Method and system for extracting transient electromagnetic signals from ground nuclear magnetic resonance

Abstract

The application belongs to the technical field of geophysical methods, and specifically discloses a method and system for extracting transient electromagnetic signals by ground nuclear magnetic resonance. The method comprises the following steps: periodically emitting nuclear magnetic resonance excitation pulses to underground media; extracting nuclear magnetic resonance off pulses as transient electromagnetic excitation signals in the off stage of each nuclear magnetic resonance excitation pulse; detecting transient electromagnetic response signals after the off of each nuclear magnetic resonance excitation pulse; and collecting nuclear magnetic resonance response signals when the off of the last nuclear magnetic resonance excitation pulse. By directly extracting high-energy off pulses as transient electromagnetic excitation signals in the off stage of the nuclear magnetic resonance excitation pulse, the signal utilization efficiency and excitation capacity of the whole system are significantly improved.

Description

TECHNICAL FIELD

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

[0002] Accurate detection of underground conductivity and groundwater distribution is of great significance for geophysical exploration, especially in the fields of mineral resource exploration, groundwater resource investigation, environmental monitoring, etc. Underground 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 techniques for detecting underground conductivity and water distribution. Transient electromagnetic method can efficiently obtain the spatial distribution information of underground resistivity by exciting electromagnetic field and receiving the response signal of the stratum, while nuclear magnetic resonance method can non-destructively evaluate the aquifer characteristics of underground water by measuring the water signal in rock and soil.

[0003] In recent years, with the increasing demand for fine and integrated geophysical exploration, how to efficiently coordinate the nuclear magnetic resonance and transient electromagnetic response signals has become the focus of technological innovation in this field. Some studies attempt to improve multi-physical field detection capability through hardware integration or data fusion, but still cannot fundamentally solve the core problems of redundant transmission system, low signal excitation efficiency and insufficient anti-interference capability. In practical applications, nuclear magnetic resonance method and transient electromagnetic method are independent systems, which usually need to be equipped with dedicated transmission and reception devices. This not only leads to large hardware size, high cost and large energy consumption, but also increases the difficulty of field layout and maintenance. In addition, there are technical bottlenecks in the timing and spatial coordination between independent systems, making it difficult to realize true synchronization acquisition and collaborative analysis, affecting the fusion effect and interpretation accuracy of multi-physical field data. SUMMARY

[0004] In view of the defects of the prior art, the purpose of the present application is to provide a method and system for extracting transient electromagnetic signals by ground nuclear magnetic resonance, which aims to solve the problem that the existing nuclear magnetic resonance method and transient electromagnetic method are independent systems, the timing and spatial coordination between independent systems have technical bottlenecks, it is difficult to realize synchronization acquisition and collaborative analysis, and it affects the fusion effect and interpretation accuracy of multi-physical field data.

[0005] To achieve the above-mentioned purpose, in a first aspect, the present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, which specifically comprises the following steps:

[0006] Step one: periodically transmitting nuclear magnetic resonance excitation pulses to the underground medium, and extracting nuclear magnetic resonance off-pulse as transient electromagnetic excitation signal in the off phase of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal includes nuclear magnetic resonance excitation pulse and nuclear magnetic resonance off-pulse;

[0007] Step two: detecting the transient electromagnetic response signal after each nuclear magnetic resonance excitation pulse is off;

[0008] Step three: collecting the nuclear magnetic resonance response signal when the last nuclear magnetic resonance excitation pulse is off;

[0009] In the application, the same transmitting coil and power source are used to excite the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal, and the same receiving coil is used to collect the transient electromagnetic response signal and the nuclear magnetic resonance response signal.

[0010] 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.

[0011] Further preferably, in step one, the voltage and current signals across the transmitting coil are detected in real time during the off phase of the nuclear magnetic resonance excitation pulse, the nuclear magnetic resonance off pulse signal containing high-frequency components is separated by high-speed sampling and digital filtering technology, and is used as the transient electromagnetic excitation signal.

[0012] Further preferably, in step one, the current amplitude of the nuclear magnetic resonance off pulse is adjusted in real time by a current control circuit according to the transmission requirements of the transient electromagnetic excitation signal, the falling edge of the nuclear magnetic resonance off pulse is obtained by using the pulse edge enhancement method, and the optimal impedance matching between the transmitting coil and the power source is achieved by using parallel or series adjustable impedance devices.

