Step-function Voltage Research Articles

Enhanced Electrochemical Hydrogenation of Benzaldehyde to Benzyl Alcohol on Pd@Ni-MOF by Modifying the Adsorption Configuration.

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal-organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm-2 h-1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency.

New horizontal and vertical field coils with optimised location for robust decentralized plasma position control in the IGNITOR tokamak

The paper deals with the improvement of the poloidal system of the IGNITOR tokamak, and the design and simulation of the robust decentralised control systems of the plasma’s vertical and horizontal position. The results were obtained on a linear model that is constructed from the circuit equations for the coils, plasma, and vacuum vessel (VV) currents, and from the force balance equations for the plasma. Two new coils that are located close to the VV have been introduced in the IGNITOR poloidal system; specifically, a Horizontal Field Coil (HFC) that is designated for the plasma vertical position control and a Vertical Field Coil (VFC) that is used for the horizontal position control. For the first time in the design of D-shaped tokamaks poloidal systems, the location of the HFC was optimised to achieve the maximum size of the plasma controllability region in the vertical direction and the location of the VFC was determined from the optimisation of the plasma position response to the voltage step function. Although the ideal position of the VFC with fast response time is on the equatorial plane, its location usually is occupied by the other devices such as ports, diagnostic system, and heating systems, so the separated two-section VFC is used. Careful calculation shows the performance is degraded by only 20 % in this layout. For the improved IGNITOR poloidal system, the new robust decentralised plasma position control systems were designed by means of two robust approaches: H∞-optimisation and Linear Matrix Inequalities (LMI). The results of the simulation of the control systems with two types of actuator models as the multiphase thyristor rectifier and the voltage inverter in Pulse- Width Modulation (PWM) mode for the new IGNITOR poloidal system are presented.

Anodic Aluminum Oxide-Based IR Emitter for High-Speed Infrared Scene Projector

Infrared scene projector (IRSP) is a tool for evaluating the performance of infrared (IR) sensors by generating and projecting virtual IR images. Developing IRSPs with a high frame rate is necessary to evaluate high-speed IR sensors. To develop IRSPs with high frame rates, porous anodic aluminum oxide (AAO) with high thermal conductivity is proposed as a constituent material of IR emitters, which emit infrared rays in IRSPs. Through structure design and fabrication, an AAO-based IR emitter having a suspended structure with a gap of $1~\mu \text{m}$ from the substrate was fabricated. The operating speed was obtained by confirming the change in the temperature, which was calculated by measuring the change in resistance after applying the step-function voltage. The operating speed of the AAO-based IR emitter was found to increase with decrease in the leg length of the device. The frame rate of the device with a $5~\mu \text{m}$ leg length was found to be 155.3 Hz, twice as fast as the conventional silicon nitride (Si3N4)-based emitters with the same leg length and pitch. Consequently, it is possible to develop the high-speed IRSPs with the application of AAO for emitter. [2019-0191]

A Bistable Comb-Drive Electrostatic Actuator Biased by the Built-In Potential of Potassium Ion Electret

A new bistable micro-electro-mechanical systems actuator functioned by the potassium ion electret technique is presented. We utilize a three-terminal comb-drive actuator with a built-in electret potential. We first describe the operation principle of the bistable device that is driven by a pulse and/or step-function voltage. We next explain the fabrication results and the procedure of the electret polarization. Device operation is demonstrated to determine the switching characteristics from one stable state to another with a 12 V pulse voltage of $300~\mu \text{s}$ duration. We also establish bistable switching operation with a step voltage of 5 V or less, which is manageable by a battery for portable equipment. Discrepancy of switching characteristics between the theory and the experiments is discussed from a point of view on the fringe electrical fields between the comb electrodes. [2016-0079]

Design of Digital Control DC Voltage Source Based on AT89C52 MCU

the system to DC voltage source as the core, AT89C52 MCU as the main controller, the output voltage to set the DC power supply through the keyboard, with a step function voltage to reality, the actual output value. This design is divided into four modules: SCM control and display module, digital to analog (D/A) conversion module, a constant voltage source module, output module. MCU control module as the core, the input signal is converted to digital quantity output; constant current source module voltage D/A conversion to analog conversion into constant pressure through a constant voltage circuit. The system has good reliability, high precision.

Solvent Effects on the Transient Characteristics of Liquid-Gate Field Effect Transistors with Silicon Substrate

The transient characteristics of electric double layer (EDL) gated field-effect transistors with Si as an active semiconductor were studied using various electrolyte solutions of LiBF4 by applying a step-function voltage to determine the optimum electrolyte for semiconductor circuits using EDLs. The tR, determined by EDL dynamics in the present experiment, was minimum as a function of the kind of solvent used owing to the competing effects of the EDL thickness and viscosity. The responses of the electrolyte solutions with various solvents at the same concentration were classified into three categories on the basis of tR: slow response of a complex-forming solvent, intermediate response of protic solvents, and fast response of nonprotic solvents. The best response time was 55 µs when a 1.0 M acetonitrile solution was used as the liquid-gate insulator.

