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    Fatigue Crack Networks in Die-Attach Layers of IGBT Modules Under a Power Cycling Test
    (IEEE, 2024) Liu, Shenyi; Vuorinen, Vesa; Liu, Xing; Fredrikson, Olli; Brand, Sebastian; Tiwary, Nikhilendu; Lutz, Josef; Paulasto-Krockel, Mervi; Department of Electrical Engineering and Automation; Electronics Integration and Reliability; Chemnitz University of Technology; ABB Group; Fraunhofer Institute for Microstructure of Materials and Systems
    The die-attach layer is a vulnerable structure that is important to the reliability of an insulated-gate bipolar transistor (IGBT) module. A new failure mechanism named fatigue crack network (FCN) has been identified in the central area of the IGBT modules' solder layer. In this article, to investigate the formation mechanism of the FCN, a fast power cycling test (PCT) (current on 0.2 s and current off 0.4 s) was designed and performed on a commercial IGBT module. Subsequently, scanning acoustic microscopy and X-ray imaging were used for nondestructive inspection of the defects of the solder layer. The cross section was based on the nondestructive inspection results. Then, electron backscattered diffraction analysis was carried out on both observed vertical and horizontal cracks. As a result, both networked vertical cracks at the center and horizontal cracks at the edge of the solder layer were detected. The recrystallization occurred during the PCT. The voids and cracks emerged at high-angle grain boundaries. A finite element simulation was performed to understand the driving force of FCN qualitatively. The stress simulation results indicate that under time-dependent multiaxial stress at the center of the solder, the defects nucleated, expanded, and connected vertically to form the FCNs.
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    One-Time Pad Incoherent Encryption with Optical Meta-Ciphertext and Dynamic Visual Keys
    (American Chemical Society, 2024-09-26) Li, Zhenfei; Du, Shuo; Wu, Xianfeng; Zhang, Jin; Zhang, Yuhang; Song, Kun; Liu, Yahong; Geng, Guangzhou; Zhu, Weiren; Zhao, Xiaopeng; Gu, Changzhi; Department of Electronics and Nanoengineering; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; Northwestern Polytechnical University; CAS - Institute of Physics; Shanghai Jiao Tong University
    In today’s ever-evolving information security landscape, the demand for robust encryption techniques is on the rise. Superior to traditional encryption schemes, one-time pad encryption provides unparalleled security due to its reliance on a unique, nonreusable key for each message. Here, a novel one-time pad incoherent encryption paradigm based on optical metasurface ciphertext and dynamic visual keys has been developed. The proposed encryption scheme exploits the inherent security of the one-time pad by ensuring information confidentiality through the use of a random and nonreusable key. Based on this foundation, optical metasurfaces are initially used to encode the ciphertext and visual key, introducing an additional layer of complexity and security. In addition, the system incorporates dynamic visual keys using a spatial light modulator, adding dynamic and visually intuitive dimensions to the encryption process. These dynamic keys enhance the security of the communication channel by introducing variability into the encryption parameters, making it extremely difficult for unauthorized parties to predict or analyze cryptographic patterns. The result is a highly secure and robust incoherent encryption system that can be found to have potential applications in secure communication and data protection domains.
