A magnetic sensor for semi-aeronautical transient electromagnetic detection and its debugging method

Abstract

The present invention belongs to the field of geophysical exploration technology and specifically discloses a magnetic sensor for semi-airborne transient electromagnetic detection and its debugging method. The sensor housing is a non-magnetic rigid hollow cylinder. The X, Y, and Z-direction magnetic core coils are strip-shaped. The hollow coil is a ring-shaped structure and is horizontally fixed inside the housing. The X and Y-direction magnetic core coils are fixed horizontally and perpendicularly to each other inside the hollow coil. The Z-direction magnetic core coil is fixed vertically inside the hollow coil. An attitude sensor is fixed inside the housing and its orientation corresponds to the axial orientation of the X, Y, and Z-direction magnetic core coils. The X, Y, and Z-direction magnetic core coils, the hollow coil, and the attitude sensor are electrically connected to a data acquisition module mounted on an aircraft via cables. The method includes the steps of obtaining a resonant frequency, debugging the hollow coil, and calculating transient electromagnetic apparent resistivity. The present invention has the characteristics of simple structure, light weight, strong signal reception capability, and high exploration result accuracy.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration technology, and in particular to a magnetic sensor for semi-aerial transient electromagnetic detection with simple structure, light weight, strong signal receiving capability and high exploration result accuracy, and a debugging method thereof. Background Art

[0002] Transient electromagnetic (TEM) is based on resistivity differences in geological bodies, identifying them by measuring the differences in eddy current fields generated by these bodies. Magnetic source TEM uses a strong pulsed electromagnetic field (hereinafter referred to as the "primary field") generated at the moment of power outage in the power supply wireframe as the source. This field excites low-resistivity geological bodies to generate eddy current fields (hereinafter referred to as the "secondary field"), which are then collected to identify the geological bodies. Magnetic source semi-airborne TEM uses a ground-based transmitting wireframe as the transmitting source and uses an aircraft-mounted magnetic sensor to collect aerial data. This method leverages the high-power transmission advantages of ground-based TEM with the rapid aerial exploration capabilities of airborne TEM, resulting in high efficiency, strong resolution, and a lightweight aerial receiving magnetic sensor.

[0003] At present, magnetic source semi-airborne transient electromagnetic detection mostly uses magnetic sensors with Z-component hollow coils. However, in actual work, mountainous conditions are often encountered. Since the transmitting wireframe is flat on the ground and produces 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 the secondary field, and in actual work, it is affected by the interference electromagnetic field of the environment, the weak secondary field signal received in the hollow coil of the magnetic sensor is difficult to be effectively identified and extracted, resulting in low accuracy of the exploration results.

[0004] In the prior art, in order to address the problems of magnetic sensors used for semi-airborne transient electromagnetic detection using magnetic sources, some have developed high-current, fast-shutoff transmitters 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. This can also, to a certain extent, increase the relative strength of the secondary field signal, facilitating subsequent extraction. However, for electric source transmitters, due to the high bus voltage and poor device parasitic parameter conditions, implementing high-current fast-shutoff technology is difficult, and there may be problems with circuit stability and reliability. Furthermore, it cannot solve the problem that the secondary field actually received in three-dimensional space is not necessarily the Z component. In addition, there are technical solutions that use multi-component sensors to replace single Z-component air-core coil magnetic sensors. By measuring multiple field quantities and multiple components, secondary field information can be more comprehensively collected to adapt to the situation where the secondary field direction is uncertain in complex terrain. However, there are still problems with the weak secondary field signals received, which are difficult to effectively extract. Furthermore, the current multi-component sensors are heavy, making them uneconomical to use on platforms such as helicopters. Furthermore, using low-cost drones makes it difficult to simultaneously carry multiple sensors for multi-field and multi-component observations. To this end, a global-local structural feature extraction method based on machine learning has been used, validated using a large amount of multi-type simulation and measured noise pollution 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 a loose structure, the processing efficiency is low, and many key parameters still rely on manual settings, which reduces the objectivity of data processing.

