Magnetic sensor for semi-aviation transient electromagnetic detection and debugging method thereof

Abstract

The invention belongs to the technical field of geophysical exploration, and particularly discloses a magnetic sensor for semi-aviation transient electromagnetic detection and a debugging method thereof. A shell of the sensor is a non-magnetic rigid hollow cylinder, X-direction magnetic core coils, Y-direction magnetic core coils and Z-direction magnetic core coils are of strip-shaped structures, a hollow coil is of an annular structure and is horizontally fixed in the shell, the X-direction magnetic core coils and the Y-direction magnetic core coils are vertically and horizontally fixed on the inner side of the hollow coil, and the Z-direction magnetic core coils are vertically fixed on the inner side of the hollow coil. The attitude sensor is fixed in the shell, the orientation of the attitude sensor corresponds to the axial orientation of the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil, and the X-direction magnetic core coil, the Y-direction magnetic core coil, the Z-direction magnetic core coil, the hollow coil and the attitude sensor are electrically connected with a data acquisition module mounted on the aircraft through cables. The method comprises the steps of obtaining the resonant frequency, debugging the hollow coil and calculating the transient electromagnetic apparent resistivity. The device has the advantages of being simple in structure, light in weight, high in signal receiving capacity and high in exploration result precision.

Description

Technical Field

[0001] The present invention relates to the technical field of geophysical exploration, and particularly relates to a magnetic sensor for semi-aerial transient electromagnetic detection with a simple structure, light weight, strong signal reception ability and high exploration result accuracy, and a debugging method thereof. Background Technique

[0002] The transient electromagnetic method is based on the resistivity difference of geological bodies, and judges and identifies geological bodies through the difference in eddy current fields generated by different resistivity geological bodies under excitation. The magnetic source transient electromagnetic method refers to using the strong pulsed electromagnetic field generated at the moment when the power supply wire frame is powered off (hereinafter simply referred to as the "primary field") as the field source. Under the excitation of this field source, low-resistivity geological bodies generate eddy current fields (hereinafter simply referred to as the "secondary field"), and the geological bodies are identified by collecting this secondary field. The magnetic source semi-aerial transient electromagnetic method uses a ground-based transmitting wire frame as the transmitter and mounts a magnetic sensor on an aircraft to collect data in the air. It can not only give full play to the high-power transmission advantage of the ground transient electromagnetic method, but also inherit the advantage of fast aerial exploration of the airborne transient electromagnetic method. Therefore, it has high working efficiency, strong resolution ability and the magnetic sensor received in the air is light in weight.

[0003] At present, magnetic source semi-aerial transient electromagnetic detection mostly uses a magnetic sensor with a Z-component air-core coil. However, in actual work, mountainous conditions are often encountered. Since the transmitting wire frame is laid flat on the ground and generates undulations, the secondary field actually received in three-dimensional space is not necessarily the Z-component; moreover, in magnetic source transient electromagnetic detection, since the intensity of the primary field is much greater than that of the secondary field, and in actual work, it is affected by the ambient interference electromagnetic field, it is difficult to effectively identify and extract the weak secondary field signal received in the air-core coil of the magnetic sensor, resulting in low accuracy of the exploration results.

[0004] In the prior art, to solve the problems existing in the magnetic sensors for semi-aerial transient electromagnetic detection of magnetic sources, a high-current fast-switching transmitter has been developed to increase the amplitude of the transmitted current pulse while reducing the pulse width, making the transmitted signal more conducive to exciting the secondary field and capable of improving the relative intensity of the secondary field signal to a certain extent for subsequent extraction. However, for an electrical source transmitter, due to the high bus voltage and poor parasitic parameter conditions of the devices, it is difficult to implement the high-current fast-switching technology, and there may be problems such as circuit stability and reliability. Moreover, it cannot solve the problem that the actually received secondary field in three-dimensional space is not necessarily the Z component. In addition, there is also a technical solution that uses a multi-component sensor to replace a single Z-component air-core coil magnetic sensor. By measuring multiple field quantities and multiple components, it can collect secondary field information more comprehensively to adapt to the situation where the direction of the secondary field is uncertain under complex terrains. However, there are still problems that the weak received secondary field signal is difficult to be effectively extracted, and the current multi-component sensors are relatively heavy, resulting in a loss of economy when carried by platforms such as helicopters, while it is difficult to carry multiple sensors simultaneously for multi-field quantity and multi-component observations when carried by low-cost unmanned aerial vehicles. Therefore, there is also a method of using a global-local structure feature extraction method based on machine learning, and validating this method with a large number of multi-type simulated and measured noise-polluted data to remove the noise received by the magnetic sensor and improve the quality of the secondary field signal. However, due to the large number of processing links and the relatively loose structure, the processing efficiency is low, and many key parameters still rely on manual settings, reducing the objectivity of data processing.

