Microscale Engineering Research Articles

Advancing Microscale Electromagnetic Simulations for Liquid Crystal Terahertz Phase Shifters: A Diagnostic Framework for Higher-Order Mode Analysis in Closed-Source Simulators

This work addresses a critical challenge in microscale computational electromagnetics for liquid crystal-based reconfigurable components: the inadequate capability of current software to accurately identify and simulate higher-order modes (HoMs) in complex electromagnetic structures. Specifically, commercial simulators often fail to capture modes such as Transverse Electric (TE11) beyond the fundamental transverse electromagnetic (TEM) mode in coaxial liquid crystal phase shifters operating in the terahertz (THz) regime, leading to inaccurate performance predictions and suboptimal designs for telecommunication engineering applications. To address this limitation, we propose a novel diagnostic methodology incorporating three lossless assumptions to enhance the identification and analysis of pseudo-HoMs in full-wave simulators. Our approach theoretically eliminates losses associated with metallic conductivity, dielectric dissipation, and reflection effects, enabling precise assessment of frequency-dependent HoM power propagation alongside the primary TEM mode. We validate the methodology by applying it to a coaxially filled liquid crystal variable phase shifter device structure, underscoring its effectiveness in advancing the design and characterization of THz devices. This work provides valuable insights for researchers and engineers utilizing closed-source commercial simulators in micro- and nano-electromagnetic device development. The findings are particularly relevant for microscale engineering applications, including millimeter-wave (mmW), sub-mmW, and THz systems, with potential impacts on next-generation communication technologies.

Loss Analysis of the Electromagnetic Metamaterial Applied to Antenna Size Reductions

The research of transformation electromagnetics uses spatial coordinate transformation method to transform Maxwell’s equations for the propagations of electromagnetic waves in space, thereby achieving the goal of designing the path of electromagnetic waves, which eventually leads to a more complex tensor design of its constitutive parameters of metamaterials. This demand for artificial design of material parameters has been combined with the rapid development of micro-scale, molecular-scale, and atomic-scale experimental engineering techniques in recent years, enabling metamaterials to be developed, fabricated, and applied in various frontier fields. In this paper, the metamaterial electromagnetic wave concentrator used to reduce the antenna size is mainly discussed and detailed simulations and researches on the electromagnetic lossy conditions of the metamaterial parameters are given, which can better verify the electromagnetic scattering performance under actual engineering conditions. Solutions and quantitative simulations for the attenuation characteristics are also provided, which can deepen the research on the engineering performance of the metamaterial electromagnetic transformation devices.

Critical pulse in multi-shot femtosecond laser ablation on metallic surfaces

Thermal effect remains a thorny issue for femtosecond-laser surface engineering and nanostructuring on metallic targets with high pulse energies or high repetition rates, which needs to be paid adequate attentions. Herein, we have experimentally investigated the heat diffusion and accumulations during single-shot and multi-shot femtosecond laser ablation on metallic surfaces. We have for the first time observed a novel phenomenon that the thermal effect was intensified abruptly when the laser-pulse number goes over a threshold (approximately between 10 and 20 for aluminum alloy with laser fluence of 6 J cm−2), accompanied with a dramatic reduction of ablated depth and complicated plasma dynamics. Based on both optical and thermodynamic analysis, we introduced a defocusing-dominated plasma-assistant model for this abnormal thermal effect. This work explored the critical experimental parameters for femtosecond-laser surface modification and processing in micro-scale engineering applications.

Single clonal tracking on biomimetic microtextured platforms for real-time guided migration analysis of myeloid-derived suppressor cell dissemination characteristics ex vivo.

Current strategies to undermine the deleterious influence of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment (TME) are lacking effective clinical solutions, in large part, due to insufficient knowledge on susceptible cellular and molecular targets. We describe here the application of biomimetic microfabricated platforms designed to analyze migratory phenotypes of MDSCs in the tumor niche ex vivo, which may enable accelerated therapeutic discovery. By mimicking the guided structural cues present in the physiological architecture of the TME, aligned microtopography substrates can elucidate potential interventions on migratory phenotypes of MDSCs at the single clonal level. Coupled with cellular and molecular biology analysis tools, our approach employs real-time tracking analysis of cell motility to probe the dissemination characteristics of MDSCs under guided migration conditions. These methods allow us to identify cellular subpopulations of interest based on their disseminative and suppressive capabilities. By doing so, we illustrate the potential of applying microscale engineering tools, in concert with dynamic live cell imaging and bioanalysis methods to uncover novel exploitable motility targets for advancing cancer therapy discovery. The inherent simplicity and extended application to a variety of contexts in tumor-associated cell migration render this method widely accessible to existing biological laboratory conditions and interests.

