Search Results (57)

This work presents an ultra-low-power on-chip energy management (EM) circuit, which is the most critical and power-intensive block in power management integrated circuits (PMICs) used for energy harvesting (EH) applications. Ultra-low power consumption was the primary design priority to ensure suitability for systems operating under strict energy limitations. The design relies on a compact latch-based core and avoids the need for extra circuits such as voltage references, comparators, or logic blocks, which helps reduce both area and power. To implement the required high resistance, a series of diode-connected zero-threshold NMOS transistors is used. This approach enables very high resistance in a compact area without additional power consumption or biasing issues at low voltages. A PMOS transistor is also integrated at the EM output to directly control different types of loads. The circuit was designed and fabricated using a 65 nm CMOS standard process. Experimental measurements from the fabricated chips show a quiescent current of 170 nA at 3 V and a voltage hysteresis of over 0.9 V. In addition, temperature and process variation were simulated to verify robust operation. These results confirm that the circuit operates reliably under ultra-low-power conditions and is well-suited for EH systems. Full article

As a key zero-carbon energy carrier, the accurate measurement of liquid hydrogen flow in its industrial chain is crucial. However, the ultra-low temperature, ultra-low density and other properties of liquid hydrogen can introduce calibration errors. To enhance the measurement accuracy and reliability of liquid hydrogen flow, this study investigates the heat and mass transfer within a 1 m³ non-vented storage tank during the calibration process of a liquid hydrogen flow standard device that integrates combined dynamic and static gravimetric methods. The vertical tank configuration was selected to minimize the vapor–liquid interface area, thereby suppressing boil-off gas generation and enhancing pressure stability, which is critical for measurement accuracy. Building upon research on cryogenic flow standard devices as well as tank experiments and simulations, this study employs computational fluid dynamics (CFD) with Fluent 2024 software to numerically simulate liquid hydrogen flow within a non-vented tank. The thermophysical properties of hydrogen, crucial for the accuracy of the phase-change simulation, were implemented using high-fidelity real-fluid data from the NIST Standard Reference Database, as the ideal gas law is invalid under the cryogenic conditions studied. Specifically, the Lee model was enhanced via User-Defined Functions (UDFs) to accurately simulate the key phase-change processes, involving coupled flash evaporation and condensation during liquid hydrogen refueling. The simulation results demonstrated good agreement with NASA experimental data. This study systematically examined the effects of key parameters, including inlet flow conditions and inlet liquid temperature, on the flow characteristics of liquid hydrogen entering the tank and the subsequent heat and mass transfer behavior within the tank. The results indicated that an increase in mass flow rate elevates tank pressure and reduces filling time. Conversely, a decrease in the inlet liquid hydrogen temperature significantly intensifies heat and mass transfer during the initial refueling stage. These findings provide important theoretical support for a deeper understanding of the complex physical mechanisms of liquid hydrogen flow calibration in non-vented tanks and for optimizing calibration accuracy. Full article

Sleep monitoring is critical for diagnosing and treating sleep disorders. Although polysomnography (PSG) remains the clinical gold standard, its complexity, discomfort, and lack of portability limit its applicability for long-term and home-based monitoring. To overcome these challenges, this study introduces a novel flexible headband system designed for multi-modal physiological signal acquisition, incorporating dry electrodes, a six-axis inertial measurement unit (IMU), and a temperature sensor. The device supports eight EEG channels and enables wireless data transmission via Bluetooth, ensuring user convenience and reliable long-term monitoring in home environments. To rigorously evaluate the system’s performance, we conducted comprehensive assessments involving 13 subjects over two consecutive nights, comparing its outputs with conventional PSG. Experimental results demonstrate the system’s low power consumption, ultra-low input noise, and robust signal fidelity, confirming its viability for overnight sleep tracking. Further validation was performed using the self-collected HBSleep dataset (over 184 h recordings of the 13 subjects), where state-of-the-art sleep staging models (DeepSleepNet, TinySleepNet, and AttnSleepNet) were applied. The system achieved an overall accuracy exceeding 75%, with AttnSleepNet emerging as the top-performing model, highlighting its compatibility with advanced machine learning frameworks. These results underscore the system’s potential as a reliable, comfortable, and practical solution for accurate sleep monitoring in non-clinical settings. Full article

