V-groove Structure Research Articles

Efficient Fog-Harvesting Origami Fan.

Fog harvesting represents a promising strategy to address the global freshwater shortage. To enhance the water collection efficiency, diverse geometric structures that can effectively drive water droplet movement are essential. Inspired by the Livistona chinensis leaf, which naturally facilitates directional droplet motion through its unique gradually varying V-groove structure, we have developed a novel origami fan structure for fog harvesting through theoretical analysis. A key feature is that we can modulate the speed of droplet transport by adjusting the opening angle of the V-shaped grooves positioned at the outer circumference. Interestingly, the water collection efficiency exhibits a linear correlation with the opening angle. The highest efficiency of the origami fan can reach 5.75 times that of the control group calculated by the projected area and 3.76 times that of the control group calculated by the real area, showcasing its significant potential for enhancing water collection from fog. The simulations demonstrate that the hollow structure enhances the condensation rate of droplets, the geometric gradient of the gradual-variation V-groove drives the condensed droplets to move rapidly on the surface, and the Janus membrane permits the aggregated droplets to transit to the fan's rear side. The synergistic action of these three components ensures a clean surface for the subsequent water-collecting cycle, contributing to the high fog-harvesting efficiency. Given its simple fabrication and superior water transfer efficiency, the origami fan holds substantial promise for widespread application in the field of droplet manipulation.

Robust All-Day Frostphobic Surfaces.

The application of solar-thermal surfaces for antifrosting and defrosting has emerged as a passive and environmentally friendly approach to mitigate the negative consequences of frost formation, such as structural damage and reduced heat transfer efficiency. However, achieving robust all-day frostphobicity solely through interfacial modification and solar-thermal effects is challenging in practical applications: The thick frost that accumulates at night strongly scatters solar radiation, rendering the solar-thermal coatings ineffective during the daytime. Additionally, these nanostructured coatings are susceptible to wear and tear when exposed to the outdoors for extended periods of time. To address these challenges, we present an innovative frostphobic surface that incorporates V-grooved structures with superhydrophobic solar-thermal layers (VSSs). The out-of-plane gradient structures facilitate spatially regulated vapor diffusion, an enhanced photothermal effect, and robust water repellency. These features not only prevent frost from covering the entire surface overnight, enabling effective solar-thermal defrosting during the daytime, but also protect the surface from deterioration. The combined merits ensure robust all-day frostphobicity and exceptional durability, making the VSS surface promising for practical applications and extending the lifespan in extreme environments.

Anisotropic V-Groove/Wrinkle Hierarchical Arrays for Multidirectional Strain Sensors with High Sensitivity and Exceptional Selectivity.

Flexible strain sensors have been continuously optimized and widely used in various fields such as health monitoring, motion detection, and human-machine interfaces. There is a higher demand for sensors that can sensitively identify both the strain amplitude and direction in real-time to adapt to complex human movements. This study proposes a flexible strain sensor construction strategy based on V-groove/wrinkle hierarchical structures via a facile and scalable prestretching approach. A gold film is sputtered on a V-groove structure soft substrate under a vertical biaxial prestrain. When the strain is released, a variety of wondrous V-groove/wrinkle hierarchical structures are formed. The microstructure and the properties of the resulting sensor can be controlled by adjusting the prestrain, which has obvious anisotropic response characteristics and exhibits high sensitivity (maximum gauge factor up to 20,727.46) and a wide sensing range (up to 51%). In addition, the resulting multidirectional sensor based on double-sided microstructures has an exceptional directional selectivity of 67.39, at an advanced level among all stretchable multidirectional strain sensors reported so far. The sensor can detect human motion signals and distinguish motion patterns, proving its great potential in the field of human motion detection and laying a foundation for high-performance wearable devices.

