The Study Of Flexible Wearable Sensors For Plant Monitoring

As important life forms on earth,plants are not only the major determinants to earth atmosphere and climates but also primary resources for food,medicine,and energy.Studying of growth mechanisms of plants and their interaction with surrounding environments are important research aspects of botany.The growth and stimulus responses of plants are slow and subtle processes that demand long-term and continuous observation.The state-of-the-art technologies of plant monitoring are low in spatial or temporal resolutions or cannot provide timely response to events that influence plant physiology.Flexible wearable devices with characteristics of portability,good biocompatibility,real-time monitoring and low energy consumption satisfy the requirements of plant real-time monitoring.Here,wearable devices based on flexible electronic for plant monitoring are demonstrated.A multifunctional stretchable leaf-mounted sensor with multiple heterogeneous sensing elements has been developed to offer optimized adaptability to plant growth and monitor leaf physiological and environmental conditions including temperature,hydration,and light illuminance.The sensor has been constructed using ultrasoft silicone substrate with an ultralow modulus（～3.0 k Pa）as well as stretchable structures,allowing 150%deformation to adapt to leaf growth.The sensor has been demonstrated to continuously and simultaneously measure plant physiology and environmental conditions for 2 days with little influence to the hosting leaf after 45 days integration.A wireless sensing platform has been developed to transmit the sensing results to a distance of 200 m.The multifunctional stretchable sensor holds the promise to advance monitoring techniques in plant biology and precision agriculture,resulting in improved capability to record slow and subtle physiological changes in plants and plant/environment interaction.A fully flexible electromagnetic sensor has been developed to conduct wearable monitoring of vibration induced by mechanical stimulation with excellent adaptability to leaf surface morphology through a suspended flexible magnet enclosed within a novel setup formed by a multi-layer flexible coil and annular origami magnetic membranes.The annular membranes not only regulate the overall distribution of the magnetic field and enhance the overall magnetism by 291%,but also greatly increase the range of the magnetic field to cover the entire region of the coil.The sensor offers a broad frequency response ranging from 1 Hz to 10 k Hz and a sensitivity of 0.59 m Vμm^-1 at 1.7 k Hz.The fully flexible format of the sensor enables various applications demonstrated by agricultural monitoring,motion detection,and machine diagnostics through direct attachment on soft and curvilinear surfaces.Similar sensors can combine multiple sensing and energy harvesting modalities to achieve battery-less and self-sustainable operation,and can be deployed in large numbers to conduct distributed sensing for machine status assessment,health monitoring,rehabilitation,and speech aid.A thinning technology for flexible photovoltaic device based on stainless steel substrate has been developed to obtain ultrathin CIGS and amorphous silicon photovoltaic devices with thickness of 25μm through chemical etching.The ultrathin solar cell can be integrated with leaves,stems,vines,or roots in differ manners of bending,crimping,and spiral winding.The ultrathin devices have no significant changes in key capabilities such as conversion efficiency,open-circuit voltage,short-circuit current,and fill factor,while offering excellent flexibility and durability.The ultrathin CIGS photovoltaic device has been attached on leaves to continuously measure light illuminance for 5 days.A energy harvesting circuit has been developed to efficiently extract milliwatts of power generated from the ultrathin morphous silicon photovoltaic device,offering sustainable energy sources for flexible wearable plant sensor.