Abstract:

Objective: This study aims to design and validate a novel DBH measurement device based on high-performance flexible strain sensors, which can be used for rapid, convenient, high-precision, non-invasive tree DBH measurement suitable for long-term in-situ monitoring. Method: The device mainly consists of three components: the core sensing unit is a flexible strain sensor whose conductive channel is constructed via a specific composite process using multi-walled carbon nanotubes (MWCNTs) and Ecoflex elastomer, operating on the principle of regular resistance change in response to applied strain (stretching caused by trunk circumference variation); a flexible connector, designed with compatible materials, is used to stably, tightly, and non-destructively wrap and fix the sensor around the trunk surface, ensuring good conformity and accommodating irregular surfaces and growth changes; peripheral acquisition circuitry is responsible for real-time acquisition, conditioning, and digitization of the sensor's resistance change signal. Result: To evaluate the performance of the device, a systematic test was conducted, and the experimental results demonstrated that the MWCNTs/Ecoflex-based flexible strain sensor exhibited a highly linear resistance-strain response within the 0–20% strain range, with a high sensitivity (Gauge Factor, GF) of 3.464, and an ultra-low Young's modulus (0.23 MPa), enabling it to conform tightly and seamlessly to the trunk surface, effectively preventing damage and ensuring non-invasiveness. The static stability tests confirmed the device's ability to maintain relative stability in resistance signal with minimal fluctuation and high reliability during long-term monitoring. The standard cylinder simulation experiments proved its high repeatability in measurement capability with good result consistency, and reliable measurement of simulated trunk diameters (within the 10.00–11.00 cm range). The results of live tree testing demonstrated that the device maintained excellent anti-interference performance under complex environmental conditions (including disturbances such as varying temperature, humidity, and cloudy or rainy weather), accurately capturing the diurnal dynamic changes in the DBH of Koelreuteria paniculata (131.9–132.5 mm), fully validating its practicality and reliability in real forest environments. Conclusion: This study has successfully developed a novel tree DBH measurement device based on a high-performance MWCNTs/Ecoflex flexible strain sensor, which achieves high sensitive detection of trunk circumference changes through innovative flexible sensing technology. Its ultra-low Young's modulus ensures non-destructive, tight conformity, guaranteeing tree-friendliness. The device possesses high measurement accuracy, excellent repeatability, stable resistance during long-term monitoring, and good adaptability to complex environments. The structural design emphasizes rapid and convenient installation to significantly improve efficiency. The device provides an innovative solution meeting the demands for rapidity, convenience, high accuracy, non-destructiveness, and long-term in-situ monitoring, holding broad application prospects in precision forestry, ecological research, and intelligent urban greening management.

Key words: forest resource survey, tree diameter measurement, flexible strain sensor, multi-walled carbon nanotubes, non-invasive