Small Capacitance Research Articles

Design of Capacitive Power Transfer System with Small Coupling Capacitance for Wireless Power Transfer

Wireless power transfer systems play an important role in the application of modern power supply technology. Wireless charging has been widely used in portable devices such as smartphones, laptops, and even some medical devices. Higher system efficiency can be achieved while reducing costs. This article describes the design of a capacitive power transfer (CPT) system using the Class-E amplifier method. When the capacitance of the coupling plate is small, the operation of Class-E amplifiers under Zero-Voltage-Switching (ZVS) conditions is very sensitive to their circuit parameters. By adding an additional capacitor to the Class-E amplifier, the coupling capacitance can be increased, resulting in better circuit performance. The high efficiency of the Class-E amplifier is verified by simulation and experimental results.

Current dependence of the low bias resistance of small capacitance Josephson junctions

The dc current-voltage characteristics of small Josephson junctions reveal features that are not observed in larger junctions, in particular, a switch to the finite voltage state at current values much less than the expected critical current of the junction and a finite resistance in the nominally superconducting regime. Both phenomena are due to the increased sensitivity to noise associated with the small capacitance of the Josephson junction and have been extensively studied a few decades ago. Here I focus on the current bias dependence of the differential resistance of the junction at low current bias in the nominally superconducting regime, using a quantum Langevin equation approach that enables a physically transparent incorporation of the noise environment of the junction. A similar approach might be useful in modeling the sensitivity of superconducting qubits to noise in the microwave regime.

Tuning Gate Potential Profiles and Current-Voltage Characteristics of Polymer Electrolyte-Gated Transistors by Capacitance Engineering.

We demonstrate that the transfer characteristics of electrolyte-gated transistors (EGTs) with polythiophene semiconductor channels are a strong function of gate/electrolyte interfacial contact area, i.e., gate size. Polythiophene EGTs with gate/electrolyte areas much larger than the channel/electrolyte areas show a clear peak in the drain current vs gate voltage (ID-VG) behavior, as well as peak voltage hysteresis between the forward and reverse VG sweeps. Polythiophene EGTs with small gate/electrolyte areas, on the other hand, exhibit current plateaus in the ID-VG behavior and a gate-size-dependent hysteresis loop between turn on and off. The qualitatively different transport behaviors are attributed to the relative sizes of the gate/electrolyte and channel/electrolyte interface capacitances, which are proportional to interfacial area. These interfacial capacitances are in series with each other such that the total capacitance of the full gate/electrolyte/channel stack is dominated by the interface with the smallest capacitance or area. For EGTs with large gates, most of the applied VG is dropped at the channel/electrolyte interface, leading to very high charge accumulations, up to ∼0.3 holes per ring (hpr) in the case of polythiophene semiconductors. The large charge density results in sub-band-filling and a marked decrease in hole mobility, giving rise to the peak in ID-VG. For EGTs with small gates, hole accumulation saturates near 0.15 hpr, band-filling does not occur, and hole mobility is maintained at a fixed value, which leads to the ID plateau. Potential drops at the interfaces are confirmed by in situ potential measurements inside a gate/electrolyte/polymer semiconductor stack. Hole accumulations are measured with gate current-gate voltage (IG-VG) measurements acquired simultaneously with the ID-VG characteristics. Overall, our measurements demonstrate that remarkably different ID behavior can be obtained for polythiophene EGTs by controlling the magnitude of the gate-electrolyte interfacial capacitance.

Electrophysiological Recording from a "Model" Cell.

The muscle cell or neuron membrane is functionally equivalent to a resistor-capacitor (RC) circuit with the membrane resistance and capacitor in parallel. Once inserted inside the membrane, an electrode introduces a serial resistance and small capacitance to the RC circuit. Through a narrow opening at its tip (∼0.1-μm), current can pass through the electrode, into the cell, and back to the outside (ground) across the membrane to complete the circuit. This arrangement enables a voltage difference between the outside and inside of the cell membrane to be recorded. To determine cell membrane properties, a current can be injected into the cell through the electrode. One complication with this approach, however, is that the voltage difference measured with the electrode includes the voltage drop across the cell membrane and that across the electrode. Furthermore, a small amount of current is drawn by the electrode capacitor, thereby slowing the current flow across the membrane. Fortunately, most amplifiers are equipped with bridge balance and capacitance compensation functions so that the effects of the electrode on cell membrane properties can be canceled out or minimized. This protocol describes the basics of setting up and conducting electrophysiological experiments using a model cell. For the novice, a model cell provides a way to learn the operation of electrophysiology equipment and software without the anxiety of damaging living cells. This protocol also illustrates passive membrane properties such as the input resistance, capacitance, and time constant.

