A low-field nuclear magnetic resonance exploration device and method for effectively shortening dead time

Abstract

The invention discloses a low-field nuclear magnetic resonance exploration device and method for effectively shortening the dead time, and relates to the field of electrical signal acquisition. The low-field nuclear magnetic resonance exploration device for effectively shortening the dead time comprises: a host computer for communicating with a main control circuit; a main control circuit for controlling and acquiring a core and integrated control device operation; a power amplifier circuit for amplifying a power signal input by the main control circuit and then transmitting an AC pulse excitation coil; the invention has the following beneficial effects: the coil adopts a transceiver integrated differential structure to suppress common-mode noise interference and improve the signal-to-noise ratio of detection; the Q-conversion circuit reduces the quality factor of the coil by connecting an energy discharge resistor in parallel at both ends of the coil, so as to achieve the purpose of quickly discharging the energy stored in the coil, and can effectively shorten the dead time; the high-isolation fast-switching radio frequency switch can effectively reduce the insertion loss and the generated noise, significantly reduce the switching time, further shorten the dead time, and improve the detection effect of a short-relaxation target body.

Description

Technical Field

[0001] The invention relates to the field of electrical signal acquisition, and in particular to a low-field nuclear magnetic resonance exploration device and method for effectively shortening dead time. Background Art

[0002] Cores are the most intuitive and practical data for understanding underground reservoirs and mineral-bearing characteristics. Using low-field indoor nuclear magnetic resonance technology to conduct indoor fine verification and analysis of core geological samples is an important means to guide non-destructive identification of geological samples and rock and soil geological surveys. The main content of core analysis is to explore the distribution of organic hydrocarbons, petroleum or polluted components in cores. This type of core fluid is divided into short relaxation components in low-field indoor magnetic resonance technology. However, the dead time of low-field nuclear magnetic resonance detection instruments will seriously affect the detection effect of short relaxation components, resulting in the inability to accurately analyze underground organic hydrocarbon pollution.

[0003] The basic working process of low-field nuclear magnetic resonance technology is to first emit a radio frequency pulse in the excitation coil. The high-power radio frequency pulse is emitted from the coil to the sample to excite the hydrogen nucleus. After the excitation pulse is removed, the remaining energy in the coil is discharged and the coil is switched to the receiving mode to start receiving the nuclear magnetic resonance echo signal. The hydrogen nucleus begins to recover to the initial equilibrium state after the excitation pulse is removed. The energy released during this period is the echo signal. This process is a relaxation process, which is manifested as an exponential decay over time. The relaxation time of components such as organic hydrocarbons and petroleum is extremely short. Dead time refers to the interval between the radio frequency system transmitting the radio frequency pulse and receiving the echo signal. In the low-field nuclear magnetic resonance system, the signal acquisition window is short. When performing conventional signal detection, the dead time is too long, resulting in the loss of early high-amplitude signals due to relaxation attenuation. When analyzing core geological samples with short relaxation times, the dead time is too long, causing such short relaxation components to completely decay outside the acquisition window, resulting in the loss of all effective signals.

[0004] The dead time mainly consists of two parts: the channel switching time of the coil transmit / receive mode and the residual energy discharge time of the coil after switching. For the former, the research on RF switch technology is relatively mature in radar and communication, but there are few RF switches designed for magnetic resonance, especially in the short dead zone scenario, which has higher requirements for insertion loss, high-power isolation and switching time. The difficulty lies in: during transmission, the switch needs to meet the tolerance of high-power RF transmission pulses and have high isolation to protect the receiving end preamplifier from damage; during reception, the switch needs to have a sufficiently low insertion loss to avoid attenuation of weak magnetic resonance signals. For the latter, coil energy release technology usually uses large resistance resistors to consume residual electrical energy in the circuit, and this method of simply connecting large resistors in series can only consume energy but cannot effectively reduce the energy release time. Existing instruments are still unable to achieve fast switching of high-frequency and high-isolation transceiver RF switches and fast discharge of coil energy. There is still a problem of long dead time, which needs to be improved.

