Variable Capacitor Research Articles

Estimation of Onset Potential for Oxygen Evolution Reaction at Platinum Surface Via Discharge of the Adsorption Capacitance of Intermediate Species

Developments in onset potential estimation for oxygen evolution reaction seeks to overcome several disadvantages in existing methods. For example, in the current tangent intersection method from the Nonfaradaic to Faradaic region, the electrocatalyst with large pseudocapacitance shows a negative slope near the onset potential in the Nonfaradaic zone. In such systems, the intersection of tangents from the Nonfaradaic to Faradaic region fails to give the onset potential. Similarly, onset potential determination from the fixed current density (10 mA/cm2) can be inaccurate for electrocatalysts having a large pseudocapacitive current. In addition, the commonly utilized methods do not provide insight into the underlying physicochemical properties that modulate reactivity around the onset potential. We propose an approach based on reaction mechanism analysis integrated with electrochemical impedance to detect the onset potential via the capacitance variation generated from the intermediate species of OER. We demonstrate our proposed method via experiments on oxygen evolution reaction in the acidic medium on platinum as the model system. The impedance analysis of such a system from the Nonfaradaic to Faradaic region shows the capacitance generated from the intermediate species (S-OH) shows the maxima at the onset potential. Further, the Tafel analysis showed the S-OH step as the rate-determining step (RDS) in a low overpotential region. Additionally, the onset potential obtained from the tangent intersection from the Nonfaradaic to Faradaic region matches that obtained from the impedance analysis. We are in the process of extending the proposed approach to more complex systems with multiple product evolutions.

Simulation on Operating Overvoltage of Dropping Pantograph Based on Pantograph–Catenary Arc and Variable Capacitance Model

When the electric locomotive pantograph is dropping, the interruption of pantograph catenary contact causes electromagnetic oscillation and arcing. The frequent arc burning that occurs due to charge accumulation results in the amplitude of overvoltage increasing gradually, posing a threat to locomotive high-voltage equipment. However, the physical mechanisms and characteristics of overvoltage are still unclear. This paper proposes a simulation model of operating overvoltage due to a dropping pantograph based on the pantograph–catenary arc and variable capacitance. Distributed RLC electromagnetic oscillation is considered, which allows the real-time calculation of arc resistance and capacitance. Under the same working conditions, the error between the simulation and test results is less than 4.0%, which proves the credibility of the model. The variation law of overvoltage under different dropping speeds or catenary phases was investigated, which shows the max amplitude is 298.20 kV and steepness is 2096.80 kV/μs at 0.30 m/s speed. The waveform shows the characteristics of high amplitude and high steepness, similar to very fast transient overvoltage (VFTO). There is a sinusoidal relationship between the catenary phase and overvoltage amplitude. The closer the catenary phase to 90°, the higher the overvoltage amplitude. The research has important guiding significance for the overvoltage formation mechanism of a traction power supply system and the insulation coordination design of high-voltage equipment.

Reduction of Reactive Power Compensation Efforts for Fusion Magnet Power Supplies Using Variable Series Capacitors

Reduction of Reactive Power Compensation Efforts for Fusion Magnet Power Supplies Using Variable Series Capacitors

The Behavior of Terminal Voltage and Frequency of Wind-Driven Single-Phase Induction Generators under Variations in Excitation Capacitances for Different Operating Conditions

This paper assesses the behavior of output voltage and frequency of wind-driven self-excited induction generators with variable excitation capacitances connected to the main and auxiliary windings under different operating conditions. The optimum values of the main winding excitation capacitance for fixed terminal voltage operation under different values of shunt capacitance, load, and speed are also evaluated. The obtained results show that the terminal voltage is highly affected by changing the main winding excitation capacitance. In addition, the frequency is greatly affected by changing the auxiliary winding excitation capacitance. However, under different operating conditions, variation in the output frequency under different values of the main winding capacitance, with fixed auxiliary winding capacitance, is acceptable. Extensive simulations were conducted and the results are discussed in this publication.