Transient electric field response of laminar premixed flames

In this study the effects of weak electric fields on laminar premixed Bunsen flames were studied using planar laser-induced fluorescence (PLIF) of the formaldehyde molecules and the OH-radicals for flame structure characterization. Simultaneously particle image velocimetry (PIV) is applied to determine the changed flow field of the flame when a positively charged electrode is placed over a laminar Bunsen type flame while the burner is grounded. By application of static fields the flame front is pushed towards the burner and is constrained, which can be attributed to the momentum transfer by the ionic wind. For rich flames the ionic wind effect is intensified due to the increase of the charge carriers and larger momentum transfer of positively charged ions to the neutral species. Consequently, a stronger flow deceleration results in the order of 0.8–1.6m/s in the post-oxidation zone at supply voltages of 6kV. The ionic wind was maximized for increased flow velocity which is attributed to the increased flame surface and number of charged species. An excitation of the flame with voltage step functions was conducted to study its transient behavior. First flame response was detected at the flame root point with a response time of 2–4ms, which is an order of magnitude faster than values provided in the literature for the integral flame. This first flame response occurred after the space charge zones were built-up and the main flame response was detected 6ms after the voltage rising edge in the whole flame.

Closed-form empirical relations to predict the dynamic pull-in parameters of electrostatically actuated tapered microcantilevers

We develop novel closed-form empirical relations to estimate the dynamic pull-in parameters of electrostatically actuated linearly tapered microcantilever beams driven by a step-function voltage. A computationally efficient single degree-of-freedom model is employed in the setting of an energy-based technique to characterize the dynamic pull-in of the distributed electromechanical model that takes into account the effects of fringing field capacitance. The model exploits the fundamental mode shape of the respective nonprismatic geometry obtained using the differential transform technique. A unique surface fitting model is proposed to characterize the variations of both pull-in displacement and pull-in voltage over a realistically wide range of system parameters. Optimum coefficients of the proposed surface fitting model are obtained using nonlinear regression analysis. The empirical estimates of dynamic pull-in parameters are validated against 3D finite element simulations and available data in the literature. Excellent agreement indicates that the proposed relationships are sufficiently accurate to be safely used for the preliminary design of tapered microcantilever beams.

On the Dynamic Response of Electrostatic MEMS Switches

The undamped dynamic response of electrostatic MEMS switches that are driven by a step-function voltage is investigated. A systematic analysis using energy methods is presented. An analytic expression for switching time is derived and this expression may be used as a design rule for electrostatic switches. The analytic predictions are validated experimentally using test structures with parallel-plates actuators. It is shown that the analysis is also applicable for switches with more general geometry.

Transient Response in Monolithic Mach–Zehnder Optical Modulator Using (Ba,Sr)TiO3 Film Sputtered at Low Temperature on Silicon

We have fabricated Mach–Zhender interferometers (MZIs) using the (Ba,Sr)TiO3 (BST) film sputter-deposited at 450 °C, which is a critical temperature for the process after metallization. An optical modulation of about 10% is achieved when 200 V is applied (electric field in BST is 1.2×104 V/cm). However, the response time of optical modulation to step function voltage is slow (1.0–6.3 s). We propose a model for the slow transient behavior based on movable ions and a long dielectric relaxation time for the BST film, and good qualitative agreement is obtained with experimental results.

State Space Analysis of a Ladder Network Representing a Transmission Line

In this paper, the state space analysis of a ladder network representing a transmission line is used to determine the transient voltage and current distribution along the line following the impact of a step function of voltage at the input terminal.

Time- and space-resolved electric potentials in a parallel-plate radio-frequency plasma

A low-input capacitance emissive probe heated by a CO2 laser has been used to investigate frequency-modulated electric potentials in a radio-frequency (rf) glow discharge plasma. An excellent time-response ability of our probe system to a sharp potential change was confirmed by potential measurements with applying a step function voltage to the plasma. The electric field distribution as the first derivative of the potential distribution obtained by the probe method was compared with that by the laser optogalvanic spectroscopy to ensure the reliability of the measurements in the sheath region. The probe method was applied to directly monitor a temporal variation of axial potential and electric field distributions between two parallel-plate electrodes in a rf argon plasma. The formation of ion sheath regions on both electrode surfaces was confirmed at any phase in a rf cycle. The results were consistent with a one-dimensional model for potential and electric field distributions in the sheath region.

A Study on the Conditions for Generation of Monopole Ultrasonic Pulse by Piezoelectric Polymer Film Transducers

Short monopole ultrasonic pulses can be radiated from piezoelectric polymer film transducers driven by a step-function voltage with a fast rising time and low output impedance. In this study, we investigated the conditions for transmitting a monopole ultrasonic pulse by simulation and experiment. We clarify that the length of the pulse width is limited by transmission time (Th ) in the direction of the thickness of the film transducer. By the simulations and experiments with the received pulse by changing the acoustic impedance of the backing material, it was also found that the backing material should be matched when the rising time of the driving step-function voltage is shorter than Th . It is also shown that the source impedance of the driving circuit is an important factor in generating short ultrasonic pulses.

