Pulse Duty Ratio Research Articles

Atomic-scale understanding of microstructural evolution in electrochemical additive manufacturing of metallic nickel

Atomic-level manufacturing is fundamentally concerned with the precise removal, addition, and migration of material at the atomic and close-to-atomic scale (ACS). Tip-based electrochemical deposition, a quintessential ACS electrochemical additive manufacturing technique, offers promising prospects for achieving bottom-up fabrication of metallic micro/nano structures. However, the complex physicochemical reactions involved in electrodes lead to a limited understanding of the mechanisms underlying atomic electrodeposition and structural evolution. For the first time, this study proposes electric double-layer controlled electrochemical kinetics and investigates the effect of direct current (DC) and pulse current (PC) on nickel atomic electrodeposition using molecular dynamics (MD) simulations. The findings reveal that compared to DC electrodeposition, PC electrodeposition results in more orderly deposition morphology, improved surface smoothness, reduced dislocation density, and lower crystal distortion, with these effects being particularly pronounced under low pulse duty ratio conditions. In addition, the pulse frequency significantly influences the morphology and structure of the deposit. The high pulse frequency yields smoother surfaces with local protrusions, while the low frequency favors the formation of orderly and dense structures excepting slightly increased roughness. This study provides critical insights into understanding the microscopic mechanisms of atomic-scale electrodeposition processes and achieving atomically controlled tip-based electrochemical additive manufacturing of micro/nanodevices.

Optimum pulse electrolysis for efficiency enhancement of hydrogen production by alkaline water electrolyzers

Alkaline water electrolysis is considered as the most feasible way to realize large-scale hydrogen production from renewable energy sources. However, the poor efficiency performance in low load limits the wide-range operation of alkaline water electrolyzers. The energy loss caused by the parasitic current is the main reason of the poor efficiency in low load. Based on the electrolyzer internal structure, an improved model of alkaline water electrolyzers is proposed and the inefficiency mechanism is illustrated. It is found that by applying pulse current for electrolysis, the efficiency of hydrogen production in low load can be enhanced greatly. The influence of the pulse current magnitude and duty ratio on the efficiency improvement is studied. Under different operation conditions, they can be regulated to achieve the maximum efficiency of hydrogen production. The electrolyzer parameters also affect the efficiency trend, especially the double layer capacitance. Finally, the results are experimentally verified on a 10 kW alkaline water electrolyzer.

DDR-Based PWM technique for fixed frequency three-phase to variable frequency K-phase power conversion using QZSDMC

This research presents a novel direct AC-to-AC topology for converting power from three phases (3φ) to five phases (5φ). The power conversion is handled by a Quasi Z Source Direct Matrix Converter (QZSDMC). This device is made up of a regular Direct Matrix Converter (DMC) and a pseudo Z-source impedance network that are serially connected. The proposed QZSDMC receives alternating current power in 3φ at a fixed voltage and frequency and outputs it in 5φ at a variable voltage and frequency to a standalone system. You can switch between buck and boost mode with a couple of switch flips. The shoot-through Duty Ratio value might help us understand the voltage transferal ratio. The authors suggested a unique control mechanism based on Direct Duty Ratio Pulse Width Modulation (DDRPWM) in this work. The method described here is only relevant when the amount of output phases is odd, not even. The paper uses MATLAB tools and experimental results to show the proposed system's operational principle in detail and prove its viability. Here, buck and boost conditions in all four quadrant modes with the proposed QZSDMC architecture, and the voltage gain constraint are addressed. It is more dependable, more efficient, and less expensive than a traditional back-to-back converter (B2BC).

Electrolytic Characteristics of Microhole Array Manufacturing Using Polyacrylamide Electrolyte in 304 Stainless Steel.

