[article-cris] Sähkötekniikan korkeakoulu / ELEC

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    Survey of bidirectional transmittance distribution function measurement facilities by multilateral scale comparisons
    (Institute of Physics Publishing, 2024-06-01) Fu, Jinglin; Ferrero, Alejandro; Quast, Tatjana; Esslinger, Michael; Santafé-Gabarda, Pablo; Tejedor, Néstor; Campos, Joaquín; Gevaux, Lou; Obein, Gaël; Aschan, Robin; Manoocheri, Farshid; Ikonen, Erkki; Porrovecchio, Geiland; Šmíd, Marek; Molloy, Ellie; Koo, Annette; Jensen, Søren A.; Oser, Rafael; Audenaert, Jan; Meuret, Youri; Källberg, Stefan; Gozhyk, Iryna; Kraus, Tobias; Schirmacher, Alfred; Department of Information and Communications Engineering; Department of Electrical Engineering and Automation; Metrology Research Institute; Physikalisch-Technische Bundesanstalt; Instituto de Óptica "Daza de Valdés"; LNE-CNAM; Czech Metrology Institute; Measurement Standards Laboratory of New Zealand; Danish Fundamental Metrology; Covestro Deutschland AG; KU Leuven; RISE Research Institutes of Sweden AB; Saint-Gobain S.A.; Temicon GmbH
    In recent years, a growing demand for the capability of performing accurate measurements of the bidirectional transmittance distribution function (BTDF) has been observed in industry, research and development, and aerospace applications. However, there exists no calibration and measurement capabilities-entry for BTDF in the database of the Bureau International des Poids et Mesures and to date no BTDF comparison has been conducted between different national metrology institutes (NMIs) or designated institutes (DIs). As a first step to a possible future key comparison and to test the existing capabilities of determining this measurand, two interlaboratory comparisons were performed. In comparison one, five samples of three different types of optical transmissive diffusers were measured by five NMIs and one DI. By specific sample choice, the focus for this study lay more on orientation-dependent scatter properties. In comparison two, where one NMI, one DI, one university, and three industrial partners investigated their measurement capabilities, the dependence on the orientation was not assessed, but two additional samples of the same material and different thickness were measured. Results of the two comparisons are presented, giving a good overview of existing experimental solutions, and showing specific sample-related problems to be solved for improved future BTDF measurements.
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    Evaluating transient behaviour of large-scale photovoltaic systems during lightning events using enhanced finite difference time domain method with variable cell size approach
    (Institution of Engineering and Technology, 2024-04-17) Hetita, Ibrahim; Mansour, Diaa Eldin A.; Han, Yang; Yang, Ping; Wang, Congling; Darwish, Mohamed M.F.; Lehtonen, Matti; Zalhaf, Amr S.; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering; University of Electronic Science and Technology of China; Tanta University; Benha University
    Photovoltaic (PV) arrays are usually installed in open areas; hence, they are vulnerable to lightning strikes that can result in cell degradation, complete damage, service disruption, and increased maintenance costs. As a result, it is imperative to develop an effective and efficient lightning protection system by evaluating the transient behaviour of PV arrays during lightning events. The aim is to evaluate the transient analysis of large-scale PV systems when subjected to lightning strikes using the finite difference time domain (FDTD) technique. Transient overvoltages are calculated at various points within the mounting system. To optimise the FDTD method's execution time and make it more suitable for less powerful hardware, a variable cell size approach is employed. Specifically, larger cell dimensions are used in the earthing system and smaller cell dimensions are used in the mounting system. The FDTD method is utilised to calculate the temporal variation of transient overvoltages for large-scale PV systems under different scenarios, including variations in the striking point, soil resistivity, and the presence of a metal frame. Simulation results indicate that the highest transient overvoltages occur at the striking point, and these values increase with the presence of a PV metal frame as well as with higher soil resistivity. Furthermore, a comparison is performed between the overvoltage results obtained from the FDTD approach and the partial element equivalent circuit (PEEC) method at the four corner points of the mounting systems to demonstrate the superior accuracy of the FDTD method. Besides, a laboratory experiment is conducted on a small-scale PV system to validate the simulation results. The calculated overvoltages obtained from the FDTD and PEEC methods are compared with the measured values, yielding a mean absolute error of 5% and 11% for the FDTD and PEEC methods, respectively, thereby confirming the accuracy of the FDTD simulation model.
