Material Processing Applications Research Articles

Secondary electron emission due to multi-species iodine ion bombardment of different target materials

Ion-induced secondary electron emission (SEE) is a fundamental surface interaction that strongly influences many plasma discharges. Recently, interest in iodine plasmas is growing due to new material processing and space propulsion applications, but data for SEE yields due to iodine ion bombardment remain scarce. Additionally, due to the formation of multiple ion species in typical iodine plasmas and surface chemical reactions leading to iodide layer formation, the effective SEE yield is expected to differ from that for individual ion species on clean surfaces. In this work, we measure the SEE yield of multi-species iodine ion beams bombarding different target materials (Mo, W, Al, Ti, Cu, carbon-carbon, and steel) in the energy range of 0.6–1.4 keV. An ion beam is produced by extracting and accelerating ions from a gridded ion source based on an inductively coupled plasma (ICP). SEE yields of downstream targets are measured using a conventional electrostatic probe technique, and the ion beam composition is determined using time-of-flight spectrometry. The beam is composed predominately of atomic (I+) and molecular (I2+) ions whose ratio changes depending on the ICP power. Yields depend strongly on the target material and beam composition and vary between 0.05 and 0.4 depending on whether potential or kinetic emission processes dominate.

Learning-Based SMPC for Reference Tracking Under State-Dependent Uncertainty: An Application to Atmospheric Pressure Plasma Jets for Plasma Medicine

The increasing complexity of modern technical systems can exacerbate model uncertainty in model-based control, posing a great challenge to safe and effective system operation under closed loop. Online learning of model uncertainty can enhance control performance by reducing plant–model mismatch. This article presents a learning-based stochastic model predictive control (LB-SMPC) strategy for reference tracking of stochastic linear systems with additive state-dependent uncertainty. The LB-SMPC strategy adapts the state-dependent uncertainty model online to reduce plant–model mismatch for control performance optimization. Standard reachability and statistical tools are leveraged along with the state-dependent uncertainty model to develop a chance constraint-tightening approach, which ensures state constraint satisfaction in probability. The stability and recursive feasibility of the LB-SMPC strategy are established for tracking time-varying targets, without the need to redesign the controller every time the target is changed. The performance of the LB-SMPC strategy is experimentally demonstrated on an atmospheric pressure plasma jet (APPJ) testbed with prototypical applications in plasma medicine and materials processing. Real-time control comparisons with learning-based MPC with no uncertainty handling and offset-free MPC showcase the usefulness of LB-SMPC for predictive control of safety-critical systems with hard-to-model and/or time-varying dynamics.

Magneto-Bioconvection Flow of Williamson Nanofluid over an Inclined Plate with Gyrotactic Microorganisms and Entropy Generation

The fluid flow through inclined plates has several applications in magneto-aerodynamics, materials processing and magnetohydrodynamic propulsion thermo-fluid dynamics. Inspired by these applications, the rate of entropy production in a bio-convective flow of a magnetohydrodynamic Williamson nanoliquid over an inclined convectively heated stretchy plate with the influence of thermal radiation, porous materials and chemical reaction has been deliberated in this paper. The presence of microorganisms aids in stabilizing the suspended nanoparticles through a bioconvection process. Also, the thermal radiation assumed an optically thick limit approximation. With the help of similarity transformations, the coupled partial differential equations are converted to nonlinear ordinary differential equations and the resulting model is numerically tackled using the shooting method. The influences of the determining thermo-physical parameters on the flow field are incorporated and extensively discussed. The major relevant outcomes of the present analysis are that the upsurge in values of Schmidt number decays the mass transfer characteristics, but the converse trend is depicted for boost up values of the thermophoresis parameter. Enhancement in bioconvection Peclet and Schmidt numbers deteriorates the microorganism density characteristics. Further, the upsurge in the Williamson parameter declines the Bejan number and irreversibility ratio.

