Voltage Hold Research Articles

Cycle versus voltage hold – Which is the better stability test for electrochemical double layer capacitors?

The stability of electrochemical double layer capacitors (EDLC) utilizing an ionic liquid and tetraethylammoninium tetrafluoroborate (TEABF4) in acetonitrile electrolyte was tested by cycling and by constant voltage hold tests. It turned out that possible degradation of the EDLC is visible in the voltage hold test after a time period which is typically much shorter if compared to the cycle tests. A constant capacitance during several thousands of cycles does not necessarily indicate stability. For capacitor cells using a carbon black as active material and an ionic liquid as electrolyte constant capacitance could be demonstrated over 12,000 cycles between 0 V and 3.75 V. Clear ageing was observed, however, during the voltage hold test at 3.75 V after 300 h. For a maximum voltage of 3.5 V both the cycle and the voltage hold test indicated stable performance over 12,000 cycles or 500 h, respectively. For capacitors using an activated carbon as active material and standard electrolyte TEABF4 in acetonitrile both tests clearly demonstrated degradation for a maximum cell voltage of 3.5 V. The evolution of capacitance loss observed for the voltage hold test at 3.25 V is in good agreement with the degradation observed at 3.5 V for the voltage hold test.

The degradation mitigation effect of cerium oxide in polymer electrolyte membranes in extended fuel cell durability tests

In this work, two formulations of cerium oxide nanoparticles were incorporated into perfluorosulfonic acid membrane electrode assemblies (MEAs) and their ability to improve the in-situ membrane durability was studied by subjecting them to 94 and 500 h open-circuit voltage hold accelerated durability tests. In the shorter test the open circuit voltage decay rate was reduced by half and the fluoride emission by at least one order of magnitude, though no effect on hydrogen crossover or performance on the baseline MEAs was measured. The presence of the additive increased the particle size but decreased the number of platinum catalyst particles that were deposited in the membrane. The main Pt band was found at the predicted location; however, the incorporation of ceria caused a broadening with particles reaching further into the membrane. In 500 h tests, ceria-containing MEAs demonstrated a seven-fold decrease in open-circuit voltage decay and three orders of magnitude reduction in fluoride emission rates with unchanged performance and hydrogen crossover, remaining effectively pristine whilst the baseline MEA underwent catastrophic failure.

One Way of Output Voltage Hold Circuit Improvement at Low Resistance Comparator

One Way of Output Voltage Hold Circuit Improvement at Low Resistance Comparator The article presents a way of improvement the important performances of an electronic low resistance comparator. The practical usage of a realized instrument prototype shows some disadvantages: the time until the result appears at the display is to long (the stationary state establishing sequence should be shorter) because of the negative influence of parasitic voltages. Modification of output voltage hold circuit gives quite convenient instrument response time. The parasitic voltage disturbance is decreased to acceptable value, even though the comparator is modified for multirange measurement. The paper describes some details of a solution and its conformation in practical usage.

Radical (HO•, H• and HOO•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Formation of radicals, such as HO•, H• and HOO•, in the membrane of the polymer electrolyte fuel cell and their attack on perfluoroalkylsulfonic acid (PFSA) and poly(styrenesulfonic acid) (PSSA) ionomers was simulated based on a kinetic framework with H2O2 as “parent” molecule and with contaminating Fe as parameter. Analysis under quasi-steady state conditions yielded radical concentrations of around 10−19 M for H•, 10−16 M for HO• and 10−10 M for HOO•. H• is formed via the reaction of HO• with H2 dissolved in the membrane. The attack of the PFSA ionomer was assumed to proceed via weak carboxylic end-groups. The corresponding calculated fluoride emission rate (FER) showed good agreement with experimental data under ex situ Fenton test conditions. The predicted FER under fuel cell operating conditions was underestimated by 2–3 orders of magnitude. It is likely that degradation via side-chain attack is prevalent during open circuit voltage hold tests. The oxidative degradation of PSSA ionomer follows an entirely different pathway, because, in addition to α-hydrogen abstraction by HO•, the aromatic ring effectively scavenges HO• to form an OH-adduct. Follow-up reactions lead to chain scission and formation of a stable hydroxylated degradation product.

