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We present three-dimensional scaling relations for the thrust production and power consumption of combined heaving and pitching hydrofoils by extending the three-dimensional pitching scaling laws introduced by Ayancik et al. ("Scaling Laws for the Propulsive Performance of Three-Dimensional Pitching Propulsors," Journal of Fluid Mechanics, Vol. 871, July 2019, pp. 1117-1138). Self-propelled inviscid simulations and previously published experimental data are used to validate the scaling laws over a wide range of motion amplitudes, Strouhal numbers, heave ratios, aspect ratios, and pitch axis locations. The scaling laws are shown to predict inviscid numerical and experimental data well, within ±25% and ±16% of the thrust and power data, respectively. It reveals that both the circulatory and added mass forces are important when considering a wide range of motion amplitudes and that nonlinear corrections to the classic linear theory are essential to modeling the power performance across a wide amplitude and aspect ratio range. By using the scaling laws as a tool, it is obtained that peak efficiency occurs when dimensionless amplitude A*>1 and for these large-amplitude motions there is an optimal nondimensional heave ratio h*, where the efficiency maximizes in the narrow range of 0.75

Quasi-static and dynamic stall control experiments, using dielectric barrier discharge plasma actuators, were performed on a square-tipped aspect-ratio-one wing, with a NACA 0015 profile, under harmonic pitching, at a Reynolds number of 3×105. Relatively low O(1) and relatively high O(10) pulse-modulated reduced excitation frequencies were introduced at the leading edge; the former produced the largest poststall lift improvements, whereas the latter produced the highest maximum lift. A reduced frequency, based on laminar separation bubble shedding, was enlisted to explain the differences between the two results. Under conditions of dynamic pitching, evidence of a dynamic stall vortex was absent, due to its interaction with the strong tip vortices, consistent with prior experimental and numerical investigations. As a general rule, performance benefits produced by excitation under quasi-static conditions were reproduced under harmonic pitching. Low-order dynamic stall and dynamic stall control models, based on a modified version of the Goman-Khrabrov delta-wing concept, were evaluated. Model constants were obtained from quasi-static data sets, and a single baseline dynamic case was employed to determine the time constants. The model produced excellent results for both baseline and controlled cases, which was attributed to similar lift and stall mechanisms exhibited by delta and rectangular low-aspect-ratio planforms. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative approach to increasing the aspect ratio of metal nanostructures fabricated using nanoimprint lithography (NIL). Although conventional NIL and metal lift-off processes can fabricate metal nanostructures, the achievable aspect ratio is often limited by the inherent constraints of NIL. In this study, we demonstrate that for an ultraviolet (UV) transparent substrate, metal nanostructures patterned via NIL can serve as a photomask. A negative-tone photoresist (PR) layer was then deposited on top of the patterned metal nanostructures. By illuminating the substrate from the backside with UV light and subsequently developing the PR, PR structures complementary and self-aligned to the metal layer were obtained. This enabled a second round of metal deposition and lift-off, thereby increasing the height of the metal structures and enhancing the aspect ratio. Experimentally, we demonstrated that this method can improve the aspect ratio from less than 1.0 to as high as 2.1. This paper also addresses the further developments and potential applications of this technique., (Creative Commons Attribution license.)

Background: Cellulose nanofibrils (CNFs) have emerged as a sustainable and environmentally friendly option for a broad range of applications. The fibrous nature and high biopersistence of CNFs call for a thorough toxicity assessment, but it is presently unclear which physico-chemical properties could play a role in determining the potential toxic response to CNF. Here, we assessed whether surface composition and size could modulate the genotoxicity of CNFs in human bronchial epithelial BEAS-2B cells. We examined three size fractions (fine, medium and coarse) of four CNFs with different surface chemistry: unmodified (U-CNF) and functionalized with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) (T-CNF), carboxymethyl (C-CNF) and epoxypropyltrimethylammonium chloride (EPTMAC) (E-CNF). In addition, the source fibre was also evaluated as a non-nanosized material. Results: The presence of the surface charged groups in the functionalized CNF samples resulted in higher amounts of individual nanofibrils and less aggregation compared with the U-CNF. T-CNF was the most homogenous, in agreement with its high surface group density. However, the colloidal stability of all the CNF samples dropped when dispersed in cell culture medium, especially in the case of T-CNF. CNF was internalized by a minority of BEAS-2B cells. No remarkable cytotoxic effects were induced by any of the cellulosic materials. All cellulosic materials, except the medium fraction of U-CNF, induced a dose-dependent intracellular formation of reactive oxygen species (ROS). The fine fraction of E-CNF, which induced DNA damage (measured by the comet assay) and chromosome damage (measured by the micronucleus assay), and the coarse fraction of C-CNF, which produced chromosome damage, also showed the most effective induction of ROS in their respective size fractions. Conclusions: Surface chemistry and size modulate the in vitro intracellular ROS formation and the induction of genotoxic effects by fibrillated celluloses. One cationic (fine E-CNF) and one anionic (coarse C-CNF) CNF showed primary genotoxic effects, possibly partly through ROS generation. However, the conclusions cannot be generalized to all types of CNFs, as the synthesis process and the dispersion method used for testing affect their physico-chemical properties and, hence, their toxic effects. [ABSTRACT FROM AUTHOR]

