A semi-aeronautical electromagnetic detection frequency domain receiving system and design method

Abstract

The present invention belongs to the technical field of geophysical exploration by semi-aeronautical frequency domain electromagnetic method, and relates to a semi-aeronautical electromagnetic detection frequency domain receiving system and a design method, comprising: an unmanned aerial vehicle, a three-component magnetic core coil sensor suspended by the unmanned aerial vehicle and performing dynamic flight detection in a detection area, a signal conditioning circuit for conditioning data received by the three-component magnetic core coil sensor, and a receiver carried on the top of the unmanned aerial vehicle, and used for receiving the signal conditioned by the signal conditioning circuit. The three-component magnetic core coil sensor comprises three mutually orthogonal magnetic bars, which are magnetic cores and are fixed by a non-metallic cubic skeleton. The signal conditioning circuit comprises three groups, which respectively receive signals from the three magnetic bars, and by adjusting the time constant of a low-pass filter circuit in the signal conditioning circuit, the sensitivity corresponding to the frequency band that affects the saturation of the receiving system receiving the signal is reduced, and by performing effective gain attenuation in the low-frequency part, data saturation can be prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of semi-aeronautical frequency domain electromagnetic geophysical exploration, and in particular relates to a semi-aeronautical electromagnetic detection frequency domain receiving system and a design method. Background Art

[0002] Semi-aerial electromagnetic detection systems can be used for geological exploration, including mineral resource exploration, oil and gas exploration, etc. By measuring the electromagnetic properties of underground rocks, ores and oil and gas layers, it can help explorers determine the distribution of underground mineral resources and guide the development and utilization of mining areas. The semi-aerial electromagnetic detection system is based on electromagnetic theory, and describes the behavior of the electromagnetic field through the Maxwell equations, involving the basic principles of electromagnetic field generation, propagation and reception. The core of the semi-aerial electromagnetic detection system is the electromagnetic sensor, and its design and manufacturing technology directly affect the survey effect. The sensor usually includes a receiving coil, which can receive the underground reflection signal in real time during the flight, and then extract the electromagnetic characteristics information of the underground medium. At the same time, the semi-aerial electromagnetic detection system can be used for environmental monitoring, including soil pollution, groundwater level changes, groundwater flow direction, etc. By measuring the electromagnetic properties of the underground medium, changes in the environment can be monitored in a timely manner, providing a scientific basis for environmental protection and governance.

[0003] Chinese patent CN201510039201 discloses a frequency domain semi-aerial electromagnetic exploration method, which adopts the working mode of transmitting on the ground and receiving electromagnetic wave signals in the air, extracts the spectrum of the signal and interprets the underground electrical structure through the apparent resistivity method of the whole area. It is a new electromagnetic exploration method. The transmitting system working on the ground transmits multi-frequency pseudo-random waves to the underground through multiple cascades, and multiple frequency signals can be obtained by excitation once, which