Current Response Time Research Articles

High-precision reconstruction of a heat flux boundary via a programmable scanning electron beam controlled by the voltage waveform design method

A scanning electron beam can be used to construct heat flux boundaries (HFBs). However, the long current response time in the deflection coil using a current control method (CCM) cause the deviation of the current waveform, potentially reducing the accuracy of the reconstructed HFB relative to the target HFB. The impact of the current response time on the reconstruction accuracy increases as the field frequency increases, and the accuracy can be reduced from 0.89 to 0.69. To shorten the current response time and improve the reconstruction accuracy, a voltage waveform design method (VWDM) is introduced as a replacement for the CCM. The result indicates that the accuracy of the HFB reconstructed by a scanning electron beam controlled by the VWDM can reach 0.91. Additionally, increasing the maximum output voltage of the power amplifier used to generate the voltage can further improve the reconstruction accuracy of the HFB with the VWDM. This study provides a new approach for the accurate construction of HFBs for rapid thermal processing, additive manufacturing and thermal assessment of hypersonic vehicles.

계통연계형 PV(Photovoltaic) 설계 및 과도상태 특성 연구

This study investigated the design of a grid-connected photovoltaic (PV) system based on solar power generation and its characteristics during ground-fault incidents. Various approaches to enhance the stability and efficiency of the PV system were explored. Experimental results confirmed that the integration of solar arrays, DC/DC converters, and inverters optimized the output characteristics of the system. In particular, the analysis focused on current changes and control mechanisms during ground fault incidents and compared the effectiveness of DC circuit breakers and superconducting fault current limiters. Simulations were performed to propose solutions to address the problem of sudden increases in fault current. The results demonstrated the effectiveness of DC circuit breakers in limiting fault currents. Additionally, the application of fault current limiters improved both fault current limitation and response times for disconnection. The results of this study enhance the safety and economic operation of solar power systems and facilitate the adoption of eco-friendly energy. The results can be used as a reference for the design and operation of solar power systems in the future and can support the implementation of renewable energy policies.

Electrochemical sensors for sensitive and selective detection of nitrite based on flexible gold microneedle like nanodendrites modified electrode

In this study, we present a new approach utilizing Au nanodendrites (Au NDs) to modify flexible screen-printed carbon electrodes (FSPCEs), offering an efficient platform for voltammetric sensing of nitrite ions in food samples. The FSPCEs are created with gold leaf-like nanodendrites through a simple, one-step electrochemical deposition process. The direct growth of these Au NDs occurs efficiently on the carbon-paste electrode, eliminating the need for binders or additional reducing agents and organic solvents, owing to the aforementioned matrix. The modified electrodes serve as promising sensing platforms for nitrite detection. The outcomes demonstrated that a significant amount of AuNPs with dendritic morphologies were dispersed throughout the FSPCE.These novel flexible electrodes act as effective electrocatalyst for NO2− oxidation due to their large electrochemical active surface area (ECSA), well-dispersed Au nanostructures, and high electrical conductivity. The optimized sensor exhibits a wide linear response range from 0.02 to 5.8 µM, with 1.0 nM limit of detection, an impressive sensitivity of 52.529 µA µM−1 cm−2 and a quick current response time (< 3 s) towards nitrite ions. Additionally, the suggested sensor demonstrates high selectivity, reproducibility, and stability. Furthermore, the FSPCEs are evaluated for their ability to selectively detect nitrite ions in various food samples such as tap water, drinking water, milk, and fruit juices, comparing the results with standard methods in real sample analysis. The fabricated sensors show promising potential for practical applications in food and environmental analysis. Consequently, Au NDs@FSPCE electrode emerged to be a novel platform for NO2− electrochemical detection. Because of their great affinity for analytical substances in solutions, gold nanodendrites supported on flexible screen-printed carbon electrodes (FSPCEs) are very useful for electrode modifications. Their increased effective surface area, which greatly raises the electrode's sensitivity and specificity for a range of analytical applications, is responsible for their high affinity.

Perovskite versus Standard Photodetectors.

