A weakly coupled transient electromagnetic system based on differential circuit

Abstract

The present invention belongs to the field of transient electromagnetic detection, and is specifically a weakly coupled transient electromagnetic system based on a differential circuit, comprising: a transmitting coil and a receiving coil are arranged in a central loop, the centers of the transmitting coil and the receiving coil coincide, they are placed in the same plane, and the receiving coil is located within the coverage of the transmitting coil; a transmitting power supply provides power to the transmitter, a Hall sensor is set on the transmitting coil, and is used to detect the current in the transmitting coil, the Hall sensor converts the current into a voltage signal and outputs it to the differential circuit, the output end of the differential circuit and the output end of the receiving coil are connected to the two input ends of the subtraction circuit, the output end of the subtraction circuit is connected to the data acquisition card after passing through an amplifier, and the data acquisition card inputs the collected data into a host computer to record the secondary field signal. The present invention overcomes the limitation of the traditional structure on the size of the receiving coil, avoids the weakening of the transmitting energy, and avoids the secondary field signal damage that may be caused by the traditional numerical calculation method.

Description

Technical Field

[0001] The invention belongs to the field of transient electromagnetic detection, in particular to a weakly coupled transient electromagnetic system based on a differential circuit. Background Art

[0002] Urbanization has brought about the scarcity of land resources. Traditional ground space faces problems such as traffic congestion, environmental pollution and excessive population density. The scientific development of underground space construction can effectively solve urban development problems and play an important role in reducing urban energy consumption. The detection principle of the small-loop transient electromagnetic method is basically the same as that of the conventional transient electromagnetic method. It is based on the principle of electromagnetic induction and uses a transmitting circuit to generate a transmitting current. When the transmitting current suddenly drops, a magnetic field will be generated around it. This magnetic field is called the primary field. During the propagation process, the primary field will induce the formation of a secondary field when encountering underground electrical structures. By recording the generated secondary field signals, the relevant physical parameters of the underground geological body can be interpreted. The small-loop towed transient electromagnetic method has the advantages of non-destructive detection and portability, and has great potential for urban underground space investigation.

[0003] In actual work, the transmitting current waveform of most transient electromagnetic systems is an oblique step wave. The transmitting current needs a certain time delay to decay to zero. The generated primary field signal will cause strong mutual inductance coupling between the small loop transceiver coils, causing the early secondary field signal to be submerged, and then causing a shallow detection blind spot. At present, common solutions include numerical calculation method and structural design method. The numerical calculation method is based on the method of subtracting the theoretical prediction value of the primary field from the full sampling data to extract a pure secondary field signal. The effectiveness of this method is highly dependent on the accuracy of the theoretical value calculation, and the numerical calculation process may have a certain negative impact on the secondary field signal. Common structural design methods include Bucking coil structure and equivalent reverse flux structure, both of which will cause the coil emission energy to be weakened.

[0004] In summary, in order to overcome the defects of traditional methods, it is particularly important to design a weakly coupled transient electromagnetic system based on differential circuits. By adjusting the transmitting circuit structure, the transmitting energy will not be weakened, and the coil coupling can be suppressed to extract the secondary field signal throughout the process, thereby improving the system's shallow detection capability.

[0005] Chinese patent publication number CN116500692B discloses an optimization method for small-loop transient electromagnetic detection. By building a small-loop transient electromagnetic non-coplanar eccentric self-compensation structure and constructing an LSTM neural network to suppress the interference of the excitation magnetic field, the primary field aliasing problem caused by mutual inductance between the small-loop transceiver coils is solved. However, the ability of this structure to suppress the primary field is greatly affected by the process, and raising the receiving coil will be affected by the air medium, etc., resulting in the loss of part of the received signal, and at the same time will cause the weakening of the transmission energy.