[0013] Further preferably, in step two, a timing synchronization circuit is used to set the collection window and reference time of the transient electromagnetic response signal.

[0014] Further preferably, in steps two and three, the characteristics of the nuclear magnetic resonance response signal and the transient electromagnetic response signal are distinguished in real time, and the collection mode is dynamically switched to the collection of the transient electromagnetic response signal or the collection of the nuclear magnetic resonance response signal according to the signal change trend.

[0015] In the second aspect, the application provides a system for extracting a transient electromagnetic signal by ground nuclear magnetic resonance, comprising:

[0016] The transmitting module is configured to periodically transmit a nuclear magnetic resonance excitation pulse to the underground medium.

[0017] The off pulse extraction module is configured to extract the nuclear magnetic resonance off pulse as the transmission 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.

[0018] a signal receiving module, configured 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;

[0019] The transmitting coil in the transmitting module is configured to excite the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal; and the receiving coil in the signal receiving module is configured to collect the transient electromagnetic response signal and the nuclear magnetic resonance response signal.

[0020] a time division multiplexing logic control module, configured to control the timing of the transmission of the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal, the turning off of the pulse extraction, the signal collection, and the switching of the signal collection mode.

[0021] Further preferably, the transmitting module comprises:

[0022] a frequency modulation unit, configured to match the center frequency of the nuclear magnetic resonance excitation pulse to the proton resonance characteristics of different underground media by adjusting the center frequency of the nuclear magnetic resonance excitation pulse;

[0023] a pulse adjustment unit, configured 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;

[0024] a control unit, configured to switch and cooperatively drive the pulse sequence in the nuclear magnetic resonance signal in multiple channels to realize multiple excitations and turn-offs in one cycle of the nuclear magnetic resonance signal.

[0025] Overall, the above technical solutions conceived by the present application have the following beneficial effects compared with the prior art:

[0026] The present application provides a method for extracting a transient electromagnetic signal by ground nuclear magnetic resonance, which combines the two physical detection methods of nuclear magnetic resonance and transient electromagnetic method, uses a nuclear magnetic resonance device to collect the nuclear magnetic resonance signal of underground media, and uses a turn-off pulse as a transient electromagnetic excitation signal in the turn-off stage. Therefore, under the excitation of the turn-off pulse, the electromagnetic response in the underground media can be effectively excited, so that the transient electromagnetic response signal can be accurately collected, and the transmission device and the receiving device can be highly integrated and multiplexed. In view of the problems of hardware redundancy, large size, and complex deployment of the previous geophysical exploration system, the same transmitting coil and power supply are used in the present application, which not only greatly reduces the equipment cost and energy consumption, but also makes the field layout and maintenance more convenient. By directly extracting a high-energy turn-off pulse as a transient electromagnetic excitation signal in the turn-off stage of the nuclear magnetic resonance excitation pulse, the signal utilization efficiency and excitation capacity of the system as a whole are significantly improved, and there is no need to additionally configure an independent transient electromagnetic transmission system, which greatly optimizes the equipment framework.

[0027] The application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, energy intensity and frequency range of the off pulse are ensured to meet actual requirements of underground conductive body and aquifer detection by optimizing transmission and matching parameters, high-speed and stable switching between different excitation and receiving modes is realized, various electromagnetic noises and crosstalk are effectively suppressed by adopting multi-stage digital filtering, time sequence synchronization and time-sharing acquisition technology, signal quality is improved, and high-precision detection on underground weak signals can be realized even in a relatively strong noise environment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a method flowchart for extracting transient electromagnetic signals by ground nuclear magnetic resonance provided by the application;

[0029] Figure 2 is a transmission waveform schematic diagram of the method for extracting transient electromagnetic signals by ground nuclear magnetic resonance provided by the application. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the application clearer, the application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0031] In the application, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In this paper, the symbol " / " represents the relationship of or, for example, A / B represents A or B.

[0032] In the application, the terms "first" and "second" in the description and claims are used to distinguish different objects, rather than to describe the specific order of the objects.

[0033] In the embodiments of the application, the words "exemplary" or "for example" are used to mean serving as an example, illustration, or description. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the application should not be interpreted as more preferred or more advantageous than other embodiments or design solutions. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0034] In the description of the embodiments of the application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0035] The embodiments of the application are described below with reference to the drawings in the embodiments of the application.