Stress fields imparted with an ultrafast laser can correct low spatial frequency surface figure error of mirrors through ultrafast laser stress figuring (ULSF): the formation of nanograting structures within the bulk substrate generates localized stress, creating bending moments that equilibrize via wafer deformation. For ULSF to be used as an optical figuring process, the ultrafast laser generated stress must be effectively permanent or risk unwanted figure drift. Two isochronal annealing experiments were performed to measure ultrafast laser-generated stress stability in fused silica and Corning ultra-low expansion (ULE) wafers. The first experiment tracked changes to induced astigmatism up to 1000 °C on 25.4 mm-diameter wafers. Only small changes were measured after each thermal cycle up to 500 °C for both materials, but significant changes were observed at higher temperatures. The second experiment tracked stress changes in fused silica and ULE up to 500 °C but with 4 to 16× higher signal-to-noise ratio. Change in trefoil on 100 mm-diameter wafers was measured, and the induced stress in fused silica and ULE was found to be stable after thermal cycling up to 300 °C and 200 °C, respectively, with larger changes at higher temperatures. Full article

Fiber–aerogel composites have gained significant attention as high-performance thermal insulation materials due to their unique microstructure, which suppresses conductive, convective, and radiative heat transfer. At room temperature, silica aerogels in particular exhibit ultralow thermal conductivity (<0.02 W/m·K), which is two to three times lower than that of still air (0.026 W/m·K). Their brittle skeleton and high infrared transparency, however, restrict how well they insulate, particularly at high temperatures (>300 °C). Incorporating microscale fibers into the aerogel matrix enhances mechanical strength and reduces radiative heat transfer by increasing scattering and absorption. For instance, it has been demonstrated that adding glass fibers reduces radiative heat transmission by around 40% because of increased infrared scattering. This review explores the fundamental mechanisms governing radiative heat transfer in fiber–aerogel composites, emphasizing absorption, scattering, and extinction coefficients. We discuss recent advancements in fiber-reinforced aerogels, focusing on material selection, structural modifications, and predictive heat transfer models. Recent studies indicate that incorporating fiber volume fractions as low as 10% can reduce the thermal conductivity of composites by up to 30%, without compromising their mechanical integrity. Key analytical and experimental methods for determining radiative properties, including Fourier transform infrared (FTIR) spectroscopy and numerical modeling approaches, are examined. The emissivity and transmittance of fiber–aerogel composites have been successfully measured using FTIR spectroscopy; tests show that fiber reinforcement at high temperatures reduces emissivity by about 15%. We conclude by outlining the present issues and potential avenues for future research to optimize fiber–aerogel composites for high-temperature applications, including energy-efficient buildings (where long-term thermal stability is necessary), electronics thermal management systems, and aerospace (where temperatures may surpass 1000 °C), with a focus on improving the materials’ affordability and scalability for industrial applications. Full article

