阅读说明：本技术 一种核磁共振地下水分层探测装置及探测方法 (Nuclear magnetic resonance underground water stratification detection device and detection method ) 是由 万玲 陈超 汪满满 周坤 林婷婷 腾飞 于 2020-05-06 设计创作，主要内容包括：本发明涉及一种核磁共振地下水分层探测装置及探测方法,包括上位机与主控单元、浅层探测发射单元、深层探测发射单元和核磁共振信号采集单元。在浅层区域,通过预极化梯度场和可调交变磁场共同作用,进行浅层地下水分层探测；在深层区域,通过SPWM逆变产生交变脉冲进行深层地下水分层探测。并对核磁共振信号进行包络与全波采集,将包络信号进行现场实时数字消噪,全波信号进行实时存储。本发明在浅层探测时利用预极化梯度场和可调交变磁场提升了探测信噪比,减小了发射能量的损耗；在深层探测时利用SPWM逆变进行交变脉冲激发,无需进行配谐激发,减小了能释时间,提升了探测效率；将包络信号进行数字消噪,提升了现场观测信号的质量。(The invention relates to a nuclear magnetic resonance underground water stratification detection device and a nuclear magnetic resonance underground water stratification detection method. In the shallow region, shallow groundwater layered detection is carried out through the combined action of a pre-polarization gradient field and an adjustable alternating magnetic field; in the deep layer area, alternating pulse is generated through SPWM inversion to carry out deep groundwater layering detection. Envelope and full wave acquisition are carried out on the nuclear magnetic resonance signals, on-site real-time digital noise elimination is carried out on the envelope signals, and real-time storage is carried out on the full wave signals. The invention utilizes the pre-polarization gradient field and the adjustable alternating magnetic field to improve the detection signal-to-noise ratio and reduce the loss of the transmitting energy during shallow layer detection; during deep detection, alternating pulse excitation is carried out by utilizing SPWM inversion, harmonic matching excitation is not needed, energy release time is shortened, and detection efficiency is improved; and the envelope signal is subjected to digital noise elimination, so that the quality of a field observation signal is improved.)

1. A nuclear magnetic resonance groundwater stratification detection apparatus, the apparatus comprising:

the upper computer, the main control unit, the shallow layer detection emission unit, the deep layer detection emission unit and the nuclear magnetic resonance signal acquisition unit,

the shallow detection unit provides a variable pre-polarization gradient field and alternating excitation pulses for shallow detection, and shallow detection alternating excitation pulses with small amplitude are generated on a shallow detection alternating pulse transmitting coil to realize layered excitation of hydrogen protons in shallow groundwater;

the deep detection transmitting unit provides larger alternating excitation current for the deep detection alternating pulse transmitting coil during deep detection so as to realize layered excitation of hydrogen protons in deep groundwater;

the nuclear magnetic resonance signal acquisition unit acquires envelope signals and full-wave signals at the same time, calculates the envelope signals of the acquired nuclear magnetic resonance envelope signals by using the digital signal processing unit, and performs digital noise elimination processing on the calculated envelope signals;

the upper computer and the main control unit are responsible for configuring transmitting parameters for the shallow layer detecting and transmitting unit and the deep layer detecting and transmitting unit and configuring receiving parameters for the nuclear magnetic resonance signal acquisition unit;

and meanwhile, the upper computer is responsible for storing the acquired nuclear magnetic common full-wave signals in real time and displaying the nuclear magnetic resonance envelope signals subjected to digital denoising.

2. The apparatus of claim 1, wherein the shallow detection transmitting unit provides a variable pre-polarization gradient field through the pre-polarization gradient field generating device, generates the variable pre-polarization gradient field on the shallow detection pre-polarization transmitting coil by controlling the high-power controllable dc power supply using the pre-polarization transmitting circuit, and generates the alternating digital signal required for shallow detection using the digital signal processing unit by generating the alternating pulse on the shallow detection alternating pulse transmitting coil using the alternating excitation pulse generating device, wherein the pre-polarization gradient field generating device comprises: the system comprises a pre-polarized field emission time sequence control module, a pre-polarized field emission driving circuit, a pre-polarized field high-power switch module, a pre-polarized field emission control circuit, a pre-polarized gradient field intensity control module, a high-power controllable direct-current power supply and a shallow detection pre-polarized current emission coil, wherein an upper computer and a main control unit configure emission parameters for the pre-polarized field emission time sequence control module, the pre-polarized field emission time sequence control module generates a pre-polarized emission time sequence control signal, controls the on and off of the pre-polarized field emission high-power switch module after power amplification is carried out by the pre-polarized field emission driving circuit, and generates pre-polarized emission current on the shallow pre-polarized current emission coil through the pre-polarized field emission control circuit; meanwhile, the pre-polarization gradient field intensity control module adjusts and controls the high-power controllable direct-current power supply in real time according to different detection depths of the shallow detection area to provide required pre-polarization field emission energy for the pre-polarization field emission control circuit; and after the pre-polarization field emission is finished, transmitting alternating excitation pulses to excite the underground water of the shallow detection area after adiabatic shutdown.

3. The apparatus of claim 2, wherein the alternating excitation pulse generating means in the shallow probe transmitting unit comprises: the device comprises an alternating pulse parameter calculation module, an alternating pulse generation module, an alternating pulse digital-to-analog conversion module, an alternating pulse power amplification module and a shallow detection alternating pulse transmitting coil; the alternating pulse parameter calculation module and the alternating pulse generation module are positioned in the digital signal processing unit A and are responsible for responding to alternating pulse transmitting parameters configured by the upper computer and the main control unit, the alternating pulse parameter calculation module calculates the frequency and the phase of a transmitted sinusoidal signal, then the alternating pulse generation module generates a sinusoidal digital signal with fixed amplitude and corresponding frequency and phase, and the alternating pulse digital-to-analog conversion module converts the generated digital signal into an analog sinusoidal signal; according to different detection depths in the shallow detection area, the alternating pulse power amplification module amplifies the simulated sinusoidal signal into an excitation signal with the required detection depth, and generates alternating excitation pulses with high precision and small amplitude on the shallow detection alternating pulse emission coil.