[0006] Therefore, it is necessary to continue to improve the structure of the transmitting and receiving coils, and on the basis of ensuring the transmitting energy, receiving coil size, receiving bandwidth, etc., suppress the primary field influence caused by the mutual inductance coupling of the coils as much as possible, and extract a more complete full-process transient secondary field signal. Summary of the invention

[0007] The problem to be solved by the present invention is to provide a weakly coupled transient electromagnetic system based on a differential circuit, suppress the primary field interference signal caused by the mutual inductance coupling between the transmitting and receiving coils, obtain as many early secondary field signals as possible, reduce the blind area of ​​shallow detection, and solve the primary field influence caused by the mutual inductance coupling of the coils.

[0008] The present invention is implemented as follows: a weakly coupled transient electromagnetic system based on a differential circuit, the system comprises a receiving system and a transmitting system, the transmitting system comprises a transmitting power supply, a transmitter, a transmitting coil, a Hall sensor and a differential circuit; the receiving system comprises a receiving coil, a subtraction circuit, an amplifier, a data acquisition card and a host computer, wherein the transmitting coil and the receiving coil are arranged in a central loop, the centers of the transmitting coil and the receiving coil coincide, they are placed in the same plane, and the receiving coil is located within the coverage of the transmitting coil; the transmitting power supply provides electrical energy for the transmitter, the Hall sensor is sleeved on the transmitting coil, and is used to detect the current in the transmitting coil, the Hall sensor converts the current into a voltage signal and outputs it to the differential circuit, the output end of the differential circuit and the output end of the receiving coil are connected to the two input ends of the subtraction circuit, the output end of the subtraction circuit is connected to the data acquisition card after passing through the amplifier, and the data acquisition card inputs the collected data into the host computer to record the secondary field signal.

[0009] Furthermore, the transmitter generates a bipolar ramp step wave for generating a transmitting current in the transmitting coil.

[0010] Furthermore, the differential circuit differentiates the voltage signal to obtain a rate of change of the primary field during the current shut-off period.

[0011] Furthermore, the differential circuit includes an operational amplifier A1, a capacitor connected to the inverting input terminal of the operational amplifier A1 , the resistor connected to the non-inverting input of operational amplifier A1 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A1 , the operation of the differential circuit is expressed as: , is the input voltage signal, is the rate of change of the primary field during the current cut-off period.

[0012] Furthermore, the subtraction circuit subtracts the change rate of the primary field during the current shut-off period obtained by the differential circuit from the measured voltage signal collected by the receiving coil to obtain the secondary field signal after eliminating the influence of the primary field.

[0013] Furthermore, the subtraction circuit includes an operational amplifier A2, and a resistor is connected to the inverting input terminal of the operational amplifier A2. , connect the resistor to the non-inverting input of operational amplifier A2 , the resistor connected to the non-inverting input of operational amplifier A2 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A2 , the operation of the subtraction circuit is expressed as: , is the measured voltage signal, It is the secondary field signal after removing the influence of the primary field.

[0014] Capacitor C and resistor in differential circuit The process of determining the parameters of is as follows: the mutual inductance coefficient between the receiving coil and the transmitting coil is calculated through the parameters of the receiving coil and the transmitting coil;

[0015] According to the mutual inductance coefficient, the theoretical value of the primary induced voltage generated in the receiving coil when the current in the transmitting coil is turned off is calculated;

[0016] The weakly coupled transient electromagnetic system based on the differential circuit is simulated, and the rate of change of the primary field during the current cut-off period is obtained through the differential circuit to obtain the primary induced voltage simulation value;

[0017] According to the primary induced voltage theoretical value and the primary induced voltage simulation value, the resistance in the differential circuit is and capacitor The value is adjusted so that the simulated value of the primary induced voltage is close to or equal to the theoretical value of the primary induced voltage.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention adopts a central loop device combined with a differential circuit to realize the extraction of the full-range transient secondary field signal. The present invention overcomes the limitation of the traditional structure on the size of the receiving coil, avoids the weakening of the transmission energy, and avoids the damage to the secondary field signal that may be caused by the traditional numerical calculation method. By suppressing the primary field interference signal caused by the mutual inductance coupling between the transmitting and receiving coils, the present invention can obtain as many early secondary field signals as possible, significantly reducing the blind area of ​​shallow detection, thereby greatly improving the overall detection capability of the system. In addition, the present invention also maintains the advantages of non-destructive detection and portability of the small-loop towed transient electromagnetic system itself, further enhancing its flexibility and practicality, and providing new technical means and solutions for the fields of underground space investigation and resource exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A structural block diagram of a weakly coupled transient electromagnetic system based on a differential circuit provided by an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of the structure of a differential circuit provided by an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the structure of a subtraction circuit provided by an embodiment of the present invention;