Numerical Simulation Study on the Effect of Resistance Microstructure on Blood Flow Resistance

The use of bionic drag-reducing microstructures in artificial blood vessels can effectively reduce their resistance to blood flow. The characteristics of the blood vessel are analysed and simplified, and the resistance reduction effects of three bionic microstructure models, namely V-shaped, rectangular and semi-circular, are compared and analysed by numerical simulations, and the resistance reduction effects of the three groove structures in the tubular model are verified. The results show that the V-shaped groove structure occupies a smaller volume compared to the rectangular and semi-circular structures of the same size, has a significant drag reduction effect, is highly achievable and stable, and is the best choice as a drag reduction microstructure for artificial blood vessels. In addition, the wall shear stresses of the V-groove structure were further analysed to verify the shear effect of this microstructure in artificial blood vessels and to reveal the shear mechanism of the V-groove microstructure.

Effects of shark bionic V-groove structures and nanofluids on thermal management of electronic components

The miniaturization of electronic components makes it difficult for the traditional radiator working medium and radiator structure to meet the requirements. The combination of nanofluids and bionic micro-surfaces is beneficial to solve the heat dissipation problem of electronic components. Based on the bionics, a CPU enhanced heat dissipation system was designed and built based on the V-shaped groove of shark scales and Fe3O4-H2O nanofluids with high heat transfer coefficient. The effects of V-groove angle, height and nanofluids concentration on the comprehensive evaluation index of the radiator were studied. The groove angle S= 1 mm (54°) and height H= 2 mm have the best heat transfer characteristics and comprehensive evaluation index, which can reduce the surface temperature by 2.16 °C and 3.71 °C at most, and increase the heat transfer efficiency by 17.58% and 28.96%. There is a critical concentration (0.3%) that makes the system cooling effect best. The results of the study have a certain reference value for the structural design of heat sink

Research on the directional characteristics of wind noise emitted by bionic rods

In this paper, the directional characteristics of wind noise emitted by different bionic rods were studied based on a hybrid computational aeroacoustics method. The noise reduction mechanism of surface grooves, pits, and bumps was analyzed, respectively. The basic principle of noise reduction is to reduce the influence of the vortex shedding on the rod by changing the shape of the rod or passive control technology to reduce the dipole sound source. The unsmooth transverse surface will increase the loss of flow on the leading edge of the rod and reduce the vertical effect of vortex shedding on the rod. The convex leading edge of the rod can help to transfer the vertical noise from low frequency to high frequency and reduce the vertical effect of wake vortex shedding to reduce the peak sound pressure level. The cost of those was the increase in the aerodynamic drag and the increase in noise in the flow direction (the increase in the amplitude of drag fluctuation). In particular, the longitudinal v-groove structure on the surface of the elliptical rod can reduce the circumferential aerodynamic noise while keeping the aerodynamic drag coefficient unchanged.

Epitaxial GaSb films directly grown on on-axis Si(001) with low defect density by MBE

In recent years, GaSb-on-Si direct heteroepitaxy has been highly desirable to extend the operating wavelength range into mid-infrared and high-mobility applications, such as free-space communications, gas sensing, and hyperspectral imaging. High-quality GaSb films on Si remain challenging due to the high density of defects generated during the growth. For this purpose, epitaxial GaSb films were grown by molecular beam epitaxy on on-axis Si(001). Due to the large lattice mismatch (12.2%) between GaSb and Si, here, we proposed a radical design and growth strategy with the primary objective of achieving the annihilation of antiphase boundaries (APBs) and the reduction of threading dislocation density (TDD). Benefitting from a V-grooved Si hollow structure, we demonstrated the growth of emerging-APB-free GaSb film on Si(001) with low mosaicity. Moreover, by introducing InGaSb/GaSb dislocation filtering layers, the atomically flat surface root mean square roughness is improved to 0.34 (on Si) and 0.14 nm (on GaAs/Si). Moreover, the corresponding TDD can be reduced to 3.5 × 107 and 2 × 107 cm−2, respectively, one order of magnitude lower than the minimum value found in the literature. These reported results are a powerful lever to improve the overall quality of epitaxial Si-based antimonide, which is of high interest for various devices and critical applications, such as laser diodes, photo-detectors, and solar cells.