[0005] In summary, it is necessary to develop a magnetic sensor for semi-aerial transient electromagnetic method of magnetic sources that can significantly improve the ability to receive secondary field signals and adapt to the uncertain direction of the secondary field under complex terrains. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a magnetic sensor for semi-aerial transient electromagnetic detection with a simple structure, light weight, strong signal reception ability, and high exploration result accuracy, and also provides a debugging method for the magnetic sensor for semi-aerial transient electromagnetic detection.

[0007] The magnetic sensor for semi-aerial transient electromagnetic detection of the present invention is implemented as follows: It includes a housing, an X-direction magnetic core coil, a Y-direction magnetic core coil, a Z-direction magnetic core coil, a hollow coil, and an attitude sensor. The housing is a non-magnetic rigid hollow cylinder. The X-direction magnetic core coil, Y-direction magnetic core coil, and Z-direction magnetic core coil are strip-shaped structures. The hollow coil is a ring structure and is horizontally fixed on the inner edge of the housing. The X-direction magnetic core coil and Y-direction magnetic core coil are horizontally and horizontally fixed on the housing inside the hollow coil perpendicular to each other. The Z-direction magnetic core coil is vertically fixed on the housing inside the hollow coil. The attitude sensor is fixed inside the housing and its orientation corresponds to the axial orientations of the X-direction magnetic core coil, Y-direction magnetic core coil, and Z-direction magnetic core coil. The X-direction magnetic core coil, Y-direction magnetic core coil, Z-direction magnetic core coil, hollow coil, and attitude sensor are respectively electrically connected to a data acquisition module mounted on an aircraft through cables.

[0008] Further, the resonance frequencies and sensitivity curves of the X-direction magnetic core coil, Y-direction magnetic core coil, and Z-direction magnetic core coil are all the same.

[0009] Further, the magnetic core materials and the number of turns of enameled wire of the X-direction magnetic core coil and Y-direction magnetic core coil are the same. The magnetic core material and the total number of turns of enameled wire of the Z-direction magnetic core coil are the same as those of the X-direction magnetic core coil. The hollow coil is wound with enameled wire and the number of turns is 0.5% to 3% of that of the X-direction magnetic core coil.

[0010] Further, the X-direction magnetic core coil, Y-direction magnetic core coil, and Z-direction magnetic core coil all adopt magnetic cores with a diameter of 1 to 2 cm and a length of 30 to 40 cm, and the number of turns of enameled wire is 10,000 to 30,000 turns. The number of turns of enameled wire of the hollow coil is 100 to 300 turns and the outer diameter is 0.8 to 1.5 m.

[0011] Further, the Z-direction magnetic core coil is evenly divided into multiple segments along the axis, and each segment is vertically fixed on the housing inside the hollow coil. The lengths and the number of turns of enameled wire of the magnetic core coils of each segment of the Z-direction magnetic core coil are the same and are connected in series in sequence by wires.

[0012] Further, the housing is a hollow cylinder made of plastic material. The hollow coil is a ring structure and is coaxially fixed on the bottom edge inside the housing. The X-direction magnetic core coil, Y-direction magnetic core coil, Z-direction magnetic core coil, and attitude sensor are adhesively pasted, bundled, or clamped on the bottom of the housing inside the hollow coil at intervals.

[0013] Furthermore, the present invention further includes a secondary field signal amplification module fixedly arranged inside the housing. The secondary field signal amplification module includes an X-direction differentiator, a Y-direction differentiator, a Z-direction differentiator, a matching capacitor, a signal amplifier I, a signal amplifier II, a signal amplifier III, a signal amplifier IV, and an analog-to-digital converter. The output end of the X-direction core coil is electrically connected to the input end of the signal amplifier I through the X-direction differentiator. The output end of the Y-direction core coil is electrically connected to the input end of the signal amplifier II through the Y-direction differentiator. The output end of the Z-direction core coil is electrically connected to the input end of the signal amplifier III through the Z-direction differentiator. The output end of the air-core coil is electrically connected to the input end of the signal amplifier IV through the matching capacitor. The output end of the signal amplifier IV is electrically connected to the input ends of the X-direction differentiator, the Y-direction differentiator, and the Z-direction differentiator respectively. The output ends of the signal amplifier I, the signal amplifier II, and the signal amplifier III are electrically connected to the input end of the analog-to-digital converter respectively. The output end of the analog-to-digital converter is electrically connected to the data acquisition module mounted on the aircraft through a cable.