Mechanical Degradation Behavior of Recast Composite PFSA Membrane and Nafion® N-112 Membrane under OCV Condition

The authors report the mechanical degradation behavior of perfluorosulfonic acid (PFSA) membranes under open circuit voltage hold condition. The degradation behavior of an ePTFE reinforced PFSA membrane impregnated with phosphotungstic acid (PTA) in cesium form was compared with that of an extruded Nafion® N-112 membrane. Membrane electrode assemblies were fabricated by spraying carbon supported platinum catalysts on either side of the membrane. Diagnostic tests were conducted before and after 100 hours of OCV hold period. Mechanical tests were performed on as-fabricated MEAs and MEAs after OCV hold test. The PTA additive was found to be very effective in reducing fluoride emission rates. However, the mechanical strength decay for both type of membranes remains significant. The composite membrane retained a comparatively higher level of residual toughness than the N112 membrane. SEM analysis revealed localized cracks form inside the membranes as a result of OCV hold.

Minimum Energy Actuation and Bounce-Back Behavior of Microbeams Using $\delta$ Voltage Pulses

Minimizing impact force during actuation reduces damage to contacting surfaces. An electrostatic actuation method for creating a soft contact between dielectric and semiconductor surfaces is described and applied to cantilevers and clamped beams. The method utilizes a short high-voltage delta-pulse followed by a low dc hold voltage to pull in the cantilever or beams. Removal of the hold voltage releases the beam back to its rest position. The height and the shape of the delta-pulse control the energy transferred to the beams and are shown to be critical in predicting minimum actuation voltages. Actuation pulses with heights even a few tenths of a volt above minimum can lead to stuck devices, whereas minimum pulses do not. The actuation method has been experimentally tested, and a simplified mathematical model has been simulated to confirm the experiment results. In addition, it is observed that a high-voltage actuation pulse applied for a longer time than necessary to actuate, but in phase with the apparent elastic response of the beam, will cause the beam to bounce upward rather than stick during actuation.

Membrane degradation mechanism during open-circuit voltage hold test

A detailed analysis is made of the relation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open-circuit voltage (OCV) hold test. Molecular-structural changes in the membrane are investigated by micro-Raman spectroscopy. When the Pt band was not significantly observed in the membrane after the test, the membrane is relatively stable. In contrast, when the Pt band was clearly formed, the membrane around it was intensively degraded. The magnitude of the fluoride ion emission rate (FER) of the effluent water from the anode and the cathode was also consistent with the location of the Pt band. It was verified that the Pt band is one of the factors accelerating membrane degradation, and the catalyst materials strongly affects the degradation. Besides, not the cation transport which enhances the degradation but the kinetics of either the H 2O 2 and/or hydroxyl radical production might be the rate determining step.

Analysis of Membrane Degradation Behavior During OCV Hold Test

A detailed analysis was made of the relation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open circuit voltage (OCV) hold test. Molecular-structural changes in the membrane were investigated by micro-Raman spectroscopy. When the Pt band was not significantly observed in the membrane after the test, the membrane was relatively stable. In contrast, when the Pt band was clearly formed, the membrane around it was intensively degraded. The magnitude of the fluoride ion emission rate (FER) of the effluent water from the anode and the cathode was also consistent with the location of the Pt band. It was verified that the Pt band is one of the factors accelerating membrane degradation.

Membrane Degradation Behavior during Open-Circuit Voltage Hold Test

The correlation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open-circuit voltage hold test was studied. The degradation behavior was investigated by measuring the fluoride ion emission in the effluent water from the anode and the cathode for various gas compositions at both electrodes. The results showed that the fluoride ion emission rate (FER) varied in accordance with the gas compositions. Cross sections of the tested MEAs were observed using a transmission electron microscope. It was found that the location of the Pt band correlated with the magnitude of the FERs. The Pt band was located close to where the mixed potential in the membrane, which was determined by the gas compositions, changed dramatically.

