Droplet‐Based Self‐Propelled Miniboat

Self‐propelled autonomous devices have huge application prospects in the field of environmental protection and energy. Nonetheless, the requirement of special chemicals or external electric and thermal energy limits their practical application. Here, a green self‐propelling method based on Laplace pressure originated from water droplets is reported. First, a triangle‐shaped miniboat composed of a superhydrophobic plate with an inclined superhydrophilic pore is fabricated. Water droplets put on superhydrophilic pore pass through the pore and form a jellyfish‐like jet, which further propels the miniboat to move spontaneously and directionally. The propelling distance, propelling time, and instantaneous propelling velocity of the miniboat is greatly affected by the pore size and the initial water droplet volume. Then, two types of devices are designed and installed on the miniboat to successively provide small water droplets from the reservoir or rain to realize the continuous and long‐distance self‐propelled motion. Moreover, a spindle‐shaped miniboat with two or four symmetrical and inclined pores is designed. Under propelling by the torque, the spontaneous and continuous rotation motion is also achieved. This finding will open a new avenue for a wide range of applications ranging from a detecting minirobot on the water surface to a power generation device from rain.     

Nano/Microrobots Meet Electrochemistry

Artificial autonomous self‐propelled nano and microrobots are an important part of contemporary technology. They are typically self‐powered, taking chemical energy from their environment and converting it to motion. They can move in complex environments and channels, deliver cargo, perform nanosurgery, act as chemotaxis and perform sense‐and‐act actions. The electrochemistry is closely interwoven within this field. In the case of self‐electrophoretically driven nano/microrobots, electrochemical mechanism has been the basis of power, which translates chemical energy to motion. Electrochemistry is also a major tool for the fabrication of these micro and nanodevices. Electrochemistry and electric fields can be used for the directing of nanorobots and for detection of their positions. Ultimately, nano and microrobots can dramatically improve performances of electrochemical sensors and biosensors, as well as of the energy generating devices. Here, all aspects in the fundamentals and applications of electrochemistry in the realm of nano‐ and microrobots are reviewed.     

Supercolloidal Spinners: Complex Active Particles for Electrically Powered and Switchable Rotation

A class of supercolloidal particles that controllably spin about their central axis in AC electric fields is reported. The rational design of these “microspinners” enables their rotation in a switchable manner, which gives rise to several interesting and programmable behaviors. It is shown that due to their complex shape and discrete metallic patches on their surfaces, these microspinners convert electrical energy into active motion via the interplay of four mechanisms at different electric field frequency ranges. These mechanisms of rotation include (in order of increasing frequency): electrohydrodynamic flows, reversed electrohydrodynamic flows, induced charge electrophoresis, and self‐dielectrophoresis. As the primary mechanism powering their motion transitions from one phenomenon to the next, these microspinners display three directional spin inversions (i.e., from clockwise to anticlockwise, or vice versa). To understand the mechanisms involved, this experimental study is coupled with scaling analyses. Due to their frequency‐switchable rotation, these microspinners have potential for applications such as interlocking gears in colloidal micromachines. Moreover, the principles used to power their switchable motion can be extended to design other types of supercolloidal particles that harvest electrical energy for motion via multiple electrokinetic mechanisms.     

Self‐Powered Iontophoretic Transdermal Drug Delivery System Driven and Regulated by Biomechanical Motions

Transdermal drug delivery (TDD) systems with feedback control have attracted extensive research and clinical interest owing to their unique advantages of convenience, self‐administration, and safety. Here, a self‐powered wearable iontophoretic TDD system that can be driven and regulated by the energy harvested from biomechanical motions is proposed for closed‐loop motion detection and therapy. A wearable triboelectric nanogenerator (TENG) is used as the motion sensor and energy harvester that can convert biomechanical motions into electricity for iontophoresis without stored‐energy power sources, while a hydrogel‐based soft patch with side‐by‐side electrodes is designed to enable noninvasive iontophoretic TDD. Proof‐of‐concept experiments on pig skin with dyes as model drugs successfully demonstrate the feasibility of the proposed system. This work not only extends the application of TENG in the biomedical field, but may also provide a cost‐effective solution for noninvasive, electrically assisted TDD with closed‐loop sensing and treatment.     

