Current Measurements Research Articles

The impact of P-type doping level and profile on performance of InAs quantum dot lasers

The impact of P-type doping level on InAs quantum dot (QD) lasers grown on GaAs (001) was investigated through the device performance characterization, i.e., measurements of threshold current, output slope efficiency, and temperature characteristics of lasers. The lasers are characterized under continuous wave operation with a ridge waveguide of 6 × 4000 μm2. In comparison to un-doped lasers, it has been demonstrated that an appropriate P-type doping level in the entire spacer can reduce the threshold current density of lasers from 215 to 86.8 A/cm2 for a doping concentration of 10 holes per QD at room temperature. Additionally, an improvement in output power slope efficiency from 0.108 to 0.191 W/A has been obtained, along with an enhanced characteristic temperature from 34.4 to 67.5 K (20–100 °C). Moreover, modulation doping has been explored to further reduce the threshold current density down to 77.9 A/cm2 at room -temperature and raise the output power, while entire spacer doping may enhance device performance at high operating temperatures. By optimization of P-type doping, remarkable enhancements in the performance of QD lasers can be achieved, which might have potential applications in cost-effective high-performance photonic integrated circuits.

Finsler currents

We propose a slight variant of Ambrosio and Kirchheim’s definition of a metric current. We show that with this new definition it is possible to obtain certain volume functionals from Finsler geometry as mass measures of currents. As an application, we obtain a whole family of extendibly convex n\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n$$\\end{document}-volume densities. This family includes the circumscribed Riemannian and the mass* volume densities.

(Invited) Electrochemical Bacterial Sensing

A better understanding of the biological functions of microorganisms is required to reduce their threats and increase their usefulness. Therefore, the importance of real-time evaluation of bacterial activity increases for various purposes such as hygiene management, development of antibacterial agents, and effective utilization of bacterial resources.1 This necessitates a quantitative assessment of metabolic processes, including growth and respiration. Here we would like to introduce the development of electrochemical methods for assessing bacterial activity.Electrochemical detection of viable bacterial cells was performed using cell membrane permeable electron mediator and redox-active pigment. On the other hand, a tetrazolium salt (MTT), was converted to an insoluble reduction form (formazan) through the respiration of microbial cells.2 The insolubility of this formazan was effectively exploited as a surface-confined redox event. The electrochemical detection of formazan was effectively coupled with the thermal lysis of microbes. The sensitivity of the present technique is up to 10,000-fold higher than that of MTT colorimetry and requires an incubation time of only 1 h, which is approximately 1/4 of that required for other metabolism-based techniques. On the other hand, Considering that oxidized MTT, which has excellent cell membrane permeability, changes into insoluble reduced formazan within cells, it is also possible to estimate the number of viable cells by focusing on the reduction current of MTT remaining in the suspension. was. Dissolved oxygen is an important substance for bacterial activity. When live bacteria in suspension were observed in real-time, it was found that uptake of MTT into bacteria was completed within 10 minutes, including the lag period. Furthermore, we also observed that the current response was dependent on viable cell density, regardless of the bacterial species present. This method allows us to quickly estimate the number of viable bacteria, making it possible to confirm the safety of food before it leaves the factory and prevent food poisoning.3 Furthermore, the measurement of the reduction current of dissolved oxygen provides an effective means for assessing the respiratory activity of bacteria in suspension.4 Organometallic nanohybrids (NHs), in which many small metal nanoparticles are encapsulated within a conductive polymer matrix, are useful as sensitive electrochemical labels because their components produce characteristic oxidation current responses. NHs made of metal nanoparticles such as gold or copper and polyaniline did not interfere with each other in terms of electrochemical signals obtained on the same electrode. Antibodies were introduced into these NHs that served as electrochemical labels to target specific bacteria. Electrochemical measurements using screen-printed electrodes dry-fixed with NH-labeled bacterial cells allowed the bacterial species and number to be estimated within minutes based on the distinct current response of the label. Our proposed method achieved simultaneous detection of enterohemorrhagic E. coli and Staphylococcus aureus in real samples. These NHs are expected to be a powerful tool as electrochemical labels and useful for rapid testing at food and pharmaceutical manufacturing sites.5 1) T. Kinoshita, K. Ishiki, D. Q. Nguyen, H. Shiigi, T. Nagaoka, Anal. Chem., 90, 4098 (2018).2) K. Ishiki, D. Q. Nguyen, A. Morishita, H. Shiigi, T. Nagaoka, Anal. Chem., 90, 10903 (2018).3) H. Ikeda, A. Tokonami, S. Nishii, X. Shan, Y. Yamamoto, Y. Sadanaga, Z. Chen, and H. Shiigi, Anal. Chem., 95, 12358-12364 (2023).4) M. Saito, K. Ishiki, D. Q. Nguyen, H. Shiigi, Anal. Chem., 91, 12793-12798 (2019).5) S. Itagaki, A. Nakao, S. Nakamura, M. Fujita, S. Nishii, Y. Yamamoto, Y. Sadanaga, H. Shiigi, Anal. Chem., 96, 3787-3793 (2024).

