Flexible Surface Research Articles

Coherent spore dispersion via drop-leaf interaction.

The dispersion of plant pathogens, such as rust spores, is responsible for more than 20% of global crop yield loss annually. However, the release mechanism of pathogens from flexible plant surfaces into the canopy is not well understood. In this study, we investigated the interplay between leaf elasticity and rainfall, revealing how a flexible leaf structure can generate a lateral flow stream, with embedded coherent structures that enhance transport. We first modeled the linear coupling between drop momentum, leaf vibration, and the stream flux from leaf surfaces. With Lagrangian diagnostics, we further mapped out the nested coherent structures around the fluttering profile, providing a dynamical description for local spore delivery. We hope the mechanistic details extracted here can facilitate the construction of physically informed analytical models for local crop disease management.

Microscopic morphology modeling and prediction of flexible polished surface with belt flapwheel

Flexible polishing technology is widely used in the precision machining of aero-engine blisk blades. It has become one of the important research contents of flexible polishing technology to systematically study the flexible polishing process and understand the connotation of the microscopic morphology of the polished surface. In this paper, the flapwheel is used as a flexible abrasive tool, and the spatial kinematics model for the abrasive grains on the surface of the flapwheel and the geometric interference model for the abrasive grains and workpiece are established by transforming the spatial geometric coordinates. Based on the surface topography model for the abrasive tool, MATLAB software was used to simulate the micro topography generation process of the flexible polishing surface with flapwheel as abrasive tool, and the three-dimensional topography of the workpiece surface and its influence law under different process parameters were obtained. The polishing experimental results verified the simulation algorithm correctness and effectiveness.

Flexible Electronics Applications of Ge‐Rich and Se‐Substituted Phase‐Change Materials in Nonvolatile Memories

Flexible electronics which are easy to manufacture and integrate into everyday items require suitable memory technology that can function on flexible surfaces. Herein, the properties of Ge‐rich GeSbTe (GST) and Se‐substituted GeSbSeTe (GSST) phase‐change alloys are investigated for application as nonvolatile write‐once and rewritable memories in flexible electronics. These materials have a higher crystallization temperature than the archetypal composition of Ge2Sb2Te5 and hence better data retention properties. Moreover, their high crystallization temperature provides for a particularly straightforward implementation of a write‐once memory configuration. Material properties of Ge‐rich GST and GSST are measured as a function of temperature using four‐point probe electrical testing, Raman spectroscopy, and X‐ray diffraction. Following this, the switching of flexible memory devices is investigated through both simulation and experiment. More specifically, crossbar memory devices fabricated using Ge‐rich GST are experimentally fabricated and tested, while the operation of GSST pore cell structures suitable for flexible memory applications is demonstrated through simulation.

Friction Behavior of Fingers on Micro-Textured Flexible Surfaces

Abstract Compared to rigid materials, people have a distinct tactile perception when touching flexible materials. Moreover, adding micro-patterns to the surface enhances the tactile experience even further. This sensation arises from the physical stimulation of frictional behavior between the skin and flexible materials. Therefore, this study focuses on human fingers as the research subjects and employs flexible materials with micro-textured surfaces as frictional objects. A friction test setup is designed to conduct a series of finger friction experiments, and theoretical explanations are provided to elucidate the reasons for performance variations. Research findings show that as the normal load increases, the frictional force gradually increases while the friction coefficient decreases. The former is attributed to the expanding contact area, while the latter is due to the inconsistent rate of frictional force increment with the normal load. The impact of friction velocity is mainly caused by changes in the viscous forces generated at the liquid film in the contact interface and the energy loss in elastic hysteresis. On the other hand, the effect of surface micro-topography is primarily a result of the transition between partial contact and full contact modes under the influence of normal load, leading to alterations in the contact area. Overall, during the finger friction process on a flexible micro-textured surface, changes in contact area play a vital role in modifying frictional performance, with adhesive friction exerting a more significant influence than deformation friction. This study summarizes the variations in frictional performance parameters based on experiments and analyzes the effects of contact area changes and deformation friction mechanisms from a theoretical perspective, providing a theoretical foundation for exploring the genesis of delicate tactile sensations during friction.