[0005] Chinese patent CN112671381B discloses a "wideband RF switch and its edge optimization method", which uses a DC-isolated AC circuit to form a control signal into a differential mode signal and a RF signal into a common mode signal. The signal-to-noise ratio of the signal is improved to a certain extent while meeting the requirements of the low-field nuclear magnetic resonance system for the RF switch. However, the proposed method does not achieve the purpose of shortening the dead time.

[0006] Chinese patent CN109884718B discloses a "magnetic resonance water detection device and method for effectively reducing dead time". The dead time is shortened to a certain extent by eliminating the coupling effect of transmission on reception through a compensation coil. However, the proposed method only shortens the dead time from the aspect of coil energy release, and still does not solve the core problem of increased dead time caused by switching of transceiver channels while maintaining high isolation in high-frequency transmission.

[0007] In summary, the existing technology fails to solve the problem of too long dead time. Summary of the invention

[0008] The object of the present invention is to provide a low-field nuclear magnetic resonance exploration device and method that can effectively shorten the dead time, so as to solve the problems raised in the above-mentioned background technology.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A low-field nuclear magnetic resonance exploration device that effectively shortens dead time, comprising:

[0011] Host computer, used to communicate with the main control circuit;

[0012] Main control circuit, used for control and acquisition core, integrated control device operation;

[0013] A power amplifier circuit is used to amplify the power signal input from the main control circuit and then transmit an AC pulse to excite the coil;

[0014] High isolation fast switching low Q value circuit (Q is the quality factor of the coil, and the recovery time of the coil is proportional to the Q value of the coil) is used to ensure that the device switches quickly between the transmission mode and the receiving mode; it has high isolation to protect the instrument amplifier circuit from being damaged by high-power signals; it can quickly discharge the energy stored in the coil by reducing the quality factor of the coil;

[0015] The instrument amplifier circuit is used to perform low-noise amplification on the echo signal received by the coil and then output it to the main control circuit;

[0016] The first end of the host computer is connected to the first end of the main control circuit, the second end of the main control circuit is connected to the first end of the power amplifier circuit, the third end of the power amplifier circuit is connected to the first end of the high isolation fast switching low Q value circuit, the second end and the third end of the high isolation fast switching low Q value circuit are respectively connected to the first end and the second end of the instrument amplifier circuit, the fourth end of the high isolation fast switching low Q value circuit is connected to the second end of the power amplifier circuit, and the third end of the instrument amplifier circuit is connected to the third end of the main control circuit.

[0017] As a further solution of the present invention: the host computer includes:

[0018] A user interface is used to generate interactive signals through human-computer interaction and output the interactive signals to the control software;

[0019] The control software is used to send control instructions to the main control circuit after receiving the interactive signal, control the start and end of the low-field nuclear magnetic resonance exploration, and receive data returned by the main control circuit;

[0020] The user interface is connected to the first end of the control software, and the second end of the control software is connected to the first end of the main control circuit.

[0021] As a further solution of the present invention: the main control circuit includes:

[0022] Communication interface, used to establish communication between the main control circuit and the host computer;

[0023] ADC, used for digital processing of the echo signal amplified by the instrument amplifier circuit;

[0024] Digital reception is used to extract the amplitude and phase information of the digitally processed echo signal and feed it back to the host computer through the communication interface;

[0025] The pulse sequence programmer is composed of a timer and a state machine. After receiving the control instruction of the host computer through the communication interface, it generates a pulse sequence, generates the corresponding control signal (the control signal required by each analog circuit) according to the timing requirements of the pulse sequence, and outputs it to the power amplifier circuit;

[0026] The first end of the communication interface is connected to the first end of the host computer, the second end of the communication interface is connected to the first end of the pulse sequence programmer, the second end of the pulse sequence programmer is connected to the first end of the power amplifier circuit, the third end of the communication interface is connected to the first end of the digital receiver, the second end of the digital receiver is connected to the first end of the ADC, and the second end of the ADC is connected to the third end of the instrument amplifier circuit.

