Low-loss Flat-panel Materials Detection System

Microwave dielectric materials are widely used in microwave communications, electronics and other fields. The research and selection of dielectric substrate must base on the electrical properties parameters of materials during microwave circuit. So it is great significance to test the electrical properties parameters of dielectric material. In the production process of dielectric material, in order to maintain the integrity of dielectric material, it is an important research topic to achieve non-contact, non-destructive online test of the electrical properties parameters of materials.One of the basic electrical properties parameters of materials is complex permittivity, we make some research on the online testing of this constant in this paper. we used multi-split cylindrical cavity for testing the complex permittivity of material, and selected the TE011 resonant mode, TE013 resonant mode, the frequency range up to 4 GHz ~ 6GHz.First of all, in theory, the electric and magnetic field expressions of multi-split cylindrical cavity and resonant cavity conditions were obtained based on mode matching method, and the functional relationship between the frequency f, quality factor Q and the complex permittivity of test samples was established .Secondly, according to the distribution of the resonant mode, the split cavity was optimized and designed, HFSS software was applied to do some relative simulation, then the cavity was manufactured and tested. The 4GHz～6GHz signal source was built, microwave detector and USB data acquisition device were bought, then the test system was built and test software was written. The parallel port mode was used to control the microwave signal source; LabView software was used to control the data acquisition process; according to the function between the frequency, quality factor and the power, the form of the least square method was used to process data, this method can obtain the frequency and quality factor of resonant system quickly, and simplify the data processing and improve the test speed.Finally, we used the built test system to test the PTFE, expanded polystyrene standard sample, and obtained the complex dielectric constant. In this paper, multi-split cylindrical cavity overcame the shortcomings of the conventional split cylindrical cavity, during testing, the conventional split cylindrical cavity must contact with the sample, and it can't use online testing, or when used in online testing, the tested sample will be worn. The build of microwave source control and power detection system is simple and economy, which was conducive to engineering applications.