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    Quantum-assisted Hilbert-space Gaussian process regression
    (American Physical Society, 2024-05-07) Farooq, Ahmad; Galvis-Florez, Cristian A.; Särkkä, Simo; Department of Electrical Engineering and Automation; Sensor Informatics and Medical Technology; Helsinki Institute for Information Technology (HIIT); Sensor Informatics and Medical Technology
    Gaussian processes are probabilistic models that are commonly used as functional priors in machine learning. Due to their probabilistic nature, they can be used to capture prior information on the statistics of noise, smoothness of the functions, and training data uncertainty. However, their computational complexity quickly becomes intractable as the size of the data set grows. We propose a Hilbert-space approximation-based quantum algorithm for Gaussian process regression to overcome this limitation. Our method consists of a combination of classical basis function expansion with quantum computing techniques of quantum principal component analysis, conditional rotations, and Hadamard and swap tests. The quantum principal component analysis is used to estimate the eigenvalues, while the conditional rotations and the Hadamard and swap tests are employed to evaluate the posterior mean and variance of the Gaussian process. Our method provides polynomial computational complexity reduction over the classical method.
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    Enhancing Hyrcanian Forest Height and Aboveground Biomass Predictions: A Synergistic Use of TanDEM-X InSAR Coherence, Sentinel-1, and Sentinel-2 Data
    (IEEE, 2024) Ronoud, Ghasem; Darvishsefat, Ali A.; Poorazimy, Maryam; Tomppo, Erkki; Antropov, Oleg; Praks, Jaan; Department of Electronics and Nanoengineering; Jaan Praks Group; University of Tehran; University of Eastern Finland; University of Helsinki; VTT Technical Research Centre of Finland
    Forest height (FH) is an important driver for aboveground biomass (AGB) that can be obtained using interferometric SAR (InSAR). However, the limited access to the quad-polarimetric data or high-accuracy terrain model makes FH retrieval a challenging task. This study aimed to retrieve FH and further predict AGB by combining TanDEM-X InSAR coherence, Sentinel-1 (S-1), and Sentinel-2 (S-2) data. A total of 125 sample plots with a size of 900 m2 were established in a broadleaved forest of Kheyroud, Iran. The Linear and Sinc models obtained by simplification of the Random Volume over Ground (RVoG) model were used for deriving FHLin and FHSinc. Further investigation was conducted when S-1 and S-2 features including backscatters and multispectral information were added to FH predictions. Using the abovementioned datasets and FH as an additional predictor, AGB was also predicted. K-nearest neighbor (k-NN), random forest (RF), and support vector regression (SVR) were employed for prediction. Lorey's mean height and AGB at sample plots were used in the accuracy assessment. Using the SVR method and synergy of FHSinc, S-1, and S-2 features, the FH prediction was improved (FHimp) with RMSE of 3.18 m and R2 = 0.59. The AGB prediction with RF and the combination of S-1 and S-2 features resulted in RMSE = 62.88 Mg.ha-1 (19.77%) that was improved to RMSE = 51.27 Mg.ha-1 (16.12%) when FHimp included. This study highlighted the capability of TanDEM-X InSAR coherence with certain geometry for FH prediction. Also, the importance of FH in AGB predictions can stimulate further attempts aiming at higher spatiotemporal accuracies.
