Bending Direction Research Articles

A Proof-of-Concept Study on an Internal-Resonance-Based Piezoelectric Energy Harvester With Coupled Three-Dimensional Bending-Torsion Motions

Abstract By exchanging the internal energy between coupled vibration modes, internal-resonance-based energy harvesters may provide an effective solution to broadening and enhancing bandwidth and power performance in dealing with natural vibration sources. With the development of piezoelectric-based transducers, thickness and face shear coefficients in proper piezoelectric elements can also generate power output from shear deformation on the core vibrating elements. However, in most cantilever-based energy harvesters that focused on bending modes, the shear responses were neglected. In this paper, we present an internal-resonance-based piezoelectric energy harvester with three-dimensional coupled bending and torsional modes, for the first time. The fine-tuned system leverages a two-to-one internal resonance between its first torsion and second bending modes to enhance the power output with piezoelectric effects. The dynamic behavior implies the coexistence of in-plane and out-of-plane motions under a single excitation frequency, and the corresponding strain changes in the bending and shear directions are captured by bonded piezoelectric transducers. Dependence between excitation levels and the internal-resonance phenomenon is justified as a critical system parameter study; the results also indicate that an intriguing non-periodic region exists near the center frequency. The outcomes of this study feature a multi-directional and multi-modal energy harvester that displays rich dynamic behaviors. The operational bandwidth is promising for broadband energy harvesting, and the output voltage is enhanced by capturing both in-plane and out-of-plane motions at the same time.

Biomechanical analysis of odontoid and transverse atlantal ligament in humans with ponticulus posticus variation under different loading conditions: Finite element study

PurposePonticulus posticus (PP) is a variation of the bone bridge that appears in the first cervical vertebra and through which the vertebral artery passes. Odontoid fractures are common spinal bone fractures in older people. This study aims to investigate the effect of neck movements on the odontoid and transverse atlantal ligament (TAL) of people with PP variation from a biomechanical view. MethodC1, C2, and C3 vertebrae of the occipital bone were analyzed using the finite element method (FEM). In this study, solid models were created with the help of normal (N), incomplete (IC), and asymmetric complete (AC) PP tomography images. The necessary elements for the models were assigned, and the material properties were defined for the elements. As boundary conditions, models were fixed from the C3 vertebra, and 74 N loading was applied from the occipital bone. Stress and deformation values in the odontoid and transverse atlantal ligament were obtained by applying 1.8 Nm moment in flexion, extension, bending, and axial rotation directions. ResultsThe stress and deformation values of all three models in odontoid and TAL were obtained, and numerical results were evaluated. In all models, stress and deformation values were obtained in decreasing order in rotation, bending, extension, and flexion movements. The highest stress and strain values were obtained in AC and the lowest values were obtained in N. In all movements of the three models, the stress and deformation values obtained in the TAL were lower than in the odontoid. ConclusionThe greatest stresses and deformations obtained in spines (AC) with PP were found in the odontoid. This may help explain the pathogenesis of odontoid fractures in older people. First, this study explains the mechanism of the formation of neck trauma in people with PP and the need for a more careful evaluation of the direction of impact. Secondly, the study reveals that the rotational motion of the neck independent of PP has more negative effects on the odontoid.