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    Achieving Near-Ideal Subthreshold Swing in P-Type WSe2 Field-Effect Transistors
    (John Wiley & Sons, 2024-09) Ali, Fida; Choi, Hyungyu; Ali, Nasir; Hassan, Yasir; Ngo, Tien Dat; Ahmed, Faisal; Park, Won Kyu; Sun, Zhipei; Yoo, Won Jong; Department of Electronics and Nanoengineering; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; Sungkyunkwan University; Chungnam National University
    The pursuit of near-ideal subthreshold swing (SS) ≈ 60 mV dec−1 is a primary driving force to realize the power-efficient field-effect transistors (FETs). This challenge is particularly pronounced in 2D material-based FETs, where the presence of a large interface trap density (Dit) imposes limitations on electrostatic control, consequently escalating power consumption. In this study, the gate controllability of 2D FETs is systematically analyzed by fabricating pre-patterned van der Waals (vdW)-contacted p-FETs, varying the WSe2 channel thickness from monolayer to ten-layer. As a result, the channel thickness is optimized to achieve efficient gate controllability while minimizing Dit. The findings demonstrate negligible hysteresis and excellent subthreshold swing (SSmin) close to the thermal limit (≈60 mV dec−1), with a corresponding Dit of ≈1010 cm−2 eV−1, comparable to Dit values observed in state-of-the-art Si transistors, when utilizing WSe2 channel thicknesses ≥ five-layer. However, reducing the WSe2 channel thickness below the trilayer, SSmin (≈91 mV dec−1) deviates from the thermal limit, attributed to a comparatively higher Dit (≈1011 cm−2 eV−1), despite the still lower than values reported for surface-contacted 2D transistors. Furthermore, all devices exhibit consistent p-type characteristics, featuring a high ION/IOFF ratio, high mobility, and excellent electrical stability confirmed over several months.
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    Interactive Evolutionary Multiobjective Optimization of Primer Design with Uncertain Objectives
    (2024) Mazumdar, Atanu; Jain, Bhavya; Mitra, Monisha; Dhar, Prodyut; Department of Electrical Engineering and Automation; Intelligent Robotics; Indian Institute of Technology (BHU) Varanasi; University of Helsinki
    The choice of primer designs for polymerase chain reaction experiments affects the results. Designing optimal combinations of forward and reverse primers requires solving multiple conflicting objectives simultaneously. Most of the tools for primer design optimize the problem by a priori scalarization or by setting constraints with preset preferences. Therefore, the decision-maker (DM) or domain expert has to re-execute the optimizer with new preferences to find satisfactory solutions. An a priori method is detrimental to decision-making since the DM cannot learn about the problem characteristics, and re-executing the optimizer with new preferences increases the number of function evaluations. In addition, the existing methods rely on a single mathematical model to estimate the melting temperature of primers. In this paper, we formulate a multiobjective optimization problem consisting of three uncertain objectives that use six different models to estimate the melting temperatures of primers. The formulated problem was solved using an interactive multiobjective evolutionary algorithm that enabled the DM to guide the solution process. We also proposed a selection criterion tailored to our problem that could find optimal primer designs according to the DM's preferences. Finally, we demonstrate the proposed interactive approach to find optimal primers for a bacterial 16S DNA sequence.
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    Enhanced Nonlinear Optical Responses in MoS2 via Femtosecond Laser-Induced Defect-Engineering
    (Wiley-VCH Verlag, 2024-10-11) Akkanen, Suvi-Tuuli; Arias Muñoz, Juan Camilo; Emelianov, Aleksei V.; Mentel, Kamila K.; Tammela, Juhani; Partanen, Mikko; Das, Susobhan; Pettersson, Mika; Sun, Zhipei; Department of Electronics and Nanoengineering; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; National Research University of Electronic Technology; University of Jyväskylä; Zhipei Sun Group
    2D materials are a promising platform for applications in many fields as they possess a plethora of useful properties that can be further optimized by careful engineering, for example, by defect introduction. While reliable high-yield defect engineering methods are in demand, most current technologies are expensive, harsh, or non-deterministic. Optical modification methods offer a cost-effective and fast mechanism to engineer the properties of 2D materials at any step of the device fabrication process. In this paper, the nonlinear optical responses of mono-, bi-, and trilayer molybdenum disulfide (MoS2) flakes are enhanced by deterministic defect-engineering with a femtosecond laser. A 50-fold enhancement in the third harmonic generation (THG) and a 3.3-fold increase in the second harmonic generation (SHG) in the optically modified areas is observed. The enhancement is attributed to resonant SHG and THG processes arising from optically introduced mid-band gap defect states. These results demonstrate a highly controllable, sub-micrometer resolution tool for enhancing the nonlinear optical responses in 2D materials, paving the way for prospective future applications in optoelectronics, quantum technologies, and energy solutions.
