Research Of Measurement Circuit Of Dielectric Constant And Dielectric Loss

With the rapid development of communication industry and electronic industry, make people more and more attention on microwave materials,people are eager to find a way to measure the properties of the dielectric materials fast and accurately. The main electric parameters of the microwave materials are permittivity and dielectric loss. The researchers have worked out many methods to measure the dielectric of different permittivity.In this paper, a digital dielectric constant and dielectric loss measurement circuit based on resonance method(variable Q value method) was designed and achieved. The physical system can realize the integration of functions of automatic collection,processing, output voltage signal data generated by medium resonance in the resonant circuit, and receive a local user operation command through a serial port. The embedded systems based on ARM realized the hardware functions, The system used STM32 series chips based on Cortex-M3 as controlling core, produced high frequency sinusoidal signal with the direct frequency synthesis module(DDS) cooperation, realized the functions of the high frequency signal filtering and power amplification with the signal processing module cooperation, got high Q value in the resonant circuit, realized the functions of data acquisition and processing with data acquisition module cooperation, communication module sent data to display,keying module achieved the function of user interaction. Using standard C language realized the system functions of software, The system used Keil developing kit to organize program processes and functions and achieved data acquisition, data processing, screen display, key response etc, and realized the functions of controlling frequency digital lock, setting standard test point, searching resonance point automatically, numerical display.Measuring the permittivity and dielectric loss based on variable Q value method, using the modern instrument technology that embedded computer was introduced, which makes the whole electrical system has the advantage of simple operation, good repeatability, data visual display etc, provided a powerful guarantee for measuring the permittivity and electric loss tangent.