Capacitance Modulation Research Articles

Hf 0.5 Zr 0.5 O 2 ‐based ferroelectric bionic electronic synapse device with highly symmetrical and linearity weight modification

Bionic electronic synapses with weight-modulation properties are promising alternative candidates when compared with traditional CMOS based neuromorphic hardware when building at-scale neural networks for efficient neuromorphic computing. In this Letter, due to the partial polarisation switching of multi-domain properties in polycrystalline Zr-doped HfO2 (HZO) ferroelectric materials, a capacitor-based bionic synapse was proposed, which showed multi-level capacitance modulation characteristics. By switching the voltage-controlled polarisation, the capacitance was gradually modulated via the variation of net polarisation vectors in the HZO layer. The potentiation and depression properties can be achieved with better linearity, symmetry and multiple states. This Letter laid the groundwork for realising the high-density integration neuromorphic computing system by using ferroelectric capacitors as the bionic synapse.

Experimental Investigation of Thermal Annealing and Ferroelectric Capacitor Area Effects for Hafnium-Zirconium Oxide Devices

In this study, we reveal that the thermal budget of post-metal annealing not only determines the formation of the ferroelectric phase and dipole domain but also the film quality of the gate stack in a metal-ferroelectric-metal capacitor. The higher leakage current caused by defect traps or grain boundaries within a gate stack would influence the stability of the ferroelectric domain switching. Furthermore, the ferroelectric domain switching and polarization current also depend on the ferroelectric capacitor area. We observe that a HfAlO ferroelectric capacitor can dominate the transfer characteristics of a p-type SnO thin-film transistor through the modulation of series capacitance in the gate stack based on a one-transistor one-capacitor series configuration. According to experimental results, the memory hysteresis window can be improved significantly with the area scaling due to the improvement of capacitance matching accuracy.

A Universal Wideband Device-Level Parallel Simulation Method and Conducted EMI Analysis for More Electric Aircraft Microgrid

The validation of electromagnetic compatibility for the microgrid of a more electric aircraft (MEA) is an essential test item before delivery for a trial flight, and it has always been urgently expected to be involved during the design stage. This article presents a universal method for wideband modeling and simulation of the MEA microgrid system in the time domain, regardless of the fact that motors are driven by which kind of converter, e.g., modular multilevel converter (MMC), 3-L neutral-point clamped (NPC), or 2-L pulsewidth modulation (PWM) converters. The insulated gate bipolar transistor and diodes are modeled with the physics-based dynamic model to emulate not only precise system-level performance of the system, but also to get an insight into the high-frequency oscillation between junction capacitance of the semiconductor modules and the parasitic parameters and high-frequency branch of other components, such as the permanent magnet synchronous motor (PMSM), transformer, and generator. To alleviate the attendant computational challenge, which could be extremely time-consuming (if no nonconvergence problem is encountered) when solved on traditional simulation platform, circuit partition based on transmission line decoupling, Norton equivalent parameter extraction, and TLM-link decoupling of submodules from the MMC bridge arms are utilized. The simulation program is executed on GPU to achieve massively parallel and accelerated solution. The accuracy and efficiency of the GPU-based parallel algorithm are validated by the comparison with the experimentally verified model in ANSYS Simplorer.

Thermal performance enhancement of phase change material using aluminum-mesh grid foil for lithium-capacitor modules

Nowadays, the most used thermal management system (TMS) is air-cooling, but due to weight and volume limitations, more promising cooling methods such as PCMs with high latent heat seems to be attractive. However, their disadvantages, like low thermal conductivity, should be managed to have an efficient TMS. Hence, aluminum-foil (PCM-Al) is added to the PCM in this work to enhance the PCM conductivity, and accurate experiments are accomplished to verify the simulation results. In this paper, a phase change material (PCM) with aluminum mesh grid foil is proposed to enhance cooling and temperature uniformity of a high-power dual-cell lithium capacitor (LiC) module. The optimization objective is keeping the temperature of the system below the safe range while maximizing the uniformity and minimizing the cost of the system. The effect of forced-convection (zero-PCM strategy), pure PCM, PCM-Al, PCM thickness, and influence of dual PCMs by different phase change temperatures on the thermal behavior of the module are studied numerically. The results indicate that the PCM-Al technique shows better thermal performance while reducing the maximum module temperature by 20%, and 13% in comparison with forced-convection and pure PCM, respectively. Moreover, 7 mm thickness is quite optimal, considering the cost, weight, and volume.