Investigation on Parameters of Atmospheric Pressure Plasma Jet by Electrical and Optical Methods

The atmospheric pressure plasma jet works under atmospheric pressure condition, has been developed for surface treatment and biomedical applications. The produced jet has been characterized by electrical and optical methods. To characterize cold atmospheric argon plasma discharge, its electron density, and electron energy (temperature) at various conditions have been estimated by using different techniques such as power balance, stark broadening, and intensity ratio methods respectively. Atmospheric pressure plasma jet (APPJ) has drawn much attention all over the world due to its applications in material processing, biomedical material processing, and thin film deposition. APPJ has been produced, using a high voltage and high frequency power supply (0-20 kV) and an operating frequency of 20 kHz. Results showed that the electron density was of the order of 1014 cm-3 and 1016 cm-3 as determined by power balance, intensity ratio, and stark broadening methods respectively while electron temperature was estimated to be about 0.46 eV and 0.53 eV at 3 kV and 4 kV respectively by using intensity ratio method. The energy dissipation per cycle of the discharge was also estimated by using the Lissajous figure method. Our results confirmed that the parameter such as electron temperature and density depend on the applied voltage, gas flow rate, and electrode distance as well.

Few-mode random fiber laser with a switchable oscillating spatial mode.

Random fiber lasers are of tremendous interest to diverse applications for optical fiber sensing, speckle-free imaging. To date, random fiber lasers with fundamental mode oscillation have been well developed. However, controllable oscillating spatial mode in random fiber lasers have not been reported yet. Here, we propose and demonstrate a few-mode random fiber laser with a switchable oscillating spatial mode based on mode injection locking. An external signal light is injected to realize the locking of transverse mode in this random fiber laser and the direct oscillations of the fundamental mode, hybrid mode, and high order mode can be realized, respectively. This random fiber laser operates in the high-order LP11 mode stably with a threshold of as low as 88 mW. High efficiency and high purity cylindrical vector beams can be obtained by removing the degeneracy of the LP11 mode. This work may pave a path towards random fiber lasers with controllable spatial modes for specific applications in mode division multiplexing, imaging, and laser material processing.

Efficient Fe:CdTe laser producing 0.35 J pulses in the 5 µm spectral range.

High-energy laser operation of a Fe2+-doped single-crystal CdTe is demonstrated at the temperature of 77 K. Pumped with 250 µs pulses of a 4.08 µm Fe:ZnSe laser, the Fe:CdTe laser produced a record output of 0.35 J, with a slope efficiency of 44%. A further up-scaling by employing high-energy pump sources is feasible, thus facilitating material-processing applications. The laser was tunable from 4.86 to 5.37 µm. In a nonselective cavity, the laser's central wavelength was 5.03 µm at 77 K, and shifted to 5.23 µm at 215 K. At the later operation point, reachable using a Peltier element, the laser still produced 0.15 J of output energy with an efficiency of 22%.

Distinctive patterns and characteristics of neon jet launched from plasma candle device

AbstractThis study reported the characterization of neon plasma jets emerging from a novel plasma device known as a plasma candle. The device launches stable, wide, and long cold plasmas in a shape resembling a flickering candle flame. The neon plasma candle (Ne‐PC) exhibited several interesting phenomena in terms of the discharge propagation and plume pattern, which are not common in other jet devices. A particular attention was paid to the dynamics of the gas flow, which was found to have significant effects on the discharge characteristics and jet shape. It is found that a porous disc in the Ne‐PC device distributed the gas flow uniformly, and subsequently enhanced the discharge initiation and formed a uniform conical jet. Moreover, the effect of the applied voltage on the flow dynamics led to a transformation in the conical shape of the jet to a fork‐like shape. This phenomenon did not appear in the helium plasma candle, and it is observed that the induced electrohydrodynamic (EHD) as well as the low velocity, diffusion coefficient, and momentum of the gas play a crucial role in this phenomenon. Optical emission spectroscopy measurements provided insights into the mechanism of the plume pattern and described its effect on the generated species. At higher applied voltages, a significant reduction in neon emissions was observed, but higher RONS were generated, due to the entrainment of the surrounding air. Furthermore, it is found that the Ne‐PC has a higher ability to generate RONS than the helium candle and neon in the conventional plasma jet devices (Ne‐CPJ), thereby suggesting its feasibility for material processing and biomedical applications.