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    Joint alignment and steering to manage interference
    (Chongqing University of Posts and Telecommunications, 2024-04) Li, Zhao; Liang, Xiujuan; Liu, Yinghou; Liu, Jia; Yan, Zheng; Department of Communications and Networking; Xidian University
    In wireless communication networks, mobile users in overlapping areas may experience severe interference, therefore, designing effective Interference Management (IM) methods is crucial to improving network performance. However, when managing multiple disturbances from the same source, it may not be feasible to use existing IM methods such as Interference Alignment (IA) and Interference Steering (IS) exclusively. It is because with IA, the aligned interference becomes indistinguishable at its desired Receiver (Rx) under the cost constraint of Degrees-of-Freedom (DoF), while with IS, more transmit power will be consumed in the direct and repeated application of IS to each interference. To remedy these deficiencies, Interference Alignment Steering (IAS) is proposed by incorporating IA and IS and exploiting their advantages in IM. With IAS, the interfering Transmitter (Tx) first aligns one interference incurred by the transmission of one data stream to a one-dimensional subspace orthogonal to the desired transmission at the interfered Rx, and then the remaining interferences are treated as a whole and steered to the same subspace as the aligned interference. Moreover, two improved versions of IAS, i.e., IAS with Full Adjustment at the Interfering Tx (IAS-FAIT) and Interference Steering and Alignment (ISA), are presented. The former considers the influence of IA on the interfering user-pair's performance. The orthogonality between the desired signals at the interfered Rx can be maintained by adjusting the spatial characteristics of all interferences and the aligned interference components, thus ensuring the Spectral Efficiency (SE) of the interfering communication pairs. Under ISA, the power cost for IS at the interfered Tx is minimized, hence improving SE performance of the interfered communication-pairs. Since the proposed methods are realized at the interfering and interfered Txs cooperatively, the expenses of IM are shared by both communication-pairs. Our in-depth simulation results show that joint use of IA and IS can effectively manage multiple disturbances from the same source and improve the system's SE.
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    Explaining crowdworker behaviour through computational rationality
    (Taylor & Francis, 2024-04-24) Hedderich, Michael A.; Oulasvirta, Antti; Department of Communications and Networking; Department of Information and Communications Engineering; Helsinki Institute for Information Technology (HIIT); User Interfaces
    Crowdsourcing has transformed whole industries by enabling the collection of human input at scale. Attracting high quality responses remains a challenge, however. Several factors affect which tasks a crowdworker chooses, how carefully they respond, and whether they cheat. In this work, we integrate many such factors into a simulation model of crowdworker behaviour rooted in the theory of computational rationality. The root assumption is that crowdworkers are rational and choose to behave in a way that maximises their expected subjective payoffs. The model captures two levels of decisions: (i) a worker's choice among multiple tasks and (ii) how much effort to put into a task. We formulate the worker's decision problem and use deep reinforcement learning to predict worker behaviour in realistic crowdworking scenarios. We examine predictions against empirical findings on the effects of task design and show that the model successfully predicts adaptive worker behaviour with regard to different aspects of task participation, cheating, and task-switching. To support explaining crowdworker actions and other choice behaviour, we make our model publicly available.
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    Autonomous underwater vehicle link alignment control in unknown environments using reinforcement learning
    (John Wiley & Sons, 2024-04-23) Weng, Yang; Chun, Sehwa; Ohashi, Masaki; Matsuda, Takumi; Sekimori, Yuki; Pajarinen, Joni; Peters, Jan; Maki, Toshihiro; Department of Electrical Engineering and Automation; Robot Learning; University of Tokyo; Meiji University; Technische Universität Darmstadt
    High-speed underwater wireless optical communication holds immense promise in ocean monitoring and surveys, providing crucial support for the real-time sharing of observational data collected by autonomous underwater vehicles (AUVs). However, due to inaccurate target information and external interference in unknown environments, link alignment is challenging and needs to be addressed. In response to these challenges, we propose a reinforcement learning-based alignment method to control the AUV to establish an optical link and maintain alignment. Our alignment control system utilizes a combination of sensors, including a depth sensor, Doppler velocity log (DVL), gyroscope, ultra-short baseline device, and acoustic modem. These sensors are used in conjunction with a particle filter to observe the environment and estimate the AUV's state accurately. The soft actor-critic algorithm is used to train a reinforcement learning-based controller in a simulated environment to reduce pointing errors and energy consumption in alignment. After experimental validation in simulation, we deployed the controller on an actual AUV called Tri-TON. In experiments at sea, Tri-TON maintained the link and angular pointing errors within 1 m and (Formula presented.), respectively. Experimental results demonstrate that the proposed alignment control method can establish underwater optical communication between AUV fleets, thus improving the efficiency of marine surveys.
