Maximum Open Voltage Research Articles

High Performance Li-Ion Capacitor Laminate Cells Based on Hard Carbon/Lithium Stripes Negative Electrodes

High performance Li-ion capacitor (LIC) laminate cells have been fabricated with activated carbon positive electrodes (PEs) and hard carbon/lithium stripes negative electrodes (NEs). The lithium stripes on the surface of NEs enable a novel pre-lithiation approach for the LIC cells. The LIC laminate cells can achieve a maximum specific power of 6 kW kg−1 and a maximum power density of 12 kW L−1. The specific energy and energy density of the LIC laminate cells are 14 Wh kg−1 and 28 Wh L−1 respectively, which is about 3 times of the traditional electric double layer capacitors (EDLCs). The DC life of such LIC cell has passed 2000 h testing while held at maximum operation voltage 3.8 V and 65°C. Extended cycle performance under 50 C rate of the LIC laminate cell has been tested: such LIC can remain 89% of the original discharge capacitance after 100,000 cycles without obvious changes in ESR value. When the LIC cell is charging and discharging under 125 C rate, the cycle life is still more than 50,000 cycles.

Investigation of Water Tree Degradation in Dry‐Cured and Extruded Three‐Layer (E‐E Type) 6.6‐kV Removed XLPE Cables

SUMMARYDry‐cured and extruded three‐layer (E‐E type) 6.6‐kV cross‐linked polyethylene (XLPE) cables were introduced into electric power systems more than 30 years ago, but they do not experience failures because of water tree degradation. Also, the degradation index of water treeing for these cables has not been established. Therefore, investigating results of residual breakdown voltage and water tree degradation of these cables will help us plan for cable replacement and determine water tree degradation diagnosis scheduling, and will be fundamental data for cable lifetime evaluation. In this study, the authors measured the ac breakdown voltages of dry‐cured and E‐E type 6.6‐kV XLPE cables removed after 18 to 25 years of operation and observed the water trees in their XLPE insulation. As a result, it was observed that breakdown voltages were larger than the maximum operating voltage (6.9 kV) and the ac voltage for the dielectric withstanding test (10.3 kV). Water trees were mainly bow‐tie water trees and their maximum length was approximately 1 mm. Although the number of measured cables was limited, the lifetime of this type of cable was estimated to be approximately 40 years, even experiencing water immersion.

Free-space terahertz radiation from a LT-GaAs-on-quartz large-area photoconductive emitter.

We report on large-area photoconductive terahertz (THz) emitters with a low-temperature-grown GaAs (LT-GaAs) active layer fabricated on quartz substrates using a lift-off transfer process. These devices are compared to the same LT-GaAs emitters when fabricated on the growth substrate. We find that the transferred devices show higher optical-to-THz conversion efficiencies and significantly larger breakdown fields, which we attribute to reduced parasitic current in the substrate. Through these improvements, we demonstrate a factor of ~8 increase in emitted THz field strength at the maximum operating voltage. In addition we find improved performance when these devices are used for photoconductive detection, which we explain through a combination of reduced parasitic substrate currents and reduced space-charge build-up in the device.

Ring-Double-Bar Slow Wave Structure for High Power TWTs

The electromagnetic properties of a ring-double-bar (RDB) slow wave structure are investigated. Use of two bars to connect neighboring rings instead of one as in a conventional ring-bar (RB) structure leads to the splitting $E$ - and $H$ -waves, with the $H$ -wave concentrated in thin layers near the rings. This effect leads to the flattening of the dispersion characteristic, similar to that in a helix with longitudinal vanes. Prototype RDB structures have been fabricated, measured, and compared with the conventional helix and RB circuits. Analysis, simulation, and cold test measurements demonstrate that the use of an RDB structure may make it possible to increase the maximum stable operating voltage of wideband traveling-wave tubes to 30–40 kV, enabling an order of magnitude increase in output power without the danger of backward wave oscillation.

Design and optimization of BCCD in CMOS technology

This paper optimizes the buried channel charge-coupled device (BCCD) structure fabricated by complementary metal oxide semiconductor (CMOS) technology. The optimized BCCD has advantages of low noise, high integration and high image quality. The charge transfer process shows that interface traps, weak fringing fields and potential well between adjacent gates all cause the decrease of charge transfer efficiency (CTE). CTE and well capacity are simulated with different operating voltages and gap sizes. CTE can achieve 99.999% and the well capacity reaches up to 25 000 electrons for the gap size of 130 nm and the maximum operating voltage of 3 V.