Flexible smart surface coating for GIS/GIL epoxy insulators

AbstractA flexible smart coating with electroluminescence effect was designed and fabricated on the surface of gas insulated switch gear (GIS)/gas insulated transmission line (GIL) epoxy insulators based on two‐step curing process. As the AC voltage increases, the luminous area on the insulator surface expands from the centre to the periphery, and the light intensity shows a linear relationship with the applied voltage. Besides, the flexible smart coating can effectively identify the location of metal particle defects and the degree of electric field distortion. The flexible smart coating enhances the surface flashover voltage due to its higher dielectric constant. Simultaneously, metal particle contamination can substantially reduce the insulation performance of epoxy insulators, particularly when they are located near the high‐voltage side. It is hoped that this study can provide a reference for the smart detection of surface defects GIS/GIL basin insulators.

A multi-layer flexible photothermal titanium nitride-based superhydrophobic surface for highly efficient anti-icing and de-icing.

Ice accumulation presents a significant challenge for various residential activities and industrial facilities. Most current de-icing methods are time-consuming and costly. Photothermal superhydrophobic surfaces have garnered significant attention in the field of anti-icing and de-icing due to their environmentally friendly and energy-saving characteristics. However, obtaining photothermal superhydrophobic surfaces with both reliable icing delay and effective photothermal de-icing capabilities at ultra-low temperatures (<-30 °C) remains significantly challenging. In this study, we prepared a multilayer flexible photothermal TiN-based superhydrophobic surface (ML-SHS), comprising an FAS@SiO2/TiN superhydrophobic layer and a PDMS/Triton X-100 flexible supporting layer. The optimal ML-SHS exhibits excellent superhydrophobicity (a water contact angle of 162.7° and a sliding angle of 2°) and an average light absorption of 95.6%, and generates a substantial surface temperature increase of 80.2 °C under 1 sun illumination. Droplets easily roll off the ML-SHS at -10 °C without solar illumination and at -35 °C under 1 sun illumination, demonstrating excellent passive anti-icing capability. Due to its excellent photothermal conversion and thermal constraint capabilities, the accumulated ice layer on the ML-SHS rapidly melts within 450 seconds at -20 °C under 1 sun illumination. The ML-SHS also possesses self-cleaning properties, mechanical durability, and chemical stability, ensuring the usability of the superhydrophobic surface under harsh conditions. Our study may offer a novel approach for the design and fabrication of photothermal superhydrophobic surfaces, facilitating efficient passive anti-icing and active de-icing in practical applications.

Harnessing laser technology to create stable metal halide perovskite-rGO conjugates as promising electrodes for Zn-ion capacitors.

We report that the direct conjugation of metal halide perovskite nanocrystals on rGO sheets can provide high performance and stable electrodes for Zn-ion capacitors. It is the first time that metal halide nanocrystals have been used to enhance the energy storage of 2D materials in capacitors by introducing an additional pseudocapacitance mechanism. In particular, we present a simple, rapid and room temperature laser-induced method to anchor CsPbBr3 nanocrystals on rGO sheets without affecting the initial morphology and crystal structure of the two components. The flexible and high surface area of the rGO sheets enables the conjugation of individual metal halide perovskite nanocrystals, giving rise to new synergetic functionalities. As a result, the specific capacitance of the perovskite-rGO conjugated electrodes can be enhanced by 178- and 152-times compared to those of the plain rGO and perovskite electrodes respectively.

Notice of Retraction: Carbon-Reinforced Flexible Band-Stop Frequency Selective Surface Design

Notice of Retraction: Carbon-Reinforced Flexible Band-Stop Frequency Selective Surface Design

A State-of-the-Art Review of Hydronic Asphalt Solar Collector Technology for Solar Energy Harvesting on Road Pavement

