In-situ And Non-destructive Sensing Of Plant Water Information Based On Self-powered Flexible And Wearable Devices

Water stress will induce negative influence to the physiological activities of plants,which may hinder plant normal growth.Therefore,it is necessary to monitor the water status of plants in real time to avoid water stress.The physiological parameters of plants such as transpiration and stem diameter can reflect the water status of plant,which can be considered as indicators for establishing methods to monitor plant water stress.However,the traditional methods have certain limitations such as hysteresis,low sensitivity,and difficulty in in-situ monitoring.Therefore,there is an urgent need to develop efficient and accurate methods for tracking the plant water stress with high sensitivity as well as in-situ,non-destructive,and real-time monitoring.Based on this,in this thesis,using plant physiology as the research foundation,different types of flexible and wearable sensors and power generators for plants are fabricated with the assistance of nanomaterials.By exploring the sensing and power generating mechanism of the devices,a flexible and self-powered system with in-situ and non-destructive sensing capability of monitoring the plant water status is fabricated.We anticipate that this system would be valuble for establishing methods for monitoring other physiological information of plants,which can pave a new way for the construction of intelligent agricultural systems in the future.The main content and results of this research can be concluded as follows:(1)In view of the irregular surface of plant leaves,it is difficult to achieve conformal contact with rigid sensors.Based on this,a flexible and wearable capacitive humidity sensor that can achieve conformal contact with the plant leaf surface is designed.First,the laserinduced graphene technology is used to prepare flexible interdigital electrodes.Compared with the traditional methods,this method is more convenient and can realize mass production.Subsequently,a capacitive flexible humidity sensor is prepared using graphene oxide as the humidity-sensitive material.The sensor exhibits a high sensitivity of 3215 p F/% RH at the frequency of 50 Hz as well as excellent bending and long-term stability.Based on the great sensing performance of the sensor,it shows potential applications for in-situ and real-time monitoring of plant transpiration,laying a foundation for the realization of in-situ and nondestructive detection of plant water status.(2)In order to solve the problem that the above-mentioned flexible sensor is difficult to adapt to the deformation of plants during the growth process,a stretchable strain sensor that can adapt to the growth and deformation of plant is designed.The stretchable strain sensor is prepared by embedding conductive composite nanomaterials between stretchable polymers.The results show that the stretchable strain sensor exhibits good stretchability(70%),high sensitivity(gauge factor of 215.4),and long-term stability.Based on the sensing performance of the strain sensor,it can be used to establish an efficient and accurate sensing method for insitu monitoring of plant water status.(3)In order to solve the energy supply problem of the above-mentioned sensors and realize the battery-free and high-precision operation of the sensor,a triboelectric nanogenerator(TENG)that can convert wind or raindrop energy in the agricultural environment into electrical energy is designed.The TENG is prepared by combining electrospinning technology and vacuum filtration technology.Then,the output performance of the TENG including output power density,stability,and adhesion force with plant leaves was tested.In addition,by simulating the external conditions of wind and rain in the natural environment,the feasibility of the TENG to convert wind energy and raindrop energy in the agricultural environment into electrical energy was verified.Based on this,the TENG can serve as a power supply for sensors,providing new possibilities for building a self-powered agricultural sensing system.(4)In order to further solve the above-mentioned problem of the limited driving source of the TENG that is unable to generate electricity continuously and stably,we design a humiditybased power generator that can convert the ubiquitous humidity in the environment into electricity.The humidity-based power generator with an asymmetric structure is fabricated using cellulose filter membrane as a flexible substrate,and carbon nanoparticles as the functional material.Subsequently,the factors that may affect the output voltage of the humidity-based power generator and the mechanism for power generation are explored.In addition,the feasibility of the humidity-based power generator to continuously generate electricity under natural environment is verified.The above results pave a new way for building a sustainable agricultural self-powered sensing system.(5)Based on the results mentioned above,an integrated self-powered flexible and wearable sensing system is established.The performance of the power supply device and the sensing device are tested.Based on this,taking the detection of the variation of plant stems as an example,the feasibility of the self-powered system for in-situ and non-destructive sensing of plant water information is verified,providing a new way for judging the plant water status in a timely manner.This system shows great significance for ensuring crop yields as well as guiding agricultural precision irrigation.