Material Processing Applications Research Articles

Nonlinear Optics in Dielectric Guided-Mode Resonant Structures and Resonant Metasurfaces.

Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in nonlinear optics research is to realize high efficiency optical functionalities in ultra-small, sub-wavelength length scale structures by leveraging interesting optical resonances in surface relief metasurfaces. Such artificial surfaces can be engineered to support high quality factor resonances for enhanced nonlinear optical interaction by leveraging interesting physical mechanisms. The aim of this review article is to give an overview of the emerging field of nonlinear optics in dielectric based sub-wavelength periodic structures to realize efficient harmonic generators, wavelength mixers, optical switches etc. Dielectric metasurfaces support the realization of high quality-factor resonances with electric field concentrated either inside or in the vicinity of the dielectric media, while at the same time operate at high optical intensities without damage. The periodic dielectric structures considered here are broadly classified into guided-mode resonant structures and resonant metasurfaces. The basic physical mechanisms behind guided-mode resonances, electromagnetically-induced transparency like resonances and bound-states in continuum resonances in periodic photonic structures are discussed. Various nonlinear optical processes studied in such structures with example implementations are also reviewed. Finally, some future directions of interest in terms of realizing large-area metasurfaces, techniques for enhancing the efficiency of the nonlinear processes, heterogenous integration, and extension to non-conventional wavelength ranges in the ultra-violet and infrared region are discussed.

Low Temperature Plasma Jets: Characterization and Biomedical Applications

For many decades non-equilibrium plasmas (NEPs) that can be generated at atmospheric pressure have played important roles in various material and surface processing applications [...]

Numerical analysis of microwave heating: Fundamentals and applications

In recent years, microwave-assisted materials processing applications are on the rise in terms of novel processes being developed and increased coverage of materials that can be processed. In general, the studies have been of experimental nature. Since microwave heating has extensive application in food processing at an industrial scale, literature on the research involving numerical studies is available in this domain. It is primarily focussed on determination of the distribution of temperature and the rate of heating of a food sample. The evolution in materials processing applications using microwaves has paved the way for exploring numerical analysis to predict and control the response parameters required for efficient material processing. This paper presents the theoretical background of electromagnetic wave propagation along with the heat transfer mechanism required in the numerical studies of microwave heating. The steps for this multiphysics-based numerical analysis are also discussed. An account of the state of microwave heating simulation research is presented as well. The unpredictability of microwave heating mechanisms coupled with fast-developing novel applications makes microwave heating simulation quite challenging. In addition, the merits of such numerical analysis present a case for extensive future research.

Hollow plasma structure during the breakdown phase of nanosecond pulsed pin–pin discharges generated with overvoltage

Atmospheric pressure nanosecond repetitive pulsed discharges are of interest for applications in combustion, material processing, plasma medicine and gas treatment. In this paper the observation of a hollow structure at the ignition stage of such discharge in a pin–pin geometry is reported. Plasma images show that the phenomenon occurs in a variety of gases (helium, humid helium, argon and air) suggesting that it is in first approximation non-species specific. The phenomenon is investigated in detail in pure helium discharges for peak applied voltages between 3 and 6 kV and 200 ns voltage pulse duration by performing time-resolved optical emission spectroscopy measurements of electron density, gas temperature and electric field. All the measurements were performed at the mid-gap during the early stages of the discharge, near the breakdown. The transition from a homogeneous filament to a hollow structure occurs between 4 and 5 kV in helium. Electron density measurements by Stark broadening of the He I line at 492.2 nm show no significant difference in electron densities for the applied voltage between 3 and 6 kV. In all cases, a maximum electron density of about 3.5 × 1021 m−3 was found. Electric field measurements performed by Stark polarization spectroscopy of the He I transition at 492.2 nm and of its forbidden counterpart show electric field strengths higher than the DC breakdown field of helium at atmospheric pressure consistent with the generation of the discharges with overvoltage. Moreover, a correlation between electric field values and the appearance of the hollow structure is observed and, remarkably, the phenomenon is not sensitive to the pre-ionization level (memory effect). Possible mechanisms for the phenomenon are discussed.