[0027] As a further solution of the present invention: the high isolation fast switching low Q value circuit includes:

[0028] Integrated transceiver differential coil, the coil is evenly wound on a non-metallic frame to avoid the adjacent interference effect caused by separate transceiver coils;

[0029] Q-conversion circuit, used to reduce the quality factor Q of the coil within a period of time after the pulse transmission is completed to quickly discharge the energy stored in the coil;

[0030] High-isolation fast-switching RF switch, used to quickly switch the device between transmit mode and receive mode, and high-isolation protection instrument amplifier circuit from being damaged by high-power signals during pulse transmission and energy discharge;

[0031] The high-isolation fast-switching radio frequency switch includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, and the Q-conversion circuit includes a first resistor and a second resistor;

[0032] The negative electrode of the first switch is connected to the first end of the instrument amplifier circuit, the positive electrode of the first switch is connected to one end of the first resistor, one end tap of the transceiver differential coil, and the negative electrode of the third switch, the other end of the first resistor is connected to the positive electrode of the second switch, the negative electrode of the second switch is grounded, the positive electrode of the third switch is connected to the third end of the power amplifier circuit, the middle tap of the transceiver differential coil is grounded, the other end tap of the transceiver differential coil is connected to the positive electrode of the fourth switch, the positive electrode of the fifth switch, and the positive electrode of the sixth switch, the negative electrode of the fourth switch is connected to the second end of the instrument amplifier circuit, the negative electrode of the fifth switch is connected to one end of the second resistor, the other end of the second resistor is grounded, and the negative electrode of the sixth switch is connected to the second end of the power amplifier circuit.

[0033] As a further solution of the present invention: the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch are PIN diode switches, and the PIN diode switches include reverse-series PIN diodes, capacitors, and RF choke inductors. The reverse-series PIN diodes are used to control the switching mode, the RF choke inductor is used to provide a bias voltage for the reverse-series PIN diodes, and the capacitors are used for DC decoupling.

[0034] A low-field nuclear magnetic resonance exploration method for effectively shortening dead time comprises the following steps:

[0035] Step 1: After receiving the control instruction from the host computer, the main control circuit decodes the control instruction and creates an instruction to generate a control signal that meets the timing requirements of the pulse sequence;

[0036] Step 2: The transmission control signal is converted into a high-current driving control signal after passing through the power amplifier circuit to quickly turn on the RF MOS tube in the power amplifier circuit, and the 600V DC high voltage is converted into a high-power RF pulse with a peak value of 2400V after chopping;

[0037] Step 3, the third switch and the sixth switch are closed, and a high-power radio frequency pulse excites the coil;

[0038] Step 4: The second switch and the fifth switch are closed to quickly discharge the energy stored in the coil;

[0039] Step 5, the first switch and the fourth switch are closed, so that the device switches from the transmitting mode to the receiving mode;

[0040] Step 6, the instrument uses an amplifier circuit to perform low-noise amplification on the echo signal received by the coil;

[0041] Step 7: The amplified echo signal is collected and digitized by the main control circuit, and the digital phase-sensitive detection algorithm is used to extract the amplitude and phase information, and the data is transmitted to the host computer through the CAN bus.

[0042] As a further solution of the present invention: Step 3 is specifically that the third switch and the sixth switch of the high-isolation fast-switching RF switch are closed, and the first switch, the second switch, the fourth switch and the fifth switch are opened; this high-power RF pulse is transmitted to the coil, and emitted by the coil into the sample to excite hydrogen nuclei.

[0043] As a further solution of the present invention: Step 4 is specifically that after the pulse transmission is completed, the second switch and the fifth switch of the high-isolation fast-switching RF switch are closed, the first switch, the third switch, the fourth switch and the sixth switch are opened, and the first resistor and the second resistor are connected in parallel at both ends of the coil to reduce the quality factor of the coil, thereby quickly discharging the energy stored in the coil.

