Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible ...Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge.In this work,a wearable capacitive-type Ga_(2)O_(3)/liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique.Owing to the photothermal effect of laser,the Ga_(2)O_(3)-wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19Ω·cm,while the untreated regions serve as active sensing layers in response to moisture changes.Under 95%relative humidity,the humidity sensor displays a highly stable performance along with rapid response and recover time.Utilizing these superior properties,the Ga_(2)O_(3)/liquid metal-based humidity sensor is able to monitor human respiration rate,as well as skin moisture of the palm under different physiological states for healthcare monitoring.展开更多
Breathing is an inherent human activity;however,the composition of the air we inhale and gas exhale remains unknown to us.To address this,wearable vapor sensors can help people monitor air composition in real time to ...Breathing is an inherent human activity;however,the composition of the air we inhale and gas exhale remains unknown to us.To address this,wearable vapor sensors can help people monitor air composition in real time to avoid underlying risks,and for the early detection and treatment of diseases for home healthcare.Hydrogels with three-dimensional polymer networks and large amounts of water molecules are naturally flexible and stretchable.Functionalized hydrogels are intrinsically conductive,self-healing,self-adhesive,biocompatible,and room-temperature sensitive.Compared with traditional rigid vapor sensors,hydrogel-based gas and humidity sensors can directly fit human skin or clothing,and are more suitable for real-time monitoring of personal health and safety.In this review,current studies on hydrogel-based vapor sensors are investigated.The required properties and optimization methods of wearable hydrogel-based sensors are introduced.Subsequently,existing reports on the response mechanisms of hydrogel-based gas and humidity sensors are summarized.Related works on hydrogel-based vapor sensors for their application in personal health and safety monitoring are presented.Moreover,the potential of hydrogels in the field of vapor sensing is elucidated.Finally,the current research status,challenges,and future trends of hydrogel gas/humidity sensing are discussed.展开更多
Humidity sensors are of significance in various fields,such as environmental and food quality monitoring,industrial processing,wearable and flexible electronics,and human health care.High-performance humidity sensors ...Humidity sensors are of significance in various fields,such as environmental and food quality monitoring,industrial processing,wearable and flexible electronics,and human health care.High-performance humidity sensors with high sensitivity,rapid response time,and good stability are of paramount importance in humidity sensing.In this paper,diversiform humidity sensors with different sensing mechanisms are summarized,including resistive,impedance,capacitive,quartz crystal microbalance(QCM),surface acoustic wave(SAW),field-effect transistor(FET),and optical fiber humidity sensors.Versatile nanomaterials such as graphene,transition-metal chalcogenide,MXenes,black phosphorus(BP),boron nitride(BN),polymers,and nanofibers were promising building-blocks for constructing humidity sensors.The latest progress in the wearable and flexible humidity sensors,and self-powered humidity sensors was summarized.The diversiform applications of the humidity sensors with great prospects were demonstrated in various fields in terms of human respiratory monitoring,skin dryness diagnosing,fingertip approaching,and non-contact switch.Moreover,the challenges and prospects of nanomaterials-based humidity sensors were discussed.展开更多
Humidity sensors with high sensitivity,rapid response,and facile fabrication process for contactless sensing applications have received considerable attention in recent years.Herein,humidity sensors based on hexagonal...Humidity sensors with high sensitivity,rapid response,and facile fabrication process for contactless sensing applications have received considerable attention in recent years.Herein,humidity sensors based on hexagonal boron nitride(h-BN)nanosheets that are synthesized by a facile ultrasonic process have been fabricated,which display an ultrahigh sensitivity of 28,384%at 85%relative humidity(RH),rapid response/recovery time(3.0/5.5 s),and long-term stability in a wide humidity detection range(11%-85%RH),superior to most of the reported humidity sensors.The high sensitivity can be ascribed to the massive hydrophilic functional groups absorbed on the h-BN nanosheet surface.Benefiting from the high humidity sensing performances,contactless Morse code messaging and human writing and speech recognition have been demonstrated.This work demonstrates the great potential of the high-performance h-BN nanosheet-based humidity sensors for future contactless sensing devices.展开更多
Flexible humidity sensors are widely used in many fields,such as environmental monitoring,agricultural soil moisture content determination,food quality monitoring and healthcare services.Therefore,it is essential to m...Flexible humidity sensors are widely used in many fields,such as environmental monitoring,agricultural soil moisture content determination,food quality monitoring and healthcare services.Therefore,it is essential to measure humidity accurately and reliably in different conditions.Flexible materials have been the focusing substrates of humidity sensors because of their rich surface chemical properties and structural designability.In addition,flexible materials have superior ductility for different conditions.In this review,we have summarized several sensing mechanisms,processing techniques,sensing layers and substrates for specific humidity sensing requirements.Aadditionally,we have sorted out some cases of flexible humidity sensors based on different functional materials.We hope this paper can contribute to the development of flexible humidity sensors in the future.展开更多
