Tolerance Research Articles

Innovative Anode Design to Enhance Both Volumetric and Gravimetric Energy Densities of LiCoO2||Graphite Pouch Cells

AbstractThe ratio of the anode (negative electrode) and cathode (positive electrode) areal capacities (N/P ratio), is an important parameter for Lithium‐ion batteries. Considering the manufacturing tolerance and battery safety, almost all of the batteries keep the N/P ratio > 1. Deviating from this ratio can lead to lithium precipitation on the anode surface, which poses significant risks. Here, by using a gradient structured graphite (Gr) anode, a new design concept is proposed that the N/P ratio could be less than 1, which can effectively achieve higher energy density without sacrificing the battery safety. This is achieved by incorporating a small quantity of silver (Ag) nanoparticles into the bottom layer of the anode (Gr‐Agx), which effectively modulates the concentration polarization of lithium ions along the thickness of the electrode. Moreover, the volumetric energy density of 4 Ah LiCoO2||Gr‐Ag0.5 (N/P = 0.8) pouch cell increases by 14.5% compared with LiCoO2||Gr (N/P = 1.1). Furthermore, the universal applicability and efficacy of the N/P < 1 design paradigm in LiFePO4||Gr cells are validated.

Design and error analysis of simple terahertz high birefringence microstructured fiber

Abstract High birefringence fibers are significant in the terahertz technology field, serving as waveguides for terahertz transmission. They are applicable in various fields such as communication, imaging. Integrating metal microstructures into polymer microstructured optical fibers can effectively modulate the transmission characteristics of the fiber, enhancing birefringence and reducing loss, thereby achieving better performance compared to traditional single-material fibers. This paper presents a structurally simple terahertz high birefringence microstructured fiber, where the introduction of gold microstructures enhances the birefringence of fiber, with a maximum birefringence of up to 1.089 × 10−2. We also discuss several manufacturing errors that may occur during the fiber fabrication process. The results indicate that the designed fiber exhibits significant manufacturing tolerance. Variations in the thickness and angle of the gold microstructures, as well as the angular offset of the elliptical cladding wall, peak-to-valley errors, and changes in the aspect ratio of the elliptical tube, have relatively minor effects on the overall transmission performance. The research findings provide insights for designing subsequent high birefringence terahertz fibers, thereby propelling advancements in this field. They offer a theoretical basis for the preparation of related microstructured fiber structures and provide valuable understanding for optimizing fiber manufacturing processes.

Assessment of land degradation susceptibility within the Shaqlawa subregion of Northern Iraq-Kurdistan Region via synergistic application of remotely acquired datasets and advanced predictive models.

Land degradation (LD) is the decline in a land's functional capacity and productive potential, which includes various anthropogenic and natural drivers. This study focuses on three primary manifestations of LD including soil erosion, landslides, and rockfalls, which are the most prevalent in the Shaqlawa district. A set of 22 LD conditioning factors, encompassing curvature, lithology, aspect, river density, soil type, lineament density, river distance, elevation, road distance, length slope (LS), land use land cover (LULC), stream power index (SPI), valley depth, profile curvature, slope, solar radiation, road density, lineament distance, rainfall, topographic wetness index (TWI), plan curvature, and normalized difference vegetation index (NDVI), were integrated into the analysis. Variance inflation factors (VIF) and tolerance (TOL) values from linear regression indicate that most LD factors have acceptable levels of multicollinearity. The Information Gain Ratio (IGR) identified key variables TWI, NDVI, and lithology-as pivotal factors for predicting LD. Additionally, the study evaluated degradation factors using various machine learning (ML) algorithms, including random forest (RF), Naive Bayes, logistic regression, rotation forest, forest penalized attributes (FPA), and Fisher's Linear discriminant analysis (FLDA). This facilitated categorizing the study area into five susceptibility categories. The FLDA model categorized the highest area under very high degradation risk at 26.72%, emphasizing the varied insights each algorithm brought to characterizing the degradation risk. Additionally, the receiver operating characteristic curves (ROC) were employed for model validation, identifying RF as the most successful model in the training dataset with an area under the curve (AUC) of 0.882, while FLDA outperformed in the testing dataset with an AUC of 0.883. The identified LD-prone areas will help land-use planners and emergency management officials apply effective mitigation strategies for similar terrains.