Carbon-based electrochemical capacitors with acetate aqueous electrolytes

This paper reports on the performance of the supercapacitor operating in aqueous acetic acid salts. Lithium, sodium and magnesium acetate aqueous solutions at various concentrations have been selected as electrolytes. Maximum operational voltage and the overall capacitor performance have been determined by several electrochemical techniques. Floating and galvanostatic charge/discharge tests proved the promising performance at high voltages (1.5V); the capacitance values have been retained at more than 80% of initial value for all tested electrolytes. Additionally, due to the the ability to operate at high voltages, the maximum energy obtained in the system with 0.5molL−1 CH3COONa is more than two times higher than with 6molL−1 KOH, i.e., conventional aqueous capacitor. Taking into account a mild character of the electrolytes used, a novel concept of eco-friendly energy storage device has been proposed.

A high-voltage high-current switch on the basis of triggered vacuum switches

A KV-25-300 high-voltage switch for dc voltages of up to 25 kV and currents of up to 300 kА for pulse powering of loads at a pulse rise rate of up to 10 kA/μs was developed and tested. The switch consists of two series-connected RVU-43-1 triggered vacuum switches, thus making it possible to reduce the breakdown probability at the maximum operating voltage to a value of <10–7. The total switching-on time delay relative to the optical control pulse is 4 ± 0.5 μs. The results of measurements and calculation of the electric strength of RVU-43-1 and KV-25-300 and the results of switching tests of the latter are presented.

乾式架橋・三層同時押出（E-E方式）の6.6kV撤去CVケーブルの水トリー劣化調査

Dry-cured and extruded three-layer (E-E type) 6.6kV cross-linked polyethylene (XLPE) cables were introduced into electric power systems more than 30 years ago, but they do not experience failures because of water tree degradation. Also, the degradation index of water treeing for these cables has not been established. Therefore, investigating results of residual breakdown voltage and water tree degradation of these cables will help us plan for cable replacement and determine water tree degradation diagnosis scheduling, and will be fundamental data for cable lifetime evaluation. In this study, the authors measured the AC breakdown voltages of dry-cured and E-E type 6.6kV XLPE cables removed after 18-25 years of operation and observed the water trees in their XLPE insulation. As a result, it was observed that breakdown voltages were larger than the maximum operating voltage (6.9kV) and the AC voltage for the dielectric withstanding test (10.3kV). Water trees were mainly bow-tie water trees and their maximum length was approximately 1mm. Although the number of measured cables was limited, the lifetime of this type of cable was estimated to be approximately 40 years, even experiencing water immersion.

Tube-Super Dielectric Materials: Electrostatic Capacitors with Energy Density Greater than 200 J·cm-3.

The construction and performance of a second generation of super dielectric material based electrostatic capacitors (EC), with energy density greater than 200 J·cm−3, which rival the best reported energy density of electric double layer capacitors (EDLC), also known as supercapacitors, are reported. The first generation super dielectric materials (SDM) are multi-material mixtures with dielectric constants greater than 1.0 × 105, composed of a porous, electrically insulating powder filled with a polarizable, ion-containing liquid. Second-generation SDMs (TSDM), introduced here, are anodic titania nanotube arrays filled with concentrated aqueous salt solutions. Capacitors using TiO2 based TSDM were found to have dielectric constants at ~0 Hz greater than 107 in all cases, a maximum operating voltage of greater than 2 volts and remarkable energy density that surpasses the highest previously reported for EC capacitors by approximately one order of magnitude. A simple model based on the classic ponderable media model was shown to be largely consistent with data from nine EC type capacitors employing TSDM.

