Change Of Bending Angle Research Articles

Plasmonic Nanocomposite for Visible Light‐Modulated Bimorph‐Actuator

AbstractSoft actuators have great potential applications in sophisticated movement and sensitive devices due to their flexible nature, good interaction, and precise control. However, existing carbon‐based optical actuators are limited in their response under visible light irradiation. The limited visible light absorbance of the carbon nanostructure brought the metallic nanoparticle into the soft actuators that can absorb visible light. This study introduces a new type of plasmonic photothermal‐bimorph actuator, using graphene oxide (GO), reduced graphene oxide (rGO), and silver nanorods (Ag NRs) to overcome the limitations of traditional optical actuators. The bimorph film is actuated by visible and near‐infrared light stimuli with various power densities showing reversible deformation behavior. The actuator shows significant bending associated with a ≈50° change in bending angle under visible light irradiation with a response time of ≈5 ± 1 sec. Furthermore, a smart photo‐controlled non‐contact switch is fabricated based on photo‐thermal conversion properties, demonstrating perfect integration of plasmonic bimorph actuators. The density functional theory based molecular dynamics calculations provide an additional understanding of the bending of actuators under external stimulus. Using illustrative demonstrations of actuators, these results hint at a method for generating multipurpose visible light‐based soft robots, supporting a new approach to developing an optical locking system.

Low temperature self-growth of organic-inorganic perovskite nanowires for high performance flexible photodetectors

There has been a huge drive to explore flexible photodetectors for the large area growth of wearable, bendable, repeatable and lightweight electronics. This work describes the large-area ordered growth of MAPbI3 nanowires on PET (polyethylene terephthalate) by self-growth method at low temperature. The devices made of MAPbI3 nanowire exhibit high detectivity and responsivity of 2.403 × 1011 Jones and 7.62 A/W, respectively. Subsequently, the devices are bent at different angles (10°, 20°, 30°, 40° and 50°) and the on/off ratio of the photodetectors decreased by only 18.8 %. The device also maintained an extremely high photocurrent (a retention rate of 84.8 %) after 1000 bending cycles at 50°. Furthermore, the fluctuations of photocurrents and dark currents are small (fluctuating ∼4 %) after repeatedly bending in the range of 0° and 50° for 150 times, revealing that the MAPbI3 nanowire flexible photoelectronic device possesses good mechanical stability and excellent repeatability. Compared with that of the non-encapsulation device, the long-term stability of the encapsulated device is improved by 52.15 %. The simulation results also show that the photocurrent changes slightly with the change of bending angle, which further verifies that the MAPbI3 nanowires possesses advanced flexibility and stability at low bending angle. This method offers a straightforward and efficient way to prepare flexible photodetectors with high performance.

Smart Free-Standing Bilayer Polyacrylamide/DNA Hybrid Hydrogel Film-Based Sensing System Using Changes in Bending Angles as a Visual Signal Readout.

Stimuli-responsive DNA hydrogels have shown great potential in sensing applications due to their attractive properties such as programmable target responsiveness, excellent biocompatibility, and biodegradability. In contrast to the extensively developed DNA hydrogel sensing systems based on the stimuli-responsive hydrogel-to-solution phase transition of the hydrogel matrix, the quantitative sensing application of DNA hydrogels exhibiting smart shape deformations has rarely been explored. Moreover, bulk DNA hydrogel-based sensing systems also suffer from high material cost and slow response. Herein, free-standing bilayer polyacrylamide/DNA hybrid hydrogel films with programmable responsive properties directed by the sequence of functional DNA units have been constructed. Compared with bulk DNA hydrogels, these DNA hydrogel films with a thickness at the micrometer scale not only greatly reduce the consumption of DNA materials but also facilitate the mass transfer of biomacromolecular substances within the hydrogel network, thus favoring their sensing applications. Therefore, a target-responsive smart DNA hydrogel film-based sensor system is further demonstrated based on the large amplitude macroscopic shape deformation of the film as a visual signal readout. As a proof of concept, Pb2+ or UO22+ ion-responsive DNA units were introduced into the active layer of the bilayer hydrogel films. In the presence of Pb2+ or UO22+ ions, the occurrence of a cleavage reaction within the DNA units leads to the release of DNA segments from the hydrogel film, inducing a dramatic shape deformation of the film, and thus sensing of Pb2+ or UO22+ ions with high specificity is achieved based on measuring the bending angle changes of these smart free-standing films. These smart DNA hydrogel film sensors with target-programmable responsiveness, simple operation, and ease of storage may hold promise for future rapid on-site testing applications.

