Gradient Grooves Research Articles

Bubble-Guidance Breaking Gas Shield for Highly Efficient Overall Water Splitting.

Overall water splitting is a promising technology for sustainable hydrogen production, but the primary challenge is removing bubbles from the electrode surface quickly to increase hydrogen production. Inspired by the directional fluid transport properties of natural biological surfaces like Nepenthes peristome and Morpho butterfly's wings, here a strategy is demonstrated to achieve highly efficient overall water splitting by a bubble-guidance electrode, that is, an anisotropic groove-micro/nanostructured porous electrode (GMPE). Gradient groove micro/nanostructures on the GMPE serve as high-speed bubble transmission channels and exhibit superior bubble-guidance capabilities. The synergistic effect of the asymmetric Laplace pressure generated between microscale porous structure and groove patterns and the buoyancy along the groove patterns pushes the produced bubbles directionally to spread, transport, and detach from the electrode surface in time. Moreover, the low adhesive nanosheet arrays are beneficial to reduce bubble size and increase bubble release frequency, which cooperatively improve mass transfer with the microscale structure. Notably, GMPE outperforms planar-micro/nanostructured porous electrode (PMPE) in hydrogen/oxygen evolution reactions, with GMPE||GMPE showing better water splitting performance than commercially available RuO2||20 wt.% Pt/C. This work improves electrodes for better mass transfer and kinetics in electrochemical reactions at solid-liquid-gas interfaces, offering insight for designing and preparing gas-involved photoelectrochemical electrodes.

Pool boiling heat transfer enhancement induced by capillary wicking from radial gradient structures: A lattice boltzmann study

With the aid of a three-dimensional lattice Boltzmann model built in the lab, the boiling state on the surface with gradient groove structure is investigated. The emphasize is placed on the impact brought by the wicking capability from the gradient structure on boiling performance. Besides the roles of distribution, number, width and depth of the grooves in the boiling process discussed in detail, the effects of wall superheat and wettability on boiling heat transfer are also explored. The results show that the wicking force generated by the gradient grooves can improve the boiling performance to an extent. Adjusting the geometry of grooves can enhance heat flux by up to 27.46% compared to a flat competitor. However, there exists a limit for the gradient defined in this study. Pursuing larger gradient values can extend the pit region at the center of surface. Upon TPCL being trapped within the pit region, it causes a negative effect on the boiling performance. The wicking capability has a positive relationship with surface wettability at a given groove number and size. In regards to the parametric effects of groove, the heat flux first increases but then declines with increasing the groove width at a fixed Jacob number. Despite the enhanced boiling performance with increasing the groove number and depth, the enhancement has an upper limit. But, the groove distribution has a minor effect on the boiling performance if TPCL is outside the pit region. This study provides quantitative evidence for the fact that wicking can promote boiling from the numerical view.

Long-Distance Continuous Self-Transport of a Droplet by Merging Droplets on a Graphene-Covered Multibranch Gradient Groove Surface.

Although the self-transport of liquid droplets by a gradient-textured substrate can break away from the energy input, the long distance and even continuous spontaneous motion of droplets will be limited by the length in the surface-gradient direction. This article introduces a novel design with a monolayer graphene-covered multibranch gradient groove surface (GMGGS). The design aims to achieve long-distance, continuous self-transport of a mercury (Hg) droplet by merging with other mercury droplets, and the process is carried out using molecular dynamics (MD) simulation. This method achieves the merging of mercury droplets through the structure of multibranch gradient grooves, and we have observed that the merged mercury droplet can be reaccelerated in the gradient groove. The results demonstrate that droplet merging allows for control over the surface morphology variations of mercury droplets within the gradient groove. This creates a forward pressure difference, which leads to reacceleration of the mercury droplets. In light of this mechanism, the trunk droplet can achieve long-distance continuous self-transport on the GMGGS by continuously merging with branch droplets. These findings will broaden our comprehension of droplet merging and self-transport behavior, offering corresponding theoretical support for the long-distance continuous self-transport of droplets.