Nature inspires innovative renewable energy solutions by advancing our road pavements, as the sun is the only infinite and accessible source of clean and green energy on our planet. In addition to the various solar energy production methods, a new paradigm for utilizing asphalt pavement as a solar collector is being developed for self-powered energy harvesting. Due to direct solar radiation, flexible paved surfaces exposed to direct sunlight can heat up to 70°C in the summer. The heat is then dissipated into the environment, causing the urban heat island effect, and accelerating thermal oxidation of asphalt pavement. This can lead to structural failure and reduced pavement performance. This study aims to present a state-of-the-art review of hydronic asphalt solar collectors (HASCs) and propose the best model to enhance the performance of asphalt solar collectors. The findings of the study concluded that asphalt has the potential to absorb solar energy and store heat energy. This can be achieved by assembling and modifying conventional asphalt structures into modern asphalt solar collector designs that consist of pipe arrangements below the paved surface filled with liquid flowing through the pavement surface. The study found that a significant limitation of previous research was that it focused on optimizing the temperature profile at various depths but did not focus on structural improvements to reduce failure and increase the performance of asphalt solar collectors. Therefore, this review study proposed a new technique of using conductive and waste materials to enhance the performance of asphalt solar collectors.

Frontend and backend electronics achieving flexibility and scalability for tomographic tactile sensing

Tactile sensing is essential for robots to adequately interact with the physical world, but creating tactile sensors for the robot’s soft and flexible body surface has been a challenge. The resistance tomography-based tactile sensors have been introduced as a promising approach to creating soft tactile skins because the sensor fabrication can be greatly simplified with the aid of a computation model. This article introduces an electronic design strategy dividing frontend and backend electronics for the resistance tomography-based tactile sensors. In this scheme, the frontend is made of the piezoresistive structure and electrodes that can be changed depending on the required geometry. The backend is the electronic circuit for resistance tomography, which can be used for various frontend geometries. To evaluate the use of a unified backend for different frontend geometries, two frontend specimens with a square shape and a circular shape are tested. The minimum detectable contact force and the minimum discernible contact distance are calculated as 0.83×10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.83 \ imes 10^{-4}$$\\end{document} N/mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}, 2.51 mm for the square-shaped frontend and 1.19×10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.19 \ imes 10^{-4}$$\\end{document} N/mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}, 3.42 mm for the circular-shaped frontend. The results indicated that the proposed electronic design strategy can be used to create tactile skins with different scales and geometries while keeping the same backend design.

An active piezoelectric plane X-ray focusing mirror with a linearly changing thickness.

X-ray mirrors for synchrotron radiation are often bent into a curved figure and work under grazing-incidence conditions due to the strong penetrating nature of X-rays to most materials. Mirrors of different cross sections have been recommended to reduce the mirror's slope inaccuracy and clamping difficulty in order to overcome mechanical tolerances. With the development of hard X-ray focusing, it is difficult to meet the needs of focusing mirrors with small slope error with the existing mirror processing technology. Deformable mirrors are adaptive optics that can produce a flexible surface figure. A method of using a deformable mirror as a phase compensator is described to enhance the focusing performance of an X-ray mirror. This paper presents an active piezoelectric plane X-ray focusing mirror with a linearly changing thickness that has the ability of phase compensation while focusing X-rays. Benefiting from its special structural design, the mirror can realize flexible focusing at different focusing geometries using a single input driving voltage. A prototype was used to measure its performance under one-dimension and two-dimension conditions. The results prove that, even at a bending magnet beamline, the mirror can easily achieve a single-micrometre focusing without a complicated bending mechanism or high-precision surface processing. It is hoped that this kind of deformable mirror will have a wide and flexible application in the synchrotron radiation field.

Minimizing Off-Axis Bending Effects on Flexible Surface Acoustic Wave Sensing Powered by Integrated Machine Learning Algorithms

Minimizing Off-Axis Bending Effects on Flexible Surface Acoustic Wave Sensing Powered by Integrated Machine Learning Algorithms

Flexible Kokotsakis Meshes with Skew Faces: Generalization of the Orthodiagonal Involutive Type

In this paper, we introduce and study a remarkable class of mechanisms formed by a 3 × 3 arrangement of rigid quadrilateral faces with revolute joints at the common edges. In contrast to the well-studied Kokotsakis meshes with a quadrangular base, we do not assume the planarity of the quadrilateral faces. Our mechanisms are a generalization of Izmestiev’s orthodiagonal involutive type of Kokotsakis meshes formed by planar quadrilateral faces. The importance of this Izmestiev class is undisputed as it represents the first known flexible discrete surface – T-nets – which has been constructed by Graf and Sauer. Our algebraic approach yields a complete characterization of all flexible 3 × 3 quad meshes of the orthodiagonal involutive type up to some degenerated cases. It is shown that one has a maximum of 8 degrees of freedom to construct such mechanisms. This is illustrated by several examples, including cases which could not be realized using planar faces. We demonstrate the practical realization of the proposed mechanisms by building a physical prototype using stainless steel. In contrast to plastic prototype fabrication, we avoid large tolerances and inherent flexibility.

