High Accuracy Surface Research Articles

Seasonal Variations of PM2.5 Pollution in the Chengdu–Chongqing Urban Agglomeration, China

During the development of the Chengdu–Chongqing Urban Agglomeration (CCUA) in China, PM2.5 pollution severely threatened public health, presenting a significant environmental challenge. This study employs a novel spatial interpolation method known as High Accuracy Surface Modeling (HASM), along with the geographical detector method, local and regional contributions calculation model, and the Hybrid Single–Particle Lagrangian Integrated Trajectory model to analyze the seasonal spatial distribution of PM2.5 concentrations and their anthropogenic driving factors from 2014 to 2023. The transport pathway and potential sources of seasonal PM2.5 concentrations were also examined. The results showed the following: (1) HASM was identified as the most suitable interpolation method for monitoring PM2.5 concentrations in the CCUA; (2) The PM2.5 concentrations exhibited a decreasing trend across all seasons, with the highest values in winter and the lowest in summer. Spatially, the concentrations showed a pattern of being higher in the southwest and lower in the southeast; (3) Industrial soot (dust) emissions (ISEs) and industry structure (IS) were the most important anthropogenic driving factors influencing PM2.5 pollution; (4) The border area between the eastern part of the Tibet Autonomous Region and western Sichuan province in China significantly contribute to PM2.5 pollution in the CCUA, especially during winter.

A Spatial Reconstruction Method of Ionospheric foF2 Based on High Accuracy Surface Modeling Theory

The ionospheric F2 critical frequency (foF2) is one of the most crucial application parameters in high-frequency communication, detection, and electronic warfare. To improve the accuracy of spatial reconstruction of the ionospheric foF2, we propose a high-accuracy surface (HAS) modeling method. This method converts difficult-to-solve differential equations into more manageable algebraic equations using direct difference approximation, significantly reducing algorithm complexity and computational load while exhibiting excellent convergence properties. We used seven stations in Brisbane, Canberra, Darwin, Hobart, Learmonth, Perth, and Townsville, with one station as a validation station and six as training stations (e.g., Brisbane as a validation station and the other stations—Canberra, Darwin, Hobart, Learmonth, Perth, and Townsville—as training stations). The training stations and the HAS method were used to train and reconstruct the validation stations at different solar activity periods, seasons, and local times. The predicted values of the validation stations were compared with the measured values, and the proposed method was analyzed and validated. The reconstruction results show the following. (1) The relative root mean square errors (RRMSEs) of HAS method prediction in different solar activity epochs were 13.67%, 7.74%, and 9.19%, respectively, which are 13.57%, 7.41%, and 6.41% higher than the prediction accuracy of the Kriging method, respectively. (2) In the four seasons, the RRMSEs of the HAS method prediction are 9.27%, 13.1%, 8.81%, and 8.09%, respectively, which are 10.83%, 11.73%, 4.25%, and 12.00% higher than the prediction accuracy of the Kriging method. (c) During the daytime and nighttime, the RRMSEs of HAS method prediction were 9.23% and 11.17%, which were 5.92% and 11.99% higher than the prediction accuracy of the Kriging method, respectively. (d) Under the validation dataset, the average predictive RRMSE of the HAS method was 10.29%, and the average predictive RRMSE of the IRI prediction model was 12.35%, with a 2.06% improvement in the predictive accuracy of the HAS method. In general, the prediction effect of the HAS method was better than that of the Kriging method, thus verifying the effectiveness and reliability of the proposed method. In summary, the proposed reconstruction method is of great significance for improving usable frequency prediction and enhancing communication performance.