Localized manipulation of spoof surface acoustic skyrmions with deep-subwavelength gradient structures

Skyrmions with stable vector field configurations have produced various derivatives with various topological textures, such as the Néel type, Bloch type, anti-type, and higher-order Néel type. Here, we theoretically and experimentally demonstrate that the vector field configuration of Néel-type skyrmionic modes can be locally manipulated using gradient grooves in a deep-subwavelength three-dimensional multilayer cylindrical structure. We experimentally observe that the skyrmionic modes can be contracted or expanded to manipulate the distribution of the velocity vectors by tuning the groove depth gradient along the structural radius, which is robust against structural deformations and defects. This type of controllable acoustic skyrmion provides new dimensions for advanced sound information processing, transportation, and data storage in compact structures.

Dropwise condensation heat transfer on vertical superhydrophobic surfaces with gradient microgrooves in humid air

Self-propelled droplet removal contributes vitally to the enhancement of condensation heat transfer performance. Here, inspired by the prickle tip of the cactus, we design and fabricate a gradient groove superhydrophobic surface. A visualization system in humid air has been established to investigate the droplet dynamic behaviors and heat transfer performance on the vertical gradient groove superhydrophobic surface. The dropwise condensation is also analyzed and compared to that on the plane and square groove superhydrophobic surfaces. The results indicate that the gradient groove superhydrophobic surface has the highest condensation heat flux among the three mentioned superhydrophobic surfaces with the increasing subcooling. The gradient grooves facilitate the condensed droplets departure under the synergistic effect of the dual-Laplace induced jumping and gravity-driven sliding removal even at higher subcooling. The dual-Laplace induced jumping possesses greater driving force, conducting the smaller droplet departure diameter and smaller angle between initial velocity and surface wall, which effectively improves the surface refreshment and further strengthens the surface heat transfer.

Acoustic metacage with arbitrary shape for broadband and ventilated sound insulation

Here, we experimentally demonstrate a novel strategy for broadband acoustic insulation of an arbitrary shaped region by arranging a localized rainbow trapped metastructure at a deep subwavelength scale. The metastructure constitutes radial gradient grooves along the azimuth direction and can help realize localized acoustic rainbow trapping. We show that such metastructures can be used to construct a region with arbitrary geometry for sound insulation and keep high ventilation simultaneously, thus, denoted as an acoustic metacage. Based on the numerical simulations and experimental observations, the results indicate that the broadband soundproof effect of the metacage is robust against the location of the acoustic source. Finally, we discuss the relationship between the soundproof efficiency and the ventilated ratio of the metacage and find that the ventilation window can still achieve a rate of 55% when the transmittance loss is above 10 dB. The proposed acoustic metacage could open up an avenue for realizing broadband sound insulation with high ventilation and an arbitrary shaped area.

High-velocity impact response of cylindrical tubes with linear gradient grooves: A comparative study

Grooved tubes benefit from optimized energy absorption characteristics compared to regular tubes. This paper investigated the crashworthiness characteristics of cylindrical tubes with various types of grooves under high-speed impact loads. Furthermore, the dynamic load response of tubes with external grooves having linear thickness distribution was studied experimentally and numerically for the first time. To assess the performance of gradient grooved tubes (GGTs), the crashworthiness of typical cylindrical specimens and tubes having internal or external grooves with uniform thickness distributions was compared. The results showed that the dynamic crush mode of GGTs was axisymmetric, progressive, and sequential. Furthermore, the mean crushing force (MCF) in GGT tubes was considerably less compared to other tubes (e.g., 89% difference between GGT and non-gradient tube). Moreover, the initial peak forces of all types of tubes having the same number of grooved sections were almost in the same range. However, the crushing force efficiency of GGTs was remarkably lower than other tubes due to their non-uniform load response. The numerical results showed that by increasing the number of grooves in GGTs, peak force, energy efficiency, and axial shortening decreased, but mean crushing and overall crushing forces increased. Altogether, the highest energy efficiency belonged to the GGT specimens, in which 17%, 4.2%, and 96% increases were observed compared to external and internal groove tubes and typical cylindrical tubes, respectively. Also, the energy efficiency increased with the number of grooves.

