Pulse Duty Research Articles

Fabrication of Nanohydroxyapatite-Chitosan Coatings by Pulse Electrodeposition Method

In this study, Mg–2 wt% Zn scaffolds were fabricated by the powder metallurgy method, and the effects of the porosity content on the microstructure, and the mechanical properties of the scaffolds were studied. Nanocomposite coatings were deposited by pulse electrodeposition (PED) method on Mg–2Zn scaffolds and studied using a scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersion spectrometer (EDS), and Fourier transform infrared spectroscopy (FT-IR). The coatings morphologies showed that optimal coating was obtained at 40 V pulse voltages, 10 min coating time and nanohydroxyapatite(nHA)/chitosan (CS) ratio = 10. The pulse-peak current density (CD), the pulse duty cycles (DC), pH and temperature were considered 10 mA/cm2, 0.2,7 and 37 °C, respectively. In optimal coating, Ca/P atomic ratio was obtained at 1.57, which is similar to the value of bone hydroxyapatite. The corrosion resistance and thermal stability of optimal coating were examined by potentiodynamic polarization and thermogravimetric analysis (TGA), respectively. The results showed that the corrosion rate of the optimal coating was 0.58 mm/year, which is very low and appropriate in compared to the Mg–2Zn with a corrosion rate of 2.09 mm/year. The TGA results indicated that the significant weight loss is about 23% and 14% for CS and optimal coating, respectively. The in vitro biocompatibility of the optimal coating was evaluated by cell adhesion, cytotoxicity, and alkaline phosphatase (ALP) assays using MG63 cells. The results indicate that the optimal nanocomposite coating was highly biocompatible, making this material more suitable for applications in bone tissue engineering and to repair bone defects caused by sports injuries.

Pulsed power to control growth of silicon nanoparticles in low temperature flowing plasmas

Low-temperature plasmas have seen increasing use for synthesizing high-quality, mono-disperse nanoparticles (NPs). Recent work has highlighted that an important process in NP growth in plasmas is particle trapping—small, negatively charged nanoparticles become trapped by the positive electrostatic potential in the plasma, even if only momentarily charged. In this article, results are discussed from a computational investigation into how pulsing the power applied to an inductively coupled plasma (ICP) reactor may be used for controlling the size of NPs synthesized in the plasma. The model system is an ICP at 1 Torr to grow silicon NPs from an Ar/SiH4 gas mixture. This system was simulated using a two-dimensional plasma hydrodynamics model coupled to a three-dimensional kinetic NP growth and trajectory tracking model. The effects of pulse frequency and pulse duty cycle are discussed. We identified separate regimes of pulsing where particles become trapped for one pulsed cycle, a few cycles, and many cycles—each having noticeable effects on particle size distributions. For the same average power, pulsing can produce a stronger trapping potential for particles when compared to continuous wave power, potentially increasing particle mono-dispersity. Pulsing may also offer a larger degree of control over particle size for the same average power. Experimental confirmation of predicted trends is discussed.

Pulse electrodeposition of aluminium coatings from molten salt bath; effect of processing parameters on the coatings’ corrosion and wear behaviour

ABSTRACT In this study, Al coatings were pulse electrodeposited from a molten salt electrolyte onto copper substrates. The effects of applied peak current density, pulse current frequency and duty cycle on the morphology, microstructure, corrosion behaviour and tribological properties of the coatings were investigated by scanning electron microscopy, X-ray diffraction, potentiodynamic polarisation, electrochemical impedance spectroscopy and pin-on-disc wear test methods. The results showed that the changes in processing parameters changed the morphological and microstructural features of the resulting coatings, which in turn affected their corrosion and wear behaviours. Coatings with smoother surfaces, finer crystallite size and more compact morphologies that were electrodeposited at higher applied peak current density (up to 80 mA cm−2), higher pulse current frequency (up to 50 Hz) and higher duty cycle (up to 50%) exhibited more corrosion and wear resistance than the others.

