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Bushing plays a significant role in insulation and mechanical support for power transformers. Its working state is closely related to the reliable operation of power transformers. To overcome the electromagnetic interference and security risks during sensor installation, a Sagnac interference optical technique for partial discharge (PD) detection is proposed in this paper. By establishing a simulation model of the sensing structure, it is verified that output signal amplitude varies periodically with the length of sensing and delay fibers. Moreover, the output value decreases with increasing probe radius. The results show that a delay fiber of 1.5 km, a sensing fiber of 3 m, and a bending radius of 5 mm are optimal parameter combinations to detect PD in a 72.5 kV defective bushing. In addition, consistent detection waveforms induced by both internal and external defects are obtained by the optical sensor and high frequency current transformer (HFCT) simultaneously, then the effectiveness of the optical sensor on detecting PD signals for bushing is verified. It is of great help to carry out online monitoring of bushing insulation defects through optical non-destructive installation.

Omnidirectional steerable forceps in keyhole procedures provide significant advantages in assisting medical practitioners with better motion coordination, improved dexterity, precision control, and reachability. However, most existing forceps lack the sense of interactive proprioception, imposing physical and cognitive challenges to the medical practitioners during manipulation. Herein, we report handheld steerable surgical forceps with two degrees-of-freedom equipped with skin-like soft stretchable strain sensors to determine the orientation and improve the perception. The performance of omnidirectional forceps integrated with sensory skin (OFISS) is characterized. Due to the reduced number of mechanical parts in the forceps by virtue of parallel continuum joints, the direct translation of motion from the proximal to the distal end is achieved. The distal parallel flexible joint enables a bending angle up to 40 and a bending radius of 7.5 mm. The hydrogel-based silver nanowire sensors mounted on the forceps like a stretchable skin show a maximum gauge factor of 11.8 under 80% strains. A mathematical model is developed to determine the tooltip orientation. The developed model validated with visual tracking shows an accuracy of 9097% for angular displacements up to 30 in all directions. Assisting medical practitioners in a clinical environment is demonstrated in a cadaveric setting by providing proprioceptive information of the tooltip through OFISS.

We numerically reveal the feasibility of designing multi-core fibers (MCFs) with the simple step-index (SI) profile within the standard 125- μ m cladding diameter. We show that the standard cladding diameter enables us to incorporate five identical cores for C-band operation, and the number of cores can be further increased with the heterogeneous core arrangement. We then propose a novel method of allocating the non-identical cores in heterogeneous MCFs (Hetero-MCFs), where the crosstalk (XT) and critical bending radius ( R pk) are improved comparing to that of Hetero-MCFs designed by the conventional method. These new types of step-index MCFs (SI-MCFs) with standard cladding diameter have potential application in the space-division multiplexing (SDM) systems.

Flexible memory devices are promising for information storage and data processing applications in portable, wearable, and smart electronics operating under curved conditions. In this work, we realized high-performance flexible ferroelectric capacitors based on Hf0.5Zr0.5O2 (HZO) thin film by depositing a buffer layer of Al2O3 on polyimide (PI) substrates using atomic layer deposition (ALD). The flexible ferroelectric HZO films exhibit high remnant polarization (Pr) of 21 µC/cm2. Furthermore, deterioration of polarization, retention, and endurance performance was not observed even at a bending radius of 2 mm after 5,000 bending cycles. This work marks a critical step in the development of high-performance flexible HfO2-based ferroelectric memories for next-generation wearable electronic devices.

Flexible electronics are becoming more and more widely used in all fields, such as wearable devices, flexible displays, flexible sensors, and so on. Therefore, it is essential to investigate the reliability of flexible electronics under various loading conditions. In this article, the mechanical and electrical behavior of printed conductors was tested under reciprocating adaptive curvature flexure bending. The silver-ink conductors of different widths were screen-printed on polyimide (PI) and polyethylene terephthalate (PET) substrates and served as the samples. Through the tests, the resistance of the conductors was measured by a four-wire method continuously. The tests were carried out under different gap distances and moving ranges. Besides the tests, SEM imaging was also performed to understand the microstructure change of the printed conductor before, during, and after the tests. Finite-element simulations were performed to track the strain history of specific locations of the printed conductor. Finally, a two-stage process of resistance increase was identified in the reciprocating adaptive curvature flexure test. The resistance change of the conductors under different loading conditions was determined. The parameters that affect the resistance change were also figured out. Cracks and delamination in the printed conductor were observed and related to the resistance increase phenomena under small tensile and compressive bending radius, respectively.

During manufacturing thin-walled tubes using free bending forming (FBF) technology, defects such as wrinkling, cracking, and cross-section distortion are easy to exist due to various forming parameters' direct and indirect influence, which seriously influences the forming quality of the rectangular tubes. Thus, in this study, the finite element (FE) modeling of thin-walled AA6061-T6 rectangular tubes manufactured by FBF technology was accomplished and verified through experimentation. Moreover, the influence of different parameters on the deformation behavior of the rectangular tubes was systematically investigated using FE modeling. The results showed that the maximum thickness changing rate and the cross-section distortion appeared once the bending die moved to the maximum eccentricity (Umax). Besides, with the increase of yield strength-Young's modulus ratio (σs/E), thickness (t0), fillet radius (Rf), clearance (Δc), friction coefficient (f), and chamfer radius of the guider (Rc), the thickness changing rate and the cross-section distortion decrease, while the bending radius enlarges simultaneously when the parameters are set within reasonable limits. Unlike the above parameters, with the improvement of the axial feeding speed (Vf), the thickness changing rate declines while the fluctuation of bending radius is not significant. Under the joint action of the axial force PL, the structural characterization of the rectangular tube and the dies of constraints, the thinning of the outer wall and the web distortion are inhibited, and the variation amplitude of them is much smaller than that of thickening of the inner wall and flange distortion during the free bending process.

Thermal power plants are users of high water consumption, and the water consumption of cooling towers accounts for more than half of the total water consumption of the whole plant. Therefore, water saving of cooling towers is the key to water saving in thermal power plants. Wave-plate demister as a component of cooling tower influences the performance of entire system. Demister realizes the collection of liquid droplets with the penalty of extra pressure loss. Curved bends and drainage hooks are proposed as enhancing structures of demister to increase separation efficiency and reducing pressure loss simultaneously. Computational result shows that interaction between curved bend and hooks improves the overall performance of demister. Moreover, effect of enhancing parameters on the performance is presented, specifically, Euler number and separation efficiency are correlated as functions of curved bend radius and hook length. Most importantly, an experiment is conducted on a real cooling tower. It shows that the overall thermal capacity is lowered with the presence of demister. Pressure drop, separation efficiency and heat transfer of the entire system are tested with and without demisters, based on which a new criterion is proposed to evaluate the influence of demister on the overall performance of cooling tower in terms of thermal efficiency and droplets collection. Performance indexes as functions of enhancing parameters and droplets dynamic are plotted. Therefore, a quick design of demister can be realized in achieving an optimal performance of cooling tower.

The PAM-Stamp 2G software package is used to simulate the tool bending of a workpiece made of an AMg5 aluminum alloy with and without taking into account the heat-affected zone (HAZ) formed during laser cutting of a sheet. The option of calculating welded workpieces is adapted to describe the HAZ. The state of stress in the workpiece during bending at various bending radii is analyzed with allowance for various HAZ widths. The influence of HAZ up to 4.5 mm wide on the workpiece thickness during bending is found to be insignificant.

A numerical degradation model based on two key-functions, the so-called selection and breakage functions, is developed and implemented into a coupled DEM-CFD approach for investigating wood pellet degradation and fines formation during pneumatic conveying by particle-wall impact. The influence of operating conditions like air flow, product flow and solids loading ratio as well as of pipe component geometry on degradation is examined. Detailed insights into the flow field and particle motion are obtained. The inter-particle and particle-wall collisions are statistically analysed since they are the major cause of particle degradation. Apart from operating conditions, the bend radius is varied in four steps, supplemented by a 90°-Elbow as the worst-case scenario and a straight pipe section for reference. Increasing air flow rates, and thus higher particle velocities, as well as decreasing pellet mass flows and smaller bend radii result in progressive particle degradation. Particle-wall collisions turned out to be the major reason for particle breakage. Numerical results are compared to experimental data and show good agreement.

Design analysis of high core count (36-core, 37-core) un-coupled multicore fiber (MCF) using the heterogeneous core has been proposed, to achieve the high spatial efficiency and ultra-low crosstalk (∼−81 dB/100 km) under the limited cladding diameter of 300 µm. To realize the ultra-low crosstalk level between the neighboring cores, the combination of two crosstalk reduction approaches, trench-assisted (TA) core and propagation direction interleaving (PDI) technique has been used. The forward and backward crosstalk characterizations have been studied in heterogeneous MCF with respect to fiber bending radius, wavelength, transmission distance, and core-pitch with both normal step-index and trench-assisted cores under single-mode propagation condition.

In this paper, a small size on-chip temperature sensor based on microring resonator (MRR) is introduced. The sensor consists of a small microring waveguide with a radius of 3.1 μm and a runway waveguide with the same bending radius. To a certain extent, it solves the problem that high sensitivity and small size cannot coexist in the current on-chip temperature sensor, and provides a reference scheme for the design of on-chip temperature sensor. The experimental results show that the sensitivity of the sensor is 100pm/℃, which breaks through the limit of 83pm/℃ for single microring. The free spectral range (FSR) is 39.25nm, and the resolution ratio is 0.47℃, the temperature measurement range is improved, and a better resolution ratio is obtained. The microring temperature sensor designed in this paper has high sensitivity and small size structure (only 360µm2), which is suitable for temperature measurement of Very Large Scale Integration (VLSI). It has great research value and application potential in the field of System-on-Chip (SoC) temperature detection.

A silicon photonic filter with an ultra-large free spectral range (FSR) is proposed and demonstrated by introducing high-order adiabatic elliptical-microrings (AEMs) with bent directional couplers (DCs). For the AEMs, the waveguides in the non-coupling regions are wide and have a minimal bending radius, while the waveguides in the coupling regions are relatively narrow and have a maximal bending radius. Both the radius and width of AEMs have varied adiabatically. Furthermore, bent DCs are used to realize a sufficient coupling between the access waveguide and the microring waveguide and suppress the higher-order mode excitation. The fabricated filters based on the 2nd-order, 3rd-order, and 4th-order AEMs have box-like spectral responses with an ultra-large FSR of ∼37 nm, which is a record for high-order microring filters to the best of our knowledge. Finally, an eight-channel silicon photonic filter with a channel-spacing of ∼3.2 nm and high extinction ratios of >30 dB is demonstrated.

Among various available materials used in transparent and flexible devices, MXenes are attracting attention as a brand-new candidate in this category. Ti3C2Tx MXene as a 2D material has exceptional properties, making it a potential material having numerous applications in different areas. Because of its high conductivity, it can be used in transparent conducting electrodes (TCEs). In this study, the MXenes etched by highly concentrated acid at 50 °C,were spin-coated on polyethylene terephthalate (PET) film and annealed at moderate temperatures up to 170 °C. The adhesion of MXene to PET was found to be remarkably improved by annealing. These TCEs exhibited a sheet resistance of ∼424 Ω/sq. and transmittance of ∼87%. The aging stability of MXene-coated PET films against oxidation under ambient conditions was studied up to 28 days and resistance change was found ∼30% during this period. The flexibility test showed low bending resistance change (∼1.5%) at 1000th cycle and cumulative resistance change of ∼20% at a bending radius of ∼3.9 mm after 1000 cycles. These transparent, flexible, and conducting electrodes were used to fabricate polymer dispersed liquid crystal (PDLC)-based flexible smart windows. The smart windows fabricated by curing PDLC mixture sandwiched between the MXene electrodes were also found flexible in ON/OFF states. The MXene-based flexible smart windows resulted in good opacity in the OFF state and high transparency in the ON state, exhibiting low threshold voltage

For many years, the number and losses of modes have restricted the large-scale application of hollow core photonic bandgap fibers (HC-PBFs) in data transmission. Researchers have successfully reduced fiber loss to an extremely low level; however, little attention has been given to the specific characteristics of the higher-order modes (HOMs) in HC-PBF. In this paper, the high-order mode characteristics of a 7-cell HC-PBF are investigated in detail, and the non-degenerate phenomenon of HE21 is observed. Through an in-depth theoretical analysis by discussing the influence of the structural deformation of the fiber near the core on the high-order mode characteristics, the cause of the phenomenon is described. Thus, an optimized 7-cell HC-PBF for supporting 6 modes is developed. Additionally, the bending losses of all the HOMs in the fiber are measured. Marked bending loss is not observed even when the bending radius is as small as 0.5 cm, which is different from a solid core four-mode fiber. These findings will provide a reference for HC-PBF as a new type of few-mode fiber for the mode division multiplexing field.

A multi-point flexible straightening process characterized by reciprocating bending is proposed. Specifically, the process is analyzed in terms of deformation mechanism and verified by numerical simulations and physical experiments of the straightening of a series of metal profiles with different materials and initial shapes. Further, the relationship between the bending radius and the times of reciprocating bending required to unify the curvature is discussed, and the distribution of residual stress after straightening is analyzed. The results show that the reciprocating bending process can eliminate the difference of the initial curvature, make the curvature of each section tend to be uniform; the times of reciprocating bending to reach the uniform curvature decreases with the decrease of bending radius. The straightness of the straightened profile obtained from the experiment and simulation is less than 0.2%, demonstrating a good feasibility of this method.

PurposeCompliant mechanisms are commonly used in the design of manipulator and surgical robotic tools for minimally invasive surgery (MIS) thanks to their compactness, ability of miniaturization and lower part count. However, conventional compliant joint has higher internal stiffness, which limits the bending radius. To overcome this problem, a novel tendon-driven manipulator structure based on monolithic compliant rolling-contact joint (CRCJ) is proposed.MethodsThe proposed rolling-contact mechanism is used to prevent cable slack during actuation, which occurs in conventional compliant joint design. By means of selective laser sintering (SLS) technique, the CRCJ can be fabricated in a monolithic structure, thus granting the CRCJ both the advantages of compliant joints and rolling-contact mechanism. Simulations with nonlinear finite element analysis (FEA) and experiments were conducted to evaluate and compare the mechanical properties of the proposed CRCJ with conventional leaf-type compliant joint including the bending and compliant motion.ResultsExperimental results showed that the CRCJ has lower bending stiffness, higher maximum bending angle (over$$180^{\circ }$$180∘) and a higher compliance compared to conventional compliant hinges, which allows a larger workspace and reduces the possibility of tissue injury. Agreement was also found between the nonlinear FEA and experiments regarding the relation between actuation force and bending angle. A primary prototype of a 3-DOF handheld laparoscopic manipulator with a diameter of 7 mm was further developed.ConclusionA dexterous tendon-driven monolithic manipulator structure based on CRCJ for MIS is proposed. A preliminary prototype of a handheld laparoscopic manipulator demonstrates the capability of the CRCJ for steerable medical devices. However, design improvements based on FEA and application-orientated prototypes considering anatomical requirements still show room for improvements.

Nowadays, the technical advances call for efficient electromagnetic interference (EMI) shielding of transparent devices which may be subject to data theft. We developed Cu–Ag and Ni–Ag meshes on flexible PET substrate for highly efficiency transparent EMI shielding coating. Cu–Ag and Ni–Ag meshes obtained with galvanic deposition of copper and nickel on thin Ag seed mesh which was made by cracked template method. Coefficients S11, S21 and shielding efficiency (SE) were measured for Cu–Ag and Ni–Ag meshes in X-band (8–12 GHz) and K-band (18–26.5 GHz). 90 s copper deposition increase SE from 23.2 to 43.7 dB at 8 GHz with a transparency of 82.2% and a sheet resistance of 0.25 Ω/sq. The achieved maximum SE was 47.6 dB for Cu–Ag mesh with 67.8% transparency and 41.1 dB for Ni–Ag mesh with 77.8% transparency. Cu–Ag and Ni–Ag meshes have high bending and long-term stability. Minimum bend radius is lower than 100 µm. This effect allows to produce different forms of transparent shielding objects, for example, origami method. Our coatings are the leading among all literary solutions in three-dimensional coordinates: of sheet resistance–optical transmittance–cost of produced.

A resonant-ring-assisted large mode area segmented cladding fiber (RR-SCF) with a high-index ring in the core is proposed. Numerical investigations of the effects of the high-index ring on the leakage losses of guiding modes, mode area, and electric field distribution of FM of the proposed fiber show the high-index ring not only increases the ratio of the loss between the fundamental mode (FM) and the higher-order modes (HOMs) but also improves the electric field distribution of the FM to be flat. By taking these advantages of the high-index-ring-assisted core, the effective single-mode (SM) operation is achieved in the proposed fiber bent in any orientation, which makes up the defect of the conventional RR-SCF that the SM output is affected by the bending orientation. Meanwhile, the mode area is enlarged. Furthermore, the effects of the heat load, duty cycle, bending, and operation wavelength on the fiber performance are analyzed. The results show single-mode operation in all bending orientations with a mode area larger than 824 μm2 can be achieved at a tight bending radius of 15 cm to 16 cm when the operating wavelength ranges from 1.06 μm to 1.76 μm. This fiber shows great potential in high-power fiber lasers.

Normal flat panel X-ray detectors are confined in imaging of curved surfaces and three-dimensional objects. Except that, their rigid panels provide uncomfortable user experience in medical diagnosis. Here, we report a flexible X-ray detector fabricated by the combination of a lead-free Cs2TeI6 perovskite film and a polyimide (PI) substrate. High-quality Cs2TeI6 polycrystalline films are prepared by a low-temperature electrospraying method. The resistivity even remained at the level of 1011 Ω·cm after 100 cycles of bending tests with a low bending radius of 10 mm. The resulting flexible Cs2TeI6 detectors exhibit better response stability than those based on rigid SnO2:F glass (FTO), which is attributed to the superior crystallization of films and the growth stress relief of flexible substrates. Furthermore, an X-ray sensitivity of 76.27 μC·Gyair-1·cm-2 and a detection limit of 0.17 μGyair·s-1 are achieved. A series of distortion-free clear X-ray images are obtained for objects with different materials and densities. These findings provide insights into flexible X-ray detectors based on perovskite films and motivate research in wearable X-ray detectors for medical radiography and dose monitoring.

The demand for roll-formed high strength steel square hollow sections has extensively increased by automotive and construction industries due to their excellent structural performances and attractive appearances. However, due to their low ductility and demand for large forming tool loads, high-strength steels are challenging to be roll-formed at room temperature. Partial heating roll forming is a recently proposed manufacturing technique aiming to overcome these difficulties by applying temperature on bend areas. In this study, the finite element software LS-DYNA was utilized to predict effective plastic strain and stress developments and associated residual stresses induced during the partial heating roll forming method. Furthermore, comparisons were made between cold roll forming and partial heating roll forming methods. The results indicate that the effective stress value during the partial heating roll forming method was lower than the cold forming method. In addition, the product manufactured by the partial heating roll forming method had smaller and uniform residual stress distributions along the section perimeter and across the section thickness than the cold-formed counterpart. Further investigations on corner geometry showed that high strength steel square hollow sections with a minimum bend radius could be successfully manufactured using the partial heating roll forming method.

Wrinkling is the key forming defect in thin-wall tube bending process, when the wall thickness-to-diameter ratio is smaller than 0.01. The granular media-based thin-wall elbow push-bending process involves filling a tube with spherical particles and pushing the tube into a die to bend a tubular blank into an elbow shape. If the wall thickness of tube is smaller than the particle size, wrinkling significantly depends on micro contact force distribution in granular media, and the granular media cannot be approximately simulated by FEM. In the present paper, an elbow tube with 0.3 mm wall thickness, 30 mm outer diameter, and 90 mm bending radius is formed by granular media-based push-bending process. The wrinkling is investigated; especially, the micro contact force distribution at the initial buckling location is observed based on a 3D FEM-DEM coupling model. In the coupling model, FEM is used to simulate bending deformation of tubular blank, and DEM is used to simulate micro contact forces of particle flow. Finally, a simplified formulation is proposed for predicting wrinkling of thin-wall elbow tube in granular media-based push-bending process and validated by experiment of an elbow tube with 0.7 mm wall thickness, 70 mm outer diameter, and 105 mm bending radius.

Pulsating heat pipes are a relatively newer generation of heat pipe which are wickless thus more economical and less fabrication-intensive. These devices are made of a capillary sized tube bent in a serpentine form to result in a closed system. In this study a single closed loop pulsating heat pipe made of 2 mm internal diameter copper tubing is experimentally investigated for two different bend radii. The performance comparison is made for two fluids – methanol and water, for varying heat loads from 10 W to 100 W, with various inclinations from vertical bottom heated mode to horizontal mode, for a constant fill ratio of 60%. The sharper bend, though making the device more compact, is found to reduce the performance. One of the bend geometries is further investigated for the effect of insulation on the adiabatic sections. The insulation is found to certainly widen the heat load range though a distinct performance improvement is not found. The variation of the frequency of pressure pulsations with respect to the fluid, heat load and inclination is also studied. Additionally, one of the geometry is tested with FC 72 fluid as well to arrive at a correlation for heat flux for varying fluids, heat fluxes and inclinations, covering 116 data points. The performance trends predicted by the correlation are in line with those reported in the literature.

The cladding pumping within a double-clad fiber structure is an effective technique to convert high-power multimode beam into high-power, almost diffraction limited beam. Since the pump efficiency is limited by the presence of higher skew-ray modes, geometrical perturbations are used to scramble the modes and to achieve a higher overlap of the electromagnetic field with the doped core. In this paper, the combined effect of fiber coiling and twisting is investigated in the double-clad fiber structure with the octagonal shape of an inner cladding. Electromagnetic field propagation through fibers with different cross-section areas, bending radii and twisting rates is numerically simulated using finite element beam propagation method. Holmium-doped double-clad fiber pumped in tandem configuration at wavelength 1950 nm is selected as an example. Nontrivial dependence of pump absorption on bending radius with the presence of local maxima is revealed. The observed impact of fiber coiling and twisting increases with the size of the cross-section area of the inner cladding.

International audience; As the GDL (Gas diffusion layer) is the most sensitive component in the fuel cell, any change in its structure causes a change in its porosity, which strongly influences the contact between the components of the fuel cell. Note that the state of contact depends on the applied clamping pressure, the thickness and the porosity of the GDL, and the geometry of the rib (bending radius) of the BPP (Bipolar plates). These components can be subject to variations coming from very high compression, so it is necessary to consider the reliability of their dimension via modeling/simulation by the integration of uncertainties. In this article, we will study the influence on the contact pressure of the uncertainties of the mechanical design parameters. A probabilistic approach (Gauss's law) is applied to evaluate the effect of the mechanical uncertainties parameter on the contact pressure between GDL/MEA and GDL/BPP.