An All Hydrophilic Fluid Diode for Unidirectional Flow in Porous Systems

A fluid diode that allows fluid flow in one direction but blocks fluid flow in the opposite direction has wide applications including oil recovery, drug delivery, and lab‐on‐a‐chip microfluidics. Many studies are conducted to facilitate directional liquid motion on the solid surface or across thin porous layers. However, the self‐driven one‐way flow inside porous systems still remains a significant challenge. Here, a novel all‐hydrophilic fluid diode (AHFD) made of porous materials with asymmetric pores is reported, which allows capillary flow in a chosen direction. The direction‐dependent flow process and the breakthrough pressure are experimentally and theoretically examined. The proposed AHFD can have many potential applications such as functional protective clothing, microfluidic valve, and oil–water separator, and the idea can be extended to develop other all lyophilic fluid diodes such as oleophilic diode.     

A Battery‐Less Arbitrary Motion Sensing System Using Magnetic Repulsion‐Based Self‐Powered Motion Sensors and Hybrid Nanogenerator

Self‐powered arbitrary motion sensors are in high demand in the field of autonomous controlled systems. In this work, a magnetic repulsion‐assisted self‐powered motion sensor is integrated with a hybrid nanogenerator (MRSMS–HNG) as a battery‐less arbitrary motion sensing system. The proposed device can efficiently detect the motion parameters of a moving object along any arbitrary direction and simultaneously convert low frequency (<5 Hz) vibrations into useful electricity. The MRSMS–HNG consists of a central magnet for the electromagnetic (EMG)–triboelectric (TENG) nanogenerator and four side magnets for motion sensors. Because all the magnets are aligned in the same magnetization direction, the repulsive force owing to the movement of the central magnet actuates the side magnets to achieve self‐powered arbitrary motion sensing. These self‐powered motion sensors exhibit a high sensitivity of 981.33 mV g^?1 under linear motion excitation and have a tilting angle sensitivity of 9.83 mV deg^?1. The proposed device can deliver peak powers of 27 mW and 56 µW from the EMG and TENG, respectively. By integrating the self‐powered motion sensors and hybrid nanogenerator on a single device, real‐time wireless transmission of motion sensor data to a smartphone is successfully demonstrated, thus realizing a battery‐less arbitrary motion‐sensing system for future autonomous control applications.     

Hierarchical Microswarms with Leader–Follower‐Like Structures: Electrohydrodynamic Self‐Organization and Multimode Collective Photoresponses

Swarming micro/nanomotors can self‐organize into cohesive groups to execute cooperative tasks. To date, research work has focused on the construction of egalitarian microswarms composed of similar individuals. The construction and collective behaviors of hierarchical leader–follower‐like microswarms are demonstrated. By inducing converging electrohydrodynamic flows under an AC electric field, dielectric microparticles with different sizes and dielectric properties can hierarchically self‐organize into leader–follower‐like microswarms under attractive electrohydrodynamic interactions, and show novel emergent collective behaviors. First, different from immobile single constituents or egalitarian clusters, the hierarchical microswarms autonomously move with tunable speed. Second, they exhibit multimode collective photoresponses emerging from different behaviors of the constituents in response to light signals. With a vertical UV signal, the photoresponsive followers tend to surround the leader and stop the microswarm. In response to sidewise UV signals, the constituents with stronger phototaxis would migrate to the position away from light stimuli, and thus the microswarms reorient parallel/antiparallel to the light direction and perform collective positive/negative phototaxis. Due to differential roles and huge design spaces of constituents, the hierarchical microswarms are envisioned to possess merits of high‐efficiency, multiresponsiveness, and multifunctions, and may serve as intelligent micro/nanorobot systems for biomedicine and microengineering.     

A Self‐Powered Angle Measurement Sensor Based on Triboelectric Nanogenerator

A self‐powered, sliding electrification based quasi‐static triboelectric sensor (QS‐TES) for detecting angle from rotating motion is reported. This innovative, cost‐effective, simply‐designed QS‐TES has a two‐dimensional planar structure, which consists of a rotator coated with four channel coded Cu foil material and a stator with a fluorinated ethylenepropylene film. On the basis of coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical rotating motion of an object mounted with the sensor. The sensor can read and remember the absolute angular position, angular velocity, and acceleration regardless being continuously monitored or segmented monitored. Under the rotation speed of 100 r min^?1, the output voltage of the sensor reaches as high as 60 V. Given a relatively low threshold voltage of ±0.5 V for data processing, the robustness of the device is guaranteed. The resolution of the sensor is 22.5° and can be further improved by increasing the number of channels. Triggered by the output voltage signal, the rotating characteristics of the steering wheel can be real‐time monitored and mapped by being mounted to QS‐TES. This work not only demonstrates a new principle in the field of angular measurement but also greatly expands the applicability of triboelectric nanogenerator as self‐powered sensors.     

