| 1. |
- Capek, Miloslav, et al.
(author)
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Characteristic Mode Decomposition of Scattering Dyadic
- 2022
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In: 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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Conference paper (peer-reviewed)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.
(author)
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Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary Full-Wave Solvers
- 2023
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:1, s. 830-839
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Journal article (peer-reviewed)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. |
- Gustafsson, Mats, et al.
(author)
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Degrees of Freedom and Characteristic Modes
- 2023
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Reports (other academic/artistic)abstract
- The number of degrees of freedom is a crucial parameter in many electromagnetic problems. In for example modern communication systems spatial diversity is often employed through multiple beams to enhance capacity and reliability. However, while the degrees of freedom can be computed, their connection to physical quantities is not as easily understood. To address this issue, this paper proposes a scattering-based formulation of characteristic mode analysis that can estimate the degrees of freedom of arbitrarily-shaped objects. The relation between the number of dominant characteristic modes and physical characteristics differs for electrically large and small objects. Specifically, for large objects, it is linked to the average shadow area, while for small objects, it is linked to their average polarizability through the forward scattering sum rule. Therefore, the average shadow area and polarizability are fundamental parameters that provide insight into the number of degrees of freedom for any object. These basic parameters also provide straightforward estimates of the minimum size of a device region required to support a desired number of electromagnetic degrees of freedom across a given spectral response.
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| 4. |
- Helander, Jakob, et al.
(author)
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Reflection-Based Source Inversion for Sparse Imaging of Low-Loss Composite Panels
- 2020
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 68:6, s. 4860-4870
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Journal article (peer-reviewed)abstract
- This article presents a bistatic reflection-based imaging technique for electromagnetic testing of conductor-backed composite panels, which is based on an inverse formulation of the numerical problem at hand, and technically extends a previously demonstrated transmission-based system. The technique exploits the a priori assumption of pixel-based sparsity and retrieves the final image using data from only a single measurement, thereby removing the necessity of a reference measurement to be conducted. To demonstrate the capability of the technique, retrieved images are presented for a synthetic proof-of-concept device under test and an industrially manufactured composite panel. The presented technique can be considered as the initial model in the development of more complex bistatic imaging systems and has been developed for the purpose of extending the opportunities to conduct reflection-based electromagnetic nondestructive testing on aircraft structural components.
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| 5. |
- Ludvig-Osipov, Andrei, et al.
(author)
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Fundamental bounds on extraordinary transmission with experimental validation
- 2018
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Reports (other academic/artistic)abstract
- This paper presents a study of extraordinary transmission (EoT) through arrays of sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the bandwidth of EoT which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize sub-wavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.
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| 6. |
- Ludvig-Osipov, Andrei, et al.
(author)
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Fundamental Bounds on Transmission Through Periodically Perforated Metal Screens With Experimental Validation
- 2020
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In: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 68:2, s. 773-782
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Journal article (peer-reviewed)abstract
- This article presents a study of transmission through arrays of periodic sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the transmission bandwidth which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize sub-wavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.
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| 7. |
- Lundgren, Johan, et al.
(author)
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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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In: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 63:3, s. 77-88
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Journal article (peer-reviewed)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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| 8. |
- Lundgren, Johan, et al.
(author)
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IR and Metasurface based mm-Wave Camera
- 2021
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118
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Journal article (peer-reviewed)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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| 9. |
- Lundgren, Johan, et al.
(author)
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Iterative Calculation of Characteristic Modes Using Arbitrary Full-Wave Solvers
- 2023
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In: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 22:4, s. 799-803
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Journal article (peer-reviewed)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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| 10. |
- Lundgren, Johan, et al.
(author)
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Measurement Characterization of Aperture Correction Technique for EMF
- 2020
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In: 14th European Conference on Antennas and Propagation, EuCAP 2020. - 9788831299008
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Conference paper (peer-reviewed)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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