Machinability investigation in electric discharge machining of carbon fiber reinforced composites for aerospace applications

AbstractThe industry is looking forward to technological advancements for productivity improvement, and this can be achieved by improving the machining performance concerned with the machinability challenges. The machinability investigation of carbon nanotubes/carbon fiber (CNTs/CF) reinforced composites is emerging with a strong application potential in the aviation industry because of their high strength and lightweight nature. However, the conventional machining practices pose a major challenge of excessive tool wear and dimensional accuracy which lead to a high production cost. Electric discharge machining is considered one of the possible solutions to treat with hard to machine materials like CNT/CF. Therefore, this work involves the machinability investigation to study the effect of pulse on duration, pulse peak current, duty factor, and gap voltage to investigate the material removal mechanism for achieving machining stability along with improved dimensional accuracy. Experiments were designed using Taguchi design followed by the analysis of variance, parametric effects, along with signal to noise ratio‐based multi‐response optimization. Findings have inferred that peak current and gap voltage were found to be significant for radial over‐cut, contributing 47.27% and 40.25%, respectively. The gap voltage was also shown to be notable for electrode wear rate and material removal rate, with contribution percentages of 43.59% and 20.11%, respectively. As a result, Vg was identified as the most influential variable in this study. This machinability study imparts a significant potential to improve the dimensional accuracy and productivity for aerospace applications.

Ultra-Uniform Copper Deposition in High Aspect Ratio Plated through Holes via Pulse-Reverse Plating

The uniformity and microstructure of the copper deposition in the high aspect ratio plated through holes (penetrating holes) are crucial for the performance of printed circuit board. We systematically investigated the effects of reverse pulse parameters in the period pulse reverse (PPR) plating on the uniformity and microstructure of the copper deposition, including reverse pulse frequency, reverse pulse duty cycle and reverse pulse current density. The Cu deposition behavior (throwing power) and its crystallographic characteristics, including grain size, crystallographic orientation, and grain boundary, were characterized by means of field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD). Our results clarify that the reverse pulse current density and duty ratio should be low to achieve the full filling and high uniformity of the through holes. The reverse pulse frequency of 1500 Hz would prevent the through holes to be fully filled. The copper electrodeposition in PTH prepared by double pulse electrodeposition has the good (111) surface texture and grain boundary distribution. This work demonstrated that the period pulse reverse (PPR) plating provides unique advantages in achieving the ultra-uniform copper deposition in the high aspect ratio plated through holes.

All-Fiber Mid-Infrared Supercontinuum Generation Pumped by Ultra-Low Repetition Rate Noise-Like Pulse Mode-Locked Fiber Laser

We demonstrate broadband mid-infrared supercontinuum generation in a piece of indium fluoride fiber pumped by an ultralow repetition rate noise-like pulse mode-locked fiber laser. This figure-9 mode-locked Tm-doped fiber laser has a long laser cavity by inserting a piece of standard single mode fiber and a piece of dispersion compensation fiber, which delivers mode-locked noise-like pulse with a repetition rate of ∼190 kHz. The mode-locked noise-like pulse train has a low pulse duty cycle of 4.38 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . With only one Tm-doped fiber amplifier, the ultra-low repetition rate noise-like pulse is amplified to ∼3 W. The pulse energy is boosted to ∼15 μJ with a peak power of ∼6.5 kW. Pumping a piece of highly nonlinear indium fluoride fiber with the amplified noise-like pulse, a flat mid-infrared supercontinuum with a covering range from ∼1500 nm to ∼4100 nm can be achieved. Due to the low operational power, no cooling installations are required to control the temperature of the supercontinuum laser system. This all-fiber mid-infrared SC laser source has a relatively simple architecture and low cost. This study demonstrates the great advantages of this type of ultra-low repetition rate noise-like pulses in mid-infrared supercontinuum generation.