Breakdown mechanism in hydrogen microdischarges from direct-current to 13.56 MHz

This paper contains the results of experimental studies of the breakdown phenomena in hydrogen microdischarges from direct current to very high radio frequencies. Measurements were performed for two types of electrode configurations, glass melting electrodes and electrodes with Bruce profiles, by varying the gap size from to , with the pressure ranging between and . The breakdown voltage curves and waveforms of the discharge voltage and current are presented and discussed. In the low-frequency region, the breakdown voltage values are comparable to the dc breakdown voltage data. The breakdown voltages recorded for high frequencies are similar to and lower than those obtained for the low-frequency region. For the gap size of , the breakdown voltage does not depend on the frequency since the strong electric field formed in microgaps overcomes the electron work function, enhancing secondary-electron production. The current-generating mechanism before breakdown is field emission, as verified by a linear Fowler–Nordheim plot with a negative slope. With increasing gap size, the breakdown voltage increases since the contribution of the field emission is progressively reduced. The breakdown voltages that correspond to the glass melting electrodes are lower since such electrodes have edge issues and an inability to achieve a homogeneous field, unlike electrodes with Bruce profiles. The results presented here could be useful both for a better understanding of the non-equilibrium processes which occur in radio-frequency microdischarges during breakdown and for determining the minimum ignition voltages in microplasma sources as well as the maximum safe operating voltage and critical dimensions in other microdevices.

Design of Reliable Analog DMTL Phase Shifter with Improved Performance for Ku Band Applications

&lt;p&gt;An analog phase shifter based on distributed MEMS transmission line (DMTL) is designed for Ku band applications. Traditional RF MEMS phase shifter comprising 6 switches has limited phase shift of 37.75° due to instability region. A new concept of stopper is incorporated to achieve high phase shift. In the present paper, optimisation of the analog phase shifter is done to increase its phase shift upto 88.63°. Phase shift is a strong function of capacitance ratio which is increased from 1.75 to 2.95. The maximum operating voltage and mechanical resonant frequency for the phase shifter are 16 V and 8.3 KHz, respectively. The switching time is calculated to 56 μs. The simulated insertion loss of the phase shifter is -1.75 dB with return loss of -20.49 dB at 17 GHz. The simulated results are verified with analytical modelling which are in close match.&lt;/p&gt;

Determination of the ion recombination correction factor for intraoperative electron beams

The ion recombination correction factor (ks) is determined for the Advanced Markus chamber exposed to electron beams produced by a dedicated intraoperative radiation therapy (IORT) accelerator at medium dose-per-pulse values. The authors evaluate five different methods. Three of them are known as Boag's modified expressions, which are based on the two-voltage-analysis method and include the free-electron component. In the fourth method the IAEA TRS-398 protocol is applied, which uses the same two-voltage-analysis method but ignores the free-electron component, and finally the fifth approach is known as the Jaffé plot. ks values were obtained in the range of 4 mGy/pulse to 42 mGy/pulse and were compared with ks values determined by means of radiochromic films, which are independent of the dose rate. It was found that ks values that resulted from the three Boag's modified expressions and the TRS-398 protocol deviated by on average 1.5% and 1.4%, respectively, from the reference ks values based on film dosimetry. These results are within the estimated relative uncertainty of ±3%. On the other hand, the absolute deviation of each method depends on the dose-per-pulse value at which the method is investigated. In conclusion, in the medium dose-per-pulse range all Boag's modified expressions could be used for ks determination. Above a dose-per-pulse value of 35 mGy/pulse, the TRS-398 approach should be avoided. At 27 mGy/pulse and a maximum operation voltage of 300 V the ks value resulting from the Jaffé plot showed a 0.3% deviation from the reference value. More investigation on the Jaffé plot is necessary at higher dose-per-pulse values.

Evaluating the quality characteristics of TLD-100T and TLD-100H exposed to diagnostic X-rays and 64 multislice CT using Taguchi's quality loss function

A thorough survey of the quality characteristics of both TLD-100T and TLD-100H is performed using either diagnostic X-rays or 64 MSCT under the same 80 kVp setting of the maximum operating voltage. Two kinds of 12 TLDs (thermoluminescent dosimeters) were randomly assigned to four groups, respectively. Each group of 3 TLDs was placed 5 cm deep in the center of a 15-cm-thick solid water phantom within the measurement and four mAs settings were used for X-rays (56, 100, 200, 315 mAs) and 64 MSCT (50, 100, 200, 400 mAs). The linearity, reproducibility, sensitivity and the minimum detectable dose limit of various TLDs were obtained from dose calibration lines to verify the integrated performance according to the Taguchi's quality loss function. Both TLDs performed similarly when exposed to X-rays. The TLD-100T outperformed TLD-100H when exposed to 64 MSCT. The low reproducibility of TLD-100H could be eliminated by doubling the number of TLDs in one position to reduce the standard deviation of TLD-100H readouts.

