[article-cris] Sähkötekniikan korkeakoulu / ELEC

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Accurate Angle-of-Arrival Sensing for Receiving and Scattering Array Antennas
(2024-07-19) Vuyyuru, Sravan K. R.; Valkonen, Risto; Kwon, Do-Hoon; Tretyakov, Sergei; Department of Electronics and Nanoengineering; Viktar Asadchy Group; Sergei Tretiakov Group; Nokia Bell Labs Finland; University of Massachusetts Amherst
Incorporating sensing capabilities into reconfigurable intelligent surfaces coupled with signal rerouting functionalities provides a promising route to integrating sensing and communication functionalities. In this paper, we propose and numerically demonstrate the feasibility of accurate angle-of-arrival detection in reconfigurable reflectarrays. A theoretical model has been formulated to articulate the sensing ability, drawing upon principles rooted in the receiving antenna theory.
The Large Interferometer For Exoplanets (LIFE): a space mission for mid-infrared nulling interferometry
(2024-08-28) Glauser, Adrian M.; Quanz, Sascha P.; Hansen, Jonah; Dannert, Felix; Ireland, Michael; Linz, Hendrik; Absil, Olivier; Alei, Eleonora; Angerhausen, Daniel; Birbacher, Thomas; Defrère, Denis; Fortier, Andrea; Huber, Philipp A.; Kammerer, Jens; Laugier, Romain; Lichtenberg, Tim; Noack, Lena; Ranganathan, Mohanakrishna; Rugheimer, Sarah; Airapetian, Vladimir; Alibert, Yann; Amado, Pedro J.; Anger, Marius; Department of Electronics and Nanoengineering; Jaan Praks Group; Swiss Federal Institute of Technology Zurich; Australian National University; Max Planck Institute for Astronomy; University of Liège; NASA Goddard Space Flight Center; KU Leuven; University of Bern; ESO; University of Groningen; Freie Universität Berlin; York University Toronto; Instituto de Astrofísica de Andalucía
The Large Interferometer For Exoplanets (LIFE) is a proposed space mission that enables the spectral characterization of the thermal emission of exoplanets in the solar neighborhood. The mission is designed to search for global atmospheric biosignatures on dozens of temperate terrestrial exoplanets and it will naturally investigate the diversity of other worlds. Here, we review the status of the mission concept, discuss the key mission parameters, and outline the trade-offs related to the mission’s architecture. In preparation for an upcoming concept study, we define a mission baseline based on a free-formation flying constellation of a double Bracewell nulling interferometer that consists of 4 collectors and a central beam-combiner spacecraft. The interferometric baselines are between 10–600m, and the estimated diameters of the collectors are at least 2m (but will depend on the total achievable instrument throughput). The spectral required wavelength range is 6–16μm (with a goal of 4–18.5μm), hence cryogenic temperatures are needed both for the collectors and the beam combiners. One of the key challenges is the required deep, stable, and broad-band nulling performance while maintaining a high system throughput for the planet signal. Among many ongoing or needed technology development activities, the demonstration of the measurement principle under cryogenic conditions is fundamentally important for LIFE.
Simultaneous Perfect Anomalous Reflection and Angle-of-Arrival Sensing Using Patch Arrays
(2024-07-19) Movahediqomi, Mostafa; Vuyyuru, Sravan K. R.; Ptitcyn, Grigory; Valkonen, Risto; Kwon, Do-Hoon; Tretyakov, Sergei A.; Department of Electronics and Nanoengineering; Viktar Asadchy Group; Sergei Tretiakov Group; University of Pennsylvania; Nokia Bell Labs Finland; University of Massachusetts Amherst
A novel optimization-based method tailored for the evolution of communication networks is presented, aimed at achieving a perfect power efficiency while accurately determining the angle of arrival of user-generated waves. Our approach involves optimizing aperiodic loaded structures, eliminating the constraints of electromagnetic periodicity while maintaining a fixed half-wavelength spacing. The proposed configuration employs practical square patches, each loaded with passive tunable elements. These load values can be dynamically adjusted, enabling a continuous scanning capability to capture user signals arriving from unknown angles.