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    Real-Time Over-the-Air Emulation of Rician Fading Channels for Mobile Antenna Testing
    (2024) Kourani, Ali; De Guzman, Mar Francis; Tian, Ruiyuan; Haneda, Katsuyuki; Department of Electronics and Nanoengineering; Katsuyuki Haneda Group; Department of Electronics and Nanoengineering; Huawei Technologies
    As the ubiquity of 5G technology permeates various domains, coupled with the introduction of new carrier frequencies under the New Radio (NR) framework, devices employing this advanced technology require stringent and repeatable operational conformance tests. Those tests are essential to ascertain the AUT performance under realistic deployment scenarios, thereby ensuring reliability. Hence emulating realistic channel characteristics is fundamental to reach a reliable evaluation of radio components. Considering small-scale fading phenomena is imperative in evaluating the operational integrity of radio devices, as it pervades everything from vehicular communications to the mobility of user equipment. This work demonstrates implementing and validating the operation of a Rician fading channel emulator which can be integrated in an over-the-air antenna testbed. It provides a real-time cost-effective solution using off-the-shelf software defined radios (SDR). The paper provides an overview on the hardware setup and the software implementation of the Rician fading emulator. The setup is tested in an anechoic chamber and comparative analysis showed a robust correlation between the empirical data and theoretical plots of the Rician fading magnitude statistics.
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    AutoPC: An Open-Source Framework for Efficient Probabilistic Reasoning on FPGA Hardware
    (2024) Periasamy, Karthekeyan; Leslin, Jelin; Korsman, Aleksi; Yao, Lingyun; Andraud, Martin; Department of Electronics and Nanoengineering; Martin Andraud Group; Kari Halonen Group; Marko Kosunen Group; Marko Kosunen Group; Department of Electronics and Nanoengineering
    In the quest for more advanced and energy-efficient edge AI, probabilistic reasoning models can complement or replace deep learning (DL) models, as they are generative, explainable, and trustworthy. However, their hardware implementation and acceleration are still in the early stages compared to DL due to more ad-hoc implementations and challenges translating them into computational steps. This recently evolved with Probabilistic Circuits (PCs), which can be trained with mainstream software and lead to more hardware-efficient inference. Yet, there is currently no single open-source framework dedicated to computing PCs on hardware. In this work, we introduce such a framework called AutoPC, allowing us to (1) compare PCs trained with different PC algorithms to find the most suited, (2) find the optimal resolution required for hardware computation with minimal cost, and (3) automatically generate FPGA hardware for executing PC models with high speed (40-200 GOPS) up to the FPGA capacity. We hope AutoPC serves as a baseline to showcase the possibilities of probabilistic reasoning and broaden the use of PCs.
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    Synergic Effect of N and Se Facilitates Photoelectric Performance in Co-Hyperdoped Silicon
    (MDPI AG, 2024-10) Sun, Haibin; Liu, Xiaolong; Xu, Caixia; Xu, Long; Chen, Yuwei; Yang, Haima; Yang, Xing; Rao, Peng; Sun, Shengli; Zhao, Li; Department of Electronics and Nanoengineering; Hele Savin Group; National Land Survey of Finland; Chongqing University; Southwest University; University of Shanghai for Science and Technology; National University of Defense Technology; Chinese Academy of Sciences (CAS)(中国科学院); Fudan University
    Femtosecond-laser-fabricated black silicon has been widely used in the fields of solar cells, photodetectors, semiconductor devices, optical coatings, and quantum computing. However, the responsive spectral range limits its application in the near- to mid-infrared wavelengths. To further increase the optical responsivity in longer wavelengths, in this work, silicon (Si) was co-hyperdoped with nitrogen (N) and selenium (Se) through the deposition of Se films on Si followed by femtosecond (fs)-laser irradiation in an atmosphere of NF3. The optical and crystalline properties of the Si:N/Se were found to be influenced by the precursor Se film and laser fluence. The resulting photodetector, a product of this innovative approach, exhibited an impressive responsivity of 24.8 A/W at 840 nm and 19.8 A/W at 1060 nm, surpassing photodetectors made from Si:N, Si:S, and Si:S/Se (the latter two fabricated in SF6). These findings underscore the co-hyperdoping method’s potential in significantly improving optoelectronic device performance.
