A droplet‐based electricity generator incorporating Kelvin water dropper with ultrahigh instantaneous power density

Harvesting renewable water energy in various formats such as raindrops,waves,and evaporation is one of the key strategies for achieving global carbon neutrality.The recent decade has witnessed rapid advancement of the droplet‐based electricity generator(DEG)with a continuous leap in the instantaneous output power density from 50W/m2 to several kW/m2.Despite this,further pushing the upper limit of the output performance of DEG is still constrained by low surface charge density and long precharging time.Here,we report a DEG incorporating the Kelvin water dropper(K‐DEG)that can generate an ultrahigh instantaneous power density of 105W/m2 upon one droplet impinging.In this design,the Kelvin water dropper continuously replenishes the high density of surface charges on DEG,while DEG fully releases these surface charges into electric output.K‐DEG with such a high output can directly light five 6‐W commercial lamps and even charge a cellphone by using falling droplets.

An intelligent spinal soft robot with self-sensing adaptability

Self-sensing adaptability is a high-level intelligence in living creatures and is highly desired for their biomimetic soft robots for efficient interaction with the surroundings.Self-sensing adaptability can be achieved in soft robots by the integration of sensors and actuators.However,current strategies simply assemble discrete sensors and actuators into one robotic system and,thus,dilute their synergistic and complementary connections,causing low-level adaptability and poor decision-making capability.Here,inspired by vertebrate animals supported by highly evolved backbones,we propose a concept of a bionic spine that integrates sensing and actuation into one shared body based on the reversible piezoelectric effect and a decoupling mechanism to extract the environmental feedback.We demonstrate that the soft robots equipped with the bionic spines feature locomotion speed improvements between 39.5%and 80%for various environmental terrains.More importantly,it can also enable the robots to accurately recognize and actively adapt to changing environments with obstacle avoidance capability by learning-based gait adjustments.We envision that the proposed bionic spine could serve as a building block for locomotive soft robots toward more intelligent machine-environment interactions in the future.

Interfacial friction at action: Interactions, regulation, and applications

Friction is a fundamental force that impacts almost all interface-related applications.Over the past decade,there is a revival in our basic understanding and practical applications of the friction.In this review,we discuss the recent progress on solid–liquid interfacial friction from the perspective of interfaces.We first discuss the fundamentals and theoretical evolution of solid–liquid interfacial friction based on both bulk interactions and molecular interactions.Then,we summarize the interfacial friction regulation strategies manifested in both natural surfaces and artificial systems,focusing on how liquid,solid,gas,and hydrodynamic coupling actions mediate interfacial friction.Next,we discuss some practical applications that are inhibited or reinforced by interfacial friction.At last,we present the challenges to further understand and regulate interfacial friction.

Vertical,capacitive microelectromechanical switches produced via direct writing of copper wires

Three-dimensional(3D)direct writing based on the meniscus-confined electrodeposition of copper metal wires was used in this study to develop vertical capacitive microelectromechanical switches.Vertical microelectromechanical switches reduce the form factor and increase the area density of such devices in integrated circuits.We studied the electromechanical characteristics of such vertical switches by exploring the dependence of switching voltage on various device structures,particularly with regard to the length,wire diameter,and the distance between the two wires.A simple model was found to match the experimental measurements made in this study.We found that the electrodeposited copper microwires exhibit a good elastic modulus close to that of bulk copper.By optimizing the 3D structure of the electrodes,a volatile electromechanical switch with a sub-5 V switching voltage was demonstrated in a vertical microscale switch with a gap distance as small as 100 nm created with a pair of copper wires with diameters of~1μm and heights of 25μm.This study establishes an innovative approach to construct microelectromechanical systems with arbitrary 3D microwire structures for various applications,including the demonstrated volatile and nonvolatile microswitches.