[0023] Figure 4 The present invention provides an implementation effect diagram of the embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] See also Figure 1A weakly coupled transient electromagnetic system based on a differential circuit is shown, comprising a receiving system and a transmitting system, wherein the transmitting system comprises a transmitting power supply 1, a transmitter 2, a transmitting coil 3, a Hall sensor 5 and a differential circuit 6; the receiving system comprises a receiving coil 4, a subtraction circuit 7, an amplifier 10, a data acquisition card 9 and a host computer 8, wherein the transmitting coil 3 and the receiving coil 4 are arranged in a central loop, the centers of the transmitting coil 3 and the receiving coil 4 coincide, they are placed in the same plane, and the receiving coil 4 is located within the coverage of the transmitting coil 3; the transmitting power supply 1 provides power to the transmitter 2, the Hall sensor 5 is sleeved on the transmitting coil, and is used to detect the bipolar oblique step wave transmitting current generated in the transmitting coil 3 and convert it into a voltage signal, the Hall sensor 5 outputs a voltage signal to the differential circuit 6, the output end of the differential circuit 6 and the output end of the receiving coil 4 are connected to the two input ends of the subtraction circuit 7, the output end of the subtraction circuit 7 is connected to the data acquisition card 9 after passing through the amplifier 10, and the data acquisition card 9 inputs the collected data into the host computer 8 for recording the secondary field signal.

[0026] Transmitter 2 is used to generate a bipolar oblique step wave transmitting current in transmitting coil 3. When the bipolar oblique step wave transmitting current suddenly drops, a magnetic field is generated around it, which is called the primary field. During the propagation process, the primary field will induce the formation of a secondary field when encountering underground electrical structures. By recording the generated secondary field signals, the relevant physical parameters of the underground geological body can be interpreted.

[0027] In the embodiment of the present invention, the Hall sensor 5 is used to measure the bipolar ramp step wave emission current and then convert it into a voltage signal, and the voltage signal is differentiated by the differential circuit 6 to obtain the rate of change of the primary field during the current cut-off period.

[0028] See also Figure 2 As shown, the differential circuit 6 includes an operational amplifier A1, a capacitor connected to the inverting input terminal of the operational amplifier A1 , the resistor connected to the non-inverting input of operational amplifier A1 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A1 , the operation of the differential circuit 6 is expressed as: , is the input voltage signal, is the rate of change of the primary field during the current cut-off period.

[0029] It can be proved theoretically that the sum of the integrals of the measured voltage signal received by the receiving coil 4 during the current cut-off period is equal to the vector sum of the primary field and the secondary field signal. That is, it can be expressed as:

[0030] ,

[0031] In the formula, Indicates that before the shutdown begins, Indicates that after the shutdown is completed, is the measured voltage signal received by the receiving coil, is the secondary field signal, is a primary field signal. Differentiating the above equation yields:

[0032] ,

[0033] In the above formula The rate of change of the primary field during the current shut-off period is subtracted from the measured voltage signal to extract the secondary field signal of the entire transient.

[0034] The rate of change of the primary field generated by the transmitting coil 3 on the receiving coil 4, that is, the primary induced voltage in the receiving coil 4,

[0035] Theoretically calculate the primary induced voltage:

[0036] ,

[0037] In the formula, is the bipolar ramp step wave emission current, is the mutual inductance coefficient between the transmitting coil and the receiving coil. When the parameters of the transmitting coil and the receiving coil are known, the mutual inductance coefficient The value of is fixed, which can be obtained by using the Newman integral formula:

[0038] ,

[0039] In the formula, is the number of turns of the receiving coil, is the number of turns of the transmitting coil, is the vacuum magnetic permeability, and its value is H / m. is the receiving coil diameter, is the transmitting coil diameter, is the angle between the receiving coil line element and the horizontal axis of the spatial rectangular coordinate system, is the angle between the transmitting coil line element and the horizontal axis of the spatial rectangular coordinate system, is the distance between the transmitting coil line element and the receiving coil line element.

