Applied DC Voltage Research Articles

Preparation of carbon dot/polyaniline composites as voltage based dielectric material for capacitor applications

Polyaniline-carbon dot (CD/PANI) composites were prepared via in-situ oxidative polymerization of aniline in the presence of carbon dots, with specific concentrations carefully controlled during synthesis. The composite was characterized using spectroscopic (FT-IR), morphological (TEM, SEM) and electrical methods. Impedance analysis was employed to investigate the transport behavior of charge carriers in the frequency range of 500 Hz to 10 MHz at 25 °C. This study provides a comprehensive analysis of the dielectric properties of the CD/PANI composite, including dielectric constant, dielectric loss, loss factor, AC conductivity, admittance, impedance, and Cole–Cole plots. The dielectric constant of the CD/PANI composite was 6.97 for 1 kHz at 0.5 V and 12.87 for 1 kHz at 5 V. The values indicate that the increase in the dielectric constant of nanocomposite with increasing voltage. This suggests that CD/PANI composite is a dielectric material whose dielectric constants are controlled by applied voltage. Notably, the dielectric constant increased with rising applied voltage and decreased with increasing frequency. Current-voltage (I-V) measurements revealed that the composite's dielectric parameters could be tuned by varying the applied DC voltage, suggesting its potential as a voltage-dependent dielectric (VDD) material for capacitor applications. Furthermore, the enhanced electrical conductivity indicates that the CD/PANI composite is a promising candidate for next-generation dielectric devices.

Pt/β-Ga2O3 Schottky devices enabling 60 Hz half-wave rectification for power-efficient pixel display

Beta-phase gallium oxide, β-Ga2O3, in transistors and diodes has been reported due to its distinctive electrical characteristics, such as wide bandgap, low leakage current, and high breakdown electric field. However, besides such conventional basic devices, more advanced device applications using β-Ga2O3 are always necessary. Here, we report on the dynamic behavior of Pt/β-Ga2O3-based Schottky diode for power-efficient organic light emitting display (OLED). Two Schottky diodes are back-to-back connected in series to form a half-wave rectifier circuit and finally integrated with an OLED diode pixel. When AC voltage is applied to the circuit at a frequency greater than 60 Hz, blinking of the OLED light is indistinguishable to human eyes. By way of the rectifier circuit, the OLED pixel efficiently saves more than 35% of the power that should be consumed by applying DC voltage.

Characterization of Three-Mode Combination Internal Resonances in Electrostatically Actuated Flexible–Flexible Microbeams

Abstract Nonlinear intermodal coupling based on internal resonances in MEMS resonators has advanced significantly over the past two decades for various real-world applications. In this study, we demonstrate the existence of various three-mode combination internal resonances between the first five flexural modes of electrostatically actuated flexible–flexible beams and dynamic modal interaction between three modes via internal resonance. We first calculate the natural frequencies of the beam as a function of the stiffnesses of the transverse and rotational springs of the flexible supports, utilizing both analytical formulation and finite element analysis (FEA). Following this, we identify six combination internal resonances among the first five modes and use applied DC voltage to validate the exactness of one commensurable internal resonance condition (ω2=ω5−ω4). Subsequently, we studied a detailed forced vibration analysis corresponding to this resonance condition by solving the five-mode coupled governing equations through numerical time integration and the method of multiple scales. The results compellingly exhibit three-mode intermodal coupling among the second, fourth, and fifth modes as a function of excitation amplitude and frequency. Alongside this, intriguing nonlinear phenomena such as threshold behavior, saturation phenomena, and autoparametric instability are observed. Finally, this paper provides a systematic methodology for investigating three-mode combination internal resonances and related nonlinear dynamics, offering significant insights that could be used in observing phonon or mechanical lasing phenomena in MEMS resonators.

Static and dynamic characteristics of electrostatically coupled MEMS beams under asymmetric actuation conditions

Abstract Electrostatically actuated microbeams have gained prominence due to their applications as micro-actuators and ultrasensitive sensors. In this study, we investigate the dynamic behavior of electrostatically coupled microbeams, specifically focusing on the effects of asymmetric actuation conditions. Our investigation encompasses both static and dynamic characteristics of the coupled microbeam system, considering various gap ratios between the beams and the fixed electrodes. Within the coupled system, two doubly clamped microbeams are positioned between two fixed electrodes. We develop a reduced-order model (ROM) to investigate static and dynamic responses of the coupled system. To validate the ROM, we rigorously compare its results with finite element (FE) simulations. Our findings reveal that the gap ratios play a pivotal role in shaping the system’s response. Notably, first two natural frequencies are important for design of micro-resonators and they exhibit complex variation with respect to the applied DC voltage. Moreover, we explore resonance frequency tunability and investigated interplay between geometric nonlinearity and nonlinear electrostatic actuation forces. These insights contribute significantly to the efficient design of MEMS resonators.

