Amplitude Of Voltage Pulse Research Articles

Electrical stimulation of microengineered skeletal muscle tissue: Effect of stimulus parameters on myotube contractility and maturation.

Skeletal muscle tissues engineered in vitro are aneural, are short in the number of fibres required to function properly and degenerate rapidly. Electrical stimulation has been widely used to compensate for such a lack of neural activity, yet the relationship between the stimulation parameters and the tissue response is subject to debate. Here we studied the effect of overnight electrical stimulation (training) on the contractility and maturity of aligned C2C12 myotubes developed on micropatterned gelatin methacryloyl (GelMA) substrates. Bipolar rectangular pulse (BRP) trains with frequency, half-duration and applied pulse train amplitudes of f=1Hz, ton =0.5ms and Vapp ={3V, 4V, 4.5V}, respectively, were applied for 12h to the myotubes formed on the microgrooved substrates. Aligned myotubes were contracting throughout the training period for Vapp ≥4V. Immediately after training, the samples were subjected to series of BRPs with 2≤Vapp ≤5V and 0.2≤ton ≤0.9ms, during which myotube contraction dynamics were recorded. Analysis of post-training contraction revealed that only the myotubes trained at Vapp =4V displayed consistent and repeatable contraction profiles, showing the dynamics of myotube contractility as a function of triggering pulse voltage and current amplitudes, duration and imposed electrical energy. In addition, myotubes trained at Vapp =4V displayed amplified expression levels of genes pertinent to sarcomere development correlated with myotube maturation. Our findings are imperative for a better understanding of the influence of electrical pulses on the maturation of microengineered myotubes.

The Role of Oxygen Vacancy Mobility at the Oxide Bulk and Electrode Interfaces for Ceria-Based Memristive Devices

Resistive switching is a recently extensively studied phenomenon for use in non-volatile memories as promising building blocks of future electronics. In such devices transition metal oxides are operated at high electric field strengths to initiate non-linear and hysteretic current-voltage relations that can be addressed in their various resistance states by voltage pulse amplitude or polarity. Despite the known importance of oxygen vacancy defects in metal-oxide memristive devices, systematic strategies on tuning their concentration and mobility in the transition metal oxide are rare. In this work, we utilized the fluorite-type ceria-gadolinia binary system Ce1-xGdxO2-x/2 (GDC) to tune the oxygen vacancy concentration in order to correlate structure and defect chemistry to the memristive properties. The mixed conduction of GDC is well investigated at high temperature, and it is possible to extrinsically dope over the wide range of 3 to 30 mol% Gd; however, has only recently been reported for ambient and high electric fields1. Therefore, we can tune the oxygen vacancy concentration, migration and association energy by the acceptor dopant as a model system to directly investigate the influence on resistive switching. For this purpose Pt-GDC-Pt sandwich structures were fabricated as resistive switching devices with cross-bar electrodes. Based on hysteretic current-voltage profiles, a maximum in resistive switching (with ROFF/RON up to 100) is found for the best ion conducting2 20 mol% Gd-doped CeO2. In-operando Raman spectroscopy revealed a homogeneous reduction of the ceria film during electroforming, together with a strong increase in conductivity. Additional high energy XPS measurements we observe the electrostatic potential drop at the electrode-oxide interface. These experimental results directly prove that the electronic charge carriers generated by the formation and redistribution of oxygen vacancies at high electric fields is the origin of memristance in doped ceria films, and that the switching happens in a rather homogeneous manner. The importance of oxygen vacancy migration in our model is further verified by the doping study. Doping levels of 10-20 mol% resulted in good switching properties, whereas for low (<10 mol%) and high (>20 mol%) concentrations no resistive switching is observed. In both cases the number of mobile oxygen vacancies is not sufficient, either because of the low extrinsic doping level, or because of the formation of bixbyite-like domains with ordered or clustered "immobile" oxygen vacancies. This clustering is observed by the appearance of new vibrational modes in Raman spectroscopy due to the reduced symmetry in a defective crystal. Excitingly, one can study based on the findings the direct implication of "free" oxygen vacancies at low and high mobilites and also of "trapped" clustered vacancies on both, resistive switching and also local structural symmetry breaks3. In conclusion, we observed a clear correlation of oxygen vacancy mobility and switching characteristics. We suggest that a high concentration of mobile oxyen vacancies is of general importance when designing oxide materials for future computing applications.

