Method and system for extracting transient electromagnetic signal through ground nuclear magnetic resonance

Abstract

The invention belongs to the technical field of geophysical methods, and particularly discloses a method and system for extracting transient electromagnetic signals through ground nuclear magnetic resonance. The method comprises the following steps: periodically transmitting nuclear magnetic resonance excitation pulses to an underground medium, and extracting nuclear magnetic resonance turn-off pulses as transient electromagnetic excitation signals at the turn-off stage of each nuclear magnetic resonance excitation pulse; after each nuclear magnetic resonance excitation pulse is turned off, detecting a transient electromagnetic response signal; and when the last nuclear magnetic resonance excitation pulse is turned off, collecting a nuclear magnetic resonance response signal. According to the invention, the high-energy turn-off pulse is directly extracted as the transient electromagnetic excitation signal in the turn-off stage of the nuclear magnetic resonance excitation pulse, so that the overall signal utilization efficiency and excitation capability of the system are remarkably improved.

Description

Technical Field

[0001] The present application belongs to the technical field of geophysical methods, and more specifically, relates to a method and system for extracting transient electromagnetic signals using ground nuclear magnetic resonance. Background Art

[0002] Accurate detection of underground electrical conductivity and groundwater distribution is of great significance for geophysical exploration, especially in the fields of mineral resource exploration, groundwater resource investigation, and environmental monitoring. Underground electrical conductivity reflects the electrical characteristics of the stratum, while groundwater distribution directly affects the quantitative assessment of water resources and the analysis of aquifer characteristics. Transient electromagnetic method and nuclear magnetic resonance method are two common technologies used to detect underground electrical conductivity and water distribution. Transient electromagnetic method can efficiently obtain spatial distribution information of underground resistivity by exciting electromagnetic fields and receiving response signals from the stratum, while nuclear magnetic resonance method can non-destructively evaluate the characteristics of groundwater aquifers by measuring water signals in rock and soil.

[0003] In recent years, with the increasing demand for refinement and integration of geophysical exploration, how to achieve efficient coordination between nuclear magnetic resonance and transient electromagnetic response signals has become the focus of technological innovation in this field. Some studies have attempted to improve the detection capabilities of multi-physics fields through hardware integration or data fusion, but they have not been able to fundamentally solve core problems such as redundancy of the transmission system, low signal excitation efficiency, and insufficient anti-interference ability. In practical applications, nuclear magnetic resonance and transient electromagnetic methods are each independent systems, and usually require dedicated transmitting and receiving devices respectively. This not only leads to large hardware size, high cost, and high energy consumption, but also increases the difficulty of on-site deployment and maintenance. In addition, there are technical bottlenecks in the timing and spatial coordination between independent systems, making it difficult to achieve truly synchronous acquisition and collaborative analysis, affecting the fusion effect and interpretation accuracy of multi-physics field data. Summary of the Invention

[0004] In response to the defects of the existing technology, the purpose of this application is to provide a method and system for extracting transient electromagnetic signals using ground-based nuclear magnetic resonance, aiming to solve the problem that the existing nuclear magnetic resonance method and transient electromagnetic method are independent systems, and there are technical bottlenecks in the timing and spatial coordination between independent systems, making it difficult to achieve synchronous acquisition and collaborative analysis, which affects the fusion effect and interpretation accuracy of multi-physical field data.

[0005] To achieve the above objectives, in a first aspect, the present application provides a method for extracting transient electromagnetic signals using ground nuclear magnetic resonance, which specifically comprises the following steps: Step 1: Periodically transmitting a nuclear magnetic resonance excitation pulse to the underground medium, and extracting the nuclear magnetic resonance off-pulse as a transient electromagnetic excitation signal during the off phase of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal includes the nuclear magnetic resonance excitation pulse and the nuclear magnetic resonance off-pulse; Step 2: After each nuclear magnetic resonance excitation pulse is turned off, the transient electromagnetic response signal is detected; Step 3: When the last NMR excitation pulse is turned off, collect the NMR response signal; The nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal are excited by the same transmitting coil and power supply; and the transient electromagnetic response signal and the nuclear magnetic resonance response signal are collected by the same receiving coil.

