The potential transformer bridge with current comparator formeasuring the voltage dependence of compressed-gas capacitors

In this paper, an alternative method for measuring the voltage dependent capacitance variation (VDCV) of compressed-gas capacitors is described. In the proposed method, the VDCV of the capacitor under test is measured by comparing it with a capacitor standard supplied with the secondary (low) voltage of a potential transformer. This transformer has its primary parallel connected with the capacitor under test. The paper presents and criticizes the test results obtained in which an uncertainty of at least 0.5 ppm is achieved     

Polarization-switching D/A converter

This paper describes a novel digital-to-analog (D/A) conversion technique, which uses the analog quantity polarization as a D/A conversion medium. It can be implemented by CMOS capacitors or by ferroelectric capacitors, which exhibit strong nonlinearity in charge versus voltage behavior. Because a ferroelectric material inherently has spontaneous polarization and generally has a large dielectric constant, the effective capacitance of a ferroelectric capacitor is much larger than that of a CMOS capacitor of the same size. This ensures less influence of bottom-electrode parasitic capacitance on a ferroelectric capacitor. Furthermore, a data converter based on ferroelectric capacitors possesses the potential nonvolatile memory function owing to ferroelectric hysteresis. Along with the architecture proposed for polarization-switching digital-to-analog converter (PDAC), its circuit implementation is introduced. Described is implementation of two 9-bit bipolar PDACs: one is based on CMOS capacitors and the other on off-chip ferroelectric capacitors. Experimental results are presented for the performance of these two prototypes.     

Measurement of capacitances and their loss factors

A method is described for measuring the capacitance values and the loss factors of a pair of capacitors simultaneously. The method uses the principle of oscillators. No standard capacitor is required. The possible errors introduced in the measurements are discussed. Both theoretical and experimental results are provided. The method can be used with any other oscillator circuit that contains only two capacitors     

Self-assembled Ti3C2Tx-MXene/PTh composite electrodes for electrochemical capacitors

Recently, MXene are being extensively utilized as an electrode material for electrochemical capacitors owing to its excellent electrochemical performance. Furthermore, its excellent properties are enhanced by compounding it with other materials as the electrode material of electrochemical capacitor. In this study, MXene has been obtained by selective etching, Polythiophene (PTh) was prepared by chemical oxidative polymerization, and MXene/PTh composites with different mass ratios have been synthesized by the vacuum filtration self-assembly method. MXene nanosheets have the comprehensive function of combining PTh nanoparticles, and acting as flexible substrates. PTh nanoparticles can provide high pseudo-capacitance and inhibit the stacking of MXene, thus achieving a good synergistic effect. The results demonstrate that the M/PTh-3 composite has the best capacitance with a maximum value of 265.96 F g^?1. The specific capacitance remains at 91.5% even after 500 cycles, which demonstrates that the composite electrode is a promising material for the high-performance electrochemical capacitor applications.

     

Frequency Dependence of Electrode Surface Effects in Parallel-Plate Capacitors

Electrode surface effects in parallel-plate capacitors lead to a variation in capacitance and conductance with frequency. A method is presented for the determination of absolute changes in capacitance and absolute values of conductance, as functions of frequency. The method involves the use of two variable parallel-plate capacitors, and requires the measurement of relative capacitance and conductance values over a range of frequencies and at a minimum of two different electrode spacings. A capacitor cell, incorporating two variable capacitor sections is described. The cell is designed for use in the investigation of the frequency characteristics of a range of electrode surfaces. Two current transformer ratio-arm bridges are used to perform the relative admittance measurements. The bridges are compensated for capacitance loading, and together cover the frequency range 11 Hz-52 kHz. Measurement precision is a few parts in 108 for each admittance component. Details of the bridges and measurement techniques are discussed and corrections for mechanical resonance effects and lead impedances are considered. Results are given for rhodium plated and plain brass electrodes under vacuum. Over the full frequency range the fractional capacitance change for rhodium, when referred to a 1-mm electrode spacing, is <4 × 10-7. Tan ? is < 1.5 × 10-7. Oil films and organic contaminants on electrode surfaces are thought to be the most likely sources of frequency dependence.     