Electrooptical effect in the plasmon structure glass–In2O3: Sn–ferroelectric–Al with a subwavelength grating

The spectral features of the electrooptical effect, in which an applied voltage changes the refractive index of a ferroelectric copolymer, are studied. Three nanostructures are investigated: two nanostructures play an auxiliary role, and the basic structure consists of a glass substrate, a transparent ITO (In2O3: Sn) layer, active copolymer layer, and an Al layer with a nanograting. This grating with a period of 400 nm meets the conditions of excitation of plasmon resonances. The light transmission coefficients of all structures are analyzed in the spectral range 400–900 nm. The transmission spectra have two characteristic plasmon dips, one of which is related to the copolymer–ITO interface and the other, to the copolymer–Al interface. The aluminum and ITO layers play the role of electrodes, which supply voltage pulses (from 0 to 15 V) to the copolymer layer. When studying the electrooptical effect, we detected spectral shifts in plasmon resonance bands when the amplitudes of both positive and negative voltage pulses (quadratic effect) increase. These shifts change the effective refractive indices (n eff) of the structural elements, reaching the minimum negative increment Δeff =–0.06.

Effects of resistive switching in Au/FeOx/Pt structures

The dynamics of forming and resistive switching in Au/iron oxide/Pt structures based on magnetite (Fe3O4) is investigated. It has been revealed that these processes have an electrochemical nature and are accompanied by formation of low-resistance conductive filaments formed by inclusions of magnetite in the matrix of high-resistance maghemite (γ-Fe2O3). It has been found that the electric field stimulates reversible redox reactions in iron oxide. The direction and rate of these reactions are determined by the polarity and the amplitude of voltage pulses. The possibility of setting the resistance of the structure by changing the amplitude of the “record” voltage pulses opens prospects for the development of multilevel memory elements.

Compact Nanosecond Magnetic Pulse Compression Generator for High-Pressure Diffuse Plasma Generation

We report on the development of a low-cost, adjustable high-voltage/high-power nanosecond-pulse generator for diffuse plasma generation in a high-pressure gas-discharge cell. The generator produces scalable impulsions of 0–40 kV, at an adjustable pulse-repetition frequency up to 7 kHz. Details pertaining to its working principles, electrical architecture, components, and specifications are presented. Voltage and current pulses are measured for resistive loads of 1.5 $\text{k}\Omega $ to 5 $\text{M}\Omega $ . The energy per pulse along with the generator’s overall efficiency is presented as a function of the input voltage. A maximum value of 13.5 mJ/pulse can be delivered to a 3- $\text{k}\Omega $ load. Our preliminary investigation using a pin-to-plate geometry in air and at pressures up to 2.75 atm [280.5 kPa] demonstrates the production of uniform diffuse plasma volumes. The domain of existence of the diffuse plasma regime is briefly explored, as a function of pressure and voltage pulse amplitude.

Characteristic radiation of nitrogen under subnanosecond breakdown in a highly nonuniform electric field near the positive-polarity electrode

Results are presented from experimental studies of elevated-pressure diffuse discharge in a highly nonuniform electric field. It is shown that, in discharges in nitrogen and air, the characteristic radiation (the K-line of nitrogen) is generated at the positive polarity of the electrode with a small curvature radius. X-ray bremsstrahlung from the anode was detected in a discharge in atmospheric-pressure air at a 12-kV amplitude of the incident voltage pulse.