Two-Step Simulation of Underwater Terrain in River Channel

When studying river hydrodynamics and water quality evolution laws on the basis of numerical simulation analysis, it is necessary to carry out topographic interpolation along the bend direction of the river on the basis of the measured river section, as this can provide accurate and reliable topographic data for river numerical modeling. In this paper, a two-step terrain simulation method based on sparse and discrete river sections is proposed by comprehensively considering the river trends and the lack of monitoring sections. On the basis of establishing a reference using the river centerline and coding the spatial relationship of the river, the linear weight method, which uses the distance and gradient change between the known sampling elevation section to realize the preliminary encryption of spatial points with any number of longitudinal sections and any horizontal distance, is carried out first. Considering the structural and anisotropic characteristics of the river, the improved inverse distance weighting (IDW) method is further used to locally interpolate the encrypted points to obtain the continuous surface of the river terrain. In order to prove the effectiveness of this method, a part of the Qinhuai River in Nanjing was taken as the research object. The experiment was carried out by setting different spacing distances for preliminary densification and by using different interpolation methods for further local terrain simulation. Root mean square error (RMSE) and mean absolute error (MAE) are used to evaluate the overall performance of different simulation methods. The experimental results show that the method proposed in this paper overcomes the obvious inaccuracy of directly using an interpolation algorithm to generate the river terrain due to sparse section data. The river terrain generated by the preliminary densification and improved IDW interpolation calculation method is more reasonable, and continuous and unobstructed, reflecting the original river terrain more accurately.

Femtosecond laser-inscribed off-axis high-order mode long-period grating for independent sensing of curvature and temperature.

We propose and demonstrate a novel curvature and temperature sensor based on an off-axis small-period long-period fiber grating (SP-LPG) which is inscribed in a single mode fiber by a femtosecond laser in one step. The total length of the SP-LPG is only 2.1 mm. The period of the SP-LPG is 30 µm, which is smaller than that of conventional long period fiber gratings. Essentially, the SP-LPG is a high-order mode long period fiber grating. Due to the off-axis structure, the SP-LPG can be used for two-dimensional vector bending sensing. The curvature can be demodulated by the intensity variation of the dips in the transmission spectrum. When the incident light is polarized, the instantaneous curvature sensitivity of the SP-LPG can exceed 20 dB/m-1. Meanwhile, a series of Bragg resonant peaks can be observed in the reflection spectrum, which can be used to monitor the fluctuation of temperature. The transmission dip is insensitive to temperature and the reflection peak is insensitive to curvature, which allows the SP-LPG to measure curvature and temperature independently. The characteristics of high curvature sensitivity, two-dimensional bending direction identification, real-time temperature measurement, and compact structure make the device expected to be applied in the field of structural health monitoring and intelligent robotics.

Silver-Reduced Poly(Ethylene Glycol) Diacrylate Composites with Microline Arrays for Directional Bending Sensors.

Herein, a soft and flexible polymer composite sensor with a surface structure is manufactured that is sensitive to a wide range of mechanical stimuli, including small actions and large motions. A polymer sensor performing with a piezoresistive mechanism is proposed by synthesizing a new conductive polymer composite to fabricate a microline structure by itself, named Ag-reduced poly(ethylene glycol) diacrylate (PEGDA) composite directional bending sensor (ACBS). A simple but effective process of forming nanoparticles (NPs) and surface structures is a notable characteristic. High sensitivity to a small stimulus was achieved by forming Ag NPs within PEGDA, particularly concentrating on the surface and applying the microline structure. With the structural characteristics of a line structure, the ACBS achieved anisotropic sensitivity to bulk motion along the arranged line direction. The excellent sensitivity of this polymer sensor was experimentally demonstrated via water droplets, blowing, and breathing. Combining the advantages of a simple synthetic and simple fabrication process along with the fabrication ability of the microsurface structure with the material itself and the conductive Ag/PEGDA integrated layer, this ACBS is outstanding as a soft and flexible polymer composite sensor and has potential application in physical devices such as wearable devices and biosensors.

Influences of the unsymmetrical bending on behaviour of structural members with a restrained lateral deflection

As reinforced concrete (RC) walls with different principal bending axes are connected by the floor diaphragms, unsymmetrical bending is frequently expected for structural members in resisting the lateral loads. In these cases, a portion of lateral reaction forces is anticipated to be perpendicular to the lateral deflection of the members which causes shear deformation and additional curvature perpendicular to the loading plane. This paper investigates these out-of-plane deformations and curvatures and their influences. Magnitude of these shear deformations and curvatures are investigated with experimental data and a theoretical solution. The results confirm that the out-of-plane curvature is related with disproportional shear and flexural stiffness of the wall in different principal bending directions and can account for a significant portion of the in-plane curvature. The curvature could introduce significantly higher strain and render the member more vulnerable to out-of-plane buckling. Methods for modelling the curvature in structural system are proposed based on nonlinear fibre element model.