[0036] As Figure 1As shown, the present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, comprising the following steps:

[0037] Step S1: periodically emitting nuclear magnetic resonance excitation pulses to the underground medium by using the nuclear magnetic resonance emission module, which contains multiple excitation and off processes in a complete nuclear magnetic resonance cycle;

[0038] Further preferably, the method for acquiring nuclear magnetic resonance signals comprises the following steps: adjusting the center frequency of the excitation pulse by the frequency modulation device in the nuclear magnetic resonance emission module to match the proton resonance characteristics of different underground media, and controlling the repetition time and width of the pulse sequence to realize the resolution and detection selectivity of different depths and properties of the underground medium, and using multi-channel synchronous acquisition technology to improve the spatial resolution of the nuclear magnetic resonance response signal; after multiple excitation-off-transient electromagnetic measurement in a complete nuclear magnetic resonance cycle, the decay ends and the nuclear magnetic resonance signals are measured uniformly;

[0039] Step S2: in the off stage of each excitation pulse, extract the off pulse as a transient electromagnetic excitation signal to realize the homologous excitation of the nuclear magnetic resonance signal and the transient electromagnetic excitation signal;

[0040] Further preferably, the current amplitude, off rate of the nuclear magnetic resonance off pulse and the impedance matching of the emission coil are designed for electromagnetic compatibility to generate a wideband and high-stability transient electromagnetic emission waveform;

[0041] Further preferably, as shown, Figure 2 in the off stage of the excitation pulse, the voltage and current signals across the coil are detected in real time, the nuclear magnetic resonance off pulse signal containing rich high-frequency components is separated by high-speed sampling and digital filtering technology, and the nuclear magnetic resonance off pulse is used as the emission excitation source of the transient electromagnetic method; after each off, the system automatically switches to the transient electromagnetic receiving mode to acquire and process the transient electromagnetic response signal, and a pulse recognition threshold is set at the signal processing end to realize the automatic extraction and marking of the off pulse;

[0042] Further preferably, the frequency range and energy intensity of the turn-off pulse are adjusted according to the electromagnetic characteristics of the underground medium to maximize the excitation efficiency of the signal and reduce possible signal attenuation; in addition, the emission duration and waveform of the turn-off pulse signal are 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, the current amplitude of the turn-off pulse is adjusted in real time by a high-precision current control circuit according to the emission requirements of the transient electromagnetic excitation signal, the turn-off 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 through parallel or series adjustable impedance units, thereby suppressing unnecessary harmonics and parasitic oscillation and improving the consistency and energy utilization rate of the wideband high-stability transient electromagnetic emission waveform.

[0043] Step S3: immediately after each excitation pulse turn-off, switch the system to the transient electromagnetic response signal receiving mode, collect the transient electromagnetic response signal through the same receiving coil, and realize multiple transient electromagnetic detections within one nuclear magnetic resonance cycle;

[0044] Further preferably, the turn-off pulse signal has sufficient frequency range and energy intensity to effectively excite the electromagnetic response in the underground medium and thereby produce a transient electromagnetic response signal; for example, Figure 2 As shown, through the collaborative design of the coil parameters and power output circuit of the nuclear magnetic resonance emission module, a single emission system can complete the signal output of both nuclear magnetic resonance and transient electromagnetic excitation modes, cooperate with the isolation relay, radio frequency switching circuit and distributed grounding system, effectively reduce the electrical coupling and crosstalk under different modes, improve the overall working stability and reliability of the system, and simplify the field detection operation process.

[0045] More specifically, by multiplexing the coil and power device of the nuclear magnetic resonance emission module, the independent emission device of the traditional transient electromagnetic method is replaced, reducing the complexity of the equipment;

[0046] Step S4: after experiencing multiple excitation-turn-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 and collect the complete nuclear magnetic resonance response signal.

[0047] Further preferably, by the time division multiplexing logic control module, after the end of the nuclear magnetic resonance acquisition phase 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, while the timing synchronization circuit is applied to strictly limit the acquisition window and reference time of the transient electromagnetic response signal, so as to improve the extraction efficiency and measurement accuracy of weak signals; wherein the automatic switching process includes real-time discrimination of nuclear magnetic resonance signal characteristics, dynamic adjustment of switching time according to the acquired signal change trend, and short-time protection of the receiving system at the switching moment to prevent transient interference in the switching process from affecting subsequent signal acquisition.