Investigations for vibration and friction torque behaviors of thrust ball bearing with self-driven textured guiding surface

In order to improve the starved lubrication condition of rolling bearings, three kinds of textures, namely dimple, groove texture, and gradient groove texture, were developed on the guiding surface of thrust ball bearings in this study. The results show that gradient groove texture has the one-way self-driving function of liquid droplets. The root mean square (RMS) value of vibration acceleration of gradient groove textured bearing (GGB) decreased by 49.1% and the kurtosis decreased by 24.6% compared with non-textured bearing (NB) due to the directional spreading effect of gradient groove textures on oil. The frequency domain analysis showed that the textures mainly suppressed the medium and high-frequency energy of bearing vibration, and the GGB was reduced the most with 65.3% and 48%, respectively. In addition, whether the grease is sufficiently sheared has a large impact on the oil guiding effect, and the friction torque of GGB could decrease by 10.5% compared with NB in the sufficiently sheared condition. Therefore, the gradient groove texture with oil self-driven effect on the guiding surface of rolling bearing can effectively improve the lubrication condition of the bearing and thus reduce the bearing vibration and friction torque, which has a promising application prospect.

T-shaped double-strip spoof surface plasmon polariton transmission lines and application to microwave resonators

A microwave double-strip spoof surface plasmon polariton (DS SSPP) is proposed for high-speed interconnects and high-performance microwave circuits. Based on the dispersion analysis, a T-shaped double-strip structure is designed to provide strong surface- and slow-wave properties from very low to very high frequencies (~ 40 GHz). It allows the tight field confinement and greatly reduces the electromagnetic wave leakage. It exhibits broadband performance with reduced ripples in the insertion loss. It also shows more constant group delay and impedance than counterpart single-strip SSPP. The compact coaxial-to-microstrip-to-DS SSPP transition are designed using gradient grooves. The measurement shows that the DS SSPP lines can exhibit the lower coupling and lower insertion loss than the microstrip lines, so that the former is well-suited for the densely packed high-speed interconnects. The designed DS SSPP is utilized for high quality (Q)-factor microwave ring resonator. The measured unloaded Q-factor is 107.9 at the resonant frequency of 8.7 GHz, which is 1.3 times higher than the microstrip ring resonator. It is found to be caused by the reduction of the radiation loss, according to the loss analysis. The size is also reduced due to the short wavelength, occupying 56.8% of that of the microstrip ring resonator. Therefore, the proposed T-shaped DS SSPP can be also applied for high-performance miniaturized microwave circuits.

Underwater Fast Bubble Generating on Pitaya Thorn and Enhanced Biomimetic Gas Collection

AbstractUnderwater bubble is vital to various applications and many technologies are applied for realizing efficient interfacial bubble generating. Here, the unique underwater bubble generating by the thorn of pitaya is reported. Extensive bubbles are generated underwater within few seconds on the thorn surface. Microbumps and dual‐scale ribs grow on the thorn surface, constructing the unique dual‐scale groove configuration along the thorn surface. Microbumps equip groove with width gradient. The mechanism of how geometric configuration of groove and surface wettability affect the bubble generating is investigated. Bioinspired study shows that groove configuration can generate bubble within 2 ms by reassembling gas column within groove, which lowers the energy barrier of bubble generating and accelerated gas molecular diffusion toward bubble. Dual‐scale groove is beneficial for strengthening surface hydrophobicity and is favorable for reassembling. Besides, width gradient induces the discrepancy of interface curvature along the groove and further accelerates the bubble generating. Accordingly, the dual‐scale gradient groove can speed up bubble generating by ≈800%. Especially, the biomimetic combinational groove can realize enhanced underwater gas collection. This research reveals a new mechanism of fast bubble generating which is of great potential for the applications based on underwater bubbles.

