Microstructure Height Research Articles

Effects of Black Silicon Surface Morphology Induced by a Femtosecond Laser on Absorptance and Photoelectric Response Efficiency

In this study, the effects of variations in the height (h) and bottom radius (r) of black silicon microstructures on their absorptance and photoelectric response efficiency were analyzed. By using the relation cot⁡θ2=hr to combine the parameters, it was found that changes in morphology affected the absorptance of black silicon microstructures, with h being directly proportional to the absorptance, while r was inversely proportional. A positive correlation was observed between cot⁡θ2 and absorptance. However, the correlation between cot⁡θ2 and photoelectric response efficiency was not significant. Through Raman spectroscopy analysis of the samples, it was concluded that as the laser ablation energy density increased, more lattice defects were introduced, weakening the charge carrier transport efficiency. This study further elucidated the mechanism by which microstructural changes impacted the absorptance and energy density of black silicon, providing valuable insights for optimizing its energy density.

A dual wave structure triboelectric sensor for heart rate and exercise monitoring

Recently, research on wearable devices for physiological exercise monitoring has garnered significant attention. Here, we propose a dual wave-structured triboelectric nanogenerator (DW-TENG) integrated with a cotton cloth, developed for smart running applications. The DW-TENG sensor leverages a flexible wave triboelectric layer composed of polydimethylsiloxane and silicone, with a copper electrode layer between them for sensing. This structure allows for customizable pressure sensitivity by adjusting the silicone hardness. Experimental results show that the DW-TENG achieves a sensitivity of 0.4 V kPa−1, with response and recovery times of 75 and 90 ms, respectively. The sensor effectively measures heart rate changes during various physical activities, including walking, running, and jumping. Electrical performance tests reveal that the DW-TENG’s output is significantly influenced by the silicone hardness, operational frequency, and microstructure height. The DW-TENG sensor demonstrates high durability and stability, maintaining consistent voltage output over 40 000 cycles. This research highlights the potential of the DW-TENG in multifunctional physiological and physical activity monitoring, providing real-time data on respiratory patterns, heart rate, and movement dynamics, thus enhancing athletic training, performance assessment, and health monitoring.

Sensitivity enhanced flexible capacitive pressure sensor microstructure optimization for biomedical applications

This paper explores the design and optimization of Flexible Capacitive Pressure Sensors (FCPS) using microfabrication technology for applications in the emerging field of flexible electronics, with a particular focus on measuring bio-signals characterized by lower pressure ranges. Sensitivity, a critical parameter for effective FCPS performance, is investigated through a comprehensive series of simulation analyses employing finite element modeling. The study involves varying geometrical and mechanical parameters that influence FCPS performance, individually adjusting each parameter while keeping others constant. Microstructures such as cuboids, truncated pyramids with an aspect ratio of 0.5, cylinders, pyramids, and cones are modeled on the dielectric material surface. The parameters considered include inter-space, base length, height, and elastic modulus, to enhance FCPS sensitivity and linearity. Among the different shapes modeled, the cone exhibits the highest sensitivity, followed by the pyramid structure. Comparative analysis indicates that the cone and pyramid shapes demonstrate 15- and 10-times higher sensitivity, respectively, compared to the cuboid structure under an applied pressure of 10 Pa. Simulation results suggest that sensitivity can be finely tuned, with higher inter-space and microstructure height, as well as lower base length and Young’s modulus of the dielectric material, contributing to increased sensitivity. However, it is noted that these conditions may lead to decreased capacitance in the absence of applied pressure due to air occupation relative to the dielectric material. The findings are further compared with existing literature, and the FCPS response analysis provides valuable insights for the future design of FCPS, particularly in the context of biomedical applications requiring precise low-pressure signal measurements. This research contributes to advancing the understanding of FCPS performance optimization and lays the groundwork for the development of sensors with enhanced sensitivity for bio-medical applications.