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    Core loss determination in electric machines using short-time transient thermal measurements
    (Institution of Engineering and Technology, 2024) Osemwinyen, Osaruyi; Hemeida, Ahmed; Martin, Floran; Gürbüz, Ismet Tuna; Belahcen, Anouar; Department of Electrical Engineering and Automation; Computational Electromechanics
    This paper introduces a novel application of the inverse modelling method, which is designed to estimate core losses in both the stator and rotor regions of an electrical machine. The technique focuses on the use of short-term transient temperature measurements obtained from the stator core of a slotless induction machine, with a focus on validating the measured temperature rise through a forward model. The measurement setup involves two primary approaches: (i) the use of thermal sensors embedded in a printed circuit board inside the stator core and (ii) surface sensors embedded on the stator yoke. Through the use of this innovative approach, the results indicate that the inverse modelling technique is highly effective in predicting core losses based on short-time transient temperature rise measurements.
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    Bonding of ceramics to silver-coated titanium—A combined theoretical and experimental study
    (John Wiley & Sons, 2024-05) Vuorinen, Vesa; Kouhia, Reijo; Könönen, Mauno; Kivilahti, Jorma K.; Department of Electrical Engineering and Automation; Electronics Integration and Reliability; University of Helsinki; Aalto University; Tampere University
    It would be very beneficial to have a method for joining of ceramics to titanium reliably. Although several techniques have been developed and tested to prevent extensive interfacial chemical reactions in titanium-ceramic systems, the main problem of the inherent brittleness of interfaces was still unsolved. To overcome this problem also in dental applications, we decided to make use of an interlayer material that needs to meet the following requirements: First, it has to be biocompatible, second, it should not melt below the bonding temperatures, and third, it should not react too strongly with titanium, so that its plasticity will be maintained. Considering possible material options only the metals: gold, platinum, palladium, and silver, fulfill the first and second requirements. To find out—without an extensive experimental testing program—which of the four metals fulfills the third requirement best, the combined thermodynamic and reaction kinetic modeling was employed to evaluate how many and how thick reaction layers are formed between the interlayer metals and titanium. With the help of theoretical modeling, it was shown that silver fulfills the last requirement best. However, before starting to test experimentally the effect of the silver layer on the mechanical integrity of dental ceramic/Ag/Ti joints it was decided to make use of mechanical analysis of the three-point bending test, the result of which indicated that the silver layer increases significantly the bond strength of the joints. This result encouraged us to develop a new technique for plating silver on titanium. Subsequently, we executed numerous three-point bending tests, which demonstrated that silver-plated titanium-ceramic joints are much stronger than conventional titanium-ceramic joints. Hence, it can be concluded that the combined thermodynamic, reaction kinetic, and mechanical modeling method can also be a very valuable tool in medical research and development work.
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    Multi-Task Adaptive Gating Network for Trajectory Distilled Control Prediction
    (IEEE, 2024-05-01) Azam, Shoaib; Kyrki, Ville; Department of Electrical Engineering and Automation; Intelligent Robotics
    End-to-end autonomous driving is often categorized based on output into trajectory prediction or control prediction. Each type of approach provides benefits in different contexts, resulting in recent studies on how to combine them. However, the current proposals are based on heuristic choices that only partially capture the complexities of varying driving conditions. How to best fuse these sources of information remains an open research question. To address this, we introduce MAGNet, a Multi-Task Adaptive Gating Network for Trajectory Distilled Control Prediction. This framework employs a multi-task learning strategy to combine trajectory and direct control prediction. Our key insight is to design a gating network that learns how to optimally combine the outputs of trajectory and control predictions in each situation. Using the CARLA simulator, we evaluate MAGNet in closed-loop settings with challenging scenarios. Results show that MAGNet outperforms the state-of-the-art on two publicly available CARLA benchmarks, Town05 Long and Longest6.
