Mechanical Flexibilities Research Articles

All-in-one stretchable coaxial-fiber strain sensor integrated with high-performing supercapacitor

Ever-increasing attempts have recently been focused on exploring stretchable fiber-shaped integrated wearables, owing to their multi-functionalities and mechanical flexibilities. However, a rational design and effective integration of multi-functional components, such as strain sensor and high-performing energy storage, into one single fiber remains a great challenge. Herein, we have achieved an all-in-one stretchable coaxial-fiber sensing system simultaneously integrating strain detection and power supporting supercapacitor. The asymmetric stretchable coaxial-fiber supercapacitor is made on an elastic fiber, with a maximum working voltage of 1.8 V, by adopting manganese dioxide and polypyrrole deposited on aligned carbon nanotube sheets as the positive and negative electrode, respectively. Benefiting from the unique coaxial-fiber integrated architecture and advanced electrode design, the optimized device delivers a high stack volumetric energy density of 1.42 mWh cm−3, and an outstanding flexibility with 85.1% capacitance retention after stretching for 6000 cycles at a strain of 200%. The all-in-one stretchable coaxial-fiber strain sensing system shows consistent self-supported performance with a superior stability and durability at repeatedly unloading/loading of 40% applied strain for 10000 cycles, after one single charge. The present work demonstrates the new proof-of-concept for integration of strain element with energy storage into a single stretchable fiber for the next generation wearables.

Fabrication and characterization of differentiated aramid nanofibers and transparent films

Aramid nanofibers (ANFs) frequently are employed as versatile building blocks for constructing high-performance nanocomposites due to its structural and performance superiority. In this paper, the different ANFs and ANF films derived from the typical aramid yarns, chopped fiber, pulp fiber and fibrid fiber, respectively, were fabricated through deprotonation with potassium hydroxide in dimethyl sulphoxide, protonation with deionized water and vacuum-assisted filtration. The physical tests such as tensile test, ultraviolet transmittance and absorbance, thermogravimetric analysis were executed to evaluate and contrast the thermodynamic and optical performances of these differentiated ANFs and ANF films. The analytical results suggested that ANFs films prepared by the different forms of aramid macrofibers presented with differentiated properties such as mechanical behaviors, transparencies and flexibilities. And also it was found that the oversized nanofiber in length led to the formation of flocculation which was adverse for ANFs films in the formation of high strength. Whereas, small diameter just facilitated for the achievement of high stiffness and transparency. By contrast, the ANFs films made from chopped nanofiber, with aspect ratio of 200–500, exhibited good transparency, thermal stability and mechanical properties with transmittance value of 83%, TG10% around 521 °C, ultimate strength (σ) of 103.41 MPa, stiffness (E) of 4.70 GPa and strain at break of 5.56%. This work offers an alternative nanoscale building block as an effective nanofiller for preparing high-performance nanocomposites with different requirements in the potential fields such as transparent coating and flexible electrode or display materials, battery separator and microporous membrane.

Nitrogen doped carbon derived from polyimide/multiwall carbon nanotube composites for high performance flexible all-solid-state supercapacitors

Flexible all-solid-state supercapacitors are desirable as potential energy storage systems for wearable technologies. Herein, we synthesize aminophenyl multiwall carbon nanotube (AP-MWCNT) grafted polyimide precursor by in situ polymerization method as a nitrogen-doped carbon precursor. Flexible supercapacitor electrodes are fabricated via a coating of carbon precursor on carbon cloth surface and carbonization at high temperature directly. The as-obtained electrodes, which can be directly used without any binders or additives, can deliver a high specific capacitance of 333.4 F g−1 at 1 A g−1 (based on active material mass) and excellent cycle stability with 103% capacitance retention after 10,000 cycles in a three-electrode system. The flexible all-solid-state supercapacitor device exhibits a high volumetric capacitance of 3.88 F cm−3 at a current density of 0.02 mA cm−3. And also the device can deliver a maximum volumetric energy density of 0.50 mWh cm−3 and presents good cycling stability with 85.3% capacitance retention after 10,000 cycles. This device cell can not only show extraordinary mechanical flexibilities allowing folding, twisting, and rolling but also demonstrate remarkable stable electrochemical performances under their forms. This work provides a novel approach to obtain carbon textile-based flexible supercapacitors with high electrochemical performance and mechanical flexibility.