High-Sensitivity and Direction Recognizable SPR Microdisplacement Sensor Based on Fiber V-Groove

It is difficult to further improve the sensitivity of fiber surface plasmon resonance (SPR) microdisplacement sensor, and it is also unable to identify the direction of microdisplacement. In this article, a high-sensitivity direction recognizable SPR microdisplacement sensor based on fiber V-groove was designed and fabricated. By CO2 laser, the V-groove was fabricated on the graded index multimode fiber, and the SPR effect was produced on the inclined plane of the sensing area by the microdisplacement beam. By controlling the flare angle of the fabricated V-groove, the SPR incident angle was adjusted, so as to effectively increase the microdisplacement sensing sensitivity. The simulation and test results indicate that the sensor with the V-groove flare angle of 88° has the wavelength average sensitivity of 5.26 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and the intensity average sensitivity of 0.032 a.u./ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . In order to solve the problem of microdisplacement direction identification, a dual V-groove structure microdisplacement sensor was designed and fabricated. When the microdisplacement direction is different, the transmission beam contacts different V-grooves, and the microdisplacement direction can be identified by the moving direction of the resonance valley. The proposed sensor greatly improves the sensitivity of optical fiber SPR microdisplacement detection and can identify the direction of microdisplacement, which has the potential application value in the field of precision displacement and positioning.

Simultaneous measurement of refractive index and temperature based on a side-polish and V-groove plastic optical fiber SPR sensor.

A simple plastic optical fiber (POF) based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and temperature. The sensor consists of a series of V-grooves along the POF and a side-polish structure at the other side of the fiber. The V-groove structure can alter the SPR excitation angle and act as a mode filter, effectively enhancing the SPR effect and narrowing the SPR wavelength width. After coating a layer of thermosensitive material-polydimethylsiloxane (PDMS) film on half part of the fiber probe, a dual-parameter sensor probe is obtained for RI and temperature measurement. Experimental results show the RI sensitivity of the prepared probe can reach 1546 nm/RIU in the RI range of 1.335-1.37 RIU and the temperature sensitivity is -0.83 nm/°C in the temperature range of 20-80°C. The sensor is simple in structure and low cost, and has potential applications in the biochemical sensing fields.

Review of phase change heat transfer enhancement by metal foam

• Enhancement characteristics of metal foam on solid-liquid phase change heat transfer and liquid-gas phase change heat transfer are reviewed. • The mechanism of metal foam enhancing phase change heat transfer and the factors affecting the phase change heat transfer process are comprehensively discussed. • Existing methods for optimizing phase change heat transfer performance within metal foam are classified and evaluated. • The practical applications of metal foam enhanced phase change heat transfer in recent years are summarized and compared. • This review will lead to a better understanding on the designing and applying of efficient metal foam-phase change heat transfer systems. Metal foam is a novel multifunctional material with high porosity, high surface density, and excellent heat transfer performance. Embedding metal foams into phase change heat transfer systems can be used to improve the comprehensive heat transfer performance, which is receiving increasing attention in the field of thermal management. This paper focuses on the lasted advances in solid-liquid phase change heat transfer and liquid-gas phase change heat transfer within metal foams, and specifically analyzes the influencing factors on phase change heat transfer performance as well as the mechanism of metal foam effects on phase change heat transfer. Different optimized techniques for improving phase change heat transfer within metal foams and the current state of metal foam engineering applications for improving phase change heat transfer are reviewed and discussed. It is concluded that the addition of metal foam can significantly enhance the heat transfer performance of solid-liquid phase change systems and liquid-gas phase change systems, but it is accompanied by an inhibitory effect on natural convection, an obstructive effect on bubble overflow and an elevated effect on pressure drop. The application of gradient porous structure, metal foam fins, V-groove structure or changing the surface wettability of metal foam is a feasible way to alleviate the above problems. Meanwhile, it is pointed out that the heat transfer performance of phase change within metal foam is influenced by the interaction of various factors, and some key issues regarding the influence mechanism of PCM-device orientation, pore distribution, surface wettability, and structural properties on heat transfer performance still need to be studied to develop more efficient and compact heat sinks.