Electromechanical modeling and simulation by the Euler–Lagrange method of a MEMS inertial sensor using a FGMOS as a transducer

In this paper, the elec tromechanical modeling of a differential capacitive sensor interconnected with a floating-gate MOS (FGMOS) transistor is shown; the model was obtained using the Euler---Lagrange theory to analyze this particular physical system used as an inertial sensor. A design methodology is also shown relating all the physical parameters involved, such as: stiffness, damping associated with the capacitive structure, parasitic capacitances present in the transistor, and the maximum operating voltages to avoid pull-in effect. Cases for symmetric and non symmetric differential capacitance comb arrays are analyzed. A model comparison between conventional mass---spring---damper mechanical systems to a specific electromechanical system for capacitive sensor with its associated readout electronics is shown.

A Low-Power and Low-Voltage Power Management Strategy for On-Chip Micro Solar Cells

Fundamental characteristics of on-chip micro solar cell (MSC) structures were investigated in this study. Several MSC structures using different layers in three different CMOS processes were designed and fabricated. Effects of PN junction structure and process technology on solar cell performance were measured. Parameters for low-power and low-voltage implementation of power management strategy and boost converter based circuits utilizing fractional voltage maximum power point tracking (FVMPPT) algorithm were determined. The FVMPPT algorithm works based on the fraction between the maximum power point operation voltage and the open circuit voltage of the solar cell structure. This ratio is typically between 0.72 and 0.78 for commercially available poly crystalline silicon solar cells that produce several watts of power under typical daylight illumination. Measurements showed that the fractional voltage ratio is much higher and fairly constant between 0.82 and 0.85 for on-chip mono crystalline silicon micro solar cell structures that produce micro watts of power. Mono crystalline silicon solar cell structures were observed to result in better power fill factor (PFF) that is higher than 74% indicating a higher energy harvesting efficiency.

Super Dielectric Materials.

Evidence is provided here that a class of materials with dielectric constants greater than 105 at low frequency (<10−2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 108 in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 104. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc.), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to “short” the individual water droplets. Potentially NPS capacitor stacks can surpass “supercapacitors” in volumetric energy density.

Alginic Acid As a New Aqueous Slurry-Based Binder for Cathode Materials of Lib

Lithium-ion batteries (LIBs) are one of the most promising energy sources for use in portable electric devices or automotive applications because of their high energy density. In commercial LIBs, poly(vinylidene fluoride) (PVdF) is widely used as binder for positive electrode (cathode) due to its enough mechanical properties, relatively high oxidation durability and good electrochemical stability.However, a large amount of PVdF binder (over 5 wt.%) is needed to obtain an electrode with enough adhesion strength, which also has disadvantage of high cost. Moreover, N-methyl-2-pyrrolidone (NMP), which is commonly used as dispersant for PVdF, suffers from the safety problem as they are toxic as well as flammable. Thus, the switching from a using PVdF/ NMP to an aqueous-based system is desired.Recently, it has been reported that CMC can be promising aqueous-based binder for a cathode.[1-2] However, few articles discuss its long-term cycle performance depending on the pH value of aqueous slurry, which is important because Al current collector is not stable in a strong alkaline solution.In this work, we report a new aqueous-based cathode by using alginate as a binder. Alginate is natural polymer, which is categorized as polysaccharide derived from brown seaweeds. In our previous study, we reported on the LIB performance of carbon anode with Alg-salt binder both in organic and ionic liquid electrolyte systems, and showed its excellent cycle performance. Here, we propose another idea: using alginic acid (AlgH) as an aqueous slurry-based binder for a cathode. Because the AlgH is soluble only in alkaline water (It is insoluble in pure water), we successfully obtained the pH-controlled aqueous slurry by an acid-base reaction between AlgH and alkali cathode-material-surface (exchange between H+ and Li+). The present LIB cell with the cathode with AlgH binder exhibited excellent cycle performance that is comparable to that with conventional PVdF binder. Thus we believe that AlgH is a promising candidate as an aqueous slurry-based binder for a cathode of LIB.The NMC(LiNi1/3Co1/3Mn1/3) cathode was prepared by mixing 90 wt.% carbon material, 8 wt.% conductive agent (carbon black), and 2 wt.% AlgH binder, which were dispersed in pure water. The resulting slurry was cast onto Al foil and dried at 120 ̊C for 12 h under a vacuum condition. The obtained electrode film was punched to be a disk shape with a diameter of 12 mm for the LiB cell test. For comparison, the NMC cathode with PVdF binder (dispersed in NMP) was also prepared. A carbon (graphite) anode was also prepared for full test cell assembly. The electrolyte used was 1mol dm-3 LiPF6 in EC:DMC (1:1 by volume). The electrochemical measurements were carried out on coin-type cells CR2032. Figure 1 shows the performance of charged and discharged full cell composed of the NMC cathode with the AlgH binder at 1C rate (1C = 150 mAg-1) and maximum operation voltage of 4.5 V. It exhibits excellent charge discharge behavior with a reasonable discharge capacity. The observed high coulombic efficiency proves that AlgH is stable without its any oxidative decomposition even at a high operation voltage of 4.5V. In addition, this result also suggests that corrosion of Al foil that significantly affects the cycle performance should be negligible. Thus, the present results suggest that AlgH acts as not only aqueous-based binder but also pH regulator. Actually, estimated pH of slurry with AlgH was 8.4, which is an acceptable value for Al since the corrosion of Al occurs in stronger alkaline solution (pH > 10).[3]Another merit of using AlgH is that we can reduce the amount of binder component. We successfully prepared the cathode with adequate mechanical property only by using 2 wt.% of AlgH. As for a conventional cathode with PVdF, however, a large amount of binder, more than twice as much as AlgH, is need to achieve adequate mechanical properties (especially adhesion strength). The present results demonstrate that AlgH is a promising candidate for binder material useful for high-voltage LIB cathodes.Figure.1 Cycle performance of full cell with NMC-based cathode based on AlgH binder at maximum operation voltage of 4.5 V. Rate: 1C = 150 mA g-1.