Research on the effects of resonance tube bending in loop thermoacoustic refrigeration system

A high-power-density heat-driven loop thermoacoustic refrigeration system has the potential to meet miniaturization requirements of vehicle waste heat recovery systems. Given the strict space constraints in vehicle power compartments and the need to reduce equipment footprint, the resonance tubes need to be bent and coiled. However, the introduction of curvature may increase losses in resonance tubes. In order to evaluate the minor losses caused by bending on resonance tubes, a double-acoustic-source driven acoustic field modulation platform was constructed to experimentally investigate bent resonance tubes with different arc lengths under two common bending angles (90° and 180°) under high working pressure. Through the acoustic field reconstruction method, the acoustic field distributions of each resonance tube were obtained, and the effects of changes in bending angle and arc length on acoustic field and acoustic power dissipation were analyzed. The results indicated that the introduction of curvature leads to an increase in traveling-standing wave ratio, acoustic power, and acoustic power dissipation, with the degree of increase influenced by both curvature and arc length. Under the same bending angle, the minor loss is directly proportional to curvature, and there is an ExpAssoc function relationship between minor loss coefficient and curvature. Under the same curvature, the minor loss is not proportional to arc length, and minor loss coefficient slightly increases with the arc length doubles. The findings fill the research gap in resonance tube bending in loop thermoacoustic systems and provide guidance for the selection of resonance tube bending parameters.

Multi-rings modulation and hole-assisted fiber under single-mode operation

In this paper, we propose a novel air-hole-assisted step refractive index fiber. Air holes located in the cladding can ensure the single-mode operation of the proposed fiber. The triangular refractive index ring structure further enlarges large mode field area. Bending performance of the proposed fiber is analyzed by the finite element method with perfectly matched layers, and the influence rule of each structure parameter on bending performance is summarized. Numerical results show that the proposed fiber can achieve stable single-mode operation over a wide wavelength range from 1.5 μm to 1.9 μm at a tight bending scale of 10 cm. Effective mode field area can reach 1002.73 μm2, and the bending loss of fundamental mode (FM) is only 0.000827 dB/m at the working wavelength of 1.55 μm; meanwhile, the loss ratio between higher-order mode (Homs) and fundamental mode is 7240. The proposed fiber is more stable compared to photonic crystal fibers. The change in bending angle does not affect the single-mode operation, and this novel fiber has potential applications in high-power lasers.

Humidity-stimulated film actuator with dual-responsive of bending deformation and discoloration

Flexible actuator can timely sense the changes of the external environment and respond accordingly. However, most intelligent response systems relied on the input of external electrical energy and can only trigger a single response, which cannot adapt to the changing environment. Here, the transparent actuating film TiO2/PVA-co-PE/SA was obtained by simple high-pressure spraying and immersion methods. Due to the excellent hygroscopicity of sodium alginate, the TiO2/PVA-co-PE/SA composite film can undergo rapid and reversible actuating deformation under external moisture stimulation. Meanwhile, the addition of titania-mica pearlescent pigment made the surface color of the composite film can be freely switched with the change of bending angle. Moreover, the actuating deformation and color variation showed excellent stability, and the maximum bending angle of the composite film can be maintained about 140°during ten consecutive cycles of moisture stimulation. The actuating film with synchronous change of shape and color has great significance in the research field of smart home and bionic system.