Perovskites have been largely implemented into optoelectronics as they provide several advantages such as long carrier diffusion length, high absorption coefficient, high carrier mobility, shallow defect levels and finally, high crystal quality. The brisk technological development of perovskite devices is connected to their relative simplicity, high-efficiency processing and low production cost. Significant improvement has been made in the detection performance and the photodetectors' design, especially operating in the visible (VIS) and near-infrared (NIR) regions. This paper attempts to determine the importance of those devices in the broad group of standard VIS and NIR detectors. The paper evaluates the most important parameters of perovskite detectors, including current responsivity (R), detectivity (D*) and response time (τ), compared to the standard photodiodes (PDs) available on the commercial market. The conclusions presented in this work are based on an analysis of the reported data in the vast pieces of literature. A large discrepancy is observed in the demonstrated R and D*, which may be due to two reasons: immature device technology and erroneous D* estimates. The published performance at room temperature is even higher than that reported for typical detectors. The utmost D* for perovskite detectors is three to four orders of magnitude higher than commercially available VIS PDs. Some papers report a D* close to the physical limit defined by signal fluctuations and background radiation. However, it is likely that this performance is overestimated. Finally, the paper concludes with an attempt to determine the progress of perovskite optoelectronic devices in the future.

Robust Deep UV Photodetectors Based on One‐Step‐Grown Polycrystalline Ga2O3 Film via Pulsed Laser Deposition toward Extreme‐Environment Application

AbstractGallium oxide (Ga2O3), with an ultrawide bandgap corresponding to the deep ultraviolet (DUV) range, has attracted significant attention in optical filter‐free photodetectors. In practical terms, DUV photodetectors employed in extreme conditions, for example, flame detection and space exploration, face the challenges of performance degradation caused by high/low‐temperature transformation. Here, DUV photodetectors are tailored with high durability and stability by one‐step‐grown β‐Ga2O3 films via pulsed laser deposition. A high‐oxygen‐pressure scheme effectively addresses the issue of film‐free deposition at specifically high temperatures, facilitating the formation of polycrystalline high‐resistivity β‐Ga2O3 films. As a result, the devices exhibit outstanding performance, including a low dark current (4.4 pA @30 V), high photoresponsivity (147.36 A W−1), and fast response time (3.1/22.6 ms). Additionally, the photoresponse performance shows minimal degradation at high temperatures up to 300 °C and even improves at low temperatures down to −100 °C, ranking it among the most robust DUV photodetectors. The mechanism of photoresponse, involving the exciton formation, bandgap evolution, carrier‐phonon scatter, etc., is also elucidated in a wide temperature range. This work provides an efficient solution for developing robust Ga2O3 DUV photodetectors with excellent performance for extreme‐condition applications.

A multistimuli‐responsive recyclable poly(vinyl alcohol)/perylene imide hydrogel of high‐performance piezoresistive sensors for human wearable devices

AbstractMultiple factors stimulate human beings in their daily lives, but uniformly collecting these signals is challenging. This study proposes a physically cross‐linked method that employs hydrogen bonding interactions to prepare poly(vinyl alcohol)/perylene imide (PVA/PI) hydrogels. The prepared PVA/PI hydrogels demonstrate favorable compressive strength (45–75 kPa) and adhesion properties. At room temperature, elongation reaches approximately 400%. Additionally, the PVA/PI hydrogels exhibit strong mechanical properties, with a maximum elongation of 200%, and high ionic‐electronic conductivity of 29.6 S m−1, even after being soaked in a 2 M HCl solution for 24 h. The water‐soluble PI in the PVA/PI hydrogels is environmentally responsive, resulting in a current response time of 100 ms under 365 nm irradiation, as well as reversible fluorescence changes across different pH levels. Both the PVA5/PI1 and PVA5/PI1/HCl2 (the concentrations were 5 wt%, 1 mg mL−1 and 2 mol L−1, respectively) hydrogels demonstrate high sensitivity (0.49 and 7.88 kPa−1) and a wide pressure monitoring range (0.088–30.67 kPa and 0.088–18.67 kPa, respectively) as pressure sensors. The first developed recyclable PVA/PI hydrogel shows promise for use in wearable sensing devices and is expected to be applied in complex environments.

