Concave Bending Research Articles

Flexible in-plane microsupercapacitors with electrospun NiFe2O4 nanofibers for portable sensing applications.

The development of wearable electronic devices in recent decades has brought new opportunities in the exploration of micro-supercapacitors as energy storage units. In this work, we report the fabrication of flexible NiFe2O4 nanofiber based in-plane micro-supercapacitors (MSCs), which can serve as energy storage receptors to drive a portable graphene pressure sensor. The obtained NiFe2O4 nanofiber electrodes exhibited a specific capacitance of 2.23 F cm(-3) at the scan rate of 100 mV s(-1), and excellent rate capability and robust cycling stability with a capacitance retention of 93.6% after 10 000 charge/discharge cycles. Moreover, the in-plane MSCs have superior flexibility and outstanding stability even after repetition of charge/discharge cycles during the convex and concave bending states. The MSCs offered a high energy density of 0.197 mWh cm(-3) and power density up to 2.07 W cm(-3). We also coupled the MSCs with a graphene pressure sensor as a micro-integrated system to implement it's pressure response function and used MATLAB to simulate this system behavior as well. The performance of the designed systems exhibited a stable pressure response, and the simulated results coincide well with the experimental data, demonstrating its feasibility in wearable electronic devices.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters.

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low Eto of 1.03-0.73 Vμm-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Ultrathin single-crystalline silicon solar cells for mechanically flexible and optimal surface morphology designs

Recently, the evolution of photovoltaic cells in together with flexible electronics rapidly grows up so as to satisfy the flexibility and elasticity needs. Therefore, it will be a breakthrough impact if it is able to develop flexible single-crystalline photovoltaic cells which are fabricated with traditional procedure and provide highly electrical properties as well. This study aims to fabricate the flexible solar photovoltaic device with practical and reproducible method. Generally, the flexible solar photovoltaic is manufactured on the 30μm-thickness single-crystalline silicon chip by chemical etching process. Versatile design on the flexible device can enhance light trapping effect. The surface texturization and antireflection layer deposition successfully minimize the reflectivity losses from the incident light. In addition, the developed devices under concave bending morphology demonstrates better operating performance than convex and flat configurations. As to the concave bending type, the significant improvement of power conversion efficiency (129% better than flat type, and 161% better than convex type) is observed from a large device current, which is related to the contribution of light trapping enhancement. In combination of all optimal conditions, the flexible device exhibits conversion efficiency up to 13.8%. The development of novel flexible solar photovoltaics with the excellent mechanical flexibility, low silicon material consumption and low fabrication cost demonstrates the potential capability for future solar cells.

Assessment of Flatness of Assumed Planar Surfaces for Ultrasound Investigation of Elastic Surfaces

This study investigate the planarity of an assumed planar surface made of an elasomer fixed on its perimeter by a square acrylic frame. The central part of this surface is insonified with two different linear array transducers (types 8811 and 8670, BK Medical), yielding 11 images forming two 3D data sets. The change in flatness of the surface was determined by cross-correlation of the matrix of received signals. The cross-correlation was calculated between signals from the same image and as well as between signals that belonged to different images. The maximal change over the entire surface investigated is found to be in the order of a wavelength at about 12MHz (λ=120μm). Specifically, the surface showed weak concave bending for the two different transducers. The data was validated using the cross-correlation coefficient function. This yielded values of 0.99± 0.01 (mean± std) when the algorithm was applied to scan-lines in the same image plane and 0.93± 0.05 when it was applied to scanlines in different image planes.

A Compact Kapton-Based Inkjet-Printed Multiband Antenna for Flexible Wireless Devices

A low-cost inkjet-printed multiband antenna envisioned for integration into flexible and conformal mobile devices is presented. The antenna structure contains a novel triangular iterative design with coplanar waveguide (CPW) feed, printed on a Kapton polyimide-based flexible substrate with dimensions of 70×70×0.11 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The antenna covers four wide frequency bands with measured impedance bandwidths of 54.4%, 14%, 23.5% and 17.2%, centered at 1.2, 2.0, 2.6 and 3.4 GHz, respectively, thus, enabling it to cover GSM 900, GPS, UMTS, WLAN, ISM, Bluetooth, LTE 2300/2500 and WiMAX standards. The antenna has omnidirectional radiation pattern with a maximum gain of 2.1 dBi. To characterize the flexibility of the antenna, the fabricated prototype is tested in convex and concave bent configurations for radii of 78 mm and 59 mm. The overall performance remains unaffected, except a minor shift of 20 MHz and 60 MHz in S11, for concave bending at both radii. The compact, lightweight and conformal design as well as multiband performance in bent configurations, proves the suitability of the antenna for future electronic devices.