[0040] The present invention avoids using a numerical calculation method to process the secondary field signal and thus causing signal loss, while also avoiding structural restrictions on the size of the receiving coil and weakening of the transmission energy.

[0041] In the embodiment of the present invention, the differential circuit 6 includes an operational amplifier A1, a capacitor C connected to the inverting input terminal of the operational amplifier A1, and a resistor connected to the non-inverting input terminal of the operational amplifier A1. ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A1 , the operation of the differential circuit is expressed as: , is the input voltage signal, is the rate of change of the primary field during the current cut-off period.

[0042] Capacitor in Differential Circuit 6 and resistor The process of determining the parameters of is as follows: the mutual inductance coefficient between the receiving coil 4 and the transmitting coil 3 is calculated by using the parameters of the receiving coil 4 and the transmitting coil 3;

[0043] Calculate the theoretical value of the primary induced voltage generated in the receiving coil 4 when the current in the transmitting coil 3 is turned off according to the mutual inductance coefficient;

[0044] The weakly coupled transient electromagnetic system based on the differential circuit is simulated, and the rate of change of the primary field during the current cut-off period is obtained through the differential circuit to obtain the primary induced voltage simulation value;

[0045] According to the primary induced voltage theoretical value combined with the primary induced voltage simulation value, the resistor in the differential circuit 6 is and capacitor Adjust the value so that the simulated value of the primary induced voltage is close to or equal to the theoretical value of the primary induced voltage. and capacitor .

[0046] In the present invention, the subtraction circuit 7 subtracts the change rate of the primary field during the current cut-off period obtained by the differential circuit 6 from the measured voltage signal collected by the receiving coil 4 to obtain the secondary field signal after eliminating the influence of the primary field.

[0047] See also Figure 3 As shown, the subtraction circuit 7 includes an operational amplifier A2, and a resistor is connected to the inverting input terminal of the operational amplifier A2. , connect the resistor to the non-inverting input of operational amplifier A2 , the resistor connected to the non-inverting input of operational amplifier A2 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A2 , the operation of the subtraction circuit 7 is expressed as: , is the measured voltage signal, It is the secondary field signal after removing the influence of the primary field.

[0048] The embodiment of the present invention uses Simulink software for circuit simulation. The radius of the receiving coil is set to 0.7 m, the number of turns is set to 32 turns, the radius of the transmitting coil is set to 0.8 m, the number of turns is 16 turns, and the central loop structure is used. The voltage of the transmitting power supply is set to 12V, and the transmitter uses four IGBT switches combined with a step pulse module to control the generation of a bipolar oblique step wave transmitting current. The transmitting current amplitude is 1.2 A, and the turn-off time is 70μs (linear turn-off, the moment of the current off segment is defined as the zero moment). The transmitting coil input end is connected, the equivalent inductance of the transmitting coil is set to 1mH, the equivalent resistance is set to 10 Ω, and the Hall sensor is connected to the differential circuit to obtain the induced voltage simulation value.

[0049] At the same time, the generated oblique step current wave data is imported into MATLAB software, and the parameters of the receiving coil and the transmitting coil are substituted into the Newman integral formula through MATLAB software to obtain the mutual inductance coefficient of 1.6128×10 -4 . And the theoretical primary induced voltage is calculated by the existing primary induced voltage calculation method.