Regulating turbulent separation by surface microstructures on a blunt plate

Microstructured surfaces can induce secondary flow and regulate flow structures of the turbulent separation flow. However, the mechanism governing the relationship between the microstructure size and the characteristic flow size remains unclear. In this study, the separated flow over a blunt flat plate with surface microstructures is studied using time-resolved particle image velocimetry experiments and implicit large-eddy simulations for the plate-thickness-based Reynolds number from 5.08×103 to 1.31×104. The ratio of the height of microstructures to the plate thickness (h/d) ranges from 0.01 to 0.1. Combining experimental and numerical results, the relationships between the separation bubble size and the microstructure size under different Reynolds numbers exhibit similarity when normalized by the separation bubble size of the smooth plate. The dimensionless separation bubble size decreases when the microstructure height increases and large microstructures (h/d = 0.1) exhibit good performance on reducing the flow separation. Near the leading edge, the distortion of two-dimensional vortices and the generation of three-dimensional hairpin vortices are promoted by the first several rows of large microstructures. Additionally, in the main separation region, secondary positive spanwise vortices emerge from large microstructures. Subsequently, the secondary vortices lift up and evolve into streamwise vortices. The characteristic scale of secondary vortices is represented by a significant peak in the spectra of spanwise wavenumbers, which is of the same magnitude as the height of large microstructures. Furthermore, increasing the microstructure height weakens the streamwise correlation of the flow, and the characteristic scale of the correlation is comparable to the height of large microstructures.

Enhanced fabrication of conical array via two-stage through mask electrochemical machining process

In response to the issues of low processing precision, poor surface quality, and low array uniformity in the fabrication process of metal array conical structures, this paper proposes a two-stage enhanced process for fabricating metal array conical structures using through-mask electrochemical machining (TMECM). The micro-convex structure with high consistency can be quickly obtained through the first electrochemical machining (ECM), and then the mask is removed and the micro-convex structure is modified twice. The top diameter of the micro-structure is reduced by using the phenomenon of electric field concentration in the ECM process, and the top curvature radius of the micro-structure is further reduced, so as to increase the height diameter ratio of the micro-structure and improve the surface quality. The results show that during the initial ECM, when the machining time is 35 s, the voltage is 20 volts, the flow rate of the acid etching solution is 1 m /s, the duty cycle is 50 %, and the frequency is 200 Hz, the stable machining of the metal array conical structure can be achieved. In the secondary electrochemical surface modification, it was found that under the conditions of working solution containing 2 mol/L nickel-based etching agent, pulse voltage of 20 V and processing time of 35 s, the method effectively improved the surface quality of the workpiece and ensured the stable manufacturing of the micro-conical array structure. The prepared microstructure height was 198 μm and the top diameter was 28 μm.

Towards understanding hybrid influencing mechanisms of substrate microstructure on SERS effect

Micro/nano hierarchical structures have been investigated as a manner to improve the enhancement factor of surface enhanced Raman scattering (SERS). However, the exploration of influencing mechanisms of substrate microstructure on SERS effect is relatively lacking at present. In this study, finite element analysis (FEA) and molecular dynamics (MD) simulations were conducted, aiming to reveal the intrinsic relationships between microstructure characterization and Raman signal intensity. The distributions of near field and far field, as well as the energy density on substrate surfaces with various microstructures were obtained, and their influencing mechanisms on electromagnetic enhancement (EM) and chemical enhancement (CM) were analyzed. Meanwhile, the adsorption capacity of probe molecule on different substrate was expounded from the perspectives of superficial area, interaction energy and surface profile characteristics. Results demonstrated that the characterization parameter S/d × h, of which S, d and h are respectively the superficial area, interval space of adjacent micro-cavities and peak-valley height of surface microstructure, significantly determines the electric enhancement factor of electric field intensity and the energy density at the same time. The substrate surface with larger superficial areas can generate higher interaction energy thereby more probe molecules can be caught successfully. In addition, the molecular clusters are easier to form near convexities compared with the concaves on the same substrate. What was studied in this work is expected to provide a theoretical reference for the structural optimization of SERS substrate with high performances.

