High-factor interpolation method based on space-time modulation and a Kalman filter for optical encoders.

A high-factor interpolation method based on space-time modulation and a Kalman filter for optical encoders is proposed. Space-time modulation employs a reference time signal to modulate the output displacement signal of the optical encoder into a displacement space-time signal. Subsequently, high-frequency pulse signals are used for interpolation, which detect the phase of the reference time signal and the displacement space-time signal to obtain displacement information from the optical encoder output. The interpolation factor of this method depends on the frequencies of the high-frequency pulse signal and the reference time signal, and is independent of the moving speed. A Kalman filter is employed to estimate the velocity, compensating for time lag errors in the displacement information output by space-time modulation to improve the real-time performance of displacement output. The proposed method is simple and effective, which can be implemented on an FPGA. The effectiveness of the proposed method is verified through simulation and experimentation.

Thermoelectric Generator Through Dual-Direction Thermal Regulation by Thermal Diodes for Waste Heat Harvesting.

Thermal energy harvesting provides an opportunity for multi-node systems to achieve self-power autonomy. Thermoelectric generators (TEGs), either by thermocouple arrangement with higher-aspect-ratios or thermoelectric films overlay, are limited by the small temperature difference and its short-duration (less than dozens of minutes), hindering the harvesting efficiency. Here, by introducing thermal diodes with dual-direction thermal regulation ability to optimize the heat flux path, the proposed TEGs exhibit enhanced power-supply capability with unprecedented long-duration (more than hours). In contrast with conventional TEGs with fixed-leg dimensions enabled single output, these compact-TEGs can supply up to fourteen output-channels for selection, the produced power ranges from 1.11 to 921.99 µW, open circuit voltage ranges from 8.07 to 51.32 mV, when the natural temperature difference is 53.84 °C. Compared to the most recent TEGs, the proposed TEGs in this study indicate higher power (more than hundreds times) and much longer output duration (2.4-120 times) in a compact manner.

Flexible Platform Composed of T-Shaped Micropyramid Patterns toward a Waterproof Sensing Interface.

Antifouling is essential to guaranteeing the sensitivity and precision of flexible sensing interfaces. Materials and structures are the two primary strategies. However, optimizing the inherent microstructures to integrate waterproofing and sensing is rarely reported. To improve the liquid repellency of micropyramid structures, this work presents a study of the design and fabrication of T-shaped micropyramid structures. These structures are patterned uniformly and largely on polydimethylsiloxane (PDMS) skin by the new process of two-step magnetic induction. The waterproofing is related to the breakthrough pressure and the liquid repellency, both of which are a function of structural characteristics, D, and material properties, θY. At the breakthrough transition, two failure models distinguished by θY appear: the depinning transition and the sagging transition. Meanwhile, when considering D in practice, some models will shift and occur early. The D value regulates the transition of the material's wettability to the liquid repellency. The influence of the material's inherent nonwettability on liquid repellency diminishes as D decreases, and the transition from completely wetting liquids to super-repellents can be achieved. Experiments demonstrate that for D = 0.3 under water the resistance is approximately 142 times larger than the depth of the structure, considerably facilitating the waterproofing of conventional micropyramid arrays. This work provides a novel method for fabricating flexible T-shaped micropyramid array structures and opens a new window on flexible sensing interfaces with excellent waterproofing.

Study on the influence of surface roughness on the diffraction efficiency of two-dimensional gratings.

This study investigates the effect of surface roughness on the diffraction efficiency of two-dimensional gratings. Firstly, a roughness model was constructed using FDTD, followed by a significant analysis of the ridge roughness, groove roughness, and sidewall roughness on diffraction efficiency. Then, the impact of each roughness type on diffraction efficiency was studied separately. Results indicate that ridge roughness has a negative impact on diffraction efficiency, whereas groove roughness and sidewall roughness have a positive impact on the diffraction efficiency of two-dimensional gratings. When ridge, groove, and sidewall roughness coexist, diffraction efficiency decreases with an increase in roughness, consistent with previous research. However, under conditions of minimal roughness, diffraction efficiency actually increases. Finally, an experiment was conducted to verify the conclusions. The results of this study have significant reference value for the application and development of precision measurement techniques for gratings.