Human metabolite moisture detection is important in health monitoring and non-invasive diagnosis.However,ultra-sensitive quantitative extraction of respiration information in real-time remains a great challenge.Herein...Human metabolite moisture detection is important in health monitoring and non-invasive diagnosis.However,ultra-sensitive quantitative extraction of respiration information in real-time remains a great challenge.Herein,chemiresistors based on imine-linked covalent organic framework(COF)films with dual-active sites are fabricated to address this issue,which demonstrates an amplified humidity-sensing signal performance.By regulation of monomers and functional groups,these COF films can be pre-engineered to achieve high response,wide detection range,fast response,and recovery time.Under the condition of relative humidity ranging from 13 to 98%,the COFTAPB-DHTA film-based humidity sensor exhibits outstanding humidity sensing perfor-mance with an expanded response value of 390 times.Furthermore,the response values of the COF film-based sensor are highly linear to the relative humidity in the range below 60%,reflecting a quantitative sensing mechanism at the molecular level.Based on the dual-site adsorption of the(-C=N-)and(C-N)stretching vibrations,the revers-ible tautomerism induced by hydrogen bonding with water molecules is demonstrated to be the main intrinsic mechanism for this effective humidity detection.In addition,the synthesized COF films can be further exploited to effectively detect human nasal and oral breathing as well as fabric permeability,which will inspire novel designs for effective humidity-detection devices.展开更多
As humidity is one of the most widely demanded environmental parameters,the precision of its detection is significant.An advanced humidity sensor will improve the validity of the humidity monitoring system.In this stu...As humidity is one of the most widely demanded environmental parameters,the precision of its detection is significant.An advanced humidity sensor will improve the validity of the humidity monitoring system.In this study,a facile chemical layer-by-layer self-assembly(CLS)method was developed for fabricating graphene oxide(GO)/polyethyleneimine(PEI)multilayer films.Owing to the chemical bonding between the PEI and GO,and the intrinsic stickiness of the PEI,layered films with different numbers of layers were successfully prepared using the CLS method and confirmed through ultraviolet-visible(UV-Vis)spectroscopy and the mass loading of quartz crystal microbalance(QCM).Morphological measurements revealed that the roughness and thickness of the films increased exponentially with the number of bilayers.The GO/PEI films were deposited on QCM electrodes using the CLS method to produce the humidity sensors.The humidity measurement results showed a high sensitivity(37.84 Hz/%RH)and rapid response/recovery(<5 s/8 s)of the optimal sensor,which was superior to that of recently developed QCM sensors.展开更多
Ti_(3)C_(2)T_(x),which is a novel two-dimensional(2 D)material,has received enormous interest in the field of sensor technology due to its large surface area,excellent electrical conductivity,and abundant active surfa...Ti_(3)C_(2)T_(x),which is a novel two-dimensional(2 D)material,has received enormous interest in the field of sensor technology due to its large surface area,excellent electrical conductivity,and abundant active surface sites.In recent years,several Ti_(3)C_(2)T_(x)-based gases and humidity sensors have been developed and reported.In this review,we focus on the latest applications of Ti_(3)C_(2)T_(x)-based nanomaterials in gas and humidity sensors.First,the synthesis of Ti_(3)C_(2)T_(x) from the dangerous fluorine-containing etching process to the safe fluorine-free preparation method was discussed,and the structures of the Ti_(3)C_(2)T_(x) controlled by different delamination methods were also outlined.Subsequently,the functionalization of pristine Ti_(3)C_(2)T_(x) and composite strategies for enhancing its gas and humidity sensing performance were reviewed.In addition,the gas and humidity sensing mechanisms of sensors based on Ti_(3)C_(2)T_(x) were also summarized.Finally,the challenges and opportunities for the use of Ti_(3)C_(2)T_(x) gas and humidity sensors were discussed to provide guidance on the promising potential of Ti_(3)C_(2)T_(x) in this field.展开更多
Humidity sensors have been widely applied to detect environment humidity in various fields. However, most of humidity sensors cannot provide performance needed for high sensitivity and fast response. We report one typ...Humidity sensors have been widely applied to detect environment humidity in various fields. However, most of humidity sensors cannot provide performance needed for high sensitivity and fast response. We report one type of capacitive-type humidity sensors composed of laser-scribed graphene(LSG) as sensing electrodes and graphene oxide/tin dioxide(GO/SnO2) as a sensing layer. The LSG is reduced graphene oxide(rGO) electrodes resulted from selective reducing of GO within a GO/SnO2 composite layer by laser scribing method, and the sensing layer is the un-scribed GO/SnO2 composite. The sensor fabrication is a one-step process which is facile and cost-efficient. When a mass ratio of GO:SnO2 in the composite reaches 1:1, the humidity sensor(named as LSG-GS1) has the best properties than other ratios, which exhibits high sensitivity in the range of 11%~97% relative humidity(RH). In addition, the LSG-GS1 also has very quick response/recovery time(20 s for adsorption and 18 s for desorption) when RH changes from 23% to 84%, and very good stability after monitoring for 41 days. Such excellent performances of the humidity sensor can be attributed to synergistic effect of SnO2 and GO within the composite layer.展开更多
In the past decade,the global industry and research attentions on intelligent skin-like electronics have boosted their applications in diverse fields including human healthcare,Internet of Things,human–machine interf...In the past decade,the global industry and research attentions on intelligent skin-like electronics have boosted their applications in diverse fields including human healthcare,Internet of Things,human–machine interfaces,artificial intelligence and soft robotics.Among them,flexible humidity sensors play a vital role in noncontact measurements relying on the unique property of rapid response to humidity change.This work presents an overview of recent advances in flexible humidity sensors using various active functional materials for contactless monitoring.Four categories of humidity sensors are highlighted based on resistive,capacitive,impedance-type and voltage-type working mechanisms.Furthermore,typical strategies including chemical doping,structural design and Joule heating are introduced to enhance the performance of humidity sensors.Drawing on the noncontact perception capability,human/plant healthcare management,human-machine interactions as well as integrated humidity sensor-based feedback systems are presented.The burgeoning innovations in this research field will benefit human society,especially during the COVID-19 epidemic,where cross-infection should be averted and contactless sensation is highly desired.展开更多
