A Low-field Nuclear Magnetic Resonance Device For Quality Identification Of Edible Oil

With the popularity of food safety awareness and people's concern about health issues,the quality of edible oil has become a hot problem.Among many detection methods,nuclear magnetic resonance(NMR)technology has been proved to be a very valuable detection method because of its lossless,fast and safe advantages.Based on the review of the edible oil quality identification and NMR technology,a low-field nuclear magnetic resonance device was developed.Design and optimization of RF coil,design and manufacture of high-precision temperature control device for magnet,the identification and evaluation of edible oil quality and other key technical problems are focused.The results of the paper are as follows:(1)Based on the theoretical model of the solenoid coil,the parameters of the RF coil are designed for optimizing the relative SNR.The results show that when the coil diameter D and height H is 5.1mm,the diameter d is 0.2mm,the number of turn n is 12.Relative SNR of the coil reaches the maximum,which is the optimal parameter model.At the same time,the solenoid coil is designed to realize the precise control.The coil electrical parameters are also been tested and analyzed.Finally,the experiment is designed and tested for verifying the accuracy and rationality of the theoretical model.(2)The improved RF circuit matching network is proposed.By comparing the two parameters,tuning the matching range and the return loss,the advantages of the circuit is verified.The actual fabrication and testing of the circuit is completed,including circuit simulation,component selection and testing.At the same time,the selection and control of the quality factor of RF probe are studied.At the frequency of 26.09MHz,the designed RF probe is designed and manufactured.(3)Based on the working principle and technical scheme,a high-precision temperature control device is designed.The temperature control system is built and the PID parameters are debugged.Based on the temperature control target 36.0?±0.1? and temperature control system program,the system temperature control performance and temperature gradient field are optimized from the sensor position,air flow performance,insulation performance and ambient temperature.The detection of system resonance frequency is determined for completing high-precision temperature control device design.(4)Working principle and detection process of the system are built to test the relaxation time T2 and T1.Accuracy and stability of the test results are verified for the accurate identification of edible oil quality by comparing with the commercial NMR instrument Bruker Minispec mq60.Finally,based on the analysis of the detection mechanism of edible oil,NMR detection method and the pulse are designed.Three kinds of brands soybean oil,Fulinmen,Jinlongyu and Luhua,which are commonly used in the market,are chosen as the sample.The cross test model was established by detecting the relaxation curves and polar compounds.The result shows that soybean oil is not available after frying 43 hours respectively.In the designed low-field NMR devices and Bruker commercial instruments,the verification error of the polar compound value are both basically less than 15%.Therefore,low-field NMR devices can be an important potential tool in the field of edible oil detection.