Alternating Current Waveform Research Articles

Physicochemical Principles of AC Electrosynthesis: Reversible Reactions.

Electrolysis integrates renewable energy into chemical manufacturing and is key to sustainable chemistry. Controlling the waveform beyond direct current (DC) addresses the long-standing obstacle of chemoselectivity, yet it also expands the parameter set to optimize, creating a demand for theoretical predictions. Here, we report the first analytical theory for predicting chemoselectivity in an alternating current (AC) electrosynthesis. The mechanism is a selective reversal of the unwanted redox reaction during periods of opposite polarity, reflected in the final reaction outcome as a time-averaged effect. In the ideal scenario of all redox reactions being reversible, square AC waveform biases the outcome toward more overoxidation/over-reduction, whereas sine AC waveform exhibits the opposite effect. However, in a more realistic scenario of some redox reactions being quasi-reversible, sine AC may behave mostly like square AC. These predictions are in numerical agreement with model experiments employing acetophenone and align qualitatively with the literature precedent. Collectively, this study provides theoretical proof for a growing trend that promotes changing waveforms to overcome limitations challenging to address by varying canonical electrochemical parameters.

High-performance fractal microsupercapacitors based on Ti3C2Tx MXene for kHz alternating current line-filtering applications

Microsupercapacitors (MSCs) are attracting attention as vital filter capacitors for microscale power conversion in alternating current (AC) line-filtering circuits due to their rapid frequency response characteristics. This study demonstrates the wafer-scale fabrication of Ti3C2Tx MXene-based MSCs with a high-potential device structure incorporating fractal microelectrodes. The experimental and simulation results show that the new structure enables increased ion-transport rates through increased absorption sites and a strong electric field, resulting in improved energy storage and frequency response performance. Therefore, by optimizing the size of the microelectrodes, the fractal MSCs (FMSCs) achieve a high specific capacitance of 615.3 μF cm−2 at 1 V s−1 and their highest frequency characteristic (f0) can reach kHz. Notably, the FMSCs exhibit excellent filtering performance in AC line-filtering circuits by successfully filtering different AC waveforms at a high frequency of 20 kHz into direct current.

Correction of storage ring optics with an improved closed-orbit modulation method

We improved a previously proposed method of using closed-orbit modulation for linear optics and coupling correction. Instead of fitting individual closed orbits, the improved method decomposes the orbit oscillation data into two orthogonal modes and fits the amplitudes of the modes at all beam position monitors. While the original method is limited to process around tens to a hundred orbits, the improved method can process thousands of orbits, which are easily available when alternating-current waveforms are applied to the two modulating correctors. The method has been experimentally demonstrated on the National Synchrotron Light Source (NSLS)-II storage ring.

Pyroelectric detector-based method for low uncertainty spectral irradiance and radiance responsivity calibrations in the infrared using tunable lasers.

The standard uncertainty of detector-based radiance and irradiance responsivity calibrations in the short-wave infrared (SWIR) traditionally has been limited to around 1% or higher by the poor spatial uniformity of detectors used to transfer the scale from radiant power. Pyroelectric detectors offer a solution that avoids the spatial uniformity uncertainty but also introduces additional complications due to alternating current (AC) measurement techniques. Herein, a new, to the best of our knowledge, method for low uncertainty irradiance responsivity calibrations in the SWIR is presented. An absolute spectral irradiance responsivity scale was placed on two pyroelectric detectors (PED) at wavelengths λ from 500 to 3400 nm. The total combined uncertainty (k=1) was ≈0.28% (>1000nm), 0.44% (900 nm), and 0.36% (≈950nm and <900nm) for PED #1 and 0.34% (>1000nm), 0.48% (900 nm), and 0.42% (≈950nm and <900nm) for PED #2. This was done by utilizing a demodulation technique to digitally analyze the time-dependent AC waveforms, which obviates the use of lock-in amplifiers and avoids associated additional uncertainty components.

Less energy and material consumption in an electrocoagulation system using AC waveform instead of DC for nickel removal: Process optimization through RSM

This study pursues two major aims, first, to compare the electrocoagulation (EC) system for Ni2+ removal from aqueous solution using direct current (DC) versus alternating current (AC), and second, to optimize the process for each mode. For this purpose, four variables, viz., current density, initial nickel concentration, initial pH of the solution, and reaction time, alongside three responses, namely remaining nickel, energy consumption, and electrode (aluminum) consumption, were considered. Accordingly, 30 experiments designed by the response surface methodology (RSM) based on the central composite design (CCD) were carried out for each type of current. The statistical analysis revealed that the quadratic models proposed by the Design Expert are reliable to predict the outcomes. As quantitative results for the DC and AC modes, the average amount of the remaining nickel was 44.06 and 43.91 mg/L, energy consumption was 34.9 and 29.2 kWh/kg Ni removed, and electrode consumption was 2.3 and 1.2 kg Al/kg Ni removed, respectively. Thus, the transition from conventional DC to AC waveform coagulation led to a more than 16% reduction in energy consumption and approximately 47% depletion in electrode consumption.