[0006] Further preferably, in step one, the center frequency of the nuclear magnetic resonance excitation pulse is adjusted to match the proton resonance characteristics of different underground media, and the repetition time and width of the nuclear magnetic resonance excitation pulse sequence are controlled to distinguish and detect underground media of different depths and properties.

[0007] Further preferably, in step one, during the nuclear magnetic resonance excitation pulse shut-off phase, the voltage and current signals at both ends of the transmitting coil are detected in real time, and the nuclear magnetic resonance shut-off pulse signal containing the high-frequency component is separated through high-speed sampling and digital filtering technology, and is used as a transient electromagnetic excitation signal.

[0008] Further preferably, in step one, according to the emission requirements of the transient electromagnetic excitation signal, the current amplitude of the nuclear magnetic resonance off pulse is adjusted in real time by the current control circuit, the off rate of the nuclear magnetic resonance off pulse adopts a pulse edge enhancement method to obtain the falling edge, and the optimal impedance matching between the transmitting coil and the power supply is achieved by connecting an adjustable impedance device in parallel or in series.

[0009] Further preferably, in step 2, a timing synchronization circuit is used to set the acquisition window and reference time of the transient electromagnetic response signal.

[0010] Further preferably, in step 2 and step 3, the characteristics of the nuclear magnetic resonance response signal and the transient electromagnetic response signal are distinguished in real time, and the mode of collecting transient electromagnetic response signals or collecting nuclear magnetic resonance response signals is dynamically switched according to the collected signal change trend.

[0011] In a second aspect, the present application provides a system for extracting transient electromagnetic signals using ground-based nuclear magnetic resonance, comprising: A transmitting module, used for periodically transmitting nuclear magnetic resonance excitation pulses to the underground medium; An off-pulse extraction module is used to extract the nuclear magnetic resonance off-pulse as the emission source of the transient electromagnetic excitation signal during the off phase of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal includes the nuclear magnetic resonance excitation pulse and the nuclear magnetic resonance off-pulse; The signal receiving module is used to detect the transient electromagnetic response signal after each nuclear magnetic resonance excitation pulse is turned off; and collect the nuclear magnetic resonance response signal when the last nuclear magnetic resonance excitation pulse is turned off; Among them, the transmitting coil in the transmitting module is used to excite the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal; the receiving coil in the signal receiving module is used to collect the transient electromagnetic response signal and the nuclear magnetic resonance response signal; The time-division multiplexing logic control module is used to perform timing control on the emission of nuclear magnetic resonance excitation pulses and transient electromagnetic excitation signals, the extraction of off-pulses, signal acquisition and the switching of acquisition modes.

[0012] Further preferably, the transmitting module includes: A frequency modulation unit is used to adjust the center frequency of the nuclear magnetic resonance excitation pulse to match the proton resonance characteristics of different underground media; A pulse adjustment unit, used to distinguish and detect underground media of different depths and properties by controlling the repetition time and width of the nuclear magnetic resonance excitation pulse sequence; The control unit is used to switch the pulse sequence in the nuclear magnetic resonance signal and drive multiple channels in a coordinated manner, realizing multiple excitations and shutdowns within a complete nuclear magnetic resonance signal cycle.

[0013] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: The present application provides a method for extracting transient electromagnetic signals using ground nuclear magnetic resonance, which combines two physical detection methods, nuclear magnetic resonance and transient electromagnetic, and uses nuclear magnetic resonance equipment to collect nuclear magnetic resonance signals of underground media, and uses the shutdown pulse as the transient electromagnetic excitation signal in the shutdown phase. Therefore, under the excitation of the shutdown pulse, the electromagnetic response in the underground medium can be effectively stimulated, thereby accurately collecting the transient electromagnetic response signal, and realizing the high integration and reuse of the transmitting device and the receiving device; in response to the problems of hardware redundancy, large size and complex deployment in previous geophysical detection systems, the present application adopts the same transmitting coil and power supply, which not only greatly reduces the equipment cost and energy consumption, but also makes on-site deployment and maintenance more convenient; by directly extracting high-energy shutdown pulses as transient electromagnetic excitation signals in the shutdown phase of the nuclear magnetic resonance excitation pulse, the overall signal utilization efficiency and excitation capability of the system are significantly improved, without the need for additional configuration of an independent transient electromagnetic transmitting system, which greatly optimizes the equipment framework.