Because of the ease with which oxide films form on its surfaces, stainless steel has strong corrosion resistance and excellent processing performance. Electrochemical machining (ECM) is a flexible process that can create microstructures on stainless steel (SS304); however, with traditional masked ECM, the efficiency and accuracy of microstructure machining are low. Proposed here is the use of a non-Newtonian fluid [polyacrylamide (PAM)] as the electrolyte. To date, there have been few papers on the electrochemical dissolution behavior of stainless-steel micromachining with a non-Newtonian fluid as the electrolyte. The aims of the study reported here were to investigate the electrochemical properties of SS304 with PAM and PAM-NaOH as electrolytes, and to explain their electrochemical corrosion mechanisms. The effects of different electrolytes were compared, and the polarization curves of SS304 in PAM and PAM-NaOH electrolyte solutions with different components were analyzed and compared with that in NaNO3 electrolyte. Then, the effects of the main processing parameters (pulse voltage, frequency, and duty ratio) on the machining performance were investigated in detail. A microhole array was obtained with a good quality comprising an average diameter of 330.11 µm, an average depth of 16.13 µm, and a depth-to-diameter ratio of 0.048. Using PAM to process microstructures on stainless-steel surfaces was shown to be feasible, and experiments indicated that the mixed electrolyte (PAM-NaOH) had not only the physical characteristics of a non-Newtonian fluid but also the advantages of a traditional electrolyte to dissolve processing products, and it effectively improved the processing accuracy of masked ECM for SS304.

High-Voltage Pulse-Assisted Operation of Single-Layer Electrochromic Systems for High Performance and Reliability.

A single-layer electrochromic device (SL-ECD) based on ionic conductors containing EC chromophores provides a very simple platform that can be readily fabricated by sandwiching the EC layer between two electrodes. The operation of SL-ECDs is governed by the diffusion of redox species due to their SL structure, which causes a relatively slow dynamic response. In this study, we propose an effective high-voltage pulse injection strategy to improve the performance of SL-ECDs. Applying a programmed voltage wave composed of DC and high-voltage pulses promotes coloration/bleaching switching without degrading device stability, which is more advantageous than applying high DC voltages. We modified the input voltage profile by considering fundamental parameters, such as the amplitude and duty ratio of additional voltage pulses. The coloration and bleaching dynamic responses with the optimized voltage wave are ∼62 and ∼20% faster, respectively, compared with those with the simple DC input. Furthermore, the additionally injected pulse aids in increasing the coloration efficiency from ∼95.3 to ∼168.6 cm2 C-1. Another notable feature of this system is that the device operates stably when a programmed voltage wave is used. These results indicate that the concept of high-voltage pulse-assisted operation of SL-ECDs is a straightforward but effective method for improving device performance without changing the EC chromophore or device structure.

A Model Describing the Process of the Electrodeposition of Zinc Loose Deposits in Pulsed Current Modes

A phenomenological model describing the change in the structural characteristics of loose zinc deposits obtained in pulsed current modes is presented. Comparison of experimental data on the structural properties of deposits with the results of model calculations indicates the adequacy of the model. To describe the features of the dendritic deposit growth and to determine the duration of the homogeneous structure formation in pulsed modes, the concept of critical thickness is introduced, at which a sharp change in the loose deposit density occurs. The dependence of the zinc deposit critical thickness on the pulse duty ratio under pulsed current modes is determined. The increasing of the pulse duty ratio leads to denser deposits with rounded dendrite shapes and fewer growth points, as compared with the deposit obtained in galvanostatic mode.

Asynchronously Pulsed Plasma for High Aspect Ratio Nanoscale Si Trench Etch Process

