kHz Pulse Frequency Research Articles

Enhancing selective production of atomic oxygen through nanosecond pulse-burst driven mode in a He/O2 dielectric barrier discharge

In this study, the temporal evolution of O atoms in a nanosecond burst-pulsed dielectric barrier discharge (DBD) is measured by two-photon absorption laser-induced fluorescence spectroscopy. The experiment is conducted at burst conditions of 50, 100, and 200 kHz pulse frequency, 10 Hz burst frequency, and 20–400 pulses in 0.1%–2% O2 + He mixtures. The accumulation effect of O atoms in the burst mode is observed and the density gradually saturates at around 100 pulses. Increasing the pulse frequency effectively enhances the O saturation density. The 0-dimensional kinetic model reveals that the saturation effect is primarily balanced by the formation and loss characteristics of O atoms. Similar saturation effect is also observed in the typical continuous periodic pulse mode (one pulse each cycle), but with a saturation density about one order of magnitude lower than that in the burst case, highlighting the burst excitation mode as an effective method for enhancing the instantaneous peak production of O atoms. Further investigations into the influence of O2 proportion on the selective production of O atoms are also performed. The results suggest that a low O2 proportion (<2%) and pulse-burst driven mode for the He/O2 DBD facilitates the selective production of O atoms while competing with O3 formation.

The effect of fs-laser micromachining parameters on surface roughness, bio-corrosion and biocompatibility of nitinol

The thermo-pseudo elastic property of nitinol attracts the manufacturing sector to produce more biomedical implants from this binary alloy. However the release of Ni ions from the implanted nitinol causes a toxic nature and poses a harmful effect if the implants are in a physiological environment for a long period. This research is an attempt to control the release of Ni ions with improved bio-corrosion resistance and biocompatibility by mitigating the process parameters of femtosecond laser micromachining. The exclusive nitinol specimens are synthesized through the blending-compaction-sintering route. The specimens are machined under three varied levels of laser parameters to the dimensions compatible with the common cardiovascular stent. The surface roughness examination confirms the very minimal surface roughness of 10.83 nm is achieved from level 2 machining condition (36 W laser power, 500 mm/s scanning speed, 9 kHz pulse frequency). The potentiodynamic polarization technique is followed in the presence of a Simulated Body Fluid (SBF) environment to assess the bio-corrosion behaviour. XRD and SEM investigating methods are employed post-corrosion test, to assess the deposition of the TiO2 layer. The minimal bio-corrosion rate is observed from the specimen with very minimal surface roughness. XRD and SEM results explore the thicker deposition of the TiO2 layer for the specimens from level 2 machining conditions, with minimal corrosion rate and surface roughness.

The influence of pulse duration and duty cycle on the energy flux to the substrate in high power impulse magnetron sputtering

The paper focuses on measurements of the total energy flux and normalized energy flux onto the substrate during high power impulse magnetron sputtering (HiPIMS) in a wide range of the pulse duration and discharge current. Al, Cr and Ti targets with a diameter 76 mm are used for sputtering. HiPIMS parameters include 1 kW discharge power, 15 to 150 А discharge current, 0.4–10 kHz pulse frequency, and 5–100 μs pulse duration. It is shown that the use of short pulses leads to ∼40 and 70% growth in the total energy flux onto floating and biased (−100 V) substrates, respectively. The energy per unit volume of the deposited coating increases by several times, if the pulse duration and the duty cycle are reduced. The paper examines reasons for the increased total and normalized energy fluxes onto the substrate observed after the pulse parameter modulation in the sputtering process.

Pulsed versus direct current electrochemical co-catalytic peroxymonosulfate-based system: Elevated degradation and energy efficiency with enhanced oxidation mechanisms

