Freezing is a typical abiotic stress on plants, which can induce physiological damages of plants. A better understanding of plant freeze-thaw characteristics contributes to solving some hot issues in plant physiology, such as cold resistance and cold acclimation. This article presents a novel sensor for in situ detection of freeze-thaw characteristics in plants based on stem temperature and water content. The measuring circuit of stem temperature was designed based on constant current source and platinum resistance. The measuring circuit of stem water content was designed based on standing wave ratio and the dielectric properties of stem tissue. The temperature resolution of the compound sensor is less than 0.1°C. The MAE and RMSE of temperature measurement are approximately 0.57°C and 0.65°C, respectively. The volumetric water content resolution of the compound sensor is less than 0.05%. The MAE and RMSE of volumetric water content measurement are approximately 1.59% and 1.81%, respectively. Moreover, a mathematical model for describing the freeze-thaw characteristics of plant stem was established and solved based on the compound sensor. Then, some freeze-thaw indicators including stem water content, ice content, freezing depth, freezing velocity, thawing depth, and thawing velocity were solved and used to interpret the freeze-thaw rules of plant stem. It can be concluded that the freeze-thaw velocity is closely related to the physicochemical properties of plant stem which also change dynamically in the freeze-thaw cycle.
High Frequency Transducer Dedicated to the High-resolution in Situ Measurement of the Distance between Two Nuclear Fuel Plates