PyBDR: Set-Boundary Based Reachability Analysis Toolkit in Python
(2025) Ding, Jianqiang; Wu, Taoran; Liang, Zhen; Xue, Bai; Department of Electrical Engineering and Automation; Platzer, Andre; Rozier, Kristin Yvonne; Pradella, Matteo; Rossi, Matteo; Nonlinear Systems and Control; CAS - Institute of Software; National University of Defense Technology
We present PyBDR, a Python reachability analysis toolkit based on set-boundary analysis, which centralizes on widely-adopted set propagation techniques for formal verification, controller synthesis, state estimation, etc. It employs boundary analysis of initial sets to mitigate the wrapping effect during computations, thus improving the performance of reachability analysis algorithms without significantly increasing computational costs. Beyond offering various set representations such as polytopes and zonotopes, our toolkit particularly excels in interval arithmetic by extending operations to the tensor level, enabling efficient parallel interval arithmetic computation and unifying vector and matrix intervals into a single framework. Furthermore, it features symbolic computation of derivatives of arbitrary order and evaluates them as real or interval-valued functions, which is essential for approximating behaviours of nonlinear systems at specific time instants. Its modular architecture design offers a series of building blocks that facilitate the prototype development of reachability analysis algorithms. Comparative studies showcase its strengths in handling verification tasks with large initial sets or long time horizons. The toolkit is available at https://github.com/ASAG-ISCAS/PyBDR.
55-100-GHz Enhanced Gilbert Cell Mixer Design in 22-nm FDSOI CMOS
(IEEE, 2024) Jokiniemi, Kimi; Ryynanen, Kaisa; Vaha, Joni; Kankkunen, Elmo; Stadius, Kari; Ryynanen, Jussi; Department of Electronics and Nanoengineering; Jussi Ryynänen Group; Marko Kosunen Group; Department of Electronics and Nanoengineering; Jussi Ryynänen Group
This article presents a wideband active millimeter wave (mmWave) CMOS downconversion mixer preceded by thorough analysis. This article aims to provide solid reasoning for the proper choice of mixer topology and present methods to achieve high mixer performance, guiding mmWave mixer design. The article first analyses passive and active mixer input impedance and switching performance with a weak sinusoidal local oscillator (LO) signal, demonstrating that passive mixer switching performance is far more dependent on the LO signal. The article then introduces different active mixer design enhancement techniques, namely, peaking inductances and individual mixer stage biasing. The article proposes an enhanced Gilbert cell mixer that uses transformer coupling between the transconductance and switching stages. The complete mixer structure with an LO buffer and an IF amplifier consumes an area of only 0.13 mm2 fabricated in a 22-nm FDSOI process. The design achieves a measured peak voltage conversion gain (CG) of 3.5 dB, an exceptionally wide 55-100-GHz RF bandwidth, and a 10-GHz IF bandwidth. The complete mixer consumes 33 mW of power from a low 0.8-V supply voltage and demonstrates an input 1-dB gain compression point of -6 dBm.
Flexibility of Electric Vehicle Charging with Demand Response and Vehicle-To-Grid for Power System Benefit
(IEEE, 2024) Jokinen, Ilkka; Lehtonen, Matti; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering
As charging load from electric vehicles (EVs) increases, its temporal demand may challenge existing power systems. However, as EVs could also supply power to the grid, they could provide benefits for the power systems. Moreover, by controlling the charging, they could reduce their charging costs. Thus, in this study the flexibility of EV charging load within charging events was modeled, considering available charging power, ambient temperature, and unidirectional and bidirectional controlled charging. Then, the charging flexibility was first analyzed by minimizing the charging costs for individual EVs. The results showed that with high electricity market prices, with high fluctuation, the EVs could reduce their charging costs up to 27% and 35%, with unidirectional and bidirectional controlled charging respectively, compared to uncontrolled charging. Secondly, the EV charging flexibility was analyzed for the benefit of the power system by an aggregator, assuming a fully electrified car sector. The benefit was measured by the required additional power source capacity and generation. During the analyzed period, 2018-2023 which peak load was 14.7 GW, with uncontrolled charging, the required power source capacity increased significantly, by 2-2.8 GW (40-54%), whereas with controlled unidirectional charging the increase was 0.3-0.8 GW (7-15%), and with bidirectional charging the capacity was the same as without EVs, or slightly less (-11-1%). However, the yearly differences were notable, and during 2020, with bidirectional charging, this capacity increased. The required power source generation was greatly affected by the assumed power generation capacities, and was lower with controlled charging, compared to uncontrolled charging.