Vertical Graphene Arrays as Electrodes for Ultra‐High Energy Density AC Line‐Filtering Capacitors

AbstractHigh‐frequency responsive electrochemical capacitor (EC), as an ideal lightweight filtering capacitor, can directly convert alternating current (AC) to direct current (DC). However, current electrodes are stuck in limited electrode area and tortuous ion transport. Herein, strictly vertical graphene arrays (SVGAs) prepared by electric‐field‐assisted plasma enhanced chemical vapour deposition have been successfully designed as the main electrode to ensure ions rapidly adsorb/desorb in richly available graphene surface. SVGAs exhibit an outstanding specific areal capacitance of 1.72 mF cm−2 at Φ120=80.6° even after 500 000 cycles, which is far better than that of most carbon‐related materials. Impressively, the output voltage could also be improved to 2.5 V when using organic electrolyte. An ultra‐high energy density of 0.33 μWh cm−2 can also be handily achieved. Moreover, ECs‐SVGAs can well smooth arbitrary AC waveforms into DC signals, exhibiting excellent filtering performance.

Vertical Graphene Arrays as Electrodes for Ultra-High Energy Density AC Line-Filtering Capacitors.

High-frequency responsive electrochemical capacitor (EC), as an ideal lightweight filtering capacitor, can directly convert alternating current (AC) to direct current (DC). However, current electrodes are stuck in limited electrode area and tortuous ion transport. Herein, strictly vertical graphene arrays (SVGAs) prepared by electric-field-assisted plasma enhanced chemical vapour deposition have been successfully designed as the main electrode to ensure ions rapidly adsorb/desorb in richly available graphene surface. SVGAs exhibit an outstanding specific areal capacitance of 1.72 mF cm-2 at Φ120 =80.6° even after 500 000 cycles, which is far better than that of most carbon-related materials. Impressively, the output voltage could also be improved to 2.5 V when using organic electrolyte. An ultra-high energy density of 0.33 μWh cm-2 can also be handily achieved. Moreover, ECs-SVGAs can well smooth arbitrary AC waveforms into DC signals, exhibiting excellent filtering performance.

Cutaneous sensation of electrical stimulation waveforms

BackgroundSkin sensation is the primary factor limiting the intensity of transcranial electrical stimulation (tES). It is well established that different waveforms generate different sensations, yet transcranial stimulation has been limited to a relatively small number of prototypical waveforms. ObjectiveWe explore whether alternative stimulation waveforms could substantially reduce skin sensation and thus allow for stronger intensities in tES. MethodsWe systematically tested a range of waveforms in a series of 6 exploratory experiments stimulating human adults on the forearm and in one instance on the head. Subjects were asked to rate skin sensation level on a numerical scale from “none” to “extreme”. ResultsHigh frequency (>1 kHz) monophasic square wave stimulation was found to decrease in sensation with increasing duty cycle, baseline, and frequency, but the sensation was never lower than for constant current stimulation. For the purpose of injecting a net direct current (DC), a constant current is optimal. For stimulation with alternating current (AC), sensation decreased with increasing frequency, consistent with previous reports. Amplitude modulation did not reduce sensation below stimulation with constant AC amplitude, and biphasic square waveforms produced higher sensation levels than biphasic sinusoidal waveforms. Furthermore, for DC stimulation, sensation levels on the arm were similar to those reported on the head. ConclusionOur comparisons of various waveforms for monophasic and biphasic stimulation indicate that conventional DC and AC waveforms may provide the lowest skin sensations levels for transcutaneous electrical stimulation. These results are likely generalizable to tES applications.

Head-Only Stunning of Turkeys Part 2: Subjective and Objective Assessment of the Application of AC and DC Waveforms.