Generation of Photonic Hooks under Point-Source Illumination from Patchy Microcylinders

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction.

Photovoltaic performance of flexible perovskite solar cells under bending state

Although flexible perovskite solar cells have made extensive progress, there is a lack of investigation on the performance of flexible perovskite solar cells under bending state. Here, two-dimensional models of flexible perovskite solar cells have been performed to reveal the effect of bending angles and directions for the first time. Simulated results are in good agreement with experimentally reported data, validating the accuracy of our model. To optimize mechanical and optical performance under bending state, silica subwavelength array is embedded on the surface of the flexible substrate. Hence, the current density of flexible perovskite solar cells has been improved by 7.3% at downwards bending 60° and 1.9% at upwards bending 60°. Our work provides a guide for the design of efficient flexible perovskite solar cells under bending state.

Design and performance evaluation of flexible tubular microreactor for methanol steam reforming reaction

To obtain the flexible microreactor for potential application in constrained space, a novel flexible tubular microreactor was designed by using a corrugated shell and a high porosity porous copper fiber rod (PCFR) as catalyst support. The effect of placement position, bending direction, and bending angle on reaction performance of flexible tubular microreactor was investigated. Then, the stability of flexible tubular microreactor was further evaluated. The experimental results showed that the placement position and bending direction had a significant influence on the reaction performance of flexible tubular microreactor. Methanol conversion of flexible tubular microreactor with the vertical placement was 6.67% higher than that with horizontal placement. Higher methanol conversion and H2 flow rate were obtained when the microreactor bent along the vertical direction. The reaction performance of flexible tubular microreactor was found to decrease as the bending angle increased, and the methanol conversion decreased by around 14.07% with a bend of 90°. When the flexible tubular microreactor was horizontal placed with a bend of 60° in the vertical direction, the reaction performance of microreactor was not changed little after 20 cyclic bending. After continuous bending for 10 h, the methanol conversion and H2 flow rate of flexible tubular microreactor were 70.58% and 0.88 mol/h, showing good reaction performance.

Bending hollow-core negative-curvature fiber for refractive index sensing based on surface plasmon resonance effect

We numerically investigated a novel refractive index (RI) sensor based on a liquid-filled and Au-coated hollow-core negative-curvature fiber (HC-NCF). In the design, the cladding area of the HC-NCF was composed of only one ring of six silica tubes, all the air holes in the fiber were filled with analytic liquids. The fiber bent in either the x or y-axis direction and Au-coated inside the single cladding tube in the corresponding bending direction. The influences of Au-coated HC-NCF structure parameters on the propagation characteristics under different bending directions were investigated using the finite element method (FEM). Moreover, the sensing performances in the RI range of 1.30–1.35 were evaluated through analyzing the position of the confinement loss peak. The simulation results showed that the HC-NCF RI sensor in the y-axis bending direction showed higher sensitivity, and the maximum sensitivity was 6.974 µm/RIU. The sensor shows high sensitivity and provides an effective method for measuring the RI of liquids.