[0005] In summary, it is necessary to develop a magnetic sensor for the magnetic source semi-airborne transient electromagnetic method that can significantly improve the secondary field signal receiving capability and adapt to the uncertain secondary field direction under complex terrain. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention provides a magnetic sensor for semi-airborne transient electromagnetic detection that has a simple structure, is light in weight, has strong signal receiving capability, and produces high-precision exploration results. It also provides a magnetic sensor debugging method for semi-airborne transient electromagnetic detection.

[0007] The magnetic sensor for semi-airborne 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, an air-core coil, and a posture sensor. The housing is a non-magnetic rigid hollow cylinder. The X-direction magnetic core coil, the Y-direction magnetic core coil, and the Z-direction magnetic core coil are strip-shaped structures. The air-core coil is an annular structure and is horizontally fixed to the edge inside the housing. The X-direction magnetic core coil and the Y-direction magnetic core coil are horizontally fixed to the housing inside the air-core coil and perpendicular to each other. The Z-direction magnetic core coil is vertically fixed to the housing inside the air-core coil. The posture sensor is fixed inside the housing and its orientation 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. The X-direction magnetic core coil, the Y-direction magnetic core coil, the air-core coil, and the posture sensor are electrically connected to a data acquisition module mounted on the aircraft via cables.

[0008] Furthermore, the resonant frequencies and sensitivity curves of the X-direction magnetic core coil, the Y-direction magnetic core coil, and the Z-direction magnetic core coil are consistent.

[0009] Furthermore, the X-direction magnetic core coil and the Y-direction magnetic core coil have the same core material and the same number of enameled wire turns; the Z-direction magnetic core coil has the same core material and the same total number of enameled wire turns as the X-direction magnetic core coil; the hollow coil is wound with enameled wire and the number of turns is 0.5-3% of that of the X-direction magnetic core coil.

[0010] Furthermore, the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil all use a magnetic core with a diameter of 1~2cm and a length of 30~40cm 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 is 100~300 turns and the outer diameter is 0.8~1.5m.

[0011] Furthermore, the Z-direction magnetic core coil is divided into multiple sections along the axial direction and each section is vertically fixed on the shell inside the hollow coil. The length and number of enameled wire turns of each section of the Z-direction magnetic core coil are the same and are connected in series in sequence using wires.

[0012] Furthermore, the shell is a hollow cylinder made of plastic material, the hollow coil is a circular ring structure and is coaxially fixed to the bottom edge of the inner side of the shell, and the X-direction magnetic core coil, Y-direction magnetic core coil, Z-direction magnetic core coil and posture sensor are adhered, bundled or clamped to the bottom of the shell inside the hollow coil at intervals.

[0013] Furthermore, the present invention also includes a secondary field signal amplification module fixedly arranged inside the shell, the secondary field signal amplification module including 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 magnetic 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 magnetic 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 magnetic 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 respectively electrically connected to the input ends of the X-direction differentiator, the Y-direction differentiator, and the Z-direction differentiator, the output ends of the signal amplifier I, signal amplifier II, and signal amplifier III are respectively electrically connected to the input end of the analog-to-digital converter, and the output ends of the analog-to-digital converter are respectively electrically connected to the data acquisition module mounted on the aircraft through cables.

[0014] Furthermore, the resonant frequency output by the hollow coil after matching the capacitor is consistent with that of the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil, and the sensitivity curve output by the hollow coil after matching the capacitor and the signal amplifier IV is consistent with that of the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil in the frequency band below the resonant frequency.

[0015] The magnetic sensor debugging method for semi-aeronautical transient electromagnetic detection of the present invention is implemented as follows: it includes the steps of obtaining the resonant frequency, debugging the air-core coil, and calculating the transient electromagnetic apparent resistivity. The specific contents are as follows:

[0016] A. Obtaining the resonant frequency: Measure the sensitivity curves of the X-direction magnetic core coil, the Y-direction magnetic core coil, and the Z-direction magnetic core coil respectively, and determine the resonant frequency on the sensitivity curves;

