Two-dimensional materials:From mechanical properties to flexible mechanical sensors

Two-dimensional(2D)materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures.The study of the mechanical properties of 2D materials plays an important role in next-generation flexible mechanical electronic device applications.Unfortunately,traditional experiment models and measurement methods are not suitable for 2D materials due to their atomically ultrathin thickness,which limits both the theoretical research and practical value of the 2D materials.In this review,we briefly summarize the characterization of mechanical properties of 2D materials by in situ probe nanoindentation experiments,and discuss the effect of thickness,grain boundary,and interlayer interactions.We introduce the strain-induced effect on electrical properties and optical properties of 2D materials.Then,we generalize the mechanical sensors based on various 2D materials and their future potential applications in flexible and wearable electronic devices.Finally,we discuss the state of the art for the mechanical properties of 2D materials and their opportunities and challenges in both basic research and practical applications.

Machine Learning‑Enhanced Flexible Mechanical Sensing

To realize a hyperconnected smart society with high productivity,advances in flexible sensing technology are highly needed.Nowadays,flexible sensing technology has witnessed improvements in both the hardware performances of sensor devices and the data processing capabilities of the device’s software.Significant research efforts have been devoted to improving materials,sensing mechanism,and configurations of flexible sensing systems in a quest to fulfill the requirements of future technology.Meanwhile,advanced data analysis methods are being developed to extract useful information from increasingly complicated data collected by a single sensor or network of sensors.Machine learning(ML)as an important branch of artificial intelligence can efficiently handle such complex data,which can be multi-dimensional and multi-faceted,thus providing a powerful tool for easy interpretation of sensing data.In this review,the fundamental working mechanisms and common types of flexible mechanical sensors are firstly presented.Then how ML-assisted data interpretation improves the applications of flexible mechanical sensors and other closely-related sensors in various areas is elaborated,which includes health monitoring,human-machine interfaces,object/surface recognition,pressure prediction,and human posture/motion identification.Finally,the advantages,challenges,and future perspectives associated with the fusion of flexible mechanical sensing technology and ML algorithms are discussed.These will give significant insights to enable the advancement of next-generation artificial flexible mechanical sensing.

Zinc Oxide Nanostructures for NO_2 Gas–Sensor Applications:A Review

Because of the interesting and multifunctional properties,recently,ZnO nanostructures are considered as excellent material for fabrication of highly sensitive and selective gas sensors.Thus,ZnO nanomaterials are widely used to fabricate efficient gas sensors for the detection of various hazardous and toxic gases.The presented review article is focusing on the recent developments of NO2gas sensors based on ZnO nanomaterials.The review presents the general introduction of some metal oxide nanomaterials for gas sensing application and finally focusing on the structure of ZnO and its gas sensing mechanisms.Basic gas sensing characteristics such as gas response,response time,recovery time,selectivity,detection limit,stability and recyclability,etc are also discussed in this article.Further,the utilization of various ZnO nanomaterials such as nanorods,nanowires,nano-micro flowers,quantum dots,thin films and nanosheets,etc for the fabrication of NO2gas sensors are also presented.Moreover,various factors such as NO2concentrations,annealing temperature,ZnO morphologies and particle sizes,relative humidity,operating temperatures which are affecting the NO2gas sensing properties are discussed in this review.Finally,the review article is concluded and future directions are presented.

Enhanced performance of triboelectric mechanical motion sensor via continuous charge supplement and adaptive signal processing

The development of automation industry is inseparable from the progress of sensing technology.As a promising self-powered sensing technology,the durability and stability of triboelectric sensor(TES)have always been inevitable challenges.Herein,a continuous charge supplement(CCS)strategy and an adaptive signal processing(ASP)method are proposed to improve the lifetime and robustness of TES.The CCS uses low friction brushes to increase the surface charge density of the dielectric,ensuring the reliability of sensing.A triboelectric mechanical motion sensor(TMMS)with CCS is designed,and its electrical signal is hardly attenuated after 1.5 million cycles after reasonable parameter optimization,which is unprecedented in linear TESs.After that,the dynamic characteristics of the CCS-TMMS are analyzed with error rates of less than 1%and 2%for displacement and velocity,respectively,and a signal-to-noise ratio of more than 35 dB.Also,the ASP used a signal conditioning circuit for impedance matching and analog-to-digital conversion to achieve a stable output of digital signals,while the integrated design and manufacture of each hardware module is achieved.Finally,an intelligent logistics transmission system(ILTS)capable of wirelessly monitoring multiple motion parameters is developed.This work is expected to contribute to automation industries such as smart factories and unmanned warehousing.

