Evaluation And Application Research Of Unilateral Fully-opened Nuclear Magnetic Resonance System Based On A Half Ring Halbach

Nuclear magnetic resonance is an interaction between the spin nuclear system and the RF plus.Traditional nuclear magnetic resonance instruments including the spectrometer?imager and analyzer depend on the highly uniform magnetic field,small samples are detected in a large magnet(permanent magnet or superconducting coil)which can produces a highly uniform magnetic field,the system is expensive,bulky,heavy and inconvenience mobile,and the shape and size of the sample are restricted by the fully enclosed or partly closed magnet structure.For the unconventional NMR(Nuclear Magnetic Resonance)the under test object can be put on one side of the magnet or surround the magnet and it broke the traditional detection mode that the samples are surrounded by the magnet.Unilateral NMR is a main form of unconventional NMR.There are two main types: bar magnet and u-shaped magnet which being armed with corresponding rf coil,spectrometer,radio frequency power amplifier and the preamplifier electronics components can make up a set of unilateral NMR system.Unilateral NMR system has characteristics of simple structure,low cost,portable,real-time detection.The test sample can be directly on the surface of the magnet without complex pretreatment.It can realize nondestructive pollution-free.Moreover unilateral magnet has natural constant gradient magnetic field which can easily carry out diffusion coefficient measurement.This article has conducted an exploration in the analysis field with unilateral nuclear NMR technology,being aimed at it can be mature and widely used in on-line measurement,quality supervision,etc in the future.This paper bases on the half ring unilateral Halbach array magnet,builts a set of unilateral NMR system,calibrates the parameters of the syatem,such as detecting depth,magnetic field intensity and gradient,explores the optimal acquisition parameters,on the basis of the calibration,determine oil content,tests water samples diffusion-relaxation,evaluates the yogurt quality in the box in room temperature,and rapid tests the adulteration milk.Results show that the oil-water ratio can be measured based on the relaxation spectrum peak position and peak area;that for different echo time the CPMG(Carr-Purcell-Meiboom-Gill)decay curves are different and the difference is caused by diffusion;that at a constant gradient magnetic field with the increases of adulteration ratio the T2 CPMG increased gradually and that after relaxation correction T2 peak position changes of boxed yogurt sample can indirectly response to its freshness.Unilateral NMR technology with its unique advantage in the emerging field of NMR analysis,such as food quality and safety,cultural relic site detection has great application prospect.Unilateral NMR technology with its unique advantage in the emerging field of NMR analysis,such as food quality and safety,cultural relic site detection has great application prospect.