Arbitrarily and repeatedly programmable multi-layer soft actuators via “stress-caching”

Multi-layered strategy is prevalent in actuator fabrication since only a mismatch of geometric changing between layer(s) under the external stimulus is required, allowing to avoid meticulous molecular synthesis. Nonetheless, their actuation manners are usually limited to simple bending, of which the direction as well as amplitude are not (re)programmable after synthesis. Here, an arbitrarily and repeatedly programmable multi-layered actuator via “stress-caching”, where a shape memory polymer (SMP) is sandwiched with two coated hydrogel layers, is presented. Via varying the swelling/de-swelling degree between the top and bottom hydrogel layers, the designed internal stress, determining the bending direction and angle, was stored within the actuator due to the constraint of the rigid SMP layer. Upon heating, the release of the cached stress induced a “snap-like” fast actuation and the resultant geometry can be designed, preserved or recovered on demand. Additionally, the flame-retardant hydrogel layers safeguarded the actuator to work at high temperatures (even directly exposed to flame), ensuring potential applications in a fire-rescuing scenario as demonstrated. Thus, our stress-caching approach shall diversify the designs of actuator since other myriad smart materials with distinct responsiveness and functionality can be straightforwardly employed.

Principle and Unified Design of Circularly Polarized Quadruple Inverted-F Antenna With Miniaturized Size and Enhanced Front-to-Back Ratio

The fundamental working principle of front-to-back ratio (FTBR) enhancement of the quadruple inverted-F antenna (QIFA) is clearly revealed for the first time, and a unified design method is then proposed in this article. The characteristic mode analysis (CMA) demonstrates that the QIFA actually operates in two orthogonal modes, and analytical derivation validates that each mode acts as a pair of parallel magnetoelectric (ME) short dipoles for radiation. More specifically, the FTBR of the antenna is determined by the amplitude ratio and phase difference of the two pairs of equivalent ME dipoles. The equivalent model and analytical method can greatly facilitate the design. First, by leading or lagging phase of either characteristic mode through excitation, the beam direction can be flexibly prescribed as forward and backward. Second, the bending direction and bending degree of radiators, respectively, determine the phase and amplitude of its equivalent magnetic dipole, by which the FTBR can be improved. A practical design is carried out with the proposed method, and the antenna achieves an electrically small size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.068\lambda _{0} \times 0.068\lambda _{0} \times 0.052\lambda _{0}$ </tex-math></inline-formula> and an FTBR of 12.3 dB.

Highly Sensitive Bending Sensor Based on Multicore Optical Fiber With Diagonal Cores Reflector at the Fiber Tip

A high-sensitivity bending sensor based on multi-core fiber Bragg gratings (MCFBGs) is presented and demonstrated. The bending sensor is based on FBGs fabricated on the symmetric distribution cores of seven-core fiber (SCF), where a 45-degree reflective cone frustum (RCF) is fabricated at the fiber end. The optical paths of two symmetric cores are connected by the 45-degree RCF. The wavelength drifts of the two FBGs on the symmetric cores caused by bending were similar in magnitude and opposite in direction, while the wavelength drifts of the two FBGs caused by temperature were similar in magnitude and direction. Therefore, the influence of temperature change on the curvature measurement can be automatically eliminated, and the bending sensitivity can be doubled by calculating the difference between the reflected wavelengths of the two FBGs. The sensor's spectral responses to the curvature at different bending directions are experimentally investigated. The maximum curvature sensitivity of the sensor is 225.9 pm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , within the curvature range from 0 to 6.9 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> .

Sawtooth Fiber MZ Vector Bending Sensor Available for Multi Parameter Measurement

In this paper, a fiber Mach Zehnder (MZ) interferometer based on sawtooth structure was proposed. It not only has the ability of bending sensing and bending direction recognition, but also can be applied to multi parameter sensing. Here we established the fiber hetero core structure with single mode fiber-multimode fiber-single mode fiber (MSM), and then fabricated the sawtooth structure on the single mode fiber in the middle by CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. Since part of the cladding on the single-mode fiber was removed, the fiber core was no longer at the neutral plane. When the sensor is bent in the 0° direction or 180° direction, the effective refractive index and optical path length of the core mode will increase or decrease, resulting in the increase or decrease of the optical path difference between the core mode and the cladding mode. And then the interference wavelength will show a red shift or blue shift, so as to realize the curvature sensing with bending direction recognition. Meanwhile, due to the local stress of the sawtooth structure in the bending, the sensitivity of the bending sensor is improved. The testing results indicate that the sensitivity of 0° bending and 180° bending are −15.16 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and 8.32 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> with the curvature range of 0–1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Moreover, the sawtooth structure sensor has excellent performance in strain, temperature and torsion sensing. The torsional sensitivity of the sensor reaches −0.30 nm/(rad/m) with torsional range of 0–13.96 rad/m, the temperature sensitivity reaches 58.90 pm/°C, and the strain sensitivity reaches −3.62 pm/μϵ. In strain sensing, there are some interference valleys insensitive to strain, which can realize the simultaneous measurement of other parameters and strain.