[0014] The present application provides a method for extracting transient electromagnetic signals using ground nuclear magnetic resonance. By optimizing emission and matching parameters, the energy intensity and frequency range of the shut-off pulse are ensured to meet the actual needs of detecting underground conductors and aquifers. The system achieves high-speed and smooth switching between different excitation and receiving modes. It adopts multi-stage digital filtering, timing synchronization and time-sharing acquisition technology to effectively suppress various types of electromagnetic noise and crosstalk, improve signal quality, and achieve high-precision detection of weak underground signals even in noisy environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of a method for extracting transient electromagnetic signals using ground nuclear magnetic resonance provided by an embodiment of the present application; Figure 2 This is a schematic diagram of the waveform of transient electromagnetic signal emission extracted by ground nuclear magnetic resonance provided in an embodiment of the present application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0017] The term "and / or" in this application describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, or B exists alone. The symbol " / " in this document indicates that the associated objects are in an "or" relationship, for example, A / B means A or B.

[0018] The terms "first" and "second" and the like in the description and claims of this application are used to distinguish different objects rather than to describe a specific order of the objects.

[0019] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0020] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more.

[0021] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0022] like Figure 1 As shown, the present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, comprising the following steps: Step S1: using a nuclear magnetic resonance emission module to periodically emit nuclear magnetic resonance excitation pulses to the underground medium, wherein a complete nuclear magnetic resonance cycle includes multiple excitation and shutdown processes; Further preferably, the method for obtaining a nuclear magnetic resonance signal comprises the following steps: adjusting the center frequency of the excitation pulse by a frequency modulation device in the nuclear magnetic resonance emission module so that it can match the proton resonance characteristics of different underground media, and achieving the discrimination and detection selectivity of different depths and properties of the underground media by controlling the repetition time and width of the pulse sequence, and using multi-channel synchronous acquisition technology to improve the spatial resolution of the nuclear magnetic resonance response signal; within a complete nuclear magnetic resonance cycle, accumulating multiple excitation-off-transient electromagnetic measurements, and then uniformly measuring the nuclear magnetic resonance signal after the decay ends; Step S2: During the off phase of each excitation pulse, extracting the off pulse as a transient electromagnetic excitation signal to achieve homologous excitation of the nuclear magnetic resonance signal and the transient electromagnetic excitation signal; Further preferably, the current amplitude, the shutoff rate and the impedance matching of the transmitting coil of the nuclear magnetic resonance shutoff pulse are designed for electromagnetic compatibility to generate a broadband and highly stable transient electromagnetic emission waveform; More preferably, Figure 2 As shown in the figure, during the excitation pulse off phase, the voltage and current signals at both ends of the coil are detected in real time. Through high-speed sampling and digital filtering technology, the nuclear magnetic resonance off pulse signal containing rich high-frequency components is separated, and the nuclear magnetic resonance off pulse is used as the emission excitation source of the transient electromagnetic method. After each shutdown, the system automatically switches to the transient electromagnetic receiving mode to collect and process the transient electromagnetic response signal. At the same time, a pulse recognition threshold is set at the signal processing end to realize the automatic extraction and marking of the off pulse. Further preferably, the frequency range and energy intensity of the shutdown pulse are adjusted according to the electromagnetic characteristics of the underground medium to maximize the signal excitation efficiency and reduce possible signal attenuation; in addition, the emission duration and waveform of the shutdown pulse signal are also precisely controlled to ensure that a clear electromagnetic response signal can be obtained, thereby improving the quality and effectiveness of the extracted transient electromagnetic excitation signal; specifically, according to the emission requirements of the transient electromagnetic excitation signal, the current amplitude of the shutdown pulse is adjusted in real time by a high-precision current control circuit, the shutdown rate adopts a pulse edge enhancement design to obtain a steeper falling edge, and the optimal impedance matching between the transmitting coil and the power supply is achieved by connecting an adjustable impedance unit in parallel or in series, thereby suppressing unnecessary harmonics and parasitic oscillations, and improving the consistency and energy utilization of the broadband and high-stability transient electromagnetic emission waveform; Step S3: After each excitation pulse is turned off, the system is immediately switched to a transient electromagnetic response signal receiving mode, and the transient electromagnetic response signal is collected through the same receiving coil to achieve multiple transient electromagnetic detections within one nuclear magnetic resonance cycle; Further preferably, the shut-off pulse signal has a sufficient frequency range and energy intensity to effectively stimulate the electromagnetic response in the underground medium, thereby generating a transient electromagnetic response signal; Figure 2As shown in the figure, by co-designing the coil parameters and power output circuit of the nuclear magnetic resonance transmission module, a single transmission system can be compatible with the signal output of both nuclear magnetic resonance and transient electromagnetic excitation modes. In combination with isolation relays, RF switching circuits and distributed grounding systems, electrical coupling and crosstalk in different modes are effectively reduced, the overall working stability and reliability of the system are improved, and the on-site detection operation process is simplified. More specifically, by reusing the coil and power supply of the nuclear magnetic resonance transmission module, the independent transmission device of the traditional transient electromagnetic method is replaced, thereby reducing the complexity of the equipment; Step S4: After undergoing multiple excitation-off-transient electromagnetic measurement processes, when the last nuclear magnetic resonance excitation pulse is turned off, switch to the nuclear magnetic resonance signal measurement mode to collect the complete nuclear magnetic resonance response signal.