Leaf prickle hairs and longitudinal grooves help wheat plants capture air moisture as a water-smart strategy for a changing climate.

The leaf features like trichome density, gradient grooves, and leaf wettability determine the efficiency to capture air moisture for self-irrigation in the wheat plant. Plants in water-scarce environments evolved to capture air moisture for their water needs either directly or indirectly. Structural features like cones, hairs, and grooves assist water capture. The morphology of crops such as wheat can promote self-irrigation under drought. To examine this further, 34 wheat genotypes were characterized for leaf traits in near optimal conditions in the field using a randomized complete block design with 3 replications. An association was found between morphological and physiological traits and yield using simple correlation plots. A core set of nine genotypes was subsequently evaluated for moisture harvesting ability and leaf wettability. Results showed that variation among genotypes exists for fog harvesting ability attributed to structural leaf features. Physiological traits, especially photosynthesis and water use efficiency, were positively associated with yield, negatively correlated with soil moisture at booting, and positively correlated with soil moisture at anthesis. The genotypes with deep to medium leaf grooves and dense hairs on the edges and adaxial surfaces (genotypes 7 and 18) captured the most moisture. This was a function of higher water drop rolling efficiency resulting from lower contact angle hysteresis. These results can be exploited to develop more heat and drought-tolerant crops.

Multiband Omnidirectional Ventilated Acoustic Barriers Based on Localized Acoustic Rainbow Trapping

In this paper, we propose a subwavelength closed surface consisting of radial gradient grooves for achieving localized acoustic rainbow trapping. Similar to conventional rainbow trapping based on a plane structured surface, we demonstrate that rainbow trapping can also be realized by a closed surface in the deep-subwavelength scale. In particular, the trapped spatial positions on the closed surface can be freely tuned by changing the structural parameters. Based on the advantages of the multiband response and subwavelength dimension of this structure, we propose an acoustic barrier consisting of an array of closed surfaces to achieve multiband sound insulation and high ventilation simultaneously. Investigated results indicate that this kind of acoustic barrier possesses the features of subwavelength scale, and multiband and omnidirectional responses for blocking incident acoustic waves, yet has high ventilation. Finally, we discuss the influence of the channel width on the magnitude and bandwidth of the transmission loss spectrum. The experimental results agree with our theoretical prediction that the material losses can broaden the response bandwidth, and form broadband sound insulation. The acoustic barrier consisting of localized rainbow trapping structures may have many applications in infrastructure requiring air-permeability and sound-proofing.

Spoof Surface Plasmon Polaritons Developed From Coplanar Waveguides in Microwave Frequencies

In this article, a new spoof surface plasmon polariton (SSPP) waveguide developed from traditional coplanar waveguide (CPW) is proposed. The asymptotic frequency of the SSPP unit cell can be easily manipulated by changing the meander groove dimensions of the SSPPs. A simple and efficient mode-conversion structure with gradient groove lengths is designed on the CPW’s ground to match the momentum of CPW to the proposed SSPPs smoothly. The designed SSPP waveguide has a good low-pass filtering property with cut-off frequency at 10.4 GHz. On this basis, another improved SSPP waveguide based on conventional grounded CPW (GCPW) is constructed, where a defected ground structure (DGS) is employed on the bottom layer of the circuit. Compared with the above work, this design has a lower cut-off frequency (8.9 GHz) and stronger field confinement. In order to validate the propagation performance, both SSPP waveguides are fabricated and measured. The measurements show that the GCPW based SSPP waveguide can effectively reduce the cut-off frequency. Such results are of great significance to the miniaturizations of plasmonic devices in microwave regime.

