Capacitance Method Research Articles

Preparation of manganese-doped cubic carbon electrode based on ZIF-8 and its capacitive deionization performance for fluoride removal

Fluoride pollution will cause serious harm to the human ecological environment. The capacitive deionization method for fluoride removal has the advantages of low cost, low energy consumption, and convenient operation. Electrode material is crucial for desalination performance. In this study, a novel manganese doped hollow cubic carbon material (MHCC) was prepared by constructing ZIF-8 with hollow cubic morphology as a precursor and carbonizing it with manganese acetate as a manganese source. Then, the derived MHCC material was characterized and tested for capacitive fluoride removal. The adsorption capacity of MHCC10 (the mass ratio of carbon material to manganese acetate tetrahydrate was 10:1) reached 6.2 mg/g and 25.5 mg/g at the initial NaF concentration of 30 mg/L and 150 mg/L respectively. It could maintain 85.5% of the initial capacity after 10 adsorption–desorption cycles. The CDI defluoridation mechanism of MHCC was analyzed. The hollow porous structure inherited from etched ZIF-8 can promote the formation of electric double layers. An appropriate amount of manganese doping has a pseudocapacitive effect, which helps to increase adsorption capacity and improve cycling performance. This work provides a new approach for the design and preparation of novel capacitive fluoride removal electrode materials.

A capacitive method and experiment for measurement of sedimentation of magnetorheological fluid

Sedimentation is one of the key issues in the practical engineering applications of magnetorheological fluids (MRFs). Testing and evaluation of the suspension stability of MRFs should be a prerequisite procedure before their applications. There are a few reported methods of measurement of sedimentation of MRFs. The opaque zone below the mudline, especially the sediment zone at the bottom in the MRF column, is the true key factor that affects the applications of MRF due to the possible irreversibility caused by the caking of the sediment zone. This study proposes a novel capacitive method on the basis of the change in dielectric constant resulting from the change in concentration of the magnetic metal particles of MRF upon sedimentation. First, an analytic model was established to present a positive correlation between the dielectric constant and volume fraction of particles throughout the entire MRF column and the theoretical expression of the dielectric constant of MRF in a test tube was obtained. Second, a capacitive sensor and the relevant experimental set-up were designed and fabricated. Especially, the effect of eccentricity error of the capacitor sensor structure on the measurement was analyzed. Then, a sedimentation experiment for prepared MRF samples was carried out, and the testing results were discussed and verified by a visual mudline observation of the supernatant zone, indicating the feasibility of testing and evaluating the suspension stability of MRF by the capacitive method.

Investigation of T-history Method Application for Sub-zero Phase Change Material Thermal Properties

The T-history method, first proposed by Zhang & Jiang, is a simple method used to determine the latent heat, specific heat, thermal conductivity, melting point, and degree of supercooling of a phase-change material (PCM). The method is based on the measurement of the temperature of the material over time. It assumes that the PCM sample and the reference material exchange thermal energy with the environment in a similar manner, because it is based on the lumped capacitance method, and the temperature distribution inside the sample is uniform. There are multiple advantages that the T history method has over conventional methods; however, the T history method also has some downfalls, which have been improved over the years by different authors. This study experimentally investigates the reliability of this technique for PCM with a phase change temperature below 0 ° C. The technique is used to first determine the properties of denoised water with a phase change temperature of 0 ° C, using ethylene glycol with a mixture ratio of 50/50 as reference material. Second, by determining the properties of KCl with a concentration of 19.5% salt to water for a phase change temperature of -10 ° C. Two analytical approaches were used, one by immersing the samples in antifreeze during the charging process and the other by exposing the samples to ambient air during the discharging phase. The experimental results were further validated using the known literature to determine the latent heat of KCl. This study found that the latent heat of KCl measured using the technique has a 6.2% difference from the known results determined by the DSC. This study recommends the use of the T history method when designing latent heat thermal energy storage systems (LHTESS), because the sample size is an important characteristic for accurate thermophysical properties during the design process.

An Analytical Model of Dynamic Power Losses in eGaN HEMT Power Devices.