Collective propulsion of viscous drop pairs based on Quincke rotation in a uniform electric field

Droplet collective propulsion is a crucial technology for microscale engineering applications. Despite great progress, current approaches to droplet manipulation still face many challenges. Here, a novel strategy for the collective propulsion of droplet pairs is proposed, which is based on two fundamental dynamics phenomena: i) the Quincke rotation; ii) the dynamics of vortex pairs. In this work, a two-dimensional (2D) numerical computation is performed to study the effect of viscosity ratio (λ = μi/μo ≤ 60, “i” and “o” indicate the drop and bulk phase) and electric field strength (E0*≤ 6.78) on the collectively propelling performance and reveal the propelled mechanisms of the droplet pair with fixed conductivity ratio Q (=σi/σo) = 0.01 and permittivity ratio S (=εi/εo) = 0.5. The novel approach to spontaneous propulsion proposed in this work achieves the remote manipulation of droplets without limiting the translation distance. The translation velocity can reach 2.0 mm/s for the examined cased in this work. In addition, the findings indicate that two factors determine the collective propulsion of droplet pairs: the strength of the Quincke vortex (Γ*) and the front vortex pair, which appears at the front end of the droplet pair and essentially counteracts the propulsion. For 5.0 < λ < 10, a weaker front vortex pair is generated. The increase in λ augments the strength of the Quincke vortex and in turn accelerates the collective propulsion. As 10 < λ < 28, the increasing λ results in a stronger front vortex pair and thus weakens the performance. As λ > 28, the direction of translation is reversed and the front vortex pair becomes weaker until it disappears completely at λ = 50. Thus, the increase in λ improves the collectively propelled performance in λ > 28. In addition, the effect of E0* on the collective propulsion is examined with varied λ (=8, 15, 50) and the fixed Q = 0.01, S = 0.5. The stronger E0* can lead to a faster translation. However, when the drop pair with the higher viscosity (λ = 50) is exposed to a stronger electric field (E0* = 5.08), two drops undergo irregular electrorotation (the direction of rotation changes alternately). The alternating up/down translation cannot produce the directional translation.

Coaching Model To Build Entrepreneurship Among Youth Unemployment

Partners often try to start building productive business, but empowerment still weak due to limited knowledge, skills, health insurance capital, technology and markets. The purpose of this program is to create a new young entrepreneurs reliable, independent and competitive among the youth unemployment. The method that used to solve the problems of these partners through the facilitation of productive economic activity based micro-scale engineering model of coaching in the form of technological and social skills through training with a participatory approach, stimulus funding and mentoring (supervision, monitoring and evaluation). Result of the evaluation of the program show that the impact of the program on the social aspects of both partners is the entrepreneurial spirit is getting stronger which can be measured in absolute numbers with Likert scale indicates the value of a score of 3.5. so it can be concluded that both partners have an entrepreneurial spirit by 75%. The impact of technological engineering shows that partners have been able to increase the procurement of oyster mushroom baglog even by purchasing, increasing turnover and expanding their marketing reach and have even diversified their business in the form of selling oyster mushroom satay. As for the impact of other social engineering is both partners have started to master the techniques of business management reasonably well and being able to access market information, read the market opportunities, technology innovations through the internet facility and has begun marketing management including control of simple bookkeeping

Review of research progress and development trend of digital image correlation

PurposeThe purpose of this paper is to provide a comprehensive review of a non-contact full-field optical measurement technique known as digital image correlation (DIC).Design/methodology/approachThe approach of this review paper is to introduce the research pertaining to DIC. It comprehensively covers crucial facets including its principles, historical development, core challenges, current research status and practical applications. Additionally, it delves into unresolved issues and outlines future research objectives.FindingsThe findings of this review encompass essential aspects of DIC, including core issues like the subpixel registration algorithm, camera calibration, measurement of surface deformation in 3D complex structures and applications in ultra-high-temperature settings. Additionally, the review presents the prevailing strategies for addressing these challenges, the most recent advancements in DIC applications across quasi-static, dynamic, ultra-high-temperature, large-scale and micro-scale engineering domains, along with key directions for future research endeavors.Originality/valueThis review holds a substantial value as it furnishes a comprehensive and in-depth introduction to DIC, while also spotlighting its prospective applications.

Microscale Engineering of n-Type Doping in Nanostructured Gallium Antimonide: AC Impedance Spectroscopy Insights on Grain Boundary Characterization and Strategies for Controlled Dopant Distribution.