Cascaded H-Bridge Low Capacitance Static Compensator With Modular Switched Capacitors

In this article, the effect of large double frequency capacitor voltage ripple (CVR) on harmonic performance, efficiency, and capacitor lifetime in the cascaded H-bridge low capacitance static reactive power compensator (StatCom) (LC-StatCom) is analytically determined. With insight provided by the analysis, an LC-StatCom with modular switched capacitors is proposed that provides a degree of freedom to control the CVR magnitude. The premise of the operation is to keep redundant capacitor modules in standby mode when operating with lower currents. In addition, it is shown that by distributing losses between additional dc-side switches and the main H-bridge switches, the proposed concept provides opportunities for choosing an optimal hybrid combination of semiconductor technologies. The proposed concept is evaluated using a simulated 8.5 MVA StatCom and feasibility of the proposed system is confirmed by experiments on a seven-level 0.8 kVA single-phase LC-StatCom prototype.

Amplitude stability analysis and experimental investigation of an AC excitation signal for capacitive sensors

Low-noise capacitive sensor is widely used in electrostatic accelerometers and inertial sensors. An AC excitation signal is necessary to realize the amplitude modulation of the slow differential capacitance. But the amplitude stability of this AC excitation signal will directly influence low-frequency performance and dynamic range of capacitive sensors which results in the deviation of scientific requirements. In this paper, a stable AC excitation signal is realized based on the classical direct digital frequency synthesis technology. The mathematical model of amplitude stability is systematically set up, and there are four main influencing factors including transition time stability of the digital-to-analog converter (DAC), frequency stability of the crystal oscillator, voltage stability of the reference and gain stability of the band-pass filter (BPF). Each contribution of these four sources is theoretically analyzed. Finally, an evaluation prototype board is achieved to investigate the stability experimentally. Performance testing results show that the amplitude stability could reach approximately 16 ppm/Hz1/2 at 1 mHz under present optimal components selection, and transition stability of the DAC is the primary factor for further improvement.

Experimental validation of piezoelectric shunt tuning with residual mode correction: Damping of plate-like structures

The effective vibration mitigation properties of piezoceramic patches with inductive-resistive shunts are investigated experimentally. A shunt tuning method is proposed, in which a consistent correction for the influence from residual vibration modes is included by an effective modal capacitance, evaluated from measured charge and voltage amplitudes in short- and open-circuit conditions, respectively. The robustness of the proposed method is verified experimentally for both a free beam and a free plate structure with four shunted piezoceramic patch pairs. A stable and fully passive inductor is produced by winding a copper wire around a magnetic core, which requires precise inductance tuning to determine the final number of turns. It is demonstrated that the effective modal capacitance interpolates consistently between the blocked and static capacitances, commonly used for single-mode tuning of piezoelectric inductive-resistive shunts. By imposing pseudo-random vibrations, the piezoelectric current and voltage signals are measured and evaluated by their frequency response functions. Spectrum peak values determine the apparent short-circuit charge to open-circuit voltage ratio for each shunt, which directly determines the shunt components by explicit tuning formulas. Good correlation between numerical and experimental results are obtained for the free beam, while for the free plate experiment effective multi-mode shunt tuning is obtained by a modified effective electromechanical coupling coefficient.