A nonlinear aeroelastic analysis framework for high-aspect-ratio wings that includes the aerodynamic effects of propellers is described. The high computational cost required for modeling aerodynamic interaction between the wing and propeller wake is reduced by taking advantage of the relatively slow dynamics of the wing. Consequently, the propeller wake is modeled as a straight vortex cylinder that does not require a computationally expensive wake updating process. By leveraging the smallness of the propeller, an averaged vortex cylinder method is proposed that calculates the induced velocities of the propeller vortex cylinder efficiently without suffering from a numerical singularity and loss of accuracy. The induced velocities are considered in the wing aerodynamic force calculation using an unsteady vortex lattice method. An efficient propeller cylinder coordinate generation method modeling the propeller-attached wing by absolute nodal coordinate formulation with a multibody dynamic theory is also proposed. The developed framework is validated by comparison with other formulations. A static aeroelastic analysis on a low-speed high-aspect-ratio wing demonstrates that the propeller-induced axial velocity causes the deflection change of 5.4%. A nonlinear dynamic result shows that the propeller decreases the vibration amplitude by 6.7% because the propeller-induced axial velocity enhances the aerodynamic damping. [ABSTRACT FROM AUTHOR]

We present a medium-fidelity aeroelastic framework for computing intermittently separating three-dimensional (3-D) flows around high-aspect ratio wings with a significantly reduced computational cost compared to the computational-fluid- dynamics-based method. To achieve that, we propose a modified three-dimensional vortex panel method with leading-edge separation controlled by leading-edge suction parameter theory, and its incorporation in a coupled aeroelastic solver for the dynamic response of these systems. Numerical verifications and simulations are presented on both attached and separated aeroelastic test cases, demonstrating the method on postflutter limit-cycle oscillation of a cantilever wing, and leading-edge separation on a deploying wing, a complex kinematic response. In both cases we were able to capture three-dimensional interactions on intermittently separating dynamic flowfields using a low computational cost. [ABSTRACT FROM AUTHOR]

Fabrication of high aspect ratio (HAR) complex micro features on high strength temperature resistant (HSTR) alloys is challenging by any conventional or non-conventional machining methods. In this study blind, HAR and complex micro features have been fabricated by micro electrochemical milling (MEM) on HSTR Cobalt alloy (Haynes-188) introducing a new strategic approach with novel flushing technique which could get rid of the need of pulsed DC power supply. Multiphysics simulation of the rotating micro-tool at different rpm and its impact on effective sludge removal has been analyzed and verified experimentally. In this study, most influencing parameters of MEM like voltage, feed rate, rpm of tool and milling layer depth have been selected to investigate their effects on the machining responses like width overcut, machined depth and surface roughness on Haynes-188 alloy. Comparison has also been made with constant and pulsed DC power source to know the influence of these process parameters on the MEM responses. Finally, several linear and non-linear blind, HAR (AR > 11) and intricate micro features have been fabricated successfully on cobalt alloy at the most suitable parametric combination, i.e., 7.5 V of machining voltage, feed rate of 0.3 mm/min, and tool rotation of 750RPM with 0.5 M of NaNO3 electrolyte. [ABSTRACT FROM AUTHOR]

This paper investigates the use of a lifting surface method coupled with a nonlinear lift curve, the nonlinear vortex lattice method (NL-VLM), toward the study of stall cells on wings. First, Spalart's spectral lifting line model is thoroughly investigated. It is found that the Gaussian filter leads to the existence of two different solutions, one directly interpolated in the lift polar and the other retrieved from the circulation distribution. Then the NL-VLM method is applied to the canonical cases of the infinite and the elliptic wing. In this model, the stall cells is represented as a sharp transition between stalled and prestalled wing section, meaning that no wing section effectively sees a negative slope of the lift against angle-of-attack relation. This sharp transition can be smoothed by introducing an artificial dissipation that also results in two separated solutions, without changing the underlying characteristics of the model. The effect of several parameters, like the grid spacing and the relaxation factor, is studied, with little effect on the wavelength of the predicted stall cells. The effect of specific parameters of the lift polar like the magnitude of the negative slope in the stall regime and the trend in the deep stall range is also investigated. It is observed that the slope of the lift versus angle of attack must not stay negative when the angle of attack goes to infinity for the system of equations to have a steady solution. The amplitude of the negative lift-curve slope has an effect on the wavelength of the cells explaining why the stall cells would not be observed for a leading-edge-type stall. Finally rectangular wings are studied for comparison to experimental data and higher-fidelity numerical simulations, showing the predictive capability of the proposed low-order model. [ABSTRACT FROM AUTHOR]

We demonstrated conformal Al2O3 passivation via atomic layer deposition (ALD) of a flexible Ag network electrode possessing a high aspect ratio. The Ag network electrode passivated by the ALD-grown Al2O3 film demonstrated constant optical transmittance and mechanical flexibility relative to the bare Ag network electrode. Owing to the conformal deposition of the Al2O3 layer on the high aspect ratio Ag network electrode, the electrode exhibited more favorable stability than its bare Ag-network counterpart. To demonstrate the feasibility of Al2O3 passivation via ALD on a flexible Ag network, the performances of flexible and transparent thin-film heaters (TFHs) with both a bare Ag network and that passivated by ALD-grown Al2O3 were compared. The performance of Al2O3/Ag network-based TFHs was minimally altered even after harsh environmental tests at 85% relative humidity and a temperature of 85 °C, while the performance of bare electrode-based TFHs significantly deteriorated. The improved stability and reliability of the Al2O3/Ag network-based TFHs indicate that the ALD-grown Al2O3 film effectively prevents the introduction of moisture and impurities into the Ag network with a high aspect ratio. The improvement in the stability of the Ag network through Al2O3 passivation implies that the ALD-grown Al2O3 film represents a promising transparent and flexible thin film passivation material for high quality Ag network electrodes with high aspect ratios.