High-efficiency polarization-independent gold-coated crossed grating under normal incidence

A gold-coated crossed grating (GCCG) is designed and fabricated to improve the signal contrast and signal-noise-ratio (SNR) of the grating interferometer (GI) with the high-efficiency polarization-independent property. The proposed grating based on two dimensional (2D) periodic gold nanocylinder structure can diffract both TE and TM polarizations into four first orders with measured diffraction efficiency (DE) of more than 21.8% and total DE of more than 88.8% at 780 nm incident wavelength under normal incidence, which shows the highest DE and brings much benefits to the SNR and compactness in practical applications. Moreover, the optimized GCCG also shows great tolerances of duty cycle, groove depth, and sidewall angle for grating fabrication. The measured DEs from the experimental results substantiate themselves with the numerical calculations. Additionally, the measured DE of the (±1, 0) order and (0, ±1) order all exceed 18% at the wavelength range from 750 nm to 810 nm and present great polarization independence at the polarization angle varying from 0° to 90°. The experimental results show the excellent performance of GCCG for improving heterodyne grating interferometer and indicate great potential for applications in microscopy techniques, semiconductor manufacturing, and material processing.

Widely tunable, narrow bandwidth, mJ level Tm:YAP laser with YAG Etalons

A Pulsed, narrow-band, tunable, end-pumped Tm:YAP laser is demonstrated in this paper. The 35 nm wavelength continuous tunability ranges from 1926 to 1961 nm, having a spectral linewidth of 0.15 nm FWHM. The tuning and spectral band narrowing were obtained using a pair of YAG Fabry-Perot Etalons. The laser was actively Q-switched using an acousto-optic modulator. At a repetition rate of 1 kHz, maximum energy per pulse of 2.3 mJ and a pulse duration of 29.5 ns were achieved, corresponding to a peak power of 80 kW. Pulse energy of mJ level was measured along with the whole laser tunability range. Slope efficiency of 31% was obtained for an absorbed pump power of 11.5 W. The combination of high pulsed energies and tunability in this special wavelength region with narrow bandwidth, allows this laser to be a suitable tool for biomedical, sensing and material processing applications.

Fast approximate learning-based multistage nonlinear model predictive control using Gaussian processes and deep neural networks

Scenario-based model predictive control (MPC) methods introduce recourse into optimal control and can thus reduce the conservativeness inherent to open-loop robust MPC. However, the uncertainty scenarios are often generated offline using worst-case uncertainty bounds quantified a priori, limiting the potential gains in control performance. This paper presents a learning-based multistage MPC (msMPC) for systems with hard-to-model dynamics and time-varying plant-model mismatch. Gaussian Processes (GP) are used to learn state- and input-dependent plant-model mismatch in real-time and accordingly adapt the scenario tree online. Due to the increased computational complexity associated with incorporating the GP predictions into the optimal control problem, the learning-based msMPC (LB-msMPC) law is approximated by a deep neural network (DNN) that is cheap-to-evaluate online and has a small memory footprint, which makes it suitable for embedded applications. In addition, we present a novel algorithm for training the DNN-based controller that uses a GP description of the plant-model mismatch to generate closed-loop simulation data, which ensures the LB-msMPC law is evaluated in regions of the state space most relevant to closed-loop operation. The proposed LB-msMPC strategy is demonstrated on a cold atmospheric plasma jet with applications in (bio)materials processing. The simulation results indicate the promise of the approximate LB-msMPC strategy for control of hard-to-model systems with fast dynamics on millisecond timescales.

Overview of Laser Applications in Manufacturing and Materials Processing in Recent Years

Abstract This article is to capture some of the important developments in the rapidly growing areas of laser-based manufacturing and materials processing and also to describe important technological issues pertaining to various laser-based manufacturing processes. The topics to be covered in this paper include more popularly used processes in industry such as laser additive manufacturing, laser-assisted machining, laser micromachining, laser forming, laser surface texturing, laser welding, and laser shock peening, although there are several additional areas of laser applications. In each section, a brief overview of the process is provided, followed by critical issues in implementing the process, such as properties, predictive modeling, and process monitoring, and finally some remarks on future issues that can guide researchers and practitioners.

