High-efficiency and high signal-to-noise ratio surface nuclear magnetic resonance detection method

A ground nuclear magnetic resonance detection method, wherein the method is based on a set of transmitting coil group consisting of a direct current transmitting coil and an alternating current transmitting coil, and the direct current transmitting coil and the alternating current transmitting coil are arranged in a concentric pattern on a surface of ground;

• the method comprises the following steps:
• step 1:
• calculating a direct current pre-polarization magnetic field generated by the direct current transmitting coil in underground space and a radio frequency excitation magnetic field generated by the alternating current transmitting coil in the underground space;
• step 2:
• calculating changes of underground magnetization intensity under an alternating action of the direct current pre-polarization magnetic field and the radio frequency excitation magnetic field;
• wherein step 1 comprises the following steps:
• step 11:
• calculating a magnetic field generated by current passing through the direct current transmitting coil and the alternating current transmitting coil;
• step 12:
• calculating an overall magnetic field generated by the direct current transmitting coil and the alternating current transmitting coil;
• the direct current transmitting coil enhances a magnetization vector of hydrogen atoms in the underground space by generating a constant magnetic field, while the alternating current transmitting coil flips a spin direction of the hydrogen atoms underground by generating a radio frequency magnetic field;
• step 2 comprises the following steps:
• step 21:
• calculating an enhancement of magnetization intensity on the hydrogen atoms by the direct current pre-polarization magnetic field;
• step 22:
• calculating a flipping effect of the radio frequency excitation magnetic field on the hydrogen atoms;
• step 23:
• calculating the changes of the underground magnetization intensity:
• based on different preset direct current emission current times and alternating current emission current times, calculating a degree of enhancement of the underground magnetization intensity by the direct current pre-polarization magnetic field and the flipping of the hydrogen atoms by the radio frequency excitation magnetic field, and obtaining a curve of underground magnetization intensity changes;
• in a whole pulse sequence, direct current pulse, alternating current pulse and pulse interval are alternated, wherein a duration of the direct current pulse is in a range of several hundred ms, a duration of the alternating current pulse is in a range of tens of ms, the pulse interval is in the range of tens of ms, and a time of a single set of pulses is within 1 second, by adjusting emission time of the direct current pulse, emission time of the alternating current pulse, and the pulse interval time, controlling the underground magnetization intensity to gradually accumulate and stabilize within a certain range.