Fabrication of biomimetic anisotropic crescent-shaped microstructured surfaces by laser shock imprinting

Abstract The crescent-shaped microstructure bionic to the slip zone of the slippery zone of the carnivorous plant genus Nepenthes was fabricated on the surface of copper foil by laser shock imprinting (LSI). The microstructure of crescent-shaped grooves was initially fabricated on the surface of the micro-mold by etching, and then the microstructure was replicated on the surface of copper foil through plastic deformation under laser shock loading. Increasing the laser shock energy or the number of shocks can increase the degree of replication of the crescent-shaped microstructure, the height of the crescent-shaped microstructure, and the contact angle of water droplets on the surface. The wettability of the surface of the crescent microstructure is anisotropic and increases with an increase in offset distance. The anisotropy of the crescent-shaped microstructure causes the solid–liquid contact line in the direction of the bottom of the arc to become a long and approximately straight line. According to the rule that controlling LSI processing parameters can fabricate surfaces with different heights and wettability, a gradient wetting surface consisting of crescent-shaped microstructures was designed to achieve the directional spreading of droplets. By altering the distribution of crescent-shaped microstructures, a type-I flow channel with the ability to limit the spreading range of water droplets was fabricated.

On the drag reduction of an inclined wing via microstructures with the immersed boundary-lattice Boltzmann flux solver

Flow separation control has a wide application prospect in drag reduction for industry. This paper numerically studies the effect of microstructures on flow separation and drag reduction. Simple morphological microstructures, derived from the tilted shark scales, are attached to the wing at an angle of attack. The spacing and height of microstructures are made dimensionless by using the microstructure width and half of the wing width, respectively, that is, d̃m=dm/dAB and h̃m=hm/(H/2). The angle of attack is set to 10°. It is found that microstructures can reduce the motion amplitude of shed vortices, thereby suppressing flow separation and reducing drag. Both the planar and curved microstructures have excellent drag reduction performance. The microstructure spacing d̃m and tilt angle θ should not be too large or too small; otherwise, it will weaken the drag reduction ability. Cases d̃m=1.51, θ=20°, and θ=30° exhibit excellent drag reduction performance. The microstructure has the characteristic for being small, yet it needs to reach a certain height h̃m to effectively reduce drag. The case h̃m=0.667 is the most superior choice. Based on the proposed microstructure shape and spacing, the drag reduction performance of microstructures can reach more than 28%. Meanwhile, the drag reduction performance of microstructures increases with the improvement of the attachment proportion pm, and case pm≥50% is suggested for significant drag reduction performance. Finally, we discuss the drag reduction performance of microstructures on the wing at different angles of attack and find that microstructures can achieve good drag reduction, provided that the pressure drag caused by the flow separation is a significant proportion of the total drag and the flow separation occurs within the controllable range of microstructures.

Spatial gas effect on the deformation behavior of embossed glass microstructures in hot embossing

Glass hot embossing is a well-established and cost-effective manufacturing method for glass microstructures. However, the spatial volume affects deformation behaviors in closed mold cavities, which determines the final shape of the embossed glass. To investigate the spatial gas effect on the glass deformation mechanism during hot embossing, we used the focused ion beam (FIB) to fabricate blind micro-hole array structures with different depths as embossing templates. The experimental results demonstrated that the spatial volume of the mold cavity has a great influence on the energy of gas expansion, thus affecting the deformation height of glass microstructures during hot embossing. The deeper the cavity depth, the bigger the surface tension, resulting in larger surface concave deformation. Due to the surface tension of gas expansion, the deformation height of the edge zone is higher than that of the center zone at a higher embossing temperature until the heated glass is completely compressed into the mold cavity. Additionally, at lower embossing temperatures (520 °C), the heated glass has a large deformation resistance and elastic recovery. The more deformation volume escape from the shallower mold cavity because of the spatial effect, thus the deformation height decreases as the cavity depth reduces. The work provides a better understanding of manufacturing glass microstructures in hot embossing.

Numerical Study on the Bearing Capacity of Lubricant Film in Journal Bearing with Micro-textured Surface

For studying the hydrodynamic lubrication performance of micro-textured radial journal bearings, a numerical model of hydrodynamic lubrication for journal bearings was established first. Solve the established numerical model using FDM, and the lubricant film pressure distribution and static characteristics of bearings were obtained. Considering the processing cost and feasibility of the processing technology, the cylindrical texture arranged in the radial of the bearing shell surface is applied, the lubricant film thickness equation considering the micro-texture is introduced into the Reynolds equation. According to the height and distribution density of microstructure, the bearing capacity parameters were obtained. The load-carrying capacity of micro structure journal bearing is significantly higher than that of plain bearing. In this paper, a practical model with cylindrical micro-textured surface is given for journal bearing applications with high capacity demand.

