Actual Electromagnetic Environment In The Low Field Pulsed Nmr Signal Analysis And Computation

Since the signal of low-field pulse NMR (nuclear magnetic resonance) is very weak and of poor SNR (Signal to Noise Ratio), however the static and RF (radio frequency) magnetic field directly dominate the magnitude of signal, so the design of static and RF field is key to low field NMR apparatus. This paper discusses the construction of simulation platform in low field NMR according to the theories of electrocircuit, NMR and FEM (Finite Element Method), and put forward a method to compensate of the inhomegeneity of static field.In term of the differential equation of NMR RF transmit circuit and BLOCH equation,this paper analyses the motion of macro magnetization in the result of transient circuit effect and point out the influence of RF field magnitude and Q of electrocircuit to the bandwidth of RF field irradiation.After the calculation of static and RF magnetic field of NMR apparatus using FEM method, the simulation result of FID is presented in conformity to signal reception principle of NMR .Experimental FID is processed with wavelet and line prediction theory and compared with the simulation result. The feasibility and confinement of simulation is discussed.In order to conquer the inhomogeneity of static field and promote the bandwidth of RF irradiation ,a so-called method of RF compensation is advanced. This method is realized using coil design theory of target field method. Design example and result are given in the end.