Research On Wood Moisture Detection Method Based On Microwave Transmission Principle

Wood is widely used in industrial production due to its light weight,easy process-ing and impact resistance.The moisture content(MC)of wood is one of the primary factors that affect its physical properties.Wood crack when its moisture content is too low,meanwhile wood is easy to rot if its moisture content is too high.How to quickly and accurately detect the moisture content of wood is an urgent issue in the wood processing industry.The numerical simulation of wood moisture content in CST have been completed.According to the simulation results,the microwave transmission type wood moisture content detection device was designed and constructed,and series of experi-ments were carried out.Based on the simulation and experiments results,a wood moisture content detection method that based on the principle of microwave transmission is proposed.The main work of this paper is shown as follows:(1)Simulation study of wood moisture content based on the principle of microwave transmission.According to the design method of the pyramid horn antenna,the pyramid horn antennas with working frequencies of 1.72GHz?2.61GHz and 8.2GHz?12.5GHz are designed respectively,and the structural parameters of the antenna are optimized;The wood simulation model is established according to the Debye dispersion model,the thesis studied the influence of the value of N in the dispersion model on the relationship between the dielectric constant of the material and the frequency,and provided a universal method for building wood simulation models at different frequencies.In CST a numerical simulation system of wood moisture content was constructed by using FIT,and the quantitative relationship between the amplitude and phase of the transmission coefficient S₂₁ and wood moisture content is investigated as well as,the best detection frequency and detection distance for different woods is determined.(2)Experiment setup is established and experiments are carried out.According to the simulation results,a wood moisture content detection system based on the principle of microwave transmission was designed.In addition,a device for fixing the antenna also was designed.And then we prepare samples of different moisture content of spruce,poplar,and larch.The experiment was performed and the experimental results are analyzed Finally.(3)Research on the detection method of wood moisture content.Firstly,the single-parameter wood moisture content detection method based on amplitude or phase is studied.The maximum average error of the measurement results is 0.88%,and the minimum average error is 0.66%.Secondly,the relationship between the moisture content three types of spruce,poplar and larch and the amplitude and phase of transmission coefficient S₂₁ are obtained,a two-parameter wood moisture content detection method based on the least square error of the error is proposed.The maximum average error of the measurement error is 0.57%,and the minimum average measurement error is 0.22%.Then the water content detection method based on BP neural network is studied.The model is used to train the water cut based on amplitude and phase.The average measurement error of moisture content prediction is 0.45%.Finally,the error analysis of the experiment is carried out.