The shortage of tellurium and toxicity of lead are major obstacles to scaling mid-temperature thermoelectric generators. We engineer quaternary lead chalcogenides with composition (Pb_0.8Ge_0.2Te)_0.95-x(PbSe)_0.05(PbS)_x (0 ≤ x ≤ 0.25), where Pb is lead, Ge is germanium, Te is tellurium, Se is selenium, S is sulfur, and x denotes the molar fraction of lead sulfide (PbS). The primary novelty lies in achieving ultra-low thermal conductivity through controlled phase segregation induced by systematic PbS incorporation. X-ray diffraction analysis reveals single-phase solid solutions up to x ≈ 0.10, with secondary PbS precipitates forming beyond this threshold. These PbS-rich phases create hierarchical microstructures that scatter phonons across multiple length scales, suppressing total thermal conductivity to 0.6 Wm⁻¹K⁻¹ at x = 0.15—approximately 84% lower than pristine lead telluride (PbTe) and approaching glass-like thermal conductivity values. Electrical transport measurements demonstrate sulfur’s role as an electron donor, enabling carrier-type control from p-type to n-type conduction. Despite moderate electrical power factors, the optimized composition (x = 0.20) achieves a peak dimensionless figure of merit ZT ≈ 0.34 at 650 K. This work demonstrates an effective strategy for tellurium-lean, lead-reduced thermoelectric materials through sulfur-induced phase segregation, providing practical design guidelines for sustainable waste heat recovery applications. Full article

This paper presents the design, fabrication, calibration, and comprehensive characterization of a homemade tri-axial fluxgate magnetometer. The magnetometer, utilizing a ring core configuration, was developed to measure ultra-low magnetic fields with high sensitivity and stability. Critical stages from material selection to sensor geometry optimization are discussed in detail. A series of critical characterization processes were conducted, including zero-field voltage determination, scale factor calculation, resolution measurement, noise analysis, bias assessment, cross-field effect evaluation, temperature dependency, and bandwidth determination. The sensor demonstrated a minimum detectable magnetic field resolution of 2.2 nT with a noise level of 1.1 nT/√Hz at 1 Hz. Temperature dependency tests revealed minimal impact on sensor output with a maximum shift of 120 nT in the range of 60 °C, which was effectively compensated through calibration to less than 5 nT. Additionally, the paper introduces a model function in matrix form to relate the magnetometer’s output voltage to the measured magnetic field, incorporating temperature dependency and cross-field effects. This work highlights the importance of meticulous calibration and optimization in developing fluxgate magnetometers suitable for various applications, from space exploration to biomedical diagnostics. Full article

Chemical nanosensors based on tin dioxide (SnO₂) and zinc oxide (ZnO) nanoparticles (NPs) were developed and characterized for the detection of low concentrations of atmospheric pollutants, such as nitrogen dioxide (NO₂) and carbon monoxide (CO). The sensing layers were prepared using three fabrication methods: drop-casting, electrospray, and spark ablation coupled with an inertial impaction printer, to compare their performance. Multiple surface characterization techniques were carried out to investigate the surface morphology and elemental composition of the deposited layers such as SEM (scanning electron microscopy) and XPS (X-ray photoelectron spectroscopy) analyses. UV light photoactivation enabled the sensors to detect ultra-low concentrations of the target gases at room temperature (100 ppb NO₂ and 1 ppm CO). The measurements were conducted at 50% relative humidity to simulate real environmental conditions. All sensors were capable of detecting the target gases. Drop-casting is the simplest and most cost-effective technique, but it is also the least reproducible. In contrast, sensors based on the spark ablation technique achieved more homogeneous sensing layers, with practically no nanoparticle agglomeration, resulting in devices with lower noise and drift in their electrical response. Full article

Titanium thin films with thicknesses of up to 105 nm were deposited on borosilicate glass implementing low-power continuous (25 W) and pulsed (85 W, with an ultra-low duty cycle) DC magnetron sputtering. The characteristics of the resulting films were studied via atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), VIS spectroscopy, and four-point-probe measurements. Both deposition modes yield films with low surface roughness, and AFM analysis showed no topographical features indicative of columnar-and-void structures. The films exhibited high optical reflectivity and stable transmittance and reflectance across the visible spectrum. The electric resistivity could be measured even at single nanometer thickness, emphasizing the metallic character of the films and approaching the bulk titanium value at higher film thicknesses. The low power regime of magnetron sputter deposition not only offers the possibility of studying the development of physical characteristics during the growth of ultra-thin films but also provides the advantage of extremely low heat development and no evident mechanical stress on the substrate during the coating process. These results outline a path for low-power DC sputtering as a reliable approach for studying the evolution of functional properties in ultra-thin films and for the gentle fabrication of coatings where thermal stress must be avoided, making the method compatible with temperature-sensitive applications. Full article