Semitransparent Flexible Organic Solar Cells Employing Doped-Graphene Layers as Anode and Cathode Electrodes.

Semitransparent flexible photovoltaic cells are advantageous for effective use of solar energy in many areas such as building-integrated solar-power generation and portable photovoltaic chargers. We report semitransparent and flexible organic solar cells (FOSCs) with high aperture, composed of doped graphene layers, ZnO, P3HT:PCBM, and PEDOT:PSS as anode/cathode transparent conductive electrodes (TCEs), electron transport layer, photoactive layer, and hole transport layer, respectively, fabricated based on simple solution processing. The FOSCs do not only harvest solar energy from ultraviolet-visible region but are also less sensitive to near-infrared photons, indicating semitransparency. For the anode/cathode TCEs, graphene is doped with bis(trifluoromethanesulfonyl)-amide or triethylene tetramine, respectively. Power conversion efficiency (PCE) of 3.12% is obtained from the fundamental FOSC structure, and the PCE is further enhanced to 4.23% by adding an Al reflective mirror on the top or bottom side of the FOSCs. The FOSCs also exhibit remarkable mechanical flexibilities through bending tests for various curvature radii.

Hybrid Ag nanowire transparent conductive electrodes with randomly oriented and grid-patterned Ag nanowire networks

To improve the electrical properties of silver nanowire (Ag NW) transparent conductive electrodes (TCEs), the density of Ag NW networks should be increased, to increase the number of percolation paths. However, because of the inverse relationship between optical transmittance and electrical resistivity, the optical properties of Ag NW TCEs deteriorate with increasing density of the Ag NW network. In this study, a hybrid Ag NW electrode composed of randomly oriented and grid-patterned Ag NW networks is demonstrated. The hybrid Ag NW electrodes exhibit significantly improved sheet resistances and slightly decreased transmittances compared to randomly oriented Ag NW networks. Hybrid Ag NW TCEs show excellent mechanical flexibilities and durabilities in bending tests with a 5 mm radius of curvature. Moreover, flexible transparent film heaters (TFHs) based on the hybrid Ag NW electrodes show elevated maximum temperatures relative to TFHs based on randomly oriented Ag NW electrodes, when operated at the same input voltages.

Liquid-phase tuning of porous PVDF-TrFE film on flexible substrate for energy harvesting

Emerging wearable and implantable biomedical energy harvesting devices demand efficient power conversion, flexible structures, and lightweight construction. This paper presents Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) micro-porous structures, which can be tuned to specific mechanical flexibilities and optimized for piezoelectric power conversion. Specifically, the water vapor phase separation method was developed to control microstructure formation, pore diameter, porosity, and mechanical flexibility. Furthermore, we investigated the effects of the piezoelectric layer to supporting layer Young's modulus ratio, through using both analytical calculation and experimentation. Both structure flexibility and stress-induced voltage were considered in the analyses. Specification of electromechanical coupling efficiency, made possible by carefully designed three-dimensional porous structures, was shown to increase the power output by five-fold relative to uncoupled structures. Therefore, flexible PVDF-TrFE films with tunable microstructures, paired with substrates of different rigidities, provide highly efficient designs of compact piezoelectric energy generating devices.

Synthesis of free-standing MnO2/reduced graphene oxide membranes and electrochemical investigation of their performances as anode materials for half and full lithium-ion batteries

MnO2 nanotubes/reduced graphene oxide (MnO2/RGO) membranes with different MnO2 contents are successfully synthesized by a facile two-step method including vacuum filtration and subsequent thermal reduction route. The MnO2 nanotubes obtained are 38 nm in diameter and homogeneously imbedded in RGO sheets as spacers. The synthesized MnO2/RGO membranes exhibit excellent mechanical flexibilities and free-standing properties. Using the membranes directly as anode materials for lithium batteries (LIBs), the membranes for half LIBs show superb cycling stabilities and rate performances. Importantly, the electrochemical performances of MnO2/RGO membranes show a strong dependence on the MnO2 nanotube contents in the hybrids. In addition, our results show that the hybrid membranes with 49.0 wt% MnO2 nanotube in half LIBs achieve a high reversible capacity of 1006.7 mAh g−1 after 100 cycles at a current density of 0.1 A g−1, which is higher lithium storage capacity than that of reported MnO2-carbon electrodes. Furthermore, the synthesized full cell (MnO2/RGO//LiCoO2) system also exhibit excellent electrochemical performances, which can be attributed to the unique microstructures of MnO2 and GRO, coupled with the strong synergistic interaction between MnO2 nanotubes and GRO sheets.