The enigmatic double-peaked stripped-envelope SN 2023aew
(EDP Sciences, 2024-09-01) Kangas, T.; Kuncarayakti, H.; Nagao, T.; Kotak, R.; Kankare, E.; Fraser, M.; Stevance, H.; Mattila, S.; Maeda, K.; Stritzinger, M.; Lundqvist, P.; Elias-Rosa, N.; Ferrari, L.; Folatelli, G.; Frohmaier, C.; Galbany, L.; Kawabata, M.; Koutsiona, E.; Müller-Bravo, T. E.; Piscarreta, L.; Pursiainen, M.; Singh, A.; Taguchi, K.; Teja, R. S.; Valerin, G.; Pastorello, A.; Benetti, S.; Cai, Y. Z.; Charalampopoulos, P.; Gutiérrez, C. P.; Kravtsov, T.; Reguitti, A.; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; Centre of Excellence in Quantum Technology, QTF; University of Turku; University College Dublin; University of Oxford; Kyoto University; Aarhus University; Oskar Klein Centre; INAF - Osservatorio Astronomico di Padova; Universidad Nacional de La Plata; University of Southampton; CSIC - Institute of Space Sciences; University of Hyogo; University of Crete; University of Warwick; Hiroshima University; Indian Institute of Astrophysics; Chinese Academy of Sciences
We present optical and near-infrared photometry and spectroscopy of SN 2023aew and our findings on its remarkable properties. This event, initially resembling a Type IIb supernova (SN), rebrightens dramatically ~90 d after the first peak, at which time its spectrum transforms into that of a SN Ic. The slowly evolving spectrum specifically resembles a post-peak SN Ic with relatively low line velocities even during the second rise. The second peak, reached 119 d after the first peak, is both more luminous (Mr = -18.75±0.04 mag) and much broader than those of typical SNe Ic. Blackbody fits to SN 2023aew indicate that the photosphere shrinks almost throughout its observed evolution, and the second peak is caused by an increasing temperature. Bumps in the light curve after the second peak suggest interaction with circumstellar matter (CSM) or possibly accretion. We consider several scenarios for producing the unprecedented behavior of SN 2023aew. Two separate SNe, either unrelated or from the same binary system, require either an incredible coincidence or extreme fine-tuning. A pre-SN eruption followed by a SN requires an extremely powerful, SN-like eruption (consistent with ~1051 erg) and is also disfavored. We therefore consider only the first peak a true stellar explosion. The observed evolution is difficult to reproduce if the second peak is dominated by interaction with a distant CSM shell. A delayed internal heating mechanism is more likely, but emerging embedded interaction with a CSM disk should be accompanied by CSM lines in the spectrum, which are not observed, and is difficult to hide long enough. A magnetar central engine requires a delayed onset to explain the long time between the peaks. Delayed fallback accretion onto a black hole may present the most promising scenario, but we cannot definitively establish the power source.
Nesting Particle Filters for Experimental Design in Dynamical Systems
(JMLR, 2024) Iqbal, Sahel; Corenflos, Adrien; Särkkä, Simo; Abdulsamad, Hany; Department of Electrical Engineering and Automation; Sensor Informatics and Medical Technology; Helsinki Institute for Information Technology (HIIT)
In this paper, we propose a novel approach to Bayesian experimental design for nonexchangeable data that formulates it as risk-sensitive policy optimization. We develop the Inside-Out SMC2 algorithm, a nested sequential Monte Carlo technique to infer optimal designs, and embed it into a particle Markov chain Monte Carlo framework to perform gradient-based policy amortization. Our approach is distinct from other amortized experimental design techniques, as it does not rely on contrastive estimators. Numerical validation on a set of dynamical systems showcases the efficacy of our method in comparison to other state-of-the-art strategies.