Pattern performance of active phased array antenna for Gaofen-3 satellite

The phased array antenna is one of the critical components of the space-borne SAR system and plays a key role in the quality of images. This paper focuses on the design of active phased array antenna for Gaofen-3 satellite, including its architecture, system design methods, key hardware, and the performance for the design implementation. The proposed phased array antenna have capabilities of beam broadening and scanning, left and right side look, polarization switching, in-orbit calibration, uploading beam-steering correction data, collecting self-checking information, and self-protection caused by over pulse width or duty cycle. The phased array antenna is mainly consisted of dual-polarized slotted waveguide antennas, TR modules, time-delay and amplifier modules and power distribution networks. Moreover, the solutions of the direct problem and inverse problem for accurately predicting the pattern and determining the states of TR modules for the required beam have been proposed. The obtained results can confirm that the cross-polarization level of both polarizations for the phased antenna array is below −35 dB. By employing the proposed antenna model, the beam steering error and dispersion error between the predicted and the measured beams in the range plane are less than 4% (100% probability) and less than 2% (95% probability). For beam steering in the azimuth plane, the beam steering error is less than 2% (90% probability), and less than 4% (100% probability). The ground and on-orbit test results have indicated that the functions and performance of the antenna meet the requirements of the SAR system.

4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

The Galactic Center (GC), with its high density of massive stars, is a promising target for radio transient searches. In particular, the discovery and timing of a pulsar orbiting the central supermassive black hole (SMBH) of our galaxy will enable stringent strong-field tests of gravity and accurate measurements of SMBH properties. We performed multiepoch 4–8 GHz observations of the inner ≈15 pc of our galaxy using the Robert C. Byrd Green Bank Telescope in 2019 August–September. Our investigations constitute the most sensitive 4–8 GHz GC pulsar survey conducted to date, reaching down to a 6.1 GHz pseudo-luminosity threshold of ≈1 mJy kpc2 for a pulse duty cycle of 2.5%. We searched our data in the Fourier domain for periodic signals incorporating a constant or linearly changing line-of-sight pulsar acceleration. We report the successful detection of the GC magnetar PSR J1745−2900 in our data. Our pulsar searches yielded a nondetection of novel periodic astrophysical emissions above a 6σ detection threshold in harmonic-summed power spectra. We reconcile our nondetection of GC pulsars with inadequate sensitivity to a likely GC pulsar population dominated by millisecond pulsars. Alternatively, close encounters with compact objects in the dense GC environment may scatter pulsars away from the GC. The dense central interstellar medium may also favorably produce magnetars over pulsars.

The effect of pulse current cathodic protection on cathodic disbondment of epoxy coatings

For coated pipelines with cathodic protection, cathodic delamination has been judged as the main reason of coating delamination. This work aims to use the pulse current cathodic protection (PCCP) to mitigate the coating cathodic delamination. Cathodic delamination tests, electrochemical impedance spectroscopy and wire beam electrode method (WBE) were used to study the effect of PCCP on the mitigation of coating disbondment. The results show that PCCP could successfully retard the cathodic delamination rates of organic coatings. Under different cathodic protection potential, the delamination area of the coating protected using PCCP is much smaller than that using direct current cathodic protection. With the increasing pulse frequency and duty ratio, the mitigation effect decreases. Within the range of pulse frequency from 5 Hz to 500 Hz and duty ratio from 0.1 to 0.9, the results of cathodic delamination tests and WBE tests indicate that when the cathodic potential is −1.5 V, the mitigation effect reaches the maximum with the pulse frequency of 5 Hz and the duty ratio of 0.1. PCCP alleviates cathodic delamination of coating mainly by intermittently shifting the surface polarization potential to positive direction and reducing the consumption of cathodic reaction charge.

Ultrasonic stimulation of milk fermentation: effects on degradation of pesticides and physiochemical, antioxidant, and flavor properties of yogurt.

Ultrasound has the potential to increase microbial metabolic activity, so this study explored the stimulatory effect of ultrasound pre-treatment on the degradation of four common pesticides (fenitrothion, chlorpyrifos, profenofos, and dimethoate) during milk fermentation by Lactobacillus plantarum and its effect on yogurt quality. Appropriate ultrasound pretreatment significantly enhanced the growth of L.plantarum. The degradation percentages of pesticides increased by 19-38% under ultrasound treatment. Ultrasonic intensity, pulse duty cycle, and duration time were key factors affecting microbial growth and pesticide degradation. Under optimal ultrasonic pre-treatment conditions, the degradation rate constants of four pesticides were at least 3.4 times higher than those without sonication. In addition, such ultrasound pretreatment significantly shortened yogurt fermentation time, increased the water holding capacity, hardness and antioxidant activity of the yogurt, and improved the flavor quality of the yogurt. Ultrasonic pretreatment significantly accelerated the degradation of the four pesticides during yogurt fermentation. In addition, such ultrasound pretreatment increased the efficiency of yogurt making and improved the quality of yogurt in terms of water holding capacity, firmness, antioxidant activity, and flavor. These findings provide a basis for the application of ultrasound to the removal of pesticide residues and quality improvement of yogurt. © 2022 Society of Chemical Industry.