[0014] Furthermore, the resonance frequency output by the air-core coil after passing through the matching capacitor is the same as that of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil. The sensitivity curve output by the air-core coil after passing through the matching capacitor and the signal amplifier IV is the same as that of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil in the frequency band below the resonance frequency.

[0015] The debugging method of the magnetic sensor for semi-airborne transient electromagnetic detection of the present invention is realized as follows: It includes steps of obtaining the resonance frequency, debugging the air-core coil, and calculating the transient electromagnetic apparent resistivity. The specific content is as follows: A. Obtaining the resonance frequency: Measure the sensitivity curves of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil respectively, and determine the resonance frequency on the sensitivity curves. B. Debugging the air-core coil: Continuously try different matching capacitors to make the resonance frequency output by the air-core coil after matching the same as that of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil, and then adjust the analog signal amplification factor of the signal amplifier IV n to make the sensitivity curve output by the air-core coil after amplification the same as that of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil in the frequency band below the resonance frequency; C. Calculating the transient electromagnetic apparent resistivity: Using the matching capacitor of the air-core coil and the analog amplification factor in the signal debugging n , by obtaining the equivalent receiving areas of the X-direction core coil, the Y-direction core coil, and the Z-direction core coil S d , and then according to the equivalent receiving areas S dCalculating the apparent resistivity of transient electromagnetic ρ Furthermore, for the magnetic core coils in the X direction, Y direction, and Z direction, the amplification factor of the analog signal is obtained through debugging n , so that the equivalent receiving area of each magnetic core coil S d meets the following formula: In the formula: S k is the area of the air-core coil, t is the number of turns of the air-core coil, n is the amplification factor of the analog signal of the air-core coil obtained according to the test.

[0016] Advantages of the present invention: 1. The magnetic sensor of the present invention uses a non-magnetic rigid hollow cylinder as the housing. The three-direction magnetic core coils inside are strip-shaped structures, and the air-core coil is a ring-shaped structure. Moreover, the air-core coil, each magnetic core coil, and the attitude sensor are integrated in the housing to form an integrated three-component magnetic sensor. As a result, the overall structure is relatively simple and easy to assemble and disassemble with the aircraft. And compared with the existing multi-component sensors, it is lighter in weight and more suitable for low-altitude unmanned aircraft such as multi-rotor UAVs and remotely controlled airships to carry, thus solving the problems that the existing multi-component sensors are too heavy, resulting in the need to use helicopters to carry and losing economy, and it is difficult for low-cost UAVs to carry multiple sensors.

[0017] 2. The magnetic sensor of the present invention is equipped with an air-core coil as a reference coil. Since the number of turns of the air-core coil is only 0.5% - 3% of that of the magnetic core coil in the X direction, the air-core coil has a weak ability to receive the secondary field. The received signals are mainly the primary field and the environmental interference field. The resonant frequency and sensitivity curve of the air-core coil output after passing through the matching capacitor and the signal amplifier are consistent with those of the three-direction magnetic core coils in the frequency band below the resonant frequency. Then, the signals of the air-core coil after matching and amplification are respectively connected to the three-direction differential devices. This can not only make the signal reception of the entire magnetic sensor more coordinated and stable, which is beneficial to improving the signal reception effect, but also subtract the primary field and environmental interference field signals received in the air-core coil from the analog signals received by the three-direction magnetic core coils respectively, effectively suppressing the influence of the primary field and the environmental interference field. And by amplifying the signals of the three-direction magnetic core coils, the ability to identify and extract weak secondary field signals can be significantly improved, solving the problem that weak secondary field signals are difficult to be effectively identified and extracted in the existing technology.

[0018] 3. The magnetic sensor of the present invention can receive secondary field signals from multiple directions and in different ways by integrating magnetic core coils in three directions. By cooperating with attitude sensors corresponding to the axial orientations of each magnetic core coil, it can not only adapt to the uncertainty of the secondary field direction under complex terrains to enhance the ability to receive secondary field signals, but also automatically correct the adverse effects of shaking and rotation on measurement data during the aircraft carrying process, thereby effectively improving the measurement accuracy and the adaptability to the use environment.

[0019] 4. The debugging method of the present invention accurately obtains the resonance frequencies of each magnetic core coil, makes the resonance frequencies and sensitivity curves of the air core coil and the magnetic core coils in three directions consistent, and then calculates the equivalent receiving area by using the matching capacitance of the air core coil and the analog amplification factor in signal debugging. S d , and then calculates the transient electromagnetic apparent resistivity according to the equivalent receiving area S d . Thereby, it can effectively reduce the errors caused by improper signal reception and processing, and the debugging process and calculation are relatively simple. It can not only improve the processing efficiency, but also improve the accuracy and reliability of the exploration results.