Fiber cladding SPR sensor based on V-groove structure

The difficulty with fiber cladding Surface Plasmon Resonance (SPR) sensors lies in coupling the core mode to the cladding mode without removing the cladding. This paper hereby endeavors to demonstrate a fiber cladding SPR sensor based on V-grooves structure by using a CO2 laser. V-grooves are engraved on single-mode fiber, step-index multimode fiber, and graded-index multimode fiber. When the transmitted light reaches the V-grooves structure, the higher-order cladding mode is excited, and a metal film is coated on the 2 cm cladding area after the V-grooves to form fiber cladding SPR sensors. This paper investigates the refractive index and bending sensing of V-groove cladding SPR sensors of single-mode, graded-index multimode, and step-index multimode fibers. The experimental results show that: the refractive index sensitivity of three kinds of sensors is 2811.34 nm/RIU, 1862.33 nm/RIU, and 1418.85 nm/RIU, respectively, and the curvature sensitivity of three types of sensors is 0.42 nm/m−1, 1.03 nm/m−1, and −6.59 nm/m−1, respectively. The proposed sensors in this paper are easy to manufacture, demonstrate quality of high sensitivity, and can be applied extensively.

High sensitivity fiber cladding SPR strain sensor based on V-groove structure.

How to couple the light in the fiber core to the cladding is an urgent issue that need to be done for the fabrication of the fiber-cladding SPR sensor, and there is no report about the fiber SPR strain sensor. Hereby, we propose and demonstrate a high sensitivity fiber cladding SPR strain sensor based on V-groove structure. By CO2 laser, the V-groove is fabricated on the single-mode fiber, and the light in the fiber core is effectively coupled to the cladding. The cladding 2cm behind the V-groove is coated with sensing gold film, and a multimode fiber is spliced with the sensing probe to construct the novel fiber cladding SPR sensor. On the basis of the investigation of the effects of different V-groove depth, number and period on the performance of fiber SPR refractive index sensor, a high sensitivity strain SPR sensor is designed and fabricated by employing the characteristic that the V-groove will deform with strain. The testing results indicate that the average refractive index sensitivity of the sensor is 2896.4nm/RIU, and the strain wavelength sensitivity is 25.92pm/µε which is much higher than that of the fiber interference and grating strain sensors, and the strain light intensity sensitivity is -4.4×10-4 a.u./µε. The proposed fiber cladding SPR strain sensor has the advantages of simple structure and convenient manufacture, and can be used for working in a narrow space.

Analytical analysis and experimental validation of optical power estimation in V-grooved polymer optical fibers

In this study, analytical and experimental research of V-grooved polymer optical fibers (POFs)’ optical power loss characteristics is carried out. A simple mathematical model that can determine the optical output power and loss in the V-grooved structure depending on the groove angle and depth has been developed using geometric optic approaches. This model is used to analyze the effects of groove parameters and fiber diameter on optical output power in detail. Then, a low-cost and efficient groove fabrication process is performed, and V-grooves with 45⁰ half-angle and 200 µm groove depth are created on POFs with diameters of 1 mm, 2 mm, and 3 mm to be used in the experiment. When the effect of groove numbers ranging from 5 to 25 on the optical output power is examined, the behavior obtained from the experimental results is compatible with the analytical results. Output power can be estimated with greater than 95% accuracy for V-groove POF structures, optimizing the ratio of groove depth to fiber core radius for a specific groove angle.

Experimental study on the wake characteristics of the circular cylinder with the V-groove surface

In order to understand the wake characteristics for the circular cylinder with the V-groove surface, the Particle Image Velocimetry (PIV) and Proper Orthogonal Decomposition (POD) technology are used to measure and analyze the flow field velocity and the flow characteristic of the wake flow of the circular cylinder with the V-groove surface. This study focuses on the length of the velocity gradient, the Reynolds stress, the turbulent kinetic energy, the vortex shedding process, and the velocity fluctuating characteristics of flow field with POD technology. Compared with the smooth cylinder, the velocity gradient of the circular cylinder with the V-groove surface are larger. The peak values of Reynolds stress of the circular cylinders with the V-groove surface (the peak values are 0.33, 0.28 and 0.24) is lower than that of the smooth cylinder (0.39), and the peak values of turbulent kinetic energy are also lower. The recirculation region of the circular cylinders with the V-groove surface is larger, the length of the recirculation region are increased by 5.9%, 13.0% and 16.1% respectively, and it implies the suppression of vortex by the V-groove structure. Otherwise, the correlation of POD mode coefficients is disturbed for the circular cylinders with the V-groove surface, further proving that the effect of V-groove structure on vortex shedding.