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    Investigating the Impact of Electrical Load Types on the Frequency Response of Low Inertia Power Systems
    (IEEE, 2024) Tofighi-Milani, Mahyar; Fattaheian-Dehkordi, Sajjad; Lehtonen, Matti; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering
    In the contemporary power system landscape, characterized by a significant integration of renewable resources and the proliferation of inverter-connected devices, system inertia is on a declining trajectory. In this evolving scenario, the influence of various load types on system frequency becomes significant. In this regard, it seems that a comprehensive study on the effect of load types on the system’s frequency is missing in the literature. Hence, this paper aims to fill this gap by aggregating various load models known to affect system frequency and subsequently assessing the influence of each load type on the power systems’ frequency response. To achieve this, the IEEE 30-bus test system is employed to investigate the impact of different load parameters and their penetration levels on the systems’ frequency response.
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    Book Review on “Antonio Moreno-Munoz; Neomar Giacomini; Energy Smart Appliances: Applications, Methodologies, and Challenges (2023)‏”
    (2024-04-25) Mousa, Hossam H. H.; Mahmoud, Karar; Lehtonen, Matti; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering
    Recently, the integration of new industrial technologies is significantly increased into the utility grid such as renewable energy sources (RESs), distributed energy resources (DERs), energy source systems (ESSs), electric vehicles (EVs), and multi-carrier energy systems (MESs). So, robust energy management strategies are required to regulate the power-exchange between the generations and end-users for improving the power system's reliability and stability and reducing the energy costs. Thus, the demand-side management (DSM) strategies and demand response (DR) programs are utilized to control the energy smart appliances for residential building which achieving by various strategies, required infrastructure, energy market signals, etc. Several textbooks and articles investigate this important topic. However, the book entitled “Antonio Moreno-Munoz; Neomar Giacomini; Energy Smart Appliances: Applications, Methodologies, and Challenges (2023)”, is the most recent prominent comprehensive reference for DSM strategies in smart grids. Hence, this article proposes a book review and discussion of its most important contributions to DSM strategies by dividing them into four main contributions. Which helps the reader in realizing the recent developments on DSM strategies based on this book’s contents.
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    Temporal interfaces in complex electromagnetic materials: an overview [Invited]
    (Optical Society of America (OSA), 2024) Mostafa, M. H.; Mirmoosa, M. S.; Sidorenko, M. S.; Asadchy, V. S.; Tretyakov, S. A.; Department of Electronics and Nanoengineering; Sergei Tretiakov Group; Viktar Asadchy Group
    Time-varying metamaterials are currently at the forefront of research, offering immense possibilities for intriguing wave manipulations. Temporal modulations of metamaterials have paved the way for unconventional realizations of magnetless nonreciprocity, wave amplification, frequency conversion, pulse shaping, and much more. Here, we overview the fundamentals and recent advancements of temporal interfaces in isotropic, anisotropic, and bianisotropic materials and metamaterials. Delving into the fundamentals of temporal scattering in media of different material classes, we draw insightful comparisons with phenomena observed at spatial interfaces. We specifically emphasize the potential of time-switched anisotropic and bianisotropic metamaterials in unlocking extraordinary temporal scattering phenomena. Furthermore, an overview of possible platforms to realize time-varying bianisotropic metamaterials is provided. Concluding with a glimpse into the future, we make a research outlook for time-varying anisotropic and bianisotropic metamaterials, highlighting their potential in obtaining exotic photonic time crystals and other dynamic electromagnetic structures.
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    The Power of Relativistic Jets: A Comparative Study
    (MDPI AG, 2024-04) Foschini, Luigi; Dalla Barba, Benedetta; Tornikoski, Merja; Andernach, Heinz; Marziani, Paola; Marscher, Alan P.; Jorstad, Svetlana G.; Järvelä, Emilia; Antón, Sonia; Dalla Bontà, Elena; Metsähovi Radio Observatory; Osservatorio Astronomico di Brera; INAF - Osservatorio Astronomico di Padova; University of Coimbra; University of Padova; University of Oklahoma
    We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look AGN) from the very large baseline array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compared the values. We found an excellent agreement between the radiative power calculated by using the Blandford and Königl model with 37 or 43 GHz data and the values derived from the high-energy (Formula presented.) -ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the (Formula presented.) -ray luminosity. We found a good agreement also for the kinetic power calculated with the Blandford and Königl model with 15 GHz data and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power.