Effect of voltage amplitude on gas density variation in an atmospheric pressure streamer discharge

Gas density variation in an atmospheric-pressure streamer discharge was visualized using the Schlieren method and was simulated by a two-dimensional axisymmetric simulation. The Schlieren images visualized the occurrence of shock waves and decrease in the gas density after the discharge. The axial distribution of the gas density was compared between experimental and simulation models, and we found that the two were in good agreement. Additionally, this paper discusses the effect of the pulse voltage amplitude on the decrease in the gas density. Our simulation results show that the pulse voltage amplitude affects the ratio of energy loss fractions of electrons by electron-impact collision processes.

A High-Voltage Pulse Generator With Continuously Variable Pulsewidth Based on a Modified PFN

The amount of stored energy is an important issue in the low-droop and high-precision pulse generation. Pulse forming network (PFN) simulating an open-ended transmission line seems to be useful due to its minimum stored energy. The drawbacks of the PFN include low-output pulse quality and constant pulsewidth, which limit their applications. Another limitation of generating rectangular pulses using PFN is that half of the charged voltage appears in the output when delivering the entire stored energy to the matched load. This paper proposes a structure of PFN-based pulse generator that overcomes the above-mentioned limitations. For continuous pulsewidth adjustment, a lossless scheme is presented. By increasing the ratio of the load magnitude to the characteristic impedance, the amplitude of the output pulse voltage would be approximately equal to that of the charged voltage. Therefore, the semiconductor switches can be utilized in the PFN pulse generator easily. In addition, the pulse quality is enhanced and faster rising time is obtained in comparison with the conventional PFNs. In this proposal, the stored energy quantity is limited to three times the energy needed for the output pulse in the case of $R_{L}=10Z_{0}$ . To verify the proposed structure, a prototype is simulated using PSPICE software, and the experimental results are presented.

Energy compression of nanosecond high-voltage pulses based on two-stage hybrid scheme.

Test results of high-voltage subnanosecond pulse generator with a hybrid, two-stage energy compression scheme are presented. After the first compression section with a gas discharger, a ferrite-filled gyromagnetic nonlinear transmitting line is used. The offered technical solution makes it possible to increase the voltage pulse amplitude from -185 kV to -325 kV, with a 2-ns pulse rise time minimized down to ∼180 ps. For the small output voltage amplitude of -240 kV, the shortest pulse front of ∼85 ps was obtained. The generator with maximum amplitude was utilized to form an ultra-short flow of runaway electrons in air-filled discharge gap with particles' energy approaching to 700 keV.

Surface charge coupling behavior of fluorinated polyimide film under DC and pulse voltage

Polyimide (PI) films have excellent electrical, mechanical and thermal properties in aspect of resisting corona, aging and radiation. However, the pulse voltage combined with dc voltage often causes concentration of local electrical field, which makes the surface charge behaviors more complex and threatens the system. As a means of surface treatment, direct fluorination has been proved as an effective way to improve the polymer properties, without compositing the bulk characteristics. Therefore, this paper intends to reveal the effects of fluorination on surface charge coupling behaviors of the PI films under dc and pulse voltage combination. The PI samples fluorinated for 0, 15, 45 and 60 min were obtained. Surface corona discharging was stressed under the combination of dc and pulse voltage. The surface charge accumulation, decay and distribution were measured coupled with an analysis of trap distribution. The results show the surface charge dynamic behaviors are strongly correlated with the fluorination time, pulse voltage amplitude and polarities of the dc and pulse voltage combination. The trap distribution results imply that the effect of fluorination and charging condition attribute to the change of trap depth and amount. Besides, surface charge behaviors are greatly improved by appropriate fluorination.