Stash: Flexible Energy Storage for Intermittent Sensors

Batteryless sensors promise a sustainable future for sensing, but they face significant challenges when storing and using environmental energy. Incoming energy can fluctuate unpredictably between periods of scarcity and abundance, and device performance depends on both incoming energy and how much a device can store. Existing batteryless devices have used fixed or run-time selectable front-end capacitor banks to meet the energy needs of different tasks. Neither approach adapts well to rapidly changing energy harvesting conditions, nor does it allow devices to store excess energy during times of abundance without sacrificing performance. This article presents Stash, a hardware back-end energy storage technique that allows batteryless devices to charge quickly and store excess energy when it is abundant, extending their operating time and carrying out additional tasks without compromising the main ones. Stash performs like a small capacitor device when small capacitors excel and like a large capacitor device when large capacitors excel, with no additional software complexity and negligible power overhead. We evaluate Stash using two applications—temperature sensing and wearable activity monitoring—under both synthetic solar energy and recorded solar and thermal traces from various human activities. Our results show that Stash increased sensor coverage by up to 15% under variable energy-harvesting conditions when compared to competitor configurations that used fixed small, large, and reconfigurable front-end energy storage.

A Harmonic Suppression Strategy Based on Adaptive Synchronous Rotating Frame Transformation for Improving the Estimation Accuracy of Sensorless Drivers With Small Capacitors

A Harmonic Suppression Strategy Based on Adaptive Synchronous Rotating Frame Transformation for Improving the Estimation Accuracy of Sensorless Drivers With Small Capacitors

Adaptive Virtual Admittance Reshaping-Based Resonance Suppression Strategy for PMSM Drives With Small DC-Link Capacitor

Adaptive Virtual Admittance Reshaping-Based Resonance Suppression Strategy for PMSM Drives With Small DC-Link Capacitor

Minimum current stress control strategy for three degree of freedom three-phase dual active bridge DC-DC converter

Compared to single-phase dual active bridge (1p-DAB) DC-DC converters, three-phase dual active bridge (3p-DAB) DC-DC converters have advantages such as high single machine power, high power density, small filtering capacitance, and are more suitable for high-voltage situations. Therefore, they have good application prospects in DC transmission and industrial high-power DC-DC converters. However, under traditional single-phase shift (SPS) control, especially in the low power range, there is a large reactive current and severe soft switch loss. This article adopts an asymmetric modulation strategy for its larger reactive power, which reduces its reactive power in the low power range with more degrees of freedom and improves the efficiency of power transmission. Taking current stress as the optimization objective, the KKT algorithm is used to solve, and the corresponding analytical solution is ultimately obtained. Finally, a simulation is built by using MATLAB software to verify the feasibility of the proposed solution.

Ku-Band Mixers Based on Random-Oriented Carbon Nanotube Films.

Carbon nanotubes (CNTs) are a type of nanomaterial that have excellent electrical properties such as high carrier mobility, high saturation velocity, and small inherent capacitance, showing great promise in radio frequency (RF) applications. Decades of development have been made mainly on cut-off frequency and amplification; however, frequency conversion for RF transceivers, such as CNT-based mixers, has been rarely reported. In this work, based on randomly oriented carbon nanotube films, we focused on exploring the frequency conversion capability of CNT-based RF mixers. CNT-based RF transistors were designed and fabricated with a gate length of 50 nm and gate width of 100 μm to obtain nearly 30 mA of total current and 34 mS of transconductance. The Champion RF transistor has demonstrated cut-off frequencies of 78 GHz and 60 GHz for fT and fmax, respectively. CNT-based mixers achieve high conversion gain from -11.4 dB to -17.5 dB at 10 to 15 GHz in the X and Ku bands. Additionally, linearity is achieved with an input third intercept (IIP3) of 18 dBm. It is worth noting that the results from this work have no matching technology or tuning instrument assistance, which lay the foundations for the application of Ku band transceivers integrated with CNT amplifiers.

Improving Carbon Nanotube-Based Radiofrequency Field-Effect Transistors by the Device Architecture and Doping Process.

The semiconducting carbon nanotube (CNT) has been considered a promising candidate for future radiofrequency (RF) electronics due to its excellent electrical properties of high mobility and small capacitance. After decades of development, great progress has been achieved on CNT-based RF field-effect transistors (FETs). However, almost all elevations are owing to advancement of the CNT materials and fabrication process, while the study of device architecture is seldom considered and reported. In this work, we innovatively combined device architecture and related doping processes to further optimize CNT-based RF FETs by guiding process or materials with collaborative optimization for the first time and explore their effect on device performance carefully and statistically. Based on more mature random-oriented CNT materials, we fabricated CNT-based RF FETs having three different gate positions of device architecture variation accompanied by suitable doping schemes. The optimized FETs obtained 2-3 times of current density (transconductance) and 1.3 times the cutoff frequency and maximum oscillation frequency compared with unoptimized devices at the same channel length. After transistor-level verification of effect, we further built a CNT RF amplifier and demonstrated almost 10 dB of transducer gain improvement operating at 8 GHz for X-band application. The achieved results from this work would help further improve CNT RF performance beyond the materials and process point of view.