A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament, which is employed to drill holes on copper targets. By shifting or rotating the focusing lens, additional aberration is imposed on the focused laser beam, and significant influence is produced on the aspect ratio and cross-sectional shape of the micro-holes. Experimental results show that when proper aberration is introduced, the copper plate with a thickness of 3 mm can be drilled through with an aspect ratio of 30, while no through-holes can be drilled on 3-mm-thickness copper plates by femtosecond laser with minimized aberration. In addition, when femtosecond laser filament with large astigmatism is used, micro-holes that had a length to width ratio up to 3.3 on the cross-section are obtained. Therefore, the method proposed here can be used to fabricate long oval holes with high aspect ratios. [ABSTRACT FROM AUTHOR]

Two numerical models of HAR ring and O-ring sealing systems for roller cone bits were established in this paper. The stress-strain distribution was analyzed by finite element method. Effects of compression ratio, fluid pressure, ambient temperature and friction coefficient on mechanical behavior and sealing performance were studied. The results show that the HAR ring has better sealing performance than O-ring in the same working condition. The HAR ring can realize multi-stage sealing to increase the reliability of sealing. The high stress region appears at the sharp corner below the shaft. The sealing performance and the von Mises stress is enhanced with compression ratio and fluid pressure increasing. Under a high working temperature field, the sealing surface of HAR ring fails easily. The contact pressure fluctuation of the sealing surface easily appears by friction coefficient. Sharp-angled regions of the HAR ring near S.S.3, S.S.5 and S.S.6 fail easily. [ABSTRACT FROM AUTHOR]

This letter presents a new strategy for the formation of continuous Cu seed layer in high aspect ratio (HAR) through-silicon-vias (TSVs) with large depth based on sequential sputtering and electroless plating. The deposited seed layer is continuous and dense even at the bottom of the TSVs, which is difficult to achieve by individual sputtering or electroless plating. Combined with the spin coating of polyimide (PI) liner, atomic layer deposition (ALD) of TiN barrier layer, and electroplating of Cu conductor, TSVs with diameter of $9~\mu \text{m}$ and depth of $141~\mu \text{m}$ are successfully fabricated, and the aspect ratio is 15.5. The TSVs are fully filled without cracks or voids, proving the good quality of seed layers. Electrical measurements show that the minimum capacitance of a single TSV is around 145 fF, and the leakage current is about 3.4 pA at 20 V, indicating good electrical properties of the fabricated TSVs and the feasibility of the proposed fabrication flow in deep HAR TSV applications. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the leaning angle in relation to the aspect ratio of the block array in 3D NAND flash memory with a high aspect ratio using TCAD simulation. The simulation data were validated through cross-verification with the Stoney equation, a standard tool for diagnosing film stress. The study confirmed a linear relationship between intrinsic stress and film deformation in single-layer structures. In multi-layer structures, the deformation of the film changes according to the intrinsic stress of the most recently deposited layer. TCAD simulation used a block array structure comprising nine strings between each common source line and a layer range of 10 to 70. The residual stress from the mold stacking process leads to leaning because of stress relaxation after slit etching. Because of the accumulation of lateral stress at each deposition stage, the maximum lateral stress increases with the number of layers. • Leaning of a Block Array in 3D NAND Flash Memory was investigated using TCAD • The simulation data were validated through cross-verification with the Stoney equation • we observed uneven lateral stress between the top and bottom areas of the block array structure's left surface, suggesting that the resultant torque is the primary cause. • The residual stress from the mold stacking process leads to leaning because of stress relaxation after slit etching. [ABSTRACT FROM AUTHOR]

It occurs that the loading point changes with the test piece in the aircraft structure test. In particularly, the large deformation of the wing will cause the issue that loading point is not perpendicular with the plan of the wing. A kind of servo loading systems is applied in composite material wing. The wing is divided into N characteristic of flying points by using the method of finite element analysis. To keep all levels of loading points are vertical with the plan of wing the fly points are moved with loading. It implements vertical following loading. This system is used to complete the high aspect ratio wing test. The test results show that the system can realize the test of the UAV by using the servo load systems, and the loading procedure is smooth. The test piece is no jitter, its deformation is uniform, and the strain data meets the test requirements which can offer a reference for the analogous loading systems.

Graphene-Coated carbon nanofibers (G-CNFs) Foams with interconnected 3D-networks have unique physical properties that make them suitable for a wide variety of applications. However, their design and fabrication strategies entail several parameters with different strengths, anisotropy, and thermal conductivity. Tuning functional properties to meet the desired application needs a deep understanding of their microstructure. Utilizing a microstructure modeling based on a Finite Element Analysis (FEA) requires adopting an accurate yet simple approach to overcome complications associated with the unique morphological characteristics of the G-CNFs Foam, covering graphene coating thickness and high aspect ratio and tortuosity, that can be neither disregarded nor roughly approximated. Here, we introduce an innovative strategy to predict the morphological, mechanical, and thermal properties of a G-CNFs Foam with a high aspect ratio and tortuosity, as well as a significant difference in composite materials' strength to overcome modeling difficulties including meshing, coating thickness, and homogenization, to name a few. This new modeling strategy is validated with experimental data from our work and the literature and provides a reliable and straightforward approach with less computational cost.