Compact solid-state Marx-bank sub-nanosecond pulse generator based on gradient transmission line theory

For non-invasive treatments in the biomedical field, sub-nanosecond pulse electric field matching ultra-wideband antennas have aroused great interest for their excellent directivity and targeted treatment. Sub-nanosecond pulse generators have proved difficult to control in pulsed power technologies despite many studies of pulse generators based on avalanche transistor theory and the Marx circuit. However, no solution exists to the problems of non-ideal waveform of the output sub-nanosecond pulse and the relatively low effectiveness of the Marx circuit. To resolve these problems, the paper describes a sub-nanosecond pulse generator simulation model based on gradient transmission line theory in PSPICE simulation software and the development of a compact solid-state sub-nanosecond pulse generator (18 cm×18 cm×4 cm). From experimental tests, trigger signals of 5-V amplitude, 5-ns rise and fall times (pulse-width 10 ns-50 ns) were generated by Field-Programmable Gate Array (FPGA). A pulse with 1600-V voltage amplitude, 300-ps full width at half maximum, 150-ps rise time, and 10-kHz high-stability repetition rate was generated in an attenuator load with high-bandwidth (8 GHz, 50 Ω). The effectiveness (Output pulse voltage amplitude / Charge voltage × Stages) of this Marx circuit reached to 41.7%, improving considerably on previous efforts.

Plasma jet seven-array discharge at atmospheric helium gas

A low temperature plasma jet array device using seven single electrodes surrounded with insulated organic glass is designed to study the discharge properties of atmospheric plasma jet. The ambient gas is atmospheric Helium gas, whose flow rate is controlled from 0 L/min to 10 L/min. This discharge device is driven by a sub-microsecond repetitive high voltage pulsed power with the pulse width about 230 ns, the rising edge about 120 ns. Using a repetitive frequency rate about 500 Hz, the high speed photographs are taken and the current pulse width is about 110 ns. The average jet length was measured under the conditions of changing gas flow rate and pulse voltage amplitudes in the experiment, in order to acquire the interactions of every plasma jet discharge. It is found that the average plasma jet length increases with the increasing voltage amplitude when the voltage amplitude is less than 20 kV and that it increases slowly when the voltage amplitude is higher, up to 35 kV. It is also found that the average jet length reaches the maximum when the gas flowrate is at a regular value, that is, the average length decreases if the gas flowrate is over or under the regular range. Besides, it is also discovered that the central electrode discharge is affected extremely by the gas flowrate. The central jet length is almost invisible when the gas flowrate is very high or very low, while the central jet with a weak discharge is longer than the surrounding jets when the gas flow rate is 1 L/min. The main reasons are that the air blocks the jet developing and the central electrode jet channel is impeded by the surrounding jets. It is easier for the surrounding electrode to develop jets.

A comparative experimental kinetic study of spontaneous and plasma-assisted cool flames in a rapid compression machine

Plasma-assisted cool flames of n-heptane were generated in the combustion chamber of a rapid compression machine coupled with a nanosecond dielectric barrier discharge, at a pressure of 1.5bar and temperature TC=650K. Increasing of the voltage pulse amplitude at the electrode resulted in a transition from no reactivity to induced cool flame and then to fast ignition. Sampling of the reacting mixture was performed at selected times during the experiments to draw mole fraction profiles of the fuel and major low temperature stable intermediates, showing a gradual increase in the mole fraction of these species after the discharge. Comparison with a spontaneous cool flame case at a slightly higher pressure shows that no new species are formed in the plasma-assisted case, and that after the initiation of reactivity by the discharge at the nanosecond timescale, the distribution and relative importance of the main reaction pathways is conserved at the millisecond timescale. Differences in the shape of the mole fraction and light emission profiles however suggest that the plasma-assisted cool flame is propagative.