Nondestructive Evaluation of Ferroelectric Multilayer Capacitors Using Electromechanical Resonances

Under the mechanically free and clamped boundary conditions, electromechanical resonances of ceramic multilayer capacitors are calculated using vibration and piezoelectric equations. Multilayer capacitors made of ferroelectric BaTiO3 and Pb(Mg1/3Nb2/3)O3 ceramics have been used to examine the theoretical calculation. Frequency spectra of impedance and phase angle, capacitance and loss tangent of the capacitors under dc bias fields are carefully measured. A sudden change around the resonant frequency is observed in these spectra. A damped resonance indicates a defective capacitor while an undamped resonance is corresponding to defect free.Experimental results suggest that it is possible to use the spectra as a real time nondestructive evaluation method.     

Active power decoupling with reduced converter stress for single-phase power conversion and interfacing

Single-phase DC–AC power electronic converters suffer from pulsating power at double the line frequency. The commonest practice to handle the issue is to provide a huge electrolytic capacitor for smoothening out the ripple. However, the electrolytic capacitors having short end of lifetime limit the overall lifetime of the converter. Another way of handling the ripple power is by active power decoupling (APD) using the storage devices and a set of semiconductor switches. Here, a novel topology has been proposed in implementing APD. The topology claims the benefit of (1) reduced stress on converter switches and (2) using smaller capacitance value, thus alleviating the use of electrolytic capacitor and in turn improving the lifetime of the converter. The circuit consists of a third leg, a storage capacitor and a storage inductor. The analysis and the simulation results are shown to prove the effectiveness of the topology.     

A New High-Speed Method of Testing Capacitors

A new high-speed method of determining the capacitance and a quantity which the writers call the pulse series resistance (PSR) of an unknown capacitor is presented. The unknown capacitor is assumed to consist of an ideal capacitor and a series resistor. The test circuit consists of a low-impedance driver, a low-loss coupling capacitor, and a wide-band high-input/low-output impedance video-type amplifier. The unknown capacitor is placed in a negative feedback loop of this amplifier. The input waveform is a trapezoid. The output waveform contains information that is indicative of the capacitance and PSR of the unknown capacitor. The information is obtained by measuring two voltages, one of which is completely independent of the other. Capacitors were measured from approximately 2 pf to 2 ?f with an accuracy of ±5 per cent. The PSR was not available for capacitors less than 100 pF because of test-circuit limitations. The capacitance and PSR of an unknown capacitor could be made available within 500 ?sec with modern voltage-measuring and calculating techniques.     

Determining the value of reference air capacitors at high frequencies

Conclusions Reference three-terminal capacitors are affected by frequencies to a greater extent than the two-terminal capacitors and, therefore, the range of their application is limited to several megahertz.The effect of distributed parameters appears in air capacitors with a rising frequency, thus raising their inductance measured at a high frequency as compared with its low-frequency value. The extent of this difference depends on the capacitor's design features and nominal value. The maximum difference amounts to about 20%.The applicability limit of (1), which corresponds to the simple equivalent circuit of the capacitor (Fig. 1) and is used for calculating its effective value, depends on the tolerated error in determining that value and on the capacitor's parameters. For an error of 1% the value of the frequency correction ²LC_o must not exceed 10%, and this approximately corresponds to the upper frequency boundary of 1/3 of the capacitor's natural resonant frequency.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 46–48, July, 1972.     

Evaluation of a Capacitance Scaling System

An improved error analysis of an existing capacitance scaling system for supporting measurements of higher valued (10 nF to 100 ) ceramic-dielectric four-terminal-pair (4TP) capacitance standards over the 100-Hz to 100-kHz frequency range is described. The capacitance scaling system uses a commercial impedance (inductance-capacitance-resistance) meter and a single-decade inductive voltage divider as an impedance comparator. Four-terminal-pair capacitors in decade (10 : 1) steps from 10 nF to 100 F are measured. The system's 10 : 1 scaling error is determined using 100-pF and 1-nF air-dielectric 4TP capacitance standards with known capacitance and loss characteristics over frequency. This paper discusses the significant reductions in measurement uncertainty that were attained through the use of improved calibration standards and measurement method refinements. Details of the uncertainty analysis for a 10-nF capacitor (in the 100-Hz to 10-kHz frequency range) and verification data are presented.     