[0048] In a second aspect, the application provides a system for extracting transient electromagnetic signals by ground nuclear magnetic resonance, comprising:

[0049] The transmitting module is used for transmitting nuclear magnetic resonance excitation pulses to the underground medium, and is internally provided with a frequency modulation unit, a pulse adjustment unit and a power amplification unit. By an external control signal, the output waveform parameters are automatically optimized according to the resonance frequency and geological conditions of the underground medium, so as to realize nuclear magnetic resonance excitation of different depths or different material types. The transmitting unit supports high-speed switching of pulse sequences and multi-channel cooperative driving, realizes multiple excitation-off in a complete nuclear magnetic resonance cycle, and provides response data with high signal-to-noise ratio for transient electromagnetic detection and nuclear magnetic resonance measurement.

[0050] Further, the transmitting unit includes a group of transmitting coils for nuclear magnetic resonance excitation and transient electromagnetic excitation signal transmission, and a power supply capable of supporting large current and high-speed on-off. The transmitting unit is structurally provided with an automatic switching switch, an isolation relay, an impedance adaptive matching network and an electromagnetic shielding layer, so as to realize nuclear magnetic resonance excitation and transient electromagnetic excitation sharing the same transmitting loop, and ensure that electromagnetic crosstalk, power loss and system noise caused by high frequency and high amplitude change are effectively suppressed during the working mode switching process, thereby improving the working efficiency and overall stability of the transmitting system.

[0051] The off-pulse extraction module is used for continuously and real-timely detecting the current and voltage information across the transmitting coil at the moment when the nuclear magnetic resonance excitation pulse is off, and automatically extracting each off-pulse signal by high-speed sampling, digital filtering, edge detection and pulse recognition, and taking the off-pulse signal as the transient electromagnetic excitation signal.

[0052] The parameter control module is used for dynamically adjusting the amplitude, slope and timing of the off-pulse according to the real-time monitored stratum feedback or preset method, so as to ensure that the transient electromagnetic excitation signal has optimal energy and wide frequency band, and has an abnormal state self-checking and protection function.

[0053] The signal receiving module comprises a receiving coil, a preamplifier, a bandwidth adjustable filter, an analog-to-digital conversion module and a digital signal processor, can sequentially collect the nuclear magnetic resonance response signal and the transient electromagnetic response signal of the underground medium through the same receiving coil, and adaptively adjusts the gain, bandwidth and sampling rate in different modes; the unit also comprises a time division multiplexing control logic, a timing synchronization module and a digital signal processing module based on adaptive filtering and multi-domain noise reduction algorithm, effectively improves the detection capability and anti-interference performance of weak signals, and provides high-quality data stream for the back-end data analysis;

[0054] The time division multiplexing logic control module is configured with a high-precision timing control chip, can implement unified timing management on the nuclear magnetic resonance emission, off-pulse extraction, signal collection and mode switching and other processes, and realizes switching between different collection modes according to the actual decay process of the nuclear magnetic resonance signal; the system parameters are dynamically adjusted in the automatic switching process, the key units are protected from transient interference, and the functions of state monitoring, abnormal response and remote adaptive adjustment are combined, so that the efficient, stable and intelligent operation of the whole system is ensured.

[0055] Compared with the prior art, the present application has the following advantages:

[0056] The present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, which combines nuclear magnetic resonance and transient electromagnetic two physical detection methods, uses nuclear magnetic resonance equipment to collect nuclear magnetic resonance signals of underground medium, and uses off-pulse as transient electromagnetic excitation signal in the off-pulse stage. Therefore, under the excitation of off-pulse, the electromagnetic response in the underground medium can be effectively excited, so that the transient electromagnetic response signal can be accurately collected, and the emission device and the receiving device can be highly integrated and multiplexed; for the problems of hardware redundancy, large size and complex deployment of the previous geophysical exploration system, the same transmitting coil and power supply are used in the present application, which not only greatly reduces the equipment cost and energy consumption, but also makes the field layout and maintenance more convenient; by directly extracting high-energy off-pulse as transient electromagnetic excitation signal in the off-pulse stage of nuclear magnetic resonance excitation pulse, the signal utilization efficiency and excitation capacity of the whole system are significantly improved, and there is no need to additionally configure an independent transient electromagnetic emission system, which greatly optimizes the equipment framework.