Extraction of two-magnon scattering and detection of inverse spin Hall effect up to 40 GHz in low-damping Fe65Co35/Pt bilayer thin film

Abstract We report an investigation of the inverse spin Hall effect (ISHE), as a measure of the pure spin current (J S ), induced by spin pumping in a Fe65Co35/Pt bilayer using coplanar waveguide ferromagnetic resonance (CPW-FMR) in the in-plane (IP) geometry over the broadband microwave frequency range of 8–40 GHz. From the IP-FMR measurements, the defect-induced two-magnon scattering (TMS) contribution is evaluated by analyzing the frequency dependence of FMR linewidth using Arias and Mills approach [Arias R and Mills D L (1999 Phys. Rev. B 60, 7395), Mills D L and Arias R (2006 Physica B 384 147–151)]. Here, we have determined a very low Gilbert damping constant (α G ) for Fe65Co35 bare film around 1.3 × 10−3, which is essential for the high spin current (>107 A/m2) generation. The enhanced value of α G ≈3.2 × 10−3 obtained for Fe65Co35/Pt bilayer film is due to spin pumping damping, α SP = 1.9 × 10−3, confirmed by the ISHE induced DC voltage (V DC ) signal measured across the edges of Pt layer. Out-of-plane (OP) angular ISHE measurements have been performed to disentangle spin pumping from spin rectification effects in the V DC signal. Further, we evaluated the effective spin-mixing conductance g eff ↑ ↓ = 3.33 × 1019 m−2, which is higher than the values reported in FeCo-alloy-based bilayer systems. The present study aims to detect the J S injected by low-damping Fe65Co35 thin films, leading to the realization of energy-efficient spintronic devices.

Investigation of Hf/Ti bilayers for the development of transition-edge sensor microcalorimeters.

The superconducting properties of 85 nm thick hafnium thin films with a 5 nm thick titanium layer on top have been investigated for three different geometries, that is, a film covering the entire 7 × 7 mm2 chip surface, bridges with a width of 200 μm and length up to 1800 μm, and bridges in the form of squares with sides from 100 to 1000 μm. The bridges were formed by a photolithographic lift-off process and are intended to be used as the main sensing element of a microcalorimeter based on a transition-edge sensor (TES) in experiments to determine the magnetic moment of neutrinos. Based on the measurements of the critical current, the critical temperature, and the width of the superconducting transition, we estimate the energy resolution δE of the TES prototypes, showing that it is possible to fabricate microcalorimeters with δE less than 1 eV using these films.

Thrust estimate method of an on-orbit Hall thruster using Hall drift current

In order to realize the thrust estimation of the Hall thruster during its flight mission, this study establishes an estimation method based on measurement of the Hall drift current. In this method, the Hall drift current is calculated from an inverse magnetostatic problem, which is formulated according to its induced magnetic flux density detected by sensors, and then the thrust is estimated by multiplying the Hall drift current with the characteristic magnetic flux density of the thruster itself. In addition, a three-wire torsion pendulum micro-thrust measurement system is utilized to verify the estimate values obtained from the proposed method. The errors were found to be less than 8% when the discharge voltage ranged from 250 V to 350 V and the anode flow rate ranged from 30 sccm to 50 sccm, indicating the possibility that the proposed thrust estimate method could be practically applied. Moreover, the measurement accuracy of the magnetic flux density is suggested to be lower than 0.015 mT and improvement on the inverse problem solution is required in the future.

Conservation of the Charge in Signal from Drift Tube Ion Mobility Spectrometers.