In this work, the pulsed electrochemical (PE) system was investigated to activate peroxymonosulfate (PMS) with the addition of Fe(III) to achieve efficient degradation of sulfamethoxazole (SMX) with reduced energy consumption, in comparison with the direct current (DC) electrochemical system. The operational conditions of PE/PMS/Fe(III) system were optimized as 4 kHz pulse frequency, 50% duty cycle, and pH 3, at which 67.6% reduction of energy consumption and enhanced degradation performance were achieved compared to the DC/PMS/Fe(III) system. Results of electron paramagnetic resonance spectroscopy analysis and quenching and chemical probe experiment revealed the presence of •OH, SO4•−, and 1O2 in the system, with •OH being the dominant role. The concentrations of these active species were averagely 15 ± 1% higher in the PE/PMS/Fe(III) system than those of the DC/PMS/Fe(III) system. Identification of SMX byproducts was achieved based on high resolution mass spectrometry analysis to predict the degradation pathways. The SMX byproducts could eventually be eliminated by the PE/PMS/Fe(III) system with extended treatment time. Overall, the PE/PMS/Fe(III) system was demonstrated with high energy and degradation performance, and is appear to be an robust strategy for practical treatment of wastewater.

Investigation of laser micro-drilling machinability and performance optimization of polymer nanocomposites reinforced with different carbon allotropes

The comparative assessment of the laser micro-drilling machinability of polymer matrix nanocomposites dispersed with conducting fillers of different carbon allotropes (carbon nanotube (CNT), graphite, and carbon black (CB)) to produce minimum taper and heat-affected zone (HAZ) has been first time reported in this article. The required composite specimens are synthesized via ultrasonicator-assisted compression molding method and characterized for their thermal, electrical, and mechanical properties. The central composite design-based response surface methodology (CRSM) is implemented for the planification of experimentation using a pulsed Nd:YAG laser and subsequent higher-order regression modeling of the desired performance indicators. The contemporary accelerated particle swarm optimization (APSO) technique and metaheuristic whale optimization algorithm (WOA) have been utilized to define optimum controllable process parameters (pulse frequency, cutting speed, lamp current, and air pressure) and the assortment of optimum conditions are justified by performing confirmatory tests. CNT-reinforced composite material exhibits superior tensile, hardness, and thermal properties whereas graphite-based polymer composite show good electrical conductivity. The most minor taper and HAZ values are observed in the laser micro-drilling of epoxy-based CNT and CB materials, respectively. The two swarm-based algorithms predict more accurate results for the desired output responses than the statistical CRSM, with the least errors compared to the values attained by the WOA. Optimal taper (with CNT/epoxy composite at 30 m/s cutting speed, 22.6 amp lamp current, 3 kHz pulse frequency, and 1 kg/cm2 air pressure) and HAZ (with CB/epoxy composite at 30 m/s cutting speed, 22.97 amp lamp current, 3 kHz pulse frequency, and 5 kg/cm2 air pressure) values obtained in the confirmatory test showed 15% and 12% errors, respectively, as compared to the predicted data in WOA.

Preparation and Investigation of Ni–Co–P Alloy Coatings Using Jet Electrodeposition with Varying Pulse Parameters

Ni–Co–P alloy coatings were successfully fabricated by jet electrodeposition with varying pulse frequencies and duty cycles in order to prolong the longevity of steel C1045 substrates. The results showed that the microstructures and properties of samples were significantly affected by pulse frequencies and duty cycles. All the samples with varying pulse frequencies and duty cycles exhibited a face-centered cubic (FCC) structure. Additionally, the average grain size of the samples reached 20.6 nm. The microhardness of the coatings was observed to first increase, and then decrease, with a rise in pulse frequencies and duty cycles. The microhardness reached 656.2 HV0.1, and the wear scar width of the coatings reached 414.4 µm at 4 kHz pulse frequency and 80% duty cycle. Additionally, the corrosion current densities (Icorr) of samples reached a minimum value of 0.74 µA·cm−2, the corrosion rates (Rcorr) reached a minimum value of 8.9 µm·year−1, and the charge transfer resistance (Rct) reached a maximum value of 8.36 × 104 Ω·cm−2, which indicated the optimal seawater corrosion resistance of the deposited coatings.

Pre-Shaped Burst-Mode Hybrid MOPA Laser System at 10 kHz Pulse Frequency

A temporal pre-shaped burst-mode hybrid fiber-bulk laser system was illustrated at a 10 kHz rate with a narrow spectral linewidth. A theoretical model was proposed to counteract the temporal profile distortion and compensate for the desired one, based on reverse process of amplification. For uniformly modulated injection, amplified shapes were recorded and investigated in series for their varied pulse duration, envelope width and amplification delay, respectively. The pre-shaped output effectively realized a uniform distribution on a time scale for both the burst envelope and pulse shape under the action of the established theoretical method. Compared with previous amplification delay methods, this model possesses the capacity to extend itself for applications in burst-mode shaping with variable parameters and characteristics. The maximum pulse energy was enlarged up to 9.68 mJ, 8.94 mJ and 6.57 mJ with a 300 ns pulse duration over envelope widths of 2 ms to 4 ms. Moreover, the time-averaged spectral bandwidths were measured and characterized with Lonrentz fits of 68.3 MHz, 67.2 MHz and 67.7 MHz when the pulse duration varied from 100 ns to 300 ns.