Efficient Synthesis of Large Finite Patch Arrays for Scanning Wide-Angle Anomalous Reflectors
(IEEE, 2024-09-24) Vuyyuru, Sravan K. R.; Valkonen, Risto; Tretyakov, Sergei A.; Kwon, Do-Hoon; Department of Electronics and Nanoengineering; Viktar Asadchy Group; Sergei Tretiakov Group; Nokia Bell Labs Finland; University of Massachusetts Amherst
A design methodology for planar loaded antenna arrays is proposed to synthesize a perfect anomalous reflection into an arbitrary direction by optimizing the scattering characteristics of passively loaded array antennas. It is based on efficient and accurate prediction of the induced current distribution and the associated scattering for any given set of load impedances. For a fixed array of finite dimensions, the deflection angles can be continuously adjusted with proper tuning of each load. We study and develop anomalous reflectors as semi-finite (finite × infinite) and finite planar rectangular arrays comprising printed patches with a subwavelength spacing. Anomalous reflection into an arbitrary desired angle using purely reactive loads is numerically and experimentally validated. Owing to the algebraic nature of load optimization, the design methodology may be applied to the synthesis of large-scale reflectors of practical significance.
Probabilistic Subgoal Representations for Hierarchical Reinforcement learning
(JMLR, 2024) Wang, Vivienne Huiling; Wang, Tinghuai; Yang, Wenyan; Kämäräinen, Joni Kristian; Pajarinen, Joni; Department of Electrical Engineering and Automation; Robot Learning; Huawei Technologies; Tampere University
In goal-conditioned hierarchical reinforcement learning (HRL), a high-level policy specifies a subgoal for the low-level policy to reach. Effective HRL hinges on a suitable subgoal representation function, abstracting state space into latent subgoal space and inducing varied low-level behaviors. Existing methods adopt a subgoal representation that provides a deterministic mapping from state space to latent subgoal space. Instead, this paper utilizes Gaussian Processes (GPs) for the first probabilistic subgoal representation. Our method employs a GP prior on the latent subgoal space to learn a posterior distribution over the subgoal representation functions while exploiting the long-range correlation in the state space through learnable kernels. This enables an adaptive memory that integrates long-range subgoal information from prior planning steps allowing to cope with stochastic uncertainties. Furthermore, we propose a novel learning objective to facilitate the simultaneous learning of probabilistic subgoal representations and policies within a unified framework. In experiments, our approach outperforms state-of-the-art baselines in standard benchmarks but also in environments with stochastic elements and under diverse reward conditions. Additionally, our model shows promising capabilities in transferring low-level policies across different tasks.
The impact of improved estimates of radio star astrometric models on the alignment of the Gaia bright reference frame to ICRF3
(EDP Sciences, 2024-09-01) Lunz, Susanne; Anderson, James M.; Xu, Ming H.; Heinkelmann, Robert; Titov, Oleg; Lestrade, Jean François; Johnson, Megan C.; Shu, Fengchun; Chen, Wen; Melnikov, Alexey; Mikhailov, Andrei; Mccallum, Jamie; Lopez, Yulia; De Vicente Abad, Pablo; Schuh, Harald; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; Technical University of Berlin; Helmholtz Centre Potsdam - German Research Centre for Geosciences; Geoscience Australia; Observatoire de Paris; U.S. Naval Observatory; CAS - Shanghai Astronomical Observatory; Yunnan Observatories; University of Tasmania; Observatorio de Yebes
We investigated the residual orientation offset and spin between the bright (G ≤ 13 mag) frame of the Gaia Early Data Release 3 (Gaia EDR3) and the third realization of the International Celestial Reference Frame (ICRF3). For this purpose, six rotation parameters (orientation offset and its time derivative, the spin), as well as corrections to the Gaia astrometric model for each star involved, are fitted to the differences in the astrometric models derived from very long baseline interferometry (VLBI) and Gaia. This study aims to find reliable estimates for the rotation parameters between the two frames. Methods. We reprocessed our previous analyses while taking into account the effect of Galactocentric acceleration on the VLBI observations. Furthermore, we replaced VLBI data for 12 stars by improved estimates of models of stellar motion from combining historical data with the new positions, rather than including the new observations directly as single-epoch positions in the analysis of the rotation parameters. Additionally, we replaced the model positions by positions obtained without correcting the calibrator data for source structure whenever possible to better reference the star position to