Microwave losses in metal-ferroelectric-metal thin-film capacitors

The design and technology of microwave ferroelectric capacitors based on Pt/(Ba,Sr)TiO₃/Cu thin-film structures are considered. The structural and electrical characteristics of a ferroelectric layer deposited over a Pt film are presented. The frequency dependence of microwave losses in a 1–30 GHz range have been measured for a capacitor ensuring approximately two-fold variation of the capacitance in a bias voltage range of ∼30 V. On the basis of an equivalent scheme, the metal-related contribution to total losses in the capacitor is determined and it is concluded that this contribution is predominating in the millimeter wavelength range.     

Thin film Ba0.25Sr0.75TiO3 voltage tunable capacitors on fused silica substrates for applications in microwave microelectronics

Thin film Au/Pt/Ba_0.25Sr_0.75TiO₃/Pt/Au/Ti capacitor structures were fabricated on fused silica substrates using pulsed laser deposition of ferroelectric films. Low-field dielectric measurements were performed as a function of frequency in the range 1-25 GHz at different external dc fields up to 360 kV/cm. Resonant microwave power absorption observed at frequencies less than 10 GHz under dc field is due to electrostriction and field induced piezoelectric effects. The effects are simulated using an electroacoustic model of the multilayer capacitor structure. A circuit model is applied to investigate the influence of series resistance and inductance of interconnect/lead strips on capacitor performance. Analysis shows that the measured loss tangent of the capacitor is mainly due to series resistance and frequency dispersion of capacitance is caused by series inductance. The de-embedded value of the loss tangent is 0.005 at 10 GHz. The measured loss tangent is less than 0.02 and tunability is up to 40% in the whole frequency range. These parameters indicate high potential of Ba_0.25Sr_0.75TiO₃ capacitors for applications in voltage controlled devices of microwave microelectronics.     

Empirically-derived capacitor characteristic formulas from distributed modelling

Diffusion equation modelling is used to develop formulas for the normally fixed values of capacitance and resistance of the traditional capacitor equivalent circuit. The formulas define the dependence of the equivalent circuit values on metal film resistivity, capacitance per unit area, areal dimensions of the metallisation and on frequency. A multilayer capacitor topology, having both capacitor plates connected at the same end, is used for the derivation, but it is shown that the results are also representative for the more standard double-end connected topologies with some restrictions above the typical self-resonance frequency of these capacitors. The formulas allow accurate prediction of dissipation factor and input impedance according to the design parameters used in constructing the capacitor, thus providing powerful tools in capacitor design. The algorithms also facilitate the determination of internal voltages, currents and power distribution within the capacitor, thus exposing the effects, for example, of partial edge disconnection. The formulas may potentially provide a better capacitor equivalent circuit with dependent variables for circuit emulation. In the paper, the derivation process is described and the formulas tested against experimental results. A simple addition to the equivalent circuit is also included to model dielectric loss which dominantly determines the dissipation factor at low frequency     

BaTiO3–P(VDF-TrFE) composite ink properties for printed decoupling capacitors

In this research a composite for printable capacitors using screen printed structures and low temperature curing ferroelectric ink was investigated. The realized ink consisted of 40 vol% barium titanate in a poly(vinylidenefluoride-trifluoroethylene) matrix. DuPont silver ink 5064H was used for the conductive lines in the design and the maximum process temperature was 130 °C. The thickness of the composite and the area of the printed capacitor were 43 μm and area 25 mm², respectively. The obtained relative permittivity of the composite was 46 and the tan δ was 0.15 at 1 MHz. Additionally, the microstructure of the composite was investigated and the temperature dependence of the dielectric properties measured. The capacitance of the parallel plate structure was approximately 200 pF at 1 MHz. This is easily adjustable by changing the printing pattern, number of layers or the filler loading. The freedom of choice in integration and capacitance value selection makes the ink highly usable in, for example, decoupling capacitors that are compatible with inorganic, organic and even flexible, substrates.     

A standard capacitor for frequencies up to 200–300 Mc

Summary The accuracy of determining the effective capacitance of coaxial cylindrical capacitors depends to a great extent on the construction of the connecting device of the instrument to which the capacitor has to be joined. The best junction device is the one which reproduces the construction of the coaxial capacitor. In this instance the error due to an edge field will be minimal and there will be no error at all due to the nonuniformity of the field.     