Metal ion-induced capacitance modulation in near-isostructural complexes-derived electrochromic coordination polymers

Coordination polymers and metal–organic frameworks have attracted immense attention across different fields of science as materials with numerous functional applications. Herein, we report the use of coordination polymers obtained from near-isostructural metal (Mn2+, Fe2+, and Co2+) bipyridine complexes as electrode materials in a symmetric supercapacitor test cell. The variation in the central metal ion (Mn2+ vs. Fe2+ vs. Co2+) in these nearly identical coordination complexes was found to dictate the capacitive performance of the coordination polymers obtained via Pd(II) cross-linking. The central metal ion not only influences the porosity, Brunauer–Emmett–Teller (BET) surface area (6.5 (Mn), 10.4 (Fe), and 29.7 (Co) m2/g), and the areal capacitance, but also the performance parameters such as the cycling stability and charge–discharge kinetics as well as the charge transfer mechanism. A 3:4:5 ratio for the areal capacitance values (9.1 (Mn), 12.2 (Fe), and 15.4 (Co) mF cm−2 at a scan rate of 5 mV/s) corroborates the modulative effect of the metal center. The cycling stabilities of these coordination polymers also followed the same order. At higher current densities (>0.50 mA cm−2), the supercapacitors fabricated from the Mn-coordination polymer were found to charge and discharge at faster rates, whereas those fabricated from Fe- or Co-coordination polymers continued to discharge at similar rates, indicating similar pore volumes for the latter as confirmed by BET surface area measurements. Although the materials used in this study resulted in modest capacitive performance, the possibilities to enhance their surface area and crystallinity is envisaged to result in the development of new, multifunctional non-carbon electrode materials with efficient electrochemical storage characteristics and tunable electro-optical properties.

Operation and control of MMC station with constraints of internal variables under unbalanced grid conditions

Modular multilevel converter (MMC) station is expected to be able to operate under unbalanced grid conditions (UGCs) and to satisfy all kinds of limits under UGC. To investigate the allowable region of MMC under UGC, this study presents a point-scanning method, which directly solves the steady-state values of MMC from non-linear dynamic equations for each possible operating point, and therefore, can access the constraints of internal variables including the sub-module capacitor voltage, arm current and modulation index. First, the complete 28th-order dynamic model of MMC, which contains the zero-sequence second-order modulation signal is derived. Next, as the premise to solve the steady state of MMC, point of common coupling voltages are solved from a proposed unbalanced grid model, which incorporates the effect of ac fault. Following that, a peak-value seeking algorithm is proposed to seek the peak values of internal dynamics of irregular waveforms to implement the constraint of internal dynamics. Next, the allowable region of MMC under UGC is depicted and analysed. Also, the power limiting control is proposed to avoid MMC under UGC, violating the limits of internal dynamics. Finally, the simulation validates the effectiveness and correctness of the proposed point-scanning method and power limiting control.

Graphene on Silicon Modulators

Graphene is a 2D material with appealing electronic and optoelectronic properties. It is a zero-bandgap material with valence and conduction bands meeting in a single point (Dirac point) in the momentum space. Its conductivity can be changed by shifting the Fermi level energy via an external electric field. This important property determines broadband and tunable absorption at optical frequencies. Moreover, its conductivity is a complex quantity, i.e. Graphene exhibits both electro-absorption and electro-refraction tunability, and this is an intriguing property for photonic applications. For example, it can be combined as an active material for silicon waveguides to realize efficient detectors, switches and modulators. In this paper, we review our results in the field, focusing on graphene-based optical modulators integrated on Silicon photonic platforms. Results obtained in the fabrication of single- and double-layer capacitive modulators are reported showing intensity and phase modulation, resilience of the generated signals to chromatic dispersion because of proper signal chirp and operation up to 50 Gb/s.