Design and Fabrication of Double-Layer Crossed Si Microchannel Structure

A four-step etching method is used to prepare the double-layer cross Si microchannel structure. In the first etching step, a <100> V-groove structure is etched on (100) silicon, and the top channel is formed after thermal oxidation with the depth of the channel and the slope of its sidewall being modulated by the etching time. The second etching step is to form a sinking substrate, and then the third step is to etch the bottom channel at 90° (<100> direction) and 45° (<110> direction) with the top channel, respectively. Hence, the bottom channel on the sink substrate is half-buried into the top channel. Undercut characteristic of 25% TMAH is used to perform the fourth step, etching through the overlapping part of the two layers of channels to form a double-layer microchannel structure. Different from the traditional single-layer microchannels, the double-layer crossed microchannels are prepared by the four-step etching method intersect in space but are not connected, which has structural advantages. Finally, when the angle between the top and bottom is 90°, the root cutting time at the intersection is up to 6 h, making the width of the bottom channel 4–5 times that of the top channel. When the angle between the top and bottom is 45°, the root cutting time at the intersection is only 4 h, and due to the corrosion along (111), the corrosion speed of the sidewall is very slow and the consistency of the width of the upper and lower channels is better than 90° after the end. Compared with the same-plane cross channel structure, the semiburied microchannel structure avoids the V-shaped path at the intersection, and the fluid can pass through the bottom channel in a straight line and cross with the top channel without overlapping, which has a structural advantage. If applied to microfluidic technology, high-efficiency delivery of two substances can be carried out independently in the same area; if applied to microchannel heat dissipation technology, the heat conduction area of the fluid can be doubled under the same heat dissipation area, thereby increasing the heat dissipation efficiency.

Study on the micro-EDM processing characteristics of Ti-6Al-4V alloy with different electrode materials

Ti-6Al-4V alloy has been widely used in industrial fields. Electrical discharge machining (EDM) is a commonly used technology for machining Ti-6Al-4V alloy. During EDM of Ti-6Al-4V alloy, the thermal and physical characteristics of tool electrode have an important influence on processing characteristics. In order to study the influence of different electrode materials on the processing characteristics of Ti-6Al-4V alloy, brass electrode, copper tungsten electrode, and tungsten electrode were used to perform EDM of Ti-6Al-4V alloy. In this paper, electrodes with V-groove array structures were designed to carry out powder mixed electrical discharge machining (PMEDM) of Ti-6Al-4V alloy, and the machining results were evaluated based on four indicators: microstructures morphology, tool electrode wear (TEW), material removal rate (MRR), and recast layer thickness (RLT). The processing results show that copper tungsten electrode is recommended to machine Ti-6Al-4V alloy because it has the highest reproduction rate (75.2%), a smaller TEW (139 μm), the highest MRR (255.39 mm3/min), and a thinner RLT (3.35 μm).

Proliferation of the Light and Gas Interaction with GaN Nanorods Grown on a V-Grooved Si(111) Substrate for UV Photodetector and NO2 Gas Sensor Applications.