In situ analysis of shear bands and boundary layer formation in metals.

Shear banding is a plastic instability in large deformation of solids where the flow becomes concentrated in narrow layers, with broad implications in materials processing applications and dynamic failure of metals. Given the extremely small length and time scales involved, several challenges persist in studying the development of shear bands. Here, we present a new approach to study shear bands at low speeds using low melting point alloys. We use in situ imaging to directly capture the essential features of shear banding, including transition from homogeneous to shear banded flow, band nucleation and propagation dynamics, and temporal evolution of the flow around a developing band. High-resolution, time-resolved measurements of the local displacement and velocity profiles during shear band growth are presented. The experiments are complemented by an analysis of the shear band growth as a Bingham fluid flow. It is shown that shear banding occurs only beyond a critical shear stress and is accompanied by a sharp drop in the viscosity by several orders of magnitude, analogous to the yielding transition in yield-stress fluids. Likewise, the displacement field around a nucleated band evolves in a manner that resembles boundary layer formation, with the band thickness scaling with time as a power law.

Process Parameter Effects over Bead Properties during Material Deposition of PTAW Process

The quality and geometry of deposited bead depend on their input process parameters and their interaction effects in fusion welding process. Minimum dilution and maximum bead size are the most desirable property in material processing applications. The effects of process parameters on dilution and bead geometry have been analysed during material deposition by Plasma Transferred Arc Welding (PTAW) process using the response surface method. The experimental data are used for modelling using three level factorial techniques. The mathematical models have been developed for bead height, width and dilution. The accuracy of the models has been checked using the analysis of variance. The effects of process parameters on bead geometry and dilution have been investigated.

DARCIAN SLIP FLOW OF ROTATING MAGNETOREACTIVE PEG CONVEYING MoS2 CASSON NANOFLUID WITH RAMPED TEMPERATURE AND CONCENTRATION

An analysis is presented to assess the impact of slip condition and rotation on an unsteady hydromanetic Darcy flow of a viscous incompressible electrically conducting non-Newtonian Casson nanofluid past an infinite oscillating vertical plate with ramped heating and concentration embedded in a homogeneous porous medium in the presence of thermal radiation and homogeneous chemical reaction of first order. The nanofluid is composed of molybdenum disulfide (MoS2) nanoparticles suspended in base fluid polyethylene glycol (PEG). A Casson fluid model presents the non-Newtonian fluid behavior. Rosseland approximation for an optically thick fluid is used to describe the radiative heat flux in the energy equation. The classical Dracy model simulates drag effects in the porous medium. The resulting simultaneous ordinary equations governing the flow are solved analytically in closed form by employing the Laplace transform technique. Graphical presentations are portrayed to examine the physical consequences of intricate physical parameters on the pertinent flow characteristics. The obtained results reveal that the velocity components are strongly diminished by intensifying magnetic parameter or slip parameter. The wall shear stresses are increasing functions of rotation parameter. This study finds applications in magnetic material processing and electrically conducting polymer dynamics.

Microstructure modification of AISI1045 steel induced by high-current pulsed pseudospark electron beam

Pseudospark electron beam is a kind of high-current pulsed electron beam. It is characterized by high current (hundreds of amperes to thousands amperes), short pulse duration (hundreds of nanoseconds to thousands nanoseconds), high frequency (hundreds Hz to thousands Hz) and self-focused beam diameter (typically 0.5-5 mm), which are more favorable for metal surface treatment compared with the conventional thermal-emission electron beam diode. The pseudospark electron beam is easy to achieve high rate of beam energy rise, plasma quenching and to obtain fast and stable repetitive operation. Some unique properties of material processing applications have been induced by the pseudospark electron beam treatment. In this paper, the mechanism and microstructure modification of AISI1045 steel by pseudospark electron beam surface treatment have been investigated. Surface microstructure and chemical composition of AISI 1045 steel pre and post pseudospark electron beam treatment are investigated by using scanning electron microscope (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). Results show that the average depth of the treated layer is several microns. The melt interface is not straight, indicating a non-uniform melting process. Besides, material’s grain size is significantly reduced after pseudospark treatment, especially in sublayer. The average grain size in the sublayer is smaller than in the top-layer. The relatively finer grain size in the sublayer is attributed to the temperature-induced dynamic thermal stress fields and the highest temperature gradient in the subsurface layer instead of on the top layer. Furthermore, the amorphous phase is observed on the surface of melted layer.