Self‐Powered Electrostatic Actuation Systems for Manipulating the Movement of both Microfluid and Solid Objects by Using Triboelectric Nanogenerator

By integrating a triboelectric nanogenerator (TENG) and an electrostatic actuation system (EAS), two kinds of self‐powered EAS are designed for manipulating the movement of both microfluid and tiny solid objects. The mechanical triggering of the TENG can generate an extremely high electrostatic field inside EAS and thus the tiny object (liquid or solid) in the EAS can be actuated by the Coulomb force. Accordingly, the tribomotion of TENG can be used as both the driving power and control signal for the EAS. The TENG device with a contact surface of 70 cm² can drive a water droplet to move across a gap of 2 cm. Meanwhile, the confluence of two droplets with the same charge polarity and different components can also be induced and controlled by this self‐powered EAS. In addition, based on the same working principle, this EAS also demonstrates its capability for manipulating solid object (e.g., a tiny steel pellet). By sliding the Kapton film along a segmented annular electrode, the tiny pellet can well follow the rotated motion of the Kapton film. The demonstrated concept of this self‐powered EAS has excellent applicability for various micro/miniature actuation devices, electromechanical systems, human–machine interaction, etc.     

Fingerprint‐Inspired Conducting Hierarchical Wrinkles for Energy‐Harvesting E‐Skin

In the field of bionics, sophisticated and multifunctional electronic skins with a mechanosensing function that are inspired by nature are developed. Here, an energy‐harvesting electronic skin (energy‐E‐skin), i.e., a pressure sensor with energy‐harvesting functions is demonstrated, based on fingerprint‐inspired conducting hierarchical wrinkles. The conducting hierarchical wrinkles, fabricated via 2D stretching and subsequent Ar plasma treatment, are composed of polydimethylsiloxane (PDMS) wrinkles as the primary microstructure and embedded Ag nanowires (AgNWs) as the secondary nanostructure. The structure and resistance of the conducting hierarchical wrinkles are deterministically controlled by varying the stretching direction, Ar plasma power, and treatment time. This hierarchical‐wrinkle‐based conductor successfully harvests mechanical energy via contact electrification and electrostatic induction and also realizes self‐powered pressure sensing. The energy‐E‐skin delivers an average output power of 3.5 mW with an open‐circuit voltage of 300 V and a short‐circuit current of 35 µA; this power is sufficient to drive commercial light‐emitting diodes and portable electronic devices. The hierarchical‐wrinkle‐based conductor is also utilized as a self‐powered tactile pressure sensor with a sensitivity of 1.187 mV Pa^‐1 in both contact‐separation mode and the single‐electrode mode. The proposed energy‐E‐skin has great potential for use as a next‐generation multifunctional artificial skin, self‐powered human–machine interface, wearable thin‐film power source, and so on.     

Single‐Thread‐Based Wearable and Highly Stretchable Triboelectric Nanogenerators and Their Applications in Cloth‐Based Self‐Powered Human‐Interactive and Biomedical Sensing

The development of wearable and large‐area fabric energy harvester and sensor has received great attention due to their promising applications in next‐generation autonomous and wearable healthcare technologies. Here, a new type of “single” thread‐based triboelectric nanogenerator (TENG) and its uses in elastically textile‐based energy harvesting and sensing have been demonstrated. The energy‐harvesting thread composed by one silicone‐rubber‐coated stainless‐steel thread can extract energy during contact with skin. With sewing the energy‐harvesting thread into a serpentine shape on an elastic textile, a highly stretchable and scalable TENG textile is realized to scavenge various kinds of human‐motion energy. The collected energy is capable to sustainably power a commercial smart watch. Moreover, the simplified single triboelectric thread can be applied in a wide range of thread‐based self‐powered and active sensing uses, including gesture sensing, human‐interactive interfaces, and human physiological signal monitoring. After integration with microcontrollers, more complicated systems, such as wireless wearable keyboards and smart beds, are demonstrated. These results show that the newly designed single‐thread‐based TENG, with the advantage of interactive, responsive, sewable, and conformal features, can meet application needs of a vast variety of fields, ranging from wearable and stretchable energy harvesters to smart cloth‐based articles.     