[0017] B. Debug the hollow coil: Keep trying different matching capacitors to make the resonant frequency of the hollow coil consistent with the X-direction core coil, Y-direction core coil, and Z-direction core coil, and then adjust the analog signal amplification factor of the signal amplifier IV. n , so that the sensitivity curve of the hollow coil after amplification is consistent with that of the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil in the frequency band below the resonant frequency;

[0018] C. Transient electromagnetic apparent resistivity calculation: using the matching capacitance of the hollow coil and the analog amplification factor in signal debugging n , by calculating the equivalent receiving area 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 area S d Calculate transient electromagnetic apparent resistivity r

[0019] Furthermore, for the X-direction magnetic core coil, the Y-direction magnetic core coil and the Z-direction magnetic core coil, the analog signal amplification factor is obtained through debugging. n , so that the equivalent receiving area of each core coil S d Complies with the following formula:

[0020]

[0021] Where: S k is the area of the hollow coil, t is the number of turns of the air-core coil, n It is the analog signal amplification factor of the air-core coil obtained from the test.

[0022] Beneficial effects of the present invention:

[0023] 1. The magnetic sensor of the present invention uses a non-magnetic rigid hollow cylinder as its shell. The three directional magnetic core coils inside are strip-shaped, and the hollow coil is a ring-shaped structure. The hollow coil, each magnetic core coil, and the attitude sensor are integrated into the shell to form an integrated three-component magnetic sensor, making the overall structure relatively simple and easy to install and remove from the aircraft. In addition, compared with existing multi-component sensors, it is lighter in weight and more suitable for low-altitude unmanned aerial vehicles such as multi-rotor drones and remote-controlled airships. This solves the problem that existing multi-component sensors are heavy, resulting in the need to use helicopters for transportation and losing economic efficiency, and that low-cost drones are difficult to carry multiple sensors.

[0024] 2. The magnetic sensor of the present invention uses 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, and the received signals are mainly the primary field and the environmental interference field. The resonant frequency and sensitivity curve output by the air-core coil after matching the capacitor and the signal amplifier are consistent with those of the magnetic core coils in the three directions in the frequency band below the resonant frequency. Then, the signals after matching and amplifying the air-core coil are respectively connected to the differentiators in the three directions, which not only makes the signal reception of the entire magnetic sensor more coordinated and stable, and is conducive to improving the signal reception effect, but also can subtract the primary field and environmental interference field signals received in the air-core coil from the analog signals received by the magnetic core coils in the three directions, effectively suppressing the influence of the primary field and the environmental interference field, and by amplifying the signals of the magnetic core coils in the three directions, the recognition and extraction capabilities of weak secondary field signals can be significantly improved, solving the problem that weak secondary field signals are difficult to be effectively recognized and extracted in the prior art.

[0025] 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 orientation of each magnetic core coil, it can not only adapt to the uncertainty of the secondary field direction under complex terrain to improve the receiving ability of secondary field signals, but also automatically correct the adverse effects of shaking and rotation on measurement data during the aircraft's onboard process, thereby effectively improving the measurement accuracy and adaptability to the use environment.

[0026] 4. The debugging method of the present invention accurately obtains the resonant frequency of each magnetic core coil, makes the resonant frequency and sensitivity curve of the hollow coil consistent with the three-directional magnetic core coil, and then uses the matching capacitance of the hollow coil and the analog amplification factor in the signal debugging to calculate the equivalent receiving area. S d , and then according to the equivalent receiving area S d Calculating transient electromagnetic apparent resistivity can effectively reduce errors caused by improper signal reception and processing. The debugging process and calculation are relatively simple, which can not only improve processing efficiency, but also enhance the accuracy and reliability of exploration results.