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    A Linear Push-Pull Average Consensus Algorithm for Delay-Prone Networks
    (2024) Makridis, Evagoras; Charalambous, Themistoklis; Department of Electrical Engineering and Automation; Distributed and Networked Control Systems; University of Cyprus
    In this paper, we address the average consensus problem of multi-agent systems for possibly unbalanced and delay-prone networks with directional information flow. We propose a linear distributed algorithm (referred to as RP-PAC) that handles asynchronous updates and time-varying heterogeneous information delays. Our proposed distributed algorithm utilizes a surplus-consensus mechanism and information regarding the number of incoming and outgoing links to guarantee state averaging, despite the imbalanced and delayed information flow in directional networks. The convergence of the RPPAC algorithm is examined using key properties of the backward product of time-varying matrices that correspond to different snapshots of the directional augmented network.
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    Signatures of top versus bottom illuminations and their predicted implications for infrared transmission microspectroscopy
    (Wiley-VCH Verlag, 2024-10) Kong, Beibei; Blümel, Reinhold; Ylä-Oijala, Pasi; Wallén, Henrik; Sihvola, Ari; Kohler, Achim; Department of Electronics and Nanoengineering; Keijo Nikoskinen Group; Ari Sihvola Group; Wesleyan University; Norwegian University of Life Sciences
    Since both top and bottom illuminations are widely used in infrared transmission measurements, in this paper, we study the effects of different illuminations on the signatures in infrared microspectroscopy. By simulating a series of dielectric samples, we show that their extinction efficiency, (Formula presented.), remains unchanged when the direction of the incident plane wave is reversed, even though the field distributions both inside and outside of the sample may be dramatically different. We find features in (Formula presented.) that are correlated with whispering gallery modes for one beam direction and correspond to completely different field distributions for the opposite beam direction. In addition, by linking the optical theorem and the reciprocity relation of far-field scattered field, we rigorously prove the invariance of (Formula presented.) for arbitrary dielectric targets under opposite plane-wave illuminations. Furthermore, we show the difference in the apparent absorbance spectrum for opposite beam directions when considering numerical apertures.
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    Cathodic arc deposited tetrahedral amorphous carbon as thin film contact pressure sensing material
    (American Institute of Physics, 2024-09-24) Haikola, Juha; Tervakangas, Sanna; Kolehmainen, Jukka; Tittonen, Ilkka; Department of Electronics and Nanoengineering; Ilkka Tittonen Group; Oerlikon Balzers Coating Finland Oy
    Tetrahedral amorphous carbon (ta-C) film was deposited using filtered pulsed cathodic arc deposition method. The ta-C structures deposited on HVOF thermally sprayed steel beam substrates were investigated for the piezoresistive properties under a direct contact pressing. Load up to 1.4 GPa were applied with point contact with no detrimental influence on the material. Linear response for the strain applied homogeneously on the whole film surface and on the local portion of the film surface under a cylindrical contact was observed. High gauge factor of the measured system of 305 was measured, showing the potential of the material as a good candidate for the sensing application on direct contact measurement devices.