A new method for compensation of the effect of charging transformer's leakage inductance on PFN voltage regulation in Klystron pulse modulators

The Line type modulators have been widely used to generate high voltage rectangular pulses to power the klystron for high power RF generation. In Line type modulator, the Pulse Forming Network (PFN) which is a cascade combination of lumped capacitors and inductors is used to store the electrical energy. The charged PFN is then discharged into a klystron by firing a high voltage Thyratron switch. This discharge generates a high voltage rectangular pulse across the klystron electrodes. The amplitude and phase of Klystron's RF output is governed by the high voltage pulse amplitude. The undesired RF amplitude and phase stability issues arises at the klystron's output due to inter-pulse and during the pulse amplitude variations. To reduce inter-pulse voltage variations, the PFN is required to be charged at the same voltage after every discharge cycle. At present, the combination of widely used resonant charging and deQing method is used to regulate the pulse to pulse PFN voltage variations but the charging transformer's leakage inductance puts an upper bound on the regulation achievable by this method. Here we have developed few insights of the deQing process and devised a new compensation method to compensate this undesired effect of charging transformer's leakage inductance on the pulse to pulse PFN voltage stability. This compensation is accomplished by the controlled partial discharging of the split PFN capacitor using a low voltage MOSFET switch. Theoretically, very high values of pulse to pulse voltage stability may be achieved using this method. This method may be used in deQing based existing modulators or in new modulators, to increase the pulse to pulse voltage stability, without having a very tight bound on charging transformer's leakage inductance. Given a stable charging power supply, this method may be used to further enhance the inter-pulse voltage stability of modulators which employ the direct charging, after replacing the direct charging with the resonant charging.

Charge coupling behavior of double-layer oil-paper insulation under dc and pulse voltages

An oil-paper insulation system which will withstand DC voltage under normal conditions is a key component of converter transformers as well as high voltage direct current (HVDC) bushings. When the system changes its state, operating overvoltage appears. This kind of overvoltage will consequently affect the application of oilimmersed facilities and the safety of entire grid. Therefore, this paper studies the charge coupling behavior of double-layer oil-paper insulation under DC and pulse voltages. From the research of different pulse voltage amplitudes, pulse numbers and polarity, conclusions can be drawn that, with the increase of the pulse voltage amplitudes, DC and pulse voltages in the same polarity cause the absolute value of the initial surface potential to decrease and then rise; while in different polarities, the charge with the same polarity as the pulse voltage increases. Furthermore, for the same pulse voltage, the absolute initial value of the DC voltage applied in the same polarity is higher than that in different polarities. Considering the pulse number effect, it is obvious that the initial value increases with the increase in the pulse number, and then reaches saturation. Also, with the increase in pulse number, the decay rate decreases and thus the charge is slowly dissipated. From the tdV/dt and the decay time curves, the peak value increases with the increase in the pulse number, while the characteristic time varies by the polarity of the DC and pulse voltages.

Influence of pulse line switch inductance on output characteristics of high-current nanosecond accelerators

Various types of high-current nanosecond accelerators are simulated numerically using an equivalent circuit representation. The influence of pulse forming line switch inductance on the amplitude and waveform of output voltage and current pulses is analyzed.

Fully printed memristors for a self-sustainable recorder of mechanical energy

Memristors have attracted significant interest in recent years because of their role as a missing electronic component and unique functionality that has not previously existed. Since the first discoveries of the existence of memristive materials, various different fabrication processes for memristors have been presented. Here, a simple additive fabrication process is demonstrated where memristors were deposited on a polymer substrate by conventional inkjet printing. The memristor structure was printed on a 125 μm thick polyethylene terephthalate (PET) substrate by sandwiching a thin layer of TiOx between two silver nanoparticle ink electrodes. Current–voltage (IV) characterization measurements were performed and they showed clear memristive behavior when voltage pulse amplitude varied between −1.5 V and 1.5 V. The corresponding resistance change is approximately between 150 Ω and 75 kΩ. In order to demonstrate the switching scheme in practical application, printed memristors and a printed voltage doubler were connected with a piezoelectric element. The element was subjected to impact-type excitation thus producing an electric charge that was able to switch the memristor between high and low resistive states. These results pave the way for an exploitation of cost-efficient, self-sufficient, all-printable memory elements for wide utilization in future electronics applications.

