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Heat transfer characteristics of a cryogenic sintered-wick miniature bent and flattened heat pipe has been experimentally investigated in this paper. The heat pipes are made of oxygen free copper for the container and nitrogen is used as the working fluid. The wick was composite wick made from sintered copper powder and grooved copper pipe. The original cylindrical copper heat pipe was 6 mm in outer diameter and 200 mm in length. The heat pipes with the bending radius of 21 mm and the bending angle of 0°, 30°, 60° and 90° and the final thickness of 2.5, 3.0, 4.0 mm were constructed and tested. The operating temperature of heat pipe was at approximately 78.25 ± 0.10 K. It was found that the performance of the heat pipe in terms of thermal resistances depends on both bending angle and final thickness. Both bending and flattening affect the thermal resistance by increasing it. The bending increased the thermal resistance from 0.88 to 1.07 K/W (6 mm, 0° to 6 mm, 90°) and the flattening increased the thermal resistance from 0.88 to 2.24 K/W (6 mm, 0° to 2.5 mm, 0°). And the combined effect of bending and flattening increased the thermal resistance from 0.88 to 1.56 K/W (6 mm, 0° to 3 mm, 90°). The bending affects heat pipe by wick deformation that obstructs liquid flow. The flattening affects the thermal resistance by the collapse of wick structure which causes a broken liquid path of returned working fluid from the condenser to the evaporator and by liquid clogging in the condenser.

This research develops a unique material to attenuate electromagnetic interference (EMI) by using spinnable multiwalled carbon nanotubes (MWNTs) combined with bio-polydimethylsiloxane (PDMS) that contains BaTiO3 (MBPBT). In particular, a plaid pattern, formed by the spinnable MWNTs, is very effective in attenuating the propagation of EM waves,which achieves over 20 dB at 8.2–12.4 GHz (X-band frequency range). This means that a filter type of the spinnable MWNTs is actively able to handle the directionality and movement of EMI propagation. In addition, the MBPBT is characterized by its strong mechanical advantage (bending radius 180°).

We treat numerical simulations to investigate how the tube wall thickness affects the confinement loss, power fraction ratio and bandwidth of terahertz (THz) negative curvature fibers at the frequency of 2.52 THz. The frequency of 2.52 THz is chosen to research since the generation from CH3OH based THz gas laser pumped by CO2 laser demonstrates the huge application prospects. We also calculate the confinement loss of bend fiber and find it is insensitive to the bend radius. The negative curvature fibers can be used as the reaction cell of THz or mid-infrared gas lasers since their superior performance characteristics.

An analytical method considering the redistribution of residual stress in the bent plate is proposed to predict the springback of the stiffened panel when milling the panel layer by layer. Two types of stiffened panel, namely, a panel with crosswise stiffeners and a panel with lengthwise stiffeners, were selected as examples and were analyzed during the removal of each layer. Moreover, a finite-element simulation of the milling process was conducted to make comparisons with the analytical results, which demonstrates similar stress distribution and springback values. The maximum stress variation and springback value appeared when the milling depth reached the initial neutral surface. When the plate thickness decreased, the errors between analytical results and FEM results increased, and the lengthwise-stiffened panel was less affected by errors than the crosswise-stiffened panel because of a larger moment of inertia. The effects of different milling thicknesses per layer, initial plate thickness, and bending radius were also analyzed. Moreover, the milling experiment was performed to make verification. The results suggest that the analytical method can predict the springback of the stiffened panel effectively. The proposed method can also be applied to other similar forming conditions.

The granular-media-based thin-wall elbow push-bending process involves filling a tube with granular media and pushing the tube into a die to bend a tubular blank into an elbow shape. By means of the mechanical characteristics of granular filler, an elbow tube with t/D

We present a study of the feasibility of transforming the multicore fiber in a supermode-interference based bending sensor into an active stage. By compensating the antisymmetric supermode losses for high curvatures, fringe visibility is improved and the sensor operating range can be extended. For a given multicore fibre length and Er3+-ion concentration sensor calibration curves allow assessing the bending radius by measuring the visibility as a function of the input pump power. The Er3+-ion concentration, available input pump power and multicore fiber length set the minimum bending radius that could be measured.

Patterning of liquid metals (LMs) at different length scales remains one of the issues hindering their practical applications. Herein, we report a robust LM patterning method enabled by transiently sealing and subsequently dissolving a sacrificial layer (a polyvinyl alcohol (PVA) thin film or an adhesive tape). In this method, the LM was filled into the channels, which were temporarily formed by sealing with a sacrificial layer, by either negative or positive pressure. Afterward, LM patterns were obtained by the dissolution of the sacrificial layer in water. This method affords a robust generation of micro- and macro-patterns of LMs in a wide range from 30 μm to 1200 μm with high reliability. To demonstrate the potential application of this method, flexible and wearable LM-based wireless charging devices were fabricated, optimized and characterized. A power transfer efficiency (PTE) up to 60% was achieved while maintaining their function even at a bending radius of 12.5 mm. As a proof-of-concept, flexible LM-based wireless charging devices were employed to power passive, implantable and wearable devices.

Perovskite cesium lead halide (CsPbBr3) has attracted considerable attention due to its excellent optoelectronic properties and superior stability against moisture, oxygen, light, and heat. In this work, the micro-environment controlled chemical vapor deposition (CVD) method has been adopted to synthesize high-quality single-crystalline CsPbBr3 microstructures, including microwires, microplates and triangular pyramids. Moreover, the structure–activity relationship between the material microstructures and the device properties is illustrated. The results show that photodetectors based on a single horizontal CsPbBr3 microwire exhibit a high responsivity (312.2 A W−1) and a fast response time of 5.8 ms. Photodetectors based on a single CsPbBr3 microplate exhibit a responsivity of 1.74 A W−1 and a response of 10 ms. These results indicate that the CsPbBr3 microwire photodetector is characterized by a higher photodetector performance when compared to the microplate due to its excellent crystallization quality and the Fabry–Perot cavity effect in the microwire. Furthermore, the flexible CsPbBr3 microwire photodetector was demonstrated on a mica substrate. The results show that the photocurrent can be maintained at 90% after 3000 cycles at a bending radius of 2.5 mm. This work demonstrates the structure–activity photodetector performance, which is essential to develop a full understanding about high-performance optoelectronic devices based on all-inorganic lead halide perovskite materials.

Controlling the Dirac point voltage of graphene is essential for realizing various practical applications of graphene. Here, control of the doping state is achieved in flexible graphene field effect transistors (GFETs) by applying mechanical bending stress. By gradually increasing the bending strain (the decrease of upward/downward bending radius), the Dirac point (VDirac) linearly shifts to left/right, which is induced by the flexoelectric effect of the ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) gate. In addition, a superior mechanical antifatigue character is obtained in the flexible GFETs, and the doping effect is recoverable. The sensitivity to strain and high bending stability not only offer an easy, controllable and nonintrusive method to obtain a specific doping level in graphene for flexible electric devices, but also highlight the enormous potential of the flexible ferroelectric PLZT-gated GFETs as wearable sensors.

We report a highly flexible ultrathin Au grid with high mechanical robustness as transparent electrode for flexible organic light-emitting devices (OLEDs). The grids are introduced to an ultrathin Au film to improve its optical transmittance and mechanical performance. With the line width of 15 μm and the gap width of 30 μm, the optimal ultrathin Au grid presents a desirable transmittance of 88.7% at 550 nm and a sheet resistance of 36 Ω/sq. Owing to the reduced tensile stress by the ultrathin grid patterns, the flexible ultrathin Au grid exhibits extraordinary mechanical stability with maintained conductivity after 48 000 bending cycles under a bending radius of 1 mm. Flexible OLEDs with high flexibility and mechanical robustness have been obtained using the ultrathin Au grid as the transparent anode by maintaining 92% initial efficiency after 4200 bending cycles. Moreover, flexible OLEDs exhibit a significantly improved current efficiency in comparison to the devices based on the continuous Au or traditional ITO anode.

The highest efficiencies for both rigid and flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are still far behind the theoretical values. This is mainly due to band tailing in absorber and a large recombination near absorber/Mo interface that block the carrier transportation and lead to Voc and FF degradation, which are mostly noticeable in flexible solar cells. In this paper, CZTSSe thin films were prepared on flexible Mo substrates by green solution-based method followed by selenization. By optimizing selenization conditions (selenization time and temperature), dense and well crystallized CZTSSe thin films without micro-cracks were obtained at 550 °C for 12 min. The best efficiency of 6.78% can be achieved with Voc and FF enhanced to 390.43 mV and 57.71%. The dramatic reductions in ideal factor A, series resistance RS, the mismatch Δ(Eg-PL) and potential fluctuation γ indicate that band tailing and recombination are significantly reduced. The performance degradation with bending radius and cycles is studied for the first time among CZTSSe solar cells. Results indicate long-term stability at repeatable release–stretch cycles. The flexible CZTSSe solar cells with high stretch ability shed light on the development of flexible solar cells.

Big-bore, low-loss, and extremely flexible hollow waveguides were fabricated for mid-infrared spectroscopic gas sensing. The waveguide with inner/outer diameter of 1.4/2.0 mm can be curved with a bending radius as small as 1.4 cm A module of gas absorption cell for spectroscopic sensing was proposed with the hollow waveguide curved into a channeled substrate. Hollow waveguide with inner coatings of silver and silver iodide films attains low loss in the mid-infrared region for methane gas detection. Sensing properties for the module was experimentally discussed. Limit of detection of 6 ppm was obtained by using an FTIR (Fourier Transform infrared spectroscopy) system and DTGS (deuterated triglycine sulfate) detector. Comparisons were made to metallic hollow waveguide only with silver inner coating.

Artificial intelligence applications require bio-inspired neuromorphic systems that consist of electronic synapses (e-synapses) able to perform learning and memory functions. However, all transparent and flexible organic e-synapses have the disadvantage of being easily dissolvable in water or organic solutions. In the present work, a stable waterproof artificial synapse based on a fully transparent electronic device, suitable for wearable applications in organic environments is for the first time demonstrated. Essential synaptic behaviors, including paired-pulse facilitation (PPF), long-term potentiation/depression (LTP/LTD), and learning–forgetting–relearning, were successfully emulated. The artificial synaptic device could achieve an optical transmittance of ∼87.5% in the visible light range, which demonstrated reliable long-term potentiation/depression under bent states with a bending radius of 5 mm. After being immersed in water and 5 types of common organic solvents for over 12 hours, the e-synapse could function with 6000 spikes without noticeable degradation in the organic environment. The neural network was constructed from e-synapses with controllable weights update and a device-to-system level simulation framework was developed with a recognition rate of 92.4%, which demonstrated the feasibility of highly transparent, biocompatible, flexible, and waterproof e-synapses used in artificial intelligence systems.

This paper presents a new shear bending method of tubes for controlling bending radius, of which the target value at the neutral plane is 0.5 times the tube diameter. The method consists of two steps using a pair of mandrels. The first step makes a space inside the tube, and the second step inserts a new mandrel into the space for transferring the mandrel shape to the bent part. As a result, the bending radius becomes a target radius, which has never been achieved by conventional shear bending, the bending radius of which has always been zero.

Organic field-effect transistors (OFETs) with hexagonal barium titanate nanocrystals (h-BTNCs) in amorphous matrix as one of the bilayer dielectric systems have been fabricated on a highly flexible 10 μm thick poly(ethylene terephthalate) substrate. The device current and mobility remain constant up to a bending radius of 4 mm, which makes the substrate suitable for wearable e-skin applications. h-BTNC films are found to be highly temperature-sensitive, and the OFETs designed based on this material showed ultraprecision measurement (∼4.3 mK), low power (∼1 μW at 1.2 V operating voltage), and ultrafast response (∼24 ms) in sensing temperature over a range of 20-45 °C continuously. The sensors are highly stable around body temperature and work at various extreme conditions, such as under water and in solutions of different pH values and various salt concentrations. These properties make this sensor unique and highly suitable for various healthcare and other applications, wherein a small variation of temperature around this temperature range is required to be measured at an ultrahigh speed.

Realization of flexible electronics is an attractive challenge because of its great potential in many applications. However, the design of flexible and highly conductive metal electrodes has been a bottleneck for the fabrication of flexible devices because bulk metals are easily fractured when subjected to elongation or compression. Here, we demonstrate metal-ceramic nanolaminates as electrodes for flexible electronic devices. Insertion of ceramic layers, each with a thickness of a few nanometers, into an otherwise metal electrode significantly improved its strength and bending stability and only slightly reduced its electrical conductivity. Finally, we demonstrated that a touch screen panel fabricated with metal-ceramic nanolaminate electrodes was stable to 200 000 cycles of folding to a bending radius of 3 mm.

A flexible microstrip grid array antenna designed on polydimethylsiloxane (PDMS) substrate and copper conductive fabric as the patch and ground plane is presented. The proposed rectangular geometry designed at 15 GHz is made of 19 cells with 22 radiating elements. The proposed antenna achieves almost 40% wideband characteristics at −10 dB reflection coefficient from 11.10 GHz until 16.2 GHz with measured maximum gain of 14.0 dBi in normal state. Analysis on performance of antenna at bend state with various value of bend radius has been done. The measured reflection coefficient shows low sensitivity to bending effect where the antenna operates well at designed frequency which is at 15 GHz. Due to these criteria, it is a suitable candidate for wearable applications.

A novel hollow-core anti-resonant fiber with a large mode area and good single mode performance is proposed for high power delivery in mid-infrared region. The structure consists of two-layer circular tubes as the cladding. By optimizing structure parameters, a broad low-loss single-mode band, in which the fundamental mode loss is lower than 4 × 10−3 dB/m and the high order mode extinction ratio (HOMER) is higher than 1000, is achieved in the wavelength region from 2.5 to 3.3 μm in which the lowest loss of 2.87 × 10−4 dB/m occurs at 3.1 μm. The effective mode area is up to 2314 μm2 with the highest HOMER of 16,600 at the wavelength of 2.8 μm. In addition, this fiber also has good bend resistance characteristics. When the fiber is bent at the bending radius of 18 cm, the mode area reaches to 2268 μm2 with the HOMER above 100 at the wavelength of 2.8 μm. Furthermore, the effective mode area can be further increased to 4714 µm2 by increasing core radius at the cost of sacrificing single mode performance and bending resistance.

A generalized solution for the bending stress/strain expression of flexible display composed of multi-stacked thin films is presented in this letter. Flexible display comprises an arbitrary number of films combined with dissimilar thicknesses and linear-elastic mechanical characteristics. Specific consequences for alternate layered systems are estimated to reveal the elementary trends of the dependencies of normalized bending strain and neutral axis (N.A.) position on the modulus and thickness ratios of the concerned layers. An actual architecture of flexible display is also provided as an example to calculate the results and is compared with the simulated predictions of finite element analysis. With various material selections of cover plate, the induced stresses on transparent conducting film and the position of the N.A. plate are separately investigated. Moreover, the impact of bending radius on the mechanical reliability of flexible encapsulation is also found. The presented results serve as a design guideline for the infrastructure optimization of flexible display devices without electrical failures.

A new multiobjective optimization framework is presented for designing large mode area photonic crystal fibers (LMA-PCFs) with effective single-mode operation in the bent state. For optimizing the structure, we utilize the multiobjective gray wolf optimizer (MOGWO) to maximize the effective mode area (EMA) and the bending loss of higher order modes (HOMs), while minimizing the fundamental mode (FM) loss. The simulation results demonstrate that this framework enables us to improve the EMA by a factor of 1.26 and increase (decrease) the bending loss of the HOMs (the FM) by a factor of 7 (17), compared to the nonoptimal design. In addition, we investigate the dependence of the optical characteristics of the optimized LMA-PCFs on the wavelength and the bending radius. We found that some optimal structures are highly wavelength dependent and are not suitable for wideband applications. Furthermore, we found that the HOM loss is very sensitive to the bending radius. The proposed framework is comprehensive and can be employed to find a broad range of optimal designs for a wide range of applications.

Cross-sectional ovalization（ovalisation）usually occurs when thin-walled tube is subjected to large plastic bending. This paper is concerned with residual deformation of tube's cross-section in radial direction when external bending moment is removed. A combination of experiments and theoretical modeling is used to study this issue. Firstly the four-point pure bending experiments involving fifteen stainless steel specimens with a range of diameter-to-thickness ratios are carried out to observe the shape of the ovalized cross-section and to obtain the cross-sectional flattening (value of ovalization) along the circumferential direction. Secondly the theoretical modeling procedure is performed to derive a rational model for predicting the maximal residual cross-sectional flattening of the thin-walled tube subjected to pure bending after unloading process, employing the thin-shell kinematics, the principle of virtual work and the classic unloading rule. Finally the model is validated by comparing the theoretical results with the experimental ones with less than 10% error. And the relationships between the residual flattening and the bending radius as well as the wall thickness are also revealed by the numerical results. The application of this investigation will play a positive role in thin-walled steel tube bending operation.

The manufacturing of shaped sandwich components is a task with technical challenge. In this paper the mechanical feasibility to produce a doubly curved panel from an initially flat sandwich plate was investigated. Experimental results of multi-point forming (MPF) and finite element analyses reveal that the formability of sandwich panel with egg-box-like (EBL) cores in plastic forming process is mainly dominated by the failure modes of face sheet plastic wrinkling, face sheet plastic dimpling and core cell fracture. Analytical models for predicting the face sheet buckling were developed, and limit bending radius for wrinkling and the critical stress for dimpling were determined as the functions of the geometric parameters and material properties of sandwich plate. The stress-based fracture limit curve and associated theoretical formulations to predict the core cell fracture were presented. The developed analytical models have been validated experimentally and using finite element simulations. Multi-point forming experiments were carried out and the feasibility of using plastic forming technique to form EBL-cored sandwich panels was demonstrated finally. Keywords: Sandwich panel, Plastic forming, Double-curvature surface, Multi-point forming, Failure behaviors during MPF, Egg-box-like core

Staggered extrusion (SE) is a new method to solve the bottleneck of traditional curvature products, such as long manufacturing cycle, many forming processes and difficult quality control. How to quantitatively control the curvature of extruded products is the key to implement this method. Herein, the upper bound method is used to calculate and analyze the power consumption of each characteristic zone in the SE process. The theoretical model of extrusion load and curvature is established. The results show that the staggered distance h has an important influence on the curvature κ. When the staggered distance h increases from 8 mm to 24 mm and other conditions remain unchanged, the curvature κ increases from 0.0546 to 0.1607. Any combination of the staggered distance h and the extrusion ratio λ corresponds to an eccentricity ratio ξ. The eccentricity ratio ξ decreases with the increase of the staggered distance h or the extrusion ratio λ. By comparison, it can be seen that the variation trend of the theoretical predicted value and the FE modelling in the steady-state extrusion stage is consistent. The experimental results are in good agreement with the curvature theory prediction model. These results provide a scientific basis for the formulation of the SE process and precisely controlling magnesium alloy curvature products.

Flexible electronics enable various technologies to be integrated into daily life and fuel the quests to develop revolutionary applications, such as artificial skins, intelligent textiles, e-skin patches, and on-skin displays. Mechanical characteristics, including the total thickness and the bending radius, are of paramount importance for physically flexible electronics. However, the limitation regarding semiconductor fabrication challenges the mechanical flexibility of thin-film electronics. Thin-Film Transistors (TFTs) are a key component in thin-film electronics that restrict the flexibility of thin-film systems. Here, we provide a brief overview of the trends of the last three decades in the physical flexibility of various semiconducting technologies, including amorphous-silicon, polycrystalline silicon, oxides, carbon nanotubes, and organics. The study demonstrates the trends of the mechanical properties, including the total thickness and the bending radius, and provides a vision for the future of flexible TFTs.

A plastic optical fiber (POF) temperature sensor with high sensitivity is experimentally demonstrated in this work. The temperature sensor is realized by a combination of macrobending and an unclad region in the fabrication of its sensor head. The POF sensor is bent into a balloon-like structure in order to introduce the effect of macrobending. For the optimization of the sensor performance, the bending radius of the balloon-like structure is varied. Experimental results suggest that the performance is optimized when the bending radius is fixed at 55 mm. With this amount of bending radius, temperature sensitivity of up to 22.2 × 1 0 − 3 ∘ C − 1 can be achieved in the range from 40°C to 80°C, with linearity of 0.99 and resolution of 0.45°C. This technique is found to improve the POF temperature sensitivity in comparison to previous developments.

The hardness of rigid electronic devices limits its application scope. People use flexible scheme to improve it, so the design of flexible circuit structure is very important. Some special structures, such as island bridge structure, mesh structure and serpentine structure, can make the circuit have the ability of deformation. However, people cannot get good results from using a single structure, but the multi-level structures may improve the flexibility. Inspired by the softness of the net in our life, combined with the honeycomb structure, we design a 2-D honeycomb mesh structure. When the mesh is stretched, the 2-D hole is deformed by stress, and the local large strain converts to the small strain of the whole structure to avoid fracture. The stretch-ability of the single-level honeycomb mesh structure is 6.77%. Then, in order to further improve the flexibility, the serpentine structure is applied to the edge of the honeycomb structure to form a two-level structure. When the primary-level honeycomb structure is stretched, the second-level serpentine structure is also appropriately stretched to improve the flexibility. Finite element analysis shows the stretch-ability is 8.3%, which is better than single-level structure. Next, we also simulate the bending angle and twist angle of the structure, which has 120 degree bending (bending radius 1.55mm), 54 degree twisting and no plastic deformation occurs. It is clear that the multi-level microstructure has better flexibility, which provides a new scheme for the fabrication of flexible electronic devices and circuit microstructure design.

This paper focuses on the solute transport characteristics of karst water tracing and its engineering application by numerical simulation and analysis of field tracer curves. First, the computation models and simulation methods of solute transport are proposed. Then, five kinds of representative geological models of karst water tracing are built, and seven cases of solute transport are studied. Solute transport characteristics in the straight pipeline model, bend model, depression model, waterfall model, and branch pipeline model are analyzed. The solute mass fraction affected by the pipeline width, flow velocity, bend radius, depression depth, the number of bends, depressions, and waterfalls are discussed. Finally, the numerical results are applied in actual tracer tests for analyzing the groundwater connection medium. Some preliminary laws and conclusions are obtained as follows: (1) The peak of solute mass fraction decreases gradually with the bend radius, pipeline width, flow velocity, the number of bends, depressions, and waterfalls rising. (2) The influence of depression depth on the tracer curve is little. (3) The time to peak increases gradually with the number of depressions and waterfalls rising, while it decreases gradually with the increase of flow velocity. (4) The distribution of the tracer curve widens gradually with the number of bends, depressions, and waterfalls rising, while it narrows gradually with the increase of flow velocity.

Thulium-doped fiber lasers have been extensively investigated as the most promising source of efficient laser emission at wavelengths around 2 μm, i. e., in the eye-safer spectral region and in the atmospheric window as well. It allows for wide range of applications including medicine, defense, distance measurement or materials processing. To enhance pump absorption efficiency along the active double-clad fiber, good overlap of the pump light and doped fiber core should be achieved along the fiber length. The overlap can be increased by breaking the circular symmetry of the inner cladding by shaping its cross-section. Further mode-mixing and better pump absorption can be achieved by coiling and twisting of double-clad fibers. In this work we present experimental measurement of 792 nm pump cladding absorption of a series of double-clad thuliumdoped fibers with respect to their bend radius, the inner cladding cross-sectional shape and twist rate. With these fibers, we assembled a set of fiber lasers with different resonator setups and tested their performance. Twisting was introduced to fiber during drawing from an octagonal, CO2 laser-shaped or mechanically grinded preform so that the twist remained frozen in the drawn fiber. We have shown that the fiber twist significantly improves the pump absorption even in the case of straight or coiled fibers with large coil radii. We provide a preliminary comparison of two fiber laser resonators.

A small-hysteresis carbon nanotube thin-film transistors through the construction of stacked architecture has been proposed due to an interaction of the effects of surface and interface trapped charges. With the help of photoresist gate dielectric, the through-holes between the upper and lower devices can be easily patterned and formed with the self-assembly interconnections. The as-fabricated device can exhibit quite small hysteresis of 0.1 V at various bending radius indicating the good flexibility and stability.

With the increasing application of the advanced high strength steel material in the automobile industry, the thickness reduction of the bending area has attracted more and more attention since the product strength is highly influenced by the quality of the bending region. In this paper, three major factors, the thickness reduction, the variation of the local bending radius within the bending zone, and the tooling mark on the product’s surface, are investigated through three different loading patterns for a free U-bending profile numerically and experimentally. The results demonstrate a thinning pattern consists of three peaks over the bending region for large bending ratio (R/t = 2.14) and only one peak for small bending ratio (R/t = 0.5). Corresponding valleys for the local radius are found to match the thinning pattern. Further, the use of finite element simulation can successfully predict the location and the severity of the wear on the product. From the experiment results, even if the metal blank only experienced one stroke, the tooling mark contains both adhesive and abrasive wear. A better understanding of the characteristics of the bending zone is achieved, and the findings can help in improving the design process for forming strategies.

Printed electronics are attractive due to their low-cost and large-area processing features, which have been successfully extended to magnetoresistive sensors and devices. Here, we introduce and characterize a new kind of magnetoresistive paste based on the anisotropic magnetoresistive (AMR) effect. The paste is a composite of 100-nm-thick permalloy/tantalum flakes embedded in an elastomer matrix, which promotes the formation of appropriately conductive percolation networks. Sensors printed with this paste showed stable magnetoresistive properties upon mechanical bending. The AMR value of this sensor is $$0.34\%$$ 0.34 % in the field of 400 mT. Still, the response is stable and allows to resolve sub-mT field steps. When printed on ultra-thin 2.5-$$\upmu \hbox {m}$$ μ m -thick Mylar foil, the sensor can be completely folded without losing magnetoresistive performance and mechanically withstand $$20\, \upmu {\hbox {m}}$$ 20 μ m bending radius. The developed compliant printed AMR sensor would be attractive to implement on curved and/or dynamic bendable surfaces for on-skin applications and interactive printed electronics.

In this paper, the response surface methodology (RSM) and finite element (FE) simulation were applied to optimize the push-bending process parameters of the thin-walled tube with polyurethane mandrel. The objective of the present work is to predict the optimal set of process parameters including the length to diameter ratio of the mandrel (L/D), the friction coefficient between die and tube ( $${\mu }_{1}$$ ), the friction coefficient between polyurethane and tube ( $${\mu }_{2}$$ ), and Poisson’s ratio of polyurethane ( $$\upsilon$$ ) to obtain qualified bent tubes. Three empirical models were developed to describe the relationship between process parameters and quality parameters of the bent tubes. In addition, the significant factors affecting the forming quality were analyzed using analysis of variance (ANOVA) of each model. Response surfaces were constructed to study the effect of each process parameter on the quality of the bent tubes. Finally, the process optimization window with the maximum thinning rate ( $$\varphi$$ ) less than 20%, the maximum thickening rate ( $$\psi$$ ) less than 17%, and the maximum cross-section ovality ( $$\xi$$ ) less than 5% of the bent tube was established. Qualified bent tubes with diameter of 144 mm, wall thickness of 2 mm, and bending radius of 280 mm were formed experimentally by following the established process window.

We are investigating to utilize multi-core fiber for increasing the concentration of optical fiber and the density of optical connector. Until now, from the viewpoint of optical mounting, the bending loss and the crosstalk of the multi-core fiber in a short distance range have not been investigated so much. In this report, we propose low-loss and easily bendable multi-core fiber with a novel double core taper structure to realize highly efficient optical coupling to a silicon photonics integrated circuit, and compact fiber mounting with small bending radius. By BPM simulation, we confirmed that it is possible to suppress the bending loss of less than 0.5 dB and the inter-channel crosstalk to -20 dB or less when the radius of curvature is 3 cm. Based on this result, we fabricated an optical fiber with the double core taper structure in order to verify the characteristics. As a result, the coupling loss was realized within 1.5 dB with low radiation loss. It is therefore considered that the double core taper structure can be sufficiently applied to the multi-core fiber.

Ni-Ti tube is used as a supporting tube for the infrared hollow fiber to obtain flexibility and strong mechanical strength. The loss of Hollow optical fiber is inversely proportional to the cube of the inner diameter. Considering this, it is expected that the large-diameter hollow optical fiber has a low loss. Even with a large inner diameter of 800 μm, the Ni-Ti tube with a wall thickness of 0.1 mm can be bent with a small force to a bending radius of 15 mm. Therefore, 800-μm-bore hollow optical fiber based on Ni-Ti tube was fabricated. In order to reduce roughness of inner surface of Ni-Ti tube which causes the additional transmission loss, an acrylic-silicon resin material is used as a buffer layer to the inner wall of Ni-Ti tube for a low-loss characteristic. For the dielectric inner-coating layer, cyclic olefin polymer (COP) is used to lower the transmission loss. The COP layer is formed by using liquid-phase coating method. The hollow fibers with optimized COP inner film thickness for CO2 laser light were fabricated and reasonable transmission losses was demonstrated.

Super-PDMS with solvent dispersibility promises flexible PDMS-based waveguides in both the cladding and the core. The PDMS can fabricate a micro ~ submicron scale structure easily like waveguide by wet process, as oppose to conventional PDMS which uses imprinting to create microstructures. The refractive index of the PDMS is about 0.1 higher than that of conventional one. Super PDMS solutions dispersed in 1,2 dichloroethane solvent maintained transparent crystals in spontaneous drying after drawing, even at a high concentration of 15 wt.%. A flexible PDMS waveguide with a conventional PDMS cladding and a super PDMS core propagated light even with a waveguide bend radius of 2.5 mm, which is smaller than the minimum bend radius of a typical optical fiber.

We present a highly stretchable and compact bow-tie antenna which operates at 5 GHz for wearable applications. The dimensions of the bow-tie antenna were 7.9 mm×17.8 mm. The stretchable antenna was fabricated with a composite mixture of silver flake and polymer binder. The composite paste was printed on polyurethane and textile using the screen printing technique. The RF performances, stretchability, bendability, and durability of the antennas were evaluated, which are critical requirements in wearable electronics. The stretchable bow-tie antennas showed excellent RF performances and stretchability up to a stretching strain of 40%. The antennas could be bent up to a bending radius of 20 mm without degrading RF performance. The stretchable antennas also exhibited outstanding mechanical endurance after 10,000 cyclic stretching tests. The antennas were not affected by the presence of the body and showed very stable RF performances, exhibiting promising results for mobile and wearable applications.

A functional piezoelectric kirigami monitors the joint motions for the prevention of musculoskeletal disorders., The prevention of work-related upper extremity musculoskeletal disorders (MSDs; e.g., neck pain and shoulder fatigue) requires frequent exercises of neck and shoulder that primarily rely on the assistance of joint motion monitoring devices. However, most available wearable healthcare sensors are rigid, bulky, and incapable of recognizing the full range of human motions. Here, we propose a kirigami-structured highly anisotropic piezoelectric network composite sensor that is able to monitor multiple information of joint motions, including bending direction, bending radius, and motion modes, and to distinguish them simultaneously within one sensor unit. On the basis of the modified template-assisted processing method, we design a functional piezoceramic kirigami with a honeycomb network structure that is stretchable (~100% strain), highly sensitive (15.4 mV kPa−1), and highly anisotropic to bending directions (17.3 times from 90° to 0°). An integrated monitoring system is further established to alarm the prolonged sedentary behaviors, facilitating the prevention of upper extremity MSDs.

A photonic crystal fiber (PCF) consisting entirely of circular air holes based on hexagonal cladding and cross-shaped core structure is proposed. The transmission properties of the proposed PCF are simulated calculation by using TOPAS as the background material, the finite element method as the calculation method, and the circular perfectly matched layer (PML) as the boundary condition. The results show that very low transmission loss, including effective material loss (EML) with 1.04 × 10-3 cm-1 , the confinement loss with 2.3 × 10-6 dB/cm, and the bending loss (when the bending radius is 1 cm) with 1.23 × 10-17 cm-1 can be got. When the proposed PCF under the optimal condition, extremely large effective area about 9.69 × 1016 μm2 and flat dispersion about 0.46 ± 0.04 ps/THz/cm can be obtained, and the proposed PCF is in the single mode. Large effective area and ultra-low loss make the proposed PCF hold great future in low loss terahertz systems. Additionally, the proposed PCF with simple structure can be drawn by many methods such as the extrusion method.

Flexible cellulose-based conductive films reveal high potential in electromagnetic interference (EMI) shielding and thermal management applications. However, the high contact electrical/thermal resistance in these films is still a challenge to face. In this work, an asymmetric sandwich structural film containing a cellulose nanofiber (CNF) skin-layer and self-supported Ti3C2Tx MXene and silver nanowire (AgNW) core-layers (CNF@MXene@AgNW film) was fabricated through layer-by-layer assembled vacuum-assisted filtration. The unique sandwich structure not only provides a highly conductive network by the highly oriented and self-supported conductive core-layers, but also maintains its structural integrity by ambilateral CNF layers. As a result, the CNF@MXene@AgNW film reveals a strong tensile strength of 118 MPa and a toughness of 4.75 MJ m−3, super-flexibility (minimum bending radius of ∼85 μm), a high electrical conductivity (37 378.2 S m−1), effective EMI shield effectiveness (SE, 55.9 dB), outstanding specific SE (SSE/t, 10 647.6 dB cm2 g−1) and high in-plane thermal conductivity (15.53 W m−1 K−1), simultaneously. More interestingly, the sandwich film also reveals outstanding solar-thermal energy conversion ability, which guarantees its normal function in extremely cold environment. The unique asymmetric sandwich structure provides a new strategy for designing and preparing high-performance EMI shielding and thermal conductive films.

We fabricated semitransparent and stretchable hybrid Ag-polytetrafluoroethylene (PTFE) conductors on a polyurethane (PU) substrate for use in high-performance wearable and self-cleaning sensors. The highly conductive Ag metal and stretchable PTFE polymer matrix were cosputtered, embedding the self-formed Ag in the PTFE matrix. Depending on the cosputtering RF and DC power ratio, the Ag-PTFE conductors showed a sheet resistance of 3.09–17.23 Ω/square and an optical transparency of 25.27–38.49% at a wavelength of 550 nm. Under the optimal cosputtering conditions, the Ag-PTFE electrode showed outstanding stretchability (strain 20%) and reversible hysteresis, enabling the production of stretchable and semitransparent conductors. In addition, the very small critical inward/outward bending radius near 1 mm and the hydrophobic surface indicate that the Ag-PTFE films could also be applied in wearable and self-cleaning devices. The suitability of the high stretchability and low sheet resistance of the sputtered Ag-PTFE conductor was verified by using it as a stretchable interconnector for commercial ELs, LEDs, and strain sensors. We applied the Ag-PTFE film as a semitransparent conductor for stretchable touch panels and electromyography sensors. Cosputtered Ag-PTFE films are promising stretchable conductors for a variety of applications in next-generation wearable devices. A conductive material created by combining metals with Teflon-like polymers can improve the stability of touch panels and wearable sensors. Han-Ki Kim and colleagues from Sungkyunkwan University in Suwon, South Korea, report that magneton sputtering, a technique that bombards surfaces with energetic ions, can be used to produce thin polytetrafluoroethylene films infused with narrow channels of silver atoms. Investigations revealed that this material remained highly conductive even after being stretched repeatedly, avoiding the fracturing problems commonly seen when metals are deposited on top of plastic substrates. The team used the new composite as flexible electrodes in a variety of applications including wrist sensors that detect a range of human motion, and forearm-attached electromyography sensors. The silver-filled polymer also had natural water-repelling properties that could be used to make devices with self-cleaning surfaces. Stretchable and wearable Ag-PTFE conductors were fabricated by the simple and mature co-sputtering process with variations in the DC/RF power ratio applied to the Ag and PTFE target. A stretching test was conducted 40% strain under all conditions and reversible to confirm that the hysteresis and stretchability were good for DC 5 W:RF 40 W.

Biocompatible materials have received increasing attention as one of the most important building blocks for flexible and transient memories. Herein, a fully biocompatible resistive switching (RS) memory electronic composed of a carbon dot (CD)-polyvinyl pyrrolidone (PVP) nanocomposite and a silver nanowire (Ag NW) network buried in a flexible gelatin film is introduced with promising nonvolatile RS characteristics for flexible and transient memory applications. The fabricated device exhibited a rewritable flash-type memory behavior, such as low operation voltage (≈-1.12 V), high ON/OFF ratio (>102), long retention time (over 104 s), and small bending radius (15 mm). As a proof of degradability, this transient memory can dissolve completely within 90 s after being immersed into deionized water at 55 °C; it can decompose naturally in soil within 6 days. This fully biocompatible memory electronic paves a novel way for flexible and wearable green electronics.

With the benefits of low latency, wide transmission bandwidth, and large mode field area, hollow-core antiresonant fiber (HC-ARF) has been a research hotspot in the past decade. In this paper, a hollow core step-index antiresonant fiber (HC-SARF), with stepped refractive indices cladding, is proposed and numerically demonstrated with the benefits of loss reduction and bending improvement. Glass-based capillaries with both high (n = 1.45) and low (as low as n = 1.36) refractive indices layers are introduced and formatted in the cladding air holes. Using the finite element method to perform numerical analysis of the designed fiber, results show that at the laser wavelengths of 980 and 1064 nm, the confinement loss is favorably reduced by about 6 dB/km compared with the conventional uniform cladding HC-ARF. The bending loss, around 15 cm bending radius of this fiber, is also reduced by 2 dB/km. The cladding air hole radius in this fiber is further investigated to optimize the confinement loss and the mode field diameter with single-mode transmission behavior. This proposed HC-SARF has great potential in optical fiber transmission and high energy delivery. [Image: see text]

Aircraft cable harnesses is part of the aircraft Electrical Wiring Interconnect System (EWIS), which are installed at aircraft assembly stage. Cable bundle wirings are the basic platform that allows power delivery and data transfer, and therefore the systems functionalities can be then performed. It is reported by Federal Aviation Administration (FAA) that chafing, bend radius and arching problems caused by improper installations and maintenance contribute much to the aircraft accident. Due to the complexities of modern aircraft with large amount of cable bundles installed, it is difficulty to fast locate those wiring fault. This paper investigates the basic characteristics of the cable harnesses and the fundamental theory of Time Domain Reflectometry (TDR) first. A new model-based approach is proposed to allow fast and more accurate wiring fault location. After that, a handheld TDR cable fault tester is developed for industry use and implemented in this research. The preliminary research result shows its capacity of accurate and time-saving wiring fault location, which is helpful in aircraft assembly line and maintenance stage.

In this paper, a trench-assisted large-mode-field-area multi-core fiber with an air-hole structure composed of 21 conventional fiber cores and 16 air holes is proposed, and it can realize dual-mode transmission. By adjusting the structural parameters, the effective mode field area of fundamental mode can be up to 1916.042 µm2 at 1550 nm. In addition, the fiber has good bending characteristics by adding a trench with a lower refractive index than the cladding. When the bending radius is 1.4 cm, the bending loss is low to 2.96 × 10–3 dB/m. This fiber is of great significance for the design of bending insensitive fiber.

Backpressure is considered as an obstruction on the flow of exhaust for any internal combustion (IC) engine. The level of backpressure can affect the amount of emissions and fuel consumption and the performance of the engine. Hence, the backpressure is considered a bad factor for an engine. Even though backpressure could not be eliminated completely, it could be minimized through design optimization of exhaust system. This paper shows the effects of exhaust manifold’s bending radius of 115 cc spark ignition (SI) engine on low-end RPM. The aim of this study was to optimize the bending radius of exhaust manifold in order to minimize backpressure. CFD analysis was conducted to predict the backpressure of exhaust manifold samples based on design of experiment (DOE) through Taguchi’s method. From the analysis result, it is observed that bending radius which is towards the outlet is the most contributing factor to the backpressure and the optimized exhaust manifold reduces backpressure by 10.5% from the existing design. The finding shows that the optimized design offers lower backpressure which could significantly reduce negative impacts to the engine’s performance.

An anti-resonant hollow-core fiber with multi-size tubes is successfully fabricated. The fiber is proved to be robustly single-mode operation with a low bending loss of 0.37dB/m (@1.65μm) under a tight bending radius of 3.5cm.

One important shortcoming of terahertz technology is the relative absence of convenient, flexible, and reconfigurable waveguides with low attenuation and small bend losses. While recent years have been marked by remarkable progress in lowering the impact of material losses using hollow-core guidance, such waveguides often have centimeter-scale diameter and are therefore not flexible. Here we experimentally and numerically investigate antiresonant dielectric waveguides made of thermoplastic polyurethane, a commonly used dielectric with a low Young’s modulus. The hollow-core nature of antiresonant fibers leads to low transmission losses using simple structures, whereas the low Young’s modulus of polyurethane makes them extremely flexible. The structures presented enable millimeter-wave manipulation in the same spirit as conventional (visible- and near-IR-) optical fibers, i.e. conveniently and reconfigurably, despite their centimeter-thick diameter. We investigate two canonical antiresonant geometries formed by one- and six-tubes, experimentally comparing their transmission, bend losses and mode profiles. The waveguides under investigation have loss below 1 dB/cm in their sub-THz transmission bands, increasing by 1 dB/cm for a bend radius of about 10 cm. We find that the six-tube waveguide outperforms its one-tube counterpart for smaller bend radii (here: 10cm); for larger bend radii, coupling to cladding tube modes can lead to a drop in transmission at specific frequencies in the six-tube waveguide that does not occur in the one-tube waveguide.

We develop a model of the forces on a spherical particle suspended in flow through a curved duct under the assumption that the particle Reynolds number is small. This extends an asymptotic model of inertial lift force previously developed to study inertial migration in straight ducts. Of particular interest is the existence and location of stable equilibria within the cross-sectional plane towards which particles migrates. The Navier-Stokes equations determine the hydrodynamic forces acting on a particle. A leading order model of the forces within the cross-sectional plane is obtained through the use of a rotating coordinate system and a perturbation expansion in the particle Reynolds number of the disturbance flow. We predict the behaviour of neutrally buoyant particles at low flow rates and examine the variation in focusing position with respect to particle size and bend radius, independent of the flow rate. In this regime, the lateral focusing position of particles approximately collapses with respect to a dimensionless parameter dependent on three length scales, specifically the particle radius, duct height, and duct bend radius. Additionally, a trapezoidal shaped cross-section is considered in order to demonstrate how changes in the cross-section design influence the dynamics of particles., Submitted for review in the Journal of Fluid Mechanics

We design a compact 37-ring-core fiber, each core can support 5 mode groups in C+L band. The theoretical inter-core crosstalk keeps lower than −50 dB/km when the bending radius is larger than 7 cm.