In this work, we present an analytical model of dynamic power losses for enhancement-mode AlGaN/GaN high-electron-mobility transistor power devices (eGaN HEMTs). To build this new model, the dynamic on-resistance (Rdson) is first accurately extracted via our extraction circuit based on a double-diode isolation (DDI) method using a high operating frequency of up to 1 MHz and a large drain voltage of up to 600 V; thus, the unique problem of an increase in the dynamic Rdson is presented. Then, the impact of the current operation mode on the on/off transition time is evaluated via a dual-pulse-current-mode test (DPCT), including a discontinuous conduction mode (DCM) and a continuous conduction mode (CCM); thus, the transition time is revised for different current modes. Afterward, the discrepancy between the drain current and the real channel current is qualitative investigated using an external shunt capacitance (ESC) method; thus, the losses due to device parasitic capacitance are also taken into account. After these improvements, the dynamic model will be more compatible for eGaN HEMTs. Finally, the dynamic power losses calculated via this model are found to be in good agreement with the experimental results. Based on this model, we propose a superior solution with a quasi-resonant mode (QRM) to achieve lossless switching and accelerated switching speeds.

I-V Characteristics Measuring System for PV Generator based on PDM Inverter

This paper presents a new method to characterize photovoltaic panels. The power electronic converter used is a Pulse Density Modulation (PDM) inverter. In this method, the inverter plays two roles: First, it is a DC inductor emulator. Second, it allows assembly between inductive and capacitive load methods. The PDM inverter is adapted to operate at very high switching frequency. In this application, it avoids the difficulties of making DC inductors with high DC current and its control remains very simple. This is an asset for increasing the power, power density and rapidity of tracers based on this method. The main disadvantage of this method, compared to methods based on DC-DC converter, is the use of twice as many semiconductor components. But this disadvantage can be compensated by a gain on reactive components. The simulations and experimental results of the proposed system are shown.

Analysis and Suppression of Rectifier Diode Voltage Oscillation Mechanism in IPOS High-Power PSFB Converters

Parasitic oscillations in the rectifier diode voltage of phase-shifted-full-bridge (PSFB) converters limit their application in high-voltage and high-power situations. The conventional analysis method for parasitic oscillation in rectifier diode voltage in PSFB converters treats the filter inductor as a constant current source and fails to consider the impact of changes in filter inductor current on the rectifier diode’s parasitic oscillation. Consequently, this approach does not apply when analyzing the rectifier diode voltage’s parasitic oscillations in high-power PSFB converters employing an input-parallel output-series (IPOS) configuration with interleaved drive. This research paper introduces an innovative equivalent circuit model for analyzing the parasitic oscillations of rectifier diode voltage in IPOS high-power PSFB converters. The model takes into account the mutual influence of rectifier diode voltage oscillations between submodules under interleaved control, considering the influence of changes in filter inductor current on rectifier diode parasitic oscillation. Based on the circuit model, we explain the mechanism of multiple oscillations of the rectifier diode voltage and the reason for the high peak of the first oscillation. Consequently, the interplay of rectifier diode voltage oscillations in IPOS high-power k-module PSFB converters under interleaved control is analyzed. To mitigate the adverse effects of rectifier diode voltage parasitic oscillation, a buffering strategy involving the connection of a resistor capacitor diode (RCD) circuit in parallel after the rectifier bridge is adopted, considering the structure of the IPOS high-power PSFB converter. The study provides a detailed analysis of the circuit’s operation mechanism upon incorporating the RCD buffer circuit and establishes the relationship between buffer capacitance, resistance, and spike voltage. Furthermore, a design method for buffer capacitors and discharge resistors in buffer circuits is presented. Finally, a 100 kW prototype is tested to verify the rectifier diode voltage oscillation mechanism of the IPOS high-power PSFB converter and the rationality of the buffer capacitor and discharge resistor design method under the interleaved drive approach.

English

Devices that measure multi-dimensional force torque are suitable for various industrial equipment / machines / processes applications. Such sensors/sensing devices can read the direct physical force and convert it into digital data. In addition to resistive strain gauges, piezoelectric, capacitive, and optoelectronic methods, there are many other ways to measure the strain. Most of these rely on detecting stresses in an elastic structure as their underlying sensing principle. Forcetorque sensors will be necessary because future human assistive equipment/machines will be more interactive with human beings in various unstructured circumstances. Due to criteria and design considerations, not only finding a suitable forcetorque sensor is challenging, but also it incurs high costs. These sensors frequently produce data that include noise and crosstalk problems. A multi-axis force-torque sensor application is discussed in this paper. To decrease noise and crosstalk mistakes, the study presented a control system that simultaneously gives motorized action and uses force as feedback. The proposed system can be evaluated using a variety of metrics; however, the fundamental design challenge is to expand the allowed sensing range while minimizing measurement errors. After thoroughly investigating the necessary data, the requirements for sensors and machine performance are examined. The development of force-torque sensors in the machine and the expansion of their application in the various service machine industries will benefit from this in-depth examination.