The Buckling Analysis of Drill String in Inclined Wellbore with a Concave Curved Geometric Defect

Some inclined boreholes have to be drilled in directional wells, but the track of inclined borehole is impossible to be a ideal straight line, there are always some geometric defects such as bending, thus the drilling string in it is bound to have initial bending due to the constraints of borehole, hence the drilling string in inclined borehole is usually a curved compressed rod. Its buckling nature is quite different from straight compressed rod, it is necessary to analyze it specially. In this paper the buckling problem of drill string in inclined borehole with a concave curved geometric defect is studied by energy method, the computing formula of buckling load for it was obtained. And the influence of initial concave bending on buckling load was discussed. The research indicates that when drilling string in inclined well bore has a initial concave bending, the greater the degree of initial bending of drill string, the greater its buckling load.

All-solid-state flexible micro-supercapacitor arrays with patterned graphene/MWNT electrodes

We report on the fabrication of all-solid-state flexible micro-supercapacitor (MSC) arrays with electrodes consisting of patterned multilayer graphene (MG) and functionalized multi-walled carbon nanotubes (MWNTs), and polyvinyl alcohol (PVA)–H3PO4 gel electrolyte. The fabricated MSC exhibited areal capacitance of 2.54mF/cm2 at a scan rate of 10mV/s, which is ∼150 times higher than that of MSC with MG electrode. The areal energy and power density were also dramatically improved via using MG/MWNT electrodes. In addition, there was no deterioration of the electrical performance over repetitive convex and concave bending with a bending radius of 2.3mm. Furthermore, both the output voltage and the total capacitance of the MSC could be controlled via the serial or parallel connection of multiple planar-type MSCs to operate high-voltage light-emitting diodes.

All fiber curvature sensor based on modal interferometer with waist enlarge splicing

A novel fiber curvature sensor based on modal interferometer with waist-enlarge splicing is proposed. A section of 30mm polarization maintaining fiber (PMF) is spliced with waist enlarge between two conventional single mode fibers (SMFs) to construct an all fiber curvature sensor. The results show that the transmission spectrum has a blue and red shift, corresponding to the opposite curvature directions. The sensitivity coefficient of −10.634nm/m−1 and 10.152nm/m−1 were acquired by concave and convex bending with the range from 0m−1 to 2.054m−1, and the corresponding resolution were 9.4×10−4m−1 and 9.85×10−4m−1, respectively. And the influence of different lengths of PMF on the sensitivity was also discussed.

Traction X-ray under general anesthesia helps to save motion segment in treatment of Lenke type 3C and 6C curves

