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Low field pulsed NMR experiment data receiving and processing

Is now time for tj (the parameter obtained by the system), the first j +1 a peak time for '.... Take a parameter, in the time interval [tj +, tj +. I] on the search for maximum signal peak point, the point is the corresponding j-a string echo peaks. Parameter values is more important: the value is small, the search interval range, may be a larger range of random noise in the amplitude of the echo taking into peak; tr value is too large, the search interval is too small, it may be because the echo peak points have been taken by mistake overflow interval. Select a time when the actual signal to noise ratio to be combined with appropriate adjustments for the analog quadrature demodulation system, it is desirable reference value: = (tj +1 a tj) / 3 (3) digital quadrature demodulation system can be greater than the reference value value. With fine sand samples for the experiment, the echo string to extract the peak signal shown in Figure 9. Figure 9 echo string of fine sand of 3.5 peak fitting of wavelet multi-resolution wavelet analysis (MRA) is the signal level at the time a foot ModernScientificInstruments2O073 different resolution levels in the wavelet decomposition of the results is the low-frequency signal decomposition component and high frequency components. When the decomposition level enough,[link widoczny dla zalogowanych], low frequency signal fully reflects the trend. On this basis, we can use wavelet decomposition to fit the echo string. Since the peak echo signal extraction is equivalent to string non-uniform sampling, so needed before wavelet decomposition of the signal interpolation, making it a uniform sampling signal. The first samples of fine sand in Figure 9 echo train signal to cubic spline interpolation, and then sym8 lO layer wavelet decomposition, by the first layer of low coefficient of lO single reconstructed to fit the signal, the results shown in Figure lO. Figure string of fine curves echo signal (by interpolation), thick black curve fitting curve for the wavelet. Figure 10 Wavelet fitting echo string 【6J 3.6 NMR spectrum of the signal solution is based on quantitative analysis of signal intensity contained in the sample proportional to the number of nuclear spin. This information is from the original series of the peak echo signal is extracted, the extract after the echo signal is one of the key technologies of the original multi-echo inversion index of relaxation spectrum, also known as solution spectrum. Observed spin-echo NMR signal series Y (t) is a single exponential decay by a series of laws to meet the superposition of the signal,[link widoczny dla zalogowanych], while the actual measurement process,[link widoczny dla zalogowanych], inevitably mixed with the noise, the observed NMR signal Y (t) that can be unified into the following form:), v = e) (4) where, for the transverse relaxation time, corresponding to the signal amplitude value; mi and is a measure of the free induction decay signals can identify the shortest and the longest transverse relaxation time; (?) for the noise. Magnetic resonance analysis, the key is how to equation (4) solved the corresponding transverse relaxation time and the extent of its share, and that out of the way through the icon, this process is called unfolding. Modern scientific instruments 20,073 unfolding algorithm for the current application in practical systems exist some shortcomings, we first solve the integral equation inversion staff to derive a low field pulsed NMR for multi-exponential transverse relaxation counter An unfolding algorithm for speech L1j. The algorithm was used for experimental peanut samples to obtain the spectrum (Fig. l1). By solving the spectrum compared with the standard sample spectra can be obtained by the quantitative calibration of specific substances. Figure 11 Experimental Peanut z spectrum 4 Conclusion In this paper, experimental low field pulsed NMR system data receiving and processing methods have been made some research into the product design for the instrument basis. The further improvement of the system will focus on the following directions: combine the latest digital electronic technology system to further digital signal processing using modern technology to further improve the signal to noise ratio and more accurate and universal applicability of the solution spectrum algorithm. References [1] Wang Lili. Transverse relaxation in low field pulsed NMR signal unfolding algorithm. Beijing: Chinese Academy master's degree thesis, 2005:1 [2] Li Jie, Tang Xiaoquan, Zhang Yiming and so on. Experimental NMR data analysis platform. Electronic Measurement Technology, 2004 (2) :1-2 [3] Wang Jinshan. Nuclear magnetic resonance spectrometer and experimental technologies. Beijing: Mechanical Industry Press ,[link widoczny dla zalogowanych],1982:209-214 [4] DonohoDL. De-noisingbysoft-thresholding. IEEE, 1995,[link widoczny dla zalogowanych],41 (3) :613-625 [5] Sudan. Low field pulsed NMR signal digital reception platform, Analysis and Research. Beijing: Chinese Academy Master Thesis, 2002 [6] Wang Lili, Zhang Yiming, Chen Jizhong. Transverse relaxation in low field pulsed NMR signal inversion analysis. Analytical Instruments, 2005 (4): 8 A l245
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