Ag nanoparticle decorated β-Ga2O3 nanowires on Si substrates: advancing photodetector technology

In this study, we present the fabrication of Ag nanoparticle (NP) decorated β-Ga2O3 nanowire (NW) on a Si-substrate, with a focus on their application in photodetection. The resulting Ag NP decorated β-Ga2O3 NW exhibited a polycrystalline morphology characterized by well-aligned rows of vertically oriented structures. The mean size of the crystallites was revealed to be approximately 15.94 nm. The fabrication of Ag NP decorated β-Ga2O3 NW displayed uniformity, with an average length of approximately ∼180 nm. The UV-Vis absorption spectroscopy analysis yielded an approximate optical bandgap value of 4.74 eV. Notably, the fabricated photodetector exhibited excellent performance characteristics. This was highlighted by the minimal dark current of −3.2 nA at a bias voltage of −1 V, accompanied by an I L/I D ratio exceeding 50. Moreover, the photodetector demonstrated rapid rise and fall times of 0.023 s and 0.021 s, respectively. The remarkable aspect lies in the simultaneous attainment of minimum dark current and swift response times. The Ag NP-decorated β-Ga2O3 NW photodetector exhibited consistent and reproducible behavior, suggesting its potential for realistic use in ultraviolet photodetection.

High-Performance ε-Ga2O3 Solar-Blind Photodetectors Grown by MOCVD with Post-Thermal Annealing

High-temperature annealing has been regarded as an effective technology to improve the performance of Ga2O3-based solar-blind photodetectors (SBPDs). However, as a metastable phase, ε-Ga2O3 thin film may undergo phase transformation during post-annealing. Therefore, it is necessary to investigate the effect of the phase transition and the defect formation or desorption on the performance of photodetectors during post-annealing. In this work, the ε-Ga2O3 thin films were grown on c-plane sapphire with a two-step method, carried out in a metal-organic chemical vapor deposition (MOCVD) system, and the ε-Ga2O3 metal-semiconductor-metal (MSM)-type SBPDs were fabricated. The effects of post-annealing on ε-Ga2O3 MSM SBPDs were investigated. As a metastable phase, ε-Ga2O3 thin film undergoes phase transition when the annealing temperature is higher than 700 °C. As result, the decreased crystal quality makes an SBPD with high dark current and long response time. In contrast, low-temperature annealing at 640 °C, which is the same as the growth temperature, reduces the oxygen-related defects, as confirmed by X-ray photoelectron spectroscopy (XPS) measurement, while the good crystal quality is maintained. The performance of the SBPD with the post-annealing temperature of 640 °C is overall improved greatly compared with the ones fabricated on the other films. It shows the low dark current of 0.069 pA at 10 V, a rejection ratio (Rpeak/R400) of 2.4 × 104 (Rpeak = 230 nm), a higher photo-to-dark current ratio (PDCR) of 3 × 105, and a better time-dependent photoresponse. These results indicate that, while maintaining no phase transition, post-annealing is an effective method to eliminate point defects such as oxygen vacancies in ε-Ga2O3 thin films and improve the performance of SBPDs.

Hydrothermal Synthesis of ZnO Nanospheres Using Apple Pectin as Biotemplate and Application for UV Sensing

In this study, spherical-like ZnO UV photodetectors based on the facile hydrothermal method, induced different concentrations of apple pectin as the biotemplate. Apple pectin can react with zinc particles and change the pH value, which plays an essential role in modifying surface morphology. Moreover, apple pectin extracted from apple peels as carbon and nitrogen sources can also be used to improve absorption properties and increase depletion region to reduce dark current. The best results were obtained when 150 mg of apple pectin was used, showing a high UV-to-dark current ratio and fast response and recovery times. The UV-to-dark current ratio is as high as 80106.1, which is better than that of pure ZnO (4.47). Fast response and recovery times are also swift. The physical properties were evaluated using various techniques, including scanning electron microscopy, photoluminescence (PL), X-ray diffraction, and energy-dispersive X-ray (EDX), respectively. The results of this study suggest that the use of apple pectin in the hydrothermal synthesis of ZnO may offer a promising approach for modifying ZnO materials.

