Design Of Automatic Frequency Control System Based On Phase-Frequency Relation In Electron Paramagnetic Resonance Spectrometer

In the experiments of electron paramagnetic resonance(EPR),the resonant fre-quency of the cavity will change due to the coupling between the sample and the cavity,thermal expansion and vibration of the cavity,and other external factors.It is required for the microwave frequency to track the resonant frequency of the cavity to avoid the distortion of the EPR spectrum.An automatic frequency control(AFC)system is gen-erally included in an EPR spectrometer to meet this requirement.There are two types of AFC systems,named no-frequency-scanning AFC system and frequency-scanning AFC system.For the frequency-scanning AFC system,an extra low-frequency oscil-lating field is required and the feedback signal is modulated into the microwave signal.For the no-frequency-scanning AFC system,the low-frequency oscillating field is not required and a dc signal is the feedback.In this thesis,an AFC system is designed for the EPR spectrometer based on the relationship between microwave phase and frequency.The AFC system enables the microwave frequency to track the resonant frequency of the cavity,which is beneficial for avoiding the distortion of the EPR spectrum.Compared with the frequency-scanning AFC system,this system will be with lower Steady-state deviation and enable the spectrometer to be with higher resolution.This thesis contains three parts.In chapter 1,we introduce the principle of EPR and the EPR spectrometer.In chapter 2,we propose an AFC system based on the re-lationship between phase and frequency,and analyze theoretically how the parameters influence the performance of the system.The chapter 3 is summary and scope.