[0050] By analyzing the theoretical value of the primary induced voltage and the simulated value of the primary induced voltage obtained by simulation, the resistance of the differential circuit is adjusted. ,capacitance 160 Ω and 1 μf respectively. ,capacitance The primary field suppression effect of the weakly coupled transient electromagnetic system based on the differential circuit is verified by comparing the primary induced voltage simulation value with the primary induced voltage theoretical value data. The results are as follows: Figure 4 As shown, the solid line is the bipolar oblique step wave emission current, the dotted line is the primary induced voltage, and the dotted line is the primary induced voltage after cancellation obtained by subtracting the primary induced voltage simulation value from the primary induced voltage theoretical value. It can be found that the cancellation effect is good and the influence of the primary field is greatly reduced, proving that the present invention can effectively suppress the primary field interference. It avoids the use of numerical calculation methods to process the secondary field signal and thus cause signal loss, while avoiding the structural limitation on the size of the receiving coil and the weakening of the emission energy, further improving the system detection capability and reducing the shallow detection blind area.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A weakly coupled transient electromagnetic system based on a differential circuit, characterized in that: The system comprises a receiving system and a transmitting system, wherein the transmitting system comprises a transmitting power supply, a transmitter, a transmitting coil, a Hall sensor and a differential circuit; the receiving system comprises a receiving coil, a subtraction circuit, an amplifier, a data acquisition card and a host computer, wherein the transmitting coil and the receiving coil are arranged in a central loop, the centers of the transmitting coil and the receiving coil coincide, they are placed in the same plane, and the receiving coil is located within the coverage of the transmitting coil; the transmitting power supply provides electric energy for the transmitter, the Hall sensor is sleeved on the transmitting coil to detect the current in the transmitting coil, the Hall sensor converts the current into a voltage signal and outputs it to the differential circuit, the output end of the differential circuit and the output end of the receiving coil are connected to two input ends of the subtraction circuit, the output end of the subtraction circuit is connected to the data acquisition card after passing through the amplifier, and the data acquisition card inputs the collected data into the host computer to record the secondary field signal.

2. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 1, characterized in that: The transmitter is used to control the generation of a bipolar oblique step wave transmitting current in a transmitting coil.

3. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 1, characterized in that: The differential circuit differentiates the voltage signal to obtain the rate of change of the primary field during the current cut-off period.

4. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 3, characterized in that: The differential circuit includes an operational amplifier A1, a capacitor connected to the inverting input terminal of the operational amplifier A1, , the resistor connected to the non-inverting input of operational amplifier A1 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A1 , the operation of the differential circuit is expressed as: , is the input voltage signal, is the rate of change of the primary field during the current cut-off period.

5. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 3, characterized in that: The subtraction circuit subtracts the change rate of the primary field during the current cut-off period obtained by the differential circuit from the measured voltage signal collected by the receiving coil to obtain a secondary field signal after eliminating the influence of the primary field.

6. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 5, characterized in that: The subtraction circuit includes an operational amplifier A2, a resistor connected to the inverting input terminal of the operational amplifier A2 , connect the resistor to the non-inverting input of operational amplifier A2 , the resistor connected to the non-inverting input of operational amplifier A2 ,resistance The other end is grounded, and the resistor connected to the inverting input and output of operational amplifier A2 , the operation of the subtraction circuit is expressed as: , is the measured voltage signal, It is the secondary field signal after removing the influence of the primary field.

7. A weakly coupled transient electromagnetic system based on a differential circuit according to claim 1, characterized in that: Capacitors in Differential Circuits and resistor The process of determining the parameters is: The mutual inductance coefficient between the receiving coil and the transmitting coil is calculated by using the parameters of the receiving coil and the transmitting coil; According to the mutual inductance coefficient, the theoretical value of the primary induced voltage generated in the receiving coil when the current in the transmitting coil is turned off is calculated; The weakly coupled transient electromagnetic system based on the differential circuit is simulated, and the rate of change of the primary field during the current cut-off period is obtained through the differential circuit to obtain the primary induced voltage simulation value; According to the primary induced voltage theoretical value and the primary induced voltage simulation value, the resistance in the differential circuit is and capacitor The value is adjusted so that the simulated value of the primary induced voltage is close to or equal to the theoretical value of the primary induced voltage.

Images