An Approach to Recover Energy From Discarded Primary Batteries Before Being Disassembled

This article demonstrates the feasibility of recovering energy from discarded primary batteries (e.g., alkaline or zinc-carbon) that would be disposed of as normal household waste based on self-adaptive pulse discharge (SAPD) method. The SAPD approach is utilized to search the optimal pulse frequency and duty cycle for different types of used batteries with the maximum allowed discharge current. To assess the performance of the proposed approach, a prototype including improved passive cell balancing circuit, SAPD control circuit, and series–parallel switching circuit of supercapacitor banks was designed and implemented to drain a battery bank that consisted of at least 6 but at most 10 used cells of different brands in series. Discharging experiments show that the energy recovery with six to ten used batteries ranges from 798 to 1455 J, and the corresponding recovery efficiency is about 33.49%–46.43%. Although outcomes are still far from being satisfactory in the efficiency with the proposed approach, the rate of energy recovery may depend on the remaining capacity of discarded batteries and so may be advantageous if the battery has a high remaining capacity. Therefore, authors conclude that there is possibly a direct link between the recovery efficiency and the remaining capacity of discarded batteries.

Computational analysis of metal transfer mode, dynamics, and heat transfer under different pulsating frequencies in pulsed wire-arc additive manufacturing

Abstract A numerical model of the metal transfer process was developed using the thermomagnetohydrodynamic equations and the phase-field method to investigate the influence of pulse frequency on the metal transfer mode, dynamics, and thermal behavior in the pulsed wire-arc additive manufacturing (WAAM) process. The control of droplet transfer mode, dynamics, and thermal behavior is essential in WAAM; otherwise, several potential defects such as high residual stresses and distortion, poor dimensional accuracy, and surface quality may occur due to uneven heat input condition and process instability. Therefore, in this study, eight sets of pulse frequencies ranging from 50 to 225 Hz, in steps of 25 Hz, using identical power source parameters, such as pulse duty cycle and average current of 25.4% and 152 A, respectively, were considered and compared for a nearly square current waveform. The results reveal that only the current pulses with a medium frequency regime (100–175 Hz) achieve the one-droplet-per-pulse mode of metal transfer. Moreover, an increase in pulse frequency leads to a shorter necking length of the pendent droplet and a significantly lower average speed and temperature of the detached droplet. The results for the heat flux analysis indicate that Joule heating and arc heating decrease due to the increase in pulse frequency, whereas the sheath heating remains almost constant using different pulse frequencies. The proposed numerical scheme provides a detailed understanding of controlling and tailoring the different metal transfer modes and their metal transfer stability during WAAM, which benefits further process optimization and control.

Large-Arc Discharge Mechanism and Avoidance in Micro-Arc Oxidation of Magnesium Alloy

The large-arc discharge problem occurs in the processing of magnesium alloy by micro-arc oxidation. It will cause local ablation of ceramic coating and even magnesium alloy matrix material. Thus, clarifying the mechanism and influencing factors is a necessary approach to avoid the large-arc discharge problem. In this study, a new “cooling time” parameter based on frequency and duty cycle is proposed to study the large-arc discharge trend and understand the relationship between large-arc discharge and process parameters. Then, the mechanism of the large-arc discharge phenomenon and the action of the cooling time were investigated by the theory of local-arc discharge mechanism and load characteristics of micro-arc oxidation. The results show that the mechanism of large-arc discharge is that the arc discharge is continuous in situ, and the aggregation or merger of arc discharge occurrence. Therefore, the large-arc problem can be resolved effectively through discretizing the arc discharge by adjusting the cooling time and regulating the pulse frequency and duty cycle. The cooling time made the location area of arc discharge and oxides fully cooled, and provided time for the sufficient discharge of the load capacitance, to effectively inhibit the problem of large-arc discharge.