An Autonomous Soft Actuator with Light‐Driven Self‐Sustained Wavelike Oscillation for Phototactic Self‐Locomotion and Power Generation

Mimicking the intelligence of biological organisms in artificial systems to design smart actuators that act autonomously in response to constant environmental stimuli is crucial to the construction of intelligent biomimetic robots and devices, but remains a great challenge. Here, a light‐driven autonomous carbon‐nanotube‐based bimorph actuator is developed through an elaborate structural design. This curled droplet‐shaped actuator can be simply driven by constant white light irradiation, self‐propelled by a light‐mechanical negative feedback loop created by light‐driven actuation, time delay in the photothermal response along the actuator, and good elasticity from the curled structure, performing a continuously self‐oscillating motion in a wavelike fashion, which mimics the human sit‐up motion. Moreover, this autonomous self‐oscillating motion can be further tuned by controlling the intensity and direction of the incident light. The autonomous actuator with continuous wavelike oscillating motion shows immense potential in light‐driven biomimetic soft robots and optical‐energy‐harvesting devices. Furthermore, a self‐locomotive artificial snake with phototaxis is constructed, which autonomously and continuously crawls toward the light source in a wave‐propagating manner under constant light irradiation. This snake can be placed on a substrate made of triboelectric materials to realize continuous electric output when exposed to constant light illumination.     

Reduction of wireless signals in indoor environments by using an active frequency selective wall based on spectrum sensing

This paper presents a wireless local area network (WLAN) spectrum control system that uses active frequency selective shielding walls to selectively reduce or pass WLAN signals in the 5 GHz band indoors. The proposed system utilizes a well‐known active frequency selective structure based on a rectangular loop with PIN diodes and is thus capable of either reducing or passing the WLAN frequency by using the on/off switching of the PIN diode based on the measured electric field strength in indoor. We designed and simulated the proposed active frequency selective shielding wallpaper by using commercial electromagnetic simulation software and confirmed that the proposed structure can reduce the WLAN signal by switching the PIN diode by applying the manufactured prototype on the exterior of an experimental apparatus containing a WLAN receiver antenna that is capable of measuring the received electric field strength. Extension of the results presented herein can be applied to reduce the wireless signal to enhance the spectrum efficiency of an indoor space.     

Robust Adaptive Microphone Array with Mainlobe and Response Ripple Control

Many existing adaptive beamformers possess robustness against arbitrary array steering vector (ASV) mismatches within presumed uncertainty set. However, when the array facing a large steering direction error, their performance degrade significantly since the uncertainty in steering direction generally gives rise to an outstanding mismatch in ASV. In the applications of microphone array, large steering direction error is often unavoidable because of the motion of target speaker. Meanwhile, in addition to conventional adaptive beamformers, microphone array also requests a controlled frequency response to target signal. In this paper, we propose a new adaptive microphone array implemented in frequency domain with controlled mainlobe and frequency response. A compact ASV uncertainty set explicitly modelling steering direction error and the other arbitrary ASV errors is exploited to derive beamformer with robust constraints on array magnitude response. Numerical results show that the proposed microphone array not only produces large controlled robust response region and robust frequency response, but also achieves high performance in SINR enhancement.     

Interface Engineering for Organic Electronics

The field of organic electronics has been developed vastly in the past two decades due to its promise for low cost, lightweight, mechanical flexibility, versatility of chemical design and synthesis, and ease of processing. The performance and lifetime of these devices, such as organic light‐emitting diodes (OLEDs), photovoltaics (OPVs), and field‐effect transistors (OFETs), are critically dependent on the properties of both active materials and their interfaces. Interfacial properties can be controlled ranging from simple wettability or adhesion between different materials to direct modifications of the electronic structure of the materials. In this Feature Article, the strategies of utilizing surfactant‐modified cathodes, hole‐transporting buffer layers, and self‐assembled monolayer (SAM)‐modified anodes are highlighted. In addition to enabling the production of high‐efficiency OLEDs, control of interfaces in both conventional and inverted polymer solar cells is shown to enhance their efficiency and stability; and the tailoring of source–drain electrode–semiconductor interfaces, dielectric–semiconductor interfaces, and ultrathin dielectrics is shown to allow for high‐performance OFETs.     