4. The device of claim 1, wherein the deep detection transmitting unit comprises an SPWM waveform control signal generating module, an alternating pulse transmission driving circuit, an alternating pulse SPWM inverting circuit, an energy storage capacitor charging control module, a controllable constant current source, a high-voltage energy storage capacitor, an alternating pulse LC filter circuit, a deep detection alternating pulse transmitting coil, a deep detection transmitting voltage and transmitting current collecting module and a PID control module; the SPWM waveform control signal generation module is positioned in the digital signal processing unit B and is responsible for responding to deep transmission configuration parameters from an upper computer and a main control unit, calculating corresponding carrier waves and modulation waves according to the required transmission duration and transmission frequency of alternating pulses, and generating SPWM waveform control signals required by the SPWM inverter circuit according to a regular sampling method; the alternating pulse emission driving circuit amplifies the power of the SPWM waveform control signal, controls the conduction and the interception of a switching tube in the alternating pulse SPWM inverter circuit, and the alternating pulse SPWM inverter circuit adopts a unipolar inversion control mode; the energy storage capacitor charging control module changes the charging voltage of the high-voltage energy storage capacitor by controlling the output current of the controllable constant current source, provides direct-current voltages with different amplitudes for the alternating pulse SPWM inverter circuit to obtain inverter currents with different amplitudes, and carries out layered detection on the alternating excitation pulses emitted by the deep detection area; the alternating pulse LC filter circuit filters out higher harmonics in the SPWM excitation pulse to obtain a smooth sine alternating excitation pulse, and the smooth sine alternating excitation pulse is transmitted through a deep detection alternating pulse transmitting coil; the deep detection emission voltage and emission current acquisition module is responsible for acquiring excitation voltages at two ends of the high-voltage energy storage capacitor and emission currents in the alternating pulse emission coil and uploading the excitation voltages and the emission currents to the PID control module located in the digital signal processor B, the PID control module compares the acquired emission voltages and the acquired emission currents with preset emission voltages and emission current values to obtain deviation values, and the pulse width of the output SPWM waveform is adjusted through the PID control module to adjust the emission alternating current waveform in real time.

5. The apparatus of claim 1, wherein the portion of the nuclear magnetic resonance signal acquisition unit that envelops the signal acquisition comprises: the device comprises a nuclear magnetic resonance envelope signal acquisition magnetic sensor, an envelope signal preamplifier circuit, an envelope signal AD acquisition circuit, an envelope signal calculation module and an envelope signal denoising module; the nuclear magnetic resonance envelope signal magnetic sensor is used for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the envelope signal preamplifier is used for amplifying the collected signals, and the envelope signal AD collection circuit is used for carrying out envelope collection on the amplified signals; the envelope signal computing module and the envelope signal noise elimination module are arranged in the digital signal processing unit C, the envelope signal computing module computes the acquired envelope signal, and spike pulse noise, power frequency harmonic noise and random noise are sequentially filtered by the envelope signal noise elimination module; and the digital signal processing unit C uploads the envelope signal subjected to noise elimination to an upper computer in real time to display the envelope signal in a time-frequency domain.

6. The apparatus of claim 1, wherein the full-wave signal acquisition section of the nuclear magnetic resonance signal acquisition unit comprises: the device comprises a nuclear magnetic resonance full-wave signal acquisition magnetic sensor, a full-wave signal pre-amplification circuit, a full-wave signal band-pass filter circuit, a full-wave signal secondary amplification circuit and a nuclear magnetic resonance full-wave signal AD acquisition module; the nuclear magnetic resonance full-wave signal magnetic sensor is used for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the full-wave signal preamplifier is used for amplifying the collected signals, the amplified signals are subjected to analog filtering by the full-wave signal band-pass filter circuit, and after being amplified by the full-wave signal secondary amplification circuit, the full-wave acquisition is carried out by using the nuclear magnetic resonance full-wave signal AD acquisition module; and uploading the collected full-wave signals to an upper computer for real-time storage.

7. A nuclear magnetic resonance underground water layering detection method is characterized by comprising the following steps:

judging the detection depth, and selecting a shallow detection mode, a deep detection mode or a full depth detection mode according to the detection depth;

if the mode is the full-depth detection mode, the method comprises the following steps:

configuring parameters for transmitting and receiving in a full-depth detection mode to a main control unit through an upper computer;

the main control unit respectively configures corresponding parameters to a shallow detection transmitting unit, a deep detection transmitting unit and a nuclear magnetic resonance signal acquisition unit, wherein the transmitting parameter of the shallow detection transmitting unit is configured to be the detection depth of 0-10 meters underground, the transmitting parameter of the deep detection transmitting unit is configured to be the detection depth of 10 meters underground, and the receiving parameter of the nuclear magnetic resonance signal acquisition unit is configured to be a shallow and deep combined detection mode;

carrying out layered detection from a shallow detection area to a deep detection area, firstly transmitting a shallow pre-polarization gradient field in the shallow detection area, transmitting shallow alternating pulses after adiabatic shutdown, and collecting nuclear magnetic resonance signals after the alternating pulses are transmitted;