ICRF3. In the same fashion, the VLBI proper motion and parallax were included for two of the stars for the first time, and data for five new stars were added. Results. The iterative solutions for the spin parameters show less scatter in the X component when the new models of stellar motion from VLBI are applied. The mean formal errors of the spin parameters decrease by about 15%, whereas those of the orientation offsets increase by about 15%. Small additional improvements in the mean formal error were achieved by including new VLBI data and by excluding stars that produce offsets in the iterative rotation parameter estimates from the beginning. The orientation offset [ϵX(T), ϵY (T), ϵZ(T)] and the spin [ωX,ωY ,ωZ] of the final baseline solution of this work were found to be (+0.322, +0.228, +0.163)±(0.203, 0.251, 0.155) mas and (+0.034, +0.072, .0.026)±(0.023, 0.025, 0.023) mas yr.1. As a consequence, no significant orientation offset of Gaia EDR3 toward ICRF3 is detected; however, the spin ωY is statistically significant at the 3σ level. The rotation parameters between the Gaia and VLBI frames in the Y direction remain the least well determined in terms of formal errors. The impact of Galactocentric acceleration on the rotation parameter analysis was found to be negligible with the currently available VLBI data. As a result, it was found that the uncorrected bright Gaia frame exhibits a closer alignment with ICRF3 compared to the corrected frame.
Residual Learning and Context Encoding for Adaptive Offline-to-Online Reinforcement Learning
(JMLR, 2024) Nakhaeinezhadfard, Mohammadreza; Scannell, Aidan; Pajarinen, Joni; Department of Electrical Engineering and Automation; Finnish Center for Artificial Intelligence, FCAI; Robot Learning
Offline reinforcement learning (RL) allows learning sequential behavior from fixed datasets. Since offline datasets do not cover all possible situations, many methods collect additional data during online fine-tuning to improve performance. In general, these methods assume that the transition dynamics remain the same during both the offline and online phases of training. However, in many real-world applications, such as outdoor construction and navigation over rough terrain, it is common for the transition dynamics to vary between the offline and online phases. Moreover, the dynamics may vary during the online fine-tuning. To address this problem of changing dynamics from offline to online RL we propose a residual learning approach that infers dynamics changes to correct the outputs of the offline solution. At the online fine-tuning phase, we train a context encoder to learn a representation that is consistent inside the current online learning environment while being able to predict dynamic transitions.
Broadband transparent Huygens' spaceplates
(Nature Portfolio, 2024) Díaz Fernández, Francisco J.; Máñez-Espina, Luis Manuel; Diaz Rubio, Ana; Asadchy, Viktar; Department of Electronics and Nanoengineering; Viktar Asadchy Group; Universitat Politècnica de València
Spaceplates have emerged in the context of nonlocal metasurfaces, enabling the compression of optical systems by minimizing the required empty space between their components. In this work, we design and analyze spaceplates that support resonances with opposite symmetries, operating under the so-called Huygens’ condition. Using the temporal coupled-mode theory, we demonstrate that the spatial compression provided by Huygens’ spaceplates is twice that of conventional single-resonance counterparts. Additionally, they can support broader operational bandwidths and numerical apertures, facilitating the reduction of chromatic aberrations. Moreover, Huygens’ spaceplates maintain nearly full transparency over a wide frequency and angular range, allowing their straightforward cascading for multi-frequency broadband operation. Finally, we propose a physical implementation of a Huygens’ spaceplate for optical frequencies based on a photonic crystal slab geometry.
Polarization management in silicon photonics
(Nature Portfolio, 2024) Shahwar, Dura; Yoon, Hoon Hahn; Akkanen, Suvi-Tuuli; Li, Diao; Muntaha, Sidra tul; Cherchi, Matteo; Aalto, Timo; Sun, Zhipei; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; VTT Technical Research Centre of Finland; Gwangju Institute of Science and Technology
Polarization management plays a key role in various applications, such as optical communications, imaging, and sensing. It not only mitigates detrimental effects (e.g., polarization mode dispersion in optical communication) but also enables advanced functionalities, such as polarization multiplexing and optical isolation. Herein, we review the state-of-the-art approaches for on-chip polarization management. Additionally, we discuss strategies for developing non-reciprocal photonic devices and the challenges associated with monolithic integration in photonics circuits.