Self-consistent field theory and calculation for gyromonotron

A self consistent field large signal theory of gyromonotron is studied in this paper. The RF field profile function satisfies a wave equation. The field is determined by cavity geometry and AC electron beam current. The RF field not only satisfies the boundary conditions at the ends of the cavity but also obeys conservation of energy for steady state interaction between electron beam and field. The parameters of a particular gyrotron are calculated numerically using present theory. Effect of some factors on gyrotron characteristic is discussed. Comparison is made between the results of the self consistent field calculations with and without conservation of energy.     

An electronically switchable leaky wave antenna

We report an electronically switchable dielectric leaky wave antenna. The main beam angle can be electronically steered using p-i-n diodes. The diodes are used as switches to control the radiation from two sets of gratings with different periods, thereby switching the main beam angle. Beam steering is achieved at a single fixed frequency; no frequency sweeping is necessary. A microwave prototype demonstrates a 35° change in beam direction at 3.5 GHz. Measured antenna patterns agree with theoretical predictions. This approach should be scalable to millimeter-wave frequencies using diodes monolithically integrated on a semiconductor waveguide     

基于MUSIC和LCMV的自适应波束形成系统

提出了在基于来波方向估计和自适应波束成形的相控阵天线系统中,用多重信号分类(MUSIC)算法实现来波方向估计,并使用线性约束最小方差(LCMV)的自适应算法控制天线的主瓣方向,实现对期望信号的跟踪,同时实现对干扰信号的零陷处理。仿真结果表明,MUSIC算法可以有效识别相控阵天线接收端的信号的入射方向,LCMV算法可以实现对有用信号的自适应跟踪和对干扰信号的抑制。     

Direct‐Current Triboelectric Generator

The first direct‐current triboelectric generator (DC‐TEG) based on sliding electrification for harvesting mechanical energy from rotational motion is reported. The DC‐TEG consists of two rotating wheels and one belt for connecting them, which are made of distinctly different triboelectric materials with a specific requirement. During the rotation, the contact‐induced electrification and the relative sliding between the two wheels and the belt can induce a continuous increase of the accumulated positive and negative triboelectric charges at the two rotating wheels, respectively, resulting in a Corona discharge and producing the observed current through an external load. The DC‐TEG can deliver an open‐circuit voltage of larger than 3200 V and a maximum power of 100 μW under an external load of 60 MΩ at a rotational speed of 1000 r min^–1. By designing a point metal discharge electrode near the accumulated positive charges on the metal wheel, the instantaneous short‐circuit current can be up to 0.37 mA. The DC‐TEG can be utilized as a direct power source to light up 1020 serially connected commercial light‐emitting diodes (LEDs) and the produced energy can also be stored in a capacitor for other uses. This work presents a DC‐TEG technology to harvest mechanical energy from rotational motion for self‐powered electronics.     

Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Hybrid light/acoustic‐powered microbowl motors, composed of gold (Au) and titanium dioxide (TiO₂) with a structure‐dependent optical modulation of both their movement and collective behavior are reported by reversing the inner and outer positions of Au and TiO₂. The microbowl propels in an acoustic field toward its exterior side. UV light activates the photochemical reaction on the TiO₂ surface in the presence of hydrogen peroxide and the Au/TiO₂ system moves toward its TiO₂ side by self‐electrophoresis. Controlling the light intensity allows switching of the dominant propulsion mode and provides braking or reversal of motion direction when TiO₂ is on the interior, or accelerated motion when the TiO₂ is on its exterior. Theoretical simulations offer an understanding of the acoustic streaming flow and self‐electrophoretic fluid flow induced by the asymmetric distribution of ions around the microbowl. The light‐modulation behavior along with the tunable structure also leads to the control of the swarm behaviors under the acoustic field, including expansion or compaction of ensembles of microbowls with interior and exterior TiO₂, respectively. Such structure‐dependent motion control thus paves the way for a variety of complex microscale operations, ranging from cargo transport to drug delivery in biomedical and environmental applications.