after the shallow detection area is detected, deep detection area detection is carried out, a deep detection SPWM alternating pulse is transmitted firstly, and nuclear magnetic resonance signal acquisition is carried out after the deep detection SPWM alternating pulse is transmitted;

if the underground shallow layer detection mode is carried out, the method comprises the following steps:

configuring parameters for transmitting and receiving in a shallow detection mode to a main control unit through an upper computer, and configuring corresponding parameters to the shallow detection transmitting unit and the nuclear magnetic resonance signal acquisition unit by the main control unit;

according to actual detection requirements, the emission parameters of the shallow detection emission unit are configured to corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be in a shallow detection receiving mode;

carrying out layered detection in a shallow detection area;

transmitting a shallow pre-polarization gradient field, transmitting shallow alternating pulses after adiabatic shutdown, and acquiring nuclear magnetic resonance signals after the alternating pulses are transmitted;

if the underground deep layer detection mode is carried out, the method comprises the following steps:

configuring parameters for transmitting and receiving in a deep detection mode to a main control unit through an upper computer, and configuring corresponding parameters to the deep detection transmitting unit and the nuclear magnetic resonance signal acquisition unit by the main control unit;

according to actual detection requirements, the emission parameters of the deep detection emission unit are configured to corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be in a deep detection receiving mode;

carrying out layered detection in the deep detection area;

the method comprises the steps of firstly emitting deep detection SPWM alternating pulses, and carrying out nuclear magnetic resonance signal acquisition after the deep detection SPWM alternating pulses are emitted.

Technical Field

The invention belongs to the field of research of geophysical exploration technology, and relates to a nuclear magnetic resonance underground water stratification detection device and a detection method.

Background

The nuclear magnetic resonance technology can be used for directly qualitatively and quantitatively detecting underground hydrogeological information and is widely applied to the field of geophysical detection. When nuclear magnetic resonance underground water detection is carried out, the layered measurement of the water content of underground water in a detection area can be realized by exciting different alternating pulse moment currents. Although the traditional nuclear magnetic resonance detector can realize the measurement of water content of various underground depths, when shallow layer detection is carried out, the detection signal-to-noise ratio is low, and an effective magnetic resonance signal is difficult to obtain; when deep layer detection is carried out, large excitation current needs to be emitted through external harmonic matching, so that the detection efficiency is reduced, and the energy release time is prolonged; and when the nuclear magnetic resonance signal is measured in a layered mode, an effective nuclear magnetic resonance signal is difficult to observe in a detection field, and the detection process is seriously influenced.

CN102053280A discloses a nuclear magnetic resonance underground water detection system with a reference coil and a detection method. Synchronously acquiring full waveform data of the nuclear magnetic resonance signal in the transmitting/receiving coil and the noise signal in the reference coil through a multi-path A/D acquisition unit, the optimal position and the number of the reference coils are distributed by calculating the maximum correlation between the noise signals acquired by the reference coils and the nuclear magnetic resonance signals, under the condition that the statistical characteristics of signals and noise are unknown, a variable-step self-adaptive algorithm is adopted, noise in nuclear magnetic resonance signals obtained by a transmitting/receiving coil is cancelled to the maximum extent, extraction of the nuclear magnetic resonance signals under multi-field source complex noise interference is realized, the problems that nuclear magnetic resonance detection in the neighborhood of a village and the surrounding area of a city is interfered more and various interference noise data are difficult to separate are effectively solved, the anti-interference performance of an instrument is improved, and a reliable detection device and a method are provided for finding underground water in the neighborhood of the village and the surrounding area of the city. Although the method can solve the problem that the interference noise data in areas with relatively serious noise levels are difficult to separate to a certain extent, the amplitude of the nuclear magnetic resonance signal in the shallow detection area is not effectively enhanced, the nuclear magnetic resonance signal with high signal-to-noise ratio is difficult to obtain in a complex noise environment, and effective data cannot be provided for subsequent accurate inversion. In addition, the method can only collect full-wave data of the nuclear magnetic resonance signal, can not carry out on-site real-time noise elimination on the collected data, is difficult to obtain an effective on-site nuclear magnetic resonance signal, and can not judge whether the collected signal is the nuclear magnetic resonance signal in real time when a detection experiment is carried out, so that the detection efficiency is influenced.

CN107966737A discloses an active field nuclear magnetic resonance detection device and detection method. The pre-polarization control circuit controls the transmitting coil to generate a pre-polarization magnetic field larger than a natural geomagnetic field through a selector switch; the release circuit is connected with the transmitting coil through a switch and used for quickly switching off the circuit to release the residual energy in the transmitting coil; and the alternating magnetic field control circuit controls the transmitting coil to generate an alternating magnetic field to excite the target water body through the change-over switch. The main control unit: and sending out a control signal to switch and control the pre-polarization control circuit, the release circuit and the alternating magnetic field control circuit. The invention combines a prepolarization field (BP) and an alternating magnetic field (Bac) generated by current to detect the water body with the tunnel disaster, and the BP field is used for improving the signal of a target water body and improving the signal-to-noise ratio; the Bac field detects the detection area layer by layer, can accurately position the disaster water, and realizes non-invasive detection of the disaster water in the tunnel under the environment with multiple angles and super-large noise. Although the method can detect the target water body layer by layer and realize the accurate positioning of the disaster water source, the nuclear magnetic resonance detection can be carried out on the disaster water body in the shallow region only by utilizing the combined action of the prepolarization field and the alternating magnetic field, and the disaster water body in the deep region cannot be detected. The intensity of the prepolarization field in the method is constant field intensity, and the intensity of the prepolarization field required cannot be adjusted in real time when shallow depth layer-by-layer detection is carried out, so that unnecessary energy loss is caused. The method utilizes the inverter circuit to transmit the alternating field, cannot transmit high-precision micro alternating current and cannot perform shallow high-resolution nuclear magnetic resonance imaging.