Neuronal firing modulation by a membrane-targeted photoswitch

Optical technologies allowing modulation of neuronal activity at high spatio-temporal resolution are becoming paramount in neuroscience. In this respect, azobenzene-based photoswitches are promising nanoscale tools for neuronal photostimulation. Here we engineered a light-sensitive azobenzene compound (Ziapin2) that stably partitions into the plasma membrane and causes its thinning through trans-dimerization in the dark, resulting in an increased membrane capacitance at steady state. We demonstrated that in neurons loaded with the compound, millisecond pulses of visible light induce a transient hyperpolarization followed by a delayed depolarization that triggers action potential firing. These effects are persistent and can be evoked in vivo up to 7 days, proving the potential of Ziapin2 for the modulation of membrane capacitance in the millisecond timescale, without directly affecting ion channels or local temperature.

Low Voltage, High Optical Power Handling Capable, Bulk Compound Semiconductor Electro-Optic Modulators at 1550 nm

AlGaAs bulk electro-optic Mach–Zehnder modulators with low ${V_\pi }$ are reported. Epilayer design is an npin , which is shown to be equivalent to a pin . Measured ${V_\pi }$ is 1 V for 1 cm long electrode and this result agrees very well with the numerical modeling. Modulator capacitance remains constant and current through the device is negligible over a wide bias range. Lowest bandgap of the material in the active waveguide region is larger than twice the photon energy at 1550 nm, significantly reducing material absorption, including two-photon absorption. Modulator characteristics remain unchanged under coupled input optical powers approaching 160 mW. Low ${V_\pi }$ combined with high optical power handling capability make these devices suitable for analog photonic links.

Capacitor Voltage Ripple Minimization of a Modular Three-Phase AC/DC Power Electronics Transformer With Four-Winding Power Channel

Power electronic transformer (PET) with modular cascaded structure has become a flexible interface between AC and DC grids. Nonetheless, the notable 2nd-order ripple power introduced from the AC source requires considerable energy storage in the module capacitors, which is likely to degrade the overall power density and increase system cost. In this paper, a power channel based four-winding PET (PC-PET) is proposed to address such an issue. Owing to the phase-crossing power channels, the low-frequency ripples can cancel each other through magnetic flux counteracting. To improve the accuracy of power decoupling, the effect compromised by inconsistent windings is considered. Accordingly, a proportional-resonant (PR) control based power decoupling strategy for PC-PET incorporated with power balance is proposed to decouple the three-phase low-frequency ripple powers, and minimize the voltage ripple in module capacitors. Additionally, the improvement of power density is discussed based on analyses on power losses, capacitor volume and transformer volume. Simulation and experimental results verified the validity of proposed control strategies.

A New Modular XRAM-Like Inductive High- Current Pulse Generator Circuit Topology

XRAM (MARX spelt back words) is currently a very important circuit for high current pulse generators. In our previous studies, an XRAM-like circuit was proposed based on multiple pulse transformer modules and a capacitor connected in parallel. Compared with the traditional XRAM circuit, the same number of inductive energy storage modules can be used to generate higher current pulses. This circuit is also capable to recover the residual energy and generate repetitive high-current pulses. However, this circuit topology requires more power electronic switches (three IGBT switches per pulse transformer module). In order to reduce the number of switches, by adding two IGBT switches in the capacitor module, a new modular XRAM-like circuit with reduced switches (one IGBT switch per pulse transformer module) is proposed in this paper. The change of the circuit topology makes the capacitor discharge the primary inductors of the pulse transformer in series during the residual energy recovery stage, instead of the parallel discharge in the previous circuit. This requires the closing time of the IGBT switch in each pulse transformer module ahead of the discharge start time of the capacitor. Working process of the proposed circuit was described in detail and simulations of a 12-module circuit were carried out to verify the circuit operation. Finally, the preliminary experimental results of a two-module laboratory prototype are presented. The results confirm the theoretical analysis and show the validity of the converter scheme.