Periodically oriented superhydrophobic microstructures prepared by laser ablation-chemical etching process for drag reduction

Superhydrophobic surface gives prominence to its application potential in the field of anti-adhesion and drag reduction in the microchannels, because of its low adhesion and high repulsion to water. In the paper, nanosecond pulse laser ablation-chemical etching (LACE) process is proposed to prepare patterned superhydrophobic surface with the microstructures which are orientation-controllable, period-adjustable and height-manageable on the 316L stainless steel. It is found that the laser scanning speed is the prerequisite for the formation of microstructures, the average laser power and laser scanning interval are important factors affecting the period and height of microstructures. The rebound coefficient of water droplets can reach 82.85% on the superhydrophobic surface with a contact angle of 154.7°(±0.6°), which indicates that the achieved surface has exceptional repellency to water. The drag reduction test experiments demonstrate that it can effectively reduce the flow resistance in the microchannels without drag reducing agents, and the maximum drag reduction rate can reach 29.83%. The work demonstrates that the LACE process, preparing superhydrophobic surfaces with the microstructures and manipulating its structural parameters with multi-dimension, can be reliably applied to drag reduction and water repellency fields.

Fabrication of 3D microstructures for flexible pressure sensors based on direct-writing printing

Microstructure plays an important role in improving the performance of flexible sensors. Changing the shape of the dielectric layer microstructure is an effective countermeasure to promote the sensitivity of capacitive sensors. Nevertheless, traditional microstructure fabrication methods have high manufacturing costs, cumbersome manufacturing processes, and single structure manufacturing, which restrict the development of flexible sensors. In this work, electro-hydro-dynamic (EHD) printing method and aerosol jet (AJ) printing method were applied to fabricate 3D microstructures, in a manner of printing the same pattern in multiple layers. The height and morphology of 3D microstructures, under different printing parameters, were compared by changing the number of printing layers and printing speed. Additionally, the printing effects of the two printing methods were compared. The results demonstrated that various shapes and highly controllable 3D microstructures could be fabricated by both methods. The EHD printing method had higher manufacturing precision, whereas the AJ printing method had higher stacking efficiency. The height and morphology of 3D microstructures could be effectively controlled by changing the number of printed layers and the printing speed of the microstructures. It is indicated that the EHD printing method and the AJ printing method both have great potential in the fabrication of 3D microstructures and that both methods had their own advantages.

Fabrication of micro-nano multi-scale hierarchical porous structure on the surface of Inconel718 nickel-base superalloy by one-step method

A new high-efficiency composite process consisting of laser machining and abrasive belt grinding was proposed to prepare multi-scale graded microstructures on the surface of Inconel718 nickel-base superalloy for aviation. The scheme is based on the machining characteristics of abrasive belt grinding, low damage molding and high-efficiency grinding and polishing, the effective combination of ultrashort pulse laser-induced surface microstructure growth, and the thermal effect in the process of high-energy beam machining, so as to realize the efficient preparation of hierarchical microstructure. In the one-step forming process, the accuracy of the material surface is ensured by abrasive belt grinding. The porous microstructure on the surface is catalyzed by the thermal effect produced by the high-energy beam laser. The scale of the porous structure is 3 µm–6 µm, the pore surface will generate nanoparticles, the size is below 100 nm, and dense nanoparticles will be generated on the surface. The porous structure can be super hydrophilic and adsorbed to form a liquid membrane. The formation of rib-like microstructures on the surface induced by ultrashort pulse laser makes the liquid film have directional spreading properties. Rib-like microstructure height is 50 µm–150 µm and it can be adjusted by setting the scanning line width. The one-step method for preparing hierarchical microstructures proposed in this study can efficiently process large-area microstructure surfaces with different wetting properties. • The porous structure, nanoparticles, and rib-like bulges can be efficiently fabricated. • The microstructure can be easily regulated.