[0044] As a further solution of the present invention: Step 5 is specifically, after the energy discharge is completed, the echo signal is prepared to be received. At this time, the second switch, the third switch, the fifth switch and the sixth switch of the high-isolation fast-switching RF switch are disconnected, and the first switch and the fourth switch are closed, so that the device is switched from the transmitting mode to the receiving mode, allowing the echo signal to enter the instrument amplifier circuit.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows: the coil of the present invention adopts a differential structure of integrated transmission and reception, which can better suppress common-mode noise interference and improve the signal-to-noise ratio of detection compared with the traditional single-ended coil; within a period of time after the pulse transmission is completed, the Q-conversion circuit reduces the quality factor of the coil by connecting the energy discharge resistor in parallel at both ends of the coil, so as to achieve the purpose of quickly discharging the energy stored in the coil, and can effectively shorten the dead time, obtain early signals, and realize the detection of short relaxation targets; the high-isolation fast-switching radio frequency switch can enable the device to quickly switch between the transmission mode and the receiving mode, and the high-isolation protection instrument amplifier circuit is not damaged by high-power signals. By designing a PIN diode switch, the PIN diode has a low-doped intrinsic (Intrinsic) semiconductor layer added between the P and N semiconductor materials. This special structure enables it to control the resistance state by adjusting the DC bias current and then control the on-off of the signal in the radio frequency circuit. The high-isolation fast-switching radio frequency switch can effectively reduce the insertion loss and the noise generated, significantly reduce the switching time, further shorten the dead time, and improve the detection effect of the short relaxation target. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The schematic diagram is a low-field nuclear magnetic resonance exploration device that effectively shortens the dead time.

[0047] Figure 2 This is a working diagram when the third switch and the sixth switch are closed.

[0048] Figure 3 This is a working diagram when the second switch and the fifth switch are closed.

[0049] Figure 4 It is a working schematic diagram when the first switch and the fourth switch are closed.

[0050] Figure 5 The present invention is a flow chart of a low-field nuclear magnetic resonance exploration method which effectively shortens the dead time.

[0051] In the figure: 1-control software, 2-user interface, 3-communication interface, 4-digital reception, 5-ADC, 6-timer, 7-state machine, 8-instrument amplifier circuit, 9-high isolation fast switching low Q value circuit, 10-power amplifier circuit, 11-transceiver integrated differential coil, 12-Q-conversion circuit, 13-high isolation fast switching RF switch. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0053] See also Figure 1 , a low-field nuclear magnetic resonance exploration device that effectively shortens the dead time, comprising:

[0054] Host computer, used to communicate with the main control circuit;

[0055] Main control circuit, used for control and acquisition core, integrated control device operation;

[0056] The power amplifier circuit 10 is used to amplify the power signal input from the main control circuit and then transmit an AC pulse to excite the coil;

[0057] The high isolation fast switching low Q value circuit 9 (Q is the quality factor of the coil, and the recovery time of the coil is proportional to the Q value of the coil) is used to ensure that the device switches quickly between the transmission mode and the receiving mode; it has high isolation and protects the instrument amplifier circuit 8 from being damaged by high-power signals; it can quickly discharge the energy stored in the coil by reducing the quality factor of the coil;

[0058] The instrument amplifier circuit 8 (differential preamplifier) ​​is used to perform low-noise amplification on the echo signal received by the coil and then output it to the main control circuit;

[0059] The first end of the host computer is connected to the first end of the main control circuit, the second end of the main control circuit is connected to the first end of the power amplifier circuit 10, the third end of the power amplifier circuit 10 is connected to the first end of the high isolation fast switching low Q value circuit 9, the second end and the third end of the high isolation fast switching low Q value circuit 9 are respectively connected to the first end and the second end of the instrument amplifier circuit 8, the fourth end of the high isolation fast switching low Q value circuit 9 is connected to the second end of the power amplifier circuit 10, and the third end of the instrument amplifier circuit 8 is connected to the third end of the main control circuit.

[0060] In this example: See Figure 1 , the host computer includes:

[0061] A user interface 2, used to generate an interaction signal through human-computer interaction and output the interaction signal to the control software 1;

[0062] The control software 1 is used to send control instructions to the main control circuit after receiving the interactive signal, control the start and end of the low-field nuclear magnetic resonance exploration, and receive data returned by the main control circuit;

[0063] The user interface 2 is connected to a first end of the control software 1 , and a second end of the control software 1 is connected to a first end of the main control circuit.