A New Multilevel AC/DC Topology Based H-Bridge Alternate Arm Converter

The current popular modular multilevel converter topology (MMC) needs a large number of cascaded sub modules and switches, a high voltage level of DC bus and a large loss. Based on these problems, a new multilevel converter topology with H-bridge alternate arm is proposed. This topology combines two structures of H-bridge sub module cascade and H-bridge switch series arm. In high-voltage and high-power applications, on the premise of outputting the same AC voltage level, this topology reduces the DC bus voltage level, system loss and cost, and the number of components, simplifies the control method, and improves the system reliability compared with the MMC structure. In this paper, the working mechanism of the topology is described in detail. On this basis, the control strategy of sub module capacitor voltage balancing is proposed. Finally, the PSIM simulation of the topology is carried out, and a single-phase prototype is made in the laboratory. The simulation and experimental waveforms are obtained, which verify the correctness and feasibility of the topology structure.

Design of closed-loop control for Solar PV based Multi-Level Inverter

Photovoltaic (PV) based multilevel inverters (MLI) have emerged as one of the best alternatives for grid/standalone applications. MLIs offer high range power handling capability with low current and voltage distortion and lesser switching losses as compare to the traditional two-level inverter. Major challenges with generally used multilevel inverter topologies relates to capacitor voltage variation, modulation techniques, and control. The major center of attention of research in this paper is to build up sophisticated modulation and voltage balancing methods for multilevel inverter topologies, competent to reach capacitor voltage parameter and to decrease power switching losses of the inverters. The present paper focuses on closed-loop control of multilevel flying capacitor inverter (FCI). In FCI, the phase shift (PS) based pulse width modulation method is designed and investigated. The closed-loop controller is designed with input voltage control of MLI, whose source is solar PV based Boost converter. Reported simulation results prove the superiority of the closed loop control in maintaining the desired output voltage for various reference values.

New modifications of a Bennet doubler circuit-based electrostatic vibrational energy harvester

In this work, theoretical and experimental studies of the conditioning circuit based on the Bennet doubler with a power source in a variable capacitor branch having one, two and three variable capacitors are carried out for electrostatic vibrational energy harvesters (e-VEHs). Analytical expressions for evaluation of the e-VEH conditioning circuit main parameters are derived. All three modifications of the conditioning circuit have two operation modes: autostabilization and the mode of unlimited capacitors charge and voltage growth. The change between the operation modes for one-, two- and three-capacitor circuits with switches takes place when the maximal-to-minimal capacitance ratio η is equal to 2, 1.618 and 1.414, respectively. For e-VEHs with switches in the autostabilization regime, a three-capacitor circuit will be the most efficient when the capacitance modulation depth η is less than 1.414, a two-capacitor circuit will be the most efficient when 1.414 <η < 1.618, and, for 1.618 <η < 2, the most efficient will be a one-capacitor circuit. In the steady-state autostabilization mode, the saturation voltage will be greater than the primary voltage source V0 if the capacitance modulation depth η is greater than 1.5, 1.366 and 1.302 for the circuit with one, two and three variable capacitors, respectively. The use of diodes instead of switches in the circuits results in the decrease of saturation voltage and leads to the increase of the critical values of ηcr when the change between the operation modes occurs. As the diode inverse currents increase, the effect of the saturation voltage reduction in the autostabilization mode becomes stronger and can even lead to the circuit nonoperabilities. The employment of the Bennet doubler based conditioning circuit modifications considered here enables solving its two main problems: operation only for the capacitance modulation depth more than 2 and the uncontrolled capacitors charge and voltage growth. It should be noted that the observed two conditioning circuit operation regimes will be also inherent for electret vibrational microgenerators and for microgenerators based on using electrodes with materials having different work functions. In addition, the considered two- and three-capacitor circuits make it possible to use e-VEHs at lower values of an external mechanical force or with greater stiffness of spring suspensions minimizing the pull-in effect probability.