The fabrication of high aspect ratio Si trenches has been becoming difficult due to the decrease in critical dimension (CD) to deep nanoscale. Especially, aspect ratio dependent etching (ARDE), which decreases the etch rate as the pattern width gets smaller, makes process uniformity get worse. In this study, the effects of bias pulsing parameters during asynchronous pulsing, which alternatively applies the source power and bias power, as well as the effect of additive gas such as CF4 and C4F8 on the nanoscale Si trench etch characteristics during Cl2/Ar plasma etching were investigated. It was found that the bias pulsing parameters during the asynchronous pulsing, such as bias pulse duty ratio and bias pulse delay time, can affect the etch characteristics such as etch rate, etch selectivity, and ARDE by changing the ion dose and ion energy during the etching. However, the variation of bias pulse parameters during the asynchronous pulsing did not change the etch profile noticeably, and it showed bowed Si trench etch profiles. To improve the etch profile, the addition of fluorocarbon gas such as CF4 and C4F8 was required, and by using C4F8 instead of CF4, more anisotropic Si etch profile without sidewall bowing could be obtained due to the improved sidewall passivation by a fluorocarbon layer even though it degraded etch selectivity and ARDE. Therefore, it is believed that by controlling the bias pulsing parameters with additive gas, nanoscale Si trench etch characteristics can be more easily controlled.

Effect of pulse parameters on ablation efficiency in dual-frequency HIFU therapy

High-intensity focused ultrasound (HIFU) has now been widely used to ablate various benign and malignant tumors. But it is still critical to increase the ablation efficiency in many clinical applications. Dual-frequency HIFU has been proven to be more efficient in ablation, but the principle on selecting the pulse parameters in this method remains to be explored. In this study, the in vitro lesion areas under different pulse repetition frequencies (PRFs), duty ratios, and frequency differences were compared, cavitation activity was also monitored during HIFU exposure. The results showed that different pulse parameters caused different types of lesions. In HIFU therapy, those pulse parameters that maximize the thermal effect, reduce heat dissipation and generate sufficient cavitation activities should be considered. But the method of evaluating or predicting the damage by using the cavitation dose is only applicable to mechanical damage.

Analysis of Source-Load Coupling Characteristics and Stability in Battery Energy Storage System

A quasi-precise modeling method based on the accurate source-load coupling model and the average model of battery energy storage system with pulsed load (BESS-PL), which retained its unique pulse characteristics and reasonably simplified the difficulty of theoretical analysis, was proposed to achieve the stability analysis of the source-load coupling and pulse characteristics of BESS-PL. Based on the quasi-precise model exchange work of the BESS-PL framework was calculated, and the influence of pulse frequency and duty cycle ratio on system stability was examined using the Bode diagram. The strength of the key parameters of the BESS-PL system, as well as the instantaneous power of source and load, were analyzed and discussed based on the waveform analysis and eigenvalue calculation of the actual test platform. This analysis and discussion further validate the stability analysis based on the quasi-precise model. The findings demonstrate that the BESS-PL system exhibits substantial coupling between the source and the pulse load, with stability being lowest at a particular frequency point in the intermediate frequency mode and the pulse duty ratio showed 50%.

Regulating the Gas–Liquid Slug Flow in Microchannels through High-Frequency Pulsatile Perturbations

The gas–liquid slug flow that is characterized with alternate formation of gas and liquid segments has been widely applied for chemical synthesis and analysis. For its applications, it is essential to precisely control the gas and liquid slug lengths. However, using the passive method, the bubble/droplet generation frequency and their sizes are influenced by multiple parameters including the channel dimension, fluid physical properties, the gas-to-liquid flow rate ratio, and so forth and hence lack control flexibility. In this work, an active approach using pulsatile perturbations to control the gas–liquid slug flow is demonstrated. A rotating valve is applied to produce a high-frequency pulsating air flow. Under its influence, either Taylor bubbles in a hydrophilic channel or liquid-in-gas droplets in a hydrophobic channel can be generated synchronously with the flow pulsation. Therefore, the gas and liquid slug lengths can be independently tuned via the air inlet pressure and the liquid flow rate, respectively. The maximum generation frequency is up to ∼1300 Hz. In addition, the effects of the pulsation frequency, the pulse duty ratio, and the liquid viscosity are also investigated. This technique provides an efficient method to regulate the gas–liquid slug flow in multiphase microreactors or microfluidic analytical systems.