CN109884719A discloses a continuous emission, fast layered detection nuclear magnetic resonance device and method, the device includes: the device comprises an upper computer, a main controller, a transmitting circuit and a receiving circuit; the energy storage of the transmitting circuit is provided by an energy storage capacitor and is connected with a transmitting bridge circuit through the energy storage capacitor to generate transmitting current in the transmitting coil. The energy storage capacitor is connected with the main controller through the relay set, and the main controller sets the capacitance value of the energy storage capacitor through the relay set; the transmitting circuit comprises a direct current power supply which charges the energy storage capacitor under the control of the main controller; the transmitting circuit comprises a bridge driver driving a transmitting bridge; the receiving circuit is connected or disconnected with the receiving coil through opening and closing of the high-voltage relay, the high-voltage relay is controlled through the main controller, the energy storage capacitor is charged at one time, current is continuously transmitted for many times, the mode of continuous collection is adopted, time waste caused in the charging process is reduced, and nuclear magnetic resonance detection time is shortened. Although the method can excite deep underground water, the method utilizes the inverter circuit to generate bipolar square waves and generates larger sine excitation pulses through harmonic matching, second-order damped oscillation is caused when emission is turned off, longer energy release time is caused, and meanwhile, the harmonic matching is needed under different emission conditions, so that the detection efficiency is reduced.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a nuclear magnetic resonance underground water stratification detection device, which utilizes a pre-polarization gradient field and an adjustable alternating magnetic field to improve the detection signal-to-noise ratio and reduce the loss of emission energy during shallow layer detection; during deep detection, alternating pulse excitation is carried out by utilizing SPWM inversion, harmonic matching excitation is not needed, energy release time is shortened, and detection efficiency is improved; the envelope signal is subjected to digital de-noising, the quality of a field observation signal is improved, the full-wave signal is stored in real time, and abundant data are provided for fine inversion.

The invention also provides a nuclear magnetic resonance underground water stratification detection method.

The present invention is achieved in such a way that,

a nuclear magnetic resonance groundwater stratification detection apparatus, the apparatus comprising:

the upper computer, the main control unit, the shallow layer detection emission unit, the deep layer detection emission unit and the nuclear magnetic resonance signal acquisition unit,

the shallow detection unit provides a variable pre-polarization gradient field and alternating excitation pulses for shallow detection, and shallow detection alternating excitation pulses with small amplitude are generated on a shallow detection alternating pulse transmitting coil to realize layered excitation of hydrogen protons in shallow groundwater;

the deep detection transmitting unit provides larger alternating excitation current for the deep detection alternating pulse transmitting coil during deep detection so as to realize layered excitation of hydrogen protons in deep groundwater; the alternating pulse emitted by the shallow layer is current of 0-10A; the deep alternating pulse emission current is 10 to 400A.

The nuclear magnetic resonance signal acquisition unit acquires envelope signals and full-wave signals at the same time, calculates the envelope signals of the acquired nuclear magnetic resonance envelope signals by using the digital signal processing unit, and performs digital noise elimination processing on the calculated envelope signals;

the upper computer and the main control unit are responsible for configuring transmitting parameters for the shallow layer detecting and transmitting unit and the deep layer detecting and transmitting unit and configuring receiving parameters for the nuclear magnetic resonance signal acquisition unit;

and meanwhile, the upper computer is responsible for storing the acquired nuclear magnetic common full-wave signals in real time and displaying the nuclear magnetic resonance envelope signals subjected to digital denoising.

Further, the shallow detection transmitting unit provides a variable pre-polarization gradient field through the pre-polarization gradient field generating device, the high-power controllable direct-current power supply is controlled, the pre-polarization transmitting circuit is used for generating the variable pre-polarization gradient field on the shallow detection pre-polarization transmitting coil, the alternating excitation pulse generating device is used for generating alternating pulses on the shallow detection alternating pulse transmitting coil, and the digital signal processing unit is used for generating alternating digital signals required by shallow detection, wherein the pre-polarization gradient field generating device comprises: the system comprises a pre-polarized field emission time sequence control module, a pre-polarized field emission driving circuit, a pre-polarized field high-power switch module, a pre-polarized field emission control circuit, a pre-polarized gradient field intensity control module, a high-power controllable direct-current power supply and a shallow detection pre-polarized current emission coil, wherein an upper computer and a main control unit configure emission parameters for the pre-polarized field emission time sequence control module, the pre-polarized field emission time sequence control module generates a pre-polarized emission time sequence control signal, controls the on and off of the pre-polarized field emission high-power switch module after power amplification is carried out by the pre-polarized field emission driving circuit, and generates pre-polarized emission current on the shallow pre-polarized current emission coil through the pre-polarized field emission control circuit; meanwhile, the pre-polarization gradient field intensity control module adjusts and controls the high-power controllable direct-current power supply in real time according to different detection depths of the shallow detection area to provide required pre-polarization field emission energy for the pre-polarization field emission control circuit; and after the pre-polarization field emission is finished, transmitting alternating excitation pulses to excite the underground water of the shallow detection area after adiabatic shutdown.