Simple SummaryIn this study, we investigated various types of application of head-only electrical stunning to turkeys, in order to improve the effectiveness of the stunning process. We used recordings of physical responses and of electroencephalograms (EEGs) to assess effectivity of stunning and various waveforms: alternating current (AC) and pulsed direct currents (DC). Depending on the waveforms, voltages between 125 and 250 V produced an effective stun in turkeys in this study.Electrical stunning is likely to remain an important stunning method for turkeys at slaughter. The purpose of this study is to understand the application of various waveforms of alternating current (AC) and pulsed direct currents (DC), head-only, to turkeys and to improve the effectiveness of handheld stunning of turkeys. We evaluated the effectiveness of stunning by documenting physical responses and recording electroencephalograms (EEGs). For the assessment of physical responses, the stunning voltage was varied depending on the proportion of animals effectively stunned at a certain voltage level. If all turkeys in a group of 10 were stunned, the voltage was decreased, and the next group was stunned. This was repeated until not all turkeys showed signs of being effectively stunned. The experiment was then repeated at the voltage level just above the one that showed incomplete effective stunning. The effects of the stunning on the EEG recording was assessed in 16 turkeys to measure the occurrence of epileptiform EEGs, in 14 turkeys to assess epileptiform EEGs after neck-cut (bleeding), and in 14 turkeys to assess the effect of increased voltage and reduced frequency on epileptiform EEGs. Assessing EEGs in a laboratory setting contributes considerably to the understanding of electrical stunning procedures. Voltages between 125 and 250 V, depending on the waveform assessed, were effective in producing an effective stun in turkeys in this study.

Design of an AC Driving Waveform Based on Characteristics of Electrowetting Stability for Electrowetting Displays

In traditional electrowetting display (EWD) drivers, direct current (DC) voltage and pulse width modulation are often used, which easily caused an electrowetting charge trapping phenomenon in a hydrophobic insulating layer. Therefore, the driving voltage must be increased for driving EWDs, and oil backflow cannot be solved. Aqueous solutions are often used as polar liquids for EWDs, and the reverse voltage of alternating current (AC) driving can cause chemical reactions between water and indium tin oxide (ITO). So, a driving waveform was proposed, which included a DC waveform and an AC waveform, to separately drive EWDs for oil rupture and open state. Firstly, a DC waveform was used when the oil was broken, and the response time was reduced by designing the DC voltage and duration. Secondly, an AC waveform was used when the oil required to be stable. Oil backflow could be suppressed by the AC waveform. The main parameters of AC waveform include reverse voltage, frequency and duty cycle. The reverse voltage of EWDs could be obtained by voltammetry. The frequency could be obtained by analyzing the rising and falling edges of the capacitance voltage curve. The experimental results showed that the proposed waveform can effectively suppress oil backflow and shorten the response time. The response time was about 86% lower than the conventional driving waveforms, and oil backflow was about 72% slower than the DC driving waveform.

Characteristics of disturbance in frequency 9-150 kHz and harmonic distortion of the on-grid rooftop photovoltaic system for resistive and inductive load

Direct current (DC) electricity generated from photovoltaic (PV) needs to be converted into alternating current (AC) using an inverter so that it could be combined with electricity from the grid. However, the inverter could distort the AC waveform in the form of harmonics and disturbance in the frequency range of 9-150 kHz caused by its switching characteristics which could reduce power quality, disrupt the power line communication (PLC) system, or other electronic equipment connected in the same network. This study investigated the characteristics of the disturbances in the frequency range of 9-150 kHz generated by the on-grid rooftop PV system and observed the correlation with harmonic distortion. There were three types of load used in this study, i.e. pure resistive loads, pure inductive loads, and combination of resistive-inductive loads. The measurements were carried out using an oscilloscope to obtain a time-domain signal, which later processed by Matlab using FFT to see its frequency response, and power quality analyzer to see its harmonic distortion. The results show that each type of load has different relationship characteristics between disturbance and harmonic distortion.

Performance of Nine-Level Transformerless Photovoltaic Powered Inverter (TPVPI) Using Technique of Equal Maximum Phase Delay Time

A simple inverter is constructed by some switching components that connected in half bridge or full bridge circuit. The switching component can be a metal oxide semiconductor field effect transistor (MOSFET), transistor or insulated gate bipolar transistor (IGBT) which is driven by simple technique of pulse wave modulation (PWM). This technique generates a square alternating current (AC) waveform but it is still AC pulse wave with rich harmonic production and it is not good for the long life of electric devices. A multilevel inverter is better than the previous inverter. Some techniques have been developed to generate multilevel inverter for main objective to generated AC waveform toward sinusoidal waveform and reduce the harmonic. Also, an inverter is constructed by a transformer which is big in size and produce losses and it can increase the harmonic. This paper presents a nine-level transformerless photovoltaic powered inverter (TPVPI) system using technique of equal maximum phase delay time. It is constructed by two main elements. The first is photovoltaic (PV) module as a main direct current (DC) voltage source and the second is four full bridge circuits in cascaded connection. The proposed technique is that each two MOSFETs for cross position in the same full bridge have a same pattern of pulse wave for the period of 0.02 s. It has a phase delay time of 0.00111 s for generating the nine-level AC waveform.