Theoretical study of microcavity-antireflection resonance hybrid modes enhanced absorption of organic solar cells

Organic solar cells based on small molecules and conjugated polymers are attracting much attention due to their merits of low costs, simple fabrication processes, light weights, and mechanical flexibilities. Metals are usually considered as promising candidates for the semi-transparent electrodes. In such devices, a strong microcavity resonance can be supported between the two electrodes, resulting in a narrowed bandwidth of light absorption, which, unfortunately, will lower the performances of organic solar cells since broadband absorption is always highly desired. To overcome this obstacle, people have proposed many designs such as using ultra-thin electrodes or using dielectric-metal hybrid electrodes. Although the light absorption bandwidth can be improved considerably, the absorption efficiency would be lowered due to the weakened microcavity resonance. This is a tough problem that always bothers both researchers and engineers. To solve this problem, we propose a light trapping scheme based on broadband hybrid modes due to the hybridization between microcavity resonance and antireflection resonance. By introducing a capping layer outside the device structure, antireflection resonance can be excited inside the capping layer and can then couple with the intrinsic microcavity resonance, inducing dual microcavity-antireflection resonance hybrid modes. The hybrid modes are of broadband and their resonant wavelengths can be easily designed by tuning the capping layer thickness and cavity length, since the capping layer thickness would affect the antireflection resonance while the cavity length would affect the microcavity resonance. By matching the resonance with the high absorption region of the active layer, the overall absorptivity of the proposed device can be greatly enhanced by~37% compared to the conventional microcavity based device where only one mode, that is, the microcavity resonance can be supported. Moreover, we compare our light trapping scheme with the surface plasmon-polaritons based scheme where surface waves are excited to help improve the light absorption. We find that the overall absorptivity of the proposed device cannot be further improved when we introduce grating structure into the device in order to excite surface plasmon-polaritons. This is mainly because the light absorption based on our hybrid mode scheme is already thorough so that the introduction of grating structure can only improve the light loss dissipated in the metal electrodes due to scatterings and diffractions by the gratings. Therefore, the proposed hybrid mode based scheme can be considered as a simple and effective light trapping scheme for organic solar cells and may find applications in both polymer and small molecular based organic solar cells.

Open Solution for Humanoid Attitude Estimation through Sensory Integration and Extended Kalman Filtering

In this paper an Extended Kalman Filter (EKF) is used in order to estimate the real state of a humanoid robot (HRP-2 robot in our case study) using the combination of the information coming from the encoders (kinematics) and from the Inertial Measurement Unit (IMU). The integration of the kinematic information into the Kalman filtering process allows a good estimation of the attitude and reduces the complexity of the problem to the use of simple kinematic transformations, even considering the existence of accelerations and mechanical flexibilities in the robot. The EKF estimator presented here is an open solution directly applicable to any humanoid robot, which is the main contribution of our approach. Experimental results are given showing the good performance of the method.

Cervical spine injuries and flexibilities following axial impact with lateral eccentricity.

Determine the effects of dynamic injurious axial compression applied at various lateral eccentricities (lateral distance to the centre of the spine) on mechanical flexibilities and structural injury patterns of the cervical spine. 13 three-vertebra human cadaver cervical spine specimens (6 C3-5, 3 C4-6, 2 C5-7, 2 C6-T1) were subjected to pure moment flexibility tests (±1.5 Nm) before and after impact trauma was applied in two groups: low and high lateral eccentricity (1 and 150 % of the lateral diameter of the vertebral body, respectively). Relative range of motion (ROM) and relative neutral zone (NZ) were calculated as the ratio of post and pre-trauma values. Injuries were diagnosed by a spine surgeon and scored. Classification functions were developed using discriminant analysis. Low and high eccentric loading resulted in primarily bony fractures and soft tissue injuries, respectively. Axial impacts with high lateral eccentricities resulted in greater spinal motion in lateral bending [median relative ROM 3.5 (interquartile range, IQR 2.3) vs. 1.4 (IQR 0.5) and median relative NZ 4.7 (IQR 3.7) vs. 2.3 (IQR 1.1)] and in axial rotation [median relative ROM 5.3 (IQR 13.7) vs. 1.3 (IQR 0.5), p < 0.05 for all comparisons] than those that resulted from low eccentricity impacts. The developed classification functions had 92 % classification accuracy. Dynamic axial compression loading of the cervical spine with high lateral eccentricities produced primarily soft tissue injuries resulting in more post-injury spinal flexibility in lateral bending and axial rotation than that associated with the bony fractures resulting from low eccentricity impacts.