Non-invasive accurate time resolved inverse battery calorimetry

Precise knowledge of the battery heat generation rate and the internal temperature rise allows accurate thermal regulation required for enabling fast charging while minimizing side reactions and avoiding thermal runaway. With the necessity of high energy density, the size of batteries is constantly increasing. Because of poor thermal conduction, the thermal lag in large batteries is significant resulting in a considerable temperature gradient within the cell. Existing calorimetry methods only account for the external heat flow measurement and the external temperature rise and therefore cannot account for the thermal lag inside the cell. Additionally, with these methods, the temporal (time-resolved) information of the heat generation rate is compromised, which makes observation and attribution of electrochemical- thermal signatures impossible. As a potential solution, various intrusive techniques such as embedded thermal sensors have been proposed in the literature. However, these techniques are limited in scope. To enable accurate measurement of time-resolved heat flux measurement in commercial batteries, we instead propose a new battery calorimetry approach by combining state-of-the-art commercial calorimetry with an inverse heat transfer algorithm. This inverse calorimetry is completely non-intrusive with no change to commercial calorimeters. The inverse calorimetry reduces the error in heat generation rate to within 10% of the actual heat generation rate compared to 50% from the lumped capacitance method (best existing method). This method enables time resolved observation of electrochemical-thermal signatures such as a negative heat generation rate due to entropy change, which could not be observed from existing calorimetry methods.

Review on the study of theory and method of electrical capacitance tomography of cryogenics propellant

Electrical capacitance tomography (ECT) is a noninvasive advanced measurement technique with the potential to be applied to cryogenic propellant monitoring in microgravity environments. This paper briefly introduces common propellant measurement techniques and reviews the development of capacitive methods for cryogenic fluid measurements. At present, ECT at cryogenic environment has only successfully reconstructed phase distribution images in liquid nitrogen–vapor nitrogen static stratified flow experiments. Sensor structure, micro-capacitance measurement technology, multi-flow pattern test, and dynamic experiment still need to be further studied.

CAPACITIVE SENSOR FOR SURFACE ICING CONTROL

Icing of the surfaces of objects leads to a decrease in their technical characteristics and can lead to emergency situations and equipment failure. For effective control of deicing systems, it is required to monitor the condition of the surface with the help of specialized sensors. One of the most promising ways to detect icing is the capacitive method based on a significant difference in the dielectric permittivity of water in liquid and solid aggregate states. Considering that the capacitance of the sensor depends on both the measurement frequency and the configuration and size of the electrodes, the analysis of the characteristics of capacitors of different geometries under different conditions was carried out and the optimal shape of the sensor and the frequency of measurements were determined. The operation of the electronic circuit of the developed icing control sensor is based on comparing the reference voltage with the voltage depending on the capacitance value of the measuring capacitor. The capacitace–voltage converter is built on the basis of a high-pass filter and a single-half-period rectifier. To improve the accuracy of determining the presence of ice on the surface, a scheme is proposed in which the capacitance of the measuring capacitor is monitored at two frequencies. The considered capacitive sensors for monitoring surface icing have a fairly simple design, but at the same time effectively fulfill their task.

Design and experiment of a novel stepwise preheating system for battery packs coupled with non-dissipative balancing function based on supercapacitors

Lithium-ion batteries have advantages such as low self-discharge rates, high energy density, and environmental benefits. They are widely used in electric vehicles. However, their further application is limited by the inconsistency between batteries after assembly and the reduced battery performance in low-temperature environments. This article proposes a novel stepwise preheating system for battery packs that integrates a non-dissipative balancing function based on supercapacitors. The supercapacitor acts as an energy transfer and storage medium for balancing the power battery pack and heating the preheating battery pack. The preheating battery pack serves as an energy supplier for heating the power battery pack and as an energy storage unit during the balancing process of the power battery pack. This article studies the influence of low-temperature environments on the discharge capacity of power batteries and supercapacitors, explores the impact of environmental temperature on the relationship between state of charge (SOC) and open-circuit voltage (OCV), and the SOC0-OCV relationship of batteries, and clarifies the relationship between temperature and SOC0 required to meet the maximum pulse discharge test. It develops a parameter matching method for a supercapacitor and a preheating battery pack that meets the preheating requirements of power battery pack. It designs the topology structure of a balancing system based on supercapacitors with the flying capacitor method. It uses the battery terminal voltage as a balancing variable and formulates a non-dissipative balancing control strategy under static conditions. Results show that the low-temperature preheating system can warm up the preheating battery pack from −25 °C to 0 °C within 7 min, raise the temperature of the power battery pack from −25 °C to 0 °C within 27 min, and further increase the temperature of the power battery pack to 8 °C, achieving its maximum pulse discharge test in low SOC0 (33.5 %) state. During the non-dissipative balancing process, the energy transfer in the battery prioritizes charging the preheating battery pack, the average balancing current is about 8 A, and the energy utilization rate is about 80 %. This study provides a new approach for coupling the preheating technology and the power battery pack balancing technology in low-temperature environments.