[0020] In summary, the present invention has the characteristics of simple structure, light weight, strong signal receiving ability, and high accuracy of exploration results. Brief Description of the Drawings

[0021] Figure 1 is a schematic plan view of the internal structure of the magnetic sensor of the present invention; Figure 2 is a signal processing flow chart of the secondary field signal amplification module of the present invention; In the figure: 1 - housing, 2 - X - direction magnetic core coil, 3 - Y - direction magnetic core coil, 4 - Z - direction magnetic core coil, 5 - air core coil, 6 - attitude sensor, 7 - secondary field signal amplification module, 71 - X - direction differentiator, 72 - Y - direction differentiator, 73 - Z - direction differentiator, 74 - matching capacitance, 75 - signal amplifier Ⅰ, 76 - signal amplifier Ⅱ, 77 - signal amplifier Ⅲ, 78 - signal amplifier Ⅳ, 79 - analog - to - digital converter. Detailed Embodiment

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention with reference to the drawings and 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.

[0023] Such as Figure 1As shown in the figure, the magnetic sensor for semi-aerial transient electromagnetic detection of the present invention includes a housing 1, an X-direction magnetic core coil 2, a Y-direction magnetic core coil 3, a Z-direction magnetic core coil 4, a hollow coil 5, and an attitude sensor 6. The housing 1 is a non-magnetic rigid hollow cylinder. The X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4 are strip-shaped structures. The hollow coil 5 is a ring-shaped structure and is horizontally fixed at the edge inside the housing 1. The X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are horizontally fixed on the housing 1 inside the hollow coil 5 perpendicular to each other, that is, their axis lines are perpendicular to each other and in the same plane. The Z-direction magnetic core coil 4 is vertically fixed on the housing 1 inside the hollow coil 5, that is, the axis line of the Z-direction magnetic core coil 4 is perpendicular to the plane where the axis lines of the X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are located. The attitude sensor 6 is fixed inside the housing 1 and its orientation corresponds to the axial orientations of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4. The X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, the Z-direction magnetic core coil 4, the hollow coil 5, and the attitude sensor 6 are respectively electrically connected to a data acquisition module mounted on an aircraft through cables.

[0024] The X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are horizontally fixed on the housing 1 perpendicular to each other, which means that their axis lines are perpendicular to each other and in the same plane.

[0025] The Z-direction magnetic core coil 4 is vertically fixed on the housing 1, which means that the axis line of the Z-direction magnetic core coil 4 is perpendicular to the plane where the axis lines of the X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are located.

[0026] The resonance frequencies and sensitivity curves of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4 are all the same.

[0027] The magnetic core materials and the number of turns of the enameled wires of the X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are the same. The magnetic core material and the total number of turns of the enameled wire of the Z-direction magnetic core coil 4 are the same as those of the X-direction magnetic core coil 2. The hollow coil 5 is wound with enameled wire and the number of turns is 0.5% - 3% of that of the X-direction magnetic core coil 2.

[0028] The X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4 all adopt magnetic cores with a diameter of 1 - 2 cm and a length of 30 - 40 cm, and the number of turns of the enameled wire is 10,000 - 30,000 turns. The number of turns of the enameled wire of the hollow coil 5 is 100 - 300 turns and the outer diameter is 0.8 - 1.5 m.

[0029] The Z-direction core coil 4 is evenly divided into multiple segments along the axial direction, and each segment is vertically fixed on the housing 1 inside the hollow coil 5. The lengths of the core coils of each segment of the Z-direction core coil 4 and the number of turns of the enameled wire are the same, and they are connected in series in sequence using a wire. Dividing the Z-direction core coil 4 into multiple segments along the axial direction can reduce the overall appearance height of the magnetic sensor, thereby making the structure more compact and reducing the sway amplitude when the magnetic sensor is mounted on an aircraft.

[0030] The attitude sensor 6 uses an existing lightweight three-axis attitude sensor to measure the axial angles of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4.

[0031] The housing 1 is a hollow cylinder made of plastic. The hollow coil 5 is a circular ring structure and is coaxially fixed to the bottom edge inside the housing 1. The X-direction core coil 2, the Y-direction core coil 3, the Z-direction core coil 4, and the attitude sensor 6 are adhesively bonded, bundled, or clamped to the bottom of the housing 1 inside the hollow coil 5 at intervals.