Factors influencing the thermoelectric characteristics of a thermoelectric generator with cold-side micro heat pipe arrays

The thermoelectric characteristics of a thermoelectric generator with cold-side micro heat pipe arrays are studied owing to their excellent heat dissipation performances. The influence of bending angle and vertical height of micro heat pipe arrays on the cold-side of a thermoelectric generator is examined. The bending angle influence factor is defined to analyze the changing law of thermoelectric characteristics. Three bending angles, five vertical heights, and nine temperature operating points are experimentally estimated with coupling parameters. The temperature difference, output power, and output current increase with increasing heat source temperature. Moreover, the growth trend of output characteristics does not show a significant slowdown over a period of time, indicating its reliability. The thermoelectric characteristics at a 130° bending angle are higher than those at other bending angles owing to the optimum capillary flow, condensation liquid backflow, and small evaporation thermal resistance of micro heat pipe arrays. The optimum vertical height changes as bending angle changes. Furthermore, the output power increases with increasing vertical height at a high heat source temperature. The innovative application of the micro heat pipe arrays in the cold-side heat dissipation of a thermoelectric module has great engineering significance for the optimal design of thermoelectric generators.

Correlation between the bending angle and protein sensing properties of molecularly imprinted hydrogel strips with a one-sided porous pattern.

A visual observation of the bending angle changes for the novel and easy detection of proteins is introduced in this study by fabricating bovine serum albumin (BSA) imprinted hydrogel strips with a one sided 3D porous structure using a combination of polystyrene colloidal crystal templating and the molecular imprinting approach using BSA as the template protein and several functional monomers.

Research on performance of rigid-hoop-reinforced multi-DOF soft actuator

In order to improve the bearing capacity of soft actuators, this article presents the development of the rigid-hoop-reinforced (spring or steel hoop) multi-DOF soft actuator. The actuator is composed of a rotary module with spring reinforcement on the silicone rubber-based body and a bending module with steel hoop reinforcement on the body. Compared with fiber-reinforced actuators, the bearing capacities of rigid-hoop-reinforced actuators made of 65Mn spring steel are improved. The radial and the axial bearing capacity for the bending module and the rotary module is raised by 29.6%, 28.2%, 30.6%, 49.6% respectively; under the same pressure, the spring-reinforced interval increases the maximum rotary angle of the rotary module, the steel hoop-reinforced interval increases the maximum bending angle of the bending module; with the same reinforcement type, the bending module with reinforcement interval of 10 mm has good bending characteristics that the bending angle changes with the pressure gently; the lower the hardness of silicone rubber base body, the better the adaptability and flexibility of the actuator, and the higher the hardness, the greater the bearing capacity of the actuator. Due to the above advantages, the rigid-hoop-reinforced multi-DOF soft actuator can be applied to medical devices which need high load-carrying capacity.

SPARC: Mechanophysiological analysis of anorectal function using simulated feces

IntroductionDefecation is a complex process that may easily get disturbed. Defecatory disorders are commonly diagnosed with anorectal manometry and the balloon expulsion test. Recently we developed a simulated electronic stool named Fecobionics that integrates several tests and simultaneously assesses pressures, orientation, bending and geometry during expulsion of the device. The aim was to use new analytical tools to calculate frictional force and tension during expulsion of Fecobionics in normal subjects.MethodsThe 12‐cm‐long 12mm OD Fecobionics contained pressure sensors at the front, rear and inside a bag, two motion processor units for measurement of orientation and bending, and impedance rings for measurement of eight cross‐sectional areas/diameters. The geometry of the bag was computed from the cross‐sectional area measurements. Eight presumed normal subjects (4F/4M) defecated Fecobionics. High‐resolution anorectal manometry and the balloon expulsion test confirm that the subjects were normal. The bending angle of the device, the frictional force between the probe and the surrounding tissue, the membrane tension, and the probe expulsion velocity were calculated.ResultsData examples are shown in figure 1. The bending angle and pressures changed during expulsion of the device with the maximum pressure recorded at the rear. The change in bending angle during defecation was approximately 40 degrees. The averaged circumferential tension, longitudinal tension and friction force change were associated with the pressure difference between the rear and the front ends (R2=0.878±0.011, p<0.005; R2=0.885±0.01, p<0.005; R2=0.411±0.007, p<0.005; respectively). The peak tensions and friction force immediately before expulsion of the rear were significantly higher than that when the front entered into the anal canal (circumferential and longitudinal tension p<0.005, and friction force p<0.05).ConclusionsFecobionics obtained reliable data under physiological conditions. Mechanical features such as frictional force and membrane tension were assessable during Fecobionics expulsion using the developed analysis.Support or Funding InformationNIH SPARC FundingTop panels: The geometry and the membrane tension distributions of the Fecobionics during expulsion. Bottom panel: The recorded pressures and bending angles in the Fecobionics during expulsion.Figure 1Acknowledgements.Abbey Chen, Cherry Wong, Wingwah Leung, Kaori Futaba, Tony Mak and Simon Ng are thanked for providing data.