Design and damping characterization of sandwich composite made of particle-filled hollow spheres and steel sheets

Sandwich composites made of particle-filled hollow sphere structures (PHSS) and steel sheets offer excellent lightweight and damping properties, ideal for high-speed machine tool components under dynamic loads. Previous research has focused on single particle-filled hollow sphere (PHS) and small PHSS, leaving a gap understanding of PHSS/steel sandwich composites. In this study a test rig was developed, and Design of Experiments and Response Surface Analysis were used to investigate the effects of sheet and core thickness (design parameters), filling ratio, and particle size (particle parameters) on the damping performance of PHSS/steel sandwiches. The results indicate that the design parameters have a significant influence on damping performance. The interaction between design and particle parameters also substantially affects damping. Minimizing particle size, increasing filling ratio, thinning the face layer, and thickening the core layer significantly improve structural damping. To address manufacturing tolerances, a finite element (FE) model-based optimization was developed to accurately determine PHSS material parameters. These parameters were used in an FE model of the PHSS-steel composite, with identified contact parameters minimizing measurement and simulation differences. The homogenized material model and the linear model using global damping parameters accurately reproduce the dynamic properties of the PHSS-steel sandwich composite in low vibration modes.

A new metasurface-assisted ultra-wideband window for a gyro-travelling-wave tube

A cylindrical-pillar-based new meta-surface-assisted ultra-wideband window is proposed, designed and simulated, in the present paper, for a wideband gyro-traveling-wave tube. The return-loss characteristics were analyzed by simulation in a high-frequency structure simulator to calculate the bandwidth at an allowable return loss of −17 dB and the center frequency of 44.42 GHz of the operating bandwidth of 32.10 GHz (28.31–60.47 GHz) which is 72.26% relative bandwidth for the operating circular TE0,1 mode. The results with respect to which parameters/characteristics were validated within 5% against those obtained using CST Microwave Studio. The sensitivity analysis was also carried out to obtain the manufacturing tolerances. Interestingly, an improvement of 8.03% (from 64.23% to 72.26%) at an allowable return-loss of −17 dB was obtained in the proposed window over the bandwidth achieved in previously reported square-pillar with cylindrical-tip-based meta-surface-assisted window.

Design and performance study of a multiband metamaterial tunable thermal switching absorption device based on AlCuFe and VO2.

In this paper, we propose a multiband adjustable metamaterial absorption device based on a Dirac semimetal (BDS) AlCuFe and a thermally controlled phase-change material VO2. The absorption device has an axially symmetric structure, resulting in polarization-independent characteristics, and when VO2 is in a high-temperature metal state, ultra-high absorption rates and sensitives at frequencies of M1 = 2.89 THz, M2 = 7.53 THz, M3 = 7.97 THz, and M4 = 9.02 THz are achieved. Using a parameter inversion method, we calculated the impedance of the absorber, proving that it achieves impedance matching and produces perfect absorption in the resonance region. Additionally, we changed the physical and chemical parameters of the absorption device, demonstrating the device's excellent tunability and manufacturing tolerance. Furthermore, by lowering the temperature of VO2 to that of a low dielectric state, additional resonant peaks with ultra-high absorption rates at frequencies M5 = 5.62 THz, M6 = 7.16 THz, M7 = 7.64 THz, and M8 = 8.80 THz were obtained, broadening the absorption band of the device. Lastly, we investigated the detection sensitivity of the device by changing the external refractive index, resulting in a maximum sensitivity of 2229 GHz RIU-1. To sum up, the absorption device has great application potential in the fields of communication, sensing, temperature detection and photoelectric instruments.

Study on the Design Method of High-Resolution Volume-Phase Holographic Gratings.