Fabrication of Silica Gel Reinforced, Cadmium Oxalate based Extrinsic Crystalline Materials and their Characterization

Cobalt-lead mixed cadmium oxalate (CoLMCO) and zinc-lead mixed cadmium oxalate (ZnLMCO) extrinsic crystalline materials were grown in oxalic acid embedded silica hydrogel. In an optimized gel environment, the extrinsic Co2+-Pb2+ and Zn2+-Pb2+ combinations fit well in the parental Cd2+ vacancies and emerged as distinct CoLMCO and ZnLMCO novel materials. The inherent properties of CoLMCO and ZnLMCO crystals were characterized by analytical and spectroscopic methods. Energy dispersive X-ray (EDX) analysis attached with field emission scanning electron microscope (FESEM) was employed to identify the chemical composition and morphology of the crystals. Fourier transform infrared (FTIR) spectral analysis confirmed the presence of oxalate group, water of crystallization and metal-oxygen bonds in the crystals. Thermal studies confirmed two phases of decomposition and ensured stability up to 1112.78 ºC for CoLMCO crystals and 1071.65 ºC for ZnLMCO crystals in a metal-oxide state. Bragg’s diffraction patterns revealed the high crystallinity of the materials and observed triclinic geometry in them. The UV-visible spectral studies of CoLMCO and ZnLMCO crystals showed maximum transparency to visible light and absorption in the UV region, possessing absorption maximum Amax = 1.588 and 1.276; optical band gap energies Eg = 5.638 eV and 5.845 eV, respectively. The V-I characteristics of the prepared crystals unveiled a feeble current flow (nA), exhibiting linear variation with applied DC voltage (0-200 V) leading leakage resistances of 1.187 GΩ (CoLMCO) and 5.176 GΩ (ZnLMCO). Dielectric constants of mixed crystals varied inversely with applied frequency and became almost stable at the mid-radio frequency range.

Frequency Response of the Diffuse-Charge Dynamics in Electrochemical Systems with a Graphene Electrode

We investigate the frequency response of diffuse-charge dynamics related to a 1:1 symmetric electrolyte containing a graphene electrode by solving the governing Poisson-Nernst-Planck equations subjected to appropriate boundary conditions in the asymptotic limit ε = λ D /H → 0, where λ D is the Debye screening length and H is the half-thickness of the electrolyte. Using the method of matched asymptotic expansion, we first solve the leading order non-linear problem for equilibrium state at a nonzero applied DC voltage in the presence of Stern layer(s). Then, we extend the leading order asymptotic analysis to derive an analytic expression for the impedance of the graphene-based electrochemical cell when a small AC voltage perturbation is added to the applied DC voltage. Finally, we use a suitable scaling of the impedance parameters to expose the impacts of the ion concentration and the DC bias voltage on the frequency response for possible applications involving the graphene-electrolyte interface.

Electrostatic Micro-Actuation System to Evaluate the Elastic Moduli of Metals with the Application of DC Voltage

Electrostatic Micro-Actuation System to Evaluate the Elastic Moduli of Metals with the Application of DC Voltage

Characteristic voltages and times from capacitance–voltage analysis of quantum dot light-emitting diodes

The characteristic voltages in the capacitance–voltage (C–V) curve of quantum dot light-emitting diodes (QLEDs) are usually linked to the start of charge injection and recombination in a working device. However, it may lead to a misunderstanding of the carrier process in QLEDs. This is because capacitance change only reflects an electrical response of additional carriers induced by a small signal loaded on an applied DC voltage but does not directly correlate with the total free carrier response governed by the working voltage. In this work, we study the frequency-dependent C–V characteristics of a blue QLED, focusing on the characteristic voltages, characteristic times, and their relationships. First of all, we identify that the charge injection point of QLEDs should be extracted by the current density–voltage–luminance characteristics rather than the C–V curve. As for the characteristic voltages obtained from the C–V curve, they are determined by voltage-dependent characteristic times in different time domains. Furthermore, the C–V characteristic is helpful to evaluate charge accumulation or leakage in blue QLED, serving as an accessible analysis tool in the carrier transport process. Our work provides a definite physical meaning of characteristic voltages in the C–V curve and exhibits the usefulness of C–V characteristics for analyzing the charge dynamics of QLED.