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    Association of the IceCube neutrinos with blazars in the CGRaBS sample
    (EDP Sciences, 2024-10-01) Kouch, Pouya M.; Lindfors, Elina; Hovatta, Talvikki; Liodakis, Ioannis; Koljonen, Karri I.I.; Nilsson, Kari; Kiehlmann, Sebastian; Max-Moerbeck, Walter; Readhead, Anthony C.S.; Reeves, Rodrigo A.; Pearson, Timothy J.; Jormanainen, Jenni; Ramazani, Vandad Fallah; Graham, Matthew J.; Metsähovi Radio Observatory; University of Turku; Institute of Astrophysics; Universidad de Chile; California Institute of Technology; Universidad de Concepción; Norwegian University of Science and Technology; Ruhr University Bochum
    The origin of high-energy (HE) astrophysical neutrinos has remained an elusive hot topic in the field of HE astrophysics for the past decade. Apart from a handful of individual associations, the vast majority of HE neutrinos arise from unknown sources. While there are theoretically motivated candidate populations, such as blazars – a subclass of active galactic nuclei with jets pointed toward our line of sight – they have not been convincingly linked to HE neutrino production yet. Here, we perform a spatio-temporal association analysis between a sample of blazars (from the CGRaBS catalog) in the radio and optical bands and the most up-to-date IceCube HE neutrino catalog. We find that if the IceCube error regions are enlarged by 1◦ in quadrature, to account for unknown systematic errors at a maximal level, a spatio-temporal correlation between the multiwavelength light curves of the CGRaBS blazars and the IceCube HE neutrinos is hinted at, least at a 2.17σ significance level. On the other hand, when the IceCube error regions are taken as their published values, we do not find any significant correlations. A discrepancy in the blazar-neutrino correlation strengths, when using such minimal and enlarged error region scenarios, was also obtained in a recent study by the IceCube collaboration. In our study, this difference arises because several flaring blazars – coinciding with a neutrino arrival time – happen to narrowly miss the published 90%-likelihood error region of the nearest neutrino event. For all of the associations driving our most significant correlations, the flaring blazar is much less than 1◦ away from the published error regions. Therefore, our results indicate that the question of the blazar-neutrino connection is highly sensitive to the reconstruction of the neutrino error regions, whose reliability is expected to improve with the next generation of neutrino observatories.
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    A Saturation Model Based on a Simplified Equivalent Magnetic Circuit for Permanent Magnet Machines
    (2024-09-04) Lelli, Francesco; Hinkkanen, Marko; Capponi, Fabio Giulii; Department of Electrical Engineering and Automation; Electric Drives; Sapienza University of Rome
    This paper proposes an explicit mathematical model to describe the nonlinear behavior of the permanent magnet synchronous reluctance machine. Although different models for the synchronous reluctance machines are available, extending them to the case of the permanent magnet machine is not trivial due to the effect of the permanent magnets on the rib saturation. This work uses a simplified equivalent magnetic circuit to derive the structure of the proposed model. A nonlinear reluctance is introduced to model the rib saturation. It can be added to the existing model for the synchronous reluctance machine to take into account the effect of the permanent magnets. A simple fitting procedure based on the steepest descent method is proposed to estimate the parameters of the model.
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    Distributed Optimization with Gradient Tracking Over Heterogeneous Delay-Prone Directed Networks
    (2024) Makridis, Evagoras; Oliva, Gabriele; Narahari, Kasagatta Ramesh; Doostmohammadian, Mohammadreza; Khan, Usman A.; Charalambous, Themistoklis; Department of Electrical Engineering and Automation; Distributed and Networked Control Systems; University of Cyprus; Universita Campus Bio-Medico di Roma; Nokia; Tufts University; Semnan University
    In this paper, we address the distributed optimization problem over unidirectional networks with possibly time-invariant heterogeneous bounded transmission delays. In particular, we propose a modified version of the Accelerated Distributed Directed OPTimization (ADD-OPT) algorithm, herein called Robustified ADD-OPT (R-ADD-OPT), which is able to solve the distributed optimization problem, even when the communication links suffer from heterogeneous but bounded transmission delays. We show that if the gradient step-size of the R-ADD-OPT algorithm is within a certain range, which also depends on the maximum time delay in the network, then the nodes are guaranteed to converge to the optimal solution of the distributed optimization problem. The range of the gradient step-size that guarantees convergence can be computed a priori based on the maximum time delay in the network.