Control of ion flux-energy distributions by low frequency square-shaped tailored voltage waveforms in capacitively coupled plasmas

Capacitively coupled plasmas are routinely used in an increasing number of technological applications, where a precise control of the quantity and the shape of the energy distribution of ion fluxes impacting boundary surfaces is required. Oftentimes, narrow peaks at controllable energies are required, e.g. to improve selectivity in plasma etching, which cannot be realized in classical discharges. We combine experimental ion flux-energy distribution measurements and PIC/MCC simulations to provide insights into the operation and ion acceleration mechanisms for discharges driven by square-shaped tailored voltage waveforms composed of low-frequency (100 kHz) pulsed and high-frequency (27.12 MHz) signals. The formation of ion flux-energy distributions with a narrow high energy peak and strongly reduced ion fluxes at intermediate energies is observed. The position of the high energy peak on the energy axis can be controlled by adjusting the low-frequency voltage pulse magnitude and duty cycle. The effects of tailoring the driving voltage waveform by adjusting these control parameters as well as its repetition rate on the plasma operation and the ion flux-energy distribution are analysed in depth. We find, e.g. that the duty cycle regime (% or %) determines if the high energy ions form at the grounded or the powered electrode and that the duration of the pulse must exceed the ion energy relaxation time, on the order of 0.5 μs.

Investigation on Performance of Various Power Control Strategies with Bifilar Coil for Induction Surface Melting Application

In recent years, induction heating applications assisted by electronic power control have been very appealing. For melting applications, induction heating is widely used as it seems to be appropriate and provides higher efficiency, zero pollutants, non-contamination of material, etc. in comparison with conventional heating. The conventional variable frequency control scheme is not sufficient for melting applications because of its high switching loss, low efficiency, and lower heat rate. A superlative control technique is required to control the output power smoothly, for a high heating rate with minimum power loss, and to lower the number of components. In this paper, a capacitorless self-resonating bifilar coil is proposed for induction surface melting applications. The performance of the system in terms of modular losses, heat rate, and efficiency is analyzed for various power methods such as pulse duty cycle control, phase shift control, pulse density modulation control, and asymmetric duty cycle control. An experimental validation is performed for the 1 kW prototype, and the heating rate, efficiency, and modular losses are calculated. The control technique is digitally validated using a PIC16F877A microcontroller with 30 kHz switching frequency. The temperature distribution is analyzed using a FLIR thermal imager. Among the tested methods, pulse density modulation-based control provides smooth and varied power control from 0% to 100% with minimum modular losses. The efficiency of the system is 89% at a rated output power and is greater than 85% for pulse density modulation control with a fast heating rate.

Research on micro-EDM discharge state detection technology based on inter-electrode impedance variation characteristics

To address the difficulty in detecting the discharge state of a narrow pulse width and small duty cycle pulse, in this study, we investigate the variation characteristics of the inter-electrode impedance in the micro-EDM process and propose a detection method to distinguish different discharge states in micro-EDM based on the change in electrical signal caused by the change characteristics. The influence of the pulse width and duty cycle on the quality of micro-EDM is summarised. The results show that the workpiece surface machining quality can be considerably improved by compressing the pulse width of the pulse power supply. A micro-EDM discharge state detection system based on the variation characteristics of the inter-electrode impedance is designed, and experiments verify the detection method. The control strategy of the discharge state detection system is analysed, and a control strategy based on the forward direction and discharge state is proposed. The machining effect of the control strategy is tested through a trial-machining experiment. According to the machining control strategy, the control signal is outputted, which can realise a stable and efficient micro-EDM process.

