VTT Research System
Not a member yet
161399 research outputs found
Sort by
FilMBot:A High-Speed Soft Parallel Robotic Micromanipulator
No full textSoft robotic manipulators are generally slow despite their great adaptability, resilience, and compliance. This limitation also extends to current soft robotic micromanipulators. Here, we introduce FilMBot, a 3-DOF film-based, electromagnetically actuated, soft kinematic robotic micromanipulator achieving speeds up to 2117 °/s and 2456 °/s in α and β angular motions, with corresponding linear velocities of 1.61 m/s and 1.92 m/s using a 4-cm needle end-effector, 0.54 m/s along the Z axis, and 1.57 m/s during Z-axis morph switching. The robot can reach ∼1.50 m/s in path-following tasks, with an operational bandwidth below ∼30 Hz, and remains responsive at 50 Hz. It demonstrates high precision (∼6.3 μm, or ∼0.05% of its workspace) in path-following tasks, with precision remaining largely stable across frequencies. The novel combination of the low-stiffness soft kinematic film structure and strong electromagnetic actuation in FilMBot opens new avenues for soft robotics. Furthermore, its simple construction and inexpensive, readily accessible components could broaden the application of micromanipulators beyond current academic and professional users.</p
Multivariate analysis on simulated moisture damage emission to indoor air
No full textMoisture damage in buildings is a significant source of indoor air problems, releasing e.g. volatile organic compounds (VOCs) and microbially produced VOCs (MVOCs), which can cause unpleasant odors and health symptoms. However, interpreting MVOCs as indicators of mold is challenging due to their various sources and limitations in analytical methods. The objective of this study was to identify the most critical factors influencing VOC emissions from moisture-damaged wall structures into the indoor environment via structural air leakages. The research was conducted using the VTT Indoor Air Quality (IAQ) Simulator and analyzed with Principal Component Analysis (PCA). The IAQ simulator was used to investigate the transport of airborne impurities from mold-contaminated wall structures in realistic building conditions and the systematic manipulation of key environmental parameters. The resulting dataset was subjected to multivariate analysis to identify the most influential factors contributing to IAQ degradation in moisture-damaged structures. The key conclusions revealed that material relative humidity was the most significant single factor affecting all VOC concentrations; higher humidity consistently increased emissions. Four specific ketones (2-pentanone, 2-hexanone, 2-heptanone, and 2-octanone) were clearly identified as originating from microbial growth, with their concentrations being significantly higher in the presence of active mold growth. Pressure differentials had only a borderline effect on gypsum board emissions, while the insulation layer showed no significant impact on any of the identified VOC components. These findings underscore the critical role of relative humidity in determining indoor VOC profiles and highlight the value of multivariate methods in assessing mold-related indoor air problems.</p
Inorganics from kraft black liquor enable rapid oxidative crosslinking and morphology control in lignin derived hard carbons
No full textThe conventional approach to converting kraft lignin (KL) into hard carbons is to start with highly purified, low-ash KL feedstocks and then rely on slow, energy-intensive oxidative stabilization and added crosslinkers to keep melting and foaming associated thermal challenges under control. Herein, we deliberately invert this paradigm. Instead of starting with highly purified KL, we retain pulping inorganics and use them as catalytic centers for oxidative crosslinking and melt suppression of KL. Spherical KL microparticles (KL-MP) were recovered from softwood black liquor by membrane filtration and spray-drying steps, intentionally retaining inorganic sodium (Na) salts as well as organically bound Na in KL-MP, and were compared to acid-precipitated, low-ash reference KL (KL-REF). During thermo-oxidative pretreatment (250 °C, 5 °C/min) in air, KL-MP undergoes inorganic-catalyzed rapid oxidative crosslinking that converts thermoplastic lignin into a rigid network, whereas KL-REF softens, foams, and fuses. Experimental analysis identifies organically bound Na-phenoxide type species as key catalytic sites. Proton magnetic resonance thermal analysis and molecular dynamics simulations reveal strongly reduced segmental mobility and Na-driven ionic clusters acting as physical crosslinking points. After pretreatment, inorganics are removed by a washing step, and the crosslinked KL-MP is carbonized, yielding low-surface-area hard carbons that retain their initial micron size and spherical morphology. As Li-ion battery anodes, the derived hard carbon shows better electrochemical performance than carbons derived from KL-REF. Overall, the work shows how otherwise undesirable inorganic impurities can simplify thermal conversion of KL, with potential for diverse applications where particle size and shape are critical