[0027] In summary, the present invention has the characteristics of simple structure, light weight, strong signal receiving capability and high precision of exploration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the internal structure of the magnetic sensor of the present invention;

[0029] Figure 2 This is a signal processing flow chart of the secondary field signal amplification module of the present invention;

[0030] In the figure: 1-shell, 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 capacitor, 75-signal amplifier I, 76-signal amplifier II, 77-signal amplifier III, 78-signal amplifier IV, 79-analog-to-digital converter. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] like Figure 1As shown, the magnetic sensor for semi-airborne 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, an air-core coil 5, and a posture 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 air-core coil 5 is an annular structure and is horizontally fixed to the edge inside the housing 1. The X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are horizontally fixed to the housing 1 inside the air-core coil 5 in a perpendicular manner. The Z-direction magnetic core coil 4 is vertically fixed to the housing 1 inside the air-core coil 5. The posture sensor 6 is fixed inside the housing 1 and its orientation corresponds to the axial orientation 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 air-core coil 5, and the posture sensor 6 are respectively electrically connected to a data acquisition module mounted on the aircraft via cables.

[0033] The X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are fixed horizontally on the housing 1 in a manner perpendicular to each other, which means that their axis lines are perpendicular to each other and are located on the same plane.

[0034] The Z-direction magnetic core coil 4 is fixed vertically on the housing 1 , which means that the axis of the Z-direction magnetic core coil 4 is perpendicular to the plane where the axis of the X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are located.

[0035] The resonant 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 consistent.

[0036] The X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 have the same core material and the same number of enameled wire turns. The Z-direction magnetic core coil 4 has the same core material and the same total number of enameled wire turns as the X-direction magnetic core coil 2. The air-core coil 5 is wound with enameled wire and has 0.5-3% of the number of turns of the X-direction magnetic core coil 2.

[0037] The X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the 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 enameled wire turns is 10,000-30,000. The number of enameled wire turns of the hollow coil 5 is 100-300 and the outer diameter is 0.8-1.5 m.

[0038] The Z-direction magnetic core coil 4 is evenly divided into multiple segments along the axial direction, each of which is vertically fixed to the housing 1 inside the hollow coil 5. Each segment of the Z-direction magnetic core coil 4 has the same length and number of enameled wire turns, and is connected in series using wires. Dividing the Z-direction magnetic core coil 4 into multiple segments along the axial direction reduces the overall height of the magnetic sensor, making the structure more compact and minimizing the vibration of the magnetic sensor when mounted on an aircraft.

[0039] The attitude sensor 6 adopts an existing lightweight three-axis attitude sensor, which is used to measure the axial angles of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4.

[0040] The shell 1 is a hollow cylinder made of plastic material, the hollow coil 5 is a circular ring structure and is coaxially fixed to the bottom edge of the inner side of the shell 1, and the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, the Z-direction magnetic core coil 4 and the posture sensor 6 are glued, bundled or clamped to the bottom of the shell 1 inside the hollow coil 5 at intervals.

[0041] like Figure 2 As shown, the present invention also 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 magnetic 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 magnetic core coil 3 is electrically connected to the input end of the signal amplifier II 76 through the Y-direction differentiator 72, and the Z-direction magnetic core coil 3 is electrically connected to the input end of the signal amplifier II 76. The output end of the core coil 4 is electrically connected to the input end of the signal amplifier III 77 through the Z-direction differentiator 73, and 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 cables.

[0042] 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 are all devices in the prior art and are not described in detail here.

[0043] The resonant frequency output by the hollow coil 5 after passing through the matching capacitor 74 is consistent with that of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic 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 consistent with that of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4 in the frequency band below the resonant frequency.

[0044] like Figure 1 and 2 As shown, the magnetic sensor debugging method for semi-aeronautical transient electromagnetic detection of the present invention includes the steps of obtaining the resonant frequency, debugging the air-core coil, and calculating the transient electromagnetic apparent resistivity. The specific contents are as follows:

[0045] A. Obtaining the resonant frequency: Measure the 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 respectively, and determine the resonant frequency on the sensitivity curves;

[0046] B. Debug the air-core coil: Keep trying different matching capacitors 74 to make the resonant frequency of the air-core coil 5 consistent with that of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4. Then adjust the analog signal amplification factor of the signal amplifier IV 78. n , so that the sensitivity curve of the hollow coil 5 after amplification is consistent with that of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4 in the frequency band below the resonant frequency;

[0047] C. Calculation of transient electromagnetic apparent resistivity: Using the matching capacitor 74 of the hollow coil 5 and the analog amplification factor in signal debugging n By calculating the equivalent receiving area of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4 S d , and then according to the equivalent receiving area S d Calculate transient electromagnetic apparent resistivity r .