A voltage waveform design method for shortening current response time of a coil

SummaryCoils are widely used in magnetorheological dampers, solenoid valves, and electron guns, where a quick response of the magnetic induction to the excitation voltage is needed. To achieve a quick response, the response time of the magnetic induction relative to the current and that of the current relative to the voltage should be shortened as much as possible. The latter is dominant in the total response time and can be shortened by using voltage control with an increased resistance or current control. The current time responses of the Helmholtz coils based on voltage control with an increased resistance and current control are measured. The results indicate that the current response times of the coils based on voltage control with resistances of 23.7 and 162 Ω and current control with a resistance of 23.7 Ω are 235.3, 42.3, and 62.1 μs, respectively. The current time responses of the voltage control are smooth, while those of the current control have large oscillations. Based on Kirchhoff's equilibrium equation, an overshoot voltage waveform design method is proposed to shorten the current response time and eliminate the current oscillations. The experimental results show that the current time response is smooth, and the current response time can be shortened by 91.8%, 54.4%, and 68.9% in comparison with those of the former three control cases. The demonstration experiments of the effect of the different control methods on the electron‐beam scanning path and hot spot distribution show that the scanning path and dwell duration are closer to the expected ones with the proposed method. The proposed method is of great value for improving the damping performance of a magnetorheological damper, the accuracy of the fluid injection of a solenoid valve, and the accuracy of the electron‐beam thermal assessment.

Mathematical Modeling of Time Response Analysis of Residual Current Devices with Electronic Switches

Today, relay contact and electronic residual current relays are used in order to protect human life against electrical shocks and machinery and equipment from malfunctions caused by excessive current. These residual current relays step in at 30 mA level and cut the current from the system. With the developed electronic switch and residual current device hybrid system, the human body residual current value and current cut-off response time were calculated using Monte Carlo Simulation frequency / intensity distributions. In the field of application, data sets were created in this study, which can be realized using physical and ambient data related to the human body resistance value. In this study, the reaction time of the system developed according to the amount of electric current, temperature of the human body, skin and moisture properties, shoes worn, decking, material type characteristics was modeled mathematically by using Monte Carlo simulation.

An Improved Calculational Model for Inductance of CRDM Based on Equivalent Magnetic Circuit

In the magnetic lifting control rod drive mechanism (CRDM), it is essential to obtain the dynamic inductance of each coil for research of a mathematical model and state monitoring. It is demonstrated from the working principle and circuit model of the CRDM that the coil inductance has a significant effect on the current step response time. This article proposes an improved equivalent magnetic circuit (IEMC) model that takes into account flux leakage and coupling. The model focuses on calculating the dynamic inductance of the CRDM. First, the magnetic reluctance expression of each unit in the IEMC model is deduced. A flux area correction coefficient is introduced to consider the edge effect of working air gaps. Then, the dynamic inductance of the CRDM is analyzed and calculated based on the proposed model. Finally, the performance of the proposed method is compared with finite element analysis (FEA) and a simplified equivalent magnetic circuit (SEMC) method. Results show that the proposed method can approach the results of FEA better than the SEMC method.

Trace Al component in ε-(AlxGa1-x)2O3 alloy films and film-based solar-blind photodetectors

