| 701. |
- Lundbäck, Jonas, et al.
(författare)
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A Generic Electromagnetic Model for DOA Estimation Using Arbitrary Multiport Antennas
- 2006
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Ingår i: IEEE Antennas and Propagation Society International Symposium 2006. - 1424401232 ; , s. 2549-2552
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Konferensbidrag (refereegranskat)abstract
- In this paper, a generic electromagnetic model is utilized for arbitrary multiport antennas e.g., vector sensors applied in DOA estimation, which was exploited for the statistical analysis of DOA and polarization estimation. By utilizing the spherical vector wave expansion of the electromagnetic field to completely characterize the multiport antennas a general framework for modelling an antenna configuration based on measurements or computations including e.g., mutual coupling is obtained. The array manifold can easily be expanded over a dense spatial grid to enable high-resolution DOA estimation without demanding further measurements of the antenna characteristics.
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| 702. |
- Lundgren, Johan, et al.
(författare)
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A Near-Field Measurement and Calibration Technique : Radio-Frequency Electromagnetic Field Exposure Assessment of Millimeter-Wave 5G Devices
- 2021
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Ingår i: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 63:3, s. 77-88
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Tidskriftsartikel (refereegranskat)abstract
- Accurate and efficient measurement techniques are needed for an exposure assessment of 5G portable devices, which are expected to utilize frequencies beyond 6 GHz with respect to radio-frequency (RF) electromagnetic field (EMF) exposure limits. At above 6 GHz, these limits are expressed in terms of the incident power density, thus requiring the EMFs to be evaluated with high precision in close vicinity to the device under test (DUT), i.e., in the near-field region of the radiating antenna. This article presents a cutting-edge near-field measurement technique suited for these needs. The technique, based on source reconstruction on a predefined surface representing the radiating aperture of the antenna, requires two sets of measurements: one of the DUT and one of a small aperture. This second measurement functions as a calibration of both the measurement probe impact on the received signal and the experimental setup in terms of the relative distance between the probe and the DUT. Results are presented for a 28- and a 60-GHz antenna array, both of which were developed for 5G applications. The computed power density is compared with simulations at evaluation planes residing as close as one fifth of a wavelength (lambda/5) away from the DUT.
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| 703. |
- 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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| 704. |
- Lundgren, Johan, et al.
(författare)
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Iterative Calculation of Characteristic Modes Using Arbitrary Full-Wave Solvers
- 2023
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 22:4, s. 799-803
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Tidskriftsartikel (refereegranskat)abstract
- An iterative algorithm is adopted to construct approximate representations of matrices describing the scattering properties of arbitrary objects. The method is based on the implicit evaluation of scattering responses from iteratively generated excitations. The method does not require explicit knowledge of any system matrices (e.g., stiffness or impedance matrices) and is well-suited for use with matrix-free and iterative full-wave solvers, such as FDTD (Finite-difference time-domain method), FEM (Finite element method), and MLFMA (Multilevel Fast Multipole Algorithm). The proposed method allows for significant speed-up compared to the direct construction of a full transition matrix or scattering dyadic. The method is applied to the characteristic mode decomposition of arbitrarily shaped obstacles of arbitrary material distribution. Examples demonstrating the speed-up and complexity of the algorithm are studied with several commercial software packages.
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| 705. |
- Lundgren, Johan, et al.
(författare)
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Measurement Characterization of Aperture Correction Technique for EMF
- 2020
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Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020. - 9788831299008
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Konferensbidrag (refereegranskat)abstract
- Techniques for accurate, robust and efficient over-the-air testing for devices in the next generation communication system are important. This work aims at presenting the use of an aperture calibration technique, through which field values and power density values are reconstructed at an arbitrary plane in the near-field from a measurement of a separate plane for devices operating in 28-60 GHz. The technique calibrates for the probe interaction, and for the measured position, providing promising results. Power density levels is important for electromagnetic field (EMF) compliance assessment of 5G. In this work the technique is utilized to reconstruct the power densities, as close as λ/5, for three different radiating devices. The results are compared with simulations. An investigation into how the technique performs - for different frequencies, using synthetic input data, various grid sampling, noise and choice of numerical parameters is carried out, showing the regions of applicability.
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| 706. |
- Lundgren, Johan, et al.