Although excellent milestones of III-nitrides in optoelectronic devices have been achieved, the focus on the optimization of their geometrical structure for multiple applications is very rare. To address this issue, we exclusively designed a prototype device to enhance the photoconversion efficiency and gas interaction capabilities of GaN nanorods (NRs) grown on a V-grooved Si(100) substrate with Si(111) facets for photodetector and gas sensor applications. Photoluminescence studies have demonstrated an increased surface-to-volume ratio and light trapping for GaN NRs grown on V-grooved Si(111). GaN NRs on V-grooved Si(100) with Si(111) facets exhibited high photodetection performance in terms of photoresponsivity (217 mA/cm2), detectivity (3 × 1013 Jones), and external quantum efficiency (2.73 × 105%) compared to GaN NRs grown on plain Si(111). Owing to the robust interconnection between NRs and a high surface-to-volume ratio, the GaN NRs grown on V-grooved Si(100) with Si(111) facets probed for NO2 detection with the assistance of photonic energy. The photo-assisted sensing makes it possible to detect NO2 gas at the ppb level at room temperature, resulting in significant power reduction. The device showed high selectivity to NO2 against other target gases, such as NO, H2S, H2, NH3, and CO. The device showed excellent long-term stability at room temperature; the humidity effect on the device performance was also examined. The excellent device performance was due to the following: (i) benefited from the V-grooved Si structure, GaN NRs significantly trapped the incident light, which promoted high photocurrent conversion efficiency and (ii) GaN NRs grown on V-grooved Si(100) with Si(111) facets increased the surface-to-volume ratio and thus improved the gas interaction with a better diffusion ratio and high light trapping, which resulted in increased response/recovery times. These results represent an important forward step in prototype devices for multiple applications in materials research.

Regulation of surface texturization through copper-assisted chemical etching for silicon solar cells

Various structures were fabricated through a copper-assisted chemical etching method for texturization of monocrystalline silicon solar cells, including nanopore, inverted pyramid, V-groove, upright pyramid and hybrid structures. Structural characteristics, etching processes and anti-reflection abilities of the textured structures were systematically analyzed. Brand new texturization results were observed in this research. A possibility that the copper-catalyzed textured structures can be terminated with silicon {1 1 0} crystalline planes is proposed, and the evidence is provided. Furthermore, the transformation of the textured structures was studied, and the agglomerated behavior of the copper nanoparticles deposited on the silicon surface during etching was demonstrated to be a prominent source for the formation of various textured structures. The influences of etchant components and initial silicon surface states on the agglomeration were also studied. Consequently, the surface morphology and anti-reflection property of the textured silicon wafers can be well regulated by controlling the agglomeration of deposited copper nanoparticles in the etching process. A minimum average reflectance of 6.19% in the wavelength range of 300–1000 nm was obtained, which indicates great potentials of this copper-assisted texturization process for the photovoltaic application. In addition, according to the experimental results and analyses, a practical guidance for texturization of silicon solar cells is provided.

Broadband omnidirectional anti-reflection property of V-groove textured silicon

Omnidirectional silicon solar cells with an outstanding anti-reflection property over a broad angular range of incident light show great potential for application in the photovoltaic industry. Many studies have been carried out to investigate the omnidirectional anti-reflection properties of different silicon textured structures. However, the omnidirectional anti-reflection property of the V-groove textured silicon has not been reported, even though the V-groove structure is also one of most frequently used anti-reflective structures for silicon solar cells. In this research, ray tracing simulation is utilized to analyze and validate the omnidirectionality of a micron-sized silicon V-groove structure. In addition, in consideration of the previous complicated fabrication methods of V-groove structure, a brand new fabrication method for the V-groove texturization onto diamond-wire-sawn monocrystalline silicon wafers through copper-assisted chemical etching is presented. Consistent with the simulations, the experimental results similarly indicate that the V-groove textured silicon not only possesses light absorption ability that is comparable to the common random pyramid structure but also exhibits an unexpected excellent omnidirectional anti-reflection property over a wide range of incident angles, demonstrating the great potential for the fabrication of omnidirectional silicon solar cells.

Investigation of a plastic optical fiber imprinted with V-groove structure for displacement sensing

A low cost and easily fabricated plastic optical fiber (POF) displacement sensor is presented. The sensor is based on the macrobending POF with a V-groove structure fabricated by a simple die-press-print method, which is easy to implement and effectively reduces the complexity of the fabrication process. The intensity modulation method is adopted for displacement sensing, which lowers the sensor system’s cost and complexity. Experiments are carried out to investigate the influence of the structural parameters on the displacement sensing performance and the proposed POF probe is optimized by changing the structure parameters. Results showed that when the V-groove structure depth is 200 μm, the length is 22 mm, the angle is 60 deg, the pitch is 2 mm, and the macrobending radius of the POF probe is 15 mm, the highest sensitivity could reach to 3.19 × 10 − 2 / mm with the measurement range of 18 mm.