Stratification and Buoyancy Effect of Heat Transportation in Magnetohydrodynamics Micropolar Fluid Flow Passing Over a Porous Shrinking Sheet Using the Finite Element Method

The current study investigates the numerical solution of steady heat transportation in magnetohydrodynamics flow of micropolar fluids over a porous shrinking/stretching sheet with stratified medium and buoyancy force. Based on similarity transformation, the partial differential governing equations are assimilated into a set of nonlinear ODEs, which are numerically solved by the finite element method. All obtained unknown functions are discussed in detail after plotting the numerical results against different arising thermophysical parameters namely, suction, magnetic, stratification, heat source, and buoyancy parameter. Under the limiting case, the numerical solution of the velocity and temperature is compared with present work. Better consistency between the two sets of solutions was determined. To verify the convergence of the numerical solution, the calculation is made by reducing the mesh size. The present study finds applications in materials processing and demonstrates convergence characteristics for the finite element method code.

Numerical evaluation on the performance of CO₂ plasma in material processing applications

ABSTRACTCarbon-dioxide (CO2) emission is a very serious problem being faced by the world. Though technologies are being developed to destroy CO2 and produce CO, the effective utilization of CO2 in new areas is limited. Thermal plasmas are being used to process materials in various fields due to its high energy density, which helps to process a large quantity of materials in a short time without polluting the environment. However, the thermal plasma material processes are not economical since gases used to produce the plasma are either costly or have poor heat transfer efficiency. Since CO2 is a cheap gas and it has high enthalpy and thermal conductivity, it can be a good candidature to produce the plasma. To prove scientifically the potential of CO2 plasma jet in thermal plasma material processes without conducting experiments, which involve costly equipments and lot of time, numerical models are developed to simulate the plasma–material interactions. Predicted heat transfer efficiency of CO2 and Ar plasma jets are compared in plasma in-flight processing of particles and jet impingement heating of solid. Results indicate that utilization of CO2 in thermal plasma material processing can save energy without compromising the quality of the product.

Tailored focal beam shaping and its application in laser material processing

Besides the optimization of the laser and processing parameters, the adaptation of the focal intensity distribution offers great potential for a well-defined control of laser processing and for improving the processing results. In this paper, different tailored intensity distributions were discussed with respect to their suitability for femtosecond laser material processing on the micro- and nanoscale such as cutting, marking, and the generation of laser-induced periodic surface structures. It was shown by means of laser processing of stainless steel that the numerical simulations for the beam shaping unit are in good agreement with the experimental results. Also, the suitability of the beam shaping device to work with a scanner and an F-theta lens as commonly used for material processing was demonstrated. In this context, the improvement of the machining results was shown experimentally, and a significant reduction of the machining time was achieved.

Vortex dynamics at the junction of Y-shaped microchannels in dilute polymer solutions

Understanding the vortex dynamics in polymer solutions is one of keys for the flow control in a wide range of polymer-related material processing applications. Vortex is generated due to the viscoelasticity of polymer solution, even if no vortex formation is expected under Newtonian flow conditions. In addition, the chaotic vortices generated in viscoelastic fluids have been recently exploited to mix different fluid streams in microfluidic devices. Herein, we investigated the vortex dynamics in dilute polyethylene oxide) solutions at the junction region of Y-shaped microchannels, which have been frequently used to mix two fluid streams. We report the formation of two types of vortices: A vortex at the stagnation point of the junction (center) and a lip vortex at the upstream of the sharp corner. Fluorescent microscopy revealed that the vortex dynamics was significantly affected by the angle between the two upstream channels, polymer concentration, and flow rate. We expect that this work will be useful for understanding the viscoelastic flow in microchannels and for the future design of microfluidic devices such as microfluidic mixers.