COx-free co-cracking of n-decane and CH4 to hydrogen and acetylene using pulsed spark plasma

Heavy hydrocarbons pyrolysis is a high energy consumption and high carbon emission process. The non-thermal plasma is a promising technology to convert heavy oil into value-add chemicals without COx emission. In this paper, n-decane was used as a model compound of the heavy hydrocarbons, and its co-cracking characteristics with CH4 by micro-second pulsed spark plasma were investigated in terms of carrier gas species and pulse frequencies. The maximum hydrogen and acetylene flow rates (48.7 mL/min and 29.9 mL/min) with energy consumption of 6.4 kW·h/m3H2 and 10.4 kW·h/m3C2H2 were achieved under the condition of 1 kHz pulse frequency. Compared with those of the Ar atmosphere, H2 and C2H2 production improved prominently by 41.4% and 133.6%. It indicates that the H radicals from CH4 plasma played a dominating role in the n-decane cracking, which was verified via controlled experiments in H2 atmosphere. The evolution of the optical emission spectroscopy (OES) revealed that the rotational temperature rose rapidly to 3700±300 K in hundreds of nanoseconds, during which the n-decane was cracked into small particles, such as H, C2, CH and so on. Based on these results, a possible reaction mechanism of the co-cracking was also discussed. This work may provide an effective COx-free method for fossil utilization.

LIPUS far-field exposimetry system for uniform stimulation of tissues in-vitro: development and validation with bovine intervertebral disc cells

Therapeutic Low-intensity Pulsed Ultrasound (LIPUS) has been applied clinically for bone fracture healing and has been shown to stimulate extracellular matrix (ECM) metabolism in numerous soft tissues including intervertebral disc (IVD). In-vitro LIPUS testing systems have been developed and typically include polystyrene cell culture plates (CCP) placed directly on top of the ultrasound transducer in the acoustic near-field (NF). This configuration introduces several undesirable acoustic artifacts, making the establishment of dose-response relationships difficult, and is not relevant for targeting deep tissues such as the IVD, which may require far-field (FF) exposure from low frequency sources. The objective of this study was to design and validate an in-vitro LIPUS system for stimulating ECM synthesis in IVD-cells while mimicking attributes of a deep delivery system by delivering uniform, FF acoustic energy while minimizing reflections and standing waves within target wells, and unwanted temperature elevation within target samples. Acoustic field simulations and hydrophone measurements demonstrated that by directing LIPUS energy at 0.5, 1.0, or 1.5 MHz operating frequency, with an acoustic standoff in the FF (125–350 mm), at 6-well CCP targets including an alginate ring spacer, uniform intensity distributions can be delivered. A custom FF LIPUS system was fabricated and demonstrated reduced acoustic intensity field heterogeneity within CCP-wells by up to 93% compared to common NF configurations. When bovine IVD cells were exposed to LIPUS (1.5 MHz, 200 μs pulse, 1 kHz pulse frequency, and ISPTA = 120 mW cm−2) using the FF system, sample heating was minimal (+0.81 °C) and collagen content was increased by 2.6-fold compared to the control and was equivalent to BMP-7 growth factor treatment. The results of this study demonstrate that FF LIPUS exposure increases collagen content in IVD cells and suggest that LIPUS is a potential noninvasive therapeutic for stimulating repair of tissues deep within the body such as the IVD.

Fabrication of Silicon Microfluidic Chips for Acoustic Particle Focusing Using Direct Laser Writing.