An Ultra-Thin and Compact Band-Pass Filter Based on Spoof Surface Plasmon Polaritons

In this work, we report an ultra-thin and compact SSPPs-based waveguide band-pass filter with metals etched on the top surface of substrate, and the side and bottom surfaces of substrate also are covered with metals. The size of this filter is $1.07\lambda _{0}\times 0.32\lambda _{0}\times 0.02\lambda _{0}$ (where $\lambda _{0}$ is the wavelength at center frequency). This proposed filter can inherit the merits of rectangular waveguide and SSPPs structure, and its lower cut-off frequency can be tuned by the width of rectangular waveguide, while the upper cut-off frequency can be tuned by the length of complementary comb-like structure. Gradient groove depths are also used to form a smooth transition from rectangular waveguide to SSPPs structure, realizing a good momentum match. The dispersion curves and electric field distributions have been thoroughly investigated to reveal the SSPP-based waveguide filter mechanism. A prototype is fabricated and measured. Both simulations and measurements validate that the band-pass filter proposed in this work has high-efficiency and low-loss transmission properties.

A Novel Evaluation Method For Particle Deposition Measurement

Abstract Normal operation of gas turbines will be affected by deposition on turbine blades from particles mixed in fuels. This research shows that it is difficult to monitor the mass of the particles deposition on the wall surface in real time. With development of electronic technology, the antenna made of printed circuit board (PCB) has been widely used in many industrial fields. Microstrip antenna is first proposed for monitoring particles deposition to analyse the deposition law of the particles accumulated on the wall. The simulation software Computer Simulation Technology Microwave Studio (CST MWS) 2015 is used to conduct the optimization design of the PCB substrate antenna. It is found that the S11 of vivaldi antenna with arc gradient groove exhibits a monotonous increase with the increase of dielectric layer thickness, and this antenna is highly sensitive to the dielectric layer thickness. Moreover, a cold-state test is carried out by using atomized wax to simulate the deposition of pollutants. A relationship as a four number of times function is found between the capacitance and the deposited mass. These results provide an important reference for the mass detection of the particle deposition on the wall, and this method is suitable for other related engineering fields.

Unidirectional Self-Driving Liquid Droplet Transport on a Monolayer Graphene-Covered Textured Substrate.

Controllable directional transport of liquid droplets on a functionalized surface has been a challenge in the field of microfluidics because it does not require energy supply, and the physical mechanism of such self-driving transport exhibits extraordinary contribution to fundamental understanding of some biological processes and the design of microfluidic apparatus. In this paper, we report a novel design of a surface microstructure that can realize unidirectional self-driving liquid mercury (Hg) droplet transport on a graphene-covered copper (Cu) substrate with a three-dimensional surface microstructure. We have demonstrated that a liquid Hg droplet spontaneously propagates on a grooved Cu substrate covered by a monolayer graphene without any external force fields. Classical molecular dynamics results provide a profound insight on the self-driving process of Hg droplets. It shows that the Hg droplet undergoes acceleration, deceleration, and return stages successively from the narrow to wide ends of the gradient groove. Intriguingly, Hg droplets can move continuously and unidirectionally on the three-dimensional graphene-covered surface microstructure when they accumulate enough kinetic energy from the gradient groove to break the energy barrier at the step junctions between the two neighboring unit cells. The design of the zigzag textured surface covered by a monolayer graphene artfully uses the facts; (1) the monolayer graphene can effectively reduce the droplet pinning on the textured surface, (2) the hydrophobic graphene layer reduces the friction between Hg droplets and the substrate, and (3) the textured surface can permeably interact with the droplets through the monolayer graphene to achieve a continuous self-driving process. The findings reported here open a door to explore the graphene-covered functional surface to directional transport of liquid droplets and provide an in-depth understanding of the self-driving mechanism for liquid droplets on graphene-covered textured substrates.