Effects of Composition and Polymerization Conditions on the Electro-Optic Performance of Liquid Crystal-Polymer Composites Doped with Ferroelectric Nanoparticles.

The presence of a polymer network and/or the addition of ferroelectric nanoparticles to a nematic liquid crystal are found to lower transition temperatures and birefringence, which indicates reduced orientational order. In addition, the electro-optic switching voltage is considerably increased when a polymer network is formed by in situ polymerization in the nematic state. However, the resulting polymer network liquid crystal switches at similar voltages as the neat liquid crystal when polymerization is performed at an elevated temperature in the isotropic state. When nanoparticle dispersions are polymerized at an applied DC voltage, the transition temperatures and switching voltages are reduced, yet they are larger than those observed for polymer network liquid crystals without nanoparticles polymerized in the isotropic phase.

Waveform Optimization Control of an Active Neutral Point Clamped Three-Level Power Converter System

Currently, the escalating integration of renewable energy sources is causing a steady weakening of grid strength. When grid strength is weak, interactions between inverters or those between inverters and grid line impedance can provoke widespread oscillations in the power system. Additionally, the diverse DC voltage application characteristics of power converter systems (PCS) may lead to over-modulation, generating narrow pulse issues that further impact control of the midpoint potential balance. Existing dead-time elimination methods are highly susceptible to current polarity judgments, rendering them ineffective in practical use. PCS, due to inherent dead-time effects, midpoint potential imbalances in three-level topologies, and narrow pulses, can elevate low-order harmonic content in the output voltage, ultimately distorting grid-connected currents. This is particularly susceptible to causing resonance in weak grids. To enhance the output voltage waveform of PCS, this article introduces a comprehensive compensation control strategy that combines dead-time elimination, midpoint potential balance, and narrow pulse suppression, all based on an active neutral point clamped (ANPC) three-level topology. This strategy gives precedence to dead-time elimination and calculates the upper and lower limits of the zero-sequence available for midpoint potential balance while fully compensating for narrow pulses. By prioritizing dead-time elimination, followed by narrow pulse suppression and finally midpoint potential balance, this method decouples the coupling between these three factors. The effectiveness of the proposed method is validated through semi-physical simulations.

Measurement of residual flux density in the single-phase transformer by applying DC voltage

The inrush current causes many adverse effects on electrical equipment. One of the reasons for inrush current is residual flux. When a no-load transformer is energized and the closing angle is inappropriate, the residual flux accelerates the core saturation, resulting in high-amplitude inrush current. It is necessary to measure the amplitude and direction of residual flux to reduce its harm. This paper proposes a novel strategy for measuring the residual flux of transformers based on externally applied DC voltages. Firstly, a relationship between residual flux and response current is established based on field-circuit coupling analysis. Then, the core-type transformer and shell-type transformer are modeled by the finite element method, and the fitted model for calculating residual flux is obtained. Finally, experiments are carried out on a square core and a 10 kV, 250 kVA single-phase transformer. The feasibility and accuracy of the proposed strategy are verified by the measurement results.

Concept and Design of a Multi-Polarization Reconfigurable Microstrip Antenna with Symmetrical Biasing Control.

Wireless communication systems have grown rapidly, moving towards being highly compact, intelligent, and flexible to adapt to changing operating requirements. Multifunctional and highly versatile antennas are key in this development to ensure system quality. Reconfigurable antennas, particularly regarding polarization, allow frequency reuse and enable the mitigation of fading effects. This work presents a square microstrip patch antenna operating in the ISM 5.8 GHz band with reconfigurable polarization by controlling its feeding. This antenna has four different states through the application of a symmetrical DC voltage that controls an RF circuit with PIN diodes. As a result, the microstrip patch can operate with three different polarizations: linear polarization and both circular polarizations (right-handed and left-handed). The antenna was fabricated to validate the proposed concept. The good agreement between the measurement and the simulation results was possible to observe regarding its polarization behaviour, impedance adaptation and radiation pattern.