[0048] In step B, the transient electromagnetic signal obtained by the airborne transient electromagnetic method generally exhibits a strong low-frequency signal and a gradually weakening trend toward high frequencies, and the signal contains primary, secondary, and transition fields. The hollow coil 5 is used as a reference coil for obtaining the primary field and environmental interference electromagnetic field signals. Its transient electromagnetic signal response is significantly different from that of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4. Signal amplification alone cannot match the signals obtained by the aforementioned three magnetic core coils. Since the resonant frequency is a key factor in the induction coil's ability to respond to signals, and for coil sensors, the frequency and sensitivity are logarithmically linearly distributed in the frequency band below the resonant frequency, the resonant frequency is calculated as follows:

[0049] ,

[0050] Where: f r is the resonant frequency, L is the inductor, C is the capacitor;

[0051] Because the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4 are all magnetic core coils, their inductance and distributed capacitance are relatively large, while the hollow coil 5 has a small number of turns, and its inductance and capacitance are smaller than those of the aforementioned three magnetic core coils, resulting in a large resonant frequency. Therefore, by matching capacitors of appropriate sizes at both ends of the signal of the hollow coil 5 to increase the total capacitance, the resonant frequency is made consistent with that of the aforementioned three magnetic core coils, and then analog signal amplification is performed. The response of the hollow coil 5 to the stronger primary field and interference field is approximately consistent with that of the aforementioned three magnetic core coils.

[0052] Since the number of turns of the enameled wire of the hollow coil 5 is small, the distributed capacitance is difficult to calculate accurately, so the capacitance matching needs to be achieved through sensitivity testing; to this end, the sensitivity curves of the three magnetic core coils are first tested, the resonant frequency is determined on the curve, and different matching capacitors 74 are continuously tried to make the resonant frequency of the hollow coil 5 consistent with the three magnetic core coils; then, through the signal amplifier IV 78, the sensitivity of the frequency band below the resonant frequency of the hollow coil 5 is adjusted to be consistent with the three magnetic core coils.

[0053] It should be noted that in transient electromagnetic exploration, there is a complex implicit function relationship between the surface response value of the uniform half-space and the resistivity of the uniform half-space. The explicit inverse function between the field and the resistivity cannot be obtained by analytical methods. The existing binary search method, translation method or segmented calculation method is usually used to indirectly calculate the apparent resistivity.

[0054] The process of calculating transient electromagnetic apparent resistivity using the binary search method is as follows:

[0055] 1) The forward formula for the one-dimensional frequency domain vertical magnetic field in a layered medium with a current line source is:

[0056]

[0057] Where: oh is the sampling angular frequency; I is the emission current; L is half the length of the current line source; y is the offset; R is the distance from the measuring point to the center of the dipole source; r TE is the reflection coefficient in TE mode; h is the height of the measuring point above the ground; l is the integral variable;J 1 is a 1st order Bessel function; x is the distance between the dipole source and the midpoint of the current line source; H ⊥ (oh) In the frequency domain oh The vertical component of the magnetic field response to the frequency;

[0058] Where: For a uniform half-space,

[0059]

[0060] Where: m is the magnetic permeability of the underground medium, r is the resistivity of underground medium, i is the imaginary unit, k 0 is the air wave number;

[0061] 2) When the line source is passed with a negative step current I(t) :

[0062]

[0063] Where: t is the time, with the power-off moment as 0; I ( t ) is the emission current at time t;

[0064] 3) Generate a frequency domain primary magnetic field around H(ω) :

[0065]

[0066] Where: H ( t ) is the moment in the time domain t The primary magnetic field at time , i is an imaginary unit, H(ω) In the frequency domain oh Frequency of the primary magnetic field;

[0067] 4) Use Fourier transform to convert the frequency domain to the time domain to obtain any time greater than zero t When , the partial derivative of the vertical magnetic field with respect to time is:

[0068]

[0069] Where: Re represents the imaginary part of the complex number;