Deployment Dynamic Modeling and Driving Schemes for a Ring-Truss Deployable Antenna

Mesh reflector antennas are widely used in space tasks owing to their light weight, high surface accuracy, and large folding ratio. They are stowed during launch and then fully deployed in orbit to form a mesh reflector that transmits signals. Smooth deployment is essential for duty services; therefore, accurate and efficient dynamic modeling and analysis of the deployment process are essential. One major challenge is depicting time-varying resistance of the cable network and capturing the cable-truss coupling behavior during the deployment process. This paper proposes a general dynamic analysis methodology for cable-truss coupling. Considering the topological diversity and geometric nonlinearity, the cable network’s equilibrium equation is derived, and an explicit expression of the time-varying tension of the boundary cables, which provides the main resistance in truss deployment, is obtained. The deployment dynamic model is established, which considers the coupling effect between the soft cables and deployable truss. The effects of the antenna’s driving modes and parameters on the dynamic deployment performance were investigated. A scaled prototype was manufactured, and the deployment experiment was conducted to verify the accuracy of the proposed modeling method. The proposed methodology is suitable for general cable antennas with arbitrary topologies and parameters, providing theoretical guidance for the dynamic performance evaluation of antenna driving schemes.

Mesh antenna cable net form finding optimization by an improved NSGA-II

The tension uniformity and surface accuracy of mesh antenna cable net are two well-accepted evaluation criteria for form finding. Traditional form finding techniques often rely on single-objective optimization and weighting factors. Although the Non-dominated Sorting Genetic Algorithm II (NSGA-II) can address the limitation, there are still challenges of wide distribution and insufficient precision of solutions. In the present work, a novel multi-objective optimization method based on an improved NSGA-II is introduced to conduct mesh antenna cable net form finding optimization. Based on the preference region (PR), a self-adaptive penalty function is proposed. The function is designed to steer the optimization process toward the PR, and enhancing the precision of the solutions. The extent of penalization for an individual solution depends on its positioning relative to the PR and is modified by a penalty coefficient that adapts dynamically to the population number within the PR. Additionally, a form finding method considering flexible frames is developed. The initial population for the flexible frame optimization is sourced from results of rigid frames, with the maximum truss node position error as the convergence criterion. Benchmark tests and case studies confirm that the improved NSGA-II enhances distributivity and convergence, while also providing form-finding results with higher surface accuracy and more uniform tension distribution.

Anti-creep pretension determination of a mesh reflector antenna for long term surface accuracy retention

During the in-orbit service, mesh reflector antennas inevitably withstand the long-term creep behavior, resulting in changes in material properties and loss of cable tensions, thus decreasing the structural stiffness and surface accuracy. Pretension design plays an important role for mesh reflector antennas in achieving high surface accuracy, and different levels of pretension also affect the antenna’s creep behavior in the time dimension, which can be actively utilized to improve stability of the antenna surface accuracy. In this paper, we present an anti-creep pretension determination method for mesh reflector antennas to improve the surface accuracy stability. The creep model in the discretized time domain is adopted to describe the cable creep behavior. The time-related nonlinear equilibrium equation of the mesh reflector antenna is established with the force density method. The time-related tangent stiffness matrix is derived and adopted to solve the nonlinear equilibrium equation by the Newton-Raphson method, providing an effective way to analyze the antenna creep phenomenon in the discretized time domain. Aiming to minimize the long-term peak value of the time-variant surface error, the pretension schemes are generated and optimized. Finally, this approach is effectively applied to a thirty-unit mesh reflector antenna and its feasibility and effectiveness are verified.

Programmable thick-panel Miura-ori for ultra-large planar antennas with one-degree-of-freedom