This paper investigates the microscale engineering aspects of n-type doped GaSb to address the challenges associated with achieving high electrical conductivity and precise dopant distribution in this semiconductor material. AC impedance spectroscopy is employed as a reliable technique to characterize the microstructural and electrical properties of GaSb, providing valuable insights into the impact of grain boundaries on overall electrical performance. The uneven distribution of dopants, caused by diffusion, and the incomplete activation of introduced dopants pose significant obstacles in achieving consistent material properties. To overcome these challenges, a careful selection of alloying elements, such as bismuth, is explored to suppress the formation of native acceptor defects and modulate band structures, thereby influencing the doping and compensator formation processes. Additionally, the paper examines the effect of microwave annealing as a potential solution for enhancing dopant activation, minimizing diffusion, and reducing precipitate formation. Microwave annealing shows promise due to its rapid heating and shorter processing times, making it a viable alternative to traditional annealing methods. The study underscores the need for a stable grain boundary passivation strategy to achieve significant improvements in GaSb material performance. Simple grain size reduction strategies alone do not result in better thermoelectric performance, for example, and increasing the grain boundary area per unit volume exacerbates the issue of free carrier compensation. These findings highlight the complexity of achieving optimal doping in GaSb materials and the importance of innovative analytical techniques and controlled doping processes. The comprehensive exploration of n-type doped GaSb presented in this research provides valuable insights for future advancements in the synthesis and optimization of high-conductivity nanostructured n-type GaSb, with potential applications in thermoelectric devices and other electronic systems.

Thermal conductivity performance in sodium alginate-based Casson nanofluid flow by a curved Riga surface

This study examines the effects of a porous media and thermal radiation on Casson-based nano liquid movement over a curved extending surface. The governing equations are simplified into a system of ODEs (ordinary differential equations) using the appropriate similarity variables. The numerical outcomes are obtained using the shooting method and Runge-Kutta Fehlbergs fourth-fifth order (RKF-45). An analysis is conducted to discuss the impact of significant nondimensional constraints on the thermal and velocity profiles. The findings show that the rise in curvature constraint will improve the velocity but diminish the temperature. The increased values of the modified Hartmann number raise the velocity, but a reverse trend is seen for increased porosity parameter values. Thermal radiation raises the temperature, while modified Hartmann numbers and the Casson factor lower the velocity but raise the thermal profile. Moreover, the existence of porous and solid fractions minimizes the surface drag force, and radiation and solid fraction components enhance the rate of thermal dispersion. The findings of this research may have potential applications in the design of heat exchangers used in cooling electronic devices like CPUs and GPUs, as well as microscale engines such as microturbines and micro-heat engines.

Transition boiling bubble powered micro-engine using a Leidenfrost bearing

Overcoming friction while generating useful torque is a challenge for micro engines. Here we report the development of a microscale engine that utilizes transition boiling as a mode of propulsion and the Leidenfrost effect as a friction-less bearing. The transition boiling micro engine shows significantly improved performance compared to a Leidenfrost engine, which uses vapor entrainment as a propulsion mechanism (up to 3 orders of magnitude higher efficiency). We characterize the performance of the transition boiling engine with temperature and develop an analytical model to model and compare the engine performance with experimental observations. Our results provide a new approach to generating torque with a virtually frictionless bearing in micro-engines unlocking applications in, e.g., remote sensing and low-grade energy harvesting.

Effects of inlet junctions on horizontally stratified flows

Horizontally stratified flows can be seen in a wide variety of micro-scale engineering problems. Recent studies have shown that diffusion at the interface between two liquids leads to a lateral flow, causing the fluid to rotate around the central axis of the channel. This lateral flow has the potential to disrupt the intended mechanism of the device or can be exploited for new device designs. The present investigation presents numerical and experimental results that provide important insights into the effects of the inlet junction on the flow field throughout the microfluidic device. The effects of four different archetypal inlet junctions—an idealized single inlet, counter-flow T junction, perpendicular flow T junction, and Y junction are considered. The results show that counter-flow T junction results in the least amount of lateral flow, while the straight channel results in the highest. The Y channel induces the second least rotation, and the perpendicular T junction creates slightly stronger lateral flows. Furthermore, based on lateral streamlines, it is suggested that the reason for the difference between these junctions can be explained by the interaction of the Dean vortices formed by the rotation of the fluid at the junction and the interaction of the Dean flow with the diffusion-induced vortices. To test this hypothesis, a less common junction (Y junction with angles higher than 180°) is modeled and has shown to reduce the lateral flow even further. Understanding the differences between the junctions would allow for more efficient microfluidic designs for various applications.