Design and evaluation of load-follow control schemes for a small district heating reactor LDR lite
No full textLoad following is needed in district heating networks, where heat demand varies significantly. LDR lite is a small light water reactor designed for flexible, low-temperature heat production. In this study two load-follow control schemes were designed for LDR lite. In the first option, control rods are used to regulate the power, while the secondary circuit temperatures are kept constant. The second option utilizes temperature feedback, adjusting the reactor power via secondary circuit pump control. The control schemes were evaluated by simulating a simplified load-follow scenario using coupled 3D neutronics and system thermal hydraulics. The control rod-driven scheme successfully followed the power demand within a narrow margin of error and reliably produced the required supply temperature to the district heating network. In contrast, the temperature feedback-driven control resulted in larger deviations, unpredictable temperature behaviour, and failed to meet the required supply temperature consistently. The results demonstrate that the control rod-driven power regulation is the more viable strategy for load following with LDR lite. Further optimization is still required, but the established control scheme provides a foundation for future research also in other fields
Understanding column-formation in axial-SPPS thermal barrier coatings:Evolution of microstructure and role of bond coat roughness
No full textColumnar yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are renowned for their exceptional resistance to thermal cyclic fatigue (TCF) and their consequent role in extending the service life of gas turbine components. Traditionally, such coatings have been produced by electron beam physical vapor deposition (EB-PVD) and, more recently, by suspension plasma spraying (SPS). Latest studies demonstrating the capability of the aqueous solution precursor route to fabricate columnar YSZ TBCs using axial plasma spraying indicate its considerable potential to overcome shortcomings associated with both EB-PVD and SPS methods. In this work, the microstructural evolution of axial solution precursor plasma-sprayed (SPPS) 8 wt% YSZ coatings is investigated, with emphasis on the role of bond coat roughness. In-flight particle generation and splat formation have been carefully examined to obtain insights into column development. Results show that a coarse bond coat surface promotes column initiation, whereas a much smoother surface favours vertical cracking, not quite leading to column formation. Careful collection of particles generated in flight confirmed their size to be predominantly in the 100–500 nm range (d50 ≈ 280 nm), leading to largely sub-micron splats (d50 ≈ 465 nm). It is postulated that such fine sizes are inadequate to rapidly roughen the growing surface for spontaneous column initiation, thereby making the initial bond coat roughness crucial in tailoring TBC microstructures. In this context, the concept of a certain ‘threshold roughness’ being necessary to trigger column formation is also proposed and needs further investigation.</p
Design and evaluation of load-follow control schemes for a small district heating reactor LDR lite
No full textLoad following is needed in district heating networks, where heat demand varies significantly. LDR lite is a small light water reactor designed for flexible, low-temperature heat production. In this study two load-follow control schemes were designed for LDR lite. In the first option, control rods are used to regulate the power, while the secondary circuit temperatures are kept constant. The second option utilizes temperature feedback, adjusting the reactor power via secondary circuit pump control. The control schemes were evaluated by simulating a simplified load-follow scenario using coupled 3D neutronics and system thermal hydraulics. The control rod-driven scheme successfully followed the power demand within a narrow margin of error and reliably produced the required supply temperature to the district heating network. In contrast, the temperature feedback-driven control resulted in larger deviations, unpredictable temperature behaviour, and failed to meet the required supply temperature consistently. The results demonstrate that the control rod-driven power regulation is the more viable strategy for load following with LDR lite. Further optimization is still required, but the established control scheme provides a foundation for future research also in other fields
Small Modular Reactors in Denmark:A Technology and Cost Review