Multi-mode piezoelectric shunt damping with residual mode correction by evaluation of modal charge and voltage

A resonant, piezoelectric shunt tuning procedure is based on the limiting eigenvalue problems associated with short and open circuiting of the piezoelectric domains attached to a vibrating structure. Whereas short circuit and open circuit frequencies are directly obtained from the eigenvalues, the associated electrical equation further determines a modal charge as an short circuit reaction force and a new modal voltage from the electric deflection in the open circuit limit. By a modal representation with short circuit mode shapes the structural equation fully decomposes, while the inherent contributions from non-resonant vibration modes in the corresponding electrical equation consistently define an effective modal capacitance, conveniently estimated by the modal charge to voltage ratio. The shunt tuning is obtained from the governing characteristic equation for the targeted vibration mode, in which the residual mode correction is explicitly represented by the effective modal capacitance. The tuning procedure with an effective modal capacitance is generalized to multiple piezoelectric domains with independent shunts for simultaneous damping of multiple vibration modes. The accuracy of the proposed shunt tuning methods is demonstrated by a numerical beam example with three piezoceramic patch pairs and independent resistive–inductive shunts. The analysis is carried out in a commercial finite element program, in which the required modal frequencies, charge and voltage are readily available as output to the short circuit and open circuit eigenvalue problems.

An Artificial Optoelectronic Synapse Based on a Photoelectric Memcapacitor

AbstractThe rapid development of artificial intelligence technology has led to the urge for artificial optoelectronic synapses with visual perception and memory capabilities. A new type of artificial optoelectronic synapse, namely a photoelectric memcapacitor, is proposed and demonstrated. This photoelectric memcapacitor, with a planar Au/La1.875Sr0.125NiO4/Au metal–semiconductor–metal structure, displays a complementary optical and electrical modulation of capacitance, which can be attributed to the charge trapping/detrapping‐induced Schottky barrier variation. It further exhibits versatile synaptic functions, such as photonic potentiation/electric depression, paired‐pulse facilitation, short‐/long‐term memory, and “learning‐experience” behavior. Moreover, the photoplasticity of the memcapacitor can be modulated by varying the frequency of applied AC voltage, thus enabling self‐adaptive optical signal detection and mimicry of interest‐modulated human visual memory. Therefore, it represents a new paradigm for artificial optoelectronic synapses and opens up opportunities for developing low‐power humanoid optoelectronic devices.

Structural analysis and dielectric investigations of pure and rare earth elements (Y and Gd) doped NiO nanoparticles

In this work, pure and 2% rare earth elements RE (RE = Y and Gd) doped NiO nanoparticles, capped with polyvinyl alcohol PVA, were prepared by coprecipitation technique. X-ray powder diffraction XRD was performed to investigate the structural properties of the prepared samples. X-ray peak profile analysis was carried out using the Debye Scherrer model DSM, the Williamson Hall WH approach by its three models: Uniform Deformation model UDM, Uniform Deformation Stress model UDSM and Uniform Deformation Energy Density model UDEDM, and using the size-strain plot SSP. It was found that doping NiO with both Y and Gd causes a decrease in the lattice parameter, lattice strain and crystallite size. Transmission Electron Microscopy TEM was done to study the particles size and morphology. The particle size trend obtained from the TEM images were agreeable with the crystallite size obtained from the XRD results. The TEM images showed homogeneous, nearly spherical and slightly agglomerated NiO nanoparticles, that can be good candidates for rechargeable Lithium ion batteries. Dielectric measurements were done by measuring the parallel-equivalent circuit mode capacitance Cp, the dielectric loss tangent D (tanδ), the impedance Z and the impedance phase angle θ. Then, the frequency and temperature dependence of the dielectric constant ε’, dielectric loss ε”, loss tangent, ac conductivity σac and the imaginary part of both impedance Z″ and modulus M” were calculated and studied. Furthermore, the Nyquist plot was studied to correlate the electrical behavior by the microstructural contributions. The ionic radius and the valency of the dopant elements were found to be the factors that affect the dielectric behavior of the prepared samples. The dopant having larger ionic radius and higher valency was found to result in a higher dielectric constant and ac conductivity and a lower dielectric loss and electrical impedance, enhancing the role of NiO nanoparticles in electrical technologies, such as solar cells.