Further, the alternating excitation pulse generating device in the shallow detection transmitting unit comprises: the device comprises an alternating pulse parameter calculation module, an alternating pulse generation module, an alternating pulse digital-to-analog conversion module, an alternating pulse power amplification module and a shallow detection alternating pulse transmitting coil; the alternating pulse parameter calculation module and the alternating pulse generation module are positioned in the digital signal processing unit A and are responsible for responding to alternating pulse transmitting parameters configured by the upper computer and the main control unit, the alternating pulse parameter calculation module calculates the frequency and the phase of a transmitted sinusoidal signal, then the alternating pulse generation module generates a sinusoidal digital signal with fixed amplitude and corresponding frequency and phase, and the alternating pulse digital-to-analog conversion module converts the generated digital signal into an analog sinusoidal signal; according to different detection depths in the shallow detection area, the alternating pulse power amplification module amplifies the simulated sinusoidal signal into an excitation signal with the required detection depth, and generates alternating excitation pulses with high precision and small amplitude on the shallow detection alternating pulse emission coil.

Further, the deep detection transmitting unit comprises an SPWM waveform control signal generating module, an alternating pulse transmission driving circuit, an alternating pulse SPWM inverter circuit, an energy storage capacitor charging control module, a controllable constant current source, a high-voltage energy storage capacitor, an alternating pulse LC filter circuit, a deep detection alternating pulse transmitting coil, a deep detection transmitting voltage and transmitting current collecting module and a PID control module; the SPWM waveform control signal generation module is positioned in the digital signal processing unit B and is responsible for responding to deep transmission configuration parameters from an upper computer and a main control unit, calculating corresponding carrier waves and modulation waves according to the required transmission duration and transmission frequency of alternating pulses, and generating SPWM waveform control signals required by the SPWM inverter circuit according to a regular sampling method; the alternating pulse emission driving circuit amplifies the power of the SPWM waveform control signal, controls the conduction and the interception of a switching tube in the alternating pulse SPWM inverter circuit, and the alternating pulse SPWM inverter circuit adopts a unipolar inversion control mode; the energy storage capacitor charging control module changes the charging voltage of the high-voltage energy storage capacitor by controlling the output current of the controllable constant current source, provides direct-current voltages with different amplitudes for the alternating pulse SPWM inverter circuit to obtain inverter currents with different amplitudes, and carries out layered detection on the alternating excitation pulses emitted by the deep detection area; the alternating pulse LC filter circuit filters out higher harmonics in the SPWM excitation pulse to obtain a smooth sine alternating excitation pulse, and the smooth sine alternating excitation pulse is transmitted through a deep detection alternating pulse transmitting coil; the deep detection emission voltage and emission current acquisition module is responsible for acquiring excitation voltages at two ends of the high-voltage energy storage capacitor and emission currents in the alternating pulse emission coil and uploading the excitation voltages and the emission currents to the PID control module located in the digital signal processor B, the PID control module compares the acquired emission voltages and the acquired emission currents with preset emission voltages and emission current values to obtain deviation values, and the pulse width of the output SPWM waveform is adjusted through the PID control module to adjust the emission alternating current waveform in real time.

Further, the part of the nuclear magnetic resonance signal acquisition unit for acquiring the envelope signal comprises: the device comprises a nuclear magnetic resonance envelope signal acquisition magnetic sensor, an envelope signal preamplifier circuit, an envelope signal AD acquisition circuit, an envelope signal calculation module and an envelope signal denoising module; the nuclear magnetic resonance envelope signal magnetic sensor is used for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the envelope signal preamplifier is used for amplifying the collected signals, and the envelope signal AD collection circuit is used for carrying out envelope collection on the amplified signals; the envelope signal computing module and the envelope signal noise elimination module are arranged in the digital signal processing unit C, the envelope signal computing module computes the acquired envelope signal, and spike pulse noise, power frequency harmonic noise and random noise are sequentially filtered by the envelope signal noise elimination module; and the digital signal processing unit C uploads the envelope signal subjected to noise elimination to an upper computer in real time to display the envelope signal in a time-frequency domain.

Further, the full-wave signal acquisition part in the nuclear magnetic resonance signal acquisition unit comprises: the device comprises a nuclear magnetic resonance full-wave signal acquisition magnetic sensor, a full-wave signal pre-amplification circuit, a full-wave signal band-pass filter circuit, a full-wave signal secondary amplification circuit and a nuclear magnetic resonance full-wave signal AD acquisition module; the nuclear magnetic resonance full-wave signal magnetic sensor is used for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the full-wave signal preamplifier is used for amplifying the collected signals, the amplified signals are subjected to analog filtering by the full-wave signal band-pass filter circuit, and after being amplified by the full-wave signal secondary amplification circuit, the full-wave acquisition is carried out by using the nuclear magnetic resonance full-wave signal AD acquisition module; and uploading the collected full-wave signals to an upper computer for real-time storage.

A nuclear magnetic resonance underground water layering detection method comprises the following steps:

judging the detection depth, and selecting a shallow detection mode, a deep detection mode or a full depth detection mode according to the detection depth;

if the mode is the full-depth detection mode, the method comprises the following steps:

configuring parameters for transmitting and receiving in a full-depth detection mode to a main control unit through an upper computer;

the main control unit respectively configures corresponding parameters to a shallow detection transmitting unit, a deep detection transmitting unit and a nuclear magnetic resonance signal acquisition unit, wherein the transmitting parameter of the shallow detection transmitting unit is configured to be the detection depth of 0-10 meters underground, the transmitting parameter of the deep detection transmitting unit is configured to be the detection depth of 10 meters underground, and the receiving parameter of the nuclear magnetic resonance signal acquisition unit is configured to be a shallow and deep combined detection mode;

carrying out layered detection from a shallow detection area to a deep detection area, firstly transmitting a shallow pre-polarization gradient field in the shallow detection area, transmitting shallow alternating pulses after adiabatic shutdown, and collecting nuclear magnetic resonance signals after the alternating pulses are transmitted;