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    Meter-Scale Distance Manipulation of Diverse Objects with Jet-Induced Airflow Field
    (Wiley-VCH Verlag, 2024-04-26) Najafi Haeri, Shahriar; Kopitca, Artur; Kandemir, Hakan; Zhou, Quan; Department of Electrical Engineering and Automation; Robotic Instruments
    In nature, wind can transport objects of diverse shapes and materials over long distances spanning meters or beyond. In contrast, most noncontact manipulation methods are effective only over centimeter-scale distances and require the manipulated objects to have specific magnetic, electrical, or other material properties and shapes. Herein, a meter-scale distance manipulation method is presented for controlling the motion of objects of diverse shapes and materials on a plane surface using a jet-induced airflow field. The airflow field is varied by controlling the direction of a single air jet projected onto a surface based on the positions of objects to steer the objects to follow desired trajectories up to 2.7 m away. A wide variety of objects can be automatically manipulated, from regularly shaped polystyrene hemispheres and sticks to irregularly shaped cotton wads and face masks as well as deformable tissue papers and plastic bags. The method is also robust, effectively manipulating objects under challenging conditions, e.g., external airflow disturbances, surface obstacles, and air–water interface. Finally, three application cases are demonstrated: collecting diverse objects into a target receptacle, hooking and retrieving heavy objects with a tethered mobile agent, and closing an electrical circuit with an untethered soft agent.
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    Multi-conductor electromagnetic coupling model for sensitive wires subject to driven wire in complex electronic systems
    (John Wiley & Sons, 2024-03-01) Jiang, Fan; Chen, Lulu; Xue, Bing; Tian, Xinxin; Ye, Liang Hua; Li, Jian Feng; Wu, Duo Long; Department of Electronics and Nanoengineering; Katsuyuki Haneda Group; Guangdong University of Technology
    A novel multi-conductor electromagnetic coupling model for the sensitive-wire subject to driven wire in a high-precision machining workbench is proposed in this paper. The general coupling model for an N-wire system is derived and is used to evaluate the wire coupling effect. Furthermore, 4-wire and 3-wire models are demonstrated to verify the accuracy through full-wave electromagnetic simulation below 10 MHz. The results show that the error between the proposed method and the full-wave electromagnetic simulation is less than 10%, demonstrating the high efficiency and accuracy of the proposed method. When the parameters of the driven power wire and the most sensitive wire are fixed and the parameters of neighboring wires are swept, the maximum fluctuation of the induced current on the most sensitive wire is 6.1 dB. The efficient calculation method proposed in this work helps reduce the risk of electromagnetic interference in complex electronic systems and improves the design efficiency of wires. It is promising to become a high-performance method with high efficiency and precision.
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    Heuristic cooperative coverage path planning for multiple autonomous agricultural field machines performing sequentially dependent tasks of different working widths and turn characteristics
    (Academic Press, 2024-06) Soitinaho, Riikka; Väyrynen, Vili; Oksanen, Timo; Department of Electrical Engineering and Automation; Autonomous Systems; Department of Electrical Engineering and Automation
    Coverage path planning is a central task in agricultural field operations such as tillage, planting, cultivation, and harvesting. In future visions, manual operation will be replaced by fleets of autonomous agricultural vehicles that perform the tasks autonomously. A step towards this transition is to enable simultaneous and safe cooperation of autonomous vehicles on the field. In this article a novel approach is presented for coverage path planning (CPP) for two autonomous tractors that perform sequentially dependent tasks simultaneously on the same area. The approach is based on the idea of computing the coverage solutions for each task by dividing them into short paths that consist of a swath and a turn. The approach ensures collision avoidance by examining that the simultaneous short paths, operated by different tractors, do not collide geometrically, and then schedules them to be operated simultaneously in real-time. The approach was demonstrated successfully in a real-world test environment with two autonomous tractors. The tractor that performed the first task was equipped with a disc cultivator and the second tractor was equipped with a seed drill. A test area of 0.8 ha was used for the demonstration drive, during which the tractors drove 22 swaths simultaneously. Both tractors completed their respective tasks.