Fault state detection and remaining useful life prediction in AC powered solenoid operated valves based on traditional machine learning and deep neural networks

Solenoid operated valves (SOV) play important roles in industrial process to control the flow of fluids. Solenoid valves can be found in so many industries as well as the nuclear plant. The ability to be able to detect the presence of faults and predicting the remaining useful life (RUL) of the SOV is important in maintenance planning and also prevent unexpected interruptions in the flow of process fluids. This paper proposes a fault diagnosis method for the alternating current (AC) powered SOV. Previous research work have been focused on direct current (DC) powered SOV where the current waveform or vibrations are monitored. There are many features hidden in the AC waveform that require further signal analysis. The analysis of the AC powered SOV waveform was done in the time and frequency domain. A total of sixteen features were obtained and these were used to classify the different operating modes of the SOV by applying a machine learning technique for classification. Also, a deep neural network (DNN) was developed for the prediction of RUL based on the failure modes of the SOV. The results of this paper can be used to improve on the condition based monitoring of the SOV.

Ultrasound generated by alternating current dielectric barrier discharge plasma in quiescent air

Dielectric barrier discharge (DBD) driven by an alternating current (AC) high-voltage power supply, also called silent discharge, has been known for more than a century since Siemens first proposed the term DBD in 1857, and penetrates into our daily lives. In our traditional view, AC-DBD is considered as an ozone generator for disinfection, an electronic emitter for depollution of gas streams, a jet actuator for flow control, and so on. However, the acoustic effect of AC-DBD is always neglected. Here, we demonstrate that an asymmetrical DBD plasma actuator which was powered by sinusoidal AC waveforms with an AC voltage of 16 kVp–p at a high voltage frequency of a few kHz can generate ultrasound in quiescent air by using a pressure-field microphone and a high accuracy phase-lock image Schlieren technique. The frequency of this induced ultrasound is approximately 100 kHz which is much higher than the sin high voltage frequency of a few kHz. It is the first time that ultrasound created by the AC-DBD is observed. This finding provides a comprehensive understanding of AC-DBD and might open up possibilities for novel industrial applications of AC-DBD by using the induced ultrasonic energy. In addition, according to the experimental results, a hypothesis is proposed on the formation mechanism of ultrasound generated by the AC-DBD plasma actuator.

Converting the pneumatic- to servo-based system in resistance spot welding: analyzing the dissimilar weld joints for two welding schemes

This experimental investigation analyzes the performance of two types of electrode-actuating systems, pertaining to welding current increments in resistance spot welding. Alternating current (AC) waveform, 75 kVA apparent power and C-typed body frame of a welding machine are engaged to undertake the entire experiment. Initially, the pneumatic-supported compression technique is employed to weld the dissimilar combinations of metal sheets; the carbon steel and stainless steel in this case. Since the pneumatic cylinder consumes reasonable amount of time to operate, it is limited to handle the single-periodic AC waveform which is designated as the single current and single force (SISF) welding scheme. As the pneumatic-based system is mechanically redesigned and refitted for the servo-supported compression, thereafter it paved ways to manipulate the compression variables as to support the dual current and dual force (DIDF) welding scheme in addition to the original SISF welding scheme. After the successful attempts for both schemes, the welded samples underwent the tensile test, hardness test, post-crack pattern recognition and finally subjected to the metallurgical observation to characterize the differences and anomalies. The result shows that the weld formations have been greatly improved in servo system for the SISF and DIDF compared to the pneumatic SISF welding scheme.

