Development Of Non-destructive Testing System Based On Microwave Two-dimensional Imaging

With the deepening of research on microwave spectral resolution and perspective at home and abroad,the application value of microwave technology in the field of agricultural product testing has been paid more and more attention.The microwave characteristic spectrum of agricultural products contains rich physical information and chemical information,which provides a scientific basis for microwave technology in non-destructive testing of agricultural products.In this paper,a microwave two-dimensional non-destructive testing imaging platform was developed.The common flour was used as the research object.The flour spectral analysis and two-dimensional imaging method were explored.The related flour spectrum and imaging method were obtained.The specific research contents are as follows:(1)Principle verification of microwave non-destructive testing.Using a single-reflection free space method,1.5 cm,1.8 cm,and 2.0 cm thick flour and 1.5 cm thick mildew flour were used as samples,and a dielectric constant test was performed on the samples to be tested by means of a vector network analyzer.The dielectric constants measured under the thickness of1.5cm,1.8cm and 2.0cm are 2.512,2.529 and 2.514 respectively.The dielectric constant of moldy flour with a thickness of 1.5cm is 3.004,and the thickness error is analyzed,and the thickness error of the test is tested.<3.0%.The experimental results show that the dielectric constant of the same batch of flour with different thickness does not change much,and the dielectric constant of flour and mildew flour of the same thickness changes significantly.The feasibility of microwave non-destructive testing to distinguish between flour and mildew flour was preliminarily verified.(2)Detection platform hardware design.The hardware design of the platform is introduced from three aspects: hardware circuit design,microwave transceiver antenna design and mechanical structure design.The hardware circuit design takes STM32 MCU as the control core.The peripheral module contains four parts: minimum system,communication interface circuit,keyboard scanning circuit and AD conversion circuit.The function,design process and design ideas of each module are introduced.The designed microwave antenna resonant frequency point is 2.357 GHz,the bandwidth at-10 dB is 2.337~2.377 GHz,and the antenna size map is given.The radiation at the upper right of the microwave transceiver antenna is selected for measurement.The radiation efficiency is-90 dB at-31 dB.%,designed to meet the requirements of directional radiation from microwave antennas.The peripheral detection circuit is designed based on the completed microwave antenna,and the mechanical structure is designed by satisfying the installation requirements of the hardware circuit and the microwave transceiver antenna.(3)Detection platform software design.The STM32 MCU and the virtual instrument LabVIEW were used to develop the lower computer program and the host computer program,and realized functions such as data acquisition,data processing,data storage,image display,system automatic control and parameter setting.(4)The system performs installation and debugging and imaging test of the whole machine.First,debug the hardware and software of the device separately.After the debugging is successful,the whole machine is coordinated.Four sets of samples of no-load,metal plate,flour and talcum powder were tested by microwave with a frequency of 2.33 GHz.The peaks of the microwave spectrum of the four samples to be tested were 940-960,90-110,880-900,respectively.Between 860 and 880,the linear fit between the characteristic spectrum and the color can be performed well,and the samples can be distinguished by different colors.The experiment preliminarily verified the feasibility of the imaging platform and proposed a future improvement plan for the platform.