Planar antennas are large spacecraft primarily used in various fields such as communication, Earth observation, astronomical observation, and scientific experiments. They require high surface accuracy, with the array needing to have uniform thickness and flat surfaces. An ultra-large planar antenna means higher receiving sensitivity and greater coverage area, which is the trend for the future. During launch, the planar antenna needs to be folded to fit into the payload capsule. In this study, a programmable thick-panel Miura-ori unit that has uniform thickness and satisfies the Bennett linkage condition is developed. After special design, this unit can be infinitely expanded in the row and column directions, allowing for the folding of planar antennas of any size (rows × columns). For each vertex inside the planar antenna, there are four panels around it, and their connection relationships all satisfy the Bennett linkage condition, resulting in the entire planar antenna having only one degree of freedom. The sector angle of each parallelogram can approach 90°, compacting the folding form of the planar antenna. Furthermore, a layout scheme for an ultra-large planar antenna is provided, the deployment ratio, envelope diameter and envelope height are derived, and the complete unfolding process of the ultra-large planar antenna is demonstrated. Finally, the effectiveness of the proposed method for satellite planar antennas is verified through an experiment.

Effect of Panel Misalignment Error Distribution on the Radiation Pattern of Leighton Chajnantor Telescope’s Antenna

The Leighton dish formerly at the Caltech Submillimeter Observatory will be reassembled to become the Leighton Chajnantor Telescope (LCT). It will be required to demonstrate high surface accuracy and controlled radiation patterns at high frequency, which are largely limited by surface error due to panel misalignment on the primary reflector. Not only the surface rms error but also the error distribution has effect on the radiation pattern of the antenna. Therefore, analyzing the effect of error distributions resulting from various panel misalignments on the radiation pattern of the antenna will facilitate better compensation of surface errors during the reassembly process. To acquire the radiation pattern of LCT’s antenna with panel misalignments, we first propose a simulation method based on physical optics and the physical theory of diffraction, which offers precise results but is time-consuming, especially at high frequencies. Then, we propose a rapid computation method that combines the method of calculating the optical path difference (OPD), the OPD fitting method, and the aperture integration method for segmented reflectors. Experimental results demonstrate that the rapid computation method is highly efficient and accurate compared to the simulation method. In order to show the effect of error distributions due to two typical panel misalignments (i.e., piston and tip-tilt) on radiation patterns, experiments are conducted using the two proposed methods for various error distributions. These experiments indicate that for the same surface rms error, smaller panel errors at smaller normalized aperture radii are more conducive to achieving improved characteristics of the radiation patterns, such as reduced peak gain losses and lower sidelobe levels. Additionally, comparison experiments also reveal that variations in piston error have a greater impact on the radiation patterns than variations in tip-tilt error under the same surface rms error.

Dynamic changes and impacts of accumulated temperature on the Tibetan plateau from 1980 to 2018 based on the fusion of simulation and observation data

In the context of global warming, the thermal conditions of the Tibetan Plateau have changed significantly in recent decades. In the present study, we analysed the spatiotemporal variation in T ≥ 0 °C accumulated temperature (AT0) on the Tibetan Plateau from 1980 to 2018 and its effect on normalized difference vegetation index (NDVI) changes by fusing climate model outputs and ground observations using the High Accuracy Surface Modeling (HASM). Cross-validation revealed that the root mean square error (RMSE) and R2 of the fused data from HASM were 1.593 °C and 0.719, respectively, which were greater than the 5.864 °C and 0.385, respectively, before fusion, indicating that HASM fusion improved the accuracy and that a more accurate AT0 could be obtained. Over the past 39 years, AT0 on the Tibetan Plateau had increased at a rate of 7.53 °C/year. The growth period was extended by 0.46 days/year, while the start and end of the growth period were 0.27 days/year earlier and 0.18 days/year later, respectively. Analysis of the decadal change in AT0 revealed that the areas with AT0 < 500 °C decreased by 5 % and that the areas with AT0 > 2000 °C increased by 6.2 %. However, a slower warming trend appeared after 2010 because of the decreasing rate of the daily mean temperature increase during the growth period. Increasing AT0 also promoted vegetation growth, especially in parts of the southern and eastern plateau regions, with a Pearson's correlation coefficient of 0.46 on the entire plateau between AT0 and the average NDVI during the growth periods. However, there was a significant negative correlation with a coefficient lower than −0.4 in the Qaidam Basin, and partial correlation analysis showed that the extension of the growth period was the main factor influencing the decrease in the NDVI in the Qaidam Basin.