We have developed a fast and simple method for fabricating microfluidic channels in silicon using direct laser writing. The laser microfabrication process was optimised to generate microfluidic channels with vertical walls suitable for acoustic particle focusing by bulk acoustic waves. The width of the acoustic resonance channel was designed to be 380 µm, branching into a trifurcation with 127 µm wide side outlet channels. The optimised settings used to make the microfluidic channels were 50% laser radiation power, 10 kHz pulse frequency and 35 passes. With these settings, six chips could be ablated in 5 h. The microfluidic channels were sealed with a glass wafer using adhesive bonding, diced into individual chips, and a piezoelectric transducer was glued to each chip. With acoustic actuation at 2.03 MHz a half wavelength resonance mode was generated in the microfluidic channel, and polystyrene microparticles (10 µm diameter) were focused along the centre-line of the channel. The presented fabrication process is especially interesting for research purposes as it opens up for rapid prototyping of silicon-glass microfluidic chips for acoustofluidic applications.

Improvement in machining accuracy of micro-dimples fabricated in a sandwich-like electrochemical micromachining unit using a porous cathode

Surface texture plays a significant role in improving interfacial performance of mechanical components. Electrochemical micromachining is a feasible method for preparing micro-dimples. Sandwich-like electrochemical micromachining (SLEMM) could be used for generating micro-dimples, in which the cathodic tool keeps in close contact with the mask firmly laminated to the anodic workpiece surface, and the dissolution of the workpiece takes place in the enclosed unit. The shallow micro-dimples could be machined with the electrolytic products accumulating on the workpiece surface in the enclosed unit of SLEMM. A porous metal cathode was employed in SLEMM resulting in an open unit, which could remove electrolytic products and generate deep micro-dimples. However, there is poor machining accuracy of micro-dimples obtained with stationary electrolyte over the porous cathode. Pulse electrochemical micromachining is an effective method for enhancing the machining accuracy of micro-dimples. Therefore, the pulse is applied to improve the machining accuracy of micro-dimples generated in SLEMM with a porous metal cathode. And the different electrolyte flow modes over the porous metal cathode are employed to investigate their influence on machining accuracy of micro-dimples. The experimental results indicate that the pulse current power supply could improve the machining accuracy of micro-dimples, compared with direct current power supply. Furthermore, the machining accuracy of micro-dimples could be improved by lateral flow mode, compared with radial flow mode. With a 40% pulse duty ratio, 4 kHz pulse frequency, 15 V applied voltage, and 6 s effective machining time, the micro-dimples have a good machining accuracy on multiple anodic workpieces.

Residual stress control of Cu film deposited using a pulsed direct current magnetron sputtering

Residual stress of 10 μm thick copper (Cu) film deposited using direct current (DC) magnetron sputtering system was analyzed for various pulsed DC power conditions. It is found that the increase of pulse frequency at a fixed duty ratio of 80% from continuous wave (CW) to 100 kHz while maintaining the time average power significantly decreased the residual stress of Cu film from 21.75 MPa to 1.8 MPa. The decrease of pulse duty ratio further decreased the residual stress by showing 0.7 MPa at 60% of duty ratio and 50 kHz pulse frequency. Therefore, compared to CW power, Cu film with ~1/30 lower residual stress could be deposited by using DC pulse power. The decrease of residual stress by pulsing and by decreasing the pulse duty ratio while keeping the same time average power was related to the denser film density and smaller grain size of deposited Cu film caused by increased instant sputter power during the pulsing.

UV nanosecond laser machining and characterization for SiC MEMS sensor application

In this paper, we design a symmetric quad-beam accelerometer structure for z-axis sensing. Considering the extremely high chemical stability of SiC, traditional dry etching is not suitable for machining SiC MEMS sensor. Thus, we put forward a method using ultraviolet laser cutting to release cantilever beam of SiC accelerometer and using laser ablating to process mass. Pulse Repetition Frequency (PRF) and processing laps are optimized to obtain high-quality surface morphology and much less thermal effect. Finally, we use the optimal parameters with 35 kHz pulse frequency, 4 processing laps, 200 mm/s scanning speed to process through-hole. Combing with Raman spectrum and EDS spectrum, the feasibility of laser machining SiC sensor is studied. The result shows that in machining cantilever beam the carbonization and generation of silicon accelerates the trepanning depth of SiC. However, in machining the hole, the thermal effect of photon energy barely adds influence on region from boundary of hole to 30 μm. Thus, it is feasible to use laser cutting to release cantilever beam while it is difficult to use laser ablating processing back cavity of accelerometer. The time of laser micromachining 4 H-SiC cantilever beam is less than 2 s. Compared with the traditional ICP etching (0.2–1.3 μm/min), etching rate with laser ablating in releasing cantilever beam significantly increases nowadays. Finally, the sensitivity of SiC accelerometer is measured to 0.644 μV/g.