Experimental investigation on the thermal characteristics of ultra-thin flattened heat pipes with bending angles

Although many works have been published with regard to devising ultra-thin flattened heat pipes (UTFHPs) and flexible heat pipes, none conceives the idea of combining flexibility with UTFHPs. This work makes great efforts to experimentally ascertaining the effects of bending on the thermal performance of UTFHPs with thickness below 1.5 mm in order to bridge the gap between flexibility and UTFHPs. The samples were tested under the bending angle from 0° to 180° with three different curvature diameters: 1.5 cm, 2 cm, and 2.5 cm. The testing results demonstrate that at constant input power, larger bending angle or smaller curvature diameter cause the thermal resistance and evaporator temperature climb up. Besides, uniformity of axial temperature was upset by bending due to continuously expanded temperature differences in adiabatic section. Maximum heat transfer capacity declined for more than 90% when the bending angle changes from 0° to 180°. The most severe degradation of it sits within the bending angle of 0° to 30° for more than 50%. But even at the largest bending deformation, the UTFHPs could still efficiently operate with low thermal resistance and low evaporator temperature within allowable input power. Finally, an empirical equation to predict the evaporator temperature at given input power, bending angle, and curvature diameter was proposed on the basis of experimental data.

Numerical Investigation of Flexural Bending in Biaxial Braided Structures for Flexor Tendon Repair

Flexor tendon repair has conventionally been done by suturing techniques. However, in recent times, there have been attempts of using fibrous braided structures for the repair of ruptured tendons. In this regard, the numerical analysis of the flexural stiffness of a braided structure under bending moments is vital for understanding its capabilities in the repair of flexor tendons. In this paper, the bending deflection, curvature, contact stresses and flexural bending stiffness in the braided structure due to bending moments are simulated using Finite Element (FE) techniques. Three dimensional geometry and FE models of five sets of biaxial braided structures were developed using a python programming script. The FE models of the hybrid biaxial braids were imported into ABAQUS (v17) for post-processing and analysis. It was established that the braided fabric with largest braid angle, θ = 52.5° had the highest flexural deflection while the lowest deflection was seen in the results of the braided structure with the least braid angle, θ = 38.5°. The results in this study also portrayed that the curvature in biaxial braids will increase with a decrease in the angle between the braided yarns. This was also consistent with the change of bending angle of the biaxial structures under a bending moment. The deformation of the structures increased with increase in the braid angles. This implies that the flexural bending stiffness decreased with increase in braid angle. The stress limits during bending of the braided structures were established to be within the range that could be handled by flexor tendons during finger bending.

Beam steering performance of bent silicon crystals irradiated with high-intensity and high-energy protons

Beam steering performance of bent silicon crystals irradiated with high-intensity and high-energy protons has been studied. In particular, crystals of the type used for collimation and extraction purposes in the Large Hadron Collider and the Super Proton Synchrotron at CERN have been irradiated at the HiRadMat CERN facility with 2.5 times 10^{13} 440 GeV/c protons, with a pulse length of 7.2 upmu s. The purpose is to study possible changes in bending angle and channeling efficiency due to thermo-mechanical stresses in case of accidental irradiation during accelerator operations. A comparison between measurements performed before and after the irradiation does not show any appreciable performance reduction in either crystal.