Volume-phase holographic gratings are suitable for use in greenhouse gas detection imaging spectrometers, enabling the detection instruments to achieve high spectral resolution, high signal-to-noise ratios, and high operational efficiency. However, when utilized in the infrared wavelength band with high dispersion requirements, gratings struggle to meet the demands for low polarization sensitivity due to changes in diffraction performance caused by phase delays in the incidence of light waves with distinct polarization states, and current methods for designing bulk-phase holographic gratings require a large number of calculations that complicate the balance of diffraction properties. To overcome this problem, a design method for transmissive bulk-phase holographic gratings is proposed in this study. The proposed method combines two diffraction theories (namely, Kogelnik coupled-wave theory and rigorous coupled-wave theory) and establishes a parameter optimization sequence based on the influence of design parameters on diffraction characteristics. Kogelnik coupled-wave theory is employed to establish the initial Bragg angle range, ensuring that the diffraction efficiency and phase delay of the grating thickness curve meet the requirements for incident light waves in various polarization states. Utilizing rigorous coupled-wave theory, we optimize grating settings based on criteria such as a center wavelength diffraction efficiency greater than 95%, polarization sensitivity less than 10%, maximum bandwidth, and spectral diffraction efficiency exceeding 80%. The ideal grating parameters are ultimately determined, and the manufacturing tolerances for various grating parameters are analyzed. The design results show that the grating stripe frequency is 1067 lines per millimeter, and the diffraction efficiencies of TE and TM waves are 96% and 99.89%, respectively. The diffraction efficiency of unpolarized light is more than 88% over the whole spectral range with an average efficiency of 94.49%, an effective bandwidth of 32 nm, and a polarization sensitivity of less than 7%. These characteristics meet the performance requirements for dispersive elements based on greenhouse gas detection, the spectral resolution of the detection instrument is up to 0.1 nm, and the signal-to-noise ratio and working efficiency are improved by increasing the transmittance of the instrument.

Iterative control decoupling tuning for precision MIMO motion systems: A matrix update method

Control decoupling is the basic control step for precision MIMO (Multi-Input-Multi-Output) motion systems. After decoupling, the MIMO logical controlled plant can be diagonal dominant so that the control design for each DOF (Degree of Freedom) can be separately treated. However, due to the manufacturing tolerances and the assembling errors, the actual CoG (Center of Gravity) and actuator positions are inconsistent with the designed values. The nominal static control decoupling matrix is inaccurate, which significantly deteriorates the decoupling performance. To address the problem, this paper develops a matrix update based iterative control decoupling tuning method. Tuning with feedback control signals to achieve accurate tuning is its first distinct feature. By employing rigid-body model information to construct more accurate basis functions, fast tuning can also be achieved, especially for relatively low control bandwidth occasions. Differing from the feedforward compensation based iterative control decoupling tuning method, the matrix update method improves the dynamics of the logical controlled plant, does not increase the control complexity and is more robust to the inaccuracy of the model information. Experimental results on the short-stroke module of a precision motion stage which is the key subsystem of the lithographic projection lens testing system present significant control decoupling performance improvement (for example the peak value of the Rx-DOF servo error caused by the Z-DOF movement is reduced from 1.29 ×10−5 m to 3.19 ×10−6 m) after just two trials.

Design and first tests of the trapped electrons experiment T-REX.

Gyrotrons are essential for electron cyclotron resonance heating in fusion reactors, making efficient operation crucial for advancing fusion energy. Past experiments revealed instability issues due to trapped electrons in the magnetron injection gun (MIG) region, causing undesired currents and operational failures. To address this, tight manufacturing tolerances are required for the MIG geometry [Pagonakis etal., Phys. Plasmas 23, 023105 (2016)]. We present the initial findings of the trapped electrons experiment developed at the Swiss Plasma Center, designed to understand the physics of electron clouds in gyrotron MIGs. T-REX replicates MIG geometries, as well as their typical electric and magnetic fields, and it is supported by 2D particle-in-cell simulations with the FENNECS code [Le Bars etal., Phys. Plasmas 29, 082105 (2022); Le Bars, Ph.D. thesis, EPFL, Lausanne, 2023]. The setup includes two coaxial electrodes in a vacuum chamber atop a superconducting magnet, with a central electrode biased to negative DC voltages and an outer one at the ground, creating a radial electric field (1-2MV/m) and an axial magnetic field (B < 0.4T). This setup mimics Penning-Malmberg traps. We present the experimental device and first findings on current distribution and also a qualitative comparison with FENNECS simulations [Le Bars etal., Comput. Phys. Commun. 303, 109268 (2024)]. Planned diagnostics include optical emission spectroscopy, phosphor screen imaging, streak camera imaging, and potentially electric field distribution via the Stark effect. This research aims to enhance gyrotron performance and reliability in fusion energy systems.