Light-driven untethered soft actuators based on biomimetic microstructure arrays.

Soft actuators based on smart materials and structures that can perform more diverse tasks skillfully, are being intensively sought. Despite the good progress made in the past few years, locomotion and transportation functionalities of the untethered soft-bodied devices for various natural terrains remain challenging. Inspired by a gecko crawling system, an untethered soft actuator with the abilities of picking up, transporting, and delivering objects controlled by NIR light is proposed. The soft actuator consisting of photo-responsive MWCNTs units and mushroom shaped microstructures, was fabricated by an integrative soft-lithography method with inking and imprinting processes. The integrated MWCNTs unit can convert NIR light irradiation into thermal energy, which can make the body of the soft actuator generate a strong shape deformation intrinsically in a self-contained way, leading to a combined discontinuous and continuous locomotion. Moreover, the integrated mushroom shaped microstructures can also realize grasping and manipulation of the object that was not constrained by the object's shapes and sizes, which was further addressed from experimental and theoretical perspectives. Thus, the combined use of smart materials and structures opens up new research avenues and represents a step forward toward future applications of light-driven untethered soft actuators.

Multidomain Oriented Particle Chains Based on Spatial Electric Field and Their Optical Application.

The manipulation technology of particles is significant in drug screening, disease detection and treatment, etc. Here, we reported the multidomain oriented particle chains based on a spatial electric field and their optical application. According to the differences in the dielectric behavior of particles, the preparation of multidomain oriented particle chains in the gel was successfully realized by using the dielectrophoretic force and electroosmotic rotation. This provides a new idea for manufacturing multistructure, multilayer, and multifunctional intelligent response materials. In addition, the factors affecting the alignment height of the particles in the gel were discussed, which was the basis for the preparation of bilayer particle chains. As an example of structural hierarchy, particle assembly has broad application prospects in optoelectronic devices and soft robots.

Amorphous Carbon-Induced Surface Defect Repair for Reinforcing the Mechanical Properties of Carbon Fiber.

Graphene oxide (GO) was prepared using metal-catalyzed crystallization of amorphous carbon on a carbon fiber surface to improve the mechanical properties of the carbon fiber (CF). The deposited GO was used for repairing of surface structure defects on CF, thereby improving the tensile strength and interfacial strength force of CF. The grown morphology of GO and the changes in CF surface microstructure before and after remediation were investigated in detail by scanning tunneling microscopy and Raman spectroscopy. The effects of surface repair on the mechanical properties of the CF and the resulting composites were investigated systematically. The results of scanning tunneling microscopy show that the graphene oxide formed on the surface of carbon fiber present uniform dispersion. Raman spectroscopy curves indicate that CF successfully remediated the defects in the CF surface. The results of mechanical properties testing show that such a remediation method could significantly enhance the tensile strength of CF and increase the interfacial strength versus raw fibers; that is, the tensile strength of CF was enhanced by 42% and the interfacial strength by 33.7%.

Formation of highly ordered micro fillers in polymeric matrix by electro-field-assisted aligning.

Nanocomposites composed by polymeric matrix with micro/nano fillers have drawn lots of attention since their dramatic properties beyond pristine polymers. The spatial distribution of the micro/nano fillers in the polymeric matrix determines the final desired properties of the nanocomposites, thus deserves to investigate. Here, we proposed an effective method of assembling the micro/nano fillers to pre-designed patterns within the polymeric matrix by AC-electro-field-assisted aligning. By pre-designed AC electric fields which could be dynamically controllable, the distribution of microparticles (acting as fillers) in the matrix was tuned to various patterns related to the electric fields, such as linear alignment and circular alignment. The field-oriented particles chains could act as endoskeletal structures, showing unique properties (i.e., mechanical, optical, and anisotropic properties) beyond those of the conventional composites with randomly distributed particles.

Laminated pyroelectric generator with spin coated transparent poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes for a flexible self-powered stimulator.

