The ultrastructure characteristic and vivid colors of butterfly wing scales have attracted considerable attention recently. Surprisingly, these hyperfine structures also endow butterfly Trogonoptera brookiana wing scales the excellent color sensitive property to liquid mediums. In this work, the characteristic features of this excellent functional surface and the mechanism of its highly sensitive response characteristics were investigated. Firstly, the extraordinary and ordered nanostructures of this butterfly wing scales were characterized by a Field Emission Scanning Electron Microscope (FESEM). Then, the ultra-depth three-dimensional (3D) microscope was used to observe the sensitive discoloration effect of the scales to liquid mediums. Afterwards, the highly spectral sensitive feature was identified by a mini spectrometer. In addition, the mechanism of this color sensitive effect of butterfly wing scales was revealed through modelling, calculation and simulation. It was found that this sensitivity is caused by the combined action of the microscale scales and the ultra-fine nanoscale structures in scale surface. On one hand, the arched and bended cover scales were stretched and superimposed by the filled ether solution. So, the color of the scales became reddish brown in an instant. On the other hand, the change of the fill mediums with different reflective index induced the modification of the surface interference, resulting in the peak shift of the reflectance spectrum. More importantly, the results of simulation and theoretical calculation were both in agreement with the experimental results. It illustrated that the butterfly Trogonoptera brookiana wings have repeatable sensitivity to liquid mediums, and obvious discoloration sensitive effect. This spectral sensitivity of butterfly wing scales has great prospect and meaning for the basic research and application of cheap, environmentally free and biodegradable sensitive element for water quality monitoring and analysis system.

We demonstrate the application of cactus-inspired structures for fog collection. The drop-on-cone system is modeled to analyze Gibbs free-energy gradients, equilibrium positions and motion of drops. Normalized free energy and free energy gra-dient are presented to characterize barrel and clam-shell drops, revealing the relations of the driving force and wettability to the half-apex angle of the cones. Small half-apex angle results in long collecting length and weak driving force. Thus it is important for fog collection to balance the driving force and collecting length with a suitable half-apex angle. Fog collection experiments on cactus-inspired structures are conducted for verification. Inflection points around 1.1? are observed, where the fog collection ability is mainly limited by the weak driving force when below the inflection points, while increases with the collecting length when above the inflection points. These indicate that the half-apex angle at the inflection point is a compromise between the driving force and collecting length, agreeing with the normalized functions. The results also prove that the hydrophilic cones are more suitable for fog collection with regard to condensation and driving force. Our research offers design guidance for efficient fog collection structure.

This study attempts to investigate how the slippery surface of Nepenthes alata pitchers restricts the attachment ability of ant Camponotus japonicus Mayr, via climbing behavior observation and friction force measurement. Ants exhibited ineffective climbing behaviors and rather small friction forces when attached to upward-oriented slippery surfaces, but opposite phenomena were shown when on inverted surfaces. Friction forces of intact, claw tip-removed and pad-destroyed ants were measured on intact and de-waxed slippery surfaces, exploring the roles of wax crystals and lunate cells in restricting ant’s attachment. On downward-directed slippery surfaces, greater forces were exhibited by intact and pad-destroyed ants; on the two slippery sur-faces, pad-destroyed ants presented slightly smaller forces and clawless ants generated considerably smaller forces. Somewhat different force was provided by clawless ants on upward and downward oriented slippery surfaces, and slightly higher force was shown when ants climbed on wax-removed surface. Results indicate that the lunate cells contribute greatly to decrease the friction force, whereas the wax crystals perform a supplementary role. Mechanical analysis suggests that the directionally growing lunate cells possess a sloped structure that effectively prevents the claw’s mechanical interlock, reducing the ant’s attachment ability considerably. Our conclusion supports a further interpretation of slippery surface’s anti-attachment mecha-nism, also provides theoretical reference to develop biomimetic slippery plate to trap agricultural insect.

The dragonfly has excellent flying capacity and its wings are typical 2-dimensional composite materials in micro-scale or nano-scale. The nanomechanical behavior of dragonfly membranous wings was investigated with a nanoindenter. It was shown that the maxima of the reduced modulus and nanohardness of the in-vivo and fresh dragonfly wings are about at position of 0.7L, where L is the wing length. It was found that the reduced modulus and nanohardness of radius of the wings of dragonfly are large. The reduced modulus and nanohardness of Costa, Radius and Postal veins of the in-vivo dragonfly wings are larger than those of the fresh ones. The deformation, stress and strain under the uniform load were analyzed with finite element simulation software ANSYS. The deformation is little and the distribution trend of the strain is probably in agreement with that of the stress. It is shown that the main veins have better stabilities and load-bearing capacities. The understanding of dragonfly wings’ nanomechanical properties would provide some references for improving some properties of 2-dimentional composite materials through the biomimetic designs. The realization of nanomechanical properties of dragonfly wings will provide inspirations for designing some new structures and materials of mechanical parts.