[0032] As Figure 2 shown, the present invention further includes a secondary field signal amplification module 7 fixedly arranged inside the housing 1. The secondary field signal amplification module 7 includes an X-direction differentiator 71, a Y-direction differentiator 72, a Z-direction differentiator 73, a matching capacitor 74, a signal amplifier I 75, a signal amplifier II 76, a signal amplifier III 77, a signal amplifier IV 78, and an analog-to-digital converter 79. The output end of the X-direction core coil 2 is electrically connected to the input end of the signal amplifier I 75 through the X-direction differentiator 71. The output end of the Y-direction core coil 3 is electrically connected to the input end of the signal amplifier II 76 through the Y-direction differentiator 72. The output end of the Z-direction core coil 4 is electrically connected to the input end of the signal amplifier III 77 through the Z-direction differentiator 73. The output end of the hollow coil 5 is electrically connected to the input end of the signal amplifier IV 78 through the matching capacitor 74. The output end of the signal amplifier IV 78 is electrically connected to the input ends of the X-direction differentiator 71, the Y-direction differentiator 72, and the Z-direction differentiator 73 respectively. The output ends of the signal amplifier I 75, the signal amplifier II 76, and the signal amplifier III 77 are electrically connected to the input end of the analog-to-digital converter 79 respectively. The output end of the analog-to-digital converter 79 is electrically connected to the data acquisition module mounted on the aircraft through a cable.

[0033] The X-direction differentiator 71, the Y-direction differentiator 72, the Z-direction differentiator 73, the signal amplifier I 75, the signal amplifier II 76, the signal amplifier III 77, the signal amplifier IV 78, and the analog-to-digital converter 79 all use devices in the prior art and will not be elaborated here.

[0034] The resonant frequency output by the hollow coil 5 after passing through the matching capacitor 74 is the same as that of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4. The sensitivity curve output by the hollow coil 5 after passing through the matching capacitor 74 and the signal amplifier Ⅳ 78 is the same as that of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 in the frequency band below the resonant frequency.

[0035] As Figure 1 and 2 shown, the magnetic sensor debugging method for semi-aerial transient electromagnetic detection of the present invention includes steps of obtaining the resonant frequency, debugging the hollow coil, and calculating the transient electromagnetic apparent resistivity, and the specific contents are as follows: A. Obtaining the resonant frequency: Measure the sensitivity curves of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 respectively, and determine the resonant frequency on the sensitivity curves; B. Debugging the hollow coil: Continuously try different matching capacitors 74 to make the resonant frequency output by the hollow coil 5 after matching the same as that of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4, and then adjust the analog signal amplification factor of the signal amplifier Ⅳ 78 n to make the sensitivity curve output by the hollow coil 5 after amplification the same as that of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 in the frequency band below the resonant frequency; C. Calculating the transient electromagnetic apparent resistivity: Using the matching capacitor 74 of the hollow coil 5 and the analog amplification factor in the signal debugging n , by obtaining the equivalent receiving areas of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 S d , and then calculating the transient electromagnetic apparent resistivity according to the equivalent receiving area S d ; ρ .

[0036] In the step B, since the transient electromagnetic signals obtained by the airborne transient electromagnetic method generally show a trend that the low-frequency signals are strong and gradually weaken towards the high-frequency, and the signals contain the primary field, the secondary field, and the transitional field. The hollow coil 5 is used as a reference coil for obtaining the primary field and the environmental interference electromagnetic field signals, and there are large differences in the transient electromagnetic signal responses between it and the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4. Only signal amplification cannot match the signals obtained by the above three core coils; since the resonant frequency is a key factor for the signal response ability of the induction coil, and for the coil sensor, in the frequency band below the resonant frequency, the frequency and the sensitivity are logarithmically linearly distributed, and the calculation of the resonant frequency is as follows: , where: fr is the resonance frequency, L is the inductance, C is the capacitance; Since the core coils 2 in the X direction, 3 in the Y direction and 4 in the Z direction are all core coils, their inductance and distributed capacitance are relatively large. While the air-core coil 5 has fewer turns, and its inductance and capacitance are smaller compared to the aforementioned three core coils, so its resonance frequency is higher. Therefore, by matching a capacitor with a suitable size across the two ends of the signal of the air-core coil 5 to increase the total capacitance, making the resonance frequency consistent with that of the aforementioned three core coils, and then amplifying the analog signal, the response of the air-core coil 5 to the strong primary field and interference field is approximately the same as that of the aforementioned three core coils.

[0037] Also, because the number of turns of the enameled wire winding of the air-core coil 5 is relatively small and the distributed capacitance is difficult to accurately calculate, the matching of the capacitance needs to be achieved through sensitivity testing. For this purpose, first, the sensitivity curves of the aforementioned three core coils are measured, the resonance frequency is determined on the curve, and different matching capacitors 74 are continuously tried to make the resonance frequency of the air-core coil 5 consistent with that of the aforementioned three core coils; then, through the signal amplifier Ⅳ78, the sensitivity of the frequency band below the resonance frequency of the air-core coil 5 is adjusted to be the same as that of the aforementioned three core coils.