Quantitative information obtained from drift tube detectors used in ion mobility spectrometry is contained in the area of peaks forming the drift time spectrum. The area of all peaks corresponds to the total charge of ions entering the drift section of the spectrometer. It was found that this charge is not conserved when the ion composition changes. This work is devoted to studying the causes of this phenomenon. Experimental research consisted of recording drift time spectra for 2-pentanone and n-heptanone, at various analyte concentrations and different opening times of the shutter grid. Measurements of the total ion current were also performed in static mode with an open grid. The research results indicated that the reasons for the lack of ion charge conservation in the drift time spectrum are ion recombination, mutual repulsion, and mobility-dependent transmission of ions through the shutter grid. The explanation of the relationships obtained experimentally was based on a simple theoretical model, which considered the phenomenon of ion transport along the reaction section and the penetration of ions through the shutter. The developed model provides a good description of the measurement results and allows the estimation of ion currents and ion concentrations in the reaction section upstream of the grid. This information is important for proper quantitative analysis as well as when the ion mobility spectrometer is used in quantitative studies of chemical ionization processes.

A hybrid fuzzy logic-based MPPT algorithm for PMSG-based variable speed wind energy conversion system on a smart grid

Recently, wind power has gained popularity as a sustainable energy source. Wind energy conversion systems (WECSs) can accept fixed speed and variable speed (VS) operations. VS-WECSs are preferable to conventional WECSs because of their higher electricity collection capacity. Maximum power point tracking (MPPT) systems are essential for maximizing the efficiency of wind energy generation in wind turbine (WT) installations linked to power grids. This study introduces a hybrid fuzzy logic controller-based MPPT (FLC-MPPT) for WTs connected to permanent magnet synchronous generators (PMSGs) to accurately determine the maximum power output of WTs. This study employs a three-phase back-to-back converter to link a PMSG to a utility grid. The reference signals for pulse width modulation controllers comprise two-phase system currents. It constructs a converter that can transfer electrical energy in both directions using insulated-gate bipolar transistor technology and is powered by a battery. The machine-side converter uses model predictive control for the present control loop. Given the generator’s susceptibility to changes in wind conditions, this factor is of the utmost importance. A WT simulation was conducted using MATLAB/Simulink and an FLC methodology was employed. The model used a PMSG. Measurements of rotor speed, power, induced voltage, and current were taken in relation to variations in wind speed. The simulation results show that the FLC-MPPT can maximize the output power over a wide range of wind speeds with a higher efficiency of 92.6% and performance of 95.7%.

Design and development of the magnetic diagnostic systems for the first operational phase of the SMART tokamak.

A set of magnetic diagnostics has been designed, manufactured, and calibrated for the first operational phase of the small aspect ratio tokamak. The sensor suite comprises of Rogowski coils; 2D magnetic probes; and poloidal, saddle, and diamagnetic flux loops. A set of continuous Rogowski coils has been manufactured for the measurement of plasma current and induced eddy currents in conductive elements. A set of flux loops and magnetic probes will be used as input for the reconstruction of the magnetohydrodynamic equilibrium. The quantity and position of these sensors have been verified to be sufficient with synthetic equilibrium reconstructions using the equilibrium fitting code and baseline scenarios computed with the Fiesta code. These sensors will also be used as input for the real-time control system, and magnetic probes will be used for the detection of plasma instabilities. The calibration procedure for the magnetic probes is described, and the results are shown. The signal conditioning and data acquisition systems are described.

Simulation of Strain in ReBCO Tapes Under Combined Helical-Hard-Way Bending and Critical Current Measurements

Simulation of Strain in ReBCO Tapes Under Combined Helical-Hard-Way Bending and Critical Current Measurements

Critical Current Measurements of Prototype REBCO Round Cables at 77 K

Critical Current Measurements of Prototype REBCO Round Cables at 77 K

Displacement damage effect of proton irradiation on vertical β-Ga2O3 and SiC Schottky barrier diodes (SBDs)