Photonic Nanowires: From Subwavelength Waveguides to Optical Sensors

Nanowires are one-dimensional (1D) nanostructures with comparatively large aspect ratios, which can be useful in manipulating electrons, photons, plasmons, phonons, and atoms for numerous technologies. Among various nanostructures for low-dimensional photonics, the 1D nanowire is of great importance owing to its ability to route tightly confined light fields in single-mode with lowest space and material requirements, minimized optical path, and high mechanical flexibilities. In recent years, nanowire photonics have increasingly been attracting scientists' interests for both fundamental studies and technological applications because 1D nanowires have more favorable properties than many other structures, such as 0D quantum dots (QDs) and 2D films. As subwavelength waveguides, free-standing nanowires fabricated by either chemical growth or physical drawing techniques surpass nanowaveguides fabricated by almost all other means in terms of sidewall smoothness and diameter uniformity. This conveys their low waveguiding losses. With high index contrast (typically higher than 0.5) between the core and the surrounding or with surface plasmon resonance, a nanowire can guide light with tight optical confinement. For example, the effective mode area is less than λ(2)/10 for a dielectric nanowire or less than λ(2)/100 for a metal nanowire, where λ is the vacuum wavelength of the light. As we increase the wavelength-to-diameter ratio (WDR) of a nanowire, we can enlarge the fractional power of the evanescent fields in the guiding modes to over 80% while maintaining a small effective mode area, which may enable highly localized near-field interaction between the guided fields and the surrounding media. These favorable properties have opened great opportunities for optical sensing on the single-nanowire scale. However, several questions arise with ongoing research. With a deep-subwavelength cross-section, how can we efficiently couple light into a single nanowire? How can we fabricate a nanowire with low optical loss? How can we activate a passive nanowire for optical sensing? And lastly, how can we adapt mature optical measurement technology onto a nanowire? In this Account, we highlight our initial attempts to address the above-mentioned challenges. First, we introduce the fabrication and functionalization of low-loss photonic nanowires. We show that nanowires fabricated by either top-down physical drawing (e.g., for amorphous nanowires) or bottom-up chemical growth (e.g., for crystalline nanowires) can yield excellent geometric and structural uniformities with surface roughness down to atomic level and minimize the scattering loss for subwavelength optical or plasmonic waveguiding. Then, relying on a near-field fiber-probe micromanipulation, we demonstrate optical launching of single nanowires by evanescent coupling, with coupling efficiency up to 90% for dielectric nanowires and 80% for plasmonic nanowires. Third, we discuss the waveguiding properties of nanowires and emphasize their outstanding capability of waveguiding tightly confined optical fields with high fractional evanescent fields. In addition, we briefly show a balance between the loss, confinement, and bandwidth in a waveguiding nanowire. Fourthly, we present promising approaches to single-nanowire optical sensors. By measuring optical absorption or spectral transmission of a nanowire and activating nanowires with sensitive dopants, we demonstrate a single-nanowire optical sensor with high sensitivity, fast response, and low optical power. This may lead to a novel platform for optical sensing at nanoscale. Finally, we conclude with an outlook for future challenges in the light manipulation and sensing applications of photonic nanowires.

A method for enabling real-time structural deformation in remote handling control system by utilizing offline simulation results and 3D model morphing

A full scale physical test facility, DTP2 (Divertor Test Platform 2) has been established in Finland for demonstrating and refining the Remote Handling (RH) equipment designs for ITER. The first prototype RH equipment at DTP2 is the Cassette Multifunctional Mover (CMM) equipped with Second Cassette End Effector (SCEE) delivered to DTP2 in October 2008. The purpose is to prove that CMM/SCEE prototype can be used successfully for the 2nd cassette RH operations. At the end of F4E grant “DTP2 test facility operation and upgrade preparation”, the RH operations of the 2nd cassette were successfully demonstrated to the representatives of Fusion For Energy (F4E). Due to its design, the CMM/SCEE robot has relatively large mechanical flexibilities when the robot carries the nine-ton-weighting 2nd Cassette on the 3.6-m long lever. This leads into a poor absolute accuracy and into the situation where the 3D model, which is used in the control system, does not reflect the actual deformed state of the CMM/SCEE robot. To improve the accuracy, the new method has been developed in order to handle the flexibilities within the control system's virtual environment. The effect of the load on the CMM/SCEE has been measured and minimized in the load compensation model, which is implemented in the control system software. The proposed method accounts for the structural deformations of the robot in the control system through the 3D model morphing by utilizing the finite element method (FEM) analysis for morph targets. This resulted in a considerable improvement of the CMM/SCEE absolute accuracy and the adequacy of the 3D model, which is crucially important in the RH applications, where the visual information of the controlled device in the surrounding environment is limited.