[0064] In this example: See Figure 1 , the main control circuit includes:

[0065] Communication interface 3, used to establish communication between the main control circuit and the host computer;

[0066] ADC5, used for digital processing of the echo signal amplified by the instrument amplifier circuit 8;

[0067] Digital receiving 4 is used to extract the amplitude and phase information of the echo signal after digital processing, and feed it back to the host computer through the communication interface 3;

[0068] The pulse sequence programmer is composed of a timer 6 and a state machine 7. After receiving the control instruction of the host computer through the communication interface 3, it generates a pulse sequence, generates corresponding control signals (control signals required by each analog circuit, transmission control signals to control the power amplifier circuit 10, the control signals of the first switch S1 to the sixth switch S6) according to the timing requirements of the pulse sequence, and outputs them to the power amplifier circuit 10;

[0069] The first end of the communication interface 3 is connected to the first end of the host computer, the second end of the communication interface 3 is connected to the first end of the pulse sequence programmer, the second end of the pulse sequence programmer is connected to the first end of the power amplifier circuit 10, the third end of the communication interface 3 is connected to the first end of the digital receiver 4, the second end of the digital receiver 4 is connected to the first end of the ADC5, and the second end of the ADC5 is connected to the third end of the instrument amplifier circuit 8.

[0070] In this example: See Figure 1 , the high isolation fast switching low Q value circuit 9 comprises:

[0071] The transceiver integrated differential coil 11 is wound evenly on a non-metallic frame to avoid the adjacent interference effect caused by the separate transceiver coils;

[0072] Q-conversion circuit 12, used to reduce the quality factor Q of the coil within a period of time after the pulse transmission is completed to quickly discharge the energy stored in the coil;

[0073] A high-isolation fast-switching radio frequency switch 13 is used to quickly switch the device between the transmitting mode and the receiving mode, and to protect the instrument amplifier circuit 8 from being damaged by high-power signals during pulse transmission and energy discharge;

[0074] The high isolation fast switching RF switch 13 includes a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, and a sixth switch S6, and the Q-conversion circuit 12 includes a first resistor R1 and a second resistor R2;

[0075] The negative electrode of the first switch S1 is connected to the first end of the instrument amplifier circuit 8, the positive electrode of the first switch S1 is connected to one end of the first resistor R1, one end of the transceiver differential coil 11, and the negative electrode of the third switch S3, the other end of the first resistor R1 is connected to the positive electrode of the second switch S2, the negative electrode of the second switch S2 is grounded, the positive electrode of the third switch S3 is connected to the third end of the power amplifier circuit 10, the middle tap of the transceiver differential coil 11 is grounded, the other end of the transceiver differential coil 11 is tapped to the positive electrode of the fourth switch S4, the positive electrode of the fifth switch S5, and the positive electrode of the sixth switch S6, the negative electrode of the fourth switch S4 is connected to the second end of the instrument amplifier circuit 8, the negative electrode of the fifth switch S5 is connected to one end of the second resistor R2, the other end of the second resistor R2 is grounded, and the negative electrode of the sixth switch S6 is connected to the second end of the power amplifier circuit 10.

[0076] The Q-conversion circuit 12 adopts a segmented discharge control method. Since the discharge resistors R1 and R2 are directly connected to the two ends of the coil, non-inductive power resistors are selected;

[0077] See also Figure 2 , in the RF pulse transmission stage, the third switch S3 and the sixth switch S6 of the high isolation fast switching RF switch 13 are closed, and the first switch S1, the second switch S2, the fourth switch S4 and the fifth switch S5 are opened. At this time, the Q value of the coil is determined by the resonant circuit of the coil itself;

[0078] See also Figure 3 After a certain period of time after the pulse emission is completed, the device enters the energy discharge stage. At this time, the second switch S2 and the fifth switch S5 of the high-isolation fast-switching RF switch 13 are closed, the first switch S1, the third switch S3, the fourth switch S4 and the sixth switch S6 are disconnected, and the first resistor R1 and the second resistor R2 are connected in parallel at both ends of the coil. The Q value of the coil is mainly determined by the resistance values ​​of the first resistor R1 and the second resistor R2, which reduces the Q value of the coil;

[0079] See also Figure 4 When the voltage across the coil drops to the diode forward voltage of 0.7 V, the Q-conversion circuit 12 no longer works, and the Q value of the coil is determined by the resonant circuit of the coil itself. At this time, the second switch S2, the third switch S3, the fifth switch S5 and the sixth switch S6 of the high isolation fast switching RF switch 13 are disconnected, and the first switch S1 and the fourth switch S4 are closed, and the device enters the echo signal receiving stage.