Background contextIn patients with structural lumbar curves, several studies have shown the advantages of stopping fusion at L3 and saving L4. However, fusing the L4 may still be deemed necessary in a significant number of patients with structural lumbar curves (ie, Lenke types 3 and 6) when fusion levels are selected by using traditional flexibility X-ray (TXR) methods such as supine side bends and traction. PurposeThe aim of this retrospective study was to evaluate the effectiveness of the traction X-ray under general anesthesia (TrUGA) method in saving the L4 in patients with Lenke types 3C and 6C curves. Study designThis was a retrospective clinical study. Patient sampleEighty-nine consecutive patients (77 females and 12 males) with adolescent idiopathic scoliosis Lenke types 3C (46 patients) and 6C (43 patients) curves and who underwent an instrumented posterior spinal fusion by a single surgeon were included. The selection of lower instrumented vertebrae (LIV) was done by using the central sacral vertical line (CSVL). LIV was defined as the uppermost vertebrae of the lumbar curve that was not intersected by CSVL on standing anteroposterior radiograph, but became parallel to the sacrum and was intersected by CSVL at the concave bending or TrUGA. The disc wedging under LIV should be parallel or near parallel and rotation of LIV should be corrected at least one to two (Nash-Moe) grades. Outcome measuresRadiological evaluation included preoperative standing AP, lateral and TXR, and intraoperative supine TrUGA, which was taken after the induction of anesthesia and before positioning the patient. LIV was determined by using TXR and TrUGA. Preoperative, postoperative with ≥2 year follow-up curve magnitudes, LIV tilt, and disc wedging below LIV and CSVL to T1 distance were all measured. A satisfactory radiographic outcome was determined to be the result if CSVL was within 2 cm of the center of T1, the LIV tilt angle was less than 10°, and any increase in thoracic and lumbar curve during follow-up was less than 5°. Clinical outcome was analyzed by using follow-up Scoliosis Research Society-22 (SRS-22) questionnaire and by the global outcome scores (GOS) for improvement and deterioration measured with a 15-point scale ranging from −7 (no improvement) to +7 (significant improvement). ResultsThe average follow-up period was 5.4 (range: 2 to 8) years. Average age at surgery was 15.5 (range: 13 to 19) years. Pedicle screw constructs were used in all patients. LIV was L3 in 85 patients, and L4 in the remaining 4 patients. Using the same selection criteria, L3 was LIV according to both the TXR and TrUGA films in 39 cases (44%) and fusion was stopped at L3. In 46 (52%) cases, TXR determined L4 to be the LIV, whereas in all those patients L3 was the LIV according to TrUGA and fusion was stopped at L3 in all. LIV was L4 according to both methods in four (4%) patients and fusion was stopped at L4. All patients had successful radiographic outcomes according to the criteria of CSVL to be within 2 cm of the center of T1, L3 tilt angle of less than 10°, and L3–L4 disc wedging to be less than 10° at the final follow-up. Average follow-up SRS-22 score was 4.3 (range: 3.3–5) and GOS was 6.1 (range: 3–7). None of the patients required additional surgery for decompensation or adding on, and there was no significant correction loss during follow-up. ConclusionTrUGA may be an alternative method for selection of fusion levels and may help to save L4 when compared with traditional radiograph methods in surgical treatment of Lenke types 3 and 6 curves.

Hexagonal warping on optical conductivity of surface states in topological insulator Bi2Te3

Angle-resolved photoemission spectroscopy studies of the protected surface states in the topological insulator Bi${}_{2}$Te${}_{3}$ have revealed the existence of an important hexagonal-warping term in its electronic band structure. This term distorts the shape of the Dirac cone from a circle at low energies to a snowflake shape at higher energies. We show that this implies important modifications of the interband optical transitions which no longer provide a constant universal background, as seen in graphene. Rather, the conductivity shows a quasilinear increase with a slightly concave upward bending as energy is increased. Its slope increases with increasing magnitude of the hexagonal distortion, as does the magnitude of the jump at the interband onset. The energy dependence of the density of states is also modified and deviates downward from linear behavior with increasing energy.

Monitoring static shape memory polymers using a fiber Bragg grating as a vector-bending sensor

We propose and demonstrate a technique for monitoring the recovery deformation of the shape-memory polymers (SMP) using a surface-attached fiber Bragg grating (FBG) as a vector-bending sensor. The proposed sensing scheme could monitor the pure bending deformation for the SMP sample. When the SMP sample undergoes concave or convex bending, the resonance wavelength of the FBG will have red-shift or blue-shift according to the tensile or compressive stress gradient along the FBG. As the results show, the bending sensitivity is around 4.07 nm/cm−1. The experimental results clearly indicate that the deformation of such an SMP sample can be effectively monitored by the attached FBG not just for the bending curvature but also the bending direction.