Drilling is a kind of processing technology with a large proportion in mechanical processing, especially the drilling of deep hole, which is facing great challenges due to the high-strength properties of materials and debris-removal challenges. Because there is no obvious cutting force in the machining process and all conductive materials can be machined, microelectrical discharge machining (EDM) is playing an important role in deep hole drilling. In this study, micro-EDM technology was used for deep hole drilling on flexible bellows. Key technologies were discussed including workpiece positioning device, process control methods and drilling parameters selection. A special clamp was designed to solve the deformation problem of bellows positioning. In order to improve the consistency of the inlet and outlet of the deep hole, a double-sided guiding device was designed to reduce the radial deflection of tool electrode caused by the high spindle speed and long suspended stretch. The tool electrode compensation method was studied to improve the precision and aspect ratio of the deep hole. In addition, the influence of parameters such as spindle speed and oil flushing pressure on the drilling process was also analyzed. The study results show that the designed devices and process can meet the drilling requirements of the deep hole on bellows; the aspect ratio of the deep hole reaches 44:1. [ABSTRACT FROM AUTHOR]

Recently, electron beam machining technology has been used in various ways depending on the industrial field. It is used in technologies in the fields of shipbuilding, aerospace, and transportation. In the case of the existing electron beam machining technology, a technology for welding or joining two materials was proposed. In this paper, in order to perform electron beam drilling, a multi-hole is created by increasing the instantaneous vaporization pressure during electron beam machining through a vaporized amplification sheet. A vaporized amplification sheet was prepared for electron beam drilling. The vaporized amplification sheet was made of a 1:3.25 combination of silicone and brass powder. Also, in order to bond the produced vaporized amplification sheet to the SUS 304 stainless steel, a primer was applied on the surface of the metal material to firmly bond the two materials with different properties. If the bonding is weak, the effectiveness decreases due to pressure leakage during electron beam machining. Multi-holes were processed using the fabricated material to fix an acceleration voltage of 120 kV and a current of 12 mA. Also, to compare the multi-hole shape and the processing result, the comparison was performed according to the exposure time of the electron beam. The lower the exposure time, the more fine holes were secured, and as the exposure time increased, the molten pool phenomenon occurred, and processing was not performed in the experimental results. [ABSTRACT FROM AUTHOR]

High aspect ratio (HAR) micro-grooves are of great significance for vacuum electronic devices. However, the fabrication of HAR micro-groove on oxygen-free copper remains challenge since the high surface quality is hard to achieve. Aiming to improve the surface quality, a hybrid and successive method, obtained by combining nanosecond laser and micro-milling (NLMM), was presented. The nanosecond laser achieves the maximum workpiece removal rate, while the subsequent micro-milling provides the desired machining quality. Compared to one-way full slot micro-milling (FSMM), the presented manufacturing method (NLMM) could improve the surface quality, namely the top burr formation and the bottom and sidewall surface roughness. Furthermore, the NLMM displayed a lower tool wear rate compared to FSMM. Finally, a desired S-shaped groove with an aspect ratio of 2.5, a width of 0.2 mm, and the cycle number of 30 was successfully fabricated. The study offers a promising aspect for improving the HAR micro-groove fabrication quality. • A novel method of laser and micro-milling hybridizing process was proposed to fabricate micro-groove on oxygen-free copper. • A S-type high aspect ratio micro-groove of oxygen-free copper with high surface quality was fabricated. • The influence of laser scanning strategy and laser parameters was studied. • The method could improve the surface quality in terms of top burr formation, the surface roughness, and reduce tool wear. [ABSTRACT FROM AUTHOR]

This paper quickly calculated the design variables to satisfy the strength and stability conditions, the dominant design verification conditions of the composite wing structure, through a genetic algorithm. It developed a variable stiffness stacking optimization process applicable to aircraft wing structure design. We proposed a laminate parameter-based optimization strategy that considers the stiffness characteristics of the two-dimensional elements used as design variables. Compared with the optimization results obtained using continuous stiffness optimization as an optimization process function of laminate sequences with genetic algorithms, we obtained a reasonable stiffness distribution while complying with critical guidelines related to individual composite layup designs. The results of the stiffness optimization design were implemented as a finite element model, and the results were verified through NASTRAN. We demonstrated the functionality of the stiffness optimization process by obtaining results satisfying the set response conditions, i.e., strength and stability, in many design areas of the wing.