Modeling Time-Evolving Electrical Conductivity in Air Ionization Plasma under DC Voltage: A Finite-Difference Time-Domain Approach for Needle-Plate Setup Based on Laboratory Experiments

In this paper, we develop a finite-difference time-domain (FDTD) model in which the time-evolving electrical conductivity of the air ionization plasma in DC voltage needed-plate setup is represented. Maxwell’s equations are solved using the FDTD method, and the associated currents and discharge fields are computed over time and in three-dimensional space. The proposed model for the electrical conductivity is dependent on time, the applied DC voltage, and the gap length. The necessary data for developing the proposed model is obtained experimentally using a standard discharge needle, with its spherical tip measuring approximately 40 μm in diameter. Once high voltage is applied, a steady state is achieved. The electrical conductivity σ(t) and its associated parameters are then calculated using nonlinear equations proposed to reproduce the experimentally obtained plasma behavior in the full-wave FDTD model. Voltage ranges from 4 kV to 9 kV, and gap distances are between 4 mm and 8 mm.

Parametric Frequency Divider Based Ising Machines.

We report on a new class of Ising machines (IMs) that rely on coupled parametric frequency dividers (PFDs) as macroscopic artificial spins. Unlike the IM counterparts based on subharmonic-injection locking (SHIL), PFD IMs do not require strong injected continuous-wave signals or applied dc voltages. Therefore, they show a significantly lower power consumption per spin compared to SHIL-based IMs, making it feasible to accurately solve large-scale combinatorial optimization problems that are hard or even impossible to solve by using the current von Neumann computing architectures. Furthermore, using high quality factor resonators in the PFD design makes PFD IMs able to exhibit a nanowatt-level power per spin. Also, it remarkably allows a speedup of the phase synchronization among the PFDs, resulting in shorter time to solution and lower energy to solution despite the resonators' longer relaxation time. As a proof of concept, a 4-node PFD IM has been demonstrated. This IM correctly solves a set of Max-Cut problems while consuming just 600 nanowatts per spin. This power consumption is 2 orders of magnitude lower than the power per spin of state-of-the-art SHIL-based IMs operating at the same frequency.

Dip-coated graphene nanoplatelets and multiwall carbon nanotubes composite ink electrode for metal-free paper-based flexible heating device

A paper-based flexible heating device (PFHD - paper-based flexible heating device) composed of a cellulose paper substrate and a carbonaceous functional electrode is reported. The functional composite electrodes containing graphene nanoplatelets (GNP - graphene nanoplatelets) and multi-walled carbon nanotubes (MWCNT) in various compositional ratios were prepared by dip-coating the oxygen plasma-treated paper substrate into the composite ink, and subsequently dried at 110 ℃ for 30 min to prepare PFHDs. The electrochemical characteristics and heat generation properties of PFHDs indicated that the GNP component in the functional electrode enhanced the electrical conductivity of the electrode, and the physical stability was enhanced mainly by the MWCNT component. Accordingly, PFHD0.33 which contains 33 % GNP and 67 % MWCNT in the functional electrode shows excellent heating performance with high stability and areal rated power of 0.68 W cm−2 (specific rated power = 45 W g−1). The measured sensitivity of PFHD0.33 is 31.50 ℃ V−1 at the applied DC voltage of 0.1–2.0 V.

DC Voltage Induces Quadratic Optical Nonlinearity in Ion-Exchanged Glasses at Room Temperature

We demonstrate that applying DC voltage at room temperature to an ion-exchanged glass induces quadratic optical nonlinearity in a subsurface region of the glass. We associate this with the EFISH (Electric-Field-Induced Second Harmonic) effect due to the Maxwell–Wagner charge accumulation in the subsurface region of the glass, in which a conductivity gradient forms as a result of the ion exchange processing. The second harmonic (SH) signal from the soda–lime glass subjected to potassium-for-sodium ion exchange is comparable with one from the same glass after thermal poling. The signal linearly increases with the duration of the ion exchange. The lower mobility of the potassium ions results in a higher SH signal from the potassium-for-sodium exchanged glass than that from the silver-for-sodium ion-exchanged one. This phenomenon is resistant to thermal annealing: only a 500 °C anneal caused noticeable degradation of the SH signal after “charging” the specimen. The phenomenon found is of interest for characterizing graded conductivity regions and providing and controlling second-order optical nonlinearity in transparent isotropic media.