Embedded parallel-actuated technology for deformable space segmented mirror

The deployable segmented space imaging system is an important solution for future ultra-large aperture space optical systems. To achieve the imaging capability of an equivalent aperture monolithic mirror, it requires not only to ensure the positional accuracy in the cophasing process, but also to have extremely high surface accuracy and curvature consistency of the sub-mirrors. However, this work is extremely challenging due to the manufacturing error of the sub-mirrors and the complex space environment. Active optical technology can ensure the surface shape accuracy of the spliced mirror by controlling the mirror surface deformation and compensating for the wavefront aberration. This article compares and analyzes the control ability of two types of deformable mirrors actuated by vertical and parallel methods. We explored the characteristics of the influence function mathematical models of the two types of actuation forms and compared the aberration and curvature correction abilities of them through finite element analysis, summarizing the advantages of the parallel actuation forms. Finally, a 300mm aperture embedded parallel-actuated deformable mirror was designed and manufactured, and relevant experiments were conducted to verify its adjustment ability. By comparing and analyzing the experimental results with the design results, the adjustment ability of the embedded parallel-actuated deformable mirror was verified.

High surface accuracy design of the electrostatically controlled deployable membrane antenna based on a thermoplastic forming method

High surface accuracy design of the electrostatically controlled deployable membrane antenna based on a thermoplastic forming method

Theoretical and experimental investigation on material removal mechanism in dual-rotation polishing of fused silica glass

Fused silica glass is utilized extensively in various optical components owing to its excellent optical properties, but its high hardness and brittleness make it difficult to process with high surface accuracy and low subsurface damage. To solve this problem, a series of experiments is carried out to explore the mechanism of material removal during dual-rotation polishing of fused quartz glass. A predictive model is proposed to predict the material removal rate and the microtopography of polished surface. This model considers fundamental physics of the dual-rotation polishing process, for instance, the surface micro-topography and the pressure distribution of the polishing pad, the brittle–ductile material removal mechanism, the planetary motion during the polishing, and the influence of chemical reactions. The reliability and accuracy of the model are quantitatively evaluated through practical experiments. It is turned out that the simulated results reasonably agree with the experimental data. In addition, simulation experiments show that a Gaussian removal function with a strong central peak can be obtained when the eccentricity is 0.9 and the rotating speed ratio is between −10 and −1. This indicates that the theoretical model can be successfully applied to the prediction and optimization of polishing processes.

Design and analysis of scissor-like hoop truss deployable antenna mechanism with arbitrary curvature support ribs

To align with the development trend of large aperture, high stiffness, and high expansion ratio for space antennas, we propose a scissor-like hoop truss deployable antenna mechanism with arbitrary curvature mesh support. Compared to classical AstroMesh-hoop structures, this configuration features parabolic support ribs under the mesh surface, eliminating the need for additional high columns. It has a lower stowed height and higher in-plane stiffness, which helps maintain high surface accuracy. Firstly, the Four-Parameter Method is proposed for the dimensional design of scissor-like chains with arbitrary curvature from the perspective of the deployable antenna support structure. This method allows for controlling the deployment configuration of the scissor-like support structure by adjusting the semi-major axis length and the focal length of the initial ellipse, the angles of the unit lines, and the x-coordinates of the fitting points. Then, a three-dimensional scissor-like hoop design with joint scale that satisfies the deployable conditions is performed. Subsequently, two major issues called over-deployment and bistability are discussed, which need to be considered when applying scissor-like elements (SLEs) to space-deployable antennas. The mechanisms behind these issues are analyzed from a kinematic perspective, and optimization methods are proposed. The effectiveness of the optimization methods is verified through dynamic software simulations and a prototype. The high in-plane stiffness of the configuration is verified by finite element analysis.