Implantable devices are promising electronics in medicine, which can perform real-time monitoring for a variety of human-body physiological conditions and control the function of some failing organs. However, the technology to power implantable devices still has some remaining challenges. This work presents a transparent self-powered pyroelectric generator driven by near infrared radiation for wireless powering of electronics. The pyroelectric device uses a highly conductive polymer, PEDOT:PSS, formed as an electrode without the use of a complex transferring process. Due to the good match between the surface energy of the PEDOT electrode and PVDF, when combined with PVDF the resulting PEDOT/PVDF/PEDOT device possesses a highly adherent interface. The influence of the PEDOT thickness on the output voltage of the device has been investigated according to the difference in its infrared transmittance and absorbance. In addition, in order to enhance the output voltage while reducing the device temperature, a laminated pyroelectric generator, in which each cell is composed of a PEDOT/PVDF/PEDOT sandwich, was further developed taking advantage of the high infrared transmittance of PEDOT and PVDF. The proposed laminated pyroelectric device could generate up to 23.4 V with six laminated cells, an enhancement of approximately 212% compared to a single cell, which could directly light up an LCD and was applied for nerve stimulation of the sciatic nerve of a frog, indicating that the proposed self-powered device could be a candidate for implantable medical electronics.

Fabrication of directional nanopillars with high-aspect-ratio using a stretching imprint process with a microcavity mold.

Directional nanopillars with high-aspect-ratio have wide applications in home or industrial appliances and biomimetic robots. Their fabrication, however, is a challenge for conventional methods. In this study, we propose a simple stretching imprint process to prepare controllable directional (30°-90° in a slanted angle) nanopillars (200-800 nm in diameter) with high aspect ratio (>30) using a microcavity mold, beyond the conventional nanoimprint process, for 1 : 1 pattern transfer from the mold to the replica. The mechanism of the stretching imprint process is further investigated, and a rheology model for the filament evolution during the stretching process is established, which clearly shows that the aspect-ratio, diameter in submicrons, slanted angle, and also the tip profile of the free-standing nanopillars can be easily controlled by the imprint process using a microcavity mold. Further experiments indicate that the fabricated directional free-standing nanopillars show strong friction anisotropy, which may find applications in biomimetic studies.

Reversible Bending Behaviors of Photomechanical Soft Actuators Based on Graphene Nanocomposites.

Photomechanical nanocomposites embedded with light-absorbing nanoparticles show promising applications in photoresponsive actuations. Near infrared (nIR)-responsive nanocomposites based photomechanical soft actuators can offer lightweight functional and underexploited entry into soft robotics, active optics, drug delivery, etc. A novel graphene-based photomechanical soft actuators, constituted by Polydimethylsiloxane (PDMS)/graphene-nanoplatelets (GNPs) layer (PDMS/GNPs) and pristine PDMS layer, have been constructed. Due to the mismatch of coefficient of thermal expansion of two layers induced by dispersion of GNPs, controllable and reversible bendings response to nIR light irradiation are observed. Interestingly, two different bending behaviors are observed when the nIR light comes from different sides, i.e., a gradual single-step photomechanical bending towards PDMS/GNPs layer when irradiation from PDMS side, while a dual-step bending (finally bending to the PDMS/GNPs side but with an strong and fast backlash at the time of light is on/off) when irradiation from PDMS/GNPs side. The two distinctive photomechanical bending behaviors are investigated in terms of heat transfer and thermal expansion, which reveals that the distinctive bending behaviors can be attributed to the differences in temperature gradients along the thickness when irradiation from different sides. In addition, the versatile photomechanical bending properties will provide alternative way for drug-delivery, soft robotics and microswitches, etc.

An infrared-driven flexible pyroelectric generator for non-contact energy harvester.