Pulsed direct-current reactive sputtering of high Young's modulus [002] oriented aluminum nitride thin films

This work reports a process-parameter optimization of [002] oriented high Young's modulus aluminum nitride (AlN) thin films deposited by pulsed direct current (DC) reactive sputtering method. Properties of deposited AlN films are mainly determined by the material's microstructure and morphology, which can be modulated by the process parameters. Commonly explored process parameters of reactive sputtering of AlN are substrate temperature, process pressure, gas composition, substrate type, etc. Process pressure and nitrogen concentration have the most significant influence on the topography and morphology of the film, deposited by the pulsed DC reactive sputtering method. DC pulse parameters such as pulse frequency and pulse duty cycle also influence the properties of deposited AlN films, which have been addressed in this work. The pulse frequency of 100 kHz and a duty cycle of 80% was found to be the most suitable pulse parameters. This paper also reports the voltage and current behavior and deposition rate dependence under varying process parameters and pulsed properties. Optimization of process parameters is commonly done by characterizing the deposited AlN films’ crystallinity, surface roughness, and residual stress. This work addresses the influences of process and pulse parameters on Young's modulus besides other characteristic properties of the film. The AlN films deposited with the optimized method and pulse parameters yield Young's modulus of up to 335 GPa while dropping the surface roughness to 1.2 nm.

Quasi-continuous-wave laser directed energy deposition on inclined NV E690 steel plates: Melt pool and temperature evolution

A quasi-continuous-wave direct metal deposition (QCW-DMD), one of directed energy deposition (DED), with different pulse frequencies and duty cycles was performed on an inclined NV E690 steel plate. Comprehensive effects including the humping effect, the melt pool evolution process, the coalescence phenomenon, the deposition morphology, and the thermal behavior were investigated. The results show that during the continuous-wave direct metal deposition (CW-DMD) and the QCW-DMD with the pulse frequency of 1 Hz, the gravity-induced humping effect and the coalescence phenomenon contribute to the increase and decrease of the melt pool numbers, respectively. A small duty cycle leads to a decrease in the average melt pool numbers. Besides, the coalescence of melt pools is formed by establishing a liquid bridge which is first mainly driven by the surface tension and then by gravity. The humping effect is overcome when the pulse frequency ranges from 5 Hz to 50 Hz, presenting a small height variation. Furthermore, the QCW mode laser can modulate the powder catchment efficiency and produce a higher cooling rate that resulted in a higher microhardness.

Conversion of CO2 in a pulsed arc discharge

We present a study of CO2 gas conversion into a mixture of CO2, CO and O2 by means of a pulsed arc discharge at atmospheric pressure. The CO2 molecule is dissociated as a result of the interaction with the highly energetic electrons and excited species produced in the plasma domain. The plasma conversion of CO2 provides a relatively simple approach to CO2 conversion without the need of special materials required by chemical reactors. In this study, the discharge operates at atmospheric pressure, which leads to a reduced efficiency compared to the low pressure operation due to the additional electron losses via elastic collisions. The operation at atmospheric pressure, however, provides simplicity, robustness and low cost of the discharge system, which makes it very attractive from an industrial point of view. Further, we use a pulsed discharge, which, in comparison to the DC discharges, provides additional possibilities for optimizing the dissociation process by controlling precisely the energy input into the plasma. This is achieved by controlling the pulse repetition rate and duty ratio in addition to the discharge current and gas flow characteristics. We present results for the CO2 dissociation rate and energy efficiency for a wide range of different discharge parameters.

Optimal Charging Strategy With Complementary Pulse Current Control of Lithium-Ion Battery for Electric Vehicles

Although the pulse charging strategy has many advantages, it is still controversial. The paradox is that it prolongs the charging time to eliminate the polarization voltage by the pulse interval, and the ac component in pulse current will increase the ohmic losses. In this article, an optimal charging strategy with a complementary pulse current of lithium-ion is proposed to address and alleviate these issues. For the pulse frequency, the optimization can be achieved through the electrochemical impedance spectroscopy (EIS) analysis to reduce the battery’s ac impedance. For the pulse amplitude, based on the battery’s internal resistance characteristics, minimize the ohmic losses to obtain the optimal amplitude. For the pulse duty cycle, it is adjusted to achieve a state of charge (SOC) balancing in the early charging stage, and the battery’s terminal voltage balancing in the later stage. Based on the optimized charging strategy, a pulse charger concept is proposed, which can flexibly control the pulse charging currents and use complementary pulses to completely eliminate the prolonged charging time caused by the pulse interval. In the end, an experimental platform for pulse chargers of lithium-ion batteries is designed, and the theoretical analysis is verified by the comparative experiments.