Melt electrowriting (MEW) approach with constant working distance has been developed to weaken the charge interferences and to enhance the architecture mechanical strength, by which various stacked architectures with high aspect ratio can be achieved. The deposited fiber guides the subsequent jet to print layer by layer along the pre-designed patterns without fiber pulsing. The position of the nozzle is raised simultaneously during the direct-writing process to maintain a constant working distance, and then, the deposition offset of the fiber layer can be decreased. The effects of the processing parameters on the MEW fibers with diameters distributed in the range of 50–125 µm have been studied. Patterns of polygon and characters with fiber layer number of 200 and aspect ratio higher than 180 are direct-written accurately. The maximum height of the direct-written patterns reaches 9 mm. The proposed approach is a good method to realize the direct additive manufacturing of high-aspect-ratio architectures and to promote its industrial applications. [ABSTRACT FROM AUTHOR]

We have fabricated very-high-aspect-ratio (VHAR) silicon and metal microstructures in complex geometric patterns. The recently developed surfactant-added tetramethylammonium hydroxide etching allows the formation of V-grooves in any pattern, i.e., not limited by the crystal direction, on a silicon surface. As the resulting sharp pits allow very deep photoelectrochemical etching, VHAR silicon microstructures (4-μm-wide and over-300-μm-deep trenches) are successfully fabricated in complex patterns (spiral and zigzag demonstrated), overcoming the prevailing limitations of simple pores and straight trenches. Furthermore, by filling the VHAR silicon mold with nickel and removing the silicon, high-aspect-ratio metal microstructures of complex patterns are also obtained. These VHAR microstructures in complex patterns, which are structurally much stronger than the simple posts and straight plates, overcome the stiction problem even when densely populated. © 2012 IEEE.

The vapor-liquid-solid (VLS) process was applied to fabricate zinc oxide nanowires (ZnO NWs) with a different aspect ratio (AR), morphological, and optical properties. The ZnO NWs were grown on a system that contains a quartz substrate with transparent conductive oxide (TCO) thin film followed by an Al-doped ZnO (AZO) seed layer; both films were grown by magnetron sputtering at room temperature. It was found that the ZnO NWs presented high crystalline quality and vertical orientation from different structural and morphological characterizations. Also, NWs showed a good density distribution of 69 NWs/μm2 with a different AR that offers their capability to be used as possible photoelectrode (anode) in potential future device applications. The samples optical properties were studied using various techniques such as photoluminescence (PL), absorption, and transmittance before and after sensitization with N719 dye. The results demonstrated that NW with 30 nm diameter had the best characteristics as feasible photoelectrode (anode) (high absorption, minimum recombination, high crystallinity). Also, the present samples optical properties were found to be improved due to the existence of N719 dye and Au nanoparticles on the tip of NWs. NWs grown in this work can be used in different photonic and optoelectronic applications.

In this paper, a study on optimum design methodology of a section structure of a composite material rotor blade using genetic algorithm is conducted, in order to calculate repetitive optimum design, analysis of strength, fatigue and vibration on blade section. In the analysis, the minimum mass of the rotor blade was defined as objective function; stress damage index, center of mass on blade section and fatigue life of blade were set as constraints. By applying genetic algorithm, laminate angle and thickness of skin, thickness, location and width of torsion box were established as design variables; the optimum design methodology on section structure of the composite material rotor blade was validated. The integrated design program of the section structure of the composite material rotor blade based on this study deals with designing the optimal rotor blade section which meets the design load and constraints given by the random position of rotor blade. By using blade’s section design variables derived from this, it can be facilitated for basic information on detailed design of rotor blade.

Etching rate is a major concern for the effective mass production of high-aspect-ratio microstructures, especially in p-type silicon. In this work, controlled electrochemical growth of high-aspect-ratio (from 15 to 110) macropores in p-type silicon at ultrafast etching rate (from 16 to 30 µm min−1) has been studied. Based on current-burst-model, pore formation was systematically investigated from the nucleation phase to stable pore growth. Good macropores with depth up to 180 µm and aspect ratio beyond 110 was achieved in just 11 min. This sets a new record on state-of-the-art p-type silicon microfabrication and can promote the development of microdevices.

Etching technique of deep silicon trenches with high aspect ratio is critical in improving integration and accuracy of Micro-Electro-Mechanical Systems(MEMS)sensor array and reducing the cost of it. To fabricate silicon isolation trenches with aspect ratio equaling to 25 μm/0.8 μm,we use and compare three kinds of MEMS process，Reactive Ion Etching(RIE),Bosch,and RIE combined with Bosch,which are all CMOS process compatible and easy to integrate with CMOS ICs.Finally it proves that RIE combined with Bosch process is better than the other two in producing deep trenches with smooth side walls.

The industries like automobile, electronics, medical and biomedical sectors provide scope for various types of micro products/features made up of copper material. Due to the higher ductility of copper the electrochemical micro machining (EMM) is a prominent technique owing it's no tool wear, high accuracy, burr free and non-contact machining surface. Although enhancing of EMM performance is significant work in the micro components manufacturing industry. Hence, in this present work the hot air is mixed with aqueous citric acid (C6H8O7) electrolyte (HAME) to machine high aspect ratio micro-holes (HAR micro-hole) and the results are compared with the dry air mixed electrolyte (DAME). The process parameters such as machining voltage (Mv), Duty cycle (Dc), and electrolyte concentration (Ec) are taken into account in evaluating the machining performance. The electrolyte temperature (Et) and frequency are kept at a constant level as 36 ± 1°C and 85 Hz respectively. The machining performances are estimated by means of material removal rate (MRR), overcut (OC) and taper angle of the HAR micro hole (TAHAR-micro-hole).The MRR shows 1.43 times improvement for HAME at the parametric combination of 20 g/L, 13 V, and Dc at 90% and reduced OC by 30.4% over DAME. The TAHAR-micro-holes are found to be 21.67° and 28.19° for the DAME and HAME respectively for the above parametric combinations. At parameters combination of 30 g/L, 13 V, and 90%, the MRR shows 2.87 times higher MRR compared to DAME. Furthermore, the use of citric acid as an electrolyte and mix of hot air contributes for higher MRR and reduced OC.The field emission scanning electron microscope (FESEM) analysis is done to understand the effect of hot air mixed electrolyte on the surface topography and inner machined surfaces of a micro-hole. [ABSTRACT FROM AUTHOR]