TiO2 films including different amounts of Ag obtained by sol-gel method on commercially pure titanium (CP-Ti) and the corrosion properties of Ag-doped TiO2 films were investigated by potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS) tests in Simulated Body Fluid (SBF) solution. The results were compared with untreated and un-doped samples. Surface characterizations before and after the corrosion tests were performed by the Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analysis. It was observed that Ag-doping for TiO2 films improved the corrosion resistance when compared with untreated and un-doped TiO2 film coated samples. The highest corrosion resistance was obtained from Ag-doped samples coated with a solution of 0.05 M Ag.

This work investigates the potential of combining hardness gradient with surface texture (an example of bionic coupling) to improve anti-wear properties. The bionic coupling of hardness gradient and Hexagonal Texture (HT) was achieved by laser heat treatment on steel specimens with pre-engraved hexagonal surface texture. The successful establishment of decreasing hardness from surface to internal bulk was verified by hardness measurements along the depth of cross-sectioned specimens and corre-lated with the observations from metallurgical microscopy. The tribological performance of bionic coupling specimens (HT-L) was examined under dry contact condition, together with respective control specimens of individual bionic features, e.g. HT-H (of similar surface hardness generated by conventional heat treatment but without hardness gradient) and SS-L (of smooth surface treated by the same laser processing as for HT-L). It is found that HT-L not only exhibits lower friction coefficient and less friction fluctuation than HT-H and SS-L, but also demonstrates a >50% reduction of wear loss compared to HT-H and SS-L (0.0343 g for HT-L vs. 0.0723 g for HT-H, P<0.001; 0.0343 g for HT-L vs. 0.0817 g for SS-L, P<0.001). Corroboratively, observations with scanning electron microscopy revealed a relatively smooth surface for worn HT-L specimen, contrasting with the rugged and grooved surfaces of worn HT-H and SS-L specimens. These results indicate that the bionic coupling of hardness gradient to hexagonal texture can indeed improve anti-wear properties, affording a new strategy to wear and friction manage-ment.

Crickets, similar to some other insects, have highly sensitive filiform hairs on their cerci that can detect miniscule changes in airflow. This study imitates the perception mechanism of these filiform sensory hairs of crickets by designing and fabricating a Multi-electrode Metal Core Piezoelectric Fiber (MMPF)-based airflow sensor. Four longitudinal conductive sheets were coated symmetrically on their surfaces with Metal-core Piezoceramic Fibers (MPF). The four fan-shaped piezoelectric ceramics with surface electrode covers were polarized. After successful polarization, the cantilevered MMPF could be used as an airflow sensor. The four electrodes on the surface were symmetrically divided into two groups. Therefore, two signals can be produced by a single fiber sensor. The theoretical model of an MMPF airflow sensor has been established. The model indicates that the ratio of the two signals is equivalent to the tangent of the airflow angle. Furthermore, the sum of the squares of the two signals is not dependent on the angle, but reflects the velocity of the airflow. Therefore, a single MMPF can be used to measure both the direction and amplitude for a given airflow. The theoretical model has been confirmed via experimental measurements.

Natural fibres are very versatile materials, their properties vary with chemical composition and physical structure. The effects of alkali, silane and combined alkali and silane treatments on the mechanical (tensile), morphological, and structural properties of Pine Apple Leave Fibres (PALF) and Kenaf Fibres (KF) were investigated with the aim to improve their com-patibility with polymer matrices. The effectiveness of the alkali and saline treatments in the removal of impurities from the fibre surfaces was confirmed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectrometry (FTIR) ob-servation. The morphological study of treated PALF and KF by SEM indicates that silane treated fibres have less impurities and lignin and hemicelluloses removed than those by other chemical treatments. Silane treated PALF and KF display better tensile strength than those of untreated, alkaline and NaOH-silane treated. Droplet test indicates that the Interfacial Stress Strength (IFSS) of alkali and silane treated PALF and KF are enhanced whereas silane treated fibres display highest IFSS. It is assumed that fibre treatments will help to develop high performance KF and PALF reinforced polymer composites for industrial appli-cations.

This article aims to develop a mathematical model for peristaltic transport of magnetohydrodynamic flow of biofluids through a micro-channel with rhythmically contracting and expanding walls under the influence of an applied electric field. The couple stress fluid model is considered to represent the non-Newtonian characteristics of biofluids. The velocity slip condition at the channel walls is taken into account because of the hydrophilic/hydrophobic interaction with negatively charged walls. The essential features of the electromagnetohydrodynamic flow of biofluid through micro-channels are clearly highlighted in the variations of the non-dimensional parameters of the physical quantities of interest such as the velocity, wall shear stress, pressure gradient, pressure rise per wave length, frictional force at the channel walls and the distribution of stream function. It reveals that the flow of biofluid is appreciably influenced by the sufficient strength of externally applied magnetic field and electro-osmotic parameter. The velocity slip condition reduces the frictional force at the channel wall. Moreover, the formation of the trapping bolus strongly depends on electro-osmotic parameter and magnetic field strength.