In recent years, energy harvesting technologies, which can scavenge many kinds of energies from our living environment to power micro/nanodevices, have attracted increasing attention. However, remote energy transmission, flexibility and electric waveform controllability remain the key challenges for wireless power supply by an energy harvester. In this paper, we design a new infrared-driven non-contact pyroelectric generator for harvesting heat energy, which avoids direct contact between the pyroelectric generator and heat source and realizes remote energy transfer exploiting the photothermal and penetrability of infrared light. The output voltage (under the input impedance of 100 MOhm) and short-circuit current of the pyroelectric generator consisting of a CNT/PVDF/CNT layer (20 mm × 5 mm × 100 µm) can be as large as 1.2 V and 9 nA, respectively, under a 1.45 W cm(-2) near-infrared laser (808 nm). We also demonstrate the means by which the pyroelectric generator can modulate square waveforms with controllable periods through irradiation frequency, which is essential for signal sources and medical stimulators. The overshoot of square waveforms are in a range of 9.0%-13.1% with a rise time of 120 ms. The prepared pyroelectric generator can light a liquid crystal display (LCD) in a vacuum chamber from outside. This work paves the way for non-contact energy harvesting for some particular occasions where near-field energy control is not available.

Graphene-Based Bioinspired Compound Eyes for Programmable Focusing and Remote Actuation.

Inspired by creatures' eyes, bioinspired compound eyes (BCEs) endowed with larger fields of view and vari-focal capability are extremely appealing in micro-optical devices. However, the present actuation strategies of BCEs commonly demand complicated fields, e.g., electro-wetting actuation, dielectrophoretic drive and pressure gradient, which greatly limits their practical applications. In this work, the photothermal conversion of graphene nanosheets (GNSs) is first utilized to fabricate lenslets toward BCEs. Under the actuation of near-infrared (nIR) pulsed laser, GNSs absorb photo energy and convert it to thermal energy, which increases the temperature of lenslets and then leads to the adjustment of lenslet curvature. At a result, BCEs manifest a reversible 4-fold zoom and a wide FOV up to 160°. In addition, BCEs also perform the programmable focusing by selectively confining nIR laser to a vari-focal region. In contrast with traditional BCEs, graphene-based BCEs are versatile with wide FOV and vari-focal ability by nIR actuation. Herein, these excellent properties make graphene-based BCEs promising for remote-driven microfluidic devices.

Improved fibroblast functionalities by microporous pattern fabricated by microelectromechanical systems.

Fibroblasts, which play an important role in biological seal formation and maintenance, determine the long-term success of percutaneous implants. In this study, well-defined microporous structures with micropore diameters of 10-60 µm were fabricated by microelectromechanical systems and their influence on the fibroblast functionalities was observed. The results show that the microporous structures with micropore diameters of 10-60 µm did not influence the initial adherent fibroblast number; however, those with diameters of 40 and 50 µm improved the spread, actin stress fiber organization, proliferation and fibronectin secretion of the fibroblasts. The microporous structures with micropore diameters of 40-50 µm may be promising for application in the percutaneous part of an implant.

Bioinspired uniform illumination by vibrated sessile droplet pinned by a hydrophilic/superhydrophobic heterogeneous surface.

We introduce a strategy to generate uniform illumination. The droplet pinned by a hydrophilic/superhydrophobic heterogeneous surface is oscillated, driven by a laterally placed loudspeaker. The vibrated droplet can be considered as a tunable lens, whose focus and focus length can be real-time tuned. The tunable "lens" is presented as a device for uniform illumination by mechanical manipulation. The incident light is scattered by the vibrated droplet during oscillation, and the irradiance distribution on the image plane becomes larger and more homogenous when the droplet is at resonance.

A metal/insulator/metal field-emission cannon.

A barrel-shaped metal/insulator/metal (MIM) field-emission cathode, also referred to as a field-emission cannon, is constructed using conventional SU-8 UV lithography combined with sputtering and lift-off processes. An array of these field-emission cannons has demonstrated uniform field emission in a luminescent pixel array. The field-emission test proves that the unique geometry of the field-emission cannon significantly improves field-emission efficiency and electron beam focus. Detailed data analysis has revealed that both conventional sharp edge field emission and MIM field emission contribute to the total emission current. The field emission starts from an edge emission at gate voltages (Vg) below 8 V. When Vg increases above 8 V, electrons tunnel into the cannon through the thin SiO2 layer and inner metal layer (i.e., the gate electrode). Thus, the MIM field emission starts to dominate.