No full textThe Danish Energy Agency has asked Ea Energy Analyses and VTT Technical Research Centre of Finland to investigate the possibilities and consequences of integrating the compact nuclear reactor technology called Small Modular Reactor technologies (SMR technologies) into the Danish energy system. The project covers two subtasks: 1) a technical analysis of SMR technologies in a Danish context 2) and a system analysis that will assess the effects and value of integrating SMR into the Danish energy system. Thisreport constitutes the reporting of the first part
Qualification of affordable open-source analog and digital Sun sensors for CubeSats
No full textThis paper presents the qualification of affordable, open-source analog (PSS) and digital Sun sensors (DSS) for CubeSats, which aim to provide cost-effective and accessible attitude determination solutions for small satellite missions. The study evaluates the performance, reliability, and suitability of these sensors in space-like conditions, addressing key factors such as accuracy, thermal stability, and radiation tolerance. Experimental results demonstrate that the PSS can achieve better than 5° precision over a field of view of 100° while maintaining low costs and power consumption. The DSS shows a precision better than 0.5° over a field of view of 36° using a photolithographically patterned optical aperture acting as a pinhole. The research highlights the potential of these sensors to democratize access to space technology, supporting academic and commercial CubeSat missions with accessible and effective attitude determination solutions
TRIM:Thermal Auto-Compensation for Resistive In-Memory Computing
No full textin-memory computing (IMC) has emerged as one of the most promising architectures to efficiently compute artificial intelligence tasks on hardware, particularly deep neural networks (DNNs). IMC can make use of analog computation principles alongside emerging nonvolatile memories (eNVM) technologies, potentially offering several orders of magnitude increased energy efficiency compared to generic processing units. Yet, the use of analog circuitry, potentially integrated with emerging technologies post-processed on top of silicon wafers, increases the susceptibility of hardware to a large spectrum of variations, for instance manufacturing, noise or temperature sensitivity. Hence, this susceptibility can hamper the large-scale deployment of IMC circuits into the market. To tackle the reliability of analog resistive-based IMC circuits regarding temperature variations, this article presents TRIM, a thermal on-chip auto-compensation method aimed at fully calibrating first-order temperature effects. TRIM is designed to maintain the computational accuracy of IMC cores in DNN applications over a wide temperature range, while being highly scalable and adaptable. In essence, the temperature compensation is realized through a complementary-to-absolute-temperature (CTAT) voltage reference integrated inside a voltage regulator and applied at the zero reference node of a multiplying digital-to-analog converter (MDAC), eliminating the need for external circuits or look-up table. The proposed methodology is demonstrated on a proof-of-concept 65 nm CMOS resistive IMC column. Measurement results showcase that the proof-of-concept auto-compensation system significantly enhances inference and multiply-and-accumulate (MAC) operation accuracy of any first-order resistive crossbar column, achieving inference accuracy recovery of 100% over a temperature range of –20 °C to 60 °C and a 91.3% improvement in MAC operation accuracy, with an area overhead of 2% and power overhead of < 0.02%.</p
A Survey on Detection, Classification, and Tracking of AAVs Using Radar and Communications Systems
No full textThe use of autonomous aerial vehicles (AAVs) for a variety of commercial, civilian, and defense applications has increased many folds in recent years. While AAVs are expected to transform future air operations, there are instances where they can be used for malicious purposes. In this context, the detection, classification, and tracking (DCT) of AAVs (DCT-U) for safety and surveillance of national air space is a challenging task when compared to DCT of manned aerial vehicles. In this survey, we discuss the threats and challenges from malicious AAVs and we subsequently study three radio frequency (RF)-based systems for DCT-U. These RF-based systems include radars, communication systems, and RF analyzers. Radar systems are further divided into conventional and modern radar systems, while communication systems can be used for joint communications and sensing (JC&S) in active mode and act as a source of illumination to passive radars for DCT-U. The limitations of the three RF-based systems are also provided. The survey briefly discusses non-RF systems for DCT-U and their limitations. Future directions based on the lessons learned are provided at the end of the survey.</p