[0023] Further preferably, through the time-sharing multiplexing logic control module, after the nuclear magnetic resonance acquisition phase is completed and the target signal is sufficiently attenuated, the receiving coil is automatically switched to the receiving channel of the transient electromagnetic response signal, and the gain and bandwidth parameters of the receiving amplifier are adaptively adjusted according to different signal types. At the same time, the timing synchronization circuit is applied to strictly limit the acquisition window and reference time of the transient electromagnetic response signal to improve the extraction efficiency of weak signals and the accuracy of measurement; wherein, the automatic switching process includes real-time discrimination of the nuclear magnetic resonance signal characteristics, dynamic adjustment of the switching timing according to the collected signal change trend, and short-term protection of the receiving system at the switching moment to prevent transient interference during the switching process from affecting subsequent signal acquisition.

[0024] In a second aspect, the present application provides a system for extracting transient electromagnetic signals using ground-based nuclear magnetic resonance, comprising: The transmitter module is used to transmit nuclear magnetic resonance excitation pulses into the underground medium. It has a built-in frequency modulation unit, a pulse adjustment unit, and a power amplifier unit. Through external control signals, it automatically optimizes the output waveform parameters according to the resonance frequency and geological conditions of the underground medium to achieve nuclear magnetic resonance excitation at different depths or for different material types. The transmitter unit supports high-speed switching of pulse sequences and multi-channel coordinated drive, achieving multiple excitation and shutdown within a complete nuclear magnetic resonance cycle, providing high signal-to-noise ratio response data for transient electromagnetic detection and nuclear magnetic resonance measurements. Furthermore, the transmitting unit includes a set of transmitting coils for transmitting nuclear magnetic resonance excitation and transient electromagnetic excitation signals and a power supply capable of supporting large current and high-speed switching. The structure is equipped with an automatic switching switch, an isolation relay, an impedance adaptive matching network and an electromagnetic shielding layer. This enables nuclear magnetic resonance excitation and transient electromagnetic excitation to share the same transmitting circuit, and ensures that electromagnetic crosstalk, power loss and system noise caused by high-frequency and high-amplitude changes are effectively suppressed during the switching of working modes, thereby improving the working efficiency and overall stability of the transmitting system. The shutdown pulse extraction module is used to continuously and in real time detect the current and voltage information at both ends of the transmitting coil at the moment when the nuclear magnetic resonance excitation pulse is turned off. Through high-speed sampling, digital filtering, edge detection and pulse recognition, it can automatically extract the shutdown pulse signal at each time and use it as a transient electromagnetic excitation signal; The parameter control module is used to dynamically adjust the characteristic parameters of the shutdown pulse, such as amplitude, slope, and timing, based on real-time formation feedback or preset methods to ensure optimal energy and wide bandwidth of the transient electromagnetic excitation signal, and has abnormal state self-detection and protection functions; The signal receiving module, which includes a receiving coil, a pre-low-noise amplifier, a bandwidth-adjustable filter, an analog-to-digital conversion module, and a digital signal processor, can sequentially acquire the nuclear magnetic resonance response signal and transient electromagnetic response signal of the underground medium through the same receiving coil, and adaptively adjust the gain, bandwidth, and sampling rate in different modes. This unit also includes time-division multiplexing control logic, a timing synchronization module, and a digital signal processing module based on adaptive filtering