Design Wideband Differential Bandpass Filter Using Slotline Surface Plasmon Polaritons

In this paper, a novel wideband differential bandpass filter (BPF) with slotline surface plasmon polaritons (SPPs) is proposed. It consists of a pair of differential microstrip-to-slotline transition, a slotline-to-SPP transition with subwavelength gradient grooves, and a slotline SPP waveguide, which supports the TEM, TE, and SPP modes, respectively. The dispersion and transmission characteristics of the proposed hybrid SPP structure are analyzed under differential-mode (DM) and common-mode (CM) operations and applied to design wideband differential filter. To validate the design concept, a filter sample has been designed, fabricated, and measured. Both simulated and measured results prove its good performance including a wide 3-dB fractional bandwidth of 147.6% centered at 4.2 GHz (f 0 ), a wide DM upper stopband to 4.8 f 0 (S 21 dd <; -30 dB), and a wide 40-dB CM suppression from 0.1 to 20 GHz.

Axial buckling modes and crashworthiness of circular tube with external linear gradient grooves

Metallic circular tube with external uniform grooves has excellent behaviors on axial crashworthiness during axial compression because it can generate stable responses. In the present research, three novel energy absorbers are proposed based on uniform grooved tube (UGT), namely, depth gradient grooved tube (D-GGT), thickness gradient grooved tube (T-GGT) and coupling gradient grooved tube (C-GGT). A theoretical model considering both the depth and thickness gradients and an efficient numerical model based on axisymmetric assumption are put forward. Meanwhile, some quasi-static compression experiments are performed to validate the theoretical and numerical models. The results conclude that the deformation of gradient grooved tubes (GGTs) under axial buckling can be classified into two modes, namely, random asymptotic buckling (RAB) and sequential asymptotic buckling (SAB). Compared with UGT, the D-GGT has a slight improvement on the axial energy performance even though the sum of depth of thin-walled sections is constant; for T-GGT, a force-displacement curve with upward trend and an obvious improvement of energy absorption are observed; specially, the energy absorption characteristics of D-GGT and T-GGT will occur simultaneously when C-GGT is subjected to axial loading.

Temperature-regulated directional bounce of impacting droplets on gradient grooves

Droplet impact dynamics on gradient textures at room temperature have been intensively studied in the past decade. The wetting gradient surfaces are reported to direct the droplet motion. In this work, we show an undirectional rebound behavior of impacting droplets on gradient grooved surfaces at high temperature. The impinging droplet rebounds towards the denser microstructure region at contact boiling state, but towards to the sparser region when at Leidenfrost film boiling state. Our analysis indicates that the non-directional rebounding direction is attributed to the unbalanced Young's forces or vapor pressure difference between the droplet and the substrate. In contact boiling regime, the droplet rebounds towards the denser region due to the unbalanced Young's force. However, in the Leidenfrost film boiling region, adequate vapor generated underneath the droplet impedes the direct contact and larger vapor pressure in the denser region causes the droplet to rebound oppositely. This study is envisioned to promote the understanding of droplet dynamics at high temperature and provide promising applications in various systems where regulating droplet motion is needed.

Spoof Surface Plasmon Polariton-Based Reconfigurable Band-Pass Filter Using Planar Ring Resonator

In this paper, we report the design, analysis, and development of spoof surface plasmon polariton (SSPP)-based reconfigurable band-pass filter using a planar ring resonator. A transition from quasi-transverse electromagnetic (QTEM) mode of microstrip to SSPP mode was implemented which has been subsequently used to develop a reconfigurable band-pass filter. Trapezoidal shape periodically corrugated metallic grooves etched on the planar metallic surface have been used in the implementation of this transition. In the designed transition, impedance and mode matching between QTEM mode and SSPP mode have been achieved using gradient grooves. The developed transition has been used in the characterization of a ring resonator corrugated with the periodical array of the trapezoidal shape grooves. This SSPP ring resonator shows multiple passbands at different frequencies within the specified frequency range. Varactor diodes have been incorporated in the SSPP ring resonator to obtain tunable passband. Three types of varactor-tuned circuits have been experimentally implemented and characterized using SMV2019-079LF diode package. These circuits will pave the path for development of other front-end circuit elements using the concept of spoof SPP.