Nonlinear shock-induced flutter of a compliant panel using a fully coupled fluid-thermal-structure interaction model

A comprehensive study has been conducted on the fully coupled aero-thermo-elastic interaction between a shock wave and a laminar boundary layer over a flexible surface with different thermal conditions. In this investigation, the flow is characterized by an oblique impinging shock on a laminar boundary layer over a compliant panel with a cavity pressure and temperature. To model the fluid–structure interaction (FSI), we have combined a finite element model of the structure with a high-order sharp interface immersed boundary method implemented in a finite-difference flow solver. We have analyzed the behavior of the FSI coupling over a wide range of parameters and various boundary conditions while the panel undergoes relaxation to its unexcited state or exhibits limit cycle oscillations. Notably, the panel oscillation and the fluctuations in the shear layer exhibit strong coupling and demonstrate a lock-in resonance frequency response. The colder wall conditions result in a reduced separation bubble and a raised aerodynamic pressure difference between the maximum and minimum instantaneous dynamic pressures, consequently amplifying the amplitude of panel oscillation. For the cases with thermal coupling, the behavior of panel oscillation is notably influenced by specific heat and thermal expansion coefficients. In these scenarios, the thermal state of the solid material emerges as the pivotal factor governing the sustained oscillation of the panel. The non-linear impact of the thermal dependency of the structural properties plays a crucial role in determining the stability of the coupled FSI system. The study revealed that the stable decaying sinusoidal oscillation undergoes a transformation into a limit-cycle oscillation when panel stiffness is affected by reduced temperature. During the sustained oscillation, a mode switch is observed between the first and second modes of deformation of the panel.

MTH subdivision scheme with sharp and semi-sharp features

In this paper, a new non-stationary bivariate subdivision scheme is proposed to obtain a more flexible limit surface. By rewriting the univariate subdivision scheme (Fakhar et al., 2022) under two different methods, the tensor product and the subdivision rules for extraordinary points/faces are constructed. The new scheme produces continuous limit surfaces of higher order, except at extraordinary points/faces where the continuity is G1. Algorithms for generating sharp and semi-sharp features on the hybrid subdivision surface are presented. Numerical examples are also given to show the performance of these new schemes.

Hiemenz stagnation point flow of a second-order micropolar slip flow with heat transfer

Purpose This paper aims to study a non-Newtonian micropolar fluid flow over a bidirectional flexible surface for multiple exact solutions of momentum boundary layer and thermal transport phenomenon subject to wall mass flux, second-order slip and thermal jump conditions. Design/methodology/approach The coupled equations are transformed into ordinary differential equations using similarity variables. Analytical and numerical techniques are used to solve the coupled equations for single, dual or multiple solutions. Findings The results show that the stretching flow, shrinking flow, the wall drag, thermal profile and temperature gradient manifest large changes when treated for special effects of the standard parameters. The role of critical numbers is definitive in locating the domains for the existence of exact solutions. The nondimensional parameters, such as mass transfer parameter, bidirectional moving parameter, plate deformation strength parameter, velocity slips, material parameter, thermal jump and Prandtl number, are considered, and their physical effects are presented graphically. The presence of governing parameters exhibits special effects on the flow, microrotation and temperature distributions, and various exact solutions are obtained for the special parametric cases. Originality/value The originality and value of this work lie in its exploration of non-Newtonian micropolar fluid flow over a bidirectional flexible surface, highlighting the multiple exact solutions for momentum boundary layers and thermal transport under various physical conditions. The study provides insights into the effects of key parameters on flow and thermal behavior, contributing to the understanding of complex fluid dynamics.

