| 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. |
- Bondarik, Alexander, et al.
(författare)
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Gridded parasitic patch stacked microstrip array antenna for 60 GHz band
- 2020
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 14:8, s. 712-717
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Tidskriftsartikel (refereegranskat)abstract
- An array antenna design based on a gridded parasitic patch stacked microstrip antenna element is presented. The radiating part in the top layer of one antenna element has nine rectangular metal patches placed in a grid with three rows and three columns with a separation of 0.1 mm between the patches. Two means of realising the array are investigated. In a regular 2 × 2 concept, the parasitic patches of individual elements are placed next to each other, forming on the top layer a uniform grid of parasitic patches with six rows and six columns. In an alternative concept named as shared array, neighbouring antenna elements share one row and one column of parasitic patches, forming on the top layer a uniform grid of parasitic patches with five rows and five columns. The antenna arrays are designed for the 60 GHz band. The measured bandwidth is 13.8 GHz for the single antenna, 15.3 GHz for the 2 × 2 array, and 12.4 GHz for the shared array. The measured realised gain at 60 GHz is 6 dBi for the single antenna, 11 dBi for the 2 × 2 array, and 10.5 dBi for the shared array. The measured radiation patterns have good agreement with simulations.
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| 3. |
- Lundgren, Johan, et al.
(författare)
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IR and Metasurface based mm-Wave Camera
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a technique to measure low-power electromagnetic fields from mm-wave devices non-intrusively by combining a metasurface, designed to absorb power and focus the radiated power in a thermally isolated region, with an infrared camera. The metasurface consists of thermally isolated elements of low mass and highly emissive material for maximal IR conversion of the incident wave. The IR camera captures the converted energy and indirectly images the incident electromagnetic field on the metasurface. The setup combines multi-scale, multi-physical processes to conduct measurements of the incident electromagnetic fields in real time. In this work, the technique is presented and discussed. Measurements are carried out to demonstrate the technique and image the electromagnetic field of a radiating device. The results compare well with simulations and the technique can measure the low power density levels of consumer devices, as well as provide a general visualization of electromagnetic fields in a live setting.
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| 4. |
- Nedic, Mitja, et al.
(författare)
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Herglotz functions and applications in electromagnetics
- 2020
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Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 491-514
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.
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| 5. |
- Pallaris, Alexandros, et al.
(författare)
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A Planar Metasurface Cloaked Dipole Antenna Designed for Multifunction Apertures
- 2023
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Ingår i: 17th European Conference on Antennas and Propagation, EuCAP 2023. - 9788831299077
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Konferensbidrag (refereegranskat)abstract
- We designed and simulated a 1 GHz planar dipole antenna that is cloaked in a band around 10 GHz. Relative to an uncloaked antenna it has a reduced extinction cross-section for the co-antenna polarization, at the cost of an increased cross-polarization. This reduced extinction cross-section characterizes a reduction in scattering and absorption, and so reduced interference to electromagnetic waves in the frequency of cloaking. The dipole antenna element is cloaked by the introduction of sub-wavelength capacitive strips surrounding its length. The cloaking results were obtained using full wave simulations, showing for the realistic, lossy design a reduction of at least 5 dB in the extinction cross-section over a bandwidth of more than 1.5 GHz in comparison with the uncloaked antenna.
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| 6. |
- Sjöberg, Daniel
(författare)
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Computation of radome reference cases using a rotationally symmetric full wave solver
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate how to compute radome reference cases for benchmarkingradome codes. Radomes are electrically large structures, and to facilitate thecomputations a rotationally symmetric structure is assumed. We show howto implement this in the commercial software Comsol Multiphysics, and howto extract the relevant data for comparison. Two example geometries areanalyzed: a spherical shell radome, and an ogive shaped radome. In eachcase, the radome is in the order of ten wavelengths, but it is still possible tosimulate on a regular laptop platform in about a minute. Using a platform withmore memory and spending more time to simulate more modes and synthesizethe results, reference cases for even larger radomes with realistic feeds can besimulated, which is suggested as a topic for future studies. Results for anogive shaped radome with a diameter of 30 and 50 wavelengths using a highlysymmetrical antenna are provided.
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| 7. |
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| 8. |
- Wingren, Niklas, et al.
(författare)
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Investigating Low-Rank Approximations for the Finite Element-Boundary Integral Method
- 2023
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Ingår i: 17th European Conference on Antennas and Propagation, EuCAP 2023. - 9788831299077
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Konferensbidrag (refereegranskat)abstract
- This paper explores acceleration of the finite element-boundary integral hybrid method using the adaptive cross approximation. Our code implementing the hybrid method in Python based on open source packages is briefly presented. A simple one-level version of the adaptive cross approximation is described and it is used to accelerate the boundary integral matrices. We present results for scattering against a dielectric sphere with a comparison to analytical results for verification. We also present results for scattering against cylinders with varying length, where cylinders were selected as a simplification of wind turbine blades. Comparisons between a full matrix assembly and the acceleration method show that significant compression can be achieved, even with a simple acceleration scheme. We also present the monostatic radar cross-section for the largest cylinder computed for multiple angles of incidence.
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| 9. |
- Wingren, Niklas, et al.
(författare)
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Measurements of microwave scattering by ultrasound in air at oblique incidence
- 2020
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Ingår i: Europhysics Letters. - : IOP Publishing. - 1286-4854. ; 131:5
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Tidskriftsartikel (refereegranskat)abstract
- Scattering of electromagnetic waves against acoustic waves has been studied in acousto-optics and radio acoustic sounding of the atmosphere, among others. Strong interaction requires phase matching, which occurs at two angles between waves. These depend on the wavelength ratio. The scattered electromagnetic wave is frequency shifted by the acoustic frequency, either up or down depending on the angle between waves. This work presents experimental verification of this scattering for 27.3 GHz microwaves and 40 kHz ultrasound in air. Both up- and down-shifting of the scattered wave is shown. Previous work has mostly focused on either nearly perpendicular or parallel incidence. In contrast, this work considers oblique incidence with frequencies differing from those used in acousto-optics and radio acoustic sounding.
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| 10. |
- Wingren, Niklas, et al.
(författare)
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Nondestructive Testing Using mm-Wave Sparse Imaging Verified for Singly Curved Composite Panels
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:1, s. 1185-1189
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Tidskriftsartikel (refereegranskat)abstract
- Nondestructive testing of composite materials is important in aerospace applications, and mm-wave imaging has been increasingly used for this purpose. Imaging is traditionally performed using Fourier methods, with inverse methods being an alternative. This communication presents a mm-wave imaging method with an inverse approach intended for nondestructive testing of singly curved composite panels with sparsely distributed flaws. It builds on previous work which was limited to imaging on planar panels. The move from planar to singly curved panels increases the applicability of the method for aerospace applications. The imaging method is reference-free due to a numerical source separation algorithm and exploits sparsity in reconstruction of scatterers. It is demonstrated using near-field measurements at 60 GHz of an industrially manufactured composite panel with deliberate flaws. Compared to a more traditional Fourier imaging method, our method generates images with higher resolution and higher dynamic range. Flaw detection is also easier using our method as it generates images with less background clutter.
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