Respiratory monitoring plays a pivotal role in health assessment and provides an important application prospect for flexible humidity sensors.However,traditional humidity sensors suffer from a trade-off between deform...Respiratory monitoring plays a pivotal role in health assessment and provides an important application prospect for flexible humidity sensors.However,traditional humidity sensors suffer from a trade-off between deformability,sensitivity,and transparency,and thus the development of high-performance,stretchable,and low-cost humidity sensors is urgently needed as wearable electronics.Here,ultrasensitive,highly deformable,and transparent humidity sensors are fabricated based on cost-effective polyacrylamide-based double network hydrogels.Concomitantly,a general method for preparing hydrogel films with controllable thickness is proposed to boost the sensitivity of hydrogel-based sensors due to the extensively increased specific surface area,which can be applied to different polymer networks and facilitate the development of flexible integrated electronics.In addition,sustainable tapioca rich in hydrophilic polar groups is introduced for the first time as a second cross-linked network,exhibiting excellent water adsorption capacity.Through the synergistic optimization of structure and composition,the obtained hydrogel film exhibits an ultrahigh sensitivity of 13,462.1%/%RH,which is unprecedented.Moreover,the hydrogel film-based sensor exhibits excellent repeatability and the ability to work normally under stretching with even enhanced sensitivity.As a proof of concept,we integrate the stretchable sensor with a specially designed wireless circuit and mask to fabricate a wireless respiratory interruption detection system with Bluetooth transmission,enabling real-time monitoring of human health status.This work provides a general strategy to construct high-performance,stretchable,and miniaturized hydrogel-based sensors as next-generation wearable devices for real-time monitoring of various physiological signals.展开更多
Flexible sensors are attractive due to potential applications in body exercise and ambient gas monitoring systems.Cellulose and its derivatives have combined superiorities such as intrinsic and structural flexibility,...Flexible sensors are attractive due to potential applications in body exercise and ambient gas monitoring systems.Cellulose and its derivatives have combined superiorities such as intrinsic and structural flexibility,ease of chemical functionalization,moisture sensitivity,and mechanical stability,enabling them to be promising candidates as flexible supporting substrates and flexible sensitive materials.Significant progress consequently has been achieved to improve mechanical,electrical,and chemical performance.The latest advance in materials synthesis,structure design,fabrication control,and working mechanism of novel cellulose-based flexible sensors are reviewed and discussed,including strain sensors,humidity sensors,and harmful gas sensors.Various strategies were summarized to enhance sensor performance by surface group modifications,inorganic and organic conducting fillers optimization,multilayer structure design.Newly emerged processing techniques of self-assembly,vacuum filtration,and 3D printing were introduced as well to construct multiscale microstructures.The integration of multiple sensors toward smart and healthy exercise monitoring system is briefly reviewed.The facing challenges and future opportunities of cellulose-based flexible sensors were discussed and proposed at the end.This review provides inspiration and guidelines on how to design and fabricate cellulose-based flexible sensors.展开更多
Grafted high density polyethylene (HDPE) films have been prepared by grafting sodium styrene sulfonate (SSS) and acrylic acid (AA) onto HDPE using preirradiation method.The structure and surface morphology of both gra...Grafted high density polyethylene (HDPE) films have been prepared by grafting sodium styrene sulfonate (SSS) and acrylic acid (AA) onto HDPE using preirradiation method.The structure and surface morphology of both grafted and ungrafted HDPE films were observed by FTIR spectroscopy and scanning electron microscope (SEM),respectively.The humidity sensing properties of grafted HDPE films were investigated.The results show that the impedance of the film decreases with increasing of relative humidity (RH).The films display high sensitivity with nearly three orders of magnitude change in the resistance during the relative humidity variation from 5% to 98%.Grafted HDPE films exhibit excellent properties as humidity sensors.展开更多
The widely used sensitive elements of humidity sensors can be divided into 3 types,i.e.,resistor,capacitor,and electrolyte.Humidity sensors consisting of these sensitive elements have corresponding signal processing c...The widely used sensitive elements of humidity sensors can be divided into 3 types,i.e.,resistor,capacitor,and electrolyte.Humidity sensors consisting of these sensitive elements have corresponding signal processing circuit unique to each type of sensitive elements.This paper presents an ispPAC (in-system programmable Programmable Analog Circuit) -based humidity sensor signal processing circuit designed with software method and implemented with in-system programmable simulators.Practical operation shows that humidity sensor signal processing circuits of this kind,exhibit stable and reliable performance.展开更多