[0038] It should be noted that in transient electromagnetic exploration, there is a complex implicit function relationship between the response value on the surface of a homogeneous half-space and the resistivity of the homogeneous half-space. At present, it is impossible to obtain the explicit inverse function between the field and the resistivity by analytical methods. Usually, the existing binary search method, translation method or piecewise calculation method is used to indirectly calculate the apparent resistivity.

[0039] The process of calculating the transient electromagnetic apparent resistivity by the binary search method is as follows: 1). The one-dimensional frequency-domain vertical magnetic field forward formula for a current line source in a layered medium is: In the formula: ω is the sampling angular frequency; I is the transmitting current; L is half of the length of the current line source; y is the offset; R is the distance from the measurement point to the center of the dipole source; r TE is the reflection coefficient in the TE mode; h is the height of the measurement point from the ground; λ is the integration variable; J 1 is the first-order Bessel function; x is the distance between the dipole source and the midpoint of the current line source; H ⊥ (ω) in the frequency domain ωVertical component magnetic field response of frequency; Where: For a uniform half-space, In the formula: μ is the magnetic permeability of the underground medium, ρ is the resistivity of the underground medium, and i is the imaginary unit, k 0 is the air wave number; 2), When a negative step current is passed through the line source I(t) : In the formula: t is the time, with the power-off moment being 0; I ( t ) is the emission current at time t; 3), Generate a primary magnetic field in the frequency domain around H(ω) : In the formula: H ( t ) is the primary magnetic field at time t in the time domain, i is the imaginary unit, H(ω) is the primary magnetic field at ω frequency in the frequency domain; 4), Use the Fourier transform to convert the frequency domain to the time domain, and the partial derivative of the magnetic field in the vertical direction with respect to time for any time greater than zero can be obtained as: t When In the formula: Re represents taking the imaginary part of a complex number; 5), It can also be calculated from the actual measurement results : In the formula: μ 0 is the magnetic permeability in vacuum, is t the magnetic induction intensity in the vertical direction at time; is the induced electromotive force at time t after rotating and projecting the induced electromotive forces of the magnetic core coil 2 in the X direction, the magnetic core coil 3 in the Y direction, and the magnetic core coil 4 in the Z direction and the equivalent receiving area to the vertical direction through the attitude sensor parameters; Since the parameters of the magnetic core coil 2 in the X direction, the magnetic core coil 3 in the Y direction, and the magnetic core coil 4 in the Z direction are all the same, there is: In the formula: S dis the equivalent receiving area of the core coil, S dx is the equivalent receiving area of the core coil 2 in the X direction, S dy is the equivalent receiving area of the core coil 3 in the Y direction, S dz is the equivalent receiving area of the core coil 4 in the Z direction; 6), Rotation projection parameters: In the formula: ε x is the induced electromotive force of the core coil 2 in the X direction, ε y is the induced electromotive force of the core coil 3 in the Y direction, ε z is the induced electromotive force of the core coil 4 in the Z direction, ψ is the heading angle obtained by the attitude sensor, θ is the pitch angle obtained by the attitude sensor, φ is the roll angle obtained by the attitude sensor; 7), Substitute different resistivity ρ' values into the formula to calculate the theoretical , and compare it with the obtained from the measured data. Continuously adjust the value of ρ' according to the size. After continuous binary search, the apparent resistivity of the underground transient electromagnetic method can be finally obtained ρ。

[0040] For the core coil 2 in the X direction, the core coil 3 in the Y direction, and the core coil 4 in the Z direction, the amplification factor of the analog signal is obtained through debugging n , so that the equivalent receiving area of each core coil S d meets the following formula: In the formula: S k is the area of the air-core coil 5, t is the number of turns of the air-core coil 5, n is the amplification factor of the analog signal of the air-core coil 5 obtained according to the test.

[0041] Example 1 S100: The core coils in three directions all use permalloy with a diameter of 1 cm as the core, and the length is 30 cm (where the core coil 4 in the Z direction is divided into 5 sections), and the number of turns of the enameled wire can be 30000 turns (each section of the core coil 4 in the Z direction is wound with 6000 turns); the air-core coil 5 is wound with the same enameled wire for 300 turns to form a ring with an outer diameter of 1 m.