In this study, we fabricated vertical Schottky barrier diodes (SBDs) based on wide bandgap semiconductor beta-phase gallium oxide (β-Ga2O3) and silicon carbide (SiC), respectively, and conducted proton irradiation experiments to analyze the radiation hardness of the SBDs comparatively. The effects of proton radiation on the performance of SBDs were assessed through measurements of forward current, capacitance, and breakdown characteristics. Both devices exhibited degradation in current and capacitance characteristics following proton irradiation, attributed to displacement damage (DD). Notably, the β-Ga2O3-based SBD demonstrated more pronounced deterioration compared to the SiC-based device despite similar vacancy distributions as confirmed by SRIM simulation. Moreover, a decrease in contact radius correlated with exacerbated degradation in the current characteristics of the β-Ga2O3-based SBD. Following proton irradiation, breakdown voltages of both devices increased due to elevated resistance induced by displacement damage. While both β-Ga2O3 and SiC-based SBDs experienced displacement damage under high fluence proton irradiation, the extent of performance degradation varied depending on the dimensions and quality of epitaxial and substrate layers.

Fast Calibration With Raw Data Verification for Current Measurement of Dual-PMSM Drives

Fast Calibration With Raw Data Verification for Current Measurement of Dual-PMSM Drives

Primary-Side Indirect Control of the Battery Charging Current in a Wireless Power Transfer Charger Using Adaptive Hill-Climbing Control Technique

This paper addresses the control task of a wireless power transfer (WPT) charger designed for electric vehicles (EVs). The challenge is to maintain a constant battery charging current when the WPT is controlled on the ground side. Indeed, the intermittent latency involved in the wireless data communication between the ground and vehicle sides leads to system instability. To overcome this issue, a new control approach has been proposed in this paper. The proposed technique ensures indirect control of the battery charging current through control of the current on the ground side. The control technique relies on an adaptive hill-climbing algorithm in conjunction with a PI-based controller. The adaptive parameter is adjusted online, during the operation of the charger, only when a new measure of the battery charging current is received on the primary side. This makes it possible to avoid the need for real-time wireless data communication. It should be noted that this aspect is crucial in ensuring the controller’s robustness and stability of the system regardless of potential delays in wireless communication and large misalignments between the coils. The validity of the proposed control technique has been confirmed through simulation. In addition, experimental validation, using a laboratory test bed, demonstrated satisfactory results.

Embroidery Triboelectric Nanogenerator for Energy Harvesting.

Triboelectric nanogenerators (TENGs) are devices that efficiently transform mechanical energy into electrical energy by utilizing the triboelectric effect and electrostatic induction. Embroidery triboelectric nanogenerators (ETENGs) offer a distinct prospect to incorporate energy harvesting capabilities into textile-based products. This research work introduces an embroidered triboelectric nanogenerator that is made using polyester and nylon 66 yarn. The ETENG is developed by using different embroidery parameters and its characteristics are obtained using a specialized tapping and friction device. Nine ETENGs were made, each with different stitch lengths and line spacings for the polyester yarn. Friction and tapping tests were performed to assess the electrical outputs, which included measurements of short circuit current, open circuit voltage, and capacitor charging. One sample wearable embroidered energy harvester collected 307.5 μJ (24.8 V) of energy under a 1.5 Hz sliding motion over 300 s and 72 μJ (12 V) of energy through human walking over 120 s. Another ETENG sample generated 4.5 μJ (3 V) into a 1 μF capacitor using a tapping device with a 2 Hz frequency and a 50 mm separation distance over a duration of 520 s. Measurement of the current was also performed at different pressures to check the effect of pressure and validate the different options of the triboelectric/electrostatic characterization device. In summary, this research explains the influence of embroidery parameters on the performance of ETENG (Embroidery Triboelectric Nanogenerator) and provides valuable information for energy harvesting applications.

Security Analysis of Distributed Consensus Filtering Under Replay Attacks.

This work studies the security of consensus-based distributed filtering under the replay attack, which can freely select a part of sensors and modify their measurements into previously recorded ones. We analyze the performance degradation of distributed estimation caused by the replay attack, and utilize the Kullback-Leibler (K-L) divergence to quantify the attack stealthiness. Specifically, for a stable system, we prove that under any replay attack, the estimation error is not only bounded, but also can re-enter the steady state. In that case, we prove that the replay attack is ϵ -stealthy, where ϵ can be calculated based on two Lyapunov equations. On the other hand, for an unstable system, we prove that the trace of estimation error covariance is lower bounded by an exponential function, which indicates that the estimation error may diverge due to the attack. In view of this, we provide a sufficient condition to ensure that any replay attack is detectable. Furthermore, we analyze the case that the adversary starts to attack only if the current measurement is close to a previously recorded one. Finally, we verify the theoretical results via several numerical simulations.

