Research On Microwave Numerical Simulation And Detection Technology Of Moisture Content In Storage Wheat

Grain is one of the important strategic materials in China,and ensuring grain security is an important task.Grain storage security is a prerequisite for achieving food security.Too high or too low grain moisture content will threaten grain storage security.Since the total annual output of wheat accounts for about 22% of the total annual output of grain in China,accurate detection of wheat content of stored wheat can ensure food security.At present,the drying method and the arrangement of moisture sensors are mainly used in China to detect the wheat moisture content.The drying method has high detection accuracy but belongs to destructive testing.The arrangement of sensors will consume a lot of manpower and material resources.The traditional microwave free space transmission method has the advantages of non-destructive detection and non-contact,and has become the mainstream method for detecting the wheat moisture content.However,this method usually requires two dielectric lenses to complete the detection,and the detection cost is high.In addition,the traditional method has a large workload and time,a long time span,and poor portability of the experimental scene.In order to solve the above problems,this paper introduces the microwave numerical simulation technology on the basis of the traditional free space transmission method to realize the rapid verification of the measurement principle and theoretical derivation formula,using the simulation system of numerical software builds model can effectively guide the construction of the laboratory wheat moisture detection system,as the subsequent wheat moisture content test provides a convenient conditions.The research work of this paper is as follows:(1)On the basis of analyzing the measurement principle of microwave transmission method,a mathematical formula for inverting the complex relative permittivity of the sample using scattering parameters is derived,the multi-value problem of the formula is solved by using the imaginary part compensation method,and the microwave numerical simulation software is used to verify the accuracy of the measurement principle and the deduced formula quickly and conveniently,thus shortening the verification time.(2)Based on the analysis of experimental requirements,the design method of cone horn lens antenna is determined,and a sample complex relative dielectric constant measurement system based on free space transmission method is proposed.The simulation model of lens antenna and measurement system is built by numerical simulation software.The gain of the antenna is increased by 8.48 d B on average after the dielectric lens is loaded,which proves the effectiveness of the lens antenna.By comparing the calculated values of the dielectric constant and loss factor of the sample with the theoretical values,the reliability of the simulation system is verified,which effectively helps the construction of the laboratory testing system.(3)On the basis of the through-reflection-transmission line calibration method,a method for correcting the amplitude and phase of the transmission parameters is proposed,and using these two methods can effectively de-embed the errors introduced by the antenna,which indicates that the correct results can be obtained only by loading the dielectric lens at the transmitting antenna,and the expensive problem of using the dual-dielectric lens detection is solved.(4)Based on the principle of free space measurement and simulation system,a wheat moisture content detection system was established and verified in the laboratory.By analyzing the relationship between the wheat dielectric constant and moisture content,a prediction model of wheat moisture content was established at a single frequency.By model forecasts and drying method are compared with the real data,the results showed that root mean square error and mean absolute error of 0.257% and 0.236% respectively,verified the accuracy of forecasting model and It provides technical support for the development of portable,low cost,green and high precision of storage wheat moisture content detection equipment.