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Method for detecting ground nuclear magnetic off-resonance in Larmor frequency unknown condition

A technology of Larmor frequency and detection method, applied in electron magnetic resonance/nuclear magnetic resonance detection, etc., can solve the problems of accurate acquisition of off-resonance signals, large phase error of MRS signals, etc., and achieve accurate MRS amplitude and phase information Effect

Active Publication Date: 2016-10-12
JILIN UNIV
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Problems solved by technology

[0006] The technical problem to be solved by the present invention is to provide an unknown Larmor frequency for ground nuclear magnetic off-resonance detection method to solve the MRS signal phase error obtained by the traditional resonance detection method due to the ubiquity of the off-resonance phenomenon under complex geological conditions. Big problem, and difficult problem of accurate acquisition of off-resonance signal at unknown Larmor frequency

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  • Method for detecting ground nuclear magnetic off-resonance in Larmor frequency unknown condition
  • Method for detecting ground nuclear magnetic off-resonance in Larmor frequency unknown condition
  • Method for detecting ground nuclear magnetic off-resonance in Larmor frequency unknown condition

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Embodiment 1

[0053] The block diagram of Embodiment 1 of a ground NMR detection method for an unknown Larmor frequency of the present invention is as follows figure 1 with 2 shown. When the geological conditions are complex and the Larmor frequency is unknown, the specific steps of this embodiment are as follows:

[0054] Step 1: Estimate the Larmor frequency f L ;

[0055] When the geological conditions are complicated, the Larmor frequency is difficult to estimate accurately. Although the present invention does not need the real Larmor frequency, its estimated value cannot be too different from the real value. For this reason, the present invention proposes the following two estimated Larmor frequencies: Er frequency f L The scheme is as follows:

[0056] Scheme 11: Use a magnetometer to measure the geomagnetic field at multiple locations at different times, and then calculate the average value as the estimated value f of the Larmor frequency L ;

[0057] Scheme 12: When the magne...

Embodiment 2

[0080] The block diagram of Embodiment 2 of a ground NMR detection method with an unknown Larmor frequency of the present invention is as follows figure 1 with 5 shown. Because the earth's magnetic field changes with time, the Larmor frequency also changes accordingly, so when the Larmor frequency is unstable, the specific steps of this embodiment are as follows:

[0081] Step 1: Estimate the Larmor frequency f L ;

[0082] Because the earth's magnetic field changes with time, the Larmor frequency also changes thereupon, and the Larmor frequency is unstable. Although the present invention does not need the real Larmor frequency, its estimated value cannot differ too much from the real value. For this reason , the present invention proposes the following two estimated Larmor frequencies f L The scheme is as follows:

[0083] Scheme 11: Use a magnetometer to measure the geomagnetic field at multiple locations at different times, and then calculate the average value as the e...

Embodiment 3

[0107] The block diagram of Embodiment 3 of a ground NMR detection method with an unknown Larmor frequency of the present invention is as follows figure 1 with 6 shown. When the temporal and spatial distribution of the geomagnetic field in the measurement area is not uniform, that is, f Larmor There are multiple values ​​at the same time, and f Larmor Present certain distribution, the specific steps of this embodiment are as follows:

[0108] Step 1: Estimate the Larmor frequency f L ;

[0109] When the temporal and spatial distribution of the geomagnetic field in the measurement area is not uniform, that is, f Larmor There are multiple values ​​at the same time, and f Larmor Present a certain distribution, although the present invention does not need the real Larmor frequency, its estimated value cannot differ too much from the real value, for this reason, the present invention proposes the following two kinds of estimated Larmor frequency f L The scheme is as follows:...

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Abstract

The invention relates to a method for detecting the ground nuclear magnetic off-resonance in the Larmor frequency unknown condition. According to the conventional nuclear magnetic resonance detection method, the transmitting frequency must be the same with the Larmor frequency. However, due to the non-uniform space-time distribution of the earth 's magnetic field, the interference of the magnetic field and the influence of strong electromagnetic noises, the Larmor frequency is difficult to be accurately obtained. Therefore, the off-resonance phenomenon exists widely. When the Larmor frequency is unknown, the frequency offset is also unknown. In this way, off-resonance signals cannot be effectively acquired. According to the technical scheme of the invention, two transmission pulses form a triggered sequence for the detection of the off-resonance phenomenon. The differences of two transmission frequencies fT1 and fT2 between the pre-estimated value of the Larmor frequency are + / - delta fset (preset frequency offset) respectively. The real parts of off-resonance signals obtained during the two transmitting processes are added up, while the imaginary parts of the off-resonance signals obtained during the two transmitting processes are subtracted. The superposed result corrects the influence of the unknown Larmor frequency, so that off-resonance signals with the frequency offset delta fset are obtained. According to the technical scheme of the invention, off-resonance signals are accurately obtained when the Larmor frequency is unknown. Therefore, the problem in the prior art that the conventional resonance detection method cannot be applied in the complex environment can be solved.

Description

technical field [0001] The invention relates to the measurement field of nuclear magnetic resonance off-resonance signals, in particular to a ground nuclear magnetic off-resonance detection method with unknown Larmor frequency. Background technique [0002] Nuclear Magnetic Resonance (MRS) technology is widely used in the fields of water resources assessment and disaster water exploration because of its advantages of direct and quantitative detection of groundwater. The principle of the groundwater NMR detection method is: by emitting an artificial alternating magnetic field to excite the hydrogen protons in the groundwater and generate relaxation signals to directly determine the occurrence status information of the groundwater such as the depth, thickness, water content and pore size of the aquifer. The emission frequency of the artificial magnetic field is determined by the earth's magnetic field B 0 It is determined that when the emission frequency is equal to the Larmo...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01V3/14
CPCG01V3/14
Inventor 蒋川东刘骏妍田宝凤易晓峰杜官峰张健
Owner JILIN UNIV
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