Thin-film High Voltage Capacitors for Hybrid Electric Vehicle Inverter Applications

The propulsion system in hybrid electric vehicles (HEVs) requires an alternating current (AC) electric motor in combination with an internal combustion engine. When the HEV is being propelled by the AC motor, the power for the motor is provided by batteries whose direct current (DC) voltage is chopped into an AC waveform via an electronic device called a power inverter. Capacitors known as DC bulk capacitors are placed between the battery and the inverter to “decouple” the AC switching inverter from the power source. Power electronics inverters use several large high voltage discrete DC bulk capacitors, which negatively influence the inverter's size, weight and are a high cost item in the assembly. The use of a high dielectric constant (Dk) ferroelectric material enables smaller, higher temperature capable, lower-cost power capacitors. Ceramic ferroelectrics, such as (Pb,La)(Zr,Ti)O3 [PLZT], offer the highest dielectric constants. Argonne National Laboratory is developing a novel film-on-foil technology for high-power capacitors utilizing PLZT. These capacitors, with an increasing dielectric constant with temperature, low equivalent series resistance and a benign failure mode, are well suited for power applications. The PLZT is deposited onto a metal foil via a chemical deposition process and the top electrode metal (Pt or Al) is then deposited by electron beam evaporation onto the top surface of the dielectric thus creating the capacitor. This project involved the fabrication and electrical evaluation of film-on-foil capacitors for HEV inverter applications. Capacitors utilizing both nickel and platinum-on-silicon as the base substrate, and PLZT as the dielectric material were fabricated. These capacitors were tested for dielectric integrity, capacitance, voltage breakdown, and benign failure mode. Results from these mechanical and electrical evaluation tests will be presented. Key processing challenges and implementation methods will also be described.

Micro-arc Oxidation Inverter Power Supply Based on the Limited Bipolar Soft-switch Control Method

In order to overcome many limitations of the conventional power supplies, such as ponderosity, big wastage, and simplex output characteristic, a dual-inverter power supply is designed to meet the different requirements of micro-arc oxidation. The main circuit structure and principle of the dual-inverter power supply for micro-arc oxidation is described, the control system and the control adjustment method are also introduced. The dual-inverter technology is adopted in micro-arc oxidation power supply. The limited bipolar control mode is applied in the power inverter circuit for adjusting the voltage, and various voltage waveform can be obtained by controlling the chopper circuit. Meanwhile, the control accuracy and response speed are improved greatly because of the higher inverter frequency. The power supply can output direct current(DC) waveform, DC pulse waveform, symmetry alternating current(AC) waveform, asymmetry AC waveform, and so on. Besides, the parameters such as pulse width, range, frequency, duty cycle can be adjusted. The experimental result shows that the power supply has many advantages, such as stable output,wonderful waveform consistency and obvious advantage in technique, and it can meet the requirements of micro-arc oxidation process fully.

Termination of reentry by a long-lasting AC shock in a slice of canine heart: a computational study.

A heart in fibrillation can be entrained by long-lasting alternating current (AC) stimuli, leading to defibrillation. To investigate the role entrainment plays in defibrillation, computer simulations of AC cardioversion in a three-dimensional slice of the canine heart were performed. A bidomain finite element model of a 1-mm thick slice across the ventricles of a canine heart was used to simulate termination of transmural reentry with AC shocks. Cardioversion defibrillation thresholds (DFTs) were determined for 200-msec (L) AC shocks at varying frequencies. At the DFT, the entire tissue is entrained by the AC shock. DFT decreases as the frequency of the long-lasting AC shock increases. We hypothesize that this decrease is due to the short period of the high-frequency AC waveform, leaving strong virtual electrode polarization (VEP) after the shock ends. To test this hypothesis, the end-shock VEP were compared for different frequencies, demonstrating stronger polarization as frequency increased. To examine whether entrainment by the long-lasting AC shock contributes to the VEP at the end of the shock, additional simulations were conducted using single-period (Z) AC waveforms. Z waveform DFTs were higher than L waveform DFTs; the Z waveform VEP was weaker than the L waveform VEP at the same frequency. This indicates that entrainment contributes to the development of stronger VEP and, thus, to lower DFT at high frequencies. This study offers for the first time a mechanistic insight into cardioversion with long-lasting AC shocks.

Discussion on “distortion of alternating-current wave form caused by cyclic variation in resistance” (Bedell and Mayer) New York, February 18, 1915. (see proceedings for February 1915)

Discussion on “distortion of alternating-current wave form caused by cyclic variation in resistance” (Bedell and Mayer) New York, February 18, 1915. (see proceedings for February 1915)

The effect of iron in distorting alternating-current wave form

It is well known that in a circuit containing no iron an impressed sinusoidal electromotive force will cause a sinusoidal current to flow, the current lagging behind the impressed electromotive force by an amount depending upon the relative values of the resistance and inductance, which in this case is constant. Assuming inductance alone in the circuit, the sine current which flows lags 90° behind the sine electromotive force and represents no power, the power-factor (cos 90°) being zero.