Research And Realization Of EPR Function In Low-field DNP Spectrometer

A microwave bridge is brought in our home-built DNP spectrometer to generate microwave signal to saturate electron transition in DNP experiment and obtain EPR signal, for achieving the spectrometer with multi-function such as NMR/DNP/EPR/MRI. The microwave transmitter of the DNP spectrometer comes to be integrated by the design of microwave bridge, as well as the realization of EPR function in DNP spectrometer. The microwave bridge includes two parts:transmitter and receiver. The transmitter is able to generate high spectrum purity and high dynamic range continues microwave, as well as pulse sequence with the fast modulation of the frequency, phase and amplitude. The receiver includes two channels of pulse mode and continues wave mode, a superheterodyne digital intermediate frequency receiver is used in the pulse channel to improve the SNR extremely with a simple structure; and a phase-sensitive detector is applied to the continues wave channel as usual. In this paper, we designed a microwave bridge with a high spectrum purity and high dynamic range transmitter, and a low noise figure detector by structure designing, circuit simulating and system measuring. And, experiments of DNP and continuous wave EPR are conducted to verify the reliability of the microwave bridge.We have done several related works about the microwave bridge designing as follows:1) The design scheme and performance index of the microwave bridge was specified, according to the demand of the EPR and DNP experiments.2) Circuit designed, system optimized, and electromagnetic compatibility designed by ADS and other design soft, based on the design scheme.3) Tested and debugged the circuit board until we got the optimal performance index4) Experiments of DNP and continuous wave EPR have been conducted to verify the reliability of microwave bridge in the basis of DNP spectrometer.