The gecko can achieve flexible climbing on various vertical walls and even ceilings, which is closely related to its unique foot adhesion system. In the past two decades, the mechanism of the gecko adhesion system has been studied in-depth, and a verity of gecko-inspired adhesives have been proposed. In addition to its strong adhesion, its easy detachment is also the key to achieving efficient climbing locomotion for geckos. A similar controllable adhesion characteristic is also key to the research into artificial gecko-inspired adhesives. In this paper, the structures, fabrication methods, and applications of gecko-inspired controllable adhesives are summarized for future reference in adhesive development. Firstly, the controllable adhesion mechanism of geckos is introduced. Then, the control mechanism, adhesion performance, and preparation methods of gecko-inspired controllable adhesives are described. Subsequently, various successful applications of gecko-inspired controllable adhesives are presented. Finally, future challenges and opportunities to develop gecko-inspired controllable adhesive are presented.

We report a controllable and scalable fabrication approach for the superhydrophobic hierarchical structures and demonstrate the excellent ability to harvest water energy when applied to water-solid contact triboelectric nanogenerator (TENG). A strategy combined with multiple photolithography and micromolding process was developed to accurately regulate the diameters and the center distances of the two-level micropillars. A variety of hierarchical structures were successfully fabricated and presented the advantages of structure control, large scale, high accuracy, and high consistency. The hydrophobic property characterizations were conducted, and the results indicated that the hierarchical structures showed a larger contact angle than the single-level structures and achieved superhydrophobicity. Then the hierarchical structures were applied to water-TENGs with flowing water continuously dripping on, and the effect of the structure parameter on the triboelectric output was analyzed. The hierarchical structures exhibited a superior ability to harvest water energy than the flat film and the single-level structures due to the enhanced friction area and superhydrophobic property. At a flowing velocity of 8 mL/s, the hierarchical structure generated the output voltage of approximately 34 V and the short-circuit current of around 5 μA. The water-TENG device exhibited a power density peak of 7.56 μW/cm² with a resistive load of 16.6 MΩ at a flowing velocity of 10 mL/s. These findings shed light on the potential applications of the hierarchical structures-based water-TENGs to water energy harvesting and self-powered sensor devices.

In this study, a giant magnetostrictive ultrasonic transducer was designed with Terfenol-D as the active material. The influence of different Terfenol-D rod structures on the performance of the giant magnetostrictive transducer was investigated. Finite element analysis was used to analyze the dynamics of the theoretical giant magnetostrictive transducer and to validate the design. Eddy current losses were simulated for Terfenol-D rods of various structures using finite element analysis in ANSYS Maxwell. Two different Terfenol-D rods were then fabricated with either slices along the axial direction or slit along the radial direction, then the impedance and amplitude of the magnetostrictive ultrasonic transducer composed of the two Terfenol-D rods were measured. The results suggest that sliced Terfenol-D rods can suppress eddy currents more effectively, resulting in higher energy conversion efficiency; therefore, the Terfenol-D rods of small giant magnetostrictive transducers should be sliced along the axial direction to suppress eddy currents, whereas radial slits should be adopted for the rods of large giant magnetostrictive transducers to ensure integrity of the Terfenol-D rod and avoid adverse effects on the vibration performance of the giant magnetostrictive transducer that are caused by cutting the rods.

The trochoidal milling mode is widely used in high-speed machining, and due to good adaptability and flexible posture adjustment, ball-end milling cutters are conducive to complex surface machining with this mode. However, the processes of material removal and formation of machined micro surfaces are very difficult to describe as the profile of cutter teeth is complex and the trajectory direction changes continuously during the trochoidal milling process. A modeling method for the generation of micro surface topography of ball-end milling in the trochoidal milling mode is put forward. In this method, the locus equation of each cutter tooth is established based on the principle of homogeneous coordinate transformation, after which a Z-MAP algorithm is designed to simulate the micro surface topography. The Z-MAP algorithm can quickly obtain the part grid nodes potentially swept by the cutter tooth within a unit time step through the establishment of servo rectangular encirclement and instantaneous sweeping quadrilateral of the element of cutter teeth; the part grid nodes actually swept are further determined through an angle summation method, and the height coordinate is calculated with the method of linear interpolation according to Taylor’s formula of multivariate functions. Experiments showed that the micro surface topography resulting from ball-end milling in the trochoidal milling mode had high consistency with the simulation, which indicates that the proposed method can predict micro surface topography in practical manufacturing. In addition, a comparison of micro surface topography between trochoidal milling and ordinary straight-linear milling was conducted, and the results showed that the former was overall superior to the latter in resulting characteristics. Based on this conclusion, the influences of cutting parameters of ball-end trochoidal milling on surface characteristics, particularly amplitude and function, were analyzed according to the simulated micro surface topography data.