We present a hybrid, semi-analytical approach to perform an eigenvalue-based flutter analysis of an Unmanned Aerial Vehicle (UAV) wing. The wing has a modern design that integrates metal and composite structures. The stiffness and natural frequency of the wing are calculated using a Finite Element (FE) model. The modal parameters are extracted by applying a recursive technique to the Lanczos method in the FE model. Subsequently, the modal parameters are used to evaluate the flutter boundaries in an analytical model based on the p-method. Two-degree-of-freedom bending and torsional flutter equations derived using Lagrange's principle are transformed into an eigenvalue problem. The eigenvalue framework is used to evaluate the stability characteristics of the wing under various flight conditions. An extension of this eigenvalue framework is applied to determine the stability boundaries and corresponding critical flutter parameters at a range of altitudes. The stability characteristics and critical flutter speeds are also evaluated through computational analysis of a reduced-order model of the wing in NX Nastran using the k- and pk-methods. The results of the analytical and computational methods are found to show good agreement with each other. A parametric study is also carried out to analyse the effects of the structural member thickness on the wing flutter speeds. The results suggest that changing the spar thickness contributes most significantly to the flutter speeds, whereas increasing the rib thickness decreases the flutter speed at high thickness values. [ABSTRACT FROM AUTHOR]

Functionalised multi‐walled carbon nanotubes (MWCNTs) are exclusively used in antibacterial activity due to their high aspect ratio and surface penetration characteristics. This study reports the synthesis of piperazine and dopamine functionalised MWCNTs to investigate antibacterial activity against strains like Staphylococcus aureus and Micrococcus luteus. MWCNTs were activated through acid oxidation and then refluxed at 75°C for 10 and 8 h in the presence of piperazine and dopamine, respectively. The functionalised MWCNTs were characterised by scanning electron microscopy, Fourier‐transform infrared spectroscopy, X‐ray diffraction and Raman spectroscopy. Moreover, functionalised MWCNTs were subjected to zone inhibition assay on agar plates. Results revealed the significant antibacterial activity against various bacteria up to 50%. Similarly, it was observed that the effect of different solvents, such as dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) was non‐prevalent to the bacterial zone of inhibition. Such facile nano‐modifications provide passage to nano‐antibacterials for advanced studies. [ABSTRACT FROM AUTHOR]

For a shape rolling process of products with a high aspect ratio, its width does not spread sufficiently, frequently resulting in the unfilling phenomenon in the width direction. This paper proposes a roll profile design for the shape rolling process; this design method improves the dimensional accuracy of a shape wire with a high aspect ratio. From among the products produced by the shape rolling process in industrial sites, those with aspect ratios of ≥ 3.3 were selected in this study, and finite element (FE) simulation of the shape rolling process was conducted to verify the effectiveness of proposed method. The results of the FE simulation showed that the proposed design method was effective in performing the rolling process for shapes with high aspect ratios. In addition, the effectiveness of the proposed method was verified by conducting an experiment for bridge-valve wire by using plasticine. The experimental results showed that target shapes were obtained with an unfilling rate as low as 0.23 % for the cross-sectional area. [ABSTRACT FROM AUTHOR]

An experimental investigation of subcooled flow boiling in a high-aspect-ratio, one-sided heating, silicon-based rectangular microchannel was conducted utilizing de-ionized water as the working fluid. The microchannel was 5.01mm wide and 0.52mm high, having a hydraulic diameter of 0.94mm and an aspect ratio (AR) of 10. The heat flux, mass flux, and inlet fluid subcooling were in the ranges of 0-30 W/cm², 200-500 kg/m² s, and 5-20 °C, respectively, while the orientations were vertical and horizontal. Parametric study on heat transfer characteristics including the onset of nucleate boiling (ONB), heat transfer coefficient (HTC), and critical heat flux (CHF) was carried out combined with flow visualization. Significant appearance of ONB without boiling hysteresis was observed in the boiling curve, accompanied with bubble nucleation. Nucleate boiling occurred first near the exit, where the HTC increased more sharply, while easier bubble nucleation was found near the sides. Unique time-dependent flow pattern consisting of isolated bubbly flow, elongated bubbly flow, partial dry-out, and rewetting process was observed. More nucleation sites were activated at higher heat flux, while higher initial heat flux and wall superheat for ONB as well as higher CHF value were obtained at higher mass flux and inlet subcooling. Compared to the vertical channel, higher wall temperature and pressure drop with larger oscillation amplitudes were found for the horizontal counterpart, where the merged bubbles agglomerated in the heating section, resulting in earlier dry-out which deteriorated heat transfer. [ABSTRACT FROM AUTHOR]