[0070] 5) It can also be calculated from the actual measurement results :

[0071]

[0072] Where: m 0 is the magnetic permeability in vacuum, for t The vertical magnetic induction intensity at all times; The induced electromotive force at time t after the induced electromotive force and equivalent receiving area of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4 are rotated and projected to the vertical direction using the attitude sensor parameters;

[0073] Since the parameters of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4 are the same, we have:

[0074]

[0075] Where: S d is the equivalent receiving area of the core coil, S dx is the equivalent receiving area of the magnetic core coil 2 in the X direction, S dy is the equivalent receiving area of the magnetic core coil 3 in the Y direction, S dz is the equivalent receiving area of the magnetic core coil 4 in the Z direction;

[0076] 6) Rotation projection parameters:

[0077]

[0078] Where: e x is the induced electromotive force of the core coil 2 in the X direction, e y is the induced electromotive force of the magnetic core coil 3 in the Y direction, e z is the induced electromotive force of the magnetic core coil 4 in the Z direction, ψ is the heading angle obtained by the attitude sensor, i is the pitch angle obtained by the attitude sensor, f is the roll angle obtained by the attitude sensor;

[0079] 7) Different resistivity r' Substitute the value into the formula calculation theory , and the Contrast, constantly adjust according to size r' The value of underground transient electromagnetic apparent resistivity can be obtained through continuous binary search. r.

[0080] For the X-direction core coil 2, the Y-direction core coil 3, and the Z-direction core coil 4, the analog signal amplification factor is obtained through debugging. n , so that the equivalent receiving area of each core coil S d Complies with the following formula:

[0081]

[0082] Where: 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 analog signal amplification factor of the air-core coil 5 obtained from the test.

[0083] Example 1

[0084] S100: All three directional core coils use a 1cm diameter Permalloy as the core, are 30cm long (the Z-direction core coil 4 is divided into 5 sections), and the number of turns of the enameled wire can be 30,000 turns (each section of the Z-direction core coil 4 is wound with 6,000 turns); the hollow coil 5 uses the same enameled wire wound 300 turns to form a ring with an outer diameter of 1m.

[0085] S200: Figure 1 As shown, the aforementioned hollow coil 5 is adhered to the bottom of a plastic housing 1 with an inner diameter of 1m. Then, the X-direction magnetic core coil 2 and the Y-direction magnetic core coil 3 are adhered horizontally and perpendicularly to the bottom of the housing 1 on the inside of the hollow coil 5. Then, each section of the Z-direction magnetic core coil 4 is adhered vertically to the bottom of the housing 1 on the inside of the hollow coil 5 and connected in sequence with wires. Then, a posture sensor 6 (such as the JY-61P posture sensor of Shenzhen Weite Intelligent Technology Co., Ltd.) is adhered to the bottom of the housing 1 with its orientation corresponding to the axial orientation of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3, and the Z-direction magnetic core coil 4. A secondary field signal amplification module 7 is adhered to the bottom of the housing 1, and the aforementioned three-direction magnetic core coils and the hollow coil 5 are connected to the corresponding interfaces of the secondary field signal amplification module 7 through wires. The output end of the secondary field signal amplification module 7 is electrically connected to the data acquisition module mounted on the aircraft through the aviation plug on the top of the housing 1 to connect the signal lines and power lines.

[0086] S300: measuring 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 respectively, and determining the resonant frequencies of the magnetic core coils on the sensitivity curves.

[0087] S400: Continuously try different matching capacitors 74 in the secondary field signal amplification module 7 to make the resonant frequency output by the hollow coil 5 consistent with the three directions of the magnetic core coils, and then adjust the analog signal amplification factor of the signal amplifier IV 78 n , so that the sensitivity curve of the hollow coil 5 after amplification is consistent with that of the three-directional magnetic core coils in the frequency band below the resonant frequency.