Deep dehumidification is crucial for industrial applications requiring ultra-low humidity levels. Traditional cooling-based dehumidification struggles to achieve low dew points efficiently due to excessive energy consumption and frost formation risks. As an alternative, desiccant-based methods, particularly solid desiccant systems, offer improved performance with lower energy demands. This study experimentally investigates a fixed-bed dehumidification system utilizing a plate-fin heat exchanger filled with a silica gel/calcium chloride composite material. The performance evaluation focuses on the influence of ambient conditions and operating parameters, including air velocity and cooling fluid temperature. Among these, the most influential parameter was the velocity of air. For the tested heat exchanger, an optimum value in the range of 0.4–0.6 m/s was identified. Under optimal conditions, the tested HEX was able to reduce the dew point of air down to −2 °C, achieving a reduction in the humidity ratio up to 13 g/kg. The results indicate that air velocity significantly impacts also heat and mass transfer, with coefficients ranging from 80 to 140 W/(m² K) and 0.015 to 0.060 kg/(m² s), respectively. The findings highlight the potential of composite desiccant fixed-bed systems for efficient deep dehumidification, outperforming conventional lab-scale components in heat and mass transfer effectiveness. A comparison with other works in the literature indicated that up to 30% increased mass transfer coefficient was achieved and up to seven times higher heat transfer coefficient was measured. Full article

Eucalyptus wood particleboard (EPB), commonly used in indoor decoration, releases volatile organic compounds (VOCs) that can adversely affect indoor air quality and human health. This study systematically examined the VOC emission characteristics of EPB using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS). A total of 65 VOCs were identified, with medium-volatility organic compounds (MVOCs) accounting for 28 compounds, low-volatility organic compounds (LVOCs) for 26, and high-volatility organic compounds (HVOCs) for 11. Terpenoids dominated the VOCs, comprising 78.46%, followed by aldehydes (10.77%) and alkanes (7.69%). Key odorant compounds (KOCs) were identified using the relative odor activity value (ROAV), with hexanal (ROAV = 100) and o-cymene (ROAV = 76.90) emerging as the most significant contributors to the overall odor profile. Thermal post-treatment at temperatures of 50–60 °C for durations of 6–12 h was found to be an effective method for reducing the residual VOCs and KOCs in the EPB, leading to a marked decrease in the peak areas of key odorants. The findings suggest several strategies for minimizing VOC emissions and eliminating residual odor, including reducing the use of miscellaneous wood materials, controlling the production of o-cymene, and employing thermal post-treatment at moderate temperatures. These measures provide a promising approach to reducing VOC and odor emissions from EPB and similar composite wood products, thereby enhancing their suitability for indoor applications. This study innovatively establishes an evaluation system for VOC emission characteristics in wood-based panels based on the ROAV. It elucidates the contribution mechanisms of key odor-active substances (e.g., hexanal and pentanal) and presents a thermal post-treatment process for source control, achieving simultaneous VOCs and odor elimination. A ROAV-guided hierarchical management strategy is proposed, providing scientific guidelines for the industrial production of high-quality particleboards with ultralow emissions (TVOC < 50 μg/m³) and minimal odor intensity (OI < Grade 3). Full article

We propose a scheme to enhance the range and precision of ultra-low temperature measurements by employing a probe qubit coupled to a chain of ancilla qubits. Specifically, we analyze a qubit chain governed by Heisenberg $XX$ and Dzyaloshinskii–Moriya (DM) interactions. The precision limits of temperature measurements are characterized by evaluating quantum Fisher information (QFI). Our findings demonstrate that the achievable precision bounds, as well as the number of peaks in the QFI as a function of temperature, can be controlled by adjusting the number of ancilla qubits and the system’s model parameters. These results are interpreted in terms of the influence of energy transitions on the range and the number of QFI peaks as a function of temperature. This study highlights the potential of the probe qubit–ancilla chain system as a powerful and precise tool for quantum thermometry in the ultra-low temperature regime. Full article