Photonic Hooks Generated by a Concave Micro-Cylinder Based on Structure-Constrained Functions.

Owing to its crooked trajectory and small full width at half-maximum, photonic hook (PH) has attracted wide attention since its inception and experimental confirmation. However, the present generation and regulation of PH are mostly dependent on the breaking of the symmetry of the system composed of the incident light and the regular structure particles, which inevitably limits the research of PH. In this work, the PH of the irregular particles is demonstrated with the help of a structure-constrained function (SCF). By varying the coefficients of the function, characteristic parameters of the PH, such as the bending angle, the effective length and the bending direction, can be effectively modulated. Meanwhile, high-quality PHs with a bending angle of up to 46° and an effective length of up to 11.90λ, as well as PHs with three bends, can be obtained using this method. The formation mechanism of the PH is revealed by simulating the distribution of the field intensity with the finite element method and analyzing with ray optics. This is the first time that we introduce a function into the investigation of PH, paving a new way for a more interesting exploration of PH.

Design of Compact, Broadband, and Low-Loss Silicon Waveguide Bends with Radius under 500 nm

Waveguide bend is an indispensable component in the on-chip compact photonic integrated circuits (PICs) and the minimum bend size greatly limits the increase of integration density of PICs. Here, we propose broadband and low-loss silicon waveguide bend schemes using air trenches on both sides and embedded germanium arc in the inner side of waveguide bend. Using these ways, the silicon waveguide bending radius can be greatly reduced to less than 500 nm and the obtained insertion loss (IL) can be as low as 0.12 dB compared with IL = 1.73 dB obtained by direct silicon waveguide bend under the same bending radius. Meanwhile, the working bandwidth can be extended over 500 nm covering the whole optical communication band by keeping IL &lt; 0.5 dB. Therefore, the proposed device schemes could push the development of on-chip PICs toward higher integration density.

Systematic shift in plume bending direction at Grotto Vent, Main Endeavour Field, Juan de Fuca Ridge implies changes in venting output along the Endeavour Segment

Analysis of the time-dependent behavior of the buoyant plume rising above Grotto Vent (Main Endeavour Field, Juan de Fuca Ridge) as imaged by the Cabled Observatory Vent Imaging Sonar (COVIS) between September 2010 and October of 2015 captures long term time-dependent changes in the direction of background bottom currents independent of broader oceanographic processes, indicating a systematic evolution in vent output along the Endeavour Segment of the Juan de Fuca Ridge. The behavior of buoyant plumes can be quantified by describing the volume, velocity, and orientation of the effluent relative to the seafloor, which are a convolved expression of hydrothermal flux from the seafloor and ocean bottom currents in the vicinity of the hydrothermal vent. We looked at the azimuth and inclination of the Grotto plume, which was captured in three-dimensional acoustic images by the COVIS system, at 3-h intervals during October 2010 and between October 2011 and December 2014. The distribution of plume azimuths shifts from bimodal NW and SW to SE in 2010, 2011, and 2012 to single mode NW in 2013 and 2014. Modeling of the distribution of azimuths for each year with a bimodal Gaussian indicates that the prominence of southward bottom currents decreased systematically between 2010 and 2014. Spectral analysis of the azimuthal data showed a strong semi-diurnal peak, a weak or missing diurnal peak, and some energy in the sub-inertial and weather bands. This suggests the dominant current generating processes are either not periodic (such as the entrainment fields generated by the hydrothermal plumes themselves) or are related to tidal processes. This prompted an investigation into the broader oceanographic current patterns. The surface wind patterns in buoy data at two sites in the Northeast Pacific and the incidence of sea-surface height changes related to mesoscale eddies show little systematic change over this time-period. The limited bottom current data for the Main Endeavour Field and other parts of the Endeavour Segment neither confirm nor refute our observation of a change in the bottom currents. We hypothesize that changes in venting either within the Main Endeavour Field or along the Endeavour Segment have resulted in the changes in background currents. Previous numerical simulations (Thomson et al., J. Geophys. Res., 2009, 114 (C9), C09020) showed that background bottom currents were more likely to be controlled by the local (segment-scale) venting than by outside ocean circulation or atmospheric patterns.