after the shallow detection area is detected, deep detection area detection is carried out, a deep detection SPWM alternating pulse is transmitted firstly, and nuclear magnetic resonance signal acquisition is carried out after the deep detection SPWM alternating pulse is transmitted;

if the underground shallow layer detection mode is carried out, the method comprises the following steps:

configuring parameters for transmitting and receiving in a shallow detection mode to a main control unit through an upper computer, and configuring corresponding parameters to the shallow detection transmitting unit and the nuclear magnetic resonance signal acquisition unit by the main control unit;

according to actual detection requirements, the emission parameters of the shallow detection emission unit are configured to corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be in a shallow detection receiving mode;

carrying out layered detection in a shallow detection area;

transmitting a shallow pre-polarization gradient field, transmitting shallow alternating pulses after adiabatic shutdown, and acquiring nuclear magnetic resonance signals after the alternating pulses are transmitted;

if the underground deep layer detection mode is carried out, the method comprises the following steps:

configuring parameters for transmitting and receiving in a deep detection mode to a main control unit through an upper computer, and configuring corresponding parameters to the deep detection transmitting unit and the nuclear magnetic resonance signal acquisition unit by the main control unit;

according to actual detection requirements, the emission parameters of the deep detection emission unit are configured to corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be in a deep detection receiving mode;

carrying out layered detection in the deep detection area;

the method comprises the steps of firstly emitting deep detection SPWM alternating pulses, and carrying out nuclear magnetic resonance signal acquisition after the deep detection SPWM alternating pulses are emitted.

Compared with the prior art, the invention has the beneficial effects that: according to the invention, different excitation modes are used for exciting hydrogen protons in the shallow layer and the deep layer of the underground, and generated nuclear magnetic resonance signals are collected, so that the underground water layered fine detection is realized. When shallow layer detection is carried out, the combined action of the pre-polarization gradient field and the adjustable alternating magnetic field is utilized to carry out layered detection on the shallow layer underground water, so that the signal to noise ratio of detection signals is improved, and the loss of energy transmitted by the pre-polarization field is reduced. The SPWM inversion is utilized to carry out alternating pulse excitation during deep detection, deep layered detection is realized, the excitation mode does not need to carry out harmonic matching, energy release time generated by second-order damping oscillation caused by harmonic matching excitation is reduced, and detection efficiency is improved. Envelope and full-wave acquisition are carried out on the nuclear magnetic resonance signals generated by excitation, and the envelope signals are subjected to field real-time digital noise elimination processing by utilizing the characteristic of small data volume of envelope acquisition, so that high-quality nuclear magnetic resonance signals are provided for a detection field, and the evaluation efficiency of the field nuclear magnetic resonance signals is improved. Meanwhile, the nuclear magnetic resonance full-wave signals are stored in real time, and abundant inversion data are provided for subsequent laboratory fine inversion.

The adjustable gradient pre-polarization field is adopted in the shallow detection area for layered detection, so that the loss of the emission energy of the pre-polarization field is reduced; the shallow alternating pulse is excited by amplifying the power of the analog alternating pulse, so that the transmitting precision of the small-amplitude alternating pulse is improved.

The SPWM inversion is utilized to carry out alternating pulse excitation during deep detection, deep layered detection is realized, the excitation mode does not need to carry out harmonic matching, energy release time generated by second-order damping oscillation caused by harmonic matching excitation is reduced, and detection efficiency is improved.

Drawings

FIG. 1 is a schematic structural diagram of an apparatus for detecting underground water stratification by nuclear magnetic resonance provided by the present invention;

FIG. 2 is a nuclear magnetic resonance underground water layered detection transmitting and receiving mode timing sequence provided by the present invention;

FIG. 3 is a schematic flow chart of a nuclear magnetic resonance groundwater stratification detection method provided by the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in fig. 1 and 2, the nuclear magnetic resonance underground water stratification detecting device comprises: the system comprises an upper computer, a main control unit 1, a shallow detection transmitting unit 2, a deep detection transmitting unit 3 and a nuclear magnetic resonance signal acquisition unit 4. The shallow layer detection unit 2 provides a variable pre-polarization gradient field (Bp) and an alternating excitation pulse (Bac) for shallow layer detection, a high-power controllable direct-current power supply is controlled, a pre-polarization emission circuit is used for generating the variable pre-polarization gradient field on a shallow layer detection pre-polarization emission coil, a digital signal processing unit is used for generating an alternating digital signal required by the shallow layer detection, the alternating digital signal is controllably amplified in power, and the shallow layer detection alternating excitation pulse with high precision and small amplitude is generated on the shallow layer detection alternating pulse emission coil, so that the hydrogen protons in shallow layer underground water are excited in a layered mode. The deep detection transmitting unit 3 provides a larger alternating excitation pulse (SPWM-Bac) for deep detection, the SPWM inversion bridge circuit is used for inversion to generate the SPWM pulse, the LC filter circuit is used for filtering the high-frequency transmission pulse to generate a smooth sine alternating excitation pulse, and layered excitation of hydrogen protons in deep groundwater is realized. The nuclear magnetic resonance signal acquisition unit 4 acquires a free induction decay nuclear magnetic resonance signal (FID) generated after excitation of each layer, acquires an envelope signal and a full wave signal simultaneously by using a nuclear magnetic resonance envelope signal acquisition magnetic sensor and a nuclear magnetic resonance full wave signal acquisition magnetic sensor, calculates the envelope signal of the acquired nuclear magnetic resonance envelope signal by using the digital signal processing unit, and performs digital noise elimination processing on the calculated envelope signal.