Humidity is a critical environmental parameter for several production processes and its control/monitoring is of great importance in maintaining the quality of goods and products. In this context, metallic oxide ceram...Humidity is a critical environmental parameter for several production processes and its control/monitoring is of great importance in maintaining the quality of goods and products. In this context, metallic oxide ceramic nanostructures are materials of great technological interest in the fabrication of moisture sensors because they have good chemical/structural stability and high surface area/volume ratio. The electrical response of these sensors relates to the chemisorbed and physisorbed layers of water molecules on the surface of the ceramic particles and to the capillary condensation of water in the microscopic pores between the particles. Based on these aspects, this work presents the fundamentals, electrical/electronic properties, influence of dopants, novel preparation procedure by electrospinning and perspectives of application of TiO2:WO3 metal oxide heteronanostructures as humidity sensors.展开更多
Two-dimensional material has been widely investigated for potential applications in sensor and flexible electronics.In this work,a self-powered flexible humidity sensing device based on poly(vinyl alcohol)/Ti_(3)C_(2)...Two-dimensional material has been widely investigated for potential applications in sensor and flexible electronics.In this work,a self-powered flexible humidity sensing device based on poly(vinyl alcohol)/Ti_(3)C_(2)Tx(PVA/MXene)nanofibers film and monolayer molybdenum diselenide(MoSe2)piezoelectric nanogenerator(PENG)was reported for the first time.The monolayer MoSe_(2)-based PENG was fabricated by atmospheric pressure chemical vapor deposition techniques,which can generate a peak output of 35 mV and a power density of42 mW m^(-2).The flexible PENG integrated on polyethylene terephthalate(PET)substrate can harvest energy generated by different parts of human body and exhibit great application prospects in wearable devices.The electrospinned PVA/MXene nanofiber-based humidity sensor with flexible PET substrate under the driven of monolayer MoSe_(2) PENG,shows high response of~40,fast response/recovery time of 0.9/6.3 s,low hysteresis of 1.8%and excellent repeatability.The self-powered flexible humidity sensor yields the capability of detecting human skin moisture and ambient humidity.This work provides a pathway to explore the high-performance humidity sensor integrated with PENG for the self-powered flexible electronic devices.展开更多
Capacitive humidity sensors were made of nanometer barium titanate.The pellets were prepared under different pressures between 3920N to 7850N force.The capacitance changes in three orders of magnitude in the relative ...Capacitive humidity sensors were made of nanometer barium titanate.The pellets were prepared under different pressures between 3920N to 7850N force.The capacitance changes in three orders of magnitude in the relative humidity range of 10%~98%,indicating high humidity sensitivity of the sensors.At a certain measuring frequency,the capacitance of the sensors increases as increasing of the preparation pressure,while the sensitivity of the sensors basically remains the same.The frequencies corresponding to the peaks of the dielectric loss of the sensors move to the higher frequency direction as increasing of the relative humidity.At a certain humidity,the frequencies corresponding to the peaks of the dielectric loss move to the higher frequency direction as increasing of the preparation pressure.展开更多
This paper reports on the fabrication and sensing characteristics of Polyimide-based humidity sensor,based on that,a new integrated circuit of humidity measurement has been designed.It is a novel capacitive-type syste...This paper reports on the fabrication and sensing characteristics of Polyimide-based humidity sensor,based on that,a new integrated circuit of humidity measurement has been designed.It is a novel capacitive-type systems on a chip structure using the MEMS process.The results show that the new sensor presents sensing characteristics over a humidity range from 10%~70% RH at 20℃,and the sensor is able to fabricated together with ICs technology.The result shows that integration of humidity sensor with integrated circuit of humidity measurement is considerably easier when they are built in sensing groove.The appeal of a new structure like this brings the possibility of applications that would require the flexibility of simple screen printing.展开更多
An impedance type humidity sensor based on the polyacrylic emulsion containing magnesium chloride (MgCl_2) without chemical modification was investigated.The impedances of the sensor were measured from various relati...An impedance type humidity sensor based on the polyacrylic emulsion containing magnesium chloride (MgCl_2) without chemical modification was investigated.The impedances of the sensor were measured from various relative humidity in the frequency range between 0.1kHz and 100 kHz.The sensor has a good sensitivity from 60%RH to 90%RH.According to the experimental results,the response time is about 240 seconds in the adsorption process and 310 seconds in the desorption process.展开更多
A novel soluble conjugated copolymer (propionic acid)-co-(propargyl alcohol) (PA-co-OHP) has been synthesized for the first time using a new palladium acetylide catalyst Pd(PPh3)2 (CoCC(CH3)2OH)2 (PPB). Thin film res...A novel soluble conjugated copolymer (propionic acid)-co-(propargyl alcohol) (PA-co-OHP) has been synthesized for the first time using a new palladium acetylide catalyst Pd(PPh3)2 (CoCC(CH3)2OH)2 (PPB). Thin film resistive humidity sensor based on the copolymer doped with HClO-4 was prepared. The impedance of the sensor changed from 103~107 W in 95%~30%RH, and the response of that is very quick (<6 sec.). Preliminary results show the copolymer is a promising humidity sensitive material.展开更多
基金This study was supported by the National Natural Science Foundation of China (52105593 and 62271439)STI 2030 —Major Projects(2022ZD0208601)the “Pioneer” and “Leading Goose” R&D Program of Zhejiang (2023C01051)。
文摘Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge.In this work,a wearable capacitive-type Ga_(2)O_(3)/liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique.Owing to the photothermal effect of laser,the Ga_(2)O_(3)-wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19Ω·cm,while the untreated regions serve as active sensing layers in response to moisture changes.Under 95%relative humidity,the humidity sensor displays a highly stable performance along with rapid response and recover time.Utilizing these superior properties,the Ga_(2)O_(3)/liquid metal-based humidity sensor is able to monitor human respiration rate,as well as skin moisture of the palm under different physiological states for healthcare monitoring.
