Design And Experimental Study Of A Flexible Wearable Sensor For In-situ Nondestructive Detection Of Plant Leaf Transpiration Information

Timely understanding of plant transpiration status is of great significance for agricultural production.Transpiration accompanies the entire process of plant life and is an important link in plant growth and development.Appropriate transpiration intensity can promote plant growth,while too high or too low can cause harm to plant health.Therefore,real-time monitoring of plant transpiration information is the basis for timely intervention and regulation.Traditional methods have a certain lag in evaluating transpiration information through environmental scale VPD rather than plant information itself.Leaf scale VPD can more timely and truthfully reflect transpiration information,so in situ wearable detection of leaf information is necessary.However,there are still certain limitations in sensitivity and biocompatibility at present.Therefore,this article draws inspiration from flexible electronic technology and designs a flexible wearable sensor that can perform in situ,sensitive,and non-destructive testing of leaf scale VPD.The main research content is as follows.（1）Design and preparation of flexible sensors for leaf temperature and humidity.To explore wearable sensing methods for leaf temperature and humidity information while reducing the impact on plant physiology,PDMS-GO-SDS flexible materials were first prepared by improving the processing technology,and a hydrophobic flexible substrate that can adhere to the leaf surface in a conformal manner was made.The substrate has good light transmittance,with transmittance in the ultraviolet and visible light bands of about 63.48%and 72.47%,respectively.Then,laser technology was used to modify its surface to improve its local hydrophilicity.Through screen printing,conductive ink was printed on top of the pattern to form a flexible interdigital electrode.On this basis,Graphite oxide（GO）was used as a humidity sensitive material to modify the electrode area,and a capacitive humidity sensor was constructed.A resistive temperature sensing element was constructed by integrating a micro platinum metal film as a temperature sensitive material onto a flexible substrate surface.A PDMS-SDS self-adhesive porous breathable film with good biocompatibility was prepared by emulsification and changing the ratio of curing agent.The film has good breathability,with a water vapor transmittance of approximately 198)2)·（88）^-2·h^-1.The transparent flexible substrate and breathable adhesive film lay the foundation for reducing the physiological impact on plants.（2）Performance testing and analysis of wearable sensors for leaf temperature and humidity.By simulating the actual working environment,its anti-interference and response characteristics were tested.The analysis results indicate that,in addition to good anti-interference performance,both humidity sensing elements and temperature sensing elements have good response performance,with a sensitivity of approximately4456 p F/%RH for humidity sensing elements and 3.93Ω/℃for temperature sensing elements.In addition,based on the measured sensor data,the functional relationships between the capacitance value of the humidity sensing element and relative humidity,as well as the resistance value of the temperature sensing element and temperature were fitted.The results show that there is a good nonlinear relationship between the capacitance value of the humidity sensing element and relative humidity,with an R² of approximately 0.9952;There is a good linear relationship between the resistance value of the temperature sensing element and temperature,with an R² of approximately0.9985.The good anti-interference and response performance of the sensor lays the foundation for the detection of leaf temperature and humidity.（3）In terms of application experiments.Using green pineapple as the experimental object,the sensor was attached to the surface of green pineapple leaves for about 20days to observe its effects on leaf nitrogen content,relative chlorophyll content,and stomatal opening.The results showed that within the sensor coverage area,the difference rate of leaf nitrogen content compared to other areas increased from-1.24%to-3.64%,and the difference rate of relative chlorophyll content compared to other areas increased from-1.03%to-2.25%,The difference rate of stomatal opening compared to other regions increased from 0.51%to-0.8%,which did not have a significant impact on plant physiological health.At the same time,the temperature,relative humidity on the leaf surface,and small environment temperature information measured by flexible wearable sensors were compared and analyzed with the data measured by commercial sensors.The results showed that compared with commercial sensors,the temperature error rate measured by wearable sensors was about 1.13%,the relative humidity error rate on the leaf surface was about 2.08%,and the small environment temperature error rate was about 1.55%.Finally,using the method of control variables,the detection effect of flexible wearable sensor on leaf-scale VPD under the influence of different environmental factors was tested in the artificial climate room,and the tracking detection was carried out in the natural actual environment.The experimental results are in good agreement with the relevant research results.The flexible wearable sensor for in-situ non-destructive detection of plant transpiration information has good practicality and can be used for monitoring plant growth processes and precise management of crops in agricultural production,which helps to play a role in smart agriculture based on the Internet of Things for plants.