High-Performance Flexible Piezoresistive Pressure Sensor Printed with 3D Microstructures.

Flexible pressure sensors have been widely used in health detection, robot sensing, and shape recognition. The micro-engineered design of the intermediate dielectric layer (IDL) has proven to be an effective way to optimize the performance of flexible pressure sensors. Nevertheless, the performance development of flexible pressure sensors is limited due to cost and process difficulty, prepared by inverted mold lithography. In this work, microstructured arrays printed by aerosol printing act as the IDL of the sensor. It is a facile way to prepare flexible pressure sensors with high performance, simplified processes, and reduced cost. Simultaneously, the effects of microstructure size, PDMS/MWCNTs film, microstructure height, and distance between the microstructures on the sensitivity and response time of the sensor are studied. When the microstructure size, height, and distance are 250 µm, 50 µm, and 400 µm, respectively, the sensor shows a sensitivity of 0.172 kPa−1 with a response time of 98.2 ms and a relaxation time of 111.4 ms. Studies have proven that the microstructured dielectric layer printed by aerosol printing could replace the inverted mold technology. Additionally, applications of the designed sensor are tested, such as the finger pressing test, elbow bending test, and human squatting test, which show good performance.

Computational Imaging in Dual-Band Infrared Hybrid Optical System with Wide Temperature Range.

The special dispersion and temperature characteristics of diffractive optical element (DOE) make them widely used in optical systems that require both athermalization and achromatic aberrations designs. The multi-layer DOE (MLDOE) can improve the diffraction efficiency of the overall broad waveband, but its diffraction efficiency decreases with changes in ambient temperature. When the ambient temperature changes, the micro-structure heights of MLDOE and the refractive index of the substrate materials change, ultimately affecting its diffraction efficiency, and, further, the optical transform function (OTF). In this paper, the influence of ambient temperature on the diffraction efficiency of MLDOE in a dual-infrared waveband is proposed and discussed, the diffraction efficiency of MLDOE caused by ambient temperature is derived, and a computational imaging method that combines optical design and image restoration is proposed. Finally, a dual-infrared waveband infrared optical system with athermalization and achromatic aberrations corrected based on computational imaging method is designed. Results show that this method can effectively reduce the diffraction efficiency of MLDOE by ambient temperature and improve the imaging quality of hybrid optical systems.

Rational Analysis of Drag Reduction Variation Induced by Surface Microstructures Inspired by the Middle Section of Barchan Dunes at High Flow Velocity

Aerodynamic drag reduction is a key element for the design of aircrafts, and it is also considered to be affected by the flow velocity. Herein, the influence of high flow velocity on the drag reduction induced by the surface microstructure inspired by a cross-section of barchan dune was investigated by the computational fluid dynamics method in this work. Overall, the drag reduction ratio was decreased while the pressure drag and viscous resistance enhanced simultaneously with the augmentation of flow velocity. Otherwise, drag analysis revealed that the total drag was a power function of flow velocity, which meant that the effect of flow velocity on drag was extremely fierce. Additionally, the microstructure improved the thickness of the boundary layer with a growth rate of 14.2%, and then reduced the viscosity resistance with limits during the development process of flow velocity. Furthermore, the micro-vortex caused by the surface microstructure provided the reverse wall shear stress, with the maximum value ranging from −4.77 Pa to −51.27 Pa, and then reduced the velocity gradient above the microstructure, thereby improving the drag reduction. However, both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) calculations showed that the excessive velocity could lead to the dissipation of micro-vortex, which augmented the contact area between the fluid and the surface, resulting in the enlargement of viscous resistance. Finally, it was confirmed that the variation of surface microstructure height had a significant influence on drag reduction at high flow velocity. The underlying mechanism of drag reduction could also provide theoretical guidance for the design and optimization of drag reduction coatings in aeronautical applications.