基金Jin Wu acknowledges financial support from the National Natural Science Foundation of China(No.61801525)the Guangdong Basic and Applied Basic Research Foundation(No.2020A1515010693)+1 种基金the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.22lgqb17)the Independent Fund of the State Key Laboratory of Optoelectronic Materials and Technologies(Sun Yat-sen University)under grant No.OEMT-2022-ZRC-05.
文摘Breathing is an inherent human activity;however,the composition of the air we inhale and gas exhale remains unknown to us.To address this,wearable vapor sensors can help people monitor air composition in real time to avoid underlying risks,and for the early detection and treatment of diseases for home healthcare.Hydrogels with three-dimensional polymer networks and large amounts of water molecules are naturally flexible and stretchable.Functionalized hydrogels are intrinsically conductive,self-healing,self-adhesive,biocompatible,and room-temperature sensitive.Compared with traditional rigid vapor sensors,hydrogel-based gas and humidity sensors can directly fit human skin or clothing,and are more suitable for real-time monitoring of personal health and safety.In this review,current studies on hydrogel-based vapor sensors are investigated.The required properties and optimization methods of wearable hydrogel-based sensors are introduced.Subsequently,existing reports on the response mechanisms of hydrogel-based gas and humidity sensors are summarized.Related works on hydrogel-based vapor sensors for their application in personal health and safety monitoring are presented.Moreover,the potential of hydrogels in the field of vapor sensing is elucidated.Finally,the current research status,challenges,and future trends of hydrogel gas/humidity sensing are discussed.
基金the National Natural Science Foundation of China(No.51777215)the Original Innovation Special Project of Science and Technology Plan of Qingdao West Coast New Area(No.2020-85).
文摘Humidity sensors are of significance in various fields,such as environmental and food quality monitoring,industrial processing,wearable and flexible electronics,and human health care.High-performance humidity sensors with high sensitivity,rapid response time,and good stability are of paramount importance in humidity sensing.In this paper,diversiform humidity sensors with different sensing mechanisms are summarized,including resistive,impedance,capacitive,quartz crystal microbalance(QCM),surface acoustic wave(SAW),field-effect transistor(FET),and optical fiber humidity sensors.Versatile nanomaterials such as graphene,transition-metal chalcogenide,MXenes,black phosphorus(BP),boron nitride(BN),polymers,and nanofibers were promising building-blocks for constructing humidity sensors.The latest progress in the wearable and flexible humidity sensors,and self-powered humidity sensors was summarized.The diversiform applications of the humidity sensors with great prospects were demonstrated in various fields in terms of human respiratory monitoring,skin dryness diagnosing,fingertip approaching,and non-contact switch.Moreover,the challenges and prospects of nanomaterials-based humidity sensors were discussed.
基金This work was supported by the National Natural Science Foundation of China(Nos.12174348,U21A2070,and 62027816)the Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001)+1 种基金the Natural Science Foundation of Henan Province(No.212300410410)the China Postdoctoral Science Foundation(Nos.2018M630830 and 2019T120631).
文摘Humidity sensors with high sensitivity,rapid response,and facile fabrication process for contactless sensing applications have received considerable attention in recent years.Herein,humidity sensors based on hexagonal boron nitride(h-BN)nanosheets that are synthesized by a facile ultrasonic process have been fabricated,which display an ultrahigh sensitivity of 28,384%at 85%relative humidity(RH),rapid response/recovery time(3.0/5.5 s),and long-term stability in a wide humidity detection range(11%-85%RH),superior to most of the reported humidity sensors.The high sensitivity can be ascribed to the massive hydrophilic functional groups absorbed on the h-BN nanosheet surface.Benefiting from the high humidity sensing performances,contactless Morse code messaging and human writing and speech recognition have been demonstrated.This work demonstrates the great potential of the high-performance h-BN nanosheet-based humidity sensors for future contactless sensing devices.
基金the National Natural Science Foundation of China(No.22008014)the Changzhou Young Scientific and Technological Talents Promotion Project,the Qing Lan Project of Jiangsu Province and China Scholarship Council(CSC).+1 种基金the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea government(MOTIE)(20215710100170)the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.2023R1A2C200769911).
文摘Flexible humidity sensors are widely used in many fields,such as environmental monitoring,agricultural soil moisture content determination,food quality monitoring and healthcare services.Therefore,it is essential to measure humidity accurately and reliably in different conditions.Flexible materials have been the focusing substrates of humidity sensors because of their rich surface chemical properties and structural designability.In addition,flexible materials have superior ductility for different conditions.In this review,we have summarized several sensing mechanisms,processing techniques,sensing layers and substrates for specific humidity sensing requirements.Aadditionally,we have sorted out some cases of flexible humidity sensors based on different functional materials.We hope this paper can contribute to the development of flexible humidity sensors in the future.