Wearable sensors developed using a novel plastic metal material

Plastic metal (PM) is a highly advanced material with numerous advantages, such as the convenience associated with its shaping and coating, precise pattern definitions, and convenience for recycling, thereby making it an excellent material for soft electronics. PM material has the ability to be plastically molded into arbitrary deformation by external forces, but it can remain intact even under large deformations as long as PM is encapsulated in polydimethylsiloxane (PDMS). This study aims to verify the feasibility of its application to wearable soft sensors, including flexible and pressure sensors. The experimental results show that with the use of synthetic conditions at a 4:1 mass ratio of liquid metal (LM) to quartz powder, PM yields the best characteristics. Apart from the good electrical conductivity (with a resistivity of 3.29 × 10− 5 Ω-cm), it also has better coating ability, plasticity, and film formability. The developed flexible sensor can sense bending angle changes in the range of 0°–180° with stable performance and with an average gauge factor $${\text{G}}{{\text{F}}_{{\text{avg}}}}$$ of 2.616. With regard to the pressure sensor, when the pressure range is from 0 to 40 psi (≈ 275.79 kPa), the resistance change rate shows a slightly concave-down quadratic curve, while the pressure is greater than 40 psi, the characteristic is a linear relationship with an average slope of 0.022. Furthermore, real-life verification of the two sensors based on experiments shows that their performances are stable and repeatable. Therefore, this study has confirmed that the sensors made of PM can be practically applied to the development of wearable sensors and has emphasized the potential for their use in dynamic sensing applications in humans or robots.

Piezoresistive effect observed in flexible amorphous carbon films

Amorphous carbon (a-C) films, deposited on Si substrates at 500 °C, were transferred onto flexible polyethylene (PE) substrates by a lift-off method, which overcomes the limit of deposition temperature. After transferring, a-C films exhibited a large piezoresistive effect. Such flexible samples could detect the change of bending angle by attaching them onto Cu foils. The ratio of the bending and non-bending resistances reaches as large as ~27.8, which indicates a potential application as a pressure sensor. Also, the a-C/PE sample revealed an enhanced sensitivity to gas pressure compared with the a-C/Si one. By controlling the bending angle, the sensitivity range can be tuned to shift to a low- or high-pressure region. The fatigue test shows a less than 1% change in resistance after 10 000 bending cycles. Our work provides a route to prepare the flexible and piezoresistive carbon-based devices with high sensitivity, controllable pressure-sensing and high stability.

Optimization of the Mars ionospheric radio occultation retrieval

Electron density is a key parameter to characterize Martian ionospheric structure and dynamics. Based on the ephemeris and auxiliary information derived from the Spacecraft, Planet, Instruments, C-matrix, and Events (SPICE) toolkit, we calculated the bending angle of signal path from the frequency residuals measured by the Mars Express Radio Science Experiment (MaRS) of the Mars Express (MEX) mission under the assumption of a spherically symmetric ionosphere. We stratified the ionosphere into layers and assumed a linear change of bending angle between layers, to derive profiles in radial distance of refractivity with the optimized parameters of upper integral limit of 4890 km and baseline correction boundary of 3690 km. Meanwhile, we also compared the retrieved electron density profiles between the frequency residuals of the single-frequency and differential Doppler of the dual-frequency. In total, ~640 electron density profiles of Martian ionosphere between April 2004 and April 2015 were retrieved successfully. There are 24 profiles identified manually that exhibit an additional sporadic layer occurrence below the normal two-layers. We also found that the peak altitude of this layer increases with the main peak altitude.

Pneumatic microfinger with balloon fins for linear motion using 3D printed molds

Polymer-based pneumatic balloon actuators consisting of novel trapezoidal vertical microballoon fins were fabricated by three-dimensional (3D) printed molds and validated experimentally. The introduction of 3D printed molds for pneumatic actuation provides additional freedom in the design of actuators, removing the limitation of extruded 2D shapes that is present with conventional microfabrication. Whereas conventional balloon actuators exhibit nonlinear response to applied pressure, the presence of balloon fins with 100s-μm width was shown to produce a linear change in bend angle with the injection of pressurized air. The balloon fins also mitigate stress concentrations that can lead to material failure. Static bending (exceeding 80° bend angle) and the mechanical force of the fabricated microfingers were tested and compared with analytical models. The expanded design space permitted by 3D printing allows actuator designs to achieve a given deflection with less stress in the material as compared to planar designs. Feasibility of this design flexibility and fast prototyping enabled by the 3D printed molding process was demonstrated by fabricating and testing various designs of microfingers. When grouped, the microfingers with balloon fins can successfully accomplish complex object transfer tasks (i.e., multi-directional actuation with independently controlled displacement).