APPRENTICESHIP SKILLS DEVELOPMENT WITHIN THE INFORMAL SECTOR OF THE GHANAIAN ECONOMY: THE CASE OF SUNYANI MAGAZINE

Apprenticeship training is one of the several means of developing the skills and competencies of the workforce in every economy. The small and micro-scale engineering enterprises since their inception, have been contributing towards the development of the country. This is particularly so in the manufacturing and engineering sectors where local tools, equipment and machinery are produced and serviced. The Sunyani magazine has become an emerging informal industrial zone where technical skills development is offered to individuals across different areas of engineering. This paper examined the nature of apprenticeship skills development and the associated challenges in an informal industrial zone through a cross-sectional survey. The findings suggest that on-the-job training model without pre- or post-training exams or test characterised the training of apprentices. During the skills development process of the apprentices, the master craftsmen examine the progress of the apprentices to ensure they are progressing and to determine when apprentices have acquired the needed skills to be considered certified. Despite the benefits offered to the local economy, lack of funding for new ventures, lack of government support, tools and equipment constrain the capacity of the informal industrial zone to scale-up its training capacity with the potential of being of greater benefits to the socioeconomic development of the country.

Microscale engineering of hollow microneedle tips: design, manufacturing, optimization and validation.

Transdermal and intradermal drug delivery utilizing microneedles is an emerging front in painless therapeutics. Drug delivery using hollow microneedles is the most preferred method for delivering generic transdermal drugs in the clinical setup. The needle tip must be extremely short as the drug is administered to sub-millimeter depths. Also, they need to be sharp enough to pierce through the skin with minimal skin flexing. There are multiple challenges in engineering a tip profile that is short and sharp at the same time. Stainless steel (SS) hypodermic needles with the lancet tip profile are ubiquitous in subcutaneous and intramuscular injections. They have long bevel lengths that make them inappropriate as microneedles. Thus, designing a unique tip profile and developing the manufacturing technology for microneedle applications are necessary. This article presents the design and optimization of microneedle tip profiles through analytical models. Further, manufacturing strategies for reliably obtaining designed profiles are discussed. The article concludes with experimental validation of improved piercing performance of the optimized tip profile compared to other tip profiles. The article discusses about tip geometries of stainless steel needles for microneedle applications, where depth of delivery is less than 1 mm. Through series of analyses, the optimum needle tip geometry evolved from single plane bevel (SPB) to hex plane bevel (HPB) progressively improving piercing performance.

Size-dependent postbuckling analysis of graphene reinforced composite microtubes with geometrical imperfection

Graphene reinforced composites have attracted a great deal of attention in recent years due to their outstanding mechanical properties. The present work focuses on the size-dependent postbuckling characteristics of functionally graded (FG) graphene platelets reinforced composite (GPLRC) multilayer microtubes containing initial geometrical imperfection. It is assumed that the distribution of GPL reinforcements in microtubes is uniform or layer-wise change across the radial direction, and five typical distribution patterns (i.e., UD, FG-X, FG-O, FG-V and FG-A) are considered. Based on the modified couple stress theory and a refined higher-order beam theory, the non-classical governing equations with the account of von Kármán geometrical non‐linearity for postbuckling analysis are derived by employing the principle of minimum potential energy and solved by using an analytical method. After validating the analytical solutions by comparing with results reported in the literature, the influences of various important parameters on the postbuckling of FG-GPLRC multilayer microtubes are investigated. It is found that the microstructure effect on the postbuckling behavior is significant when the outer radius of the microtube is comparable to the material length scale parameter. Moreover, the initial geometrical imperfection decreases the postbuckling load-carrying capacity at small deflection, but increases it at large deflection. Additionally, our results indicate that the FG-V distribution pattern produces the highest postbuckling load-carrying capacity for FG-GPLRC multilayer tubes, which differs from the cases for FG-GPLRC multilayer beams, plates and thin shells where the FG-X distribution pattern always has the best reinforcing effect. The present work could provide theoretical guidelines for the optimal design and safety assessment of graphene reinforced composite tubular structures, and may find potential application in microscale engineering devices and systems.

Electro-Osmotic Propulsion of Jeffrey Fluid in a Ciliated Channel Under the Effect of Nonlinear Radiation and Heat Source/Sink.