[0088] S500: Using the matching capacitor 74 of the air-core coil 5 and the analog amplification factor in signal debugging n By calculating the equivalent receiving area of the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4 S d , and then according to the equivalent receiving area S d , using the binary search method, translation method or segmented calculation method in the existing technology to calculate the transient electromagnetic apparent resistivity r ;

[0089] Among them, for the X-direction magnetic core coil 2, the Y-direction magnetic core coil 3 and the Z-direction magnetic core coil 4, the analog signal amplification factor is obtained through debugging n , so that the equivalent receiving area of each core coil S d Complies with the following formula:

[0090]

[0091] Where: 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 analog signal amplification factor of the air-core coil 5 obtained from the test.

[0092] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A magnetic sensor for semi-aeronautical transient electromagnetic detection, characterized in that: The invention comprises a shell (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 a posture sensor (6), wherein the shell (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 to the edge inside the shell (1), the X-direction magnetic core coil (2) and the Y-direction magnetic core coil (3) are horizontally fixed to the hollow coil and are perpendicular to each other. The Z-direction magnetic core coil (4) is fixed vertically on the shell (1) inside the hollow coil (5); the attitude sensor (6) is fixed inside the shell (1) and its orientation corresponds to the axial orientation 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 the aircraft through cables.

2. The magnetic sensor for semi-airborne transient electromagnetic detection according to claim 1, characterized in that: The resonant 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 consistent.

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

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

5. The magnetic sensor for semi-airborne transient electromagnetic detection according to claim 3, characterized in that: The Z-direction magnetic core coil (4) is evenly divided into multiple sections along the axial direction, and each section is vertically fixed on the housing (1) inside the hollow coil (5). The length and number of enameled wire turns of each section of the Z-direction magnetic core coil (4) are the same and are connected in series in sequence using conductive wires.

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

7. The magnetic sensor for semi-airborne transient electromagnetic detection according to any one of claims 1 to 6, characterized in that: The secondary field signal amplification module (7) is fixedly arranged inside the housing (1), and 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 magnetic 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 magnetic core coil (3) is electrically connected to the input end of the signal amplifier II (76) through the Y-direction differentiator (72), and the Z-direction magnetic core coil (3) is electrically connected to the input end of the signal amplifier II (76). The output end of the 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), and the output end of the analog-to-digital converter (79) is electrically connected to the data acquisition module mounted on the aircraft through cables.

8. The magnetic sensor for semi-airborne transient electromagnetic detection according to claim 7, characterized in that: The resonant frequency output by the hollow coil (5) after being matched with the capacitor (74) is consistent with that of the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4); the sensitivity curve output by the hollow coil (5) after being matched with the capacitor (74) and the signal amplifier IV (78) is consistent with that of the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4) in the frequency band below the resonant frequency.

9. A magnetic sensor debugging method for semi-aeronautical transient electromagnetic detection according to claim 7 or 8, characterized in that: It includes the steps of obtaining the resonant frequency, debugging the hollow coil, and calculating the transient electromagnetic apparent resistivity. The specific contents are as follows: A. Obtaining the resonant frequency: measuring the 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) respectively, and determining the resonant frequency on the sensitivity curves; B. Debugging the hollow coil: Continuously try different matching capacitors (74) to make the resonant frequency of the hollow coil (5) after matching consistent with the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4), and then adjust the analog signal amplification factor of the signal amplifier IV (78). n , so that the sensitivity curve output by the hollow coil (5) after amplification is consistent with that of the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4) in the frequency band below the resonant frequency; C. Calculation of transient electromagnetic apparent resistivity: Using the matching capacitance (74) of the hollow coil (5) and the analog amplification factor in signal debugging n , by calculating the equivalent receiving area of the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4) S d , and then according to the equivalent receiving area S d Calculate transient electromagnetic apparent resistivity ρ .

10. The magnetic sensor debugging method for semi-airborne transient electromagnetic detection according to claim 9, characterized in that: For the X-direction magnetic core coil (2), the Y-direction magnetic core coil (3) and the Z-direction magnetic core coil (4), the analog signal amplification factor is obtained by debugging n , so that the equivalent receiving area of each core coil S d Complies with the following formula: Where: S k is the area of the hollow coil (5), t is the number of turns of the air-core coil (5), n is the analog signal amplification factor of the hollow coil (5) obtained from the test.

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