Automatic Measurement System Of Complex Permittivity And Permeability For Microwave Absorbing Materials Using Coaxial Transmission/reflection Method

The measurement of electromagnetic parameters of microwave absorbing materials has been an important issue in the field of electromagnetic field and microwave engineering. With the development of stealth materials technology, the computer aided optimization design of microwave absorbing materials also requires accurate measurement of materials’ electromagnetic parameters at microwave frequencies. It is of important practical value to build the convenient and reliable measurement system of electromagnetic parameters for microwave absorbing materials.In this thesis, the scattering matrix of two-port microwave network model was analyzed. The main parameters to be measured were confirmed based on the measurement principle of coaxial line transmission/reflection method. Then the software and hardware of automatic microwave electromagnetic parameters measurement system is set up using virtual instrument technology. The measurement requirements of the coaxial test method specified in ASTM D7449/D7449M-08 was consulted. At last, the errors in the measurement system are analyzed and discussed.Hardware components including vector network analyzer, computer, GPIB-USB controller, coaxial line and specimen holder are chosen according to hardware fixture and measurement requirements. Data acquisition for measurement is implemented by a vector network analyzer(HP8720B) controlled by a Lab VIEW program via VISA interface. Event structure and state engine design pattern is adopted and modular design method is used in the software of the system, which is able to complete automatic measurement, instrument configuration, measured data processing and data saving through interface module, drive module, data collecting and dealing module and data saving module programming. The scattering parameters of the specimen in the coaxial line are collected and the complex permittivity and permeability is calculated automatically by the program. The program written by LabVIEW is featured with friendly interface, good operation and strong scalability.The system is able to measure electromagnetic parameters of material in 2~18 GHz band. The measurement results of paraffin, silicone rubber and a microwave absorbing material indicates that this system is accurate and reliable.