A dynamic obstacle avoidance method for collaborative robots based on trajectory optimization

Background Collision detection is crucial in the design of robot planning algorithms. Efficient distance sensors can provide high-resolution environmental collision information to the robot's planning algorithm. However, this also leads to the robot obstacle avoidance performance being limited by the performance of the sensors. Therefore, it becomes a challenge to achieve efficient obstacle avoidance with low-resolution environmental information. Methods First, we use a self-developed capacitive array non-contact distance sensing flexible surface for sensing the proximity of colliding objects. Second, we designed an optimization-based dynamic obstacle avoidance planning algorithm, using only the minimum separation distance and penetration direction as obstacle avoidance information, and referring to the idea of stochastic gradient descent, using real-time collision avoidance information to do single-step optimization adjustment. Results We conducted the dynamic obstacle avoidance test experiment by connecting the electronic skin to the semi-physical prototype and the full physical prototype. The experiments show that efficient dynamic obstacle avoidance can be realized under the maximum effective range of only 5~7cm, and it has strong flexibility to avoid different shapes of dynamic obstacles in a non-contact manner, and finally arrive at the target position. Conclusions In this paper, an online obstacle avoidance planning algorithm designed based on an optimization method that is not limited to the shape of obstacles is proposed, and the effectiveness of the algorithm is verified by physical experiments in combination with a self-developed flexible distance sensing surface. It is of great significance for the safe operation of human-robot interaction in collaborative robots.

Fabrication Model Design and Analysis of Flexible Polarization Surface Polariton Resonance with a Dual-Wing Antenna Structure Platform for Diverse Multiband Characteristics in the Measurement Environment

Fabrication Model Design and Analysis of Flexible Polarization Surface Polariton Resonance with a Dual-Wing Antenna Structure Platform for Diverse Multiband Characteristics in the Measurement Environment

An Error Estimation System for Close-Range Photogrammetric Systems and Algorithms.

Close-range photogrammetry methods are widely used for non-contact and accurate measurements of surface shapes. These methods are based on calculating the three-dimensional coordinates of an object from two-dimensional images using special digital processing algorithms. Due to the relatively complex measurement principle, the accurate estimation of the photogrammetric measurement error is a non-trivial task. Typically, theoretical estimations or computer modelling are used to solve this problem. However, these approaches cannot provide an accurate estimate because it is impossible to consider all factors that influence the measurement results. To solve this problem, we propose the use of physical modelling. The measurement results from the photogrammetric system under test were compared with the results of a more accurate reference measurement method. This comparison allowed the error to be estimated under controlled conditions. The test object was a flexible surface whose shape could vary smoothly over a wide range. The estimation of the measurement accuracy for a large number of different surface shapes allows us to obtain new results that are difficult to obtain using standard approaches. To implement the proposed approach, a laboratory system for the error estimation of close-range photogrammetric measurements was developed. The paper contains a detailed description of the developed system and the proposed technique for a comparison of the measurement results. The error in the reference method, which was chosen to be phasogrammetry, was evaluated experimentally. Experimental testing of the stereo photogrammetric system was performed according to the proposed technique. The obtained results show that the proposed technique can reveal dependencies that may not be detected by standard approaches.

Flexible and Biocompatible Antifouling Polyurethane Surfaces Incorporating Tethered Antimicrobial Peptides through Click Reactions.

Efficient, simple antibacterial materials to combat implant-associated infections are much in demand. Herein, the development of polyurethanes, both cross-linked thermoset and flexible and versatile thermoplastic, suitable for "click on demand" attachment of antibacterial compounds enabled via incorporation of an alkyne-containing diol monomer in the polymer backbone, is described. By employing different polyolic polytetrahydrofurans, isocyanates, and chain extenders, a robust and flexible material comparable to commercial thermoplastic polyurethane is prepared. A series of short synthetic antimicrobial peptides are designed, synthesized, and covalently attached in a single coupling step to generate a homogenous coating. The lead material is shown to be biocompatible and does not display any toxicity against either mouse fibroblasts or reconstructed human epidermis according to ISO and OECD guidelines. The repelling performance of the peptide-coated materials is illustrated against colonization and biofilm formation by Staphylococcus aureus and Staphylococcus epidermidis on coated plastic films and finally, on coated commercial central venous catheters employing LIVE/DEAD staining, confocal laser scanning microscopy, and bacterial counts. This study presents the successful development of a versatile and scalable polyurethane with the potential for use in the medical field to reduce the impact of bacterial biofilms.