Self-calibration method of optical fiber shape sensor placement angle deviation based on GA

A self-calibration method based on genetic algorithm (GA) is used to achieve the placement angle correction of optical fiber shape sensor. This method can automatically calibrate the placement angle of the sensor directly, with no need of complex experimental calibration process. The method is verified by simulation and experiment under different bending directions and curvature, the maximum error of curvature and bending directions is decreased by 9.6%, 7.0°, and 11.3%, 7.2° by the self-calibration method in the simulation and experiment, respectively. This method provides a new correction method for optical fiber shape sensing, which is more convenient and effective than the traditional calibration method, especially in the field of long distance and large structure, which needs a large number of measuring points and needs to be laid and calibrated in the scene.

Analysis of Bending Degree of Basilar Artery Using Image Processing.

The basilar artery, which is the core of the posterior circulation, supplies blood to the brainstem and cerebellum. When basilar artery blood circulation is impaired, several symptoms can occur. In addition, the bending of the basilar artery causes stroke and infarction. Therefore, an image processing method for analyzing the bending degree of the basilar artery is introduced herein. To analyze the bending degree, the coordinates of the center points of the basilar artery are extracted using image processing techniques such as Canny edge detection, the contour technique, and the distance conversion technique. An image reconstructed using the three-dimensional scatter plot function in MATLAB and vector plots is used to calculate the vectors for each central point of the basilar artery. Meanwhile, the angle of each central point is calculated by selecting the first central point where the basilar artery begins, the central point with the greatest bending degree, and the central point at which the branching ends. The greater the bending degree of the basilar artery is, the larger the magnitude of the vector in the bending direction. The obtained results are verified by experts in the field, and the proposed algorithm demonstrates good performance.

An Automatic Extraction Method of Rebar Processing Information Based on Digital Image

Reinforced steel is one of the most important building materials in civil engineering and improving the intelligence of steel reinforcement engineering can greatly promote the intelligent development of the construction industry. This research addressed the problems of the slow speed and poor accuracy of manually extracting rebar processing information, which leads to a low degree of rebar processing intelligence. Firstly, based on digital image processing technology, image preprocessing methods such as binarization and grayscale were used to eliminate redundant information in a detail drawing of a rebar. An image segmentation method based on pixel statistics was proposed to store the geometric and non-geometric information of the detail drawing of the rebar separately. Next, the bending angle was extracted by line thinning and corner detection, and the bending direction of the steel bar was determined based on the mathematical characteristics of the vector product. Finally, the non-geometric information was extracted by combining the morphological algorithm and the Optical Character Recognition (OCR) engine. According to the characteristics of the information sequence, an information mapping method was proposed to realize the integration of geometric and non-geometric information. The applicability and accuracy of this method for extracting the steel bar’s information were tested by experiments, and it was shown that the method also provides a theoretical basis for realizing the intelligentization and informatization of steel bar processing.