[0042] S200: As shown Figure 1 in the figure, paste the aforementioned hollow coil 5 at the bottom of the plastic housing 1 with an inner diameter of 1 m. Then, horizontally paste the X-direction core coil 2 and the Y-direction core coil 3 perpendicular to each other inside the hollow coil 5 at the bottom of the housing 1. Next, vertically paste each section of the Z-direction core coil 4 at the bottom of the housing 1 inside the hollow coil 5 and connect them in sequence with wires. Subsequently, paste the attitude sensor 6 (such as the JY-61P attitude sensor of Shenzhen Vetter Intelligent Technology Co., Ltd.) at the bottom of the housing 1 with its orientation corresponding to the axial orientations of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4. Also, paste the secondary field signal amplification module 7 at the bottom of the housing 1, and connect the corresponding interfaces of the aforementioned three-direction core coils and the hollow coil 5 to the secondary field signal amplification module 7 through wires. The output end of the secondary field signal amplification module 7 electrically connects each signal wire and power supply wire to the data acquisition module mounted on the aircraft through the aviation plug at the top of the housing 1.

[0043] S300: Measure the sensitivity curves of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 respectively, and determine the resonance frequencies of the core coils on the sensitivity curves.

[0044] S400: Continuously try different matching capacitors 74 in the secondary field signal amplification module 7 to make the resonance frequency output after the matching of the hollow coil 5 consistent with that of the aforementioned three-direction core coils. Then, adjust the analog signal amplification factor of the signal amplifier Ⅳ 78 n so that the sensitivity curve output after the amplification of the hollow coil 5 is consistent with that of the three-direction core coils in the frequency band below the resonance frequency.

[0045] S500: Utilize the matching capacitor 74 of the hollow coil 5 and the analog amplification factor in the signal debugging n to obtain the equivalent receiving areas of the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4 S d , and then, according to the equivalent receiving areas S d , use the binary search method, translation method, or segmented calculation method in the prior art to calculate the transient electromagnetic apparent resistivity ρ ; Among them, for the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4, obtain the analog signal amplification factor n through debugging so that the equivalent receiving areas of the respective core coils S d meet the following formula: In the formula:S k is the area of the air-core coil 5, t is the number of turns of the air-core coil 5, n is the amplification factor of the analog signal of the air-core coil 5 obtained according to the test.

[0046] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A magnetic sensor for semi-aerial transient electromagnetic detection, characterized in that: It includes a housing (1), an X-direction magnetic core coil (2), a Y-direction magnetic core coil (3), a Z-direction magnetic core coil (4), a hollow coil (5), and an attitude sensor (6). The housing (1) is a non-magnetic rigid hollow cylinder. The X-direction magnetic core coil (2), Y-direction magnetic core coil (3), and Z-direction magnetic core coil (4) are strip-shaped structures. The hollow coil (5) is a ring structure and is horizontally fixed at the edge inside the housing (1). The X-direction magnetic core coil (2) and Y-direction magnetic core coil (3) are horizontally fixed on the housing (1) inside the hollow coil (5) perpendicular to each other. The Z-direction magnetic core coil (4) is vertically fixed on the housing (1) inside the hollow coil (5). The attitude sensor (6) is fixed inside the housing (1) and its orientation corresponds to the axial orientations of the X-direction magnetic core coil (2), Y-direction magnetic core coil (3), and Z-direction magnetic core coil (4). The X-direction magnetic core coil (2), Y-direction magnetic core coil (3), Z-direction magnetic core coil (4), hollow coil (5), and attitude sensor (6) are respectively electrically connected to a data acquisition module mounted on an aircraft through cables.

2. The magnetic sensor for semi-aerial transient electromagnetic detection according to claim 1, characterized in that: The resonance frequencies and sensitivity curves of the X-direction magnetic core coil (2), Y-direction magnetic core coil (3), and Z-direction magnetic core coil (4) are all the same.

3. The magnetic sensor for semi-aerial transient electromagnetic detection according to claim 2, characterized in that: The magnetic core materials and the number of turns of enameled wire of the X-direction magnetic core coil (2) and Y-direction magnetic core coil (3) are the same. The magnetic core material and the total number of turns of enameled wire of the Z-direction magnetic core coil (4) are the same as those of the X-direction magnetic core coil (2). The hollow coil (5) is wound with enameled wire and the number of turns is 0.5% - 3% of that of the X-direction magnetic core coil (2).

4. The magnetic sensor for semi-aerial transient electromagnetic detection according to claim 3, wherein: The X-direction magnetic core coil (2), Y-direction magnetic core coil (3), and Z-direction magnetic core coil (4) all use magnetic cores with a diameter of 1 - 2 cm and a length of 30 - 40 cm, and the number of turns of enameled wire is 10,000 - 30,000 turns. The number of turns of enameled wire of the hollow coil (5) is 100 - 300 turns and the outer diameter is 0.8 - 1.5 m.