Characteristics study of a dual-wavelength polarization filter based on gold-filled square lattice photonic crystal fiber

This study proposes a polarization filter based on gold-filled photonic crystal fiber (PCF) with a square lattice structure. Utilizing the finite element method (FEM), the filtering characteristics of the model were numerically simulated. The dispersion relation and loss characteristics of this structure were analyzed, and the optimal structural parameters were obtained through structural adjustments. Furthermore, the performance of the filter was evaluated under a 2% variation in manufacturing tolerances for gold film thickness (), air hole spacing (), and air hole diameters () and (). Results indicated that at the 1310 nm and 1550 nm communication windows, the confinement losses of the filter were 1354.6 dB/cm and 869.04 dB/cm, respectively, while the losses for the -polarization were merely 16.97 dB/cm and 0.98 dB/cm. When the filter length was set to 0.5 mm, the maximum extinction ratios (ERs) for the two windows reached 588.2 dB and 370.6 dB, and the filter bandwidth extended to 640 nm. Moreover, the characteristics of the filter under manufacturing tolerances were computed, revealing that the filter’s performance remained stable and feasible despite manufacturing errors. The proposed rectangular gold-coated PCF is anticipated to have broad applications in optical fiber communication and optical information processing.

Design and Manufacture of 30-Degree Projection Lens for Augmented Reality Waveguide.

A projection lens with a 30-degree field of view is developed for use in augmented reality (AR) glasses, including a waveguide combiner designed for a 0.35-inch LCoS panel. The entrance pupil diameter of the lens is 14 mm and the lens has an effective focal length of 16.443 mm; an F-number of 1.175. This paper has four key issues: optical projection lens design, lens manufacturing and assembly tolerance analysis, projection lens resolution testing, and AR glasses system resolution testing of panel images projected by the projection lens. After lens manufacture, the lens was tested, achieving a central field image quality of 57 cycles/mm, an angular resolution of 33 pixels per degree (PPD), a 0.7 field image quality of 40.3 cycles/mm, and an angular resolution of 23 pixels per degree (PPD). Imaging performance testing based on a diffraction-type waveguide shows a resolution of 57 cycles/mm in the center area and an angular resolution of 33 PPD.

Chirped grating for TE-five/TM-three reflective distribution feature

This research expounds on a novel reflective chirped grating, characterized by its differentiated functionality under various polarization modes. Under perpendicular incidence, this intricately grating produces a quintuple-channel diffraction output of the 0th, ±1st, and ±2nd orders in transverse electric (TE) polarization and a triple-channel diffraction output of the 0th and ±1st orders in transverse magnetic (TM) polarization. Both polarization modes exhibit excellent overall diffraction efficiency and uniformity. At an incident wavelength of 1550 nm, the diffraction efficiencies for the 0th, ±1st, and ±2nd orders under TE polarization are 20.16%, 19.27%, and 20.25%, respectively. Simultaneously, under TM polarization, the efficiencies for the 0th and ±1st orders are 31.79% and 31.57%, respectively. Grating parameters were meticulously derived using the finite element method (FEM) and subsequently corroborated through rigorous coupled-wave analysis (RCWA) to ensure superior grating accuracy. The study also exhaustively analyzes the manufacturing tolerances and robustness of the grating, affirming its practical applicability and effectiveness in practical applications. The dual-function grating splitter proposed in this paper enables the implementation of multiple functionalities within simple setups, suitable for applications requiring varied beam splitting. As photonic systems and fiber technology evolve, the potential applications of dual-function reflective splitters in these fields are increasingly highlighted.