[0080] In this example: See Figure 1The first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are PIN diode switches. The PIN diode switch includes a reverse-series PIN diode, a capacitor, and an RF choke inductor. The reverse-series PIN diode is used to control the switch mode, the RF choke inductor is used to provide a bias voltage for the reverse-series PIN diode, and the capacitor is used for DC decoupling.

[0081] The packaging structure of the PIN diode adopts low-loss, high-shielding-effective packaging materials to effectively reduce the impact of external electromagnetic interference on switch performance; the PIN diode can choose model MA4P7441F-1091T.

[0082] In this example: See Figure 5 , a low-field nuclear magnetic resonance exploration method for effectively shortening the dead time, comprising the following steps:

[0083] Step 1, after receiving the control instruction from the host computer, the main control circuit decodes the control instruction and creates an instruction to generate a control signal that meets the timing requirements of the pulse sequence; the control signal includes: a transmission control signal, a control signal of the first switch S1 to the sixth switch S6;

[0084] Step 2, the transmission control signal is converted into a high-current driving control signal after passing through the power amplifier circuit 10 to quickly turn on the radio frequency MOS tube in the power amplifier circuit 10, and the 600V DC high voltage is converted into a high-power radio frequency pulse with a peak value of 2400V after chopping;

[0085] Step 3, the third switch S3 and the sixth switch S6 are closed, and a high-power radio frequency pulse excites the coil;

[0086] Step 4: The second switch S2 and the fifth switch S5 are closed to quickly discharge the energy stored in the coil;

[0087] Step 5, the first switch S1 and the fourth switch S4 are closed, so that the device switches from the transmitting mode to the receiving mode;

[0088] Step 6, the instrument uses an amplifier circuit 8 to perform low-noise amplification on the echo signal received by the coil;

[0089] Step 7: The amplified echo signal is collected and digitized by the main control circuit, and the digital phase-sensitive detection algorithm is used to extract the amplitude and phase information, and the data is transmitted to the host computer through the CAN bus.

[0090] In this example: See Figure 2Specifically, step 3 is as follows: the third switch S3 and the sixth switch S6 of the high-isolation fast-switching RF switch 13 are closed, and the first switch S1, the second switch S2, the fourth switch S4 and the fifth switch S5 are opened; this high-power RF pulse is transmitted to the coil and emitted by the coil to the sample to excite hydrogen nuclei.

[0091] In this example: See Figure 2 Specifically, step 4 is as follows: after the pulse transmission is completed, the second switch S2 and the fifth switch S5 of the high-isolation fast-switching RF switch 13 are closed, the first switch S1, the third switch S3, the fourth switch S4 and the sixth switch S6 are disconnected, and the first resistor R1 and the second resistor R2 are connected in parallel at both ends of the coil to reduce the quality factor of the coil, thereby quickly discharging the energy stored in the coil.

[0092] In this example: See Figure 2 Specifically, step 5 is to prepare to receive the echo signal after the energy discharge is completed. At this time, the second switch S2, the third switch S3, the fifth switch S5 and the sixth switch S6 of the high isolation fast switching RF switch 13 are disconnected, and the first switch S1 and the fourth switch S4 are closed, so that the device is switched from the transmitting mode to the receiving mode, allowing the echo signal to enter the instrument amplifier circuit 8.

[0093] The present invention sends instructions through the host computer, and the main control circuit generates all the control signals required by the entire timing and instrument. The power amplifier circuit 10 amplifies the low-power signal of the main control circuit into a signal with very high power to excite the coil; the coil adopts a differential structure of transmitting and receiving, which can better suppress common-mode noise interference and improve the signal-to-noise ratio of detection compared with the traditional single-ended coil; the Q-conversion circuit 12 reduces the quality factor of the coil by connecting the energy discharge resistor in parallel at both ends of the coil within a period of time after the pulse transmission is completed, so as to achieve the purpose of quickly discharging the energy stored in the coil, effectively shorten the dead time, obtain early signals, and realize the detection of short-relaxation targets; the high-isolation fast-switching radio frequency switch 13 can enable the device to quickly switch between the transmission mode and the receiving mode, and the high-isolation protection instrument amplifier circuit 8 is not affected by large The power signal is damaged. By designing a PIN diode switch, a low-doped intrinsic semiconductor layer is added between the P and N semiconductor materials. This special structure enables it to control the resistance state by adjusting the DC bias current and thus control the on-off of the signal in the RF circuit. The high-isolation fast-switching RF switch 13 can effectively reduce the insertion loss and the noise generated, significantly reduce the switching time, further shorten the dead time, and improve the detection effect of short-relaxation targets; the instrument amplifier circuit 8 performs low-noise amplification on the echo signal received by the coil; the main control circuit, as the control and acquisition core of the instrument, generates all timing and control signals according to the timing requirements of the pulse sequence, collects and processes the amplified signals, and completes the communication with the host computer.