Microstructure and mechanical properties of ultrasonic pulse frequency tungsten inert gas welded Ti-22Al-25Nb (at.%) alloy butt joint

Microstructural observations of cross sections of butt joints of Ti-22Al-25Nb (at.%) alloy manufactured using ultrasonic pulse frequency tungsten inert gas welding method at different welding parameters without and with welding wire, the butt joint at 50 KHz pulse frequency with welding wire has the largest equiaxed crystal zone, finest columnar crystals, and improves damage of dendritic crystals and overburning. The tensile strength, yield strength and elongation of butt joint at 50 KHz welding frequency with welding wire are the highest, compared with those of butt joints at other welding parameters without welding wire, and the fracture of it is ductile fracture mode of dimples. Further, fusion zone composed of α2 + β/B2 two phases and heat affected zone composed of α2 + O + β/B2 three phases in the butt joint having the highest tensile strength are determined using X-ray diffraction technology. In this butt joint, the microhardness of heat affected zone is the highest, followed by that of base material, fusion zone lowest.

Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma

Radio-frequency driven atmospheric pressure plasmas are efficient sources for the production of reactive species at ambient pressure and close to room temperature. Pulsing the radio-frequency power input provides additional control over species production and gas temperature. Here, we demonstrate the controlled production of highly reactive atomic oxygen and nitrogen in a pulsed radio-frequency ( MHz) atmospheric-pressure plasma, operated with a small % air-like admixture (/ at ) through variations in the duty cycle. Absolute densities of atomic oxygen and nitrogen are determined through vacuum-ultraviolet absorption spectroscopy using the DESIRS beamline at the SOLEIL synchrotron coupled with a high resolution Fourier-transform spectrometer. The neutral-gas temperature is measured using nitrogen molecular optical emission spectroscopy. For a fixed applied-voltage amplitude (234 V), varying the pulse duty cycle from 10% to 100% at a fixed 10 kHz pulse frequency enables us to regulate the densities of atomic oxygen and nitrogen over the ranges of – and – , respectively. The corresponding 11 K increase in the neutral-gas temperature with increased duty cycle, up to a maximum of K, is relatively small. This additional degree of control, achieved through regulation of the pulse duty cycle and time-averaged power, could be of particular interest for prospective biomedical applications.

Decolorization of molasses-based distillery wastewater by means of pulse electro-Fenton process

The decolorization of actual molasses wastewater using the electro-Fenton (EF) process was investigated. The optimization of decolorization was performed by means of a Box-Behnken design (BBD), with the operating parameters studied being the applied voltage, H2O2 dosage and reaction time. The results showed that the color removal efficiency reached 88.50% under the optimal conditions, in which 2.86V, 15.8% H2O2/wastewater ratio and 90.7min reaction time were applied. The pulse electro-Fenton (PEF) process using the applied voltage and reaction time in the obtained optimal condition was performed afterward. The effects of pulse frequency, pulse duty cycle, electrode distance, H2O2/wastewater ratio and H2O2 stepwise addition were studied. From the results, under the optimal conditions of 2.5kHz pulse frequency, 25% pulse duty cycle, 2cm electrode distance and 15.8% H2O2/wastewater ratio, the color and COD removal efficiencies reached 89.59% and 40.71%, respectively. Under these conditions, the PEF process could reduce the energy consumption by at least 75% compared with the regular EF process. Additionally, compared with stepwise addition, the single step addition of H2O2 was more effective in color removal.