基金supported by the National Key Research and Development Program of China(2022YFB3205500,and 2022YFC3104700)the National Natural Science Foundation of China(62101329 and 61971284)+4 种基金the Shanghai Sailing Program(21YF1421400)the Natural Science Foundation of Shanghai(23ZR1430100)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(SL2020ZD203,SL2021MS006 and SL2020MS031)Scientific Research Fund of Second Institute of Oceanography,Ministry of Natural Resources of P.R.China(SL2003)Startup Fund for Youngman Research at Shanghai Jiao Tong University.
文摘Human metabolite moisture detection is important in health monitoring and non-invasive diagnosis.However,ultra-sensitive quantitative extraction of respiration information in real-time remains a great challenge.Herein,chemiresistors based on imine-linked covalent organic framework(COF)films with dual-active sites are fabricated to address this issue,which demonstrates an amplified humidity-sensing signal performance.By regulation of monomers and functional groups,these COF films can be pre-engineered to achieve high response,wide detection range,fast response,and recovery time.Under the condition of relative humidity ranging from 13 to 98%,the COFTAPB-DHTA film-based humidity sensor exhibits outstanding humidity sensing perfor-mance with an expanded response value of 390 times.Furthermore,the response values of the COF film-based sensor are highly linear to the relative humidity in the range below 60%,reflecting a quantitative sensing mechanism at the molecular level.Based on the dual-site adsorption of the(-C=N-)and(C-N)stretching vibrations,the revers-ible tautomerism induced by hydrogen bonding with water molecules is demonstrated to be the main intrinsic mechanism for this effective humidity detection.In addition,the synthesized COF films can be further exploited to effectively detect human nasal and oral breathing as well as fabric permeability,which will inspire novel designs for effective humidity-detection devices.
基金financially supported by the National Natural Science Foundation of China(No.U19A2070)the National Science Funds for Excellent Young Scholars of China(No.61822106)the National Science Funds for Creative Research Groups of China(No.61421002)。
文摘As humidity is one of the most widely demanded environmental parameters,the precision of its detection is significant.An advanced humidity sensor will improve the validity of the humidity monitoring system.In this study,a facile chemical layer-by-layer self-assembly(CLS)method was developed for fabricating graphene oxide(GO)/polyethyleneimine(PEI)multilayer films.Owing to the chemical bonding between the PEI and GO,and the intrinsic stickiness of the PEI,layered films with different numbers of layers were successfully prepared using the CLS method and confirmed through ultraviolet-visible(UV-Vis)spectroscopy and the mass loading of quartz crystal microbalance(QCM).Morphological measurements revealed that the roughness and thickness of the films increased exponentially with the number of bilayers.The GO/PEI films were deposited on QCM electrodes using the CLS method to produce the humidity sensors.The humidity measurement results showed a high sensitivity(37.84 Hz/%RH)and rapid response/recovery(<5 s/8 s)of the optimal sensor,which was superior to that of recently developed QCM sensors.
基金financially supported by the National Natural Science Foundation of China(No.U19A2070)the National Science Funds for Excellent Young Scholars of China(No.61822106)the National Science Funds for Creative Research Groups of China(No.61421002)。
文摘Ti_(3)C_(2)T_(x),which is a novel two-dimensional(2 D)material,has received enormous interest in the field of sensor technology due to its large surface area,excellent electrical conductivity,and abundant active surface sites.In recent years,several Ti_(3)C_(2)T_(x)-based gases and humidity sensors have been developed and reported.In this review,we focus on the latest applications of Ti_(3)C_(2)T_(x)-based nanomaterials in gas and humidity sensors.First,the synthesis of Ti_(3)C_(2)T_(x) from the dangerous fluorine-containing etching process to the safe fluorine-free preparation method was discussed,and the structures of the Ti_(3)C_(2)T_(x) controlled by different delamination methods were also outlined.Subsequently,the functionalization of pristine Ti_(3)C_(2)T_(x) and composite strategies for enhancing its gas and humidity sensing performance were reviewed.In addition,the gas and humidity sensing mechanisms of sensors based on Ti_(3)C_(2)T_(x) were also summarized.Finally,the challenges and opportunities for the use of Ti_(3)C_(2)T_(x) gas and humidity sensors were discussed to provide guidance on the promising potential of Ti_(3)C_(2)T_(x) in this field.
基金supported by the Fujian Provincial Department of Science and Technology (No. 2018H0041,2018H0042,2018T3010,2019T3017 and 2019T3024)。
文摘Humidity sensors have been widely applied to detect environment humidity in various fields. However, most of humidity sensors cannot provide performance needed for high sensitivity and fast response. We report one type of capacitive-type humidity sensors composed of laser-scribed graphene(LSG) as sensing electrodes and graphene oxide/tin dioxide(GO/SnO2) as a sensing layer. The LSG is reduced graphene oxide(rGO) electrodes resulted from selective reducing of GO within a GO/SnO2 composite layer by laser scribing method, and the sensing layer is the un-scribed GO/SnO2 composite. The sensor fabrication is a one-step process which is facile and cost-efficient. When a mass ratio of GO:SnO2 in the composite reaches 1:1, the humidity sensor(named as LSG-GS1) has the best properties than other ratios, which exhibits high sensitivity in the range of 11%~97% relative humidity(RH). In addition, the LSG-GS1 also has very quick response/recovery time(20 s for adsorption and 18 s for desorption) when RH changes from 23% to 84%, and very good stability after monitoring for 41 days. Such excellent performances of the humidity sensor can be attributed to synergistic effect of SnO2 and GO within the composite layer.