[0094] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered as exemplary and non-restrictive in all respects.

[0095] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A low-field nuclear magnetic resonance exploration device that effectively shortens the dead time, characterized in that: The low-field nuclear magnetic resonance exploration device that effectively shortens the dead time comprises: Host computer, used to communicate with the main control circuit; Main control circuit, used for control and acquisition core, integrated control device operation; A power amplifier circuit is used to amplify the power signal input from the main control circuit and then transmit an AC pulse to excite the coil; High isolation fast switching low Q value circuit, used to ensure that the device switches quickly between the transmission mode and the receiving mode; with high isolation, the instrument amplifier circuit is protected from damage by high-power signals; it can quickly discharge the energy stored in the coil by reducing the quality factor of the coil; The instrument amplifier circuit is used to perform low-noise amplification on the echo signal received by the coil and then output it to the main control circuit; The first end of the host computer is connected to the first end of the main control circuit, the second end of the main control circuit is connected to the first end of the power amplifier circuit, the third end of the power amplifier circuit is connected to the first end of the high isolation fast switching low Q value circuit, the second end and the third end of the high isolation fast switching low Q value circuit are respectively connected to the first end and the second end of the instrument amplifier circuit, the fourth end of the high isolation fast switching low Q value circuit is connected to the second end of the power amplifier circuit, and the third end of the instrument amplifier circuit is connected to the third end of the main control circuit; High isolation fast switching low Q value circuit includes: Integrated transceiver differential coil, the coil is evenly wound on a non-metallic frame to avoid the adjacent interference effect caused by separate transceiver coils; Q-conversion circuit, used to reduce the quality factor Q of the coil within a period of time after the pulse transmission is completed to quickly discharge the energy stored in the coil; High-isolation fast-switching RF switch, used to quickly switch the device between transmit mode and receive mode, and high-isolation protection instrument amplifier circuit from being damaged by high-power signals during pulse transmission and energy discharge; The high-isolation fast-switching radio frequency switch includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, and the Q-conversion circuit includes a first resistor and a second resistor; The negative electrode of the first switch is connected to the first end of the instrument amplifier circuit, the positive electrode of the first switch is connected to one end of the first resistor, one end tap of the transceiver differential coil, and the negative electrode of the third switch, the other end of the first resistor is connected to the positive electrode of the second switch, the negative electrode of the second switch is grounded, the positive electrode of the third switch is connected to the third end of the power amplifier circuit, the middle tap of the transceiver differential coil is grounded, the other end tap of the transceiver differential coil is connected to the positive electrode of the fourth switch, the positive electrode of the fifth switch, and the positive electrode of the sixth switch, the negative electrode of the fourth switch is connected to the second end of the instrument amplifier circuit, the negative electrode of the fifth switch is connected to one end of the second resistor, the other end of the second resistor is grounded, and the negative electrode of the sixth switch is connected to the second end of the power amplifier circuit.

2. The low-field nuclear magnetic resonance exploration device for effectively shortening dead time according to claim 1, characterized in that: The host computer includes: A user interface is used to generate interactive signals through human-computer interaction and output the interactive signals to the control software; The control software is used to send control instructions to the main control circuit after receiving the interactive signal, control the start and end of the low-field nuclear magnetic resonance exploration, and receive data returned by the main control circuit; The user interface is connected to the first end of the control software, and the second end of the control software is connected to the first end of the main control circuit.