Roadmap on electromagnetic metamaterials and metasurfaces
(Institute of Physics Publishing, 2024-07) Cui, Tie Jun; Zhang, Shuang; Alù, Andrea; Wegener, Martin; Pendry, Sir John; Luo, Jie; Lai, Yun; Wang, Zuojia; Lin, Xiao; Chen, Hongsheng; Chen, Ping; Wu, Rui Xin; Yin, Yuhang; Zhao, Pengfei; Chen, Huanyang; Li, Yue; Zhou, Ziheng; Engheta, Nader; Asadchy, Viktar; Simovski, Constantin; Tretyakov, Sergei; Yang, Biao; Campbell, Sawyer D.; Hao, Yang; Werner, Douglas H.; Sun, Shulin; Zhou, Lei; Xu, Su; Sun, Hong Bo; Zhou, Zhou; Li, Zile; Zheng, Guoxing; Chen, Xianzhong; Li, Tao; Zhu, Shining; Zhou, Junxiao; Zhao, Junxiang; Liu, Zhaowei; Zhang, Yuchao; Zhang, Qiming; Gu, Min; Xiao, Shumin; Liu, Yongmin; Zhang, Xianzhe; Tang, Yutao; Li, Guixin; Zentgraf, Thomas; Koshelev, Kirill; Kivshar, Yuri; Li, Xin; Badloe, Trevon; Huang, Lingling; Rho, Junsuk; Wang, Shuming; Tsai, Din Ping; Bykov, A. Yu; Krasavin, A. V.; Zayats, A. V.; McDonnell, Cormac; Ellenbogen, Tal; Luo, Xiangang; Pu, Mingbo; Garcia-Vidal, Francisco J.; Liu, Liangliang; Li, Zhuo; Tang, Wenxuan; Ma, Hui Feng; Zhang, Jingjing; Luo, Yu; Zhang, Xuanru; Zhang, Hao Chi; He, Pei Hang; Zhang, Le Peng; Wan, Xiang; Wu, Haotian; Liu, Shuo; Jiang, Wei Xiang; Zhang, Xin Ge; Qiu, Cheng Wei; Ma, Qian; Liu, Che; Li, Long; Han, Jiaqi; Li, Lianlin; Cotrufo, Michele; Caloz, C.; Deck-Léger, Z. L.; Bahrami, A.; Céspedes, O.; Galiffi, E.; Huidobro, P. A.; Cheng, Qiang; Dai, Jun Yan; Ke, Jun Cheng; Zhang, Lei; Galdi, Vincenzo; di Renzo, Marco; Department of Electronics and Nanoengineering; Kostantin Simovski Group; Sergei Tretiakov Group; Southeast University, Nanjing; University of Hong Kong; City University of New York; Karlsruhe Institute of Technology; Imperial College London; Soochow University; Nanjing University; Zhejiang University; Xiamen University; Tsinghua University; University of Pennsylvania; National University of Defense Technology; Pennsylvania State University; Queen Mary University of London; Fudan University; Jilin University; Wuhan University; Heriot-Watt University; University of California; University of Shanghai for Science and Technology; Harbin Institute of Technology; Northeastern University; Southern University of Science and Technology; Paderborn University; Australian National University; Beijing Institute of Technology; Pohang University of Science and Technology; City University of Hong Kong; King's College London; Tel Aviv University; Chinese Academy of Sciences; Ramón y Cajal University Hospital; Nanjing University of Aeronautics and Astronautics; Nanyang Technological University; National University of Singapore; Xidian University; Peking University; KU Leuven; Universidade de Lisboa; University of Sannio; Université Paris-Saclay; Stanford University
Host galaxy of low-luminosity compact sources
(EDP Sciences, 2024-09-01) Vietri, Amelia; Berton, Marco; Järvelä, Emilia; Kunert-Bajraszewska, M.; Ciroi, S.; Varglund, Irene; Dalla Barba, B.; Sani, E.; Crepaldi, Luca; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; University of Padova; Nicolaus Copernicus University in Toruń; Anne Lähteenmäki Group; European Southern Observatory Santiago; University of Oklahoma
The term 'active galactic nuclei'(AGN) is applied to a huge variety of objects, classified on the basis of their properties at different wavelengths. Peaked sources (PSs) represent a class of AGN at the first stage of evolution, characterised by a peaked radio spectrum. Among these radio sources, low-luminosity compact (LLC) sources can be identified as PSs accreting with a high Eddington rate, harbouring low-power jets, and hosting low-mass black holes. These properties are also shared by narrow-line Seyfert 1 galaxies (NLS1s). In 2016, LLCs were hypothesised to be the parent population of NLS1s with a flat radio