Impact of Ammonium Perchlorate Content on Electrically Controlled Gel Polymer Electrolyte Monopropellants

A group of five electrically controlled monopropellants were developed, and their fundamental rheological, electrochemical, thermal, and combustion properties were characterized. A baseline monopropellant was composed of lithium perchlorate complexed with polyethylene glycol to form an ionically conductive gel polymer electrolyte. Subsequent candidates were supplemented with varying amounts of ammonium perchlorate at a fixed polymer-to-oxidizer ratio to determine the effects of shifting oxidizer content on the fundamental properties. The ignition of the gel monopropellants using an applied DC voltage potential at atmospheric conditions was observed and determined to be primarily the result of an electrolytic reaction. Time-resolved infrared thermography confirmed initial heating and initiation of the gels at the cathode once temperatures had reached the decomposition temperature of the polymer. Fourier transform infrared analysis of collected residue from experiments halted before ignition revealed lithium deposition on the cathode, supporting electrochemical activity. It was found that the electrolytic ignition delay time was affected by the oxidizer content, the magnitude of the applied voltage, and the distance between the electrodes supplying the voltage.

Three-Phase Open-End Induction Motor Drive Interfaced to Higher Voltage DC Bus

In applications that require a three phase induction motor to be driven by an inverter from a DC bus input of much higher voltage than needed, the option is to use a step down DC-DC converter before the inverter or use high voltage rating switches in the inverter along with low modulation index. In either case, disadvantages include poor efficiency, high voltage rated switches, etc. In open end winding three phase induction motor drives, the three separated windings are driven by 3-phase inverters from both sides. The arrangement is equivalent to three 1-phase inverters driving each winding separately from the same DC bus in parallel. This paper proposes an inverter scheme for open end induction motor drives, using a 1-phase inverter for each winding supply, but all three inverters being connected in series by their DC bus to the higher applied DC voltage. Unlike existing techniques for interfacing an induction motor drive to a higher voltage DC bus, the proposed scheme requires lower voltage switches with lower voltage bus capacitors to drive the lower voltage motor from a higher voltage DC bus. The series connected DC bus capacitor voltages are shown to remain balanced during normal operation.

A Frequency Reconfigurable Graphene-Based Microstrip Antenna with Mushroom-Like EBG

The growing demand for wireless applications has led to network congestion issues. In response, network operators have recommended a transition to higher frequencies, particularly within the unlicensed millimeter-wave (mm-wave) spectrum. This shift aims to fulfill users' desires for rapid data transmission within personal networks, whether at home or in the office, exemplified by technologies like WiGig technology and indoor applications. However, a significant challenge in achieving high data transfer speeds within this frequency range lies in the design of the antenna. These antennas must strike a balance between size and performance. Microstrip Patch (MP) antennas have gained recognition for their compact form and seamless integration into mobile communication systems. Nonetheless, they grapple with limitations such as poor gain and narrow bandwidth, largely attributable to surface waves negatively impacting antenna performance. In this study, we introduce, design, and optimize an MP antenna tailored for 60 GHz applications. To enhance the performance of the MP antenna, we introduce various mushroom-like Electromagnetic Bandgap (EBG) structures. These structures address the propagation of the surface waves issue that affects the antenna performance. Additionally, to create a tunable frequency antenna the variable conductivity of the graphene material is used in the form of implanted slots on the patch and tuned by applied DC voltage on the slots. Finally, the parameters of the MP antenna undergo enhancement based on simulation results obtained through CST software.

High-performance cation electrokinetic concentrator based on a γ-CD/QCS/PVA composite and microchip for evaluating the activity of P-glycoprotein without any interference from serum albumin.

The development of cation electrokinetic concentrators (CECs) has been hindered by the lack of commercial anion-exchange membranes (AEMs). This paper introduces a γ-cyclodextrin-modified quaternized chitosan/polyvinyl alcohol (γ-CD/QCS/PVA) composite as an AEM, which is combined with a microchip to fabricate a CEC. Remarkably, the CEC only concentrates cationic species, thereby overcoming the interference of the highly abundant, negatively charged serum albumin in the blood sample. P-Glycoprotein (P-gp) is recognized as an efflux transporter protein that influences the pharmacokinetics (PK) of various compounds. The CEC was used to evaluate the activity of P-gp by detecting the positively charged rhodamine 123 (Rho123 is a classical substrate of P-gp) with no interference from serum albumin in the serum sample. Using the CEC, the enrichment factor (EF) of Rho123 exceeded 105-fold under DC voltage application. The minimal sample consumption of the CEC (<10 μL) enables reduction of animal sacrifice in animal experiments. Here, the CEC has been applied to evaluate the transport activity of P-gp in in vitro and in vivo experiments by detecting Rho123 in the presence of P-gp inhibitors or agonists. The results are in good agreement with those reported in previous reports. Therefore, the CEC presents a promising application potential, owing to its simple fabrication process, high sensitivity, minimal sample consumption, lack of interference from serum albumin and low cost.