In this paper, we examine an ultra-compact on-chip balanced filter based on novel hybrid resonators (NHRs) comprising short transmission line sections (STLSs) and series LC blocks using low-temperature co-fired ceramic (LTCC) technology. Based on a rigorous theoretical analysis, the proposed NHR demonstrates the potential for intrinsic ultra-wideband differential-mode (DM) and common-mode (CM) suppression without any additional suppressing structures. Furthermore, the resonance of NHRs was determined by four degrees of freedom, providing flexibility for miniaturization. Theoretical extensions of the Nth-order topology can be easily achieved by the simple coupling schemes that occur exclusively between STLSs. For verification, a balanced filter covering the 5G band n78 with an area of 0.065λ_g × 0.072λ_g was designed using the proposed optimization-based design procedure. An ultra-low insertion loss of 0.8 dB was obtained. The quasi-full CM stopband with a 20 dB rejection level ranged from 0 to 12.9 GHz. And the ultra-wide upper DM stopband with a 20 dB rejection level ranged from 4.4 to 11.5 GHz. Good agreement between the theoretical, simulated, and measured results indicate the validity of the proposed design principle. Full article

The emergence of the COVID-19 pandemic in 2020 led to the implementation of legal restrictions on individual activities, significantly impacting traffic and air pollution levels in urban areas. This study employs a state-space intervention method to investigate the effects of three major COVID-19 lockdowns in March 2020, November 2020, and January 2021 on London’s air quality. Data were collected from 20 monitoring stations across London (central, ultra-low emission zone, and greater London), with daily measurements of NO_x, PM₁₀, and PM_2.5 for four years (January 2019–December 2022). Furthermore, the developed model was adjusted for seasonal effects, ambient temperature, and relative humidity. This study found significant reductions in the NO_x levels during the first lockdown: 49% in central London, 33% in the ultra-low emission zone (ULEZ), and 37% in greater London. Although reductions in NO_x were also observed during the second and third lockdowns, they were less than the first lockdown. In contrast, PM₁₀ and PM_2.5 increased by 12% and 1%, respectively, during the first lockdown, possibly due to higher residential energy consumption. However, during the second lockdown, PM₁₀ and PM_2.5 levels decreased by 11% and 13%, respectively, and remained unchanged during the third lockdown. These findings highlight the complex dynamics of urban air quality and underscore the need for targeted interventions to address specific pollution sources, particularly those related to road transport. The study provides valuable insights into the effectiveness of lockdown measures and informs future air quality management strategies. Full article

Particulate and gaseous emissions were studied from a large two-stroke slow-speed diesel engine equipped with an open-loop scrubber, installed on a 78,200 metric tonnes (deadweight) containership, under real operation. This paper presents the on-board emission measurements conducted upstream and downstream of the scrubber with heavy fuel oil (HFO) and ultra-low sulfur fuel oil (ULSFO). Particle emissions were examined under various dilution ratios and temperature conditions, and with two thermal treatment setups, involving a thermodenuder (TD) and a catalytic stripper (CS). Our results show a 75% SO₂ reduction downstream of the scrubber with the HFO to emission-compliant levels, while the use of the ULSFO further decreased SO₂ levels. The operation of the scrubber produced higher particle number levels compared to engine-out, attributed to the condensational growth of nanometer particle cores, salt and the formation of sulfuric acid particles in the smaller size range, induced by the scrubber. The use of a TD and a CS eliminates volatiles but can generate new particles when used in high-sulfur conditions. The results of this study contribute to the generally limited understanding of the particulate and gaseous emission performance of open-loop scrubbers in ships and could feed into emission and air quality models for estimating marine pollution impacts. Full article