Effects of thickness and annealing on the residual stress of TiO2 film

Film stress will lead optical elements to distort in the surface shape; it must be studied for manufacturing high surface accuracy optical thin film. As the most commonly used film material in the visible/near-infrared spectrum, it is essential to research the state of stress in TiO2 film. The orthogonal experiment approach is used to investigate the impact of film thickness, annealing temperature, and annealing time on the residual stress of the TiO2 film deposited by EBE. It is shown that the film thickness effects the residual stress most. The order in which the residual stress varies with respect to the film stress, annealing temperature, and annealing time is then given, and the AFM test is utilized to explore the cause of the change in the residual stress. This study is of great benefit for designing low-stress optical film systems and preparing ultra-low surface shape accuracy thin film devices.

Programming quadric metasurfaces via infinitesimal origami maps of monohedral hexagonal tessellations: Part II

In Part I of this study, it was shown that all the three known types of monohedral hexagonal tessellations of the plane, those composed of equal irregular hexagons, have just a single deformation mode when tiles are considered as rigid bodies hinged to each other along the edges. A gallery of tessellated plates was simulated numerically to demonstrate the range of achievable deformed shapes. In Part II, the displacement field was first derived and a continuous interpolant for each type of tessellated plate. It turns out that all corresponding metasurfaces are described by quadrics. Afterwards, a parametric analysis was carried out to determine the effect of varying angles and edge lengths on the curvature, and the values of the geometric Poisson ratio of the plates. Finally, a method of fabrication is proposed based on the additive manufacturing of stiff tiles of negligible deformability and flexible connectors. Using this modular technique, it is possible to join together different monohedral tessellated plates able to deform into piece-wise quadrics. The nodal positions in the deformed configuration of the realized plates are measured after enforcing one principal curvature to assume a chosen value. The estimate of the other principal curvature confirms the analytical predictions. The presented tessellated plates permit to realize doubly curved shape-morphing metasurfaces with assorted shapes, which also can feature a certain surface roughness, and they can be employed in all applications demanding high surface accuracy and few actuators or just one.

Configuration Investigation, Structure Design and Deployment Dynamics of Rigid-Reflector Spaceborne Antenna with Deviation-Angle Panel.

Rigid-reflector spaceborne antennas (RRSAs) are well-suited for high-frequency application scenarios due to their high surface accuracy. However, the low stowing efficiency of RRSAs limits the aperture diameters and further deteriorates the electromagnetic (EM) performances in terms of gain, resolution and sensitivity. After conducting systematic feature analysis with respect to several typical RRSAs, we propose a novel type of RRSA to solve the aforementioned problems. Inspired by the pose adjustment process for a higher stowing efficiency of traditional RRSAs, we also propose a new segmentation scheme of a reflective surface consisting of a deviation-angle panel that facilitates a higher stowing efficiency. Based on this scheme, its corresponding folded configuration is implemented by combining Euler's rotation theorem and the idea of parameter identification. In addition, we also compare the stowing efficiency of different schemes to verify the high stowing efficiency of the configuration. Finally, we perform mechanism/structure design and deployment dynamics to demonstrate that the antenna can be successfully deployed and exhibits excellent deployment quality. The results suggest that the proposed antenna possesses higher stowing efficiency than that of the same kind, with a stable deployment and interference-free process.

Enhancing the Spatial Resolution of Hyperspectral Images Combining High-Accuracy Surface Modeling and Subpixel Unmixing

Enhancing the Spatial Resolution of Hyperspectral Images Combining High-Accuracy Surface Modeling and Subpixel Unmixing

Robust Surface Recognition With the Maximum Mean Discrepancy: Degrading Haptic-Auditory Signals Through Bandwidth and Noise.