Assessment of drilling characteristics of alumina coated on aluminium using CO2 laser

Abstract This paper reports experimental investigation of effect of laser parameters on the drilling responses of alumina coated aluminium substrates using 1.8 kW CO 2 pulsed mode laser. Alumina was deposited on 4 mm thick Al 6065 plates by plasma spray technique. The main influencing factors were: Laser power on spatter deposition and Heat Affected Zone; Pulse frequency on entrance and exit circularities; Piercing time on taper, heat affected zone and exit circularity. Genetic algorithm optimization results indicated simultaneous improvement of 5.2% in hole quality at 416.6 W laser power, 1.4 kHz pulse frequency and 0.4 s piercing time. Response Surface Methodology indicated minimum spatter deposition area of 11.57 mm 2 , Heat Affected Zone 0.589 mm, taper 2.35° and maximum circularity at entrance 0.88 and exit 0.905 at 400 W laser power, 1.2 kHz frequency and 0.48 s piercing time. These results were in close agreement with those of Genetic algorithm. The optimum values were validated through confirmatory experiments.

Parametric Study of Pulsed CO2 Laser Surface Treatment of Alumina Ceramics

AbstractThis paper focuses on investigating the influence of laser power, pulse frequency and scanning speed on material removal rate and surface roughness during CO2 laser surface treatment of alumina ceramics. Pulse frequency and laser power were the significant factors influencing the material removal rate and surface roughness, respectively. Adequate response surface models were established to correlate the laser parameters and the measured responses. Grey relational analysis predicted the optimal responses at 90 W laser power, 5 kHz pulse frequency and 400 mm/s scanning speed. Desirability function based Multi objective optimization results indicated that minimum material removal rate (0.5117 mm3/s) and surface roughness (0.5968 µm) are achieved at 90 W laser power, 5 kHz pulse frequency and 337.37 mm/s scanning speed which were in close agreement with Grey Relational results. Increase in homogeneity and smoothness of the laser treated alumina surface along with formation of micro recast particles away from the laser traverse path were evidenced by the SEM micrographs.

Synthesis of ultra-smooth and ultra-low friction DLC based nanocomposite films on rough substrates

Rough TiC/a-C films were intentionally grown on smooth surface to simulate a rough finishing of industrial substrates. Surface roughness and growth dynamics of TiC/a-C nanocomposite films deposited on such rough surfaces by non-reactive pulsed-DC (p-DC) sputtering of graphite targets at 350 kHz pulse frequency were studied using atomic force microscopy, cross-sectional scanning electron microscopy. Intensive concurrent ion impingement during the film growth at higher pulse frequency of p-DC sputtering leads to rapid smoothing of such initial rough surfaces. It was shown that rapid smoothing of initially rough surfaces with RMS roughness ~ 6 nm to < 1 nm can be effectively achieved by 350 kHz p-DC sputtering. These films exhibit dense and glassy microstructure. The surface roughness strongly influences the frictional behavior of TiC/a-C nanocomposite films where the rougher surfaces yielded higher steady state friction coefficient (CoF). The observed dynamic smoothing phenomenon was applied to obtain ultra-smooth and ultra-low friction (μ ~ 0.05) TiC/a-C:H nanocomposite films on industrial polished steel substrates by 200 and 350 kHz p-DC sputtering of Ti-targets in an argon/acetylene atmosphere.

Surface textured ZnO:Al thin films by pulsed DC magnetron sputtering for thin film solar cells applications

Transparent conducting thin films of ZnO:Al (Al-doped ZnO, AZO) were prepared via pulsed DC magnetron sputtering with good transparency and relatively lower resistivity. The AZO films with 800 nm in thickness were deposited on soda-lime glass substrates keeping at 473 K under 0.4 Pa working pressure, 150 W power, 100 μs duty time, 5 μs pulse reverse time, 10 kHz pulse frequency and 95% duty cycle. The as-deposited AZO thin films has resistivity of 6.39 × 10 −4 Ω cm measured at room temperature with average visible optical transmittance, T total of 81.9% under which the carrier concentration and mobility were 1.95 × 10 21 cm −3 and 5.02 cm 2 V −1 s −1, respectively. The films were further etched in different aqueous solutions, 0.5% HCl, 5% oxalic acid, 33% KOH, to conform light scattering properties. The resultant films etched in 0.5% HCl solution for 30 s exhibited high T total = 78.4% with haze value, H T = 0.1 and good electrical properties, ρ = 8.5 × 10 −4 Ω cm while those etched in 5% oxalic acid for 150 s had desirable H T = 0.2 and relatively low electrical resistivity, ρ = 7.9 × 10 −4 Ω cm. However, the visible transmittance, T total was declined to 72.1%.