The Influence of Anion–Cation Combinations on the Physicochemical Properties of Advanced Electrolytes for Supercapacitors and the Capacitance of Activated Carbons

AbstractThis work represents a systematic study of four conductive salts and their influence on the physicochemical properties of propylene‐carbonate‐based electrolytes for electrochemical double‐layer capacitors (EDLCs). State‐of‐the‐art tetraethylammonium tetrafluoroborate is compared with tetraethylammonium bis(trifluoromethanesulfonyl)imide, N‐butyl‐N‐methylpyrrolidinium tetrafluoroborate, and N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide. By applying these salts, operating voltages of up to 3.5 V can be achieved while retaining a high performance. Furthermore, the influence of the conductive salts on the carbon–electrolyte interface is studied by comparing the electrochemical performance of five commercial porous carbons in the respective electrolytes. The choice of conductive salt has a great influence on the electrochemical performance and maximum operating voltage of an EDLC system, as well as on the specific capacitance of the chosen carbon material; this makes the choice of both materials crucial for successful EDLC design.

Bi-Helix SWS for High-Power TWTs

We have studied the electromagnetic properties of bi-helix slow-wave structures (SWSs) with added azimuthal conductors in the form of: 1) metal rings connecting the helices and 2) an azimuthally conducting screen formed by metal rings with and without capacitive gaps. We show that these added azimuthal conductors suppress backward-wave oscillation and enable stable high-voltage, high-power operation of traveling-wave tubes (TWTs). Prototype circuits were fabricated and the dependence of phase velocities of the in-phase (fundamental) and opposite-phase (BWO) modes on frequency and on the geometrical parameters of the rings were measured and analyzed. Novel, easily fabricated designs of bi-helix SWSs with circular metallization on diaphragm supports are proposed. These practical designs will make it possible to increase the maximum stable operating voltage of wideband TWTs to 30-40 kV, with a corresponding increase in output power without the danger of BWO.

Influences of low-temperature postdeposition annealing on memory properties of Al/Al2O3/Al-rich Al-O/SiO2/p-Si charge trapping flash memory structures

Charge trapping flash (CTF) memory structure was fabricated on a SiO2/p-Si substrate using Al-rich Al-O as a charge trapping layer. Capacitance–voltage curves of the specimen indicated a large memory window width of 4.8 V with a maximum operation voltage of 7 V due to the charge trapping in the Al-rich Al-O layer. With N2 postdeposition annealing treatment at 350 °C, charge retention characteristics of the CTF memory structure were drastically improved without any serious loss in charge trap density. Furthermore, the proposed structure showed excellent memory characteristics, such as endurance and stable data retention even at 100 °C.