Maintain Power Transmission and Efficiency Tracking Using Variable Capacitors for Dynamic WPT Systems

This study introduces a new method for real-time efficiency tracking and stable output power of Dynamic Wireless Power Transfer (DWPT) systems using variable capacitors. A preliminary detailed discussion and an analysis of the DWPT system are carried out to show how the system can optimize power transmission and efficiency when the relative positions of transmitter and receiver change using a dynamic real-time control of the variable capacitors belonging to the compensation networks. This paper shows a detailed model of the DWPT system, including magnetic coupling analysis, circuit dynamics analysis, and efficiency characteristics analysis, in order to modify the control input values as needed. By utilizing a group optimization strategy, the transmission efficiency can be quickly maximized without using a position detection module. Simulation results demonstrate the effectiveness of the proposed method under various dynamic conditions, achieving significant improvements in energy efficiency and transmission reliability of the DWPT system. This research provides a powerful method to increase the overall performances of DWPT systems, which will help the development of future wireless charging technology.

Calligraphic interdigitated capacitive sensors for green electronics

This study presents a novel approach to fabricating interdigitated capacitive (IDC) touch sensors using graphite-based pencils on a wood substrate. The sensors were designed to detect touches and pressure variations, offering a cost-effective and environmentally friendly solution for sensor fabrication. The fabrication process involved abrasion of graphite pencils on a wooden substrate to create conductive traces, followed by the integration of interdigitated electrode structures. Capacitance variations resulting from touch interactions were investigated to calibrate sensor responses for tailored tasks. The sensitivity of the sensor was found to be 1.2 pF/kPa, highlighting its responsiveness to pressure variations. Additionally, the sensors were interfaced with an Arduino Uno microcontroller board to demonstrate practical applications, such as replicating arrow key functionality. Additionally, the sensors exhibit sensitivity to environmental factors, with the relative change in capacitance increasing from 0.1 to 0.65 as relative humidity ranges from 30 to 90%. Furthermore, variations in temperature from 30 to 60ºC result in a relative change in capacitance increasing to approximately 0.5. The results indicate the feasibility and versatility of using wood-based substrates and graphite-based pencils for fabricating IDC touch sensors, offering promising prospects for sustainable and accessible sensor technology.

Gallium arsenide octave-bandwidth microwave voltage-controlled oscillator having discrete varicap

Modern reconfigurable communication systems demand microwave voltage-controlled oscillators (VCOs) possessing an octave-wide bandwidth. Many advanced applications require also a low phase noise and a low current consumption for such VCOs. To meet an octave-bandwidth specification in combination with a low phase noise and a low current consumption it is desirable to implement a microwave monolithic integrated circuit (MMIC) technology. In-house gallium arsenide (GaAs) MMIC technology is implemented to build VCOs in this work. At the same time, in order to achieve a high-Q wide frequency tuning range, we implemented also a discrete variable capacitance diode (varicap). The discrete varicap is stacked above MMIC oscillator chip. A vertical design structure of the discrete varicap guarantees a high overlap capacitance ratio (K>20) along with reduced affect of the parasitic reactance. A high overlap capacitance ratio is needed for an octave-wide frequency tuning, while reduced affect of the parasitic reactance increases Q-factor of the VCO resonator. Hence, a sequential integration of the discrete varicap over monolithic oscillator chip resolves referred tough challenges in the design of VCO. Integrated VCO is finally packaged as a surface-mount device (SMD). At that SMD ceramic package is sealed with the metal lid. The oscillator circuitry is based on the conventional negative resistance approach with a positive feedback realized by common-source capacitance. An active element of the oscillator is a pseudomorphic high electron-mobility transistor (pHEMT). The gate length of a transistor is 0.15 µm. The width of the gate varies from 240 µm to 360 µm depending on working frequencies of the VCO. The varicap is built on the GaAs epitaxial heterostructure having customized gradient doping profile with abrupt junction. Nonlinear behavioral model of the varicap is extracted from the diode measurements and is further used for VCO simulation. Two types of VCO have been designed, fabricated and tested. First (second) type of VCO provides a tuning range from 5 to 10 GHz (from 10 GHz to 20 GHz), respectively. The measurement results demonstrate an output power of 3.9 dBm; a current consumption of 30 mA at a supply voltage of 5 V; a phase noise of minus 90 dBc/Hz at 100 kHz offset (minus 85 dBc/Hz at 100 kHz offset) for the first (second) type of VCO, respectively.