Mathematical modeling of mechanical system in microfluidics is an emerging area of interest in microscale engineering. Since microfluidic devices use the hair-like structure of artificial cilia for pumping, mixing, and sensing in different fields, electro-osmotic cilia-driven flow helps to generate the fluid velocity for the Newtonian and viscoelastic fluid. Due to the deployment of artificial ciliated walls, the present research reports the combined effect of an electro-osmotic flow and convective heat transfer on Jeffrey viscoelastic electrolytic fluid flow in a two-dimensional ciliated vertical channel. Heat generation/absorption and nonlinear radiation effects are included in the present mathematical model. After applying Debye-Huckel approximation and small Reynolds number approximation to momentum and energy equation, the system of nonlinear partial differential equation is reduced into nonhomogenous boundary value problem. The problem determines the velocity, pressure, and temperature profiles by the application of semi-analytical technique known as homotopy perturbation method (HPM) with the help of software Mathematica. The graphical results of the study suggest that HPM is a reliable methodology for thermo physical electro-osmotic rheological transport in microchannels.

Fluid actuation and buoyancy driven oscillation by enzyme-immobilized microfluidic microcapsules.

Mimicking microorganism's locomotion and actuation under fluid is difficult to realize. To better comprehend the motility in non-living matter, self-propelled synthetic systems are being developed as a fast-growing area of research. Inspired by the self-powered enzyme micropumps where the enzyme catalysis was harnessed to create motion, herein, enzyme-immobilized microfluidic microcapsules (MCs) were used as a microscale engine to maneuver the fluid flow. The fluid actuation was tuned by various parameters such as substrate concentration, reaction rate, diameter of MCs and the population of the MCs inside the flow chamber. The same MCs, when suspended in a solution, showed buoyancy driven motility by creating oxygen bubbles via an enzymatic reaction and the velocity of the MCs was directly dependent on the number of nucleated oxygen bubbles generated on the MC surface.

Metals by Micro-Scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties.

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects-a significant step toward the potential establishment of AM techniques in microfabrication.

Advances in the Application of Biomimetic Endometrium Interfaces for Uterine Bioengineering in Female Infertility.

The Asherman’s syndrome, also known as intrauterine adhesion, often follows endometrium injuries resulting from dilation and curettage, hysteroscopic resection, and myomectomy as well as infection. It often leads to scarring formation and female infertility. Pathological changes mainly include gland atrophy, lack of vascular stromal tissues and hypoxia and anemia microenvironment in the adhesion areas. Surgical intervention, hormone therapy and intrauterine device implantation are the present clinical treatments for Asherman’s syndrome. However, they do not result in functional endometrium recovery or pregnancy rate improvement. Instead, an increasing number of researches have paid attention to the reconstruction of biomimetic endometrium interfaces with advanced tissue engineering technology in recent decades. From micro-scale cell sheet engineering and cell-seeded biological scaffolds to nano-scale extracellular vesicles and bioactive molecule delivery, biomimetic endometrium interfaces not only recreate physiological multi-layered structures but also restore an appropriate nutritional microenvironment by increasing vascularization and reducing immune responses. This review comprehensively discusses the advances in the application of novel biocompatible functionalized endometrium interface scaffolds for uterine tissue regeneration in female infertility.

Micro-scale spatial location engineering of COF–TiO2 heterojunctions for visible light driven photocatalytic alcohol oxidation

COF and TiO2 core–shell structured heterojunctions with the spatial location of two semiconductors either in the core or on the shell are precisely designed.

Cyclic phase transformation behavior of nanocrystalline NiTi at microscale

Cuboidal micropillars of nanocrystalline superelastic NiTi shape memory alloys with an average grain size of 65 nm were fabricated by focused ion beam and then subjected to cyclic compression. It is found that the micropillars have maintained superelasticity for over 106 full-transformation cycles under a maximum compressive stress of 1.2 GPa. Functional degradation of the micropillars mainly occurs in the first 104 cycles where hysteresis loop area and forward transformation stress rapidly decrease from initial 11 MPa (MJ/m3) and 586 MPa to 6 MPa and 271 MPa. In the 104 ~ 106 cycles, stress-strain responses of the micropillars show asymptotic stabilization. Residual strain is accumulated to 3.3% and multiple ~50 nm wide extrusions are found at the surface of the micropillars after 106 cycles. SEM and TEM studies indicate that cyclic phase transformation results in formation and glide of transformation-induced dislocations that create surface steps and the extrusions. The dislocations inhibit reverse transformation and result in residual martensite and residual stresses. The dislocations and the residual martensite lead to the functional degradation. The role of the residual martensite in the functional degradation is further verified by 21% recovery of the residual strain and an increase of 278 MPa in the forward transformation stress after heating up the cyclically deformed micropillars to 100 °C. The recorded over 106 phase transformation cycles under a maximum stress of 1.2 GPa of the NiTi shape memory alloys at microscale open up new avenues for applications of the material in microscale devices and engineering.