[0057] The present application provides a method for extracting transient electromagnetic signals by ground nuclear magnetic resonance, which optimizes the emission and matching parameters to ensure that the energy intensity and frequency range of the off-pulse can meet the actual needs of underground conductive body and aquifer detection, and realizes high-speed and smooth switching between different excitation and receiving modes, adopts multi-stage digital filtering, timing synchronization and time division collection technology, effectively suppresses various electromagnetic noises and crosstalk, and improves the signal quality, so that high-precision detection of underground weak signals can be realized even in a noisy environment.

[0058] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method of extracting transient electromagnetic signals from ground nuclear magnetic resonance, characterized by, The method comprises the following steps: Step 1: periodically transmitting nuclear magnetic resonance excitation pulses to the underground medium, and extracting nuclear magnetic resonance off-pulses as transient electromagnetic excitation signals during the off period of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal comprises the nuclear magnetic resonance excitation pulse and the nuclear magnetic resonance off-pulse; Step 2: detecting the transient electromagnetic response signal after the off of each nuclear magnetic resonance excitation pulse; Step 3: collecting the nuclear magnetic resonance response signal when the off of the last nuclear magnetic resonance excitation pulse; In the step 1, the voltage and current signals across the transmitting coil are detected in real time during the off period of the nuclear magnetic resonance excitation pulse, and the nuclear magnetic resonance off-pulse signal is separated by high-speed sampling and digital filtering technology and used as the transient electromagnetic excitation signal; In the step 1, the current amplitude of the nuclear magnetic resonance off-pulse is adjusted in real time by a current control circuit according to the transmission requirements of the transient electromagnetic excitation signal, the off rate of the nuclear magnetic resonance off-pulse is obtained by using the pulse edge enhancement method to obtain the falling edge, and the optimal impedance matching of the transmitting coil and the power supply is realized by using parallel or series adjustable impedance devices. In the step 1, 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.

2. The method of claim 1, wherein, In the step 2, the acquisition window and the reference time of the transient electromagnetic response signal are set by using a time sequence synchronization circuit.

3. The method of claim 1, wherein, In the steps 2 and 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 collecting the nuclear magnetic resonance response signal is switched dynamically according to the signal change trend.

4. The method according to claim 1 or 3, characterized in that, The method comprises the following steps:

5. A system for extracting transient electromagnetic signals from ground nuclear magnetic resonance, characterized in that, A transmitting module for periodically transmitting nuclear magnetic resonance excitation pulses to the underground medium; An off-pulse extraction module for extracting nuclear magnetic resonance off-pulses as transient electromagnetic excitation signals during the off period of each nuclear magnetic resonance excitation pulse; wherein the nuclear magnetic resonance signal comprises the nuclear magnetic resonance excitation pulse and the nuclear magnetic resonance off-pulse; A signal receiving module for detecting the transient electromagnetic response signal after the off of each nuclear magnetic resonance excitation pulse; and collecting the nuclear magnetic resonance response signal when the off of the last nuclear magnetic resonance excitation pulse; In the transmitting module, the transmitting coil is used to excite the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal; and in the signal receiving module, the receiving coil is used to collect the transient electromagnetic response signal and the nuclear magnetic resonance response signal; A time-sharing multiplexing logic control module for time sequence control of the transmission of the nuclear magnetic resonance excitation pulse and the transient electromagnetic excitation signal, the off-pulse extraction, the signal collection, and the switching of the collection mode. ​ The turn-off pulse extraction module is used for detecting the current and voltage information between the two ends of the transmitting coil in real time at the moment of the turn-off of the nuclear magnetic resonance excitation pulse, and through high-speed sampling, digital filtering, edge detection and pulse recognition, the extraction of the nuclear magnetic resonance turn-off pulse signal each time is realized, and the nuclear magnetic resonance turn-off pulse signal each time is taken as the transient electromagnetic excitation signal.

6. The system of claim 5, wherein, The transmitting module comprises: A frequency modulation unit is used for adjusting the center frequency of the nuclear magnetic resonance excitation pulse to match the proton resonance characteristics of different underground media; A pulse adjustment unit is used for controlling the repetition time and width of the nuclear magnetic resonance excitation pulse sequence to distinguish and detect underground media of different depths and properties; A control unit is used for switching and multi-channel cooperative driving of the pulse sequence in the nuclear magnetic resonance signal, and multiple excitations and turn-offs are realized in a complete cycle of the nuclear magnetic resonance signal.

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