Vectorial Holograms with a Dielectric Metasurface: Ultimate Polarization Pattern Generation

Controlling the polarization of light has been of interest for various applications in laser materials processing, display systems, and spectroscopy among others. Despite great advancements, the le...

Study on processing characteristics and mechanisms of thermally assisted laser materials processing

Nanosecond pulsed lasers have been widely applied to interact with and characterize many different materials, and industrial users are exploring more avenues for various application processes. For the purpose of achieving broader application, the current challenge is to achieve a high processing efficiency for laser materials processing. In this study, thermally assisted laser materials processing (TALMP), which introduces heat from an external source to increase the workpiece material's temperature and make it easier to carry out ablation or modification, was developed and investigated. Moreover, to investigate the materials processing characteristics and mechanisms of TALMP, practical applications using TALMP, including surface ablation on WC-Co, and surface polishing on additive manufactured Ti-6Al-4V, were carried out. The results showed that TALMP can be successfully applied to various materials by different laser materials processing applications. Due to the workpiece material's high temperature and heat content, the coupling between laser and target materials can be enhanced; thus, physical ablation and modification for laser surface ablation can be achieved effectively. However, with a high offset temperature, a little decrease of ablation accuracy and quality could occur, and a two-step approach is proposed to eliminate this unwanted effect. Moreover, this strategy is proven to be able to achieve the desired surface ablation with high efficiency and high-quality surfaces. For thermally assisted surface polishing, due to higher temperature field with long duration, a smoother and flatter polished surface can be obtained more easily. The experimental results proved the superiority and versatility of TALMP.

Computational unsteady flow analysis for third‐grade fluid from an isothermal vertical cylinder through a Darcian porous medium

AbstractThe present study describes a mathematical model for free‐convective laminar incompressible boundary layer flow of a third‐grade fluid of the Reiner‐Rivlin differential type, external to an evenly heated semi‐infinite vertical cylinder through a two‐dimensional porous medium. Assuming a homogenous‐isotropic porous medium, simulation of bulk drag effects at low Reynolds number is conducted with the Darcy model. The resulting partial differential equation boundary value problem is normalized using suitable transformation variables. The highly nonlinear time‐dependent coupled conservation equations along with boundary conditions are resolved computationally with an optimized Crank‐Nicolson finite difference code. Validation with previous studies is included. The heat transport and skin‐friction coefficients are computed for different values of emerging nondimensional parameters. Furthermore, steady‐state and transient fluid flow variables are shown graphically. An enhanced fluid velocity is observed for increased Darcy number and the reverse trend is computed for higher values of third‐grade viscoelastic parameter. Also, the rate of heat transfer is observed to increase with greater Darcy number and a reduction in third‐grade viscoelastic parameter. A key observation which is drawn from the present study is that for third‐grade fluid the flow variables deviate significantly from a hot cylindrical wall as compared with a Newtonian fluid. The study is relevant to thermal polymer coating applications in aerospace materials processing.

Microwave Sintering of Alumina at 915 MHz: Modeling, Process Control, and Microstructure Distribution.

Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in most dielectric materials. However, up to now, this technology is not widely spread for high-temperature material processing applications (>1200 °C), because its reproducibly and ability to sinter large size samples (>30 cm3) still needs to be improved. In this context, this paper describes both an empirically designed 915 MHz single-mode cavity made from SiC susceptors and refractory thermal insulation, and the 3D modeling of the process in order to improve our understanding of it. Different susceptors geometries and coupling slit position were numerically tested in order to better understand how these parameters impact the field homogeneity and the process stability. It was found that positioning the largest surface of the susceptors parallel to the electrical field allows a very uniform and hybrid heating of the material, while avoiding plasma or thermal instabilities. This was correlated to the 3D modeling results. Finally, thanks to a fully-automatized system this apparatus was used to sinter large size (~30 cm3) low-loss dielectric alumina samples. The sintered materials were subsequently characterized in terms of density, grain size distribution, and homogeneity. The reproducibility was also discussed, demonstrating the process efficiency and reliability.