The movable super-diffraction optical needle (MSON) is a tightly focused beam like a "needle", which can realize vector scanning on the focusing plane. Not only does it have a long focal depth, but its resolution also exceeds the diffraction limit. The modulation and control technology required for generating MSON by oblique incidence is explored in this manuscript for the purpose of processing high-aspect-ratio, sub-wavelength structures. As the optical needle generated by traditional methods is static and sensitive to variation of the angle information of the incident beam, here we introduce a confocal scanning system by using a two-dimensional galvanometer system, a scan lens, and a tube lens to control the oblique incidence angle. The effects of the oblique incidence angle on the resolution, depth of focus, uniformity, and side lobes of the MSON were analyzed. Further, the voltage-controlled liquid crystal located between the scan lens and the 2D galvanometer system can be used to compensate for the additional phase difference caused by oblique incidence. The aspect ratio is defined as the ratio of depth of focus to resolution. By modulating and controlling the light field, the MSON with high aspect ratio (7.36), sub-diffractive beam size (0.42λ), and long depth of focus (3.09λ) has been obtained with homogeneous intensity, and suppressed side lobes. High speed, high axial positioning tolerance, and high-resolution laser processing can also be achieved, which removes the restrictions presented by traditional laser processing technology, for which high resolution and long depth of focus cannot be achieved simultaneously. [ABSTRACT FROM AUTHOR]

Even though the micro hole with diameter smaller than micro-meters could be made by micro-EDM process, however, the deep micro hole with high aspect ratio is a critical challenge due to the flushing problem. By conventional micro-EDM process, micro hole with the aspect ratio larger than 5~7 is still quite difficult to achieve perforations drilling. Flushing process is the key-point for deep micro hole drilling by micro-EDM. In order to improve the flushing problem, the single and dual notch cross-sectional micro tools made by WEDG technology were used for micro-EDM drilling in this study. The notch zone provides the space gap for non-flushable debris to avoid the abnormal electro-discharge generation between micro tool and work-piece. The machining characteristics of EDM drilling such as tool wear, section shape area, machining time and micro hole diameter by different cross-section micro electrode tool have been investigated in this study. The experimental results show that the single cross-sectional tools with larger notching area enhance the aspect ratio of micro hole drilling to 10 times. The roundness of tungsten carbide micro hole is approximately 0.001 mm. In the near future, it is quite possible to achieve the excellent productivity of high aspect ratio micro hole by micro EDM drilling while the notch cross-sectional micro tools are available in the commercial market. [ABSTRACT FROM AUTHOR]

Micro-forming tool is very important for micro-hole drilling. Electrical discharge machining (EDM) is used in micro-fabrication because of low reaction force. Moreover, micro-electrode is an important micro-tool. In this study, this paper proposes a micro-pin-forming method in which a rotating cylindrical electrode approaches a forming plate. As the processing area in this method is larger than those other methods, a higher removal rate is achieved compared to other methods. Moreover, a high aspect ratio of the micro-pin is achieved. A rotating WC-Co rod of 0.5 mm diameter is moved through the plate that is a zinc alloy plate of 2 mm width and 5 mm thickness. The result showed thad a micro-pin electrode of 90 μm diameter and 5 mm length can be gotten reproducibly. However, a micro-pin forming smaller than 10 μm in diameter is difficult to obtain using the machine tools currently available in the market. Miniaturization limits through micro-pin forming by the EDM are determined based on the discharge conditions, grain size of pin material, thermal residual stress, and lateral vibration of the micro-pin caused by the rotation of the micro-pin. In this study, it is considered that micro-pin vibration caused by its rotation, which affects the miniaturization limits. The rotational speed of the micro-pin is an important factor for high aspect ratio of the micro-pin forming. Finally, the forming of a micro-pin of 8 μm diameter and 250 μm length is performed considering the rotation of the micro-pin. [ABSTRACT FROM AUTHOR]

High aspect ratio micro-grooves are critical structures in the micro-electromechanical system. However, problems like rapid tool wear, low processing efficiency, and inferior machined quality in micro-milling of high aspect ratio micro-grooves by length–diameter ratio tools are particularly significant. In this work, a combined micro-milling method based on water-free alcohol as the cutting fluid and laser deburring is proposed to investigate the high aspect ratio micro-groove generation of oxygen-free high-conductivity copper TU1. Parametric experiments and high aspect ratio micro-groove experiments were conducted to investigate the surface quality, cutting forces, and tool wear. The water-free alcohol was employed to improve the tool life and machined surface quality. In the case of the oxygen-free high-conductivity copper TU1 material, a satisfactory high aspect ratio micro-groove (groove-width = 0.2 μm and aspect ratio = 2.5) with a nanoscale surface roughness (Ra = 68 nm) was obtained under the preferred machining conditions. Furthermore, the deburring process of the high aspect ratio micro-groove by the laser technology was conducted to achieve ideal machined quality of the top surfaces. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative numerical method for the design and optimization of high-aspect-ratio composite wings equipped with passive control systems, specifically, Folding WingTip (FWT) and Twist WingTip (TWT) devices. The aim is to enhance Gust Load Alleviation (GLA) performance in the baseline wing. Recent numerical studies have indicated that the inclusion of spring devices and wingtip modifications can offer additional benefits in alleviating gust loads during flight. The baseline wing is designed using a comprehensive multi-disciplinary optimization framework, taking into account aerostructural constraints and exploiting the anisotropic properties of composite materials. The proposed methodology integrates Finite Element (FE) software, an in-house Reduced Order Model (ROM) framework for nonlinear aeroelastic analyses, and Particle Swarm Optimization (PSO). This method, implemented in the Nonlinear Aeroelastic Simulation Software (NAS2) package, facilitated the streamlined design of composite wings with optimized aeroelastic and structural performance. The paper is divided into two main parts. Part 1 introduces a Multidisciplinary Design Optimization (MDO) approach for high-aspect-ratio composite wings, leading to the development of a baseline wing model. Part 2 evaluates the effectiveness of the FWT and TWT devices in alleviating gust loads on the baseline wing, with a focus on the Root Bending Moment (RBM) as a critical criterion for comparison. In wingtip modeling, geometrical nonlinearity is incorporated, and elastic trim is adjusted in each iteration to accommodate shape changes under load and aerodynamic panel movement is synchronized with structural adjustments. [ABSTRACT FROM AUTHOR]