基金supported by the National Science and Technology Innovation 2030 Major Project(Grant No.2022ZD0208601)the National Natural Science Foundation of China(Grant No.52105593 and 51975513)the Natural Science Foundation of Zhejiang Province,China(No.LR20E050003)。
文摘In the past decade,the global industry and research attentions on intelligent skin-like electronics have boosted their applications in diverse fields including human healthcare,Internet of Things,human–machine interfaces,artificial intelligence and soft robotics.Among them,flexible humidity sensors play a vital role in noncontact measurements relying on the unique property of rapid response to humidity change.This work presents an overview of recent advances in flexible humidity sensors using various active functional materials for contactless monitoring.Four categories of humidity sensors are highlighted based on resistive,capacitive,impedance-type and voltage-type working mechanisms.Furthermore,typical strategies including chemical doping,structural design and Joule heating are introduced to enhance the performance of humidity sensors.Drawing on the noncontact perception capability,human/plant healthcare management,human-machine interactions as well as integrated humidity sensor-based feedback systems are presented.The burgeoning innovations in this research field will benefit human society,especially during the COVID-19 epidemic,where cross-infection should be averted and contactless sensation is highly desired.
基金J.W.acknowledges financial supports from the National Natural Science Foundation of China(61801525)the Guangdong Basic and Applied Basic Research Foundation(2020A1515010693)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(22lgqb17).
文摘Respiratory monitoring plays a pivotal role in health assessment and provides an important application prospect for flexible humidity sensors.However,traditional humidity sensors suffer from a trade-off between deformability,sensitivity,and transparency,and thus the development of high-performance,stretchable,and low-cost humidity sensors is urgently needed as wearable electronics.Here,ultrasensitive,highly deformable,and transparent humidity sensors are fabricated based on cost-effective polyacrylamide-based double network hydrogels.Concomitantly,a general method for preparing hydrogel films with controllable thickness is proposed to boost the sensitivity of hydrogel-based sensors due to the extensively increased specific surface area,which can be applied to different polymer networks and facilitate the development of flexible integrated electronics.In addition,sustainable tapioca rich in hydrophilic polar groups is introduced for the first time as a second cross-linked network,exhibiting excellent water adsorption capacity.Through the synergistic optimization of structure and composition,the obtained hydrogel film exhibits an ultrahigh sensitivity of 13,462.1%/%RH,which is unprecedented.Moreover,the hydrogel film-based sensor exhibits excellent repeatability and the ability to work normally under stretching with even enhanced sensitivity.As a proof of concept,we integrate the stretchable sensor with a specially designed wireless circuit and mask to fabricate a wireless respiratory interruption detection system with Bluetooth transmission,enabling real-time monitoring of human health status.This work provides a general strategy to construct high-performance,stretchable,and miniaturized hydrogel-based sensors as next-generation wearable devices for real-time monitoring of various physiological signals.
基金the NSFC Funds under Grant 52075440National Key Research and Development Program of China(No.2021YFD1600402)+2 种基金Central Guidance on Local Science and Technology Development Fund of Shaanxi Province(No.2020-ZYYD-NCC-9)Shaanxi Provincial Department of Education Collaborative Innovation Center Project(20JY052)National Natural Science Foundation of China(No.52072075)。
文摘Flexible sensors are attractive due to potential applications in body exercise and ambient gas monitoring systems.Cellulose and its derivatives have combined superiorities such as intrinsic and structural flexibility,ease of chemical functionalization,moisture sensitivity,and mechanical stability,enabling them to be promising candidates as flexible supporting substrates and flexible sensitive materials.Significant progress consequently has been achieved to improve mechanical,electrical,and chemical performance.The latest advance in materials synthesis,structure design,fabrication control,and working mechanism of novel cellulose-based flexible sensors are reviewed and discussed,including strain sensors,humidity sensors,and harmful gas sensors.Various strategies were summarized to enhance sensor performance by surface group modifications,inorganic and organic conducting fillers optimization,multilayer structure design.Newly emerged processing techniques of self-assembly,vacuum filtration,and 3D printing were introduced as well to construct multiscale microstructures.The integration of multiple sensors toward smart and healthy exercise monitoring system is briefly reviewed.The facing challenges and future opportunities of cellulose-based flexible sensors were discussed and proposed at the end.This review provides inspiration and guidelines on how to design and fabricate cellulose-based flexible sensors.
文摘Grafted high density polyethylene (HDPE) films have been prepared by grafting sodium styrene sulfonate (SSS) and acrylic acid (AA) onto HDPE using preirradiation method.The structure and surface morphology of both grafted and ungrafted HDPE films were observed by FTIR spectroscopy and scanning electron microscope (SEM),respectively.The humidity sensing properties of grafted HDPE films were investigated.The results show that the impedance of the film decreases with increasing of relative humidity (RH).The films display high sensitivity with nearly three orders of magnitude change in the resistance during the relative humidity variation from 5% to 98%.Grafted HDPE films exhibit excellent properties as humidity sensors.