Evaluation of a novel parabolic plasma electrode advantage in a triode extraction system of a helicon ion source: simulation and experiment

An industrial type of Amirkabir helicon ion source (AHIS-II) equipped with a novel triode extraction system has been designed and developed at the Helicon Plasma Laboratory of Amirkabir University of Technology for material-processing applications. An experimental study was conducted to investigate the effects of two new types of plasma electrodes on ion beam characteristics. In particular, the Khoshhal electrode as a new improved plasma electrode and the optimized Pierce plasma electrode were both compared in inductively coupled plasma in the m = +1, −1 helicon plasma modes of operation. In this work, the AHIS-II device, with its ability to work continuously, was able to extract a ∼1 mA argon ion beam using a triode extraction system equipped with a Khoshhal plasma electrode at a 20 kV extraction voltage in the m = +1 helicon mode of operation. As part of this work, the R parameter, the ratio of the voltageapplied to the plasma and acceleration electrodes in triode extraction systems was introduced, and its effects on ion beam characteristics including beam emittance, diameter, and current were studied. In this study, beam optical characteristics including beam emittance, diameter, current, and profile were calculated and measured by the IBSimu ion optical code. The analysis of the argon ion beam highlights that the ion beam characteristics can be affected not only by the plasma electrode geometry design, R parameter, and extraction voltage associated with the extraction process, but also by the plasma source’s operational parameters, such as the RF power delivered to the half-helix antenna and the gas flow rate.

Influence of 2.09-μm pulse duration on through-silicon laser ablation of thin metal coatings

A robust Ho:YAG chirped pulse amplifier with a simple dispersion management was developed for material processing applications. The amplifier produces 3.2 ps pulses centered at 2.09 μm with energies up to 1.6 mJ. At 10 kHz repetition rate this results in 16 W of average power. Both pulse stretching and compression in the amplifier is realized within a single chirped volume Bragg grating. With the developed amplifier we study laser ablation of a gold layer through a carrier substrate and, particularly, the effect of pulse duration on the process. A balance between nonlinear effects within the carrier and interaction with the thin ablation layer makes few picosecond pulses most suitable for non-thermal ablation. Furthermore, since only a few-microjoules of pulse energy is required for de-bonding, the developed 16 W amplifier can be potentially operated at MHz repetition rates for high throughput.

Variable optical elements for fast focus control

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications.

Effect of SiC on structure and property of 2017 aluminium alloy

ABSTRACT In its early days, microwave was mainly used in food industries. Later, it was demonstrated by researchers that all metal powders absorb microwaves at room temperature and only the bulk metal reflects microwaves with slight surface penetration. Hence, in recent days, microwave energy is being aggressively used for an extensive range of applications in material processing. This is because of its several major advantages in terms of processing time, heating rates, improved mechanical properties, etc. The study deals with the compacted 2017 aluminium–copper-based alloy powder interacting with microwaves at 470ºC and describes how density and hardness vary with respect to changes in wt.% (0%, 5% and 10%) of silicon carbide (SiC) in aluminium alloy. The study reveals that aluminium alloy with 10% SiC possesses the highest hardness and the lowest density among all. Further, microstructural investigation was carried out to validate results. Results showed that addition of SiC resulted in improvement in hardness and reduction in density of 2017 aluminium alloy which makes the alloy mechanically stronger and lighter, which are the two most desirable attributes for any structural applications.

Shaping caustics into propagation-invariant light

Structured light has revolutionized optical particle manipulation, nano-scaled material processing, and high-resolution imaging. In particular, propagation-invariant light fields such as Bessel, Airy, or Mathieu beams show high robustness and have a self-healing nature. To generalize such beneficial features, these light fields can be understood in terms of caustics. However, only simple caustics have found applications in material processing, optical trapping, or cell microscopy. Thus, these technologies would greatly benefit from methods to engineer arbitrary intensity shapes well beyond the standard families of caustics. We introduce a general approach to arbitrarily shape propagation-invariant beams by smart beam design based on caustics. We develop two complementary methods, and demonstrate various propagation-invariant beams experimentally, ranging from simple geometric shapes to complex image configurations such as words. Our approach generalizes caustic light from the currently known small subset to a complete set of tailored propagation-invariant caustics with intensities concentrated around any desired curve.

High-repetition rate, mid-infrared, picosecond pulse generation with µJ-energies based on OPG/OPA schemes in 2-µm-pumped ZnGeP2.