Colored Diffuse Mini Jets in Runaway Electrons Preionized Diffuse Discharges

Optical emission of the nanosecond diffuse discharge initiated by runaway electrons in an inhomogeneous electric field was investigated in a single-pulse and pulse-periodic modes in different gases (air, nitrogen, and argon). The amplitude of voltage pulses, pulse rise time, and interelectrode distance were, respectively, 200 kV, 0.5 ns, and 13 mm for single-pulse mode, and 13 kV, 4 ns, and 2 mm for pulse-periodic mode. In the single-pulse mode, the diffuse mini jets (DMJs) of different colors with lengths up to 7 mm appear near electrodes. Blue DMJs were observed near electrodes with a small radius of curvature made of a stainless steel. Red DMJs were observed near the grounded flat electrode made of aluminum and in the center of discharge gap near a spark channel. It was shown that radiation intensity of DMJs increased with the increase in nitrogen pressure up to 0.4 MPa, but subsequent increase in pressure up to 0.7 MPa led to the decrease in radiation intensity. In the pulse-periodic mode, colored DMJs are observed as well, the size of which was $\sim 1$ mm. In this mode, the spectral and amplitude-temporal parameters of the radiation of DMJs have been studied. It was shown that the color of DMJs is determined by the radiation of electrode metal vapors. It was shown that the DMJs originate from the bright spots (explosive centers) on electrodes.

Supershort avalanche electron beam inSF6and krypton

Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam (SAEB) generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride (${\mathrm{SF}}_{6}$) in an inhomogeneous electric field were studied. One pulser operated at negative polarity with voltage pulse amplitude of $\ensuremath{\sim}130\text{ }\text{ }\mathrm{kV}$ and rise time of 0.3 ns. The other pulser operated at negative polarity with voltage pulse amplitude of 70 kV and rise time of $\ensuremath{\sim}1.6\text{ }\text{ }\mathrm{ns}$. SAEB parameters in ${\mathrm{SF}}_{6}$ are compared with those obtained in krypton (Kr), nitrogen (${\mathrm{N}}_{2}$), air, and mixtures of ${\mathrm{SF}}_{6}$ with krypton or nitrogen. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers. Moreover, amplitudes of the SAEB current in ${\mathrm{SF}}_{6}$ and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in ${\mathrm{N}}_{2}$ and air (ranging from hundreds of milliamps to several amperes). Furthermore, the concentration of ${\mathrm{SF}}_{6}$ additive could significantly reduce the SAEB current in ${\mathrm{N}}_{2}\text{\ensuremath{-}}{\mathrm{SF}}_{6}$ mixture, but it slightly affected the SAEB current in $\mathrm{Kr}\text{\ensuremath{-}}{\mathrm{SF}}_{6}$ mixture because of the atomic/molecular ionization cross section of the gas had a much greater impact on the SAEB current rather than the electronegativity.

A high-power generator of nanosecond pulses with an amplitude of up to 500 kV and a repetition rate of up to 50 Hz

A pulsed-power high-voltage generator, which is combined with an electric-discharge chamber, is designed for selective disintegration of quartz raw minerals and other nonconductive natural and artificial materials. The main parameters of the generator are as follows: the voltage-pulse amplitude, up to 500 kV; the discharge-current amplitude, up to 30 kA; the duration of current pulses (the half-period an oscillatory discharge), 70–90 ns; and the pulse repetition rate, up to 50 Hz. The generator is characterized by a high efficiency, a long service life, the possibility of long continuous operation, and the fulfillment of the electromagnetic compatibility requirements. The experience of the operation of three constructed installations testifies to their high reliability: the number of accumulated pulses in a typical mode (450 kV, 20 Hz) exceeded 108 pulses without a repair or replacement of units.