spectrum (F-NLS1s), suggesting that the former may be the same objects as the latter but, instead, seen at a higher inclination. Based on radio luminosity functions and optical spectra analysis, ten LLCs were identified as valid F-NLS1s candidates. To account for the missing piece to the puzzle and verifying whether these LLCs could be hosted in late-type galaxies as NLS1s, we performed a photometric decomposition of their Pan-STARRS1 images in all five filters. We used the 2D fitting algorithm GALFIT for the single-band analysis and its extension GALFITM for the multi-band analysis. Considering that the morphological type and the structural parameters of the host may be dependent on the wavelength, we found six out of ten LLCs hosted in late-type galaxies, probably with pseudo-bulges, along with three point-like sources and one object of an uncertain classification. Although this study is based on a small sample, it represents the first morphological analysis of LLC host galaxies. These results confirm the trend observed in NLS1s, indicating late-type and disc-like host galaxies for LLCs and supporting the validity of the parent population scenario.
Fault-Tolerant Topology of Dual Active Bridge Converter for On-Board Charger in Electric Vehicles
(IEEE, 2024-09-16) Babalou, Milad; Torkaman, Hossein; Pouresmaeil, Edris; Department of Electrical Engineering and Automation; Renewable Energies for Power Systems; Shahid Beheshti University
The on-board chargers (OBCs) are commonly utilized in electric vehicles (EVs) due to their cost-effectiveness and ease of installation. The performance of EVs to supply power back to the grid has sparked interest in bidirectional power flow solutions. Dual-active-bridge (DAB) dc-dc converters have gained prominence as a promising power interface between energy storage components and the power bus. However, failures in the active devices of DAB converters can result in converter disconnection. In this paper, a fault-tolerant DAB (FT-DAB) converter is proposed to improve the reliability of the OBC. In order to ensure uninterrupted operation in short-circuit (SC) and open-circuit (OC) faults of the semiconductors, the topology of the single-phase DAB is modified in such a way that the single transformer is replaced with dual-transformers in addition to employing an H5 structure for each bridge. The proposed FT-DAB converter is investigated in various faulty conditions, in which, the post-fault performance and the maximum level of the output power are discussed in detail. Finally, the FT-DAB is prototyped and tested under various post-fault scenarios. Experimental test results validate the reliable and uninterrupted operation of the FT-DAB.
Induced electric fields in MRI settings and electric vestibular stimulations: same vestibular effects?
(Springer, 2024-09-11) Bouisset, Nicolas; Laakso, Ilkka; Department of Electrical Engineering and Automation; Electromagnetics in Health Technology; Western University
In Magnetic Resonance Imaging scanner environments, the continuous Lorentz Force is a potent vestibular stimulation. It is nowadays so well known that it is now identified as Magnetic vestibular stimulation (MVS). Alongside MVS, some authors argue that through induced electric fields, electromagnetic induction could also trigger the vestibular system. Indeed, for decades, vestibular-specific electric stimulations (EVS) have been known to precisely impact all vestibular pathways. Here, we go through the literature, looking at potential time varying magnetic field induced vestibular outcomes in MRI settings and comparing them with EVS-known outcomes. To date, although theoretically induction could trigger vestibular responses the behavioral evidence remains poor. Finally, more vestibular-specific work is needed.