Data Retention and Readout Degradation Properties of Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si Structure Ferroelectric-Gate Field Effect Transistors

We discuss the data retention and readout degradation properties of ferroelectric-gate field-effect transistors (FeFETs) with Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si structures. We first point out that to read out the stored data correctly, unselected FeFETs should be turned off during the readout process and that this process causes a significant reduction of ON readout current. We next characterize the data retention properties of Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si structure n-channel FeFET by taking the readout process into account. It is shown that the retention property measured by applying positive readout pulses after holding at VG=0 V for 30 s, is similar to that measured by the conventional method in which drain current is continuously measured at a positive hold voltage.

A Soft-Landing Waveform for Actuation of a Single-Pole Single-Throw Ohmic RF MEMS Switch

A soft-landing actuation waveform was designed to reduce the bounce of a single-pole single-throw (SPST) ohmic radio frequency (RF) microelectromechanical systems (MEMS) switch during actuation. The waveform consisted of an actuation voltage pulse, a coast time, and a hold voltage. The actuation voltage pulse had a short duration relative to the transition time of the switch and imparted the kinetic energy necessary to close the switch. After the actuation pulse was stopped, damping and restoring forces slowed the switch to near-zero velocity as it approached the closed position. This is referred to as the coast time. The hold voltage was applied upon reaching closure to keep the switch from opening. An ideal waveform would close the switch with near zero impact velocity. The switch dynamics resulting from an ideal waveform were modeled using finite element methods and measured using laser Doppler vibrometry. The ideal waveform closed the switch with an impact velocity of less than 3 cm/s without rebound. Variations in the soft-landing waveform closed the switch with impact velocities of 12.5 cm/s with rebound amplitudes ranging from 75 to 150 nm compared to impact velocities of 22.5 cm/s and rebound amplitudes of 150 to 200 nm for a step waveform. The ideal waveform closed the switch faster than a simple step voltage actuation because there was no rebound and it reduced the impact force imparted on the contacting surfaces upon closure

Phenomenon Analysis of PEFC for Automotive Use(1) Membrane Degradation Behavior During OCV Hold Test

The correlation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open circuit voltage (OCV) hold test was studied. It was found that the location of the Pt band correlated with the magnitude of the FERRs. The Pt band was observed close to where the mixed potential in the membrane, which was determined by the gas compositions, changed dramatically.

Capacitor matching insensitive algorithmic ADC requiring no calibrations

A novel implementation of the algorithmic ADC is proposed in this paper. The ADC is based on an algorithmic 1.5-bit stage in which voltage multiplication is replaced by voltage addition. A floating voltage hold circuit is proposed which enables the accurate addition of signal voltages without requiring precision components. An experimental 12 bit 3.3 MS/s algorithmic ADC in 0.25 μm standard CMOS is described. It occupies 0.15 mm 2 of die area and dissipates 5.5 mW. The power and area FOMs are well below those previously reported for 1.5-bit stage algorithmic ADCs.

Comparison of the energy performance of pulse generation circuits for PEF

Pulse shaped voltages are required for preservation of food with PEF. Several pulse forms generated by a variety of circuits are compared with respect to required energy. The analysis includes square pulses, trapezoidal pulses, exponential decay pulses and oscillatory and over-damped oscillatory pulses. The base of comparison is the establishment of a certain minimum voltage level during certain minimum time. The comparison concerns the dissipation in a resistive load, which is considered to be representative for a category of loads, including PEF. Furthermore, the ratio between initial capacitor voltage and corresponding threshold voltage is compared as this parameter reflects the required hold voltage of the switch in the circuit. The analysis shows that the efficiency approaches 100% for hard switched circuits and circuits with transmission lines. For highly damped RLC-circuits with capacitor C, inductor L and load resistance R the maximum obtainable efficiency is between 37 and 47% where the capacitor C has to be charged to 1.6–1.8 times the desired threshold voltage. For oscillating damped sinusoids the maximum efficiency is between 47 and 52%, however, the capacitor has to be charged to 1.8–3 times the threshold voltage. Graphs with an example are provided to determine circuit parameters from a certain pulse specification.