Rollable Multisegment Dielectric Elastomer Minimum Energy Structures for a Deployable Microsatellite Gripper

Debris in space presents an ever-increasing problem for spacecraft in Earth orbit. As a step in the mitigation of this issue, the CleanSpace One (CSO) microsatellite has been proposed. Its mission is to perform active debris removal of a decommissioned nanosatellite (the CubeSat SwissCube). An important aspect of this project is the development of the gripper system that will entrap the capture target. We present the development of rollable dielectric elastomer minimum energy structures (DEMES) as the main component of CSO's deployable gripper. DEMES consist of a prestretched dielectric elastomer actuator membrane bonded to a flexible frame. The actuator finds equilibrium in bending when the prestretch is released and the bending angle can be changed by the application of a voltage bias. The inherent flexibility and lightweight nature of the DEMES enables the gripper to be stored in a rolled-up state prior to deployment. We fabricated proof-of-concept actuators of three different geometries using a robust and repeatable fabrication methodology. The resulting actuators were mechanically resilient to external deformation, and display conformability to objects of varying shapes and sizes. Actuator mass is less than 0.65 g and all the actuators presented survived the rolling-up and subsequent deployment process. Our devices demonstrate a maximum change of bending angle of more than 60° and a maximum gripping (reaction) force of 2.2 mN for a single actuator.

The Effect of Normal Anisotropy on Thin-walled Tube Bending

Thin-walled tube bending has common applications in the automobile and aerospace industries. The rotary-draw-bending method is a complex physical process with multi-factor interactive effects and is one of the advanced tube forming processes with high efficiency, high forming precision, low consumption and good flexibility for bending angle changes. However, it may cause a wrinkling phenomenon, over thinning and cross-section distortion if the process parameters are inappropriate. Wrinkles propagate in thin-walled tube, but in some cases, localize in a finite zone and lead to failure. Wrinkling prediction in thin-walled tube bending processes has been an important and challenging subject in the related industry. In this paper, the plastic deforming behavior and wrinkling mechanism for a thin-walled tube is simulated and the results are compared with the available experimental ones. Next, the effect of anisotropy on ovalization, thickness and wrinkling of tube is investigated using FEM. Numerical results are presented showing the effects of the various kinds of materials and geometric parameters on wrinkling using anisotropic yield function.

Finite Element Analysis and Experimental Investigations on Laser Bending of AISI304 Stainless Steel Sheet

Laser bending is a thermal forming process, where a sheet metal gets bent due to residual stresses induced by a controlled defocused laser beam. The present paper deals with the deformation of stainless sheet in laser bending process under temperature gradient mechanism. Finite element simulation was carried out to determine the temperature field and deformation of the sheet metal for different laser powers. Bending angle was found to increase nonlinearly with the increase of laser power up to a certain value of the latter. Bending angles calculated by finite element method were found to be in good correlation, when compared with the analytical and experimental results. After a certain value of laser power, the rate of change of bending angle was decreased, which is called the saturation power. Laser bending process was also investigated beyond the surface melting temperature. After saturation zone, bending angle was seen to increase due to a further increase of laser power and surface melting. Temperature fields of the laser bent samples in different zones were investigated through numerical simulations. Metallurgical changes of the samples for different processing regions were also studied using the scanning electron microscopy and Vickers’ microhardness tester. For stainless steel samples, there was no microstructural change in the region before saturation. After saturation zone, surface microstructure got refined due to surface melting of a thin layer and subsequent rapid quenching. Microhardness of the samples at different processing zones was measured using Vickers’ microhardness tester. Average microhardness was found to increase from normal deformation zone towards the melting zone. The results are helpful to identify the optimum processing conditions for laser bending process under temperature gradient mechanism.