We report on two different concepts to generate µJ-level mid-infrared laser pulses with sub-10 ps pulse duration via nonlinear parametric generation at high pulse repetition rates. Both schemes rely on the recent development of compact and efficient CPA-free, Ho:YLF-based 2-µm laser sources pumping the highly nonlinear crystal ZnGeP2 used for parametric amplification. The first concept comprises a simplified OPG/OPA scheme efficiently producing signal and idler radiation at fixed wavelengths of 3.0 and 6.5 µm, respectively. In the second concept, we demonstrate a wide spectral tunability of the picosecond, µJ pulses over the entire tuning range between 2.5 and 12 µm maintaining a constant bandwidth of sub-20 cm-1 by integrating a two-color pumping scheme and a spectral shaper into the setup. The presented compact and efficient mid-IR picosecond radiation sources offer a way towards low-cost mid-IR material processing and spectroscopic applications.

Experimental Study of Cold Atmospheric Pressure Plasma Jet and Its Application in the Surface Modification of Polypropylene

The cold plasma technology is gaining popularity as one of the most effective tools for a wide range of applications. Cold atmospheric pressure plasma jet (CAPPJ) has attracted considerable attention in recent times for materials processing such as surface modification and biomedical applications. The cold atmospheric pressure plasma jet sustained in pure argon has been used here to modify the surface properties of polypropylene. CAPPJ has been generated by a high voltage power supply 5 kV at an operating frequency of 20 kHz. This paper reports the diagnostics of CAPPJ in argon environment by electrical and optical methods and its application in the surface modification of polypropylene (PP). The surface properties of the untreated and plasma-treated PP samples were characterized by contact angle measurements, surface free energy determination, scanning electron microscopy and Fourier transform infrared spectroscopy analysis. Most of the previous work has used RF power supply which is more expensive compared to the power supply used in the present study. The plasma jet is designed with locally available materials and can be used for continuous treatment for long time. We have successfully developed a plasma device that is able to generate a non-equilibrium atmospheric pressure argon plasma jet of low temperature. Therefore, a cost-effective system of generating a plasma jet at atmospheric pressure with potential applications in materials processing and biomedical research has been developed.

Spectral measurements of inductively coupled and m = +1, −1 helicon discharge modes of the constructed plasma source

In the present context, the industrial type of Amirkabir helicon plasma source has been introduced that was designed and constructed at the Helicon Plasma Laboratory of Amirkabir University of Technology with the aim of using it in material processing applications. Helicon plasma in two m = +1 and m = −1 modes of operation was studied, and also its application was compared with the inductively coupled plasma (ICP) mode in this experimental work. This study was performed by employing two techniques including optical emission spectroscopy and imaging using a camera with polarizing filters, in which the images and spectra of ICP and m = +1, −1 helicon plasma modes were recorded under the experimental conditions. The effects of the device operational parameters on the argon plasma emission spectra were investigated in the wavelength range of 350–950 nm. It was observed from the comparison of the plasma spectra that the ionization rate increases significantly for the plasma helicon mode than ICP and also for m = +1 helicon mode of operation than m = −1. In this work, the values of device operational parameters such as the RF power delivered to the half-helix antenna, external magnetic field intensity, and the injected gas flow rate were varied in the range of 400–900 W, 100–300 mT, and 1–10 SCCM in the experiment, respectively. In addition, the optimum values of RF power, magnetic field intensity, and the injected gas flow rate for achieving the maximum ionization rate were, respectively, obtained as 900 W, 300 mT, and 3 SCCM.

ТЕХНІКО-ТЕХНОЛОГІЧНІ РІШЕННЯ ПРОЦЕСУ ОДЕРЖАННЯ ВОЛОКНА З ЛУБ’ЯНИХ КУЛЬТУР

The paper is devoted to solving problems related to developing scientific bases for resource-saving technologies in bast crops complex processing. The work contains theoretical and experimental research in processing flax and hemp raw materials. The work objective is to find ways to improve the production conditions for processing bast fibre plants and to solve the problems of ameliorating the qualitative and quantitative bast fibre characteristics by improving the technological features of stem material processing and structural design application to the joint connections of the devices for processing bast-fibre raw materials. The paper also analyses current trends in the flax and hemp processing industry development, investigates the technical and technological features of processing bast-fibre crop stems and assesses the directions for increasing their processing efficiency.