文摘The widely used sensitive elements of humidity sensors can be divided into 3 types,i.e.,resistor,capacitor,and electrolyte.Humidity sensors consisting of these sensitive elements have corresponding signal processing circuit unique to each type of sensitive elements.This paper presents an ispPAC (in-system programmable Programmable Analog Circuit) -based humidity sensor signal processing circuit designed with software method and implemented with in-system programmable simulators.Practical operation shows that humidity sensor signal processing circuits of this kind,exhibit stable and reliable performance.
基金The authors acknowledge the financial support from Bahia State Research Foundation(FAPESB,Project 1252/2018).
文摘Humidity is a critical environmental parameter for several production processes and its control/monitoring is of great importance in maintaining the quality of goods and products. In this context, metallic oxide ceramic nanostructures are materials of great technological interest in the fabrication of moisture sensors because they have good chemical/structural stability and high surface area/volume ratio. The electrical response of these sensors relates to the chemisorbed and physisorbed layers of water molecules on the surface of the ceramic particles and to the capillary condensation of water in the microscopic pores between the particles. Based on these aspects, this work presents the fundamentals, electrical/electronic properties, influence of dopants, novel preparation procedure by electrospinning and perspectives of application of TiO2:WO3 metal oxide heteronanostructures as humidity sensors.
基金supported by the National Natural Science Foundation of China(51777215)National Natural Science Foundation of China(51775306)+1 种基金Beijing Municipal Natural Science Foundation(4192027)the Graduate Innovation Fund of China University of Petroleum(YCX2020097)。
文摘Two-dimensional material has been widely investigated for potential applications in sensor and flexible electronics.In this work,a self-powered flexible humidity sensing device based on poly(vinyl alcohol)/Ti_(3)C_(2)Tx(PVA/MXene)nanofibers film and monolayer molybdenum diselenide(MoSe2)piezoelectric nanogenerator(PENG)was reported for the first time.The monolayer MoSe_(2)-based PENG was fabricated by atmospheric pressure chemical vapor deposition techniques,which can generate a peak output of 35 mV and a power density of42 mW m^(-2).The flexible PENG integrated on polyethylene terephthalate(PET)substrate can harvest energy generated by different parts of human body and exhibit great application prospects in wearable devices.The electrospinned PVA/MXene nanofiber-based humidity sensor with flexible PET substrate under the driven of monolayer MoSe_(2) PENG,shows high response of~40,fast response/recovery time of 0.9/6.3 s,low hysteresis of 1.8%and excellent repeatability.The self-powered flexible humidity sensor yields the capability of detecting human skin moisture and ambient humidity.This work provides a pathway to explore the high-performance humidity sensor integrated with PENG for the self-powered flexible electronic devices.
基金The project is supported by the National Natural Science Foundation of China (60074031, 60474052).
文摘Capacitive humidity sensors were made of nanometer barium titanate.The pellets were prepared under different pressures between 3920N to 7850N force.The capacitance changes in three orders of magnitude in the relative humidity range of 10%~98%,indicating high humidity sensitivity of the sensors.At a certain measuring frequency,the capacitance of the sensors increases as increasing of the preparation pressure,while the sensitivity of the sensors basically remains the same.The frequencies corresponding to the peaks of the dielectric loss of the sensors move to the higher frequency direction as increasing of the relative humidity.At a certain humidity,the frequencies corresponding to the peaks of the dielectric loss move to the higher frequency direction as increasing of the preparation pressure.
基金This work was supported by National Natural Science Foundation of China, Under Grant No.(60676044)
文摘This paper reports on the fabrication and sensing characteristics of Polyimide-based humidity sensor,based on that,a new integrated circuit of humidity measurement has been designed.It is a novel capacitive-type systems on a chip structure using the MEMS process.The results show that the new sensor presents sensing characteristics over a humidity range from 10%~70% RH at 20℃,and the sensor is able to fabricated together with ICs technology.The result shows that integration of humidity sensor with integrated circuit of humidity measurement is considerably easier when they are built in sensing groove.The appeal of a new structure like this brings the possibility of applications that would require the flexibility of simple screen printing.
文摘An impedance type humidity sensor based on the polyacrylic emulsion containing magnesium chloride (MgCl_2) without chemical modification was investigated.The impedances of the sensor were measured from various relative humidity in the frequency range between 0.1kHz and 100 kHz.The sensor has a good sensitivity from 60%RH to 90%RH.According to the experimental results,the response time is about 240 seconds in the adsorption process and 310 seconds in the desorption process.
文摘A novel soluble conjugated copolymer (propionic acid)-co-(propargyl alcohol) (PA-co-OHP) has been synthesized for the first time using a new palladium acetylide catalyst Pd(PPh3)2 (CoCC(CH3)2OH)2 (PPB). Thin film resistive humidity sensor based on the copolymer doped with HClO-4 was prepared. The impedance of the sensor changed from 103~107 W in 95%~30%RH, and the response of that is very quick (<6 sec.). Preliminary results show the copolymer is a promising humidity sensitive material.