Physical sensors for skin-inspired electronics

Skin,the largest organ in the human body,is sensitive to external stimuli.In recent years,an increasing number of skin-inspired electronics,including wearable electronics,implantable electronics,and electronic skin,have been developed because of their broad applications in healthcare and robotics.Physical sensors are one of the key building blocks of skin-inspired electronics.Typical physical sensors include mechanical sensors,temperature sensors,humidity sensors,electrophysiological sensors,and so on.In this review,we systematically review the latest advances of skin-inspired mechanical sensors,temperature sensors,and humidity sensors.The working mechanisms,key materials,device structures,and performance of various physical sensors are summarized and discussed in detail.Their applications in health monitoring,human disease diagnosis and treatment,and intelligent robots are reviewed.In addition,several novel properties of skin-inspired physical sensors such as versatility,self-healability,and implantability are introduced.Finally,the existing challenges and future perspectives of physical sensors for practical applications are discussed and proposed.

Recent progress in three-dimensional flexible physical sensors

Three-dimensional(3D)functional systems are of rapidly growing interest over the past decade,from the perspective of both the fundamental and applied research.In particular,tremendous efforts have been devoted to the developments of 3D flexible,physical sensors,partly because of their substantial advantages over planar counterparts in many specific performances.In this review,we summarize recent advances in diverse categories of 3D flexible physical sensors,covering the photoelectric,mechanical,temperature,magnetic,and other physical sensors.This review mainly focuses on their design strategies,working principles and applications.Finally,we offer an outlook on the future developments,and provide perspectives on the remaining challenges and opportunities in this area.

Bio-inspired micro/nanostructures for flexible and stretchable electronics

The remarkable ability of biological systems to sense and adapt to complex environmental conditions has inspired the design of next-generation electronics with advanced functionalities.This review focuses on emerging bio-inspired strategies for the development of flexible and stretchable electronics that can accommodate mechanical deformations and integrate seamlessly with biological systems.We will provide an overview of the practical considerations in the materials and structure designs of flexible and stretchable electronics.Recent progress in bio-inspired pressure/strain sensors,stretchable electrodes,mesh electronics,and flexible energy devices are then discussed,with an emphasis on their unconventional micro/nanostructure designs and advanced functionalities.Finally,current challenges and future perspectives are identified and discussed.

Research on the measurement of connecting bars'axial force of JUNO central detector

Background The Jiangmen Underground Neutrino Observatory(JUNO)is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy and precisely measure oscillation parameters and study the solar neutrino,supernova neutrino,geo-neutrino,etc.JUNO's central detector(CD)has 20 kilo-ton liquid scintillator as target mass,which is contained by a huge acrylic sphere with the inner diameter of 35.4 m,and the acrylic sphere is supported by a stainless steel structure through 590 connecting bars.Motivation Part of the connecting bars bear pull force and the other bars bear push force.There is a direct relationship between the stress of connecting bars and that of acrylic sphere.For the installation process of the CD,the pretightening force and axial force of the connecting bars should be monitored with accuracy,and for the filling process and running condition,the precise measurement of axial force can indicate the safety of structure of the CD.Methods Statistical method was used to evaluate the performance of measurement schemes,and 4-fiber Bragg grating measurement scheme was determined to be the final scheme,which can get the measurement uncertainty better than 0.7 kN.Performance of different measurement schemes are discussed in detail,and some related finite element analysis and evalu-ation method are also introduced in this paper.