Fabrication of microstructured polymers by a simple biotemplate embossing method and their characterization

AbstractIn this work, microstructures were developed on a polymer surface using an embossing process by utilizing the transverse section of a wood as a biotemplate/mold. Microstructured polymers obtained by the proposed practical method were characterized by optical microscope for rough imaging, by scanning electron microscope for morphological properties and by Fourier transform infrared spectroscopy for surface chemistry. Utilization of a fluoropolymer eliminates the anti-stick surface pre-treatment and facilitates intact demolding of polymer structures from micro-voids of the wood. The height of the polymer microstructures was measured as 4 to 6 μm. Dimensions of the wood micro-voids can be tuned via acid/base treatment process. A drastic increase in heights of polymer microstructures (26 μm) was observed for the sample stamped by the acid/base treated biotemplate. The proposed method, which delivers well-organized microstructure patterns on fluoropolymer surfaces, can be utilized in the production of specialty surfaces, such as antibacterial, stick/anti-stick and water repellent.

Utilizing a Diffractive Focus Beam Shaper to Enhance Pattern Uniformity and Process Throughput during Direct Laser Interference Patterning.

Uniform periodic microstructure formation over large areas is generally challenging in Direct Laser Interference Patterning (DLIP) due to the Gaussian laser beam intensity distribution inherent to most commercial laser sources. In this work, a diffractive fundamental beam-mode shaper (FBS) element is implemented in a four-beam DLIP optical setup to generate a square-shaped top-hat intensity distribution in the interference volume. The interference patterns produced by a standard configuration and the developed setup are measured and compared. In particular, the impact of both laser intensity distributions on process throughput as well as fill-factor is investigated by measuring the resulting microstructure height with height error over the structured surface. It is demonstrated that by utilizing top-hat-shaped interference patterns, it is possible to produce on average 44.8% deeper structures with up to 60% higher homogeneity at the same throughput. Moreover, the presented approach allows the production of microstructures with comparable height and homogeneity compared to the Gaussian intensity distribution with increased throughput of 53%.

Tunable Wide Range and High Sensitivity Flexible Pressure Sensors with Ordered Multilevel Microstructures

AbstractWith the rapid development of healthcare and human‐machine interactions, there is a growing demand for flexible electronic skin to have a high sensitivity over a wide range. While current multilevel and hierarchical structures inspired by nature broadened the sensing range, the structural design still lacks systematic study. Hereby, an ordered multilevel microstructure is proposed, and the design strategy for performance regulation of piezoresistive pressure sensors is studied. Both microstructure height and spatial distribution are investigated systematically through simulation and experiments. The flexible piezoresistive pressure sensor is fabricated by combining a fast, cost‐effective laser marking technology, molding, and pneumatic spray. The fabricated sensors show high sensitivity (1.5 – 8.3 kPa−1) over a wide range (0.01 – 200 kPa), and have a detection limit of 10 Pa, a response time of below 70 ms, and a mechanical stability over 10 000 cycles. This design and fabrication strategy can be further optimized by combining advanced materials and fabrication systems, and is expected to be applicable for a wide range of flexible materials.

Research on Composite Drag Reduction Characteristics of ‎Biomimetic Microstructural Surface

The objective of this work is to investigate the effect of the bionic microstructure surface on flow field structure of the slab. The motivation behind this study is to investigate the effect of the bionic microstructure parameters including the height and intersection angle of microstructure in order to improve the drag reduction characters. The numerical simulation is performed on the bionic microstructure model of the V-shaped and serrated bionic microstructures using the RNG k-ε model. The drag reduction rates of two bionic microstructures under different dimensionless sizes are ob13.79 tained. The drag reduction efficiency is up to 8.76% when the dimensionless height of microstructure is at and the intersection angle for V-shaped microstructure. In addition, combined with wall temperature control of drag reduction technology, the influence of wall temperature on the drag reduction effect is also analyzed. Compared with the flow field structure of the surface boundary layer of the smooth plate, the wall microstructure divides the surface boundary layer into two parts: the bottom and the tip. The average velocity profile is moved up and the thickness of the linear bottom layer is increased. A large number of "quiet" fluids are gathered at the bottom of the surface boundary layer. In addition, the existence of wall microstructure can weaken the momentum exchange in the boundary layer and restrain the spreading vortex motion of the fluid in the near-wall region. The "secondary vortex pair" on both sides of the tip of the microstructures can effectively limit the lateral pulsation of fluid So as to achieve a good drag reduction effect‎.