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    Optimizing decentralized implementation of state estimation in active distribution networks
    (Institution of Engineering and Technology, 2024) Gholami, Mohammad; Eskandari, Aref; Fattaheian-Dehkordi, Sajjad; Lehtonen, Matti; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering; Iran University of Science and Technology; Mazandaran University of Science and Technology
    The challenges facing active distribution networks have highlighted the position of the distribution system state estimation (DSSE) process in the distribution management systems as its most important function. Here, regarding the extensive scale of distribution networks and the weaknesses of centralized methods, the decentralized implementation of the DSSE process has received considerable attention. However, predefined network partitioning is supposed in previous works and zone size effects on the performance of the DSSE process have not been assessed. In response, a method for finding the optimal number of network zones and their size is proposed here. For this purpose, initially, an algorithm is used to partition the network into all possible configurations with different sizes. Subsequently, performance metrics affected by zone sizes, such as execution time, accuracy of the DSSE results, and reliability in achieving the results at the control centre, are modelled. Finally, by applying the decentralized DSSE method across all partitioning scenarios and calculating performance metrics, the most efficient and cost-effective partitioning scenario can be identified. The performance of the proposed method is evaluated using the modified 77-bus UK distribution network as an active test case, and the findings are subsequently presented and analysed.
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    Spacing Vector and Varying Distance Constrained Positioning Using Dual Feet-Mounted IMUs
    (IEEE, 2024) Ma, Xiaofeng; Sarkka, Simo; Department of Electrical Engineering and Automation; Sensor Informatics and Medical Technology; Helsinki Institute for Information Technology (HIIT)
    The zero velocity update (ZUPT) offers an effective correction method for sensor drift in indoor positioning systems using foot-mounted inertial measurement units (IMUs). However, the heading drift is still a problem in positioning systems using IMUs. This paper develops methods for positioning using two foot-mounted IMUs to solve this problem. The proposed method is based on the use of a time-varying distance constraint and a spacing-vector constraint. Our methods are experimentally compared against other distance-constraint-based methods using a dataset that we collected for this purpose. The results show that our method has better control of the separation between the trajectories of the feet.
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    High-density EMG reveals atypical spatial activation of the gastrocnemius during walking in adolescents with Cerebral Palsy
    (Elsevier Ltd, 2024-12) Thurston, Maxwell; Peltoniemi, Mika; Giangrande, Alessandra; Vujaklija, Ivan; Botter, Alberto; Kulmala, Juha Pekka; Piitulainen, Harri; Department of Electrical Engineering and Automation; Bionic and Rehabilitation Engineering; University of Jyväskylä; Polytechnic University of Turin; University of Helsinki
    Children with Cerebral Palsy (CP) exhibit less-selective, simplified muscle activation during gait due to injury of the developing brain. Abnormal motor unit recruitment, altered excitation-inhibition balance, and muscle morphological changes all affect the CP electromyogram. High-density surface electromyography (HDsEMG) has potential to reveal novel manifestations of CP neuromuscular pathology and functional deficits by assessing spatiotemporal details of myoelectric activity. We used HDsEMG to investigate spatial-EMG distribution and temporal-EMG complexity of gastrocnemius medialis (GM) muscle during treadmill walking in 11 adolescents with CP and 11 typically developed (TD) adolescents. Our results reveal more-uniform spatial-EMG amplitude distribution across the GM in adolescents with CP, compared to distal emphasis in TD adolescents. More-uniform spatial-EMG was associated with stronger ankle co-contraction and spasticity. CP adolescents exhibited a non-significant trend towards elevated EMG-temporal complexity. Homogenous spatial distribution and disordered temporal evolution of myoelectric activity in CP suggests less-structured and desynchronized recruitment of GM motor units, in combination with muscle morphological changes. Using HDsEMG, we uncovered novel evidence of atypical spatiotemporal activation during gait in CP, opening paths towards deeper understanding of motor control deficits and better characterization of changes in muscular activation from interventions.