New Fused-Silica-Dielectric 10-and 100-pF Capacitors and a System for Their Measurement

New instruments have been designed to bring to standards laboratories the improved accuracy of capacitor calibrations developed by the National Bureau of Standards. The new 10-and 100-pF reference standard capacitors, based upon an NBS design, use a fused-silica dielectric with gold electrodes to provide the time and voltage stability required for calibrations to parts in 107. To maintain the capacitor temperature constant to within 0.01 °C, one model of the capacitors is designed for use in an oil bath, the other model is fitted with a new, stable, thermostatically controlled air bath. The system to measure these capacitors with a precision of parts in 108 consists of a bridge, detector, and oscillator. For these special measurements and for the general calibration of a wide range of capacitors, the new transformer-ratio-arm bridge has 12 capacitance decades and a range of 10 MAF-10-7 pF, and five conductance decades and a range of 103110-10 tmho. The new phasesensitive detector and power oscillator provide high sensitivity to bridge imbalance over the frequency range 10 Hz-100 kHz.     

An RC Discharge Digital Capacitance Meter

A simple digital capacitance meter which utilizes the RC discharge is proposed and the wide range capability from 0.1 pF to 10 mF and the excellent linearity to ± (0.02 percent of reading + 1 digit) are shown. The RC discharge capacitance meter provides the capacitance to be measured at a frequency which is reciprocal to the product of the discharge resistance and the measured capacitance. Therefore, the meter can be used to test the frequency dependence of the capacitor even though the test signal is a dc voltage. The proposed RC Discharge Capacitance Meter can also be used in applications such as the measurement of the deviation from the preset value, or the torellance check of capacitance to make the GO or NO-GO decision by adding a few logic gates.     

A novel method of measurement of L and C

A novel method of measurement of component values of inductors and capacitors is described. The technique is independent of the voltage across or current through the unknown inductor or capacitor, as it involves only a set of phase measurements. The unknown capacitor/inductor is connected in series with a known standard resistance and this series circuit is excited by a source of required voltage and frequency. The resistive and reactive parts of the unknown component are measured by measuring the phase displacement between the three voltages, namely, voltage applied, voltage across the inductor/capacitor and the voltage across standard resistance. The proposed scheme is verified both by simulation as well as by building a prototype. The relationship between the range of the measurement and obtainable accuracy level is established. For the prototype built, with a one decade span in the measurement range, a commercially acceptable accuracy of ±2.0% was achieved. However, this accuracy can be further improved by suitable circuit modifications     

Experimental study of the voltage coefficient of precisecompressed-gas capacitors

A study of the voltage coefficient of precise compressed-gas capacitors is described. A series of measuring methods based on the formula for calculating the voltage coefficient is presented: measuring the variations of capacitance when the capacitor is tilted in various directions to a specific angle; measuring the variations in capacitance when the capacitor is tilted in a specific direction to various angles; and measuring the variations in the coordinates of the electrodes when these electrodes are subjected to various mechanical forces, etc. These methods were used to test a 350 kV, 50 pF capacitor, and its voltage coefficient was found to be less than one part in a million from 0 kV up to 350 kV     

电容器级钽粉关键技术与开发研究

引述了Ta电容器与Al电容器、多层陶瓷电容器相比突出的性能与应用特征，分析了Ta电容器片式化、小型化促进电容器级Ta粉高比容化发展的新趋势，叙述了航空、航天和军工领域对高压电容器高可靠性能的需求，以及对中高压Ta粉向更高电压、更低SER方向发展的引领，回顾了电容器用高比容Ta粉、中高压Ta粉发展应用进程，介绍了经典氟钽酸钾（K2TaF7）金属Na还原法、电子束熔炼法、球磨片式化法生产的高比容Ta粉、高压Ta粉、中压（片状）Ta粉的性能、产品品级及关键技术，分析了30～80kμFV／gTa粉耐压性能影响因素，介绍了Ta粉高比容化、高压化新技术、装置、产品形貌、性能及优缺点，在此基础上提出了电容器级Ta粉高比容化、高压化创新进步的思路。