case where the apertures have the geometry of a classical waveguide. The fields outside the screen are expanded in Floquet modes, while the fields inside the apertures are expanded in waveguide modes, obtained by the finite element method (FEM). Excellent agreement between computed and measured transmission is found for a thick screen at the X-band (8.2-12.4 GHz). Moreover, the present method and the spectral Galerkin method (which assumes that the thickness of the screen is zero) is compared for very thin screens, e.g., for a frequency selective surface (FSS). Investigation of the thickness dependence is also done, and it is found that the bandwidth decreases when the thickness dependence is also done, and it is found that the bandwidth decreases when the thickness of the screen is increased. Finally two complex geometries, hexagonal and tripole apertures, are studied.http://lup.lub.lu.se/record/144431scopus:0034437333engJournal Electromagnetic Waves and Applications; 14(9), pp 28-1303 (2000)ISSN: 1569-3937Elektroteknik och elektronikAnnan elektroteknik och elektronikThick screens perforated with a periodic array of apertures with arbitrary cross-sectioncontributiontojournal/articleinfo:eu-repo/semantics/articletextDetermination of normalized electric eigenfields in microwave cavities with sharp edges
https://lup.lub.lu.se/search/publication/c070638c-6439-4b5e-8fcb-0d7e25c69af4
Helsing, JohanKarlsson, Anders2016The magnetic field integral equation for axially symmetric cavities with perfectly conducting piecewise smooth surfaces is discretized according to a high-order convergent Fourier--Nyström scheme. The resulting solver is used to accurately determine eigenwavenumbers and normalized electric eigenfields in the entire computational domain.application/pdfhttp://lup.lub.lu.se/record/8165500http://dx.doi.org/10.1016/j.jcp.2015.09.054http://lup.lub.lu.se/search/ws/files/1841746/8165517.pdfwos:000365041900019scopus:84945574441enginfo:eu-repo/semantics/openAccessJournal of Computational Physics; 304, pp 465-486 (2016)ISSN: 0021-9991Beräkningsmatematikmagnetic field integral equation (MFIE)corner singularityNyström discretizationbody of revolution (BOR)radio frequency (RF) cavitywakefieldDetermination of normalized electric eigenfields in microwave cavities with sharp edgescontributiontojournal/articleinfo:eu-repo/semantics/articletextAn explicit kernel-split panel-based Nyström scheme for integral equations on axially symmetric surfaces
https://lup.lub.lu.se/search/publication/449d6988-63fe-4e39-8f61-7aa3e673733a
Helsing, JohanKarlsson, Anders2014A high-order accurate, explicit kernel-split, panel-based, Fourier–Nyström discretization scheme is developed for integral equations associated with the Helmholtz equation in axially symmetric domains. Extensive incorporation of analytic information about singular integral kernels and on-the-fly computation of nearly singular quadrature rules allow for very high achievable accuracy, also in the evaluation of fields close to the boundary of the computational domain.application/pdfhttp://lup.lub.lu.se/record/4436126http://dx.doi.org/10.1016/j.jcp.2014.04.053http://lup.lub.lu.se/search/ws/files/1500028/4581003.pdfwos:000336620900037scopus:84900811104enginfo:eu-repo/semantics/openAccessJournal of Computational Physics; 272, pp 686-703 (2014)ISSN: 0021-9991MatematikAnnan elektroteknik och elektronikSingular kernelBoundary integral equationBody of revolutionHigh order discretizationAcoustic resonatorHelmholtz equationAn explicit kernel-split panel-based Nyström scheme for integral equations on axially symmetric surfacescontributiontojournal/articleinfo:eu-repo/semantics/articletext