Predictive control of 2D spatial thermal dose delivery in atmospheric pressure plasma jets

Atmospheric pressure plasma jets (APPJs) are unique devices for processing of heat and pressure sensitive (bio)materials. However, operational challenges of APPJs such as run-to-run variability in dynamics and sensitivity to disturbances can complicate safe and reliable delivery of the spatially distributed cumulative effects of plasma, or plasma dose, to complex surfaces. This paper presents a hierarchical feedback control strategy based on model predictive control for regulating the spatial thermal dose delivery to a surface. Closed-loop control experiments demonstrate the effectiveness of the proposed control strategy in drastically improving the spatial uniformity of thermal dose delivery in the presence of step changes in the jet tip-to-surface distance as well as abrupt changes in the substrate type. The proposed feedback control strategy shows promise for improving the reliability and effectiveness of spatially uniform treatment of complex surfaces in medical and materials processing applications of APPJs.

Design and Manufacturing Method of Fundamental Beam Mode Shaper for Adapted Laser Beam Profile in Laser Material Processing.

Many laser material processing applications require an optimized beam profile, e.g., ring shape or Top-Hat profiles with homogeneous intensity distribution. In this study, we show a beam shaping concept leading to a phase shifting element with binary height profile as well as a very low periodicity with near diffraction limited spot size. Further advantages of so-called Fundamental Beam Mode Shaping (FBS) elements are the simplified handling, and a high efficiency and homogeneity. The calculated height profile of FBS elements are transferred in fused silica substrates using a combination of microlithography technologies, reactive ion etching (RIE) and ion beam etching (IBE). The experiments demonstrated a linear relation between the etching depth after RIE and IBE. The optical evaluation of the manufactured FBS beam mode shaper confirmed the presented concept design.

Experimental demonstration of anamorphic M2 laser transformation in polar coordinates

Transforming the beam of a highly multimode laser into a narrow annular shape with almost diffraction-limited ring width is a potentially useful technique for certain material processing applications, such as drilling and cutting. In a previous article, we have described and simulated a theoretical method of realizing such transformation. Here, we provide experimental verification of this method, based on transforming the laser beam quality parameter M2 in polar coordinates. The transformation is done using a dedicated diffractive optical element, which we call a “spinner.” A comparison of the results for the spinner optical system versus a standard axicon ring shaping has been done, both in the focal plane and in defocus positions. Measured results have been compared with the theoretical model and simulations.

Three-dimensional Patterning of Engineered Biofilms with a Do-it-yourself Bioprinter.

Biofilms are aggregates of bacteria embedded in a self-produced spatially-patterned extracellular matrix. Bacteria within a biofilm develop enhanced antibiotic resistance, which poses potential health dangers, but can also be beneficial for environmental applications such as purification of drinking water. The further development of anti-bacterial therapeutics and biofilm-inspired applications will require the development of reproducible, engineerable methods for biofilm creation. Recently, a novel method of biofilm preparation using a modified three-dimensional (3D) printer with a bacterial ink has been developed. This article describes the steps necessary to build this efficient, low-cost 3D bioprinter that offers multiple applications in bacterially-induced materials processing. The protocol begins with an adapted commercial 3D printer in which the extruder has been replaced with a bio-ink dispenser connected to a syringe pump system enabling a controllable, continuous flow of bio-ink. To develop a bio-ink suitable for biofilm printing, engineered Escherichia coli bacteria were suspended in a solution of alginate, so that they solidify in contact with a surface containing calcium. The inclusion of an inducer chemical within the printing substrate drives expression of biofilm proteins within the printed bio-ink. This method enables 3D printing of various spatial patterns composed of discrete layers of printed biofilms. Such spatially-controlled biofilms can serve as model systems and can find applications in multiple fields that have a wide-ranging impact on society, including antibiotic resistance prevention or drinking water purification, among others.