As shown in fig. 1, the upper computer and the main control unit 1 are responsible for configuring transmission parameters for the shallow detection transmitting unit 2 and the deep detection transmitting unit 3, and configuring receiving parameters for the nuclear magnetic resonance signal acquisition unit 4. And meanwhile, the upper computer is responsible for storing the acquired nuclear magnetic common full-wave signals in real time and displaying the nuclear magnetic resonance envelope signals subjected to digital denoising.

As shown in fig. 1, the pre-polarization gradient field generating apparatus in the shallow detection transmitting unit 2 includes: the device comprises a pre-polarized field emission time sequence control module 5, a pre-polarized field emission driving circuit 6, a pre-polarized field high-power switch module 7, a pre-polarized field emission control circuit 8, a pre-polarized gradient field intensity control module 9, a high-power controllable direct-current power supply 10 and a shallow detection pre-polarized current emission coil 11. The upper computer and the main control unit 1 configure transmitting parameters for the prepolarization field transmitting time sequence control module 5, the prepolarization field transmitting time sequence control module 5 generates prepolarization transmitting time sequence control signals, the power amplification is carried out by the prepolarization field transmitting drive circuit 6, then the opening and closing of the prepolarization field transmitting high-power switch module 7 are controlled, and prepolarization transmitting current is generated on the shallow prepolarization current transmitting coil 11 by the prepolarization field transmitting control circuit 8. Meanwhile, the pre-polarization gradient field intensity control module 9 adjusts and controls the high-power controllable direct-current power supply 10 in real time according to different detection depths of the shallow detection area to provide the required pre-polarization field emission energy for the pre-polarization field emission control circuit 8. And after the pre-polarization field emission is finished, transmitting alternating excitation pulses to excite the underground water of the shallow detection area after adiabatic shutdown.

As shown in fig. 1, the alternating excitation pulse generating apparatus in the shallow detection transmitting unit 2 includes: the device comprises an alternating pulse parameter calculation module 13, an alternating pulse generation module 14, an alternating pulse digital-to-analog conversion module 15, an alternating pulse power amplification module 16 and a shallow detection alternating pulse transmitting coil 17. The alternating pulse parameter calculation module 13 and the alternating pulse generation module 14 are located in the digital signal processing unit a12 and are responsible for responding to the alternating pulse transmission parameters configured by the upper computer and the main control unit 1, the alternating pulse parameter calculation module 13 calculates the frequency and the phase of a transmitted sinusoidal signal, then the alternating pulse generation module 14 generates a sinusoidal digital signal with a fixed amplitude and corresponding frequency and phase, and the alternating pulse digital-to-analog conversion module 15 converts the generated digital signal into an analog sinusoidal signal. According to the difference of the detection depth in the shallow detection area, the alternating pulse power amplification module 16 amplifies the analog sinusoidal signal into an excitation signal with the required detection depth, and generates an alternating excitation pulse with high precision and small amplitude on the shallow detection alternating pulse transmitting coil 17.

As shown in fig. 1, the deep detection transmitting unit 3 includes an SPWM waveform control signal generating module 19, an alternating pulse transmission driving circuit 20, an alternating pulse SPWM inverting circuit 21, an energy storage capacitor charging control module 22, a controllable constant current source 23, a high-voltage energy storage capacitor 24, an alternating pulse LC filter circuit 25, a deep detection alternating pulse transmitting coil 26, a deep detection transmitting voltage and transmitting current collecting module 27, and a PID control module 28. The SPWM waveform control signal generation module 19 is located in the digital signal processing unit B18, and is responsible for responding to deep layer transmission configuration parameters from the upper computer and the main control unit 1, calculating corresponding carrier waves and modulation waves according to the required transmission duration and transmission frequency of the alternating pulse, and generating the SPWM waveform control signal required by the SPWM inverter circuit according to a regular sampling method. The alternating pulse emission driving circuit 20 amplifies the power of the SPWM waveform control signal, and controls the conduction and cut-off of the switching tube in the alternating pulse SPWM inverter circuit, and the alternating pulse SPWM inverter circuit adopts a unipolar inversion control mode. The energy storage capacitor charging control module 22 changes the charging voltage of the high-voltage energy storage capacitor 24 by controlling the output current of the controllable constant current source 23, provides direct-current voltages with different amplitudes for the alternating pulse SPWM inverter circuit 21 to obtain inverter currents with different amplitudes, and carries out layered detection on the alternating excitation pulses emitted by the deep detection area. The alternating pulse LC filter circuit 25 filters out higher harmonics in the SPWM excitation pulse to obtain a smooth sinusoidal alternating excitation pulse, which is transmitted by the deep detection alternating pulse transmitting coil 26. The deep detection emission voltage and emission current collection module 27 is responsible for collecting the excitation voltage at two ends of the high-voltage energy storage capacitor 24 and the emission current in the alternating pulse emission coil 26 and uploading the collected excitation voltage and emission current to the PID control module 28 located in the digital signal processing unit B18, the PID control module 28 compares the collected emission voltage and emission current with the preset emission voltage and emission current value to obtain a deviation value, and the pulse width of the output SPWM waveform is adjusted by the PID regulator to adjust the emission alternating current waveform in real time, so as to avoid the influence on the alternating pulse emission current due to the variation of the emission voltage value and the emission coil load parameter.