Closed-loop identification of an industrial robot containing flexibilities

Closed-loop identification of an industrial robot of the type ABB IRB 1400 is considered. Data are collected when the robot is subject to feedback control and moving around axis one. Both black-box and physically parameterized models are identified. A main purpose is to model the mechanical flexibilities. It is found that a model consisting of three-masses connected by springs and dampers gives a good description of the dynamics of the robot.

Effect of thermal depolarization and thermomechanical coupling on harmonic oscillations and dissipative warming of conical piezoceramic shells

The thermoelectromechanical behavior of thick-wall elements in the form of plates and cylindrical shells formed from piezoactive viscoelastic materials subjected to harmonic deformation, including depolarization of the material due to a warming temperature close to critical T c (Curie point) has been examined in [2, 3, 4, 51. Experimental data [1, 6] indicate that for piezoceramic temperatures close to T c, the piezomoduli decrease precipitously. The values of the mechanical flexibilities and dielectric constants beyond the Curie point are not, as a rule, known. The phenomenon of depolarization in the region of a body where the warming temperature attains or exceeds Tc, is therefore modeled by zeroing the piezomoduli. The flexibilities and dielectric constants are set equal to their value when T=Tc. This paper examines the problem of the axisymmetric electromechanical oscillations and the dissipative wanning of a conical shell with a half-span angle or, which is fabricated from a piezoceramic polarized throughout its thickness h in two opposing directions relative to the median surface. Convective heat exchange with the surrounding medium takes place on the contour and conical surfaces. Oscillations are excited by the harmonic difference in the electric potential V o cos cot applied to the electrified conical surfaces. The dissipative properties of the piezoceramic are described by the concept of complex electromechanical characteristics, the read and imaginary components of which are functions of temperature. Electrical-load and heat-exchange conditions are considered such that the temperature of dissipative wanning in certain regions of the shell may reach the critical value T c, for which depolarization of the piezoceramic is initiated. The solution of the stated problem involving the oscillations and wanning of a conical piezoshell is described by a system of coupled equations of shells of revolution [3], which include equations of axisymmetric harmonic oscillations

On Transfer Function Zeros of General Colocated Control Systems With Mechanical Flexibilities

In our previous work, it was shown that for simple control systems with mechanical flexibilities such as spring-mass systems or uniform cross-section linear elastic beams, the complex conjugate transfer function zeros can be interpreted as the resonances of a sub-portion of the flexible structure with additional constraints imposed by the sensor and actuator. In this paper, the aforementioned intuitive physical observation is verified mathematically for general lumped and distributed parameter flexible control systems with colocated sensor/actuator.

Hybrid adaptive control for tracking of rigid-link flexible-joint robots

A hybrid adaptive tracking controller for rigid-link flexible-joint (RLFJ) robot manipulators is designed. The controller is hybrid in the sense that an adaptive indirect controller is used to compensate for parametric uncertainties in the rigid-link equation whereas an adaptive robust controller corrects for the dynamics (i.e. mechanical flexibilities) and parametric uncertainty associated with the actuators. That is, in spite of these detrimental uncertainties and effects, we are still able to ensure a global asymptotic stability (GAS) result for the link position tracking error.

Physical Interpretation of Transfer Function Zeros for Simple Control Systems With Mechanical Flexibilities

Physical interpretation of the transfer function zeros of simple control systems with mechanical flexibilities is presented. It is shown that for discrete spring-mass systems and elastic beams, the poles are the resonant frequencies of the flexible structure and the complex conjugate zeros are the resonant frequencies of a substructure constrained by the sensor and actuator. It is also shown that when the flexible control systems become nonminimum phase, the real zeros are the results of nonpropagation of energy within the substructure.