Effect of pulse duty ratio on temperature rise induced by focused ultrasound combined with magnetic microbubbles

Development of acoustic/magnetic contrast agent microbubbles with various diagnostic and therapeutic functions has attracted more and more attention in medical ultrasound, biomedical engineering and clinical applications. Superparamagnetic iron oxide nanoparticles (SPIO) have unique magnetic characteristics and wonderful biocompatibility, so they can be used as MRI contrast agents to improve image contrast, spatial resolution and diagnostic accuracy. Our previous work shows that the multimodal diagnostic and therapeutic microbubble agents can be successfully constructed by embedding SPIO particles into the coating shell of conventional ultrasound contrast agent (UCA) microbubbles, which in turn changes the size distribution and shell properties of UCA microbubbles, thereby affecting their acoustic scattering, cavitation and thermal effects. However, previous studies only considered the influence factors such as acoustic pressure and microbubble concentration. The relevant investigation regarding the influence of ultrasound temporal characteristics on the dynamic response of magnetic microbubbles is still lacking. This work systematically measures the temperature enhancement effect of the SPIO-albumin microbubble solution flowing in the vascular gel phantom exposed to pulsed ultrasound with various temporal settings (e.g. duty cycle, PRF and single pulse length). Meanwhile, a two-dimensional finite element model is developed to simulate and verify the experimental observations. The results show that the increase of duty cycle of pulse signal should be the crucial factor affecting the temperature enhancement effect of flowing SPIO-albumin microbubble solution under the exposure to high-intensity focused ultrasound. The current results help us to better understand the influence of different acoustic setting parameters on the thermal effect of dual-modal magnetic UCA microbubbles, and provide useful guidance for ensuring the safety and effectiveness of the application of SPIO-albumin microbubbles in clinics.

Parameter optimization and quality analysis of pulsed laser joining of 316L stainless steel and polylactic acid

To realize the joining of dissimilar material 316L stainless steel with polylactic acid (PLA), the laser-assisted metal-plastic direct joining (LAMP) method was applied, and the process parameters were optimized based on the method of orthogonal experiment, and the quality of the joint was studied. The influence law of each influencing factor of the joining process on the joint quality and joint morphology was obtained through orthogonal experiments, to find out the maximum influencing factor and obtain the optimal process combination. By a universal tensile testing machine to find out the influence of the process parameters on the joint failure modes. The results showed that the laser power, pulse duty ratio, and laser speed had a major influence on the shear force, elongation at break and joint width. The maximum shear force achieved by the optimized method was 1694.379 N, reaching 88.73 % of the tensile force of the PLA base material, and the elongation at break was 5.47 %, reaching 76.91 % of the base material, obtained a more satisfactory joint effect. The correspondence between five joint morphologies and four failure modes is established, and different process parameters can be selected according to different applications of 316L stainless steel-PLA composite materials, to optimize industrial manufacturing.

Double duty ratio PWM control method for a novel HSV actuator with low power consumption

This paper presents a novel high speed valve (HSV) actuator with low power consumption. The structure design of tapered armature and control method of double duty ratio pulse width modulation (PWM) are proposed in the HSV actuator to improve steady and transient characteristics. The electric-magneto-mechanical model of the HSV actuator is established and investigated by theoretical analysis. Parameters improvement of the HSV actuator is analyzed by the model, and optimized results for a prototype actuator have been obtained. The experimental and simulation curves agree well with the changing trend, and show that the opening time of the HSV actuator is 7.3 ms, the closing time is 20 ms, and power consumption in maintenance stage is 1.35 W, within the stroke of 2.5 mm. Compared with normal driving method, the proposed structure and method have the advantages of opening time reduced by 37%, closing time reduced by 29%, and steady-state power consumption reduced by 93.5%. The proposed structure and method in the HSV actuator are available to meet the driving requirements of both steady and transient performance in fluid control systems better, especially in power shortage or power supply inconvenient engineering.