(författare)
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Near-Field Measurement and Calibration Technique for RF EMF Exposure Assessment of mm-wave 5G Devices
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Accurate and efficient measurement techniques are needed for exposure assessment of 5G portable devices---which are expected to utilize frequencies beyond 6 GHz---with respect to the radio frequency electromagnetic field exposure limits. Above 6 GHz, these limits are expressed in terms of the incident power density, thus requiring that the electromagnetic fields need to be evaluated with high precision in close vicinity to the device under test (DUT), i.e., in the near-field region of the radiating antenna. This work presents a cutting-edge near-field measurement technique suited for these needs. The technique---based on source reconstruction on a predefined surface representing the radiating aperture of the antenna---requires two sets of measurements; one of the DUT, and one of a small aperture. This second measurement functions as a calibration of both the measurement probe impact on the received signal, and the experimental setup in terms of the relative distance between the probe and the DUT. Results are presented for a 28 GHz and a 60 GHz antenna array; both developed for 5G applications. The computed power density agrees well with simulations at evaluation planes residing as close as one fifth of a wavelength away from the DUT.
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| 707. |
- Lundmark, Robert, et al.
(författare)
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Evaluation of the liberalisation process of the Swedish electricity market
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this pre-study is to map the literature covering the liberalisation of the Swedish electricity market, elaborating on the possible consensus, as well as highlight any patterns that may explain differences in opinions. Moreover, the aim is to present material that accommodates decisions on the directions further research in the social sciences on the electricity market may take.
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| 708. |
- Löv, Åsa, et al.
(författare)
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Evaluating the ability of standardised leaching tests to predict metal(loid) leaching from intact soil columns using size-based elemental fractionation
- 2019
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Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 222, s. 453-460
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory-based leaching tests are frequently used for in situ risk assessments of contaminant leaching to groundwater and surface waters. This study evaluated the ability of three standardised leaching tests to assess leaching of lead (Pb), zinc (Zn), arsenic (As) and antimony (Sb) from four intact soil profiles, by considering particulate (0.45-8 mu m; percolation test), colloidal (10 kDa-0.45 mu m) and truly dissolved (<10 kDa) fractions of these elements. Deionised water was used as the percolation test leachant, while either deionised water or 1 mM CaCl2 was used in batch tests. Data from an irrigation experiment were used as reference. The results indicated that in percolation tests, leachate should be collected at a liquid:solid ratio (L/S) range of 2-10, instead of 0-0.5 or 0.5-2. Even at L/S = 2-10, the percolation test overestimated total Pb concentration, mainly because of greater mobilisation of particle-bound Pb, but appeared suitable for categorising soils into high/low risk with respect to mobilisation of particulate and colloidal contaminants. The batch test performed better with CaCl2 than with deionised water when standard membrane filtration (0.45 gm) was used, as the high Ca2+ concentration reduced colloidal mobilisation, avoiding overestimation of concentrations of elements such as Pb. However, the higher Ca2+ concentration and lower pH could result in overestimated concentrations of weakly sorbed elements, e.g. Zn. (C) 2019 The Authors. Published by Elsevier Ltd.
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| 709. |
- Löv, Åsa, et al.
(författare)
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Particle- and colloid-facilitated Pb transport in four historically contaminated soils - Speciation and effect of irrigation intensity
- 2018
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927. ; 96, s. 327-338
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Tidskriftsartikel (refereegranskat)abstract
- Due to the low solubility of lead (Pb) in many soils, colloidal and particulate transport may have large effects on Pb leaching. However, the role of colloidal and particulate transport varies considerably between soils and the mechanisms controlling mobilisation are complex and poorly known. Furthermore, increased frequency of high-intensity rainfall events is expected in some parts of Europe and North America in response to climate change, which might increase the mobilisation of particles and colloids. In this work, we investigated transport of particulate ( > 0.45 mu m), colloidal (10 kDa-0.45 mu m) and truly dissolved ( < 10 kDa) Pb in an irrigation experiment on intact soil columns from four historically contaminated soils. We also investigated the effect of irrigation intensity (2-20 mmh(-1)) on Pb leaching in these fractions. The mechanism binding Pb on particles and colloids was evaluated by extended X-ray absorption fine structure (EXAFS) spectroscopy and geochemical modelling. A 10-fold increase in irrigation intensity brought about at most a three-fold change in leached particulate and colloidal Pb concentrations. In contrast, the fraction of leached Pb associated with particles and colloids varied by one order of magnitude between soils. Hence, the results suggest that it is more important to consider soil type than potential future increases in rainfall. For one soil with high concentrations of both arsenic (As) and Pb, geochemical modelling indicated that mimetite, Pb-5(AsO4)(3)Cl(s), was the major Pb species in the colloidal and particulate fractions. For the other three soils, EXAFS of Pb on isolated particles and colloids indicated that ferrihydrite was a major phase-sorbing Pb and this was supported by geochemical equilibrium modelling. Thus geochemical modelling can be used to indicate the speciation of Pb in particles and colloids leached in intact soils.
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| 710. |
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