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    Recent Advances of VO2 in Sensors and Actuators
    (MDPI AG, 2024-04) Darwish, Mahmoud; Zhabura, Yana; Pohl, László; Department of Electrical Engineering and Automation; Electronics Integration and Reliability; Budapest University of Technology and Economics; Department of Electrical Engineering and Automation
    Vanadium dioxide (VO2) stands out for its versatility in numerous applications, thanks to its unique reversible insulator-to-metal phase transition. This transition can be initiated by various stimuli, leading to significant alterations in the material’s characteristics, including its resistivity and optical properties. As the interest in the material is growing year by year, the purpose of this review is to explore the trends and current state of progress on some of the applications proposed for VO2 in the field of sensors and actuators using literature review methods. Some key applications identified are resistive sensors such as strain, temperature, light, gas concentration, and thermal fluid flow sensors for microfluidics and mechanical microactuators. Several critical challenges have been recognized in the field, including the expanded investigation of VO2-based applications across multiple domains, exploring various methods to enhance device performance such as modifying the phase transition temperature, advancing the fabrication techniques for VO2 structures, and developing innovative modelling approaches. Current research in the field shows a variety of different sensors, actuators, and material combinations, leading to different sensor and actuator performance input ranges and output sensitivities.
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    A Carbon Emission Allowance Bargaining Model For Energy Transactions Among Prosumers
    (IEEE, 2024-04-12) Xiang, Yue; Qing, Guiping; Fang, Mengqiu; Li, Zhengmao; Yao, Haotian; Liu, Junyong; Guo, Zekun; Liu, Jichun; Zeng, Pingliang; Department of Electrical Engineering and Automation; Multi-energy System Planning and Operation; Sichuan University; University of Hull; Hangzhou Dianzi University
    The carbon pricing is the main issue of the carbon trading market for enabling cost-effective decarbonization in the energy networks. A nodal carbon pricing model is firstly proposed based on the sharing and integration of the intra-regional carbon emission allowance. In this regard, the game theory is introduced to construct a multi-agent carbon emission allowance bargaining model in this letter. The alternating direction multiplier method is adopted to solve the model considering the competitional burden and privacy-preserving. Numerical results demonstrate that it could significantly reduce the carbon emissions of regional energy networks and improve the economic benefits of prosumers.
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    Thermal Boundary Conductance of Direct Bonded Aluminum Nitride to Silicon Interfaces
    (American Chemical Society, 2024-04-23) Nieminen, Tarmo; Koskinen, Tomi; Kornienko, Vladimir; Ross, Glenn; Paulasto-Kröckel, Mervi; Department of Electrical Engineering and Automation; Department of Electronics and Nanoengineering; Electronics Integration and Reliability; Ilkka Tittonen Group; Department of Electrical Engineering and Automation
    Heat accumulation and self-heating have become key issues in microelectronics owing to the ever-decreasing size of components and the move toward three-dimensional structures. A significant challenge for solving these issues is thermally isolating materials, such as silicon dioxide (SiO2), which are commonly used in microelectronics. The silicon-on-insulator (SOI) structure is a great demonstrator of the limitations of SiO2 as the low thermal conductivity insulator prevents heat dissipation through the bottom of a device built on a SOI wafer. Replacing SiO2 with a more thermally conductive material could yield immediate results for improved heat dissipation of SOI structures. However, the introduction of alternate materials creates unknown interfaces, which can have a large impact on the overall thermal conductivity of the structure. In this work, we studied a direct bonded AlN-to-SOI wafer (AlN-SOI) by measuring the thermal conductivity of AlN and the thermal boundary conductance (TBC) of silicon (Si)/AlN and Si/SiO2/aluminum-oxygen-nitrogen (AlON)/AlN interfaces, the latter of which were formed during plasma-activated bonding. The results show that the AlN-SOI possesses superior thermal properties to those of a traditional SOI wafer, with the thermal conductivity of AlN measured at roughly 40 W m-1 K-1 and the TBC of both interfaces at roughly 100 MW m-2 K-1. These results show that AlN-SOI is a very promising structure for improving heat dissipation in future microelectronics.