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    Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability
    (IEEE, 2024) Emadi, Fahimeh; Vuorinen, Vesa; Liu, Shenyi; Paulasto-Krockel, Mervi; Department of Electrical Engineering and Automation; Electronics Integration and Reliability
    To meet the essential demands for high-performance microelectromechanical system (MEMS) integration, this study developed a novel Cu-Sn-based solid-liquid interdiffusion (SLID) interconnect solution. The study utilized a metallization stack incorporating a Co layer to interact with low-temperature Cu-Sn-In SLID. Since Cu6(Sn,In)5 forms at a lower temperature than other phases in the Cu-Sn-In SLID system, the goal was to produce single-phase (Cu,Co)6(Sn,In)5 interconnects. Bonding conditions were established for the Cu-Sn-In/Co system and the Cu-Sn/Co system as a reference. Thorough assessments of their thermomechanical reliability were conducted through high-temperature storage (HTS), thermal shock (TS), and tensile tests. The Cu-Sn-In/Co system emerged as a reliable low-temperature solution with the following key attributes: 1) a reduced bonding temperature of 200 °C compared to the nearly 300 °C required for Cu-Sn SLID interconnects to achieve stable phases in the interconnect bondline; 2) the absence of the Cu3Sn phase and resulting void-free interconnects; and 3) high thermomechanical reliability with tensile strengths exceeding the minimum requirements outlined in the MIL-STD-883 method 2027.2, particularly following the HTS test at 150 °C for 1000 h.
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    Improving protection reliability of series-compensated transmission lines by a fault detection method through an ML-based model
    (Institution of Engineering and Technology, 2024) Ebrahimi, Hossein; Golshannavaz, Sajjad; Yazdaninejadi, Amin; Pouresmaeil, Edris; Department of Electrical Engineering and Automation; Renewable Energies for Power Systems; Urmia University; Shahid Rajaee Teacher Training University
    This article addresses the distance protection challenges associated with the series-compensated transmission lines and the impact of fault resistance by employing a machine-learning model. In the proposed model, stacked layers of bidirectional long short-term memory (Bi-LSTM) cells are fed by voltage and current signals to distinguish between different fault scenarios. This method takes advantage of only local bus measurements to prevent information leakage in communication channels. Moreover, to make the proposed method harmonics-robust and improve the correlation interpretation between the features for the Bi-LSTM model, the 3-phase raw measurement signals are passed through a discrete Fourier transform (DFT) which extracts their fundamental frequency component magnitudes and angles. Then, an extensive amount of fault scenarios including different compensation levels, fault resistances, and fault locations in normal and power-swing operational conditions are simulated to train the model. Finally, to validate the performance of the proposed protection method in the series-compensated transmission lines, distinctive studies are also carried out based on electromagnetic transient simulations. The obtained results confirm the remarkable performance of the proposed method in discriminating fault types, faulty phases, internal or external faults, and normal or power-swing conditions of the power system.
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    Applying Bayesian Approach in Real-Time Monitoring of Converter-Driven Oscillation
    (2024-01-30) Cheng, Hock Lim; Department of Electrical Engineering and Automation
    Increased use of wind and solar power is leading to significant changes in various properties of power systems. As these inverter-based resources are replacing synchronous generators, the existing dynamic characteristics of power systems change, and new stability phenomena are introduced in the system. Especially, converter-driven stability and oscillations caused by converters are an urgent and growing concern in power systems. Consequently, it is highly important to develop methods for detecting and monitoring converter-driven oscillations. This paper proposes a Bayesian approach for monitoring converter-driven oscillations. The approach utilizes ambient measurements and is able to identify the modal parameters (such as frequency and damping ratio) of the converter-driven oscillations continuously, in real-time. The performance of the proposed method is validated with measurements from two real-life events observed in the Finnish power system. The results show that the proposed approach is highly effective in rapidly detecting and monitoring converter-driven oscillations. It is recommended that transmission system operators implement a real-time monitoring method, such as the method proposed in this paper, for detecting and monitoring converter-driven oscillations.