ε-(AlxGa1-x)2O3 alloy thin films containing Al fractions of 0, 2.9 at%, and 4.7 at% with ε-Ga2O3 templates were fabricated on (0001) c-sapphire by tin-assisted PLD technique. Sn is a surface-mediated surfactant to stabilize the formation of epsilon phase. XRD reveals that the peak position of ε-(AlxGa1-x)2O3 shifts to a higher diffraction angle and that ε-(AlxGa1-x)2O3 is accompanied by a deterioration of crystal quality when the Al composition increases from 0 to 4.7 at%. With Al content increasing, XPS demonstrates the appearance of more aluminum atoms bound to oxygen atoms and higher oxygen vacancy density in ε-(AlxGa1-x)2O3 films. The optical bandgap for ε-(AlxGa1−x)2O3 thin films with various Al components are 4.97 eV, 5.09 eV and 5.16 eV, respectively. The solar-blind photodetectors were fabricated on ε-(AlxGa1-x)2O3 alloy thin films with various Al fractions. The photo-to-dark current ratio, responsiveness, detectivity and response time (rise time/decay time) for ε-(AlxGa1-x)2O3 (x = 2.9 at%) PDs were 2.7 × 103, 4.2 A/W, 1.23 × 1013 Jones and 2.09 s/0.49 s.

Programmable Current Source Design for Multi-channel Magnetic Field Generator* Programmable current source

The three-dimensional motion of magnetic micro-robots requires the control of multiple magnetic field generators working simultaneously. The current program-controlled current sources in the market are generally expensive and it is difficult to control multiple program-controlled current sources by a single controller to change the output current at the same time. In order to compress the experimental cost, reduce the experimental threshold, realize the simultaneous control of multiple magnetic field generators and make them work stably, this paper proposes a special program-controlled current source design for multiple magnetic field generators, and verifies the feasibility of the design through experimental tests. The results show that the dedicated current source is able to output 0.3∼6.5A under ±12V switching power supply test when each current source is connected to a 1.5 ohm solenoid coil with internal resistance. The system meets the requirements of 3% or less output current error and fast response time while greatly reducing costs and achieving good interactivity.

Bdot probe and Rogowski coil cross-calibration and sensor fusion in pulsed direct current capacitor discharges.

Bdot probes and Rogowski coils are used in the measurement of transient magnetic fields and currents, respectively. They both share the mechanism of creating an induced electromotive force response via Faraday's law, which scales linearly with the pulsed magnetic field. High power capacitor direct current (DC) discharge systems release a single pulse of current that is both very high and very fast (≲1 ms). To capture these transient data and characterize these systems, high current tolerant and fast response time sensors are required. While these measuring devices have been well studied and utilized for almost 100 years, a comprehensive and detailed description of the custom design, calibration, and sensor fusion application of these tools for use in various pulsed DC capacitor value discharges is largely missing in the literature. Using robust analytical calculations, finite element analyses, and empirical methods, we have developed a sensor fusion protocol for current and magnetic field probes (with relative errors of ±13% and ±15%, respectively) for use in any geometry of high speed pulsed DC current calibrated capacitor discharge systems. This paper comprehensively outlines the design and sensor fusion methodologies that allow for the deployment of in-house built Bdot probes and Rogowski coils to a wide range of pulsed DC systems and demonstrates their use in a characteristic plasma environment.

Normalized Dynamic Characterization and Application of Multiple Heat Storage Materials Based on Standard Thermal Resistance

Based on the standard thermal resistance and the heat current method, the transient heat transfer thermal resistance between the heat storage material and the heat transfer fluid is deduced. Through analog circuit analysis method, the transient heat current model and dynamic response time constant of heat storage-heat exchange processes are obtained. Based on this model, the node temperature is introduced for refining the heat transfer thermal resistance, and the transient heat current model of the third-order circuit coupled with the heat storage and heat transfer processes is obtained. Through numerical simulation verification and application comparison analysis, it is found that the normalized dynamic model based on multiple time constants is feasible to characterize the dynamic characteristics of heat storage materials, and can directly compare and analyze different heat exchange and heat storage materials. The case study found that when exchanging heat with solid heat storage materials, the dynamic heat exchange capacity of liquid metal is better than that of molten salt, while the heat exchange between air and ceramic materials reaches a steady state faster than that of water vapor and CO₂.

