Fiber Position Research Articles

Warping and springback reduction in bending of U-profiles through partial heating over the cross-section

Bending of profiles is challenging due to the high stiffness and possible deformations in the process. Especially bending of profiles with asymmetric cross-section regarding the force initiation axis leads to unwanted warping of the bent profile. This warping results from the position difference between the force initiation axis and the shear center, implying torsion moments on the profile. To prevent profile warping the use of shape-bound tools or a change of the force initiation axis position are common practices, though these methods reduce the flexibility of the process. A new method to prevent profile warping during bending is the use of partial, cross-sectional heating. Due to thermal softening in one profile area a quasi-symmetric bending case is achieved, which changes the position of the stress-free fiber and thus reduces the torsion moment. In this work, the warping and springback behavior of partially heated U-profiles consisting of S500MC steel after a three-roll push bending process is investigated using experimental methods. Through partial heating of one profile area to up to 600°C, a warping reduction of 83 % and a springback reduction of 69 % were achieved.

Rigidity of Circular Plates with Radial Ribs, Placed on One Side, Neglecting the Influence of Welding Seams. Nerves with Constant Thickness and Height Along the Entire Length

Abstract The present study refers to a plane circular plate, provided with equidistant radial ribs, placed on one side (fig. 1), these having the same geometry of the cross section (thickness and height) along their entire length (fig.2). There is a change in the position of the neutral fiber of the ribbed plate and also in its bending rigidity, along the radius of the plate, in different cases.

Retracted: Water Transport in GDL Microstructures of Nonuniform Fiber Diameter Arrangement

In proton exchange membrane fuel cells (PEMFCs), the gas diffusion layer (GDL) plays an important role in the transport of reactants, water, heat, and electrons. Microstructure manipulation of porous media via a nonuniform fiber diameter arrangement could potentially be used to improve water transport behavior in GDLs. A numerical modeling approach is used to simulate GDL microstructures with uniform and nonuniform fiber diameters. The reconstructed porous microstructures’ water saturation and porosity are compared. The simulations of three-dimensional (3D) two-phase flow volume of fluid (VOF) models were completed on the OpenFOAM platform using the finite volume method (FVM). Simulations demonstrate that by adopting a nonuniform microstructural fiber diameter design, both porosity and water transport behaviors can be altered. As a result of the nonuniform fibrous arrangement, the ability to improve GDL performance by controlling water transport and porosity is possible. The results indicate that by manipulating the GDL microstructure, additional water pathways can be created, resulting in slightly increased water saturation. We propose that water transport can be improved by microstructural manipulation of the GDL, specifically by optimizing the arrangement and position of nonuniform fibers.

Transfer learning and generalization of a neural-network-based multimode fiber position and imaging sensor under thermal perturbations

Fiber specklegrams created through multimode fibers have been utilized in a wide variety of imaging and sensing applications. In a practical environment it is useful to have a system that, after an initial calibration, produces reconstructed images and tracks the current state of relevant physical quantities such as the position or shape of the fiber. Neural networks provide the ability to extract and generalize the information contained in the specklegrams in order to produce accurate predictions even when experimental conditions are altered from their calibration state. Using a single-layer fully-connected network, we demonstrate the capability to perform robust image reconstruction under discrete position and temperature perturbations, as well as to classify the fiber position for different reconstructed images and thermal perturbations. On a test set with the same thermal state and bend configuration as for the training data, the network achieves near-perfect reconstruction and classification accuracy. Further, our neural network can generalize its position classification and image reconstruction capabilities across a 30 °C temperature perturbation with a high degree of accuracy, providing measurements that are robust to these variations, as well as calibrations that are stable and effective for several days. Moreover, using a low-temperature training set to initialize network weights, transfer learning is demonstrated by re-calibrating on a small set of data and shown to significantly improve robustness and performance of the imaging system on a high-temperature perturbation test set.

Field calibration for multidirectional spectroradiometers

A mobile calibration system for a multidirectional spectroradiometer (MUDIS) to transfer the absolute radiometric calibration from the laboratory to the location of the outdoor-measurement (field calibrator) has been developed. The main part of the calibration system comprises an aluminium sphere with a diameter of 40 cm, mounting adapters and a ventilation system. The MUDIS device is capable of measuring spectral radiance from 320 to 600 nm in 113 different directions simultaneously within 1 s. When repeating radiance measurements inside the mobile field sphere, the relative standard deviation (RSD) for wavelengths between 320 and 600 nm is less than 1.8% (320 nm) for all directions with minimum RSD of 0.6% at 382 nm. The reproducibility depends not only on the wavelength but also on the individual fibre position on the hemispherical input optics, with maximum of 4.5% RSD, but most directions show a lower deviation. On average, the RSD for the channels is less than 0.9%. The calibrator enables measurements of the spectral radiance with less uncertainty than with the previous indirect calibration method, which uses measurements of a scanning reference array spectroradiometer.

Evaluation of the geometrical parameters of collector mesh on the fog collection efficiency

Fog collectors have gained increasing attention as an efficient solution to overcome the water scarcity concerns in arid and semiarid environments. Besides the rapid advances made in various collector designs, the role of geometrical characteristics of the fog collector meshes is not fully understood. Therefore, the main objective of the present research is to address this issue and investigate the effects of textile features on the efficiency of conventional meshes which has not been discussed in previous works. The collection efficiencies of various conventional structures (plain-woven, plain-knitted, and 3-D spacer) with different characteristics (fiber diameter, fiber spacing, fiber arrangement, shading coefficient, and test direction) were investigated using a custom-made fog collecting device. The weight of collected water over time and the onset time were measured to assess the performance of different samples. Moreover, a simple simulation of a plain-woven structure was developed using Computational Fluid Dynamics (CFD) to perform further analysis. The results revealed that in the woven structure, the collection efficiency was improved by changing the shading coefficient to an optimum value and simultaneous decreasing fiber diameter. In the spacer fabrics, the position and arrangement of the spacer fibers posed considerable effects on the collection efficiency. 3-D spacer meshes showed highest value of collection efficiencies and onset time in comparison to the other examined meshes. The results of simulation of woven structures were also validated by comparing computed and measured collection efficiencies.

Landmark movement trajectory: A simple reference to understand the dominant muscle contraction in a dynamic smile expression

Insight into the roles of perioral muscles play in smiling is essential to the relevant esthetic and reconstructive treatment. This study analyzed specific landmarks' movement trajectories to understand the dominant muscle activity in smiling. Sixty volunteers (aged 18-45 years) were included, and standardized frontal view images were obtained by three-dimensional photogrammetry. Each image sequence frame was referenced and superimposed onto the neutral image. Six surface landmarks were digitized on each frame to form the entire movement trajectories from resting to maximal smile. The perioral muscles were divided into different groups according to the inserting position of muscular fibers and the contracting direction. The movement paths of landmarks were analyzed to find the major muscle groups involved. The dominant muscle groups throughout smiling were successfully identified by landmark trajectory analysis in all 60 volunteers. Zygomaticus major was the dominant force for the beginning of most smiles. Apart from the zygomaticus major, other perioral muscles played a dominant role throughout smile expression, including levator anguli oris, buccinator and risorius, depressor anguli oris, and the upward muscle group of the upper lip were all identified. Besides, a notable high percentage of smiles presented a mixed pattern, indicating the cooperation of several muscle groups during smiling. Landmark movement trajectory provides a simple reference to understand the dominant perioral muscles in smiling. It can help surgeons get more information for the dynamic treatment of smiles.

Low voltage optical fiber positioner robot based on minimum inductance hollow cup motors

With the further transformation of The Large Sky Area Multi-Object Fiber Spectroscopic Telescope, the new generation of fiber positioner robot chooses a 4 mm hollow cup motor with minimum phase inductance. Because the load of the fiber positioner robot is constant and the inertia of the motor is very small, an open loop positioning control method based on Space Vector Pulse Width Modulation is proposed, and the specific open loop parameters are directly tuned by relevant experimental strategies. The critical factors of the open loop driving mode are discussed in detail from four aspects: subdivision, fundamental frequency, wave generation mode and peak current. Based on the actual fiber positioner robot, the hardware driver and assessment platform are built. The positioning tests show that the method proposed is practical and effective, and meets the precision positioning demand of the new generation optical fiber positioner robot.

Design of a dielectric chiral micro-structured fiber applied in a fiber optic current sensor

During the process of drawing the screwed silicon-based fiber, there will be a uniform rotation rate in it, which results in a decrease of circular polarization degree of the fiber. In order to solve this problem, we presented a kind of dielectric chiral micro-structured fiber owing higher circular polarization degree. Meanwhile, the air holes of fiber will collapse during the progress of fiber drawing, which will change the position of air holes. As a result, the circular polarization degree of the fiber decreases. In order to reduce the change of circular polarization degree caused by the position fluctuation of the air holes, a highly symmetrical micro-structured dielectric chiral fiber was firstly designed in this paper. Then, we established a physical error model considering the fluctuation of the air holes’ position which was the design basis of the air holes’ position, size, and chiral parameters of the specific microstructure fiber. Next, comparing the circular polarization degree S3 of screwed silicon-based fiber and that of the dielectric chiral micro-structured fiber by simulation, it was proved that the dielectric chiral micro-structured fiber we designed has a higher circular polarization degree S3 than that of screwed silicon-based fiber. Finally, we applied the fiber designed in this paper as the fiber sensing coil in a fiber optic current sensor, and compared it with the fiber optic current sensor utilizing the original fiber sensing coil in ratio error. The simulation results proved that compared with the original system, dielectric chiral micro-structured fiber utilized as the fiber sensing coil in a fiber optic current sensor will decrease the ratio error by an order of magnitude in theory.

Number and Distribution of Fiducial Fibers in a Spectroscopic Survey Telescope

To date, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has been in operation for 12 yr. To improve the telescope's astronomical observation accuracy, the original open-loop fiber positioning system of LAMOST is in urgent need of upgrading. The upgrade plan is to install several fiber view cameras (FVCs) around primary mirror B to build a closed-loop feedback control system. The FVCs are 20 m from the focal surface. To reduce a series of errors when the cameras detect the positions of the optical fibers, we designed fiducial fibers on the focal surface to be fiducial points for the cameras. Increasing the number of fiducial fibers can improve the detection accuracy of the FVC system, but it will also certainly reduce the number of fiber positioners that can be used for observation. Therefore, the focus of this paper is how to achieve the quantity and distribution that meet the requirements of system detection. In this paper, we introduce the necessity of using fiducial fibers, propose a method for selecting their number and present several methods for assessing the uniformity of their distribution. Finally, we implement particle swarm optimization to find the best distribution of fiducial fibers.

An experimental investigation on the influence of temporary plugging fibers and particles on the fracture conductivity

After temporary plugging and fracturing, some of the difficult-to-degrade temporary plugging agents (fibers and particles) in the fractures will affect the conductivity and ultimately affect the rate of oil production. However, the influence law and mechanism of the fibers and particles on the fracture conductivity are still unclear. In order to solve this problem, based on the FCS-842 fracture conductivity test system, the influence law and mechanism of fibers and particles on the fracture conductivity were investigated. The experimental results show that the larger particles support the fracture wall when particles are contained, resulting in higher conductivity. Further studies have found that high fibers content will lead to a significant decrease in the fracture conductivity under low closure pressure. However, high particles content means high fracture conductivity. The placement position of fibers and particles also affects the fracture conductivity. When the pressure is 10 MPa, the conductivity is maximum when the fibers and particles are placed at the fracture opening. Then, when the pressure increases, the conductivity drops sharply by about 88%. When the closure pressure is ≥ 20 MPa, the conductivity is the highest when the fibers and particles are placed at the fracture tip, followed by the middle of the fracture and the smallest at the fracture opening. After analysis, at the fracture opening, the high flow velocity forms a fiber “Barrier” in the fracture, which makes the conductivity decrease rapidly. In the middle of the fracture, the “Dot-net” structure composed of fibers and particles makes the fracture conductivity decrease, but the decrease amplitude and speed are small. At the fracture tip, the lower flow rate makes the fibers and particles form “Clusters”, and the large flow channel between the clusters makes the fracture conductivity higher than the former two. When the fibers and particles are evenly laid, the fibers are easy to form clusters with the particles to block the flow channel, reducing the fracture conductivity.

Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

In the closed-loop detection system of the LAMOST, the lens of the fiber view camera system must focus the end of the optical fiber to accurately acquire the fiber position. It is difficult to evaluate the fibers image with a very small proportion of the image with the traditional autofocus algorithm, whether it is recognition of the front illuminated by the fiber ceramic ferrules, or the light-emitting spot of the fibers in the black background, that is, the recognition of the back illumination of the fibers. In this paper, we propose an autofocus determination method for the LAMOST closed-loop control under front and back illumination conditions. Under the condition of front illumination, to greatly reduce the calculation time, the system first pre-recognizes the focusing target through the Faster R-CNN and then uses an optimized contrast algorithm to evaluate the image definition of the corrected focusing target ROI. Then, the algorithm is compared with Tenengrad gradient and Laplacian gradient calculations using the Sobel operator and Laplacian operator in OpenCV. The results show that this method takes only one-ninth of the time required by the other methods to obtain the same accuracy. Under the condition of back illumination, we use the average number and average brightness of spot pixels as the evaluation basis of image sharpness. This method can complete the evaluation of image sharpness in the process of spot recognition and provide initial data for the subsequent detection for closed-loop control. The focus accuracy of the camera is of great significance for thousand-fiber metrology, which will have an important influence on the accuracy of astronomical observations. These focusing methods not only play an important role in the closed-loop control of the LAMOST but also apply to the focusing of closed-loop detection systems of other multi-target optical fiber spectral astronomical telescopes.

Setting Up and Assessing a New Micro-Structured Waveguiding Fluorescent Architecture on Glass Entirely Elaborated by Sol-Gel Processing.

Channel waveguides with diffraction gratings at their input and output for light injection and extraction, respectively, are extensively exploited for optical and photonic applications. In this paper, we report for the first time on such an architecture on glass entirely elaborated by sol–gel processing using a titanium-oxide-based photoresist that can be imprinted through a single photolithography step. This work is more particularly focused on a fluorescent architecture including channel waveguides doped with a ruthenium-complex fluorophore (tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II), Rudpp). The study demonstrates that this original sol–gel micro-structured architecture is well adapted to efficient channel waveguide/diffraction grating coupling and propagation of the fluorescence excitation and emission signals in the core of the channel waveguide. It demonstrates, in particular, a relatively large tolerance of several degrees in the angular injection fiber positioning and an important axial and vertical fiber spatial positioning tolerance of more than 100 µm at the Rudpp emission wavelength. The measurements also indicate that, in the conditions tested in this work, a Rudpp concentration of around 0.1 mM and a channel waveguide length of 2 to 5 mm offer the best trade-off in terms of excitation signal propagation and emission signal detection. This work constitutes a promising preliminary step toward the integration of our architecture into a microfluidic platform for fluorescence measurement in a liquid medium and waveguiding configuration.

Acoustic emission-based damage analysis of steel fibre reinforced concrete in progressive cyclic uniaxial tension tests

Although direct tension tests (DTT) on steel fibre reinforced concrete (SFRC) are difficult to perform, they are of interest because of the uniform tensile stress distribution. Therefore, this paper reports on 31 DTT under monotonic or progressive cyclic loading. All test specimens are notched and continuously monitored with acoustic emission (AE) sensors and clip gauges. The aim is a better understanding of the (cyclic) uniaxial tensile behaviour of SFRC by AE-based damage monitoring. The research shows the importance of fibre distribution and orientation on the load–displacement behaviour. Micro-cracking is detected in the loading cycle prior to fracture by means of AE analysis. Failure mode analysis of the AE signals shows more than 99% mode I damage and indicates the onset of macro-cracking. Localisation of AE events validates the fibre position, the damage stages and the main crack position. Based on AE analyses, differences in damage development are identified even when the post-peak behaviour of the DTT specimens is similar. As such, the obtained experimental data set has an added value to the limited existing research of AE monitoring during DTT on SFRC.

Influence of Reynolds number on the dynamics of rigid, slender and non-axisymmetric fibres in channel flow turbulence

We investigate experimentally the dynamics of non-axisymmetric fibres in channel flow turbulence, focusing specifically on the importance of the fibre size relative to the flow scales. To this aim, we maintain the same physical size of the fibres and we increase the shear Reynolds number. Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. Fibres are slender – length to diameter ratio of 120 – rigid, curved and neutrally buoyant particles and their shape ranges from low curvature – almost straight fibres – to moderate curvature. In all cases, fibre size remains small compared with the channel height (${\leqslant }1.5\,\%$). Three-dimensional and time-resolved recordings of the laser-illuminated measurement region are obtained from four high-speed cameras and used to infer fibre dynamics. With the aid of multiplicative algebraic reconstruction techniques, fibre position, orientation, velocity and rotation rates are determined. Our measurements span over the half-channel height, from wall to centre, and allow a complete characterisation of the fibre dynamics in all regions of the flow. Specifically, we measure fibre preferential distribution and orientation. We observe that the fibre dynamics is always influenced by their curvature. Through a comparison between measurements of the near-wall dynamics of the fibres and the near-wall dynamics of the flow, we identify a causal relationship between fibre velocity and orientation, and the near-wall turbulence dynamics. Finally, we have been able to provide original measurements of the tumbling rate of the fibres, for which we report the influence of fibre curvature. We underline that our measurements confirm previous findings obtained in numerical and experimental works.

Recent Advances in Dental Sensors

There have been advancements in sensing technologies in dentistry. Clinical applications in dentistry including Diagnosis as well monitoring disease and health in dental tissues are made easy with the advanced technologies in imaging and sensing tools. These recent advances in optical sources and detectors have unique applications including non-destructive testing, high speed and cost-effective electronic circuits, and novel signal processing methods. Some of the recent advances include optical coherence tomography, occlusal stabilization splint with stress-sensor system for bruxism, periodontal probe based on the fluorescent fiber position sensor, dental implantable temperature sensor for real time diagnosis of infectious periodontal disease, diamond probe/ perio2000 system, dental pulse oximeter with customized sensor holder, periodontal probe based on the flouroscent fiber position sensor etc.

Wide Bandwidth Silicon Nitride Strip-Loaded Grating Coupler on Lithium Niobate Thin Film

In this research, a vertical silicon nitride strip-loaded grating coupler on lithium niobate thin film was proposed, designed, and simulated. In order to improve the coupling efficiency and bandwidth, the parameters such as the SiO2 cladding layer thickness, grating period, duty cycle, fiber position, and fiber angle were optimized and analyzed. The alignment tolerances of the grating coupler parameters were also calculated. The maximum coupling efficiency and the −3 dB bandwidth were optimized to 33.5% and 113 nm, respectively. In addition, the grating coupler exhibited a high alignment tolerance.

Realization of precise positioning of fiber positioning unit R mechanism based on Preisach model

Realization of precise positioning of fiber positioning unit R mechanism based on Preisach model

Metrological Traceability of High Polarization Extinction Ratio (PER) Based on Precision Coaxial Rotating Polarization-Maintaining Fiber

This article proposes a metrological traceability method for polarization extinction ratio (PER) ranging from 0 up to 70 dB, while the common method is limited to 50 dB. A precision alignment coupling point is designed and manufactured using two polarization-maintaining fibers (PMFs). By rotating one of the PMFs to change the axis-alignment angle and to control the distribution of light energy in the fast and slow axis, a traceability chain from the PER to the rotation angle is established. With extremely low-stress clamping of the PMF, 5-D precision adjustment of the fiber position, and precision coaxial rotation in the order of arc seconds, accurate and controllable generation of any PER in the range of 0–70 dB can be achieved. A high PER traceability system is designed and built, which is successfully used in the traceability of PER to the angle of circumference. The expanded uncertainty ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k = 2$ </tex-math></inline-formula> ) in the ranges of 0–30 dB, 30–50 dB, and 50–70 dB is 0.01, 0.06, and 1.20 dB, respectively. Controlled generation of high PER (50–70 dB) with metrological traceability is realized for the first time as far as we know.

Thermally drawn rechargeable battery fiber enables pervasive power

The increasing demand for mobile computing, communications, and robotics presents a growing need for suitable portable power solutions in non-flat customized electronic devices. Fibers as fundamental building blocks of fabrics and 3D-printed objects provide unique opportunities for developing pervasive multidimensional power systems. The characteristic small diameter (<10−3 m) and high aspect ratios (>106) of fibers and expansion of fibers into 2D and 3D power systems necessitate ultra-long lengths to meet the energy specifications of portable electronic systems. Here, we present a Li-ion battery fiber, fabricated for the first time using a thermal drawing method which occurs with simultaneous flows of multiple complex electroactive gels, particles, and polymers within protective flexible cladding. This top-down approach allows for the production of fully-functional and arbitrarily long lithium-ion fiber batteries. The continuous 140 m fiber battery demonstrates a discharge capacity of ∼123 mAh and discharge energy of ∼217 mWh. The scalability and material tunability of these fibers position them for use in varied non-planar electronic systems, including a 1D-flexible electronic fiber, a 2D-large-scale machine woven electronic fabric (∼1.6 m2), and a 3D-printed structural electronic system. The fiber battery satisfies the requirements of portable electronics systems as it is machine washable, flexible, usable underwater, and fire/rupture-safe. We have demonstrated the powering of a submarine drone, LiFi fabric, and flying drone communication through different rechargeable fiber battery schemes, which paves the way for the emergence of the pervasive battery-powered electronics.