How Interface Geometry Dictates Water’s Thermodynamic Signature in Hydrophobic Association

As a common view the hydrophobic association between molecular-scale binding partners is supposed to be dominantly driven by entropy. Recent calorimetric experiments and computer simulations heavily challenge this established paradigm by reporting that water's thermodynamic signature in the binding of small hydrophobic ligands to similar-sized apolar pockets is enthalpy-driven. Here we show with purely geometric considerations that this controversy can be resolved if the antagonistic effects of concave and convex bending on water interface thermodynamics are properly taken into account. A key prediction of this continuum view is that for fully complementary binding of the convex ligand to the concave counterpart, water shows a thermodynamic signature very similar to planar (large-scale) hydrophobic association, that is, enthalpy-dominated, and hardly depends on the particular pocket/ligand geometry. A detailed comparison to recent simulation data qualitatively supports the validity of our perspective down to subnanometer scales. Our findings have important implications for the interpretation of thermodynamic signatures found in molecular recognition and association processes. Furthermore, traditional implicit solvent models may benefit from our view with respect to their ability to predict binding free energies and entropies.

Three-Dimensional Numerical Simulation and Experimental Study of Sheet Metal Bending by Laser Peen Forming

Laser peen forming (LPF) is a purely mechanical forming method achieved through the use of laser energy to form complex shapes or to modify curvatures. It is flexible and independent of tool inaccuracies that result from wear and deflection. Its nonthermal process makes it possible to form without material degradation or even improve them by inducing compressive stress over the target surface. In the present study, a fully three-dimensional numerical model is developed to simulate the forming process of laser peen forming. The simulation procedure is composed of several steps mainly including the shock pressure prediction, the modal analysis, and the forming process calculation. System critical damping is introduced to prevent unnecessary long post-shock residual oscillations and to greatly decrease the solution time for simulation. The bending profiles and angles with different thicknesses are experimentally measured at different scanning lines and scanning velocities to understand the process and validate the numerical model. The calculated bending profiles and angles agree well with the trend of the measured results. But it is found that simulations with the Johnson–Cook model are more consistent, matching the experimental results for the thick sheet metal with a convex bending, while the elastic-perfectly-plastic model produces a better agreement even though with underestimated values for the thinner sheet metal with a concave bending. The reason for this phenomenon is discussed, combining the effects of strain rate and feature size. Both the simulation and the experiments show that a continuous decrease in bending angle from concave to convex is observed with increasing specimen thickness in general. Large bending distortion is easier to induce by generating a concave curvature with LPF, and the angle of bending distortion depends on the number of laser shocks.

Adhesive Elastic–Plastic Microcontact Analysis of Truncated Cylinder-on-Flat with Asperities

Adhesion interaction during micro-contacts of deformable rough bodies is characterized in this study using finite element based methodology. The interacting bodies are a truncated cylinder and a flat. Surfaces roughness is simulated by multiple asperities on a cylindrical segment. Lennard–Jones potential methodology is used to calculate adhesion forces by volume integration over the contacting bodies as well as over all asperities, both undeformed and deformed. Cylindrical segment of the asperity is deformed basically in two cylindrical segments. The flat body is deformed the least at the center and maximum at the outer portion of contact width, causing concave bending of the upper body with multi-asperity interfaces. Radius of asperities decreases from the center to outer periphery along the contact width. Adhesion force at each asperity is minimum at the center and maximum at the outer portion of the contact width in the deformed state after complete unloading. The total adhesion force between all asperities and lower body depends on number of asperities, and its maximum value decreases after deformation and occurs at separation distance greater than that for undeformed contact. Its maximum value increases with increasing number of asperities for the undeformed state and decreases with increasing number of asperities for the deformed state. On the other hand, total adhesion force between asperities, truncated cylindrical body and lower body increases with increasing number of asperities for both undeformed and deformed states due to the contribution of truncated segment/lower body interaction, and its location shifts towards the center of contact with increasing number of asperities.

Using patterned carbon nanotube films with optical anisotropy to tune the diffracted color from flexible substrates

We combine transverse electric (TE) and transverse magnetic (TM) polarized light of various incident angles with optical thin film theory to investigate the optical anisotropy of carbon nanotube (CNT) films. We also determined the relationship between the optical anisotropy and diffraction phenomena in grating-patterned CNT films. For TE polarized light, the diffraction intensity remains almost unchanged upon varying the incident angle. For TM-polarized light, however, the diffraction intensity decreases upon increasing the angle of incidence. We deform and bend flexible substrates to induce dynamic modulation of the diffraction colors from the CNT gratings. Convex bending of the surface increases the period of the CNT gratings, thereby causing more penetration of diffracted light; concave bending decreases the period of the CNT gratings, causing the diffracted light to weaken in intensity in the CNT forest.