and multi-domain noise reduction algorithms, effectively improving weak signal detection capabilities and anti-interference performance, while providing high-quality data streams for back-end data analysis. The time-sharing multiplexing logic control module is equipped with a high-precision timing control chip, which can implement unified timing management for multiple processes such as nuclear magnetic resonance emission, shutdown pulse extraction, signal acquisition and mode switching, and switch between different acquisition modes according to the actual attenuation process of the nuclear magnetic resonance signal; dynamically adjust system parameters during automatic switching to protect key units from transient interference in transition states, and combine functions such as status monitoring, abnormal response and remote adaptive adjustment, thereby ensuring the overall efficient, stable and intelligent operation of the system.

[0025] In summary, compared with the prior art, this application has the following advantages: The present application provides a method for extracting transient electromagnetic signals by using ground nuclear magnetic resonance, which combines two physical detection methods, nuclear magnetic resonance and transient electromagnetic, and uses nuclear magnetic resonance equipment to collect nuclear magnetic resonance signals of underground media, and uses the shutdown pulse as the transient electromagnetic excitation signal in the shutdown phase. Therefore, under the excitation of the shutdown pulse, the electromagnetic response in the underground medium can be effectively stimulated, thereby accurately collecting the transient electromagnetic response signal, and realizing the high integration and reuse of the transmitting device and the receiving device; in response to the problems of hardware redundancy, large size and complex deployment in previous geophysical detection systems, the present application adopts the same transmitting coil and power supply, which not only greatly reduces the equipment cost and energy consumption, but also makes on-site deployment and maintenance more convenient; by directly extracting high-energy shutdown pulses as transient electromagnetic excitation signals in the shutdown phase of the nuclear magnetic resonance excitation pulse, the overall signal utilization efficiency and excitation capability of the system are significantly improved, without the need for additional configuration of an independent transient electromagnetic transmitting system, which greatly optimizes the equipment framework.

[0026] The present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance. By optimizing the emission and matching parameters, it ensures that the energy intensity and frequency range of the shut-off pulse can meet the actual needs of underground conductors and aquifer detection. The system achieves high-speed and stable switching between different excitation and receiving modes. It adopts multi-stage digital filtering, timing synchronization and time-sharing acquisition technology to effectively suppress various types of electromagnetic noise and crosstalk, improve signal quality, and achieve high-precision detection of weak underground signals even in noisy environments.

[0027] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A method for extracting transient electromagnetic signals using ground nuclear magnetic resonance, characterized in that: The following steps are involved: Step 1: Periodically transmitting a nuclear magnetic resonance excitation pulse to the underground medium, and extracting the nuclear magnetic resonance off-pulse as a transient electromagnetic excitation signal during the off phase of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal includes the nuclear magnetic resonance excitation pulse and the nuclear magnetic resonance off-pulse; Step 2: After each nuclear magnetic resonance excitation pulse is turned off, the transient electromagnetic response signal is detected; Step 3: When the last NMR excitation pulse is turned off, collect the NMR response signal; The nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal are excited by the same transmitting coil and power supply; and the transient electromagnetic response signal and the nuclear magnetic resonance response signal are collected by the same receiving coil.