Recording ten-fold larger IKr conductances with automated patch clamping using equimolar Cs+ solutions.

Background: The rapid delayed rectifier potassium current (IKr) is important for cardiac repolarization and is most often involved in drug-induced arrhythmias. However, accurately measuring this current can be challenging in human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes because of its small current density. Interestingly, the ion channel conducting IKr, hERG channel, is not only permeable to K+ ions but also to Cs+ ions when present in equimolar concentrations inside and outside of the cell. Methods: In this study, IhERG was measured from Chinese hamster ovary (CHO)-hERG cells and hiPSC-CM using either Cs+ or K+ as the charge carrier. Equimolar Cs+ has been used in the literature in manual patch-clamp experiments, and here, we apply this approach using automated patch-clamp systems. Four different (pre)clinical drugs were tested to compare their effects on Cs+- and K+-based currents. Results: Using equimolar Cs+ solutions gave rise to approximately ten-fold larger hERG conductances. Comparison of Cs+- and K+-mediated currents upon application of dofetilide, desipramine, moxifloxacin, or LUF7244 revealed many similarities in inhibition or activation properties of the drugs studied. Using equimolar Cs+ solutions gave rise to approximately ten-fold larger hERG conductances. In hiPSC-CM, the Cs+-based conductance is larger compared to the known K+-based conductance, and the Cs+ hERG conductance can be inhibited similarly to the K+-based conductance. Conclusion: Using equimolar Cs+ instead of K+ for IhERG measurements in an automated patch-clamp system gives rise to a new method by which, for example, quick scans can be performed on effects of drugs on hERG currents. This application is specifically relevant when such experiments are performed using cells which express small IKr current densities in combination with small membrane capacitances.

Role of fluorination in the high-frequency response of azobenzene-based molecular junction: First-principles calculations

Photochromic molecules such as azobenzene present a great potential to tune the device functionality under external stimuli. Fluorination is known to further enhance the functionality of azobenzene due to significant contributions to the structural and electronic properties. Here, we conduct quantum capacitance and quantum transport calculations to study the effect of fluorination on the high-frequency response of azobenzene-based molecular junctions. We found that fluorination results in smaller capacitance in both trans and cis conformations. However, this processes significantly reduces the cutoff frequency of the molecular junctions due to the reduced conductivity. cis isomers of both pristine and fluorinated azobenzene molecular structures show smaller cutoff frequencies as compared to trans configurations due to the enhanced capacitance. These findings can be useful in developing azobenzene-based functional device structures.

Booster Circuit for Harvesting Renewable Energy Based on Bioelectric Microbial Fuel Cells Whose Power Can Be Adjusted

Microbial fuel cells (MFCs) represent a promising technology that converts organic waste into electrical energy through bacterial activity. The process involves capturing a low voltage of approximately 0.4 V generated by the MFC using a small capacitor, which is then stored and transferred to a larger capacitor to increase the capacity. In order for this energy to be used for general AC-powered devices, an inverter is essential to convert the DC output to AC. This system, consisting of a series of capacitors and inverters, along with voltage dampers and rectifiers, forms a circuit that can potentially function as an efficient low-power generator. The effectiveness of this arrangement remains to be tested, which will determine its viability as a renewable energy storage solution.

A 43.5dB Gain Unipolar a-IGZO TFT Amplifier with Parallel Bootstrap Capacitor for Bio-signals Sensing Applications.

In this paper, a high gain amplifier with phase compensation loop is presented. A structure of parallel gate cross-coupled transistors to both ends of differential pair drain and source is designed to improves the load impedance, which obtains sufficient gain and further reduces power consumption. A novel capacitor bootstrap load circuit is proposed. The capacitor bootstrap topology is constructed by the drain source resistance of the transistor working in the cut-off region, where the gate source parasitic capacitor of the transistor is in parallel with the bootstrap capacitor rather than the existing series structure, thereby only a small bootstrap capacitor is required. By avoiding the use of large capacitors, chip area can be effectively reduced without compromising performance such as gain and bandwidth. The amplifier is fabricated using 10-μm n-type a-IGZO TFT technology. Measurement results show that the proposed amplifier achieves a voltage gain of 43.5dB and a common mode rejection ratio of 61.2dB while maintaining low power consumption. The amplifier also exhibits a -3dB bandwidth covering 0.4~2.1KHz, encompassing major bioelectric frequency bands. A real-time ECG signal was successfully captured using the fabricated TFT amplifier and gel electrodes. It has great potential in flexible sensing and acquisition applications such as electro cardiogram (ECG), electro encephalogram (EEG), pulse detection, and other wearable applications.