Experiments on Monopole Ultrasonic Pulse Radiated from Piezoelectric Polymer Film Transducers

We found experimentally that short monopole ultrasonic pulses can be radiated from a piezoelectric polymer film transducer driven by a step-function voltage with a fast rising time and low output impedance. We clarified that the pulse width of the received ultrasonic monopole pulse depends on the rising time of step-function driving voltage, and is limited by transmission time (Th) in the thickness direction of the film.

Simulation of open and shorted RC interconnect waveforms for voltage step function with low and high transient response

This paper presents the waveform response interconnect analysis of the BiCMOS and ECL gates, modeled by uniformly distributed Resistance-Capacitance (RC) along the wire network, for node voltage step function. Two cases of interconnects, open and shorted waveform transient responses, are analysed. The current and voltage transient responses are plotted along the RC interconnect length for low normalized transient time τ = 0.0 and 0.01 and high normalized transient time τ up to 5. The simulation is carried out using two Laplace transformations. The second inverse Laplace transformation is determined by the contour integration, Heaviside expansion theorem, and bisection technique algorithms. The results show that the distribution of the current and voltage transient responses oscillate around the RC interconnect length axis having positive and negative values for normalized transient time τ = 0.0 and 0.01. Verification of the simulation analysis has been done for the two cases of the RC interconnect. Moreover, the results discriminate a positive current and voltage transient responses for normalized transient time higher than τ = 0.1, which is a very important criterion and should be taken into consideration during interconnect design techniques.

Time coding in the midbrain of mormyrid electric fish. II. Stimulus selectivity in the nucleus exterolateralis pars posterior.

The anterior and posterior exterolateral nuclei (ELa and ELp) of the mormyrid midbrain are thought to play a critical role in the temporal analysis of the electric discharge waveforms of other individuals. The peripheral electroreceptors receiving electric organ discharges (EODs) of other fish project through the brainstem to ELa via a rapid conducting pathway. EODs, composed of brief, but stereotyped waveforms are encoded as a temporal pattern of spikes. From previous work, we know that phase locking is precise in ELa. Here it is shown that evoked potentials recorded from ELp show a similar high degree of phase locking, although the evoked potentials last much longer. Single-unit recordings in ELp reveal two distinct populations of neurons in ELp: type I cells are responsive to voltage step functions, and not tuned for stimulus duration; type II cells are tuned to a specific range of stimulus durations. Type II cells are less responsive than type I cells, tend to respond with bursts of action potentials rather than with single spikes, have a longer latency, show weaker time locking to stimuli, and are more sensitive to stimulus polarity and amplitude. The stimulus selectivity of type II cells may arise from convergence of type I cell inputs. Despite the loss of rapid conduction between ELa and ELp, analysis of temporal features of waveforms evidently continues in ELp, perhaps through a system of labeled lines.

Electrorheological relaxation times derived from pressure response experiments in the flow mode

We examine the experimental pressure response for a set of electrorheological valves operating at several steady flow rates to step function voltage inputs and analyse the factors that may contribute to the complex forms observed. Using a numerical algorithm incorporating a viscoelastic model for the fluid the response of the valve flow profile to changes in rheology is found to be relatively fast compared to the experimental pressure response and thought not to feature as a significant contribution to the final shape. The dynamic interaction of the valve and its associated system of pump and connecting pipes is investigated using a multi-element lumped parameter model and reveals a frequency spectrum containing resonances comparable to the experimental results. A simple lumped parameter model is less successful. Using the multi-element model for the system an upper bound can be placed on the basic response time of the electro-stress itself under realistic engineering conditions.

Comparison of classical nucleation theories with monte carlo simulations of ising models

We present Monte Carlo results for switching in two and three dimensional Ising models in order to compare with classical nucleation theory. For the case of step-function voltage pulses classical n...

Characteristics of Artificial AE Source using Piezoelectric Ceramics.

A piece of piezoelectric ceramics attached to an aluminum alloy plate was subjected to voltage, and surface displacements of the opposite side were detected by a capacitive displacement sensor. The source waveforms were calculated by a deconvolution integral using Green's function. It was demonstrated that the shape of source waveforms due to the step function of voltage is a triangle, and the rise time of the waveform depends only on the resonance frequency in the thickness direction of ceramics. A wide range of the frequency spectrum of the source waveform was obtained. It was also found that source waveforms due to one period of the sine function of voltage contain three peak values. The shape of waveforms was varied by frequency and phase of applied voltage. Consequently, the artificial AE source using piezoelectric ceramics will be useful for source waveform analysis. Also, it is convenient to prepare learning waveforms for the waveform analysis using a neural network.

Energy Losses in Charging and Discharging of Capacitors

Analytical expressions are derived for the energy loss incurred in charging and discharging of lossy, i.e. dispersive capacitors under nearly step-function voltage, such as might be expected in the presence of a finite series resistance and with step-function rise and fall of the voltage. It is shown that the energy loss in the process of charging and discharging may amount to a large fraction of the total stored energy in the capacitor and this may give rise to a significant amount of heating. A physically realistic characteristic function is assumed for the capacitor, corresponding to a frequency-independent pendent loss over a large range of frequencies, such as might be obtained in many low-loss materials.