Behavior analysis of comb-drive actuators operating in near-zero-overlap configuration

Comb structures are widely used in micro-electromechanical systems as basic components of electrostatic actuators, capacitive sensors, resonators and energy harvesters. Typically, they are operated with a large overlap of the comb fingers, in the linear region. Here we study the behavior of comb-drive actuators during the displacement along the axis of the fingers in the unconventional regime where the fingers are slightly overlapping (around the width d of the fingers), which has recently gained attention in the MEMS community. In the intermediate region where the overlap approaches zero, fringing electric fields induce a non-linear variation of the capacitance, yielding a significant electrostatic force between the combs even without finger overlap with a maximum gradient occurring in this region. The comb capacitance variation with overlap was calculated using analytical and FEM modeling and confirmed with experimental results. We explored the implications of this condition in both static and dynamic modes, highlighting the effect of spring softening arising from the second derivative of the capacitance. These findings introduce new operational possibilities for actuators and sensors and substantial tunability in frequency for resonators.

High‐Performance Textile‐Based Capacitive Strain Sensors via Enhanced Vapor Phase Polymerization of Pyrrole and Their Application to Machine Learning‐Assisted Hand Gesture Recognition

Sensors based on everyday textiles are extremely promising for wearable applications. The present work focuses on high‐performance textile‐based capacitive strain sensors. Specifically, a conductive textile is obtained via vapor‐phase polymerization of pyrrole, in which the usage of methanol co‐vapor and the addition of imidazole to the iron chloride oxidant solution are shown to maximize conductivity. A technique to provide insulation and mechanical resistance using thermoplastic polyurethane and polystyrene‐block‐polyisoprene‐block‐polystyrene/barium titanate composite is developed. Such insulated conductive elastics are then used to fabricate highly sensitive twisted yarn capacitive sensors. A textile glove is subsequently embedded with such sensors. The wireless measurement and transmission system demonstrate efficacy in capturing capacitance variations upon strain and monitoring hand motions. A machine learning model to recognize 12 gestures is implemented—100% classification accuracy is obtained.

Abnormal transition of the electron energy distribution with excitation of the second harmonic in low-pressure radio-frequency capacitively coupled plasmas

The self-excited second harmonic in radio-frequency capacitively coupled plasma was significantly enhanced by adjusting the external variable capacitor. At a lower pressure of 3 Pa, the excitation of the second harmonic caused an abnormal transition of the electron energy probability function, resulting in abrupt changes in the electron density and temperature. Such changes in the electron energy probability function as well as the electron density and temperature were not observed at the higher pressure of 16 Pa under similar harmonic changes. The phenomena are related to the influence of the second harmonic on stochastic heating, which is determined by both amplitude and the relative phase of the harmonics. The results suggest that the self-excited high-order harmonics must be considered in practical applications of low-pressure radio-frequency capacitively coupled plasmas.

Kinetic simulations of capacitively coupled plasmas driven by tailored voltage waveforms with multi-frequency matching

Impedance matching is crucial for optimizing plasma generation and reducing power reflection in capacitively coupled plasmas (CCP). Designing these matchings is challenging due to the varying and typically unknown impedance of the plasma, especially in the presence of multiple driving frequencies. Here, a computational design method for impedance matching networks (IMNs) for CCPs is proposed and applied to discharges driven by tailored voltage waveforms (TVW). This method is based on a self-consistent combination of particle in cell/Monte Carlo collision simulations of the plasma with Kirchhoff’s equations to describe the external electrical circuit. Two Foster second-form networks with the same structure are used to constitute an L-type matching network, and the matching capability is optimized by iteratively updating the values of variable capacitors inside the IMN. The results show that the plasma density and the power absorbed by the plasma continuously increase in the frame of this iterative process of adjusting the matching parameters until an excellent impedance matching capability is finally achieved. Impedance matching is found to affect the DC self-bias voltage, whose absolute value is maximized when the best matching is achieved. Additionally, a change in the quality of the impedance matching is found to cause an electron heating mode transition. Poor impedance matching results in a heating mode where electron power absorption in the plasma bulk by drift electric fields plays an important role, while good matching results in the classical α-mode operation, where electron power absorption by ambipolar electric fields at the sheath edges dominates. The method proposed in this work is expected to be of great significance in promoting TVW plasma sources from theory to industrial application, since it allows designing the required complex multi-frequency IMNs.