Research on the application of fiber-optical current sensor in power battery

Abstract Compared with the total current, the current in each parallel branch will help to achieve better battery management for new energy vehicles. However, today, accurate measurement of branch current is very difficult because the space between branches in the power battery pack is very limited. In this study, the fiber-optic current mini-sensor is used to meet this challenge. A saddle-sensing fiber structure has been designed to achieve surface measurement in response to the specific interconnection of circuitry in battery packs. A computer simulation was used to validate the feasibility, and experimental testing showed positive results. The specific experiments confirmed that the relative error between the saddle fiber-optic current sensor and conventional fiber-optic loop current sensor does not exceed 0.0119%. It meets the requirements of the automotive industry standards.

Trends in mass utilization of a magnetically shielded Hall thruster operating on xenon and krypton

The trends in mass utilization with increasing discharge voltage and current are investigated for a magnetically shielded Hall thruster operating on xenon and krypton. A 9 kW class shielded thruster is operated with discharge voltages from 300 to 600 V and discharge currents from 15 to 30 A on xenon and krypton. Experimental measurements of discharge current, thrust, anode efficiency, and ion velocity as a function of axial position are used to calibrate a multi-fluid 2D Hall thruster code at all operating conditions. The results of these calibrated simulations are employed to interrogate the plasma properties inside the thruster channel. A simplified 0D model for mass utilization evaluated on spatial averages of the simulated plasma parameters is employed to interpret the response of this efficiency mode with power for each propellant. It is found that with both higher voltage and current, mass utilization increases for both gases and their relative gap in this efficiency decreases. This can be attributed to the higher plasma densities and ionization rate coefficients at high voltage, and solely to higher plasma densities at high current. The driving factors for the increase in mass utilization are examined in the context of its nonlinear response to internal plasma properties. The behavior of mass utilization is also discussed in context of the gap in overall efficiency between the propellants. Finally, the implications of these results for improving the performance of high power Hall thrusters operating on krypton are examined.

C-Shape Busbar With Frequency Invariant Points for Wideband Current Measurement

C-Shape Busbar With Frequency Invariant Points for Wideband Current Measurement

Fat quantification in dual-layer detector spectral CT: How to handle iron overload, varying tube voltage and radiation dose Indices.

Opposed to other spectral CT techniques, fat quantification in dual-layer detector CT (dlCT) has only recently been developed. The impact of concomitant iron overload and dlCT-specific protocol settings such as the dose right index (DRI), a measure of image noise and tube current, on dlCT fat quantification was unclear. Further, spectral information became newly available <120 kV. Therefore, this study's objective was to evaluate the impact of iron, changing tube voltage, and DRI on dlCT fat quantification. Phantoms with 0 and 8mg/cm3 iron; 0 and 5mg/cm3 iodine; 0, 10, 20, 35, 50, and 100% fat and liver equivalent, respectively, were scanned with a dlCT (CT7500, Philips, the Netherlands) at 100kV/20DRI, 120kV/20DRI, 140kV/20DRI, and at 120kV/16DRI, 120kV/24DRI. Material decomposition was done for fat, liver, and iodine (A1); for fat, liver, and iron (A2); and for fat, liver, and combined reference values of iodine and iron (A3). All scans were analyzed with reference values from 120kV/20DRI. For statistics, the intraclass correlation coefficient (ICC) and Bland-Altman analyses were used. In phantoms with iron and iodine, results were best for A3 with a mean deviation to phantom fat of 1.3±2.6% (ICC 0.999 [95%-confidence interval 0.996-1]). The standard approach A1 yielded a deviation of -2.5±3.0% (0.998[0.994-0.999]), A2 of 6.1±4.8% (0.991[0.974-0.997]). With A3 and changing tube voltage, the maximal difference between quantified fat and the phantom ground truth occurred at 100kV with 4.6±2.1%. Differences between scans were largest between 100kV and 140kV (2.0%[-7.1-11.2]). The maximal difference of changing DRI occurred between 16 and 24 DRI with 0.4%[-2.2-3.0]. For dlCT fat quantification in the presence of iron, material decomposition with combined reference values for iodine and iron delivers the most accurate results. Tube voltage-specific calibration of reference values is advisable while the impact of the DRI on dlCT fat quantification is neglectable.