2. The method according to claim 1, characterized in that In step one, the center frequency of the nuclear magnetic resonance excitation pulse is adjusted to match the proton resonance characteristics of different underground media, and the repetition time and width of the nuclear magnetic resonance excitation pulse sequence are controlled to distinguish and detect underground media of different depths and properties.

3. The method according to claim 1 or 2, characterized in that In step one, during the nuclear magnetic resonance excitation pulse off phase, the voltage and current signals at both ends of the transmitting coil are detected in real time. Through high-speed sampling and digital filtering technology, the nuclear magnetic resonance off pulse signal is separated and used as a transient electromagnetic excitation signal.

4. The method according to claim 3, characterized in that In step one, according to the emission requirements of the transient electromagnetic excitation signal, the current amplitude of the nuclear magnetic resonance shutdown pulse is adjusted in real time through the current control circuit. The shutdown rate of the nuclear magnetic resonance shutdown pulse adopts the pulse edge enhancement method to obtain the falling edge, and the optimal impedance matching between the transmitting coil and the power supply is achieved by connecting an adjustable impedance device in parallel or in series.

5. The method according to claim 1, wherein In step 2, a timing synchronization circuit is used to set the acquisition window and reference time of the transient electromagnetic response signal.

6. The method according to claim 1 or 5, characterized in that In step 2 and step 3, the characteristics of the nuclear magnetic resonance response signal and the transient electromagnetic response signal are distinguished in real time, and the mode of collecting the transient electromagnetic response signal or the nuclear magnetic resonance response signal is dynamically switched according to the change trend of the collected signals.

7. A system for extracting transient electromagnetic signals using ground-based nuclear magnetic resonance, characterized in that: include: A transmitting module, used for periodically transmitting nuclear magnetic resonance excitation pulses to the underground medium; An off-pulse extraction module is used to extract a nuclear magnetic resonance off-pulse as a transient electromagnetic excitation signal during the off phase of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal includes a nuclear magnetic resonance excitation pulse and a nuclear magnetic resonance off-pulse; The signal receiving module is used to detect the transient electromagnetic response signal after each nuclear magnetic resonance excitation pulse is turned off; and collect the nuclear magnetic resonance response signal when the last nuclear magnetic resonance excitation pulse is turned off; Among them, the transmitting coil in the transmitting module is used to excite the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal; the receiving coil in the signal receiving module is used to collect the transient electromagnetic response signal and the nuclear magnetic resonance response signal; The time-division multiplexing logic control module is used to perform timing control on the emission of nuclear magnetic resonance excitation pulses and transient electromagnetic excitation signals, the extraction of off-pulses, signal acquisition and the switching of acquisition modes.

8. The system according to claim 7, characterized in that The shutdown pulse extraction module is used to continuously and in real time detect the current and voltage information at both ends of the transmitting coil at the moment the nuclear magnetic resonance excitation pulse is turned off. Through high-speed sampling, digital filtering, edge detection and pulse recognition, the nuclear magnetic resonance shutdown pulse signal is extracted each time and used as a transient electromagnetic excitation signal.

9. The system according to claim 7 or 8, characterized in that The transmitting module includes: A frequency modulation unit is used to adjust the center frequency of the nuclear magnetic resonance excitation pulse to match the proton resonance characteristics of different underground media; A pulse adjustment unit, used to distinguish and detect underground media of different depths and properties by controlling the repetition time and width of the nuclear magnetic resonance excitation pulse sequence; The control unit is used to switch the pulse sequence in the nuclear magnetic resonance signal and drive multiple channels in a coordinated manner, realizing multiple excitations and shutdowns within a complete nuclear magnetic resonance signal cycle.

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