Characterization of fatigue crack growth in directed energy deposited Ti-6Al-4V by marker load method

Fatigue crack growth properties of materials are crucial for evaluating damage tolerance in additive manufacturing (AM) metallic structures. However, the unique microstructures and defects of AM materials result in highly complex fatigue crack growth behaviors. Currently, there is a lack of systematic fatigue crack growth rate measurement methods specifically targeting this characteristic. Therefore, taking directed energy deposited Ti-6Al-4V titanium alloy as the object of the study, fatigue crack growth tests were conducted in three orthogonal build orientations of the material using marker load method. Additionally, the visual measurement and compliance methods were also employed to measure fatigue crack growth rates, and the anisotropy of fatigue crack growth property was analyzed. Subsequently, anisotropic fatigue crack growth behaviors were characterized by optical microscope, scanning electron microscope, confocal microscope, and electron backscatter diffraction, suggesting that the microstructure is the primary factor affecting overall fatigue crack growth. Furthermore, nanoindentation tests were conducted to obtain the micromechanical properties within and among columnar grains in different build orientations, clarifying the homogeneity and anisotropy of mechanical properties. Finally, a fatigue crack growth rate measurement method based on marker load method was established, and the advantages of this method in AM materials and structures were summarized by comparing the results with those obtained using these two mature methods.

Determination of Acceptable Ranges of Asymmetric Manufacturing Tolerances based on Structural Analysis for a Drone Wing

Determination of Acceptable Ranges of Asymmetric Manufacturing Tolerances based on Structural Analysis for a Drone Wing

Improved buckling reduction factors for existing steel columns accounting for different imperfections

The presented research aims to develop global and local buckling reduction factors that account for the impact of amplified geometrical imperfections and the variability of residual stresses on the buckling resistance. The improved buckling coefficients might be necessary for analysing existing structures, which often have larger imperfections than the manufacturing tolerances. Advanced GMNI analyses are employed to investigate pure local and global buckling resistances of I- and box-section columns, incorporating accurate non-amplified local and global imperfections. A parametric study is conducted to systematically investigate the impact of enlarging the imperfection factors and varying residual stresses. The local and global buckling formulas specified in EN1993-1-5 and EN1993-1-1 are calibrated against laboratory test results and/or GMNI analyses to account for the influence of imperfections and residual stresses. Similar calibration process is performed within the current study by modifying the imperfection factor α in the buckling formulas taking into account the enlarged imperfection magnitude. The result of the current study enables designers to refine the estimation of the buckling capacity when actual imperfections and residual stresses deviate from those employed during the design phase.

Analytical Solution to Estimate the Effect of Underlying Tunnel Excavations on the Existing Tunnel

ABSTRACTThe tunneling underlying inevitably leads to the displacement of adjacent soil, greatly influencing the deformation of the tunnel above. Most theoretical studies primarily concentrate on analyzing the mechanical equilibrium of individual tunnel sections, ignoring the energy generated by the system during tunnel deformation. Based on this, in view of the energy relationship, the overlying tunnel's deformation is simulated by using the Rayleigh–Ritz method. Further, its potential energy equation can be established based on the Vlasov foundation. The corresponding energy variational solution is solved according to the minimum potential energy principle, leading to an analytical solution for the shield tunneling‐induced overlying tunnel's response. The efficacy of the suggested method is verified by contrasting it with centrifuge experiments and field case studies derived from prior studies. Relative to the Winkler foundation model, which deviated from the suggested approach, the results derived from the suggested method show a closer correlation with the collected measurement data. Further parameter studies show that the vertical clearance and skew angle between two tunnels, the volume loss rate, and elastic modulus are significant factors affecting the tunnel behaviors due to tunneling underneath. The suggested theoretical model can be applied to forecast potential risks that an existing tunnel may encounter during the excavation of a new tunnel underlying in similar engineering projects.

