Research And Design On Measurement System Based On Resonant Cavity Perturbation Method

The technology of microwave measurement is a new kind of nondestructivetexting technology that was developed after the ultrasonic wave, infrared, laser andray of detection. It has been widely used in science technology, economic, social lifeand other fields. Perturbation method is a common used method in microwavemeasurement. To measure the changes of frequency shift ascertain the parameter ofmeasured medium, in this way microwave can be used in the non-electricitymeasurement as a sensor. This paper designs the whole plan of resonator measuringsystem which sets the measurement of glucose solution concentration as an examplebased on perturbation principle. The design ideas of system, hardware structure,program realization and results analysis, have been given in detail. In thismeasurement system the single-chip computer AT89C52is used as the control and theprocessing core. It mainly includes the cavity measuring module, resonance frequencytracking module and equal-precision frequency measurement module.The measuring principle of perturbation method is discussed in detail in this paper,the relationship between resonance frequency shift and solution concentration isdeduced, the microwave cavity used for measuring solution concentration is designed,the cavity size and coupling structure are optimized in the electromagnetic simulationsoftware, and the cavity loading solution using numerical simulation method isanalyzed. The response laws of cavity on frequency modulation signal is obtained andthe resonant frequency automatic tracking module based on this laws is designed, thehardware circuit of tracking module is designed and analyzed. According to amplitudeand phase discrimination of the demodulation signal, we use MCU to control outputvoltage of D/A converter and make the output carrier frequency of VCO consistentwith the resonance frequency, which tracking accuracy can get to KHz. Theequal-precision frequency measurement module used for measuring resonancefrequency shift is designed. Through hardware description language FPGA softwaredesign, compile simulation and sequential analysis can be carried out, the accuracy offrequency measurement can get to10-7. We obtain the relationship between theresonance frequency shift and glucose solution through simulation which verify thefeasibility of this method. In the end of this dissertation, the main program of systemis given and achieves the measurement system control base on the single-chipcomputer.