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.

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.

Competition between heating and cooling during dynamic self-heating degradation of amorphous InGaZnO thin-film transistors

The dynamic self-heating (SH) instability of a-InGaZnO (a-IGZO) thin-film transistors (TFTs) was systematically investigated under static drain bias and pulsed gate voltage. The a-IGZO TFTs exhibited three distinct degradation stages, including a slightly positive shift of threshold voltage (ΔVth), then a gradually negative ΔVth, and finally an accelerated negative shift leading to normally-on characteristics. The underlying mechanisms were clarified to be SH-enhanced positive bias stress (PBS) instability, SH-generated donor defects, and the donor-populated central channel, respectively. By changing the duty ratio, frequency, peak, and base periods of gate pulses. The competition between heating and cooling periods was found to dominate the behavior and degree of dynamic SH degradations, suggesting a feasible instability-relieving method by sophisticatedly adjusting the dynamic operating conditions.

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.

Study on the electrically enhanced process for cadmium removal by a pulse in a sulfuric acid system

Aiming at the problems of low cadmium removal efficiency in zinc replacement and poor pressing plate effect of cadmium residues in the latter stage of the process, a novel electrically enhanced replacement method for cadmium removal based on a pulsed electric field was proposed. Comparative experiments with different current types verified the superiority of pulse current in the cadmium removal process to other known methods. At 45 °C, anode current density of 20 A·m−2, cathode-to-anode area ratio of 1:3, pulse duty ratio of 1:4, and pulse frequency of 500 Hz, the cadmium removal efficiency reached 96.80% in three hours. Furthermore, electrochemical test results for anodic reaction illustrated that the rise in solution acidity and Cd2+ concentration accelerated the replacement of zinc to cadmium. Correspondingly, increases in temperature, Cd2+ concentration, and solution pH inhibited the dissolution of the precipitated cadmium.

Probing the Anti-Corrosion Behavior of X65 Steel Underwater FSW Joint in Simulated Seawater

To detect the corrosion resistance of a friction stud welding (FSW) joint in simulated seawater (a 3.5 wt% NaCl solution), the pulse electrochemical deposition method was used for electroplating Ni coating with different duty ratios (50%, 80%, and 100%) on the surface of FSW joint. The microstructure and surface structure of the coating were observed by micro-spectroscopy and other characterization methods. The corrosion behavior of the coating was analyzed by means of macroscopic electrochemical testing. The local corrosion law of joint surface and coating surface defects were innovatively explored by using micro-zone electrochemical scanning system. The coating characterization results showed that, as the duty ratio continues to increase, the coating surface becomes denser and smoother, and the corrosion products such as Fe2O3, Fe3O4, and FeOOH are generated. The results of macroscopic electrochemical experiment indicated that the coating with 100% duty ratio has the lowest corrosion current density and the maximum polarization resistance. The scanning vibrating electrode technique results showed that the corrosion current density in the defect area is higher than that in the coating area, and the maximum corrosion current density decreases with the increase of duty ratio. The localized electrochemical impedance spectroscopy results indicated that the localized impedance at the welded zone was the largest, and with the increase of the pulse duty ratio, the impedance diffusion in the defect area was decreasing.

A Random Pulse Position-Based Selective Noise Cancellation Modulation Method for SVPWM Driven PMSMs

Permanent magnetsynchronous motors (PMSMs) are usually driven by the SVPWM technique, which leads to annoying sideband noise near the switching frequency. Traditional random modulation techniques increase the possibility of resonance with the motor structure. This study proposes a novel random pulse position modulation-based strategy to eliminate the current harmonics and electromagnetic noise at a specific frequency. The proposed method adopts a constant switching frequency. A unique design between the pulse position and duty ratio cancels the current harmonics and acoustic noise at the selected frequency. The results show that resonance can be avoided effectively if the chosen frequency is close to the natural frequency. It is concluded that the proposed method is beneficial at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in the low speed applications.