Sliding a tool across a surface generates rich sensations that can be analyzed to recognize what is being touched. However, the optimal configuration for capturing these signals is yet unclear. To bridge this gap, we consider haptic-auditory data as a human explores surfaces with different steel tools, including accelerations of the tool and finger, force and torque applied to the surface, and contact sounds. Our classification pipeline uses the maximum mean discrepancy (MMD) to quantify differences in data distributions in a high-dimensional space for inference. With recordings from three hemispherical tool diameters and ten diverse surfaces, we conducted two degradation studies by decreasing sensing bandwidth and increasing added noise. We evaluate the haptic-auditory recognition performance achieved with the MMD to compare newly gathered data to each surface in our known library. The results indicate that acceleration signals alone have great potential for high-accuracy surface recognition and are robust against noise contamination. The optimal accelerometer bandwidth exceeds 1000 Hz, suggesting that useful vibrotactile information extends beyond human perception range. Finally, smaller tool tips generate contact vibrations with better noise robustness. The provided sensing guidelines may enable superhuman performance in portable surface recognition, which could benefit quality control, material documentation, and robotics.

Optimized Surface Adjustment Method for Large Deployable Cable Network Antennas

Large deployable mesh reflectors typically require high surface accuracy and have large apertures. The accumulation of machining errors in a large number of cables can lead to significant deviations between the final manufactured surface and the theoretical surface, particularly due to the large number of cables involved. Adjusting the mesh reflector is often necessary to meet the surface accuracy requirements. However, traditional surface adjustment methods can be challenging to converge and time-consuming. To address this issue, our paper proposes an engineering surface based on measured manufacturing errors as a substitute for the theoretical surface. This method can save time on the coarse adjustment of surface accuracy for large deployable mesh reflectors, reducing the overall surface accuracy adjustment time by 30%.

Optimization of a novel, bidirectional, double-ring, deployable mesh antenna with a super-large aperture

The development of large antennas deployable in space is particularly important. A mesh antenna would be ideal because of its high surface accuracy and storage ratio. Here, we develop a novel, double-ring, deployable mesh antenna, then perform mass evaluation and modal analyses. The antenna exhibited better stiffness and a greater storage ratio, compared with typical mesh antennas. However, the mass was excessive. To overcome this problem, we designed a lightweight 5-m truss antenna, then measured its stiffness and strength. We optimized the computer-aided design of a mesh antenna with a super-large aperture, and we performed form-finding analysis of the cable-net. The new antenna included bidirectional deployment and exhibited a greater storage ratio and stiffness, compared with the conventional AstroMesh antenna. The first-order natural frequency was twofold greater than that of the AstroMesh antenna. Our work will aid fabrication of antennas with super-large apertures.

Effect of Wheel Path in Raster Grinding on Surface Accuracy of an Off-Axis Parabolic Mirror

Off-axis parabolic mirrors have extensive applications in X-ray optics, with the precision of their curvature directly impacting grazing-incidence focusing performance. Notably, the off-axis parabolic surface has non-rotating and non-symmetrical characteristics. Ultra-precision raster grinding utilizing a diamond wheel is a common method. Crucially, establishing an optimal wheel path stands as the key to ensuring surface accuracy during off-axis paraboloid grinding. In this study, according to the double curvature property of an off-axis parabolic surface, two different wheel paths were compared: one tracing the meridian direction (parabolic generatrix) and the other following the arc vector direction (arc). The results showed that the wheel path in raster grinding stepping along the arc vector direction can obtain a smaller scallop height and higher surface accuracy. The surface accuracy of one step along the arc vector direction is 9.6 μm, and that of the other step along the meridian direction is 32.6 μm. A model of the scallop height was established based on the relative relationship between adjacent wheel paths, and the error is within 5%. According to the correlation between scallop height and shape error, we conducted an analysis of the spatial distribution of shape errors under varying wheel paths. The wheel path that steps along the arc vector is more suitable for raster grinding of the off-axis paraboloid. The above study can provide theoretical guidance for the wheel path planning of off-axis parabolic mirrors with high surface accuracy.