Capacitive Extensometry for the Estimation of Meaningful Stretch-Dependent Dielectric Strength of Dielectric Elastomer

The electromechanical performance of a dielectric elastomer (DE) is greatly influenced by the dielectric strength of the elastomeric materials. The dielectric strength of an elastomer profoundly depends on the state of mechanical stretch. In this work, the stretch-dependent dielectric strength for DE is measured for all possible modes of stretches using compliant electrodes. Dielectric breakdown measurement using compliant electrodes considers voltage-induced deformation, which reflects the actual working condition energy transduction. Hence, the measured strength is for a meaningful value of a working DE. Capacitive extensometry and optical method are the two leading methods for the same. We compare the extensometry and optical methods in estimating the true value of dielectric breakdown strength of DEs at high prestretches. Furthermore, we propose a modified thickness stretch-based power law for the dielectric breakdown strength. Using the capacitive extensometry method, we verify the model on comprehensive experimental data on three types of elastomers, i.e., acrylic, silicone, and natural rubber. This work proposes a general framework for estimating the meaningful stretch-dependent dielectric strength of DEs.

Postoperative Control of Technological Parameters of the Ion Implantation Process by the Method of Capacitance–Voltage Characteristics

Postoperative Control of Technological Parameters of the Ion Implantation Process by the Method of Capacitance–Voltage Characteristics

A Dual Mode Nondestructive Evaluation Sensor With Simultaneous Inductive and Capacitive Outputs

Conventional electromagnetic Non-Destructive Evaluation (NDE) techniques are usually sensitive to either conductors or insulators. The emerging non-destructive assessment of "insulator-conductor" composite structures is thus faced with cost and efficiency problems due to this limitation. In this paper, a novel detection technique that combines inductive and capacitive methods is proposed for the inspection of "insulator-conductor" composite structures. A new structure of a planar inductive-capacitive dual-mode sensor in which the inductive and capacitive modes can be excited simultaneously with a single excitation signal without the need for mode switching is developed. The output signal of this sensor is analyzed in relation to the spatial electromagnetic field using equivalent circuit analysis and finite element (FE) simulation. A signal conditioning module for the proposed sensor is designed and a dual-mode test system that simultaneously detects signals from both modes is built. Experimental results from the test system show that the proposed detection method is sensitive to defects in both the insulating and conducting layers of the "insulator-conductor" composite structure and thus can detect corrosion under the insulation, surface cracks on the conductor and interface debonding with the detected signals able to reflect the size of the defects. The detection information of the two modes is complementary, proving that the method is able to comprehensively evaluate "insulator-conductor" composite structures.

Capacitive Resistivity Method Applied to the Environmental Diagnosis and Management of Contaminated Area of Gas Station

This article presents a case study of fuel underground contamination where the geophysical method was applied to support for decision making regarding environmental management activities. The application of geophysical methods that measure electrical resistivity in the study of contaminated areas and their correlations with organic contaminants are discussed, in addition to the presentation of theoretical and practical aspects of Capacitive Resistivity (CR) method. The importance of this work is based on the evaluation of the potential for identification of free phase of organic contaminant by the capacitive method and the assessment of the effectiveness of the remediation implemented through the geophysical data obtained. The method applied was able to identify the highest electrical resistivities related to fuel in the subsurface and indicated the inefficiency of the current remediation by the inadequate positioning of the extraction wells and the inaccuracies in the monitoring of underground contamination and allowed the proposition of recommendations related to management of the case based on geophysical information. From results, it is concluded that the Capacitive Resistivity method can be applied in similar cases of leaks in gas stations to diagnose contamination and to guide the adoption of more appropriate actions of environmental management.

Comparison of Wood Moisture Meters Operating on Different Principles of Measurement

This experiment compared commercially available moisture meters (three capacitive metersand one resistance meter) and tested their predictive ability at different moisture conditions on selected beech (Fagus sylvatica) and spruce (Picea abies (L.) Karst.) wood samples. The measurements were carried out on the samples at specified moisture intervals ranging from 5% to 30% moisture content (MC). The resistance meter showed a close correlation to gravimetric MC values; the influence of the measuring direction for MC below 17% was found when higher MCs in the transverse direction for both species were archieved. The difference was 4.6 times higher for softwood and 1.6 times higher for hardwood. Differences between radial and tangential transverse measuring were not observed. The close correlation coefficient of MC measurements was also found for capacitive methods. The effect of the direction was found for all the tested meters when higher MC values in the longitudinal measurements were found. This effect was especially significant at an MC of wood higher than 20 wt.%. For two capacitive methods, the effect of annual ring deflection only in the spruce samples was found where higher MC values in the tangential direction were observed.