5. The magnetic sensor for semi-aerial transient electromagnetic detection according to claim 3, characterized in that: The Z-direction magnetic core coil (4) is evenly divided into multiple segments along the axis, and each segment is vertically fixed on the housing (1) inside the hollow coil (5). The lengths and the number of turns of enameled wire of the magnetic core coils of each segment of the Z-direction magnetic core coil (4) are the same and are connected in series in sequence with wires.

6. The magnetic sensor for semi-aerial transient electromagnetic detection according to claim 1, characterized in that: The housing (1) is a hollow cylinder made of plastic material. The hollow coil (5) is a ring structure and is coaxially fixed at the bottom edge inside the housing (1). The X-direction magnetic core coil (2), Y-direction magnetic core coil (3), Z-direction magnetic core coil (4), and attitude sensor (6) are pasted, tied, or clamped to the bottom of the housing (1) inside the hollow coil (5) at intervals.

7. The magnetic sensor for semi-aerial transient electromagnetic detection according to any one of claims 1 to 6, characterized in that: It further includes a secondary field signal amplification module (7) fixedly arranged inside the housing (1). The secondary field signal amplification module (7) includes an X-direction differentiator (71), a Y-direction differentiator (72), a Z-direction differentiator (73), a matching capacitor (74), a signal amplifier I (75), a signal amplifier II (76), a signal amplifier III (77), a signal amplifier IV (78), and an analog-to-digital converter (79). The output end of the X-direction core coil (2) is electrically connected to the input end of the signal amplifier I (75) through the X-direction differentiator (71). The output end of the Y-direction core coil (3) is electrically connected to the input end of the signal amplifier II (76) through the Y-direction differentiator (72). The output end of the Z-direction core coil (4) is electrically connected to the input end of the signal amplifier III (77) through the Z-direction differentiator (73). The output end of the air-core coil (5) is electrically connected to the input end of the signal amplifier IV (78) through the matching capacitor (74). The output end of the signal amplifier IV (78) is electrically connected to the input ends of the X-direction differentiator (71), the Y-direction differentiator (72), and the Z-direction differentiator (73) respectively. The output ends of the signal amplifier I (75), the signal amplifier II (76), and the signal amplifier III (77) are electrically connected to the input end of the analog-to-digital converter (79) respectively. The output end of the analog-to-digital converter (79) is electrically connected to the data acquisition module mounted on the aircraft through a cable.

8. The magnetic sensor for semi-airborne transient electromagnetic detection according to claim 7, characterized in that: The resonance frequency output by the air-core coil (5) after passing through the matching capacitor (74) is the same as that of the X-direction core coil (2), the Y-direction core coil (3), and the Z-direction core coil (4). The sensitivity curve output by the air-core coil (5) after passing through the matching capacitor (74) and the signal amplifier IV (78) is the same as that of the X-direction core coil (2), the Y-direction core coil (3), and the Z-direction core coil (4) in the frequency band below the resonance frequency.

9. A debugging method for a magnetic sensor used in semi-aerial transient electromagnetic detection according to claim 7 or 8, characterized in that: It includes steps of obtaining the resonance frequency, debugging the air-core coil, and calculating the transient electromagnetic apparent resistivity. The specific contents are as follows: A. Obtaining the resonance frequency: Measure the sensitivity curves of the X-direction core coil (2), the Y-direction core coil (3), and the Z-direction core coil (4) respectively, and determine the resonance frequency on the sensitivity curves. B. Debug the air-core coil: Continuously try different matching capacitors (74) to make the resonant frequency output after the matching of the air-core coil (5) the same as that of the X-direction core coil (2), Y-direction core coil (3), and Z-direction core coil (4). Then, adjust the analog signal amplification factor of the signal amplifier IV (78). n Make the sensitivity curve output after the amplification of the air-core coil (5) the same as that of the X-direction core coil (2), Y-direction core coil (3), and Z-direction core coil (4) in the frequency band below the resonant frequency; C. Transient electromagnetic apparent resistivity calculation: Using the matching capacitance (74) of the air-core coil (5) and the analog amplification factor in signal debugging n , by obtaining the equivalent receiving areas of the magnetic core coil (2) in the X direction, the magnetic core coil (3) in the Y direction, and the magnetic core coil (4) in the Z direction S d , and then calculating the transient electromagnetic apparent resistivity according to the equivalent receiving area S d ρ .​ 10. The magnetic sensor debugging method for semi-aerial transient electromagnetic detection according to claim 9, characterized in that: For the X-direction core coil (2), Y-direction core coil (3), and Z-direction core coil (4), the amplification factor of the analog signal is obtained through debugging n , so that the equivalent receiving area of each core coil S d meets the following formula: Wherein: S k is the area of the air-core coil (5), t is the number of turns of the air-core coil (5), n is the amplification factor of the analog signal of the air-core coil (5) obtained according to the test.

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