We propose a control moment generator to control the attitude of an insect-like tailless Flapping-wing Micro Air Vehicle (FW-MAV), where the flapping wings simultaneously produce the flight force and control moments. The generator tilts the stroke plane of each wing independently to direct the resultant aerodynamic force in the desired direction to ultimately generate pitch and yaw moments. A roll moment is produced by an additional mechanism that shifts the trailing edge, which changes the wing rotation angles of the two flapping wings and produces an asymmetric thrust. Images of the flapping wings are captured with a high-speed camera and clearly show that the FW-MAV can independently change the stroke planes of its two wings. The measured force and moment data prove that the control moment generator produces reasonable pitch and yaw moments by tilting the stroke plane and realizes a roll moment by shifting the position of the trailing edge at the wing root.

A micro air vehicle with a bird-mimetic up-down and twisting wing drive system was developed in this study. The Flap-ping-wing Micro Air Vehicle (FMAV), with a 50 cm wingspan and a double-crank drive system, performed successful flights of up to 23 min. The performance and capabilities of the FMAV were enhanced by adapting a number of unique features, such as a bird-mimetic wing shape with a span-wise camber and an up-down and twisting wing drive mechanism with double-crank linkages. This lift-enhancing design by mimicking the flapping mechanism of a bird’s wing enabled the 210 g FMAV to fly autonomously in an outdoor field under wind speeds of less than 5 m•s−1. Autonomous flight was enabled by installing a flight control computer with a micro-electro-mechanical gyroscope and accelerometers, along with a micro video camera and an ultralight wireless communication system inside the fuselage. A comprehensive wind tunnel test shows that the FMAV with a high-camber wing and double-crank mechanism generates more lift and less net thrust than the FMAV with a flat wing and single-crank mechanism, which confirms the improved performance of the developed FMAV, as well as the superior slow flying or hovering capabilities of the FMAV with a high-camber wing and double-crank wing drive system.

The bionic propulsion can be used on the aerostat and other automatic vehicles. The general single oscillating tail fin can induce the yawing and whole airship rolling because of the lateral force and the gravity moment of heavier oscillating tail fin. The parallel twin oscillating tail fins by symmetrical swing mode can eliminate the lateral force and gravity moment through the symmetrical swing of the two tail fins. The propulsive characteristics of parallel twin fins have not been investigated up to now. In this paper, we investigated the propulsive characteristics and mechanism of parallel twin oscillating airfoils using consistent and symmetrical swing mode. By using the numerical calculation and analysis, the consistent swing mode may decrease the total propulsion efficiency. While, the symmetrical swing mode can improve the propulsion efficiency and reduce the lateral force and gravity moment. This mode can be used to propel the aerostat and automatic underwater vehicles efficiently.

Wing kinematics in forward-flying fruit-flies was measured using high-speed cameras and flows of the flapping wing were calculated numerically. The large lift and thrust coefficients produced by the wing were explained. The wing flaps along a forward-tilting stroke plane. In the starting portion of a half-stroke (an upstroke or downstroke), the wing pitches down to a small pitch angle; during the mid portion (the wing has built up its speed), it first fast pitches up to a large pitch angle and then maintains the pitch angle; in the ending portion, the wing pitches up further. A large aerodynamic force (normal to the wing surface) is produced during the mid portion of a half-stroke. The large force is produced by the fast-pitching-up rotation and delayed-stall mechanisms. As a result of the orientation of wing, the thrust that propels the insect is produced by the upstroke and the major part of the vertical force that supports the weight is produced by the downstroke. In producing the thrust the upstroke leaves a “vortex ring” that is almost vertical, and in producing the vertical force the downstroke leaves a “vortex ring” that is almost horizontal.

Brain-Computer Interface (BCI) techniques have advanced to a level where it is now eliminating the need for hand-based activation. This paper presents a novel attempt to remotely control an animal’s behavior by human BCI using a hybrid of Event Related Desynchronization (ERD) and Steady-State Visually Evoked Potential (SSVEP) BCI protocols. The turtle was chosen as the target animal, and we developed a head-mounted display, wireless communication, and a specially designed stimulation device for the turtle. These devices could evoke the turtle’s instinctive escape behavior to guide its moving path, and turtles were remotely controlled in both indoor and outdoor environments. The system architecture and design were presented. To demon-strate the feasibility of the system, experimental tests were performed under various conditions. Our system could act as a framework for future human-animal interaction systems.

This paper proposes a novel method for Small Unmanned Helicopter (SUH) system identification based on Improved Particle Swarm Optimization (IPSO). In the proposed IPSO, every particle will do a local search as a “self-check” before up-dating the global velocity and position. Then, the global best particle is created by a certain number of elitist particles in order to get a rapid rate of convergence during calculation. Thus both the diversity and convergence speed can be taken into considera-tion during a search. Formulated by the first principles derivation, a state-space model is built for the analysis of dynamic modes of an experimental SUH. The helicopter is equipped with an Attitude Heading Reference System (AHRS) and the corresponding data storage modules, which are used for flight test data measurement and recording. After data collection and reconstruction, the input and output data are utilized to determine the corresponding aerodynamic parameters of the state-space model. The predictive accuracy and fidelity of the identified model are verified by making a time-domain comparison between the responses from the simulation model and the responses from actual flight experiments. The results show that the characteristics of the experimental SUH can be determined accurately using the identified model and the new method can be used for SUH system identification with high efficiency and reliability.