Polarization-independent and high-efficiency 2D dielectric transmission grating under Littrow incidence

In this paper, a transmission two-dimensional (2D) all-dielectric grating with cuboid arrays is proposed, which has high diffraction efficiency and good polarization independence under Littrow mounting conditions at an incident wavelength of 780 nm. The optimization results indicate that when the incident wavelength is 780 nm, the diffraction efficiency of the (−1, 0) order of transverse electric (TE) and transverse magnetic (TM) polarizations can reach 98.62% and 98.23%, respectively, with the polarization-dependent loss (PDL) of 0.017 dB. To the best of our knowledge, high-efficiency polarization-independent 2D transmission grating with a simpler and more effective structure is proposed for the first time, which demonstrates significant enhancements in bandwidth and manufacturing tolerances while maintaining high diffraction efficiency. The results suggest that the grating has great potential for applications in high-precision displacement measurements such as grating interferometers.

Experimental Determination of Influences of Static Eccentricities on the Structural Dynamic Behavior of a Permanent Magnet Synchronous Machine

In electrified vehicles, the masking noise behavior of internal combustion engines is absent, making the tonal excitation of the electric machine particularly noticeable in vehicle acoustics, which is perceived as disturbing by consumers. Due to manufacturing tolerances, the tonal NVH characteristics of the electric machine are significantly influenced at wide frequency ranges. This paper presents a systematic exploration of the influence of static eccentricity as one manufacturing tolerance on the NVH behavior of Permanent Magnet Synchronous Machines (PMSMs). The study utilizes a novel test bench setup enabling isolated variations in static eccentricity of up to 0.2 mm in one PMSM. Comparative analysis of acceleration signals reveals significant variations in the dominance of excitation orders with different eccentricity states, impacting critical operating points and dominant frequency rages of the electric machine. Despite experimentation, no linear correlation is observed between increased eccentricity and changes in acceleration behavior. Manufacturing eccentricity and deviations in rotor magnetization are discussed as potential contributors to the observed effects. The findings emphasize static eccentricity as a critical parameter in NVH optimization, particularly in electrified powertrains. However, the results indicate that further investigations are needed to explore the influence of eccentricities and magnetization deviations on NVH behavior comprehensively.

Maximum temperature of steel bridges due to multiple under-bridge fire sources

In this study, an analytical model was developed and predictive equations were proposed to estimate the maximum temperature of steel bridges in the event of a fire originating from complex facilities beneath the bridge. Based on statistical data, a representative shape of steel bridges in South Korea was selected. A representative Heat Release Rate (HRR) curve for the complex facility was selected, and a parametric study was conducted, including variables such as Heat Release Rate Per Unit Area (HRRPUA), fully developed time, vertical clearance, and the area of the complex facility. Through correlation analysis, key parameters influencing the maximum temperature in steel bridges were examined. Based on the results, both linear and non-linear temperature prediction equations were suggested. The non-linear equation demonstrated higher predictive performance than the linear equation. This study provides foundational data for enhancing the accuracy of fire analysis methods and temperature prediction models for steel bridges.

Statistical Characterization of Emitter Fabrication over Electrospray Array Thruster

A method for characterizing the variance in fabrication of emitters and extractors in a porous conical electrospray array thruster is presented. Coherence scanning interferometry is used to produce topographic maps of 543 of 576 sites within the array. The emitter and extractor geometries, features of size a few hundred micrometers, are modeled as a spherically capped cone recessed from a circular aperture. Regressing this model against the topographic maps yields a set of salient parameters that describe the geometry of a site, including the tip radius and height of the emitter and its offset from the extractor aperture. Statistics over the emitter geometries are computed, which represent manufacturing tolerances. It is found that key parameters like the emitter tip radius are highly variable (mean 25.8 μm and standard deviation 20.9 μm), highlighting the stochastic nature of the manufacturing process. Correlations between the tip radius and emitter height indicate that this variability arises from blunting of the emitters during fabrication, and the observation that emitters are shorter than nominal is explained by an increase in effective cutting diameter of the tools. Further analysis indicates that determining the mean emitter tip radius of the entire population within 5% error requires over 300 individual emitter measurements. These results indicate that accurately quantifying emitter variability at scale requires rigorous and extensive analysis, and the implications of this emitter variability for device performance and design are discussed.