Ultrahigh-responsivity deep-UV photodetector based on heterogeneously integrated AZO/a-Ga2O3 vertical structure

ZnO:Al (AZO) and a-Ga2O3 thin films were successively deposited on a sapphire substrate by magnetron sputtering and the photoelectric properties of AZO/a-Ga2O3 heterojunction vertical structure to solar blind ultraviolet light were investigated. The device shows a high photo-to-dark current ratio (2.2 × 103), low dark current (11.4 nA), large responsivity (67.26 A/W) and fast response and recovery times of 1.53 μs and 2.25 ms under 254 nm light illumination at 10 V. Additionally, the device exhibits an obvious self-powered effect with light-dark current ratio (183.3) and the responsivity (2.92 × 10−2 A/W) at 0 V. The high response is attributed to the separation of photogenerated electron-hole pairs due to built-in field in the depletion width of AZO and Ga2O3. The analysis shows that there exists a quasi-Zener tunneling internal gain mechanism, which increases the performance of the device. The comprehensive performance of the device implied a wide potential in optoelectronics applications.

Design and co-optimization of a laminated isolation bearing based on magnetorheological elastomer

Magnetorheological elastomer (MRE) base isolation is regarded as one of the most promising candidates in adaptive base isolation filed for civil structure. The field is rapidly evolving with significant technological advancements, while MRE device developing remains a spotlight of interest, essential for the future developments of MRE control system. Other than previous research in MRE device developing, which lacks a theoretical design combining the requirements of applied object, meanwhile, which only focus on the magnetic-controllable range without an integrated performance optimization. This report presents an efficient design and optimization of MRE isolation bearing (MRE-IB) according to the requirements of a scaled frame structure, by simultaneously considering the superior magnetic-controllable performance, low power consumption and fast current response time as the optimization objectives. After an efficient design, co-simulation and optimization, the optimized MRE-IB is manufactured and evaluated. The evaluated results verify the validity and reliability of the proposed optimization method. Besides the intrinsic importance of providing theoretical foundation and reference value for the design and optimization of MRE vibration isolators, this study can also conduce to the efficient design and optimization of other MRE devices, such as MRE absorbers, MRE buffers, and so on.

Investigation of a Highly Sensitive Au Nanoparticle-Modified ZnO Nanorod Humidity Sensor

In this article, pure ZnO and Au nanoparticle-modified (ANM) ZnO nanorods (NRs) were well prepared on a glass substrate via the hydrothermal method at 90 °C for 6 h, and the pure ZnO and ANM ZnO NR humidity sensors were fabricated. The crystal and optical properties of the ZnO and ANM ZnO NRs were investigated through scanning electron microscopy (SEM), XRD, photoluminescence (PL), and TEM analyses. The structures of the relative humidity (RH) sensors demonstrated high photo-to-dark current contrast ratios and short response and recovery times during RH measurement. The ANM ZnO NR RH sensor showed better humidity sensing performance than the pure ZnO NR humidity sensor. Under 80% RH, the results of photo-to-dark current contrast ratios, response time, and recovery time were 9.82, 192.44, and 122.42 s, respectively, better than those in pure ZnO NRs RH sensor. These results indicated that humidity sensing property could effectively be improved by Au nanoparticle adsorption.

Method of improving performance of the low-inductance PMSM drive system

The disc coreless permanent magnet synchronous machine (PMSM) has a special coreless structure. This kind of PMSM has very low inductance, which is referred to as the low-inductance PMSM(LIPMSM) in this paper. The LIPMSM offers many advantages to drive systems. However, the current fluctuates strongly when driven by general converters, which makes the LIPMSM difficult to be popularized into modern drive systems. To tackle the above problems, a converter with output inductance is used. The influences of the inductance on the performance of the LIPMSM system are analysed, including current fluctuations, the maximum speed without flux weakening and the current response time. Based on above analyses, a method of obtaining the optimal inductance is proposed to obtain the optimal inductance simply and efficiently. The method has been verified through simulations and experiments. The system cannot work due to the huge current fluctuations when driven by the general converter. By using the converter with the optimal inductance, the current fluctuations have been reduced to 2 A. The experimental LIPMSM can reach 11000 rpm with very short response time of the current. Therefore, the LIPMSM system performance can been improved significantly and meet the requirements by using the converter with the optimal inductance.