The volumetric thermal capacitor method for nonlinear heat transfer in phase-change materials

Recently, there was an increase in the study of phase change materials mainly due to thermal storage studies or modeling of manufacturing processes. Usually, these problems, which have a moving boundary, are solved with the enthalpy formulation. This paper presents a new methodology to address the unsteady enthalpy term in the heat diffusion equation. The Volumetric Thermal Capacitor method is developed to solve the non-linear heat diffusion equation with the enthalpy function. The alternative method applies the integration by parts rule to divide the enthalpy term into three components. This approach allows the use of non-linear thermal properties without simplifications or generalized considerations. The method is compared to the classical formulation. The routines were implemented and executed in parallel on a CUDA-C in-house code. Simulated and lab-controlled experiments validated the proposed methodology. The results highlighted the differences between the models for experiments with intense heat flux. The proposed model presented a better agreement with the experimental data than the classical model for high-temperature cases. The Volumetric Thermal Capacitor method proved to be more stable and accurate than the classical method.

Design of Amplifier Circuit of Optical Fiber Sensor and Its Application in Cloud Computing of Mechanical Vibration Fault

Photoelectric detection technology has been widely used in industry, agriculture, medicine, and other fields. The signal collected by photoelectric signal detection equipment is weak and vulnerable to noise interference. Therefore, a preamplifier circuit with good performance is needed to amplify the original signal effectively. Firstly, considering that a single-mode fiber coupler is more sensitive to the length of the coupling region, a coupled optical fiber vibration sensor is designed. Secondly, the appropriate operational amplifier (Op-amp) is chosen based on the photodetector. By listing and selecting the OPA656 Op-amp produced by TI Company, the basic current and voltage conversion circuit of photoelectric detection equipment is analyzed. In addition, a basic trans-impedance circuit with a phase compensation function is proposed and the calculation method of optimal phase compensation capacitance is derived. Finally, in the process of monitoring the vibration data of equipment, cloud computing technology (fuzzy C-means clustering algorithm+MapReduce model) is used for distributed processing of mechanical vibration data. In the test, the coupled optical fiber vibration sensor designed with an amplifier circuit and moving coil vibration sensor are placed on the ship equipment at the same time, and the rubber hammer is employed to hit the surface of the ship machinery. The test results of the two sensors are the same, which proves that the optical fiber sensor designed in this study meets the requirements of vibration measurement.

Simple model for the laser powder interaction during direct metal deposition

In this paper, a simple model is presented for simulating laser and powder interaction during a coaxial laser cladding process, which is a very important part of direct metal deposition. The powder is delivered coaxially with the laser. The idea is to completely melt the powder before it hits the substrate. The laser is being attenuated as it propagates through the cloud of powders. The laser beam that penetrated through the cloud is used to melt the substrate. The track of 3D printing is formed by resolidification as the laser or the substrate scans. The laser attenuation is modeled by the Beer–Lambert law. The heat transfer within each powder is modeled by a lumped capacitance method. We use an enthalpy formulation to easily model and track the melting. The resulting 1D differential equation is solved numerically using Euler's method. The enthalpy and temperature plot is presented. We make use this model to determine the standoff distance. The effects of powder velocity, laser power, powder number density, and powder radius on the standoff distance are investigated and presented.

In Situ Detection of Electrochemical Reaction Surface Area by Optical Weak Measurement.

The surface area is key to electrochemical systems, including those in electrocatalysis and energy storage. Studies have shown that the surface area of the electrocatalyst directly affects the electrochemical activity, adsorption performance, and stability of the electrocatalyst. This paper used an optical weak measurement (WM) method, which has little impact on the analyte, to measure the reaction surface area (RSA) that actually participated in the electrochemical reaction. Then compared the RSA obtained by the WM with the total surface area (TSA) obtained by the standard Brunauer-Emmett-Teller (BET) measurement and the active surface area (ASA) obtained by the electrochemical double-layer capacitance (EDLC) method. Their growth trend was consistent, indicating the reliability of the WM method. Compared with the above two methods, the WM method is an in situ detection and easy to operate experimentally, which can help researchers to consider the effect of surface area on electrocatalyst performance more rationally.