(poster) ALD SiO2 provides efficient Ge surface passivation with a tailorable charge polarity
(2024) Leiviskä, Oskari; Liu, Hanchen; Fung, John; Isometsä, Joonas; Vähänissi, Ville; Savin, Hele; Department of Electronics and Nanoengineering; School common, ELEC; Hele Savin Group
Atomic layer deposited (ALD) thin films have proven to be a highly effective method to reduce electronic recombination losses caused by defects present at the Si surfaces. Likewise, germanium (Ge) surfaces suffer from the same recombination problem and indeed, various ALD-based surface passivation schemes have been tried recently on them as well. The current methods utilize mainly so-called field effect passivation based on the negative fixed charge present in the film, such as aluminum oxide (Al2O3). The fixed charge induces an electric field to the vicinity of the substrate surface and thus prevents surface recombination by repelling electrons away from the surface. The negative charge can, however, be detrimental for certain applications. Therefore, there is a motivation to find a material which provides either a positive fixed charge or even better the ability to tailor the charge polarity. In this work we propose plasma-enhanced atomic layer deposited (PE-ALD) silicon oxide (SiO2) layers as a positive charge containing material for passivation of Ge surfaces and apply them as further charge tailoring interlayers for Ge/Al2O3 interfaces, as was demonstrated previously for Si/Al2O3 interfaces. First, we study 10 nm thick PE-ALD SiO2 films on n-type single-crystalline Ge wafers from which the charge polarity is determined. Next, the impact of PE-ALD SiO2 layers at Ge/Al2O3 interface is studied by varying the SiO2 interlayer thickness in the range of 1-20 nm. The passivation quality is monitored by measuring the minority carrier lifetime (τeff) and the thin film charge (Qtot) is determined from contactless capacitance-voltage (C-V) measurement. The results demonstrate that a bare PE-ALD SiO2 film provides lifetimes in a similar range (> 1 ms) as previous state-of-the-art Ge surface passivation schemes. Surface recombination is seen to increase when depositing negative corona charge at the surface (i.e. effective neutralization of fixed charge) indicating the formation of positive charge on the Ge/SiO2 interface. Figure 1 presents both the τeff and the Qtot obtained with an SiO2 interlayer with varying nominal thickness at Ge/Al2O3 interface. C-V measurements show that ALD SiO2 interlayers at the Ge/Al2O3 interface allow us to tailor the effective charge polarity from negative to positive by gradually increasing the SiO2 layer thickness from ultrathin to thicker layers. Changes in the interlayer thickness at the Ge/Al2O3 interface caused a shift from negative effective charge to positive as the thickness of SiO2 increased. This also influences the τeff measured from these samples, implying an altering presence of field-effect passivation.
Predicting the Bistatic Scattering of a Multi-Port Loaded Structure Under Arbitrary Excitation: The S-Parameters Approach
(IEEE, 2024) Kuznetsov, Aleksandr D.; Holopainen, Jari; Viikari, Ville; Department of Electronics and Nanoengineering; Ville Viikari Group
Various applications, including reconfigurable intelligent surfaces (RISs), radio frequency identification, and ambient backscatter devices, are based on scattering. Predicting the scattering properties of these systems accurately and universally in a computationally efficient manner is crucial. In this article, we propose a model for predicting the scattering properties of an electromagnetic structure controlled by loads terminated to multiple ports. This model is based on: 1) S-parameters describing the coupling between the ports; 2) embedded element radiation patterns associated with each port; and 3) structural scattering under multiple incident wave directions. To construct the model, one set of electromagnetic descriptions (e.g., simulations or measurements) needs to be done for a structure before computing the scattering properties of the structure for arbitrary tunable load values. Unlike many other methods, the proposed method fully takes into account structural scattering in different directions simultaneously and requires no simplifications or approximations to the scattering structure, such as the assumption of local periodicity or element identity. This method facilitates characterizing the scattering ability of the structure in terms of bistatic cross section (BCS), also known as bistatic radar cross section (bRCS), and can be beneficial, for instance, in designing RISs and backscatter systems. Simulations and experiments at different frequencies verified the proposed model.

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