Revolutionary building approach for maximal photovoltaic system results to improve maximum power point tracking in solar inverter

Due to the inherent frequency ripple in single-phase photovoltaic (PV) grid-connected solar inverters, the Maximum Power Point Tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a Robust Sliding-Mode Control (RSMC) is proposed in this article. The frequency pulsation on the DC link is effectively canceled with the passive LC decoupling path. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small DC-link capacitor becomes possible. The resonance between the LC circuit and the main DC-link capacitor appears, which can be damped through an active damping method. The proposed RSMC offers good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the DC-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of RSMC is presented, and a detailed parameter optimization design of the LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-phase grid-connected solar inverter, and the results validate the effectiveness of the proposed strategy.

Minimization of Common Mode Voltage and Capacitor Voltage Unbalance of 3-Phase 4-Wire 3-Level NPC inverter using 4D-SVM

This paper elucidates the implementation of Four-dimensional Space Vector Modulation (4D-SVM) for reduction of Common Mode Voltage (CMV) and Capacitor Voltage Unbalance (CVU) of 3-phase 4-wire 3-level Neutral Point Clamped inverter (3L-NPCI). CMV and CVU are major drawbacks of neutral point clamped inverter circuit; It leads to affect the performance of inverter in terms of bearing failure, unequal voltage stress across various switching devices, the magnitude of load current increases, increases in total harmonic distortion (THD), tripping of ground fault relays and malfunction of various sensitive electronics and control unit. The 4D-SVM algorithm is developed to reduce the CMV and CVU; with help of the nearest state vector (NSV) control method CMV range is reduced and by proper utilization of large and small vector capacitor voltage unbalance is minimized. 4D-SVM for 3-phase 4-wire 3-level includes 81 switching state vectors with a non-redundant switching concept. This algorithm is implemented without using any trigonometric equations, lookup tables, and angle determinations. This proposed system provides a comprehensive analysis of 4D-SVM for reduction of CMV range and CVU for the 3L-NPCI system. The minimization of CMV and CVU is achieved using MatLab-Simulink and FPGA processor for simulation and experimental results respectively.

A Practical Control Method for Single-Phase Input PMSM Drives with Small DC-link Capacitor

A Practical Control Method for Single-Phase Input PMSM Drives with Small DC-link Capacitor

Thermal Control of Quasi-2-Level Super-Switch by Power Routing

The requirement of power converters for Medium Voltage (MV) and High Voltage (HV) applications accelerates faster than the development of semiconductor switches capable of handling such voltage levels. For that reason, it is common to use the series connection of semiconductors with auxiliary snubbers. In contrast, an increased number of semiconductors is more likely to cause reliability problems due to increased redundancy, unequal thermal conditions, or different remaining lifetime. On the other hand, the quasi-2-level super-switch (Q2L SS) yields increased flexibility, enabling precise readjustments of the voltage and switching losses of individual devices of the converter due to the utilization of small capacitors. The power routing capability of the Q2L SS to redistribute the switching losses from the overheated semiconductors is presented in this paper. The influence of power routing on performance of Q2L SS is investigated with the Double Fourier analysis and experimental results.

Modeling and Suppression Method of Low Order Harmonics for Three-Level Inverter With Small Capacitance Value

Modeling and Suppression Method of Low Order Harmonics for Three-Level Inverter With Small Capacitance Value

Experimental Investigation on SiC MOSFET Turn-Off Power Loss Reduction Using the Current Sink Capacitor Technique

This paper investigates the current sink capacitor technique as a method to minimize the turn-off power losses of SiC MOSFETs operated with zero-voltage switching (ZVS). The method is simple and is based on adding auxiliary capacitors in parallel to the transistors, allowing the sink capacitor to take over part of the channel current, thus limiting the power loss while also advantageously lowering the dvds/dt ratio. The technique is validated and experimentally studied based on a single-pulse test setup with 1200 V-rated SiC MOSFETs, with several capacitances and gate resistance values, at various switched currents up to roughly 60 A. It is shown that by employing even very small capacitances, in the range of nanofarads, the turn-off power loss can be reduced by over tenfold, with a negligible impact on the volume and complexity of the system. Thus, the presented method can be effectively employed to improve soft-switched power converters.