Curvature optical fiber sensor by using bend enhanced method

Deflection curvature measurement can offer a number of advantages compared with the well-established strain measurement alternative. It is able to measure thin structure; fiber has no resistance with force, which leads to a high precision. There are many kinds of curvature gauges with different operation principles. A low-cost curvature optical fiber sensor using bend enhanced method to improve its curvature measurement sensitivity was developed in recent years. This sensor can distinguish between convex bending and concave bending and has a good linearity in measuring large curvature deformation. Whisper gallery ray theory and Monte Carlo simulation are new achievements by computer experiment. The operation mechanism of this curvature optical fiber sensor is presented based on light scattering theory. The attenuation is ascribed to the transmission mode changing by the curvature of the fiber, which affects the attenuation of the surface scattering. The mathematical model of relationship among light loss, bending curvature, surface roughness, and parameters of the fiber’s configuration is also presented. We design different kinds of shapes of sensitive zones; each zone has different parameters. Through detecting their output optical attenuations in different curvatures and fitting the results by exponential decaying functions, the proposed model is demonstrated by experimental results. Also, we compare the experimental results with the theoretical analysis and discuss the sensitivity dependence on bending direction.

Electrical Characteristics of Driver LSI with 35 m Thickness for Flexible Display

Electrical characteristics of the mechanically flexible driver LSI as thin as 35μm mounted directly on a flexible display panel were precisely analyzed. The high-voltage transistors on this LSI show the current decrease by 10-30% in high voltage region, comparing with that of an ordinary thickness LSI. These phenomena can be associated with a self-heating effect. We considered the thermal diffusion on the thin chip by changing material of the measurement stage. Moreover, we analyzed the transistor characteristics on the thin chip under convex and concave bending conditions. The drain current change by piezoresistive effect was observed.

Experimental study on distortion of Al-6013 plate after friction stir welding

Friction stir welding (FSW) experiments with different panel dimensions and welding parameters have been designed to study the distortion of FSW. The FSW experiments were carried out with a load control facility to make the welding parameters reliable. The distortion of FSW is much smaller than that of arc welding, but it is still very significant. Three-dimensional distortion measuring system was applied to further study distortion trends. The results show that the distortion after FSW is in saddle shape, with convex bending in longitudinal direction and concave bending in transverse direction. This distortion pattern is in contrary with that of traditional arc welding. It is also found that increasing the panel length increases the longitudinal distortion but almost do not influence the transverse distortion. Increasing the rotation speed increases both longitudinal distortion and transverse distortion. The influence of welding speed on distortion is not very clear.

Experimental approach and RSM procedure on the examination of springback in wiping-die bending processes

Abstract In this work, springback has been investigated using experimental and theoretical approaches. Hence, the springback evolution with different die radius and stroke values was obtained on wiping-die bending process. In addition, the relative angular error was measured at the end of several bent tests for different clearance values and graphics were plotted. The experimental results have been also plotted for different cut directions of specimens in order to display the anisotropic effect on springback. Measurements were also carried out for concave and convex bending cases referring to the strip curvature. RSM methods, using three die radii and seven clearance values, were constructed for cubic interpolation functions and two cut specimen directions. The effects of each investigated parameter on springback and convenience of the obtained graphics were discussed in details.

Energy-Level Effects on the Deformation Mechanism in Microscale Laser Peen Forming

Laser microscale peen forming has recently received more and more attention as a viable laser processing technology as it not only imparts desirable residual stress for improvement of fatigue life of the material, but can also precisely control part deformation. In the present study, the effect of energy level on the deformation mechanism in laser microscale peen forming was investigated by both numerical and experimental methods. Deformation curvatures and residual stress distributions of both sides of the specimen, characterized by X-ray microdiffraction, were compared with the results obtained from FEM simulation. The forming mechanism for convex and concave bending was explained in terms of the resulting pressure, compressive stress distribution, and plastic strain. Differences in residual stress distribution patterns were also investigated as a function of the forming mechanism.