Radio frequency plasma processing effects on the emission characteristics of a MeV electron beam cathode

Experiments have proven that surface contaminants on the cathode of an electron beam diode influence electron emission current and impedance collapse. This letter reports on an investigation to reduce parasitic cathode current loss and to increase high voltage hold off capabilities by reactive sputter cleaning of contaminants. Experiments have characterized effective radio frequency (rf) plasma processing protocols for high voltage anode–cathode (A–K) gaps using a two-stage argon/oxygen and argon rf plasma discharge. Time-resolved optical emission spectroscopy measures contaminant (hydrogen) and bulk cathode (aluminum) plasma emission versus transported axial electron beam current turn on. Experiments were performed at accelerator parameters: V=−0.7 to −1.1 MV, I(diode)=3–30 kA, and pulse length=0.4–1.0 μs. Experiments using a two-stage low power (100 W) argon/oxygen rf discharge followed by a higher power (200 W) pure argon rf discharge yielded an increase in cathode turn-on voltage required for axial current emission from 662±174 kV to 981±97 kV. The turn-on time of axial current was increased from 100±22 to 175±42 ns.

Electrical Properties of CdSe Photovoltaic Electrodeposits in a Marine Environment

Semiconductive thin ®lms of CdSe prepared by electrodeposition have been tested under corrosive conditions in a saline atmosphere and their electrical properties (I±V curves) measured before and after exposure. The preparation conditions of CdSe electrodeposits have been studied [1±6], as have their substrate effects [7]. They are intended for photovoltaic generation of electricity, and they have a direct band gap ranging between 1.35 and 1.75 eV following the sample composition. They also present good electrical properties (such as carrier mobility and long lifetime), high absorption coef®cients in the visible and infrared part of the solar spectrum and relative stability against corrosion when used in polychalcogenite solutions. In this letter, the electrical properties of the surface of CdSe deposits exposed to corrosive conditions in a NaCl environment are presented. The deposits were prepared under potentiostatic control in a three-electrode setup in an acidic solution typically containing 1.5 mmol ly1 of selenium oxide and 0.2 mol ly1 of cadmium sulfate with a pH of 2.2. The electrolytic bath contained ethylene glycol (1=3) to obtain the required temperature of 113 8C. Rotating disc electrodes of nickel cylinders (10 mm diameter) were used. The counter electrode was a at carbon surface, and the reference was a Cd electrode. The deposition voltage used was y102.5 mV at 0.5 mA. The deposits were exposed in a salt spray chamber with a continuous spraying of a 5% NaCl solution, for 1 month, at 30 8C. The surface of the specimens was examined by scanning electron microscopy (SEM), and a typical micrograph is shown in Fig. 1. The surface stays smooth but cracks are created at speci®c sites that are found by electron dispersive analysis (EDA) a higher content of nickel than that of the unexposed surface. Oxygen and chloride compounds are also encountered on the exposed sample. The deposits were examined by X-ray diffraction (XRD) before and after exposure (Fig. 2). The crystalline deposits of CdSe mainly exhibit a cubic blende structure with pronounced (1 1 1) preferred orientation instead of the normal hexagonal wurtzite structure (1 0 0). Profound differences were not found because the thicknesses of the formed layers are beyond the sensitivity of the method. An investigation of the I±V characteristics of the fabricated samples at a given illumination level before and after surface corrosion process was performed by employing a high-precision pA-meterDC voltage source instrument (HP4140B). In all cases, the d.c. voltage hold time and step recovery time (between successive bias-setting applications) was kept at a constant value of 0.1 ms for comparison purposes. Fig. 3 presents typical experimental results. The generalized I±V relationship of a photovoltaic cell, subjected to external polarity and illumination, is given by Equation 1 [8]:

Nuclear instrumentation for a soft X-ray detection system on a small satellite, CATSAT

Nuclear instrumentation has been designed and tested for a large field of view soft X-ray sensor utilizing Si avalanche photodiodes (APDs). The instrument will be launched on a low cost satellite mission in mid 1998. The mission's primary scientific objective is to determine the distance scale to the sources of cosmic gamma ray bursts by utilizing interstellar absorption effects observable in their X-ray emission at energies below 2 keV. The soft X-ray (SXR) sensor incorporates 7 identical panels, each with 16 APDs collectively collimated to a 1 steradian field of view. The SXR panels are radiatively cooled to -35 degrees C, and taken together, view a full hemisphere. The instrumentation for each of the sensors in the SXR detector includes a low noise, charge sensitive preamplifier/shaping amplifier and an analog electronics unit (AEU) containing a voltage amplifier, peak track and hold circuit, and threshold-timing logic. Each panel has an analog to digital interface (ADI) based on a field programmable gate array (FPGA), which controls the digitization of the event amplitudes, implements the in-flight calibration (IFC) for each APD, and coordinates the data output to and command input from the instrument CPU.

Electromyography with acrylic plug surface electrodes after delivery.

Pelvic floor neuromuscular function was evaluated with surface electromyography using acrylic plug electrodes and interactions between neuromuscular function and factors pertinent to the delivery process were explored. Fifty-two women who were primiparas participated in this prospective cohort study. Circumvaginal and circumrectal muscles were assessed. Corrected vaginal-rectal flicks and holds were calculated. The results were compared by delivery route, birthweight, race, lactational status, and delivery anesthetic and to a group of nulliparous subjects. The mean interval from delivery was 46.3 days. Birthweight, race, lactational status, and anesthetic technique were not associated with statistically significant changes in electrical activity, although our ability to detect such differences was low due to the small number of subjects. Women who delivered vaginally had lower vaginal flick voltage than those delivering abdominally. Women who delivered vaginally had lower vaginal flick and hold voltages and rectal flick voltage when compared with nulliparous women studied earlier. Abdominally delivered women had values similar to the nulliparous group. Women delivering vaginally had less surface electromyographic activity in the circumvaginal muscles, implying that vaginal delivery impairs the neuromuscular function of the pelvic floor.

New analog memory devices demonstrated using heterojunction acoustic charge transport device technology

A new analog memory (AM) has been demonstrated using heterojunction acoustic charge transport (HACT) technology. The initial HACT AMs had storage time capabilities of 100 μs at 25 °C. The Schottky electrode storage array had 36 memory cells, each cell holding 2 charge packets, giving a maximum signal frequency of half the Nyquist frequency. Hold voltages in the 6–8 V range were found to be adequate, and effective storage was obtained at the same dc transport current level that resulted in the best charge transport efficiency. Storage times in the millisecond range are possible with cooling.

Experiments with high-voltage insulators in the presence of tritium

During the final deuterium-tritium phases of the TFTR and JET tokamaks half of the neutral injectors will be used to produce tritium neutral beams to maintain an equal mix of deuterium and tritium in the core plasma, and such requirements may also occur in future devices. This will require that the voltage hold off capabilities of the high voltage insulators in the accelerators be unimpaired by any charge buildups associated with the beta decay of adsorbed layers. We report tests in which we measured the drain currents under high dc voltage of TFTR and JET accelerator insulators while they were successively exposed to vacuum, deuterium and tritium. There did not appear to be any substantial reduction in hold-off capability with tritium, although at some voltages there was a small increase in the leakage current. We also compared the breakdown properties of a plastic tubing filled with deuterium and then tritium at varying pressures, since such tubing has been considered as a high-voltage break in the gas feed system for TFTR, and the presence of large numbers of electron-ion pairs might lead to enhanced Paschen breakdown. We found no significant differences in the behavior for the geometry used.