Aluminium nitride (AlN) ceramic is a typically difficult-to-machine material used in electronic packaging. Laser and chemical milling enhanced micro milling (LCMEM), a high-quality and efficient processing method for AlN, is proposed in this study. Rough machining is completed by repeated alternating laser ablation and chemical removal; the final finish is achieved by micro milling (MM). To achieve precise laser and chemical milling parameters based on the target structure, a laser and chemical milling (LCM) prediction model is established and verified; this can be used to predict the morphology of the grooves after LCM. The change trend of the grooves after LCM with the laser parameters is investigated. It was found that LCMEM can improve the surface quality by 60 %, and an optimal finishing surface with a surface roughness Ra value of 54 nm can be obtained when the feed per tooth is 0.4 µm/z. Lastly, this study uses LCMEM to produce a high aspect ratio groove with aspect ratio of 2.5 and depth of 1250 µm. Compared with conventional MM, LCMEM reduces the allowance of MM by 71.95 %, improves the groove accuracy, and reduces tool wear. [ABSTRACT FROM AUTHOR]

A novel method for the deposition of thin films of dopant elements on the inner walls of a hole with a high aspect ratio aimed at doping germanium is here described. GeAl x and Sb were evaporated from a W filament inserted inside a hole 10 mm in diameter and 80 mm deep (aspect ratio 8:1). The filament was previously coated by sputtering with either GeAl x or Sb film. The filament heating process is fast enough to ensure very limited temperature increase on the inside walls of the hole as demonstrated by a heat balance calculation, thus preventing the introduction of contaminant species in the doped semiconductor. The filament was inserted in a purpose-built sample holder where planar substrates acted as the inner walls of the hole. The thickness distribution of the films evaporated on these substrates was characterized and correlated with the thickness distribution of the sputtered films deposited on the filament. In view of the final application of this process, i.e., doping of coaxial Ge-based gamma radiation detectors, GeAl x and Sb films were evaporated on Ge substrates and then subjected to pulsed laser melting to induce metal diffusion and doping of Ge surface. Measurements of the electrical activation of the laser melted samples pointed out the successful doping by both elements, i.e., p + doping for Al and n + doping for Sb. [ABSTRACT FROM AUTHOR]

Due to its advantages of good surface quality and not being affected by material hardness, electrochemical machining (ECM) is suitable for the machining of blisk, which is known for its hard-to-machine materials and complex shapes. However, because of the unstable processing and low machining quality, conventional linear feeding blisk ECM has difficulty in obtaining a complex structure. To settle this problem, the vibration-assisted ECM method is introduced to machine blisk channels in this paper. To analyze the influence of vibration on the process of ECM, a two-phase flow field model is established based on the RANS k-ε turbulence model, which is suitable for narrow flow field and high flow velocity. The model is coupled with the electric field, the flow field, and the temperature field to form a multi-physics field coupling model. In addition, dynamic simulation is carried out on account of the multi-physics field coupling model and comparative experiments are conducted using the self-developed ECM machine tool. While a shortcut appeared in the contrast experiment, machining with vibration-assisted channel ECM achieved fine machining stability and surface quality. The workpiece obtained by vibration-assisted channel ECM has three narrow and straight channels, with a width of less than 3 mm, an aspect ratio of more than 8, and an average surface roughness Ra in the hub of 0.327 μm. Compared with experimental data, the maximum relative errors of simulation are only 1.05% in channel width and 8.11% in machining current, which indicates that the multi-physics field coupling model is close to machining reality.

High-aspect ratio silicon (Si) nanostructures are important for many applications. Metal-assisted chemical etching (MACE) is a wet-chemical method used for the fabrication of nanostructured Si. Two main challenges exist with etching Si structures in the nanometer range with MACE: keeping mechanical stability at high aspect ratios and maintaining a vertical etching profile. In this work, we investigated the etching behavior of two zone plate catalyst designs in a systematic manner at four different MACE conditions as a function of mechanical stability and etching verticality. The zone plate catalyst designs served as models for Si nanostructures over a wide range of feature sizes ranging from 850 nm to 30 nm at 1:1 line-to-space ratio. The first design was a grid-like, interconnected catalyst (brick wall) and the second design was a hybrid catalyst that was partly isolated, partly interconnected (fishbone). Results showed that the brick wall design was mechanically stable up to an aspect ratio of 30:1 with vertical Si structures at most investigated conditions. The fishbone design showed higher mechanical stability thanks to the Si backbone in the design, but on the other hand required careful control of the reaction kinetics for etching verticality. The influence of MACE reaction kinetics was identified by lowering the oxidant concentration, lowering the processing temperature and by isopropanol addition. We report an optimized MACE condition to achieve an aspect ratio of at least 100:1 at room temperature processing by incorporating isopropanol in the etching solution.