3. The low-field nuclear magnetic resonance exploration device for effectively shortening dead time according to claim 1, characterized in that: The main control circuit includes: Communication interface, used to establish communication between the main control circuit and the host computer; ADC, used for digital processing of the echo signal amplified by the instrument amplifier circuit; Digital reception is used to extract the amplitude and phase information of the digitally processed echo signal and feed it back to the host computer through the communication interface; The pulse sequence programmer is composed of a timer and a state machine. After receiving the control instruction of the host computer through the communication interface, it generates a pulse sequence, generates a corresponding control signal according to the timing requirements of the pulse sequence, and outputs it to the power amplifier circuit; The first end of the communication interface is connected to the first end of the host computer, the second end of the communication interface is connected to the first end of the pulse sequence programmer, the second end of the pulse sequence programmer is connected to the first end of the power amplifier circuit, the third end of the communication interface is connected to the first end of the digital receiver, the second end of the digital receiver is connected to the first end of the ADC, and the second end of the ADC is connected to the third end of the instrument amplifier circuit.

4. The low-field nuclear magnetic resonance exploration device for effectively shortening dead time according to claim 1, characterized in that: The first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch are PIN diode switches, which include reverse-series PIN diodes, capacitors, and RF choke inductors. The reverse-series PIN diodes are used to control the switch mode, the RF choke inductors are used to provide a bias voltage for the reverse-series PIN diodes, and the capacitors are used for DC decoupling.

5. A low-field nuclear magnetic resonance exploration method for effectively shortening dead time, applied to the low-field nuclear magnetic resonance exploration device for effectively shortening dead time as claimed in any one of claims 1 to 4, characterized in that: The low-field nuclear magnetic resonance exploration method for effectively shortening the dead time comprises the following steps: Step 1: After receiving the control instruction from the host computer, the main control circuit decodes the control instruction and creates an instruction to generate a control signal that meets the timing requirements of the pulse sequence; the control signal includes: a transmission control signal, a Q-conversion control signal, and a high-isolation fast-switching RF switch control signal; Step 2: The transmission control signal is converted into a high-current driving control signal after passing through the power amplifier circuit to quickly turn on the RF MOS tube in the power amplifier circuit, and the 600V DC high voltage is converted into a high-power RF pulse with a peak value of 2400V after chopping; Step 3, the third switch and the sixth switch are closed, and a high-power radio frequency pulse excites the coil; Step 4: The second switch and the fifth switch are closed to quickly discharge the energy stored in the coil; Step 5, the first switch and the fourth switch are closed, so that the device switches from the transmitting mode to the receiving mode; Step 6, the instrument uses an amplifier circuit to perform low-noise amplification on the echo signal received by the coil; Step 7: The amplified echo signal is collected and digitized by the main control circuit, and the digital phase-sensitive detection algorithm is used to extract the amplitude and phase information, and the data is transmitted to the host computer through the CAN bus.

6. The low-field nuclear magnetic resonance exploration method for effectively shortening dead time according to claim 5, characterized in that: Specifically, step 3 is as follows: the third switch and the sixth switch of the high-isolation fast-switching RF switch are closed, and the first switch, the second switch, the fourth switch and the fifth switch are opened; this high-power RF pulse is transmitted to the coil and emitted by the coil into the sample to excite hydrogen nuclei.

7. The low-field nuclear magnetic resonance exploration method for effectively shortening dead time according to claim 5, characterized in that: Specifically, step 4 is as follows: after the pulse transmission is completed, the second switch and the fifth switch of the high-isolation fast-switching RF switch are closed, the first switch, the third switch, the fourth switch and the sixth switch are disconnected, and the first resistor and the second resistor are connected in parallel at both ends of the coil to reduce the quality factor of the coil, thereby quickly dissipating the energy stored in the coil.

8. The low-field nuclear magnetic resonance exploration method for effectively shortening dead time according to claim 5, characterized in that: Specifically, step 5 is to prepare to receive the echo signal after the energy discharge is completed. At this time, the second switch, the third switch, the fifth switch and the sixth switch of the high-isolation fast-switching RF switch are disconnected, and the first switch and the fourth switch are closed, so that the device is switched from the transmitting mode to the receiving mode, allowing the echo signal to enter the instrument amplifier circuit.

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