As shown in fig. 1, the part of the nuclear magnetic resonance signal acquisition unit 4 for acquiring the envelope signal includes: the device comprises a nuclear magnetic resonance envelope signal acquisition magnetic sensor 29, an envelope signal preamplification circuit 30, an envelope signal AD acquisition circuit 31, an envelope signal calculation module 33 and an envelope signal noise elimination module 34. The nuclear magnetic resonance envelope signal magnetic sensor 29 is responsible for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the envelope signal preamplification circuit 30 amplifies the collected signals, and the envelope signal AD acquisition circuit 31 carries out envelope acquisition on the amplified signals. The envelope signal calculating module 33 and the envelope signal denoising module 34 are arranged in the digital signal processing unit C32, the envelope signal calculating module 33 calculates the acquired envelope signal, and then the envelope signal denoising module 34 sequentially filters spike noise, power frequency harmonic noise, and random noise. The digital signal processing unit C32 uploads the envelope signals subjected to noise elimination to an upper computer in real time to be displayed in a time-frequency domain, so that the quality of the detected nuclear magnetic resonance signals can be improved, field detection personnel can conveniently observe the signals in real time on site, and the detection efficiency is improved.

As shown in fig. 1, the full-wave signal acquisition section in the nuclear magnetic resonance signal acquisition unit 4 includes: the device comprises a magnetic sensor 35 for acquiring nuclear magnetic resonance full-wave signals, a full-wave signal pre-amplification circuit 36, a full-wave signal band-pass filter circuit 37, a full-wave signal secondary amplification circuit 38 and a module 39 for acquiring nuclear magnetic resonance full-wave signals AD. The magnetic sensor 35 is responsible for collecting nuclear magnetic resonance signals excited by the shallow detection unit or the deep detection unit, the full-wave signal pre-amplification circuit 36 amplifies the collected signals, the amplified signals are subjected to analog filtering by the full-wave signal band-pass filtering circuit 37, and after being amplified by the full-wave signal secondary amplification circuit 38, full-wave collection is performed by the nuclear magnetic resonance full-wave signal AD collection module 39. The acquired full-wave signals are uploaded to an upper computer to be stored in real time, and abundant inversion data are provided for subsequent laboratory fine inversion.

As shown in fig. 3, a nuclear magnetic resonance groundwater stratification detection method includes: the method can be divided into a shallow detection mode, a deep detection mode and a full-depth detection mode according to different detection depths, the shallow detection mode can detect a water-containing layer area of 0-10 m underground, the deep detection mode can detect a detection area of 10-150 m underground, and different detection modes are selected under different actual detection requirements.

If underground full-depth detection is carried out, a full-depth detection mode is selected on the upper computer, and the following steps are carried out: the method comprises the steps that firstly, the upper computer is used for configuring parameters for transmitting and receiving in a full-depth detection mode to the main control unit, and the main control unit is used for configuring corresponding parameters to the shallow detection transmitting unit, the deep detection transmitting unit and the nuclear magnetic resonance signal acquisition unit respectively. The transmitting parameters of the shallow layer detection transmitting unit are configured to be the detection depth of 0 meter to 10 meters underground, the deep layer detection transmitting unit is configured to be the detection depth of 10 meters underground to the required detection depth, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be the shallow layer and deep layer combined detection mode. And then carrying out layered detection from the shallow detection region to the deep detection region. In the shallow detection area, shallow pre-polarization gradient field is transmitted, shallow alternating pulse is transmitted after adiabatic shutdown, and nuclear magnetic resonance signals are acquired after the alternating pulse is transmitted. And after the shallow detection area is detected, deep detection area detection is carried out, the deep detection SPWM alternating pulse is transmitted firstly, and nuclear magnetic resonance signal acquisition is carried out after the deep detection SPWM alternating pulse is transmitted. And finally, evaluating a field detection result, and evaluating the detection result on the spot according to the time-frequency domain information of the nuclear magnetic resonance envelope signal subjected to real-time digital noise elimination.

If the underground shallow layer detection is carried out, a shallow layer detection mode is selected on the upper computer, and the following steps are carried out: the method comprises the steps that firstly, shallow detection mode transmitting and receiving parameters are configured to a main control unit through an upper computer, and then the main control unit configures corresponding parameters to a shallow detection transmitting unit and a nuclear magnetic resonance signal acquisition unit. According to actual detection requirements, the transmitting parameters of the shallow detection transmitting unit are configured to be corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be in a shallow detection receiving mode. And then carrying out layered detection in the shallow detection area. The method comprises the steps of firstly transmitting a shallow pre-polarization gradient field, transmitting shallow alternating pulses after adiabatic shutdown, and acquiring nuclear magnetic resonance signals after the alternating pulses are transmitted. And finally, evaluating a field detection result, and evaluating the detection result on the spot according to the time-frequency domain information of the nuclear magnetic resonance envelope signal subjected to real-time digital noise elimination.

If the underground deep layer detection is carried out, a deep layer detection mode is selected on the upper computer, and the following steps are carried out: the method comprises the steps that firstly, an upper computer is used for configuring parameters for transmitting and receiving in a deep detection mode to a main control unit, and then the main control unit is used for configuring corresponding parameters to a deep detection transmitting unit and a nuclear magnetic resonance signal acquisition unit. According to the actual detection requirement, the emission parameters of the deep detection emission unit are configured to be corresponding layered detection depths, and the receiving parameters of the nuclear magnetic resonance signal acquisition unit are configured to be a deep detection receiving mode. And then carrying out layered detection in the deep detection area. The method comprises the steps of firstly emitting deep detection SPWM alternating pulses, and carrying out nuclear magnetic resonance signal acquisition after the deep detection SPWM alternating pulses are emitted. And finally, evaluating a field detection result, and evaluating the detection result on the spot according to the time-frequency domain information of the nuclear magnetic resonance envelope signal subjected to real-time digital noise elimination.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.