Parametric Correlation Analysis between Equivalent Electric Circuit Model and Mechanistic Model Interpretation for Battery Internal Aging

In modern electric vehicle applications, understanding the evolution of the internal electrochemical reaction throughout the aging of batteries is as relevant as knowing their state of health. This article demonstrates the feasibility of correlating a mechanistic model of the battery internal electrochemical reactions with an equivalent electrical circuit (EEC) model, providing a practical and understandable interpretation of the internal reactions for electrical specialists. By way of electrochemical impedance spectroscopy analysis and automatic control theory, a methodology for correlating the resistance and capacitance variations of the EEC model and how they reflect the electrochemical reaction changes is proposed. These changes are represented through the time constants of the three RC parallel arrays from an EEC model. PS-260 lead–acid batteries were analyzed throughout the SOC and their useful life to validate this methodology. The result analysis allows us to establish that the first RC array corresponds to the negative electrode reactions in the range of 1.48 Hz to 10 kHz, the second RC array to the positive electrode reactions and generation of sulfates in the range of 0.5 to 1.48 Hz, and the third RC array to the generation of sulfates and their diffusion in the range of 0.01 to 0.5 Hz.

The collector current model of the IGBT based on the gate charge

In this study, a dynamic and static collector current (IC) model of the IGBT based on the gate charge is proposed. The gate charge could be easily obtained by measuring the voltage across the gate mirror circuit capacitance, and the transconductance obtained from the IC–VGE curve is mainly used. This model does not need the device structure parameters such as doping concentration, length, and thickness, thus is low cost and highly convenient. First, the gate charge is derived by integrating the currents of the variable capacitors CGE and CGC during the turn-on and turn-off transients, and an analytical relationship between the dynamic IC and QG is researched. Second, a static collector current IC is established, and the gate charge is obtained through current integration during the period of the Miller capacitance plateau. The influence of the temperature on the static transconductance is studied, and the accuracy of the static current model is improved. Finally, the performance of the model is optimized with various voltages, temperatures, and currents. The experimental results reveal that the proposed model achieves a collector current error of less than 5.6 % under various operating conditions, which verifies the accuracy of the proposed model.

Stability of giant dielectric properties in co‐doped rutile TiO2 ceramics under temperature and humidity

AbstractThis research investigated the influence of temperature and humidity on the giant dielectric (GD) properties of 1% indium tin oxide and 1% Ta2O5 co‐doped TiO2 ceramics sintered at different temperatures. A single phase of rutile TiO2 was obtained in all sintered samples. The mean grain size increased with higher sintering temperatures, resulting in ceramics with a relative density exceeding 98%. A uniform dispersion of dopants and major elements was achieved. Remarkably, the dielectric constant increased significantly from 2 × 103 to 3.7 × 104 with a rising sintering temperature, primarily due to the enlarged grain size. Concurrently, the authors observed low loss tangents, ranging from tanδ≈0.016 to 0.024 at 1 kHz. Slight variations in the dielectric constant were observed with temperature from room temperature up to 210°C, while maintaining remarkably low tanδ. The GD properties were attributed to space charge polarisation at internal interfaces and defect dipoles. Further research explored the impact of environmental conditions on dielectric properties. Remarkably, the ceramics exhibited minimal capacitance variations of less than 10% within the relative humidity range of 30%–95% and temperatures from 15 to 85°C, indicating excellent dielectric stability.

Multiphase LLC DC-Link Converter with Current Equalization Based on CM Voltage-Controlled Capacitor

In this study, a current-equalization technology utilizing a variable-capacitance technique for a multiphase inductor–inductor–capacitor (LLC) converter is studied. Accordingly, the proposed method involves adjusting the resonant capacitance of the LLC resonant converter to balance the currents between phases. This is achieved primarily by biasing ferroelectric multilayer ceramic capacitors (MLCCs) through a step-down circuit and a common-mode bias structure. These ferroelectric MLCCs serve as the resonant elements, allowing for variable capacitance by leveraging capacitance sensitivity to their trans voltages. This approach provides additional control flexibility to the resonant circuit. Furthermore, since each phase operates independently, the circuit can be scaled to accommodate any number of phases. Moreover, all switches in the circuit have zero-voltage switching (ZVS) turn-on, minimizing switching losses. This study initially analyzes and evaluates the proposed common-mode bias variable capacitance technique and the corresponding operational principles. Subsequently, a two-phase LLC experimental circuit based on a field-programmable gate array (FPGA) digital controller is utilized to assess current equalization and efficiency. That is to say, this experimentation aims to validate the effectiveness of the current-equalization variable-capacitance technique in an LLC resonant converter.

Harnessing Quantum Capacitance in 2D Material/Molecular Layer Junctions for Novel Electronic Device Functionality.

Two-dimensional (2D) materials promise advances in electronic devices beyond Moore's scaling law through extended functionality, such as non-monotonic dependence of device parameters on input parameters. However, the robustness and performance of effects like negative differential resistance (NDR) and anti-ambipolar behavior have been limited in scale and robustness by relying on atomic defects and complex heterojunctions. In this paper, we introduce a novel device concept that utilizes the quantum capacitance of junctions between 2D materials and molecular layers. We realized a variable capacitance 2D molecular junction (vc2Dmj) diode through the scalable integration of graphene and single layers of stearic acid. The vc2Dmj exhibits NDR with a substantial peak-to-valley ratio even at room temperature and an active negative resistance region. The origin of this unique behavior was identified through thermoelectric measurements and ab initio calculations to be a hybridization effect between graphene and the molecular layer. The enhancement of device parameters through morphology optimization highlights the potential of our approach toward new functionalities that advance the landscape of future electronics.

30‐3: Direct Observation of 2 Delta L in a‐IGZO TFT Using Scanning Capacitance Microscopy

Herein, we have directly investigated a 2 delta L as the diffusion length in a‐IGZO TFT using a scanning capacitance microscopy (SCM) technique at the cross section of TFTs instead of indirect normal transmission line method (TLM). Moreover, we revealed that the difference of 2 delta L leads the variation of total parastic capacitance in devices, which play a key role in the properites of EL currents in case of display devices.

Capacitance Energy Control for FESSs: Tracking Performance Analysis and Robust Design Against Variations of Speed, Load, and Capacitance

Capacitance Energy Control for FESSs: Tracking Performance Analysis and Robust Design Against Variations of Speed, Load, and Capacitance

Investigation of self-excited induction generator for supporting domestic loads and its extension to a microgrid

This study provides a technical and financial analysis for the incorporation of a microgrid structure with a wind energy conversion system for producing electricity. This study’s primary aim is to provide solutions for issues that arise when isolated induction generators are employed with microgrids. A closed-loop smart electronic load controller is used to regulate the loads in the system that are supplied by the generator. A switched variable capacitor bank is used to supply reactive power initially during a voltage dip at varying winds and loads to sustain the voltage profile. Additionally, a simple voltage control loop-based controller for the generator-side converter maintains the voltage at a steady level. Using HOMER software, an economic study of the suggested wind-based microgrid structure is also presented. A laboratory experimental setup is used to support the MATLAB/Simulink study of the proposed method and its control. The findings support the feasibility of implementing the suggested plan in grid-isolated regions for supplying critical loads.

A Precursor-Derived Ultramicroporous Carbon for Printing Iontronic Logic Gates and Super-Varactors.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor.