Abstract: We propose and experimentally demonstrate a sharply bent multimode silicon waveguide by introducing a pair of mode converters. The principle of the multimode bend is based on the eigenmode conversion between straight and bent waveguides, and the particle swarm optimization is adopted to engineer the geometry. The device is fabricated on the standard silicon-on-insulator platform using one lithography/etching, and no additional steps are required. The measured results show that the insertion loss is <0.2 dB, and the inter-mode crosstalk is <-22 dB with a bend radius of 5 μm, from 1500 to 1600 nm. A comparable performance can be achieved using a conventional scheme with 40 μm radius.

Abstract: Perovskite ceramics and single crystals are commonly hard and brittle due to their small maximum elastic strain. Here, large-scale BaTi0.95Co0.05O3 (BTCO) film with a SrRuO3 (SRO) buffered layer on a 10 µm thick mica substrate is flexible with a small bending radius of 1.4 mm and semitransparent for visible light at wavelengths of 500–800 nm. Mica/SRO/BTCO/Au cells show bipolar resistive switching and the high/low resistance ratio is up to 50. The resistive-switching properties show no obvious changes after the 2.2 mm radius memory being written/erased for 360 000 cycles nor after the memory being bent to 3 mm radius for 10 000 times. Most importantly, the memory works properly at 25–180 °C or after being annealed at 500 °C. The flexible and transparent oxide resistive memory has good prospects for application in smart wearable devices and flexible display screens.

Abstract: Ultimately low-loss 90° waveguide bend composed of clothoid and normal curves is proposed for dense optical interconnect photonic integrated circuits. By using clothoid curves at the input and output of 90° waveguide bend, straight and bent waveguides are smoothly connected without increasing the footprint. We found that there is an optimum ratio of clothoid curves in the bend and the bending loss can be significantly reduced compared with normal bend. 90% reduction of the bending loss for the bending radius of 4 μm is experimentally demonstrated with excellent agreement between theory and experiment. The performance is compared with the waveguide bend with offset, and the proposed bend is superior to the waveguide bend with offset in terms of fabrication tolerance.

Abstract: Understanding bend loss in single-ring hollow-core photonic crystal fibers (PCFs) is becoming of increasing importance as the fibers enter practical applications. While purely numerical approaches are useful, there is a need for a simpler analytical formalism that provides physical insight and can be directly used in the design of PCFs with low bend loss. We show theoretically and experimentally that a wavelength-dependent critical bend radius exists below which the bend loss reaches a maximum, and that this can be calculated from the structural parameters of a fiber using a simple analytical formula. This allows straightforward design of single-ring PCFs that are bend-insensitive for specified ranges of bend radius and wavelength. It also can be used to derive an expression for the bend radius that yields optimal higher-order mode suppression for a given fiber structure.

Abstract: We present the development, manufacturing, and performance of spherically bent crystal analyzers (SBCAs) of 100 mm diameter and 0.5 m bending radius. The elastic strain in the crystal wafer is partially released by a "strip-bent" method where the crystal wafer is cut into strips prior to the bending and the anodic bonding process. Compared to standard 1 m SBCAs, a gain in intensity is obtained without loss of energy resolution. The gain ranges between 2.5 and 4.5, depending on the experimental conditions and the width of the emission line measured. This reduces the acquisition times required to perform high energy-resolution x-ray absorption and emission spectroscopy on ultra-dilute species, accessing concentrations of the element of interest down to, or below, the ppm (ng/mg) level.

Abstract: The VDA238-100 standard for tight radius bending (v-bending) of sheet materials has received widespread acceptance with automotive suppliers and material producers to characterize local formability However, the test fixture and tooling in the v-bend test standard is not amenable to direct strain measurement and the operator cannot terminate the test at the onset of crack initiation as the outer bend surface is not visible Consequently, fracture is identified using a load threshold and the bend angle estimated from an analytical formula based upon the punch displacement and tooling geometry Bend angles are not directly transferable and must be interpreted relative to the sheet thickness and bend radius unlike a strain measurement By obtaining an in-situ strain measurement on the surface using digital image correlation (DIC), the plane strain fracture limit can be accurately identified at the onset of cracking and remove ambiguity in translating the bend angles to practical forming operations and simulations A novel inverted VDA test frame was developed to incorporate DIC strain measurement during the bend test and a variety of advanced high strength sheet materials were evaluated It was observed that the VDA bend test creates a homogeneous strain state of plane strain across the width of the sample along with a proportional strain path to fracture without necking that is ideal for fracture characterization A correlation is developed to relate the bend angle with the major strain for the materials considered and accounts for the sheet thickness and bend radius A comparison of the bend angle obtained using the formula in the VDA standard based on the punch displacement was in very good agreement with manual measurements and an algorithm to measure the bend angle using DIC analysis was developed

Abstract: Swirl-switching is a low-frequency oscillatory phenomenon which affects the Dean vortices in bent pipes and may cause fatigue in piping systems. Despite thirty years worth of research, the mechanism that causes these oscillations and the frequencies that characterise them remain unclear. Here we show that a three-dimensional wave-like structure is responsible for the low-frequency switching of the dominant Dean vortex. The present study, performed via direct numerical simulation, focuses on the turbulent flow through a 90 \degree pipe bend preceded and followed by straight pipe segments. A pipe with curvature 0.3 (defined as ratio between pipe radius and bend radius) is studied for a bulk Reynolds number Re = 11 700, corresponding to a friction Reynolds number Re_\tau \approx 360. Synthetic turbulence is generated at the inflow section and used instead of the classical recycling method in order to avoid the interference between recycling and swirl-switching frequencies. The flow field is analysed by three-dimensional proper orthogonal decomposition (POD) which for the first time allows the identification of the source of swirl-switching: a wave-like structure that originates in the pipe bend. Contrary to some previous studies, the flow in the upstream pipe does not show any direct influence on the swirl-switching modes. Our analysis further shows that a three- dimensional characterisation of the modes is crucial to understand the mechanism, and that reconstructions based on 2D POD modes are incomplete.

Abstract: We propose and design a kind of heterogeneous rod-assisted and trench-assisted multi-core fiber (Hetero-RA-TA-MCF) with 32 cores arranged in square-lattice structure (SLS), and then we introduce the design method for Hetero-RA-TA-MCF. Simulation results show that the Hetero-RA-TA-32-Core-Fiber achieves average effective area (Aeff) of about 74 μm2, low crosstalk (XT) of about -31 dB/100km, threshold value of bending radius (Rpk) of 7.0 cm, relative core multiplicity factor (RCMF) of 8.74, and cable cutoff wavelength (λcc) of less than 1.53 μm.

Abstract: This paper describes a six-mode 19-core fiber with 114 spatial modes, which was designed and fabricated for weakly-coupled mode-division-multiplexed (MDM) transmission over uncoupled cores. The 19 identical graded-index cores were packed on a hexagonal lattice with a 62-μm pitch in a ∼318-μm-diameter cladding. The cladding diameter is large, but still mechanically reliable by assuming a 2% proof test and 40-mm minimum fiber bend radius. The inter-core crosstalk is negligibly suppressed and the calculation indicated that a 50-μm core pitch (corresponding to the 266-μm-diameter cladding) is achievable without significant crosstalk degradation. Though the fiber was intended for the weakly-coupled MDM transmission, the differential mode delay (DMD) within a degenerated mode group of LP21 and LP02 modes was not well suppressed. Thus, further DMD suppression within each mode group or splitting the degeneracy of the modes is required to realize multiple-input multiple-output (MIMO) digital signal processing with reduced complexity. Additionally, a numerical investigation revealed that the intra-core inter-modal crosstalk at a butt coupling was induced not only by the misalignment, but also by the refractive index profile mismatch between the butt-coupled cores. Therefore, the tight tolerance on the refractive index profile is important both for DMD control and modal crosstalk suppression.

Abstract: Artificial ferromagnetic nanofiber networks with new electronic, magnetic, mechanical and other physical properties can be prepared by electrospinning and may be regarded as the base of bio-inspired cognitive computing units. For this purpose, it is necessary to examine all relevant physical parameters of such nanofiber networks. Due to the more or less random arrangement of the nanofibers and the possibility of gaining bent nanofibers in this production process, elementary single nanofibers with varying bending radii, from straight fibers to those bent along half-circles, were investigated by micromagnetic simulations, using different angles with respect to the external magnetic field. As expected from the high aspect ratios and the resulting strong shape anisotropy, all magnetization reversal processes took place via domain wall processes. Changing the cross-section from circular to a circle-segment or a rectangle significantly altered the coercive fields and its dependence on the bending radius, especially for the magnetic field oriented perpendicular (90 deg) to the fiber axes. In all three cross-sections, an angle of 45° between the fiber orientation and the external magnetic field resulted in the smallest influence of the bending radius. The shapes of the longitudinal and transverse hysteresis curves showed strong differences, depending on cross-section, bending radius and orientation to the magnetic field, often depicting distinct transverse magnetization peaks perpendicular to the fibers for fibers which were not completely oriented parallel to the magnetic field. Varying these parameters thus provides a broad spectrum of magnetization reversal processes in magnetic nanofibers and correspondingly scenarios for a variety of fiber-based information processing.

Abstract: In this paper, a simple fabricated and low cost acoustic vibration sensor based on macro-bend coated single-mode fiber (SMF-28) is proposed and developed. The fiber optic sensor comprises of a bending structure and the macro-bending loss was employs as the sensing mechanism for the detection of leakage of pipeline at low frequency. The measurement system involving the proposed fiber sensor is presented and investigated. Through this system, the fiber sensor is characterized by measuring the power loss corresponding to the vibration at various bending radius and number of wrapping turns. Furthermore, the proposed fiber sensor is also implemented in field test (water pipeline) and it is able to detect vibrations at the frequency range of 20 Hz to 2500 Hz.

Abstract: Gas sensing system has found applications in industrial process and environmental monitoring. Infrared hollow waveguide is one of the best choices for gas cell in spectroscopic sensing due to the advantages of low loss, flexibility, and fast response. In order to miniaturize the gas sensing system while maintain optical path length, long hollow waveguide can be coiled into a small box to reduce physical dimensions. Bending causes additional loss for hollow waveguide, therefore it is necessary to optimize the parameters for bent hollow waveguide cell. In this paper, a calculation method was established to analyze the performance of a gas sensing system with a bent hollow waveguide as the absorption cell. Simulation results show the relationship between gas absorption intensity and system parameters such as waveguide length, bore diameter, bending radius, system noise, and divergence angle of the light source. Optimized parameters for the waveguide cell were given based on the simulation results. An experimental system was set up by using a Fourier transform infrared (FTIR) spectrometer and flexible hollow waveguides. Preliminary experiments on waveguide length, bending radius, and system signal-to-noise ratio (SNR) were conducted and the measured data agree well with simulation results.

Abstract: A novel high-power orthogonal over-mode circular waveguide (CWG) TE 11 -TM 01 mode converter is presented. This mode converter is made up by two orthogonal CWGs and two metal plates. One metal plate is used to achieve phase shift of two semicircular waveguide TE 11 modes. In the bend, phase difference between the two TE 11 modes is changed from π to 2π, which meets the requirement of mode conversion at the end of the metal plate. The other metal plate is used to reflect and suppress CWG TE 21 mode, and thus power-handling capacity is greatly improved because lager radius of CWG can be utilized. After optimizing basic parameters, simulation results show that the mode converter has virtues of high power-handling capacity, high conversion efficiency, and a very small bend radius. Finally, test result of the VSWR has a good agreement with simulation result and insertion loss is 0.12 dB at 8.4 GHz. All of that prove the feasibility of the mode converter.

Abstract: A cover element for a foldable electronic device that includes a foldable glass element, first and second primary surfaces, and a compressive stress region extending from the first primary surface to a first depth that is defined by a stress σ 1 of at least about 100 MPa in compression at the first primary surface. The device also includes a polymeric layer disposed over the first primary surface. The glass element has a stress profile such that when the glass element is bent to a target bend radius of from 1 mm to 20 mm, to induce a bending stress σ B at the first primary surface in tension, σ 1 +σ B < 400 MPa (in tension). Further, the cover element can withstand a pen drop height of at least 1.5 times that of a control pen drop height of the cover element without the layer according to a Drop Test 1.

Abstract: Bending of a thin-walled tube with small relative bending radius is a hot topic which has aroused extensive attention in recent years. The main disadvantage of tube parts with small bending radius fabricated by available bending approaches is non-uniform wall thickness, large springback, poor fatigue performance, and wrinkle that is difficult to control for thin-walled tube bending. In order to solve this problem, a Bend-Bulge Forming (BBF) process combining rotary draw bending and hydroforming that realizes the fabricating of thin-walled elbows with small bending radius has been put forward in this study, and both FEM simulations and experiments were carried out. Meanwhile, in order to reveal the deformation behavior and the failure during BBF process, theoretical and FEM analysis were conducted by free expansion with bent tubes. The results show that the axial feeds play a prominent role in the hydroforming process. It can promote the tube wall outside of the bend contact with hydroforming die and avoid the excessive thinning. At the same time, the tube wall inside of the bend which is thickened during bending operation can be deformed sufficiently. Finally, the final parts fabricated by the BBF process have approximately constant wall thickness and high precision.

Abstract: A novel bending machine has been designed and tested. It enables flexible electronics to be subjected to repeated bending with constant radius and tension. In-situ electrical characterization can give accurate analysis of lifetime distributions if sufficiently many samples are ran to failure, allowing reliability prediction models to be developed. Four sets of test samples with different combinations of substrate, routing, interconnect technology and components were examined. A poor level of reliability was observed when using anisotropic conductive paste to form interconnects, whereas a significantly higher level of reliability was observed when using a bismuth-tin solder paste. The assembly of larger components resulted in shortened time to failure, whereas increasing the bending radius prolonged the observed lifetimes.

Abstract: The invention discloses a method of increasing a three-dimensional free bending forming limit of metal. The method comprises the following step: in a bending forming process, a motion eccentric distance U (the distance of the center of a bending die deviating from an origin of coordinates) of the bending die (2) and a distance V between the center of the bending die and the front end of a guide mechanism (3) are subjected to optimal combination. The problem that small bending radius bending can not be realized due to the fact that a pipe bending radius of the existing free bending forming equipment is large is solved effectively; the method has an important guiding significance in improving the three-dimensional free bending forming quality of the metal; and the method is simple and feasible, is high in production efficiency, and has important engineering application values and obvious economic benefits in the fields of engineering like aviation and spaceflight.

Abstract: The invention discloses an aviation titanium alloy 3D free bend warm forming device and a forming method The forming method comprises the following steps: (1) the free bend forming test is performed for an aviation titanium alloy pipe heated to a specific temperature before bending of a pipe in forming space to obtain a relation curve between an eccentric distance U of the pipe at the specific temperature and a bending radius R; when the titanium alloy bent pipe is technologically analyzed, the eccentric distance Un is firstly obtained from the curve when the bending radius is Rn; and then, Un is substituted into a three-dimensional free bend forming analysis formula to obtain forming process parameters aiming at the complex bent pipe; and (2) in the forming process, an infrared temperature measurer measures the surface temperature of the pipe in real time; and the real-time feedback adjustment is performed for the feeding speed of the pipe along a Z axle to guarantee stable heating temperature of the pipe As the local induction heating is performed for the titanium alloy pipe, the forming method can preferably eliminate such defects as low plasticity, high deformation resistance and difficult bending formation in the cold bend forming process of the titanium alloy pipe, and improves the forming quality of the aviation titanium alloy bent pipe

Abstract: The invention relates to a superconducting magnet based on a ReBCo coating superconducting sheet. Each superconducting sheet and each insulating sheet both adopt a circular ring sheet structure, and the inner diameter and the outer diameter of the superconducting sheet and the insulating sheet are the same; the insulating sheets and the superconducting sheets are arranged alternately to form the superconducting magnet; and flanges are arranged on the upper and lower parts of the superconducting magnet, and the flanges are fixedly connected through an insulating pull rod. By virtue of the superconducting sheets, bending and winding links are omitted, so that the superconducting magnet can be manufactured conveniently; meanwhile, the superconducting magnet is simple in structure and has no limitation on the bending radius; only simple stacking instead of deforming, is required in the forming process of the superconducting magnet, so that influence to the flow capacity of the superconducting material is low; the superconducting magnet, the outer radius of which is slightly smaller than the inner radius, can be combined and nested at occasions where higher magnetic field is required, so as to obtain the required magnetic field; liquid nitrogen is adopted to provide a low-temperature environment; the superconducting magnet is excited by adopting a flux pump technology; and in addition, by combination of the advantages of the high-temperature superconducting ReBCo coating conductor, low-temperature liquid nitrogen cooling, and the flux pump, the superconducting magnet has the advantages of low power consumption, high efficiency, simple structure, and simple and convenient operation.

Abstract: The invention discloses a bending formation method of a small-curvature bending radius L type thin-wall aluminum alloy bent pipe. Two ends of the bent inner side of a long pipe blank of an aluminum alloy thin-wall pipe blank are grooved by 35-45 degrees; a protective agent is coated at the external of the pipe blank; oily molybdenum disulfide is sprayed in the semi-cylindrical surface of an area from the from part of the bent inner side of the pipe blank to the front part pi D, so that a material on the bent inner side of the pipe is facilitated to flow and to improve wrinkling; a traditional polyurethane round bar is replaced; multiple polyurethane cylinder blocks are filled in the pushed end of the pipe blank; and compared with an integral polyurethane filler rod, the taking out is easier after formation, and the forming efficiency is improved. Meanwhile, the polyurethane cylinder blocks with proper hardness, thickness and diameter facilitate internal support of the bent pipe, and are not liable to generate wrinkles on the bent inner side; and the jacking force of a core head is reinforced during forming to supply enough internal pressure into the pipe through a filler to force a lot of materials to flow to the front groove so as to prevent wrinkling to form the qualified small-curvature bending radius L type thin-wall aluminum alloy pipe.

Abstract: A novel structure of overmode circular waveguide bend is investigated, which is used to transmitter circular waveguide TM 01 mode with high power-handing capacity, high transmission efficiency and small bend radius. Metal plates and metal rod are used to change the type of waveguide. In the bend of the structure, circular waveguide is split into four sector waveguides, and the phase difference between sector waveguide TE 11 modes changes from 0 to 2π, that means the phases of sector waveguide TE 11 modes are also same after bending. Four sector waveguide TE 11 modes with same phase convert to coaxial TEM mode at the end of the metal plates, which finally converts to circular waveguide TM 01 mode and is outputted. Microwave propagates with singlemode in the bend of the structure, that can avoid exciting high-order mode. Experimental test results show that VSWR is below 1.3 in the range of 8.25–8.55 GHz and less than 1.07 at 8.4 GHz and the insertion loss is 0.2 dB at 8.4 GHz, which prove the feasibility of the structure of the overmode circular waveguide bend.

Abstract: An ultralow bending-loss trench-assisted single-mode optical fiber is designed and fabricated in this letter. The experimental results show that the fiber can support an ultralow bending loss of 0.05 dB/turn at a sharp bend radius of 5 mm at 1550 nm. This letter is considered to be of significance for the design and fabrication of bend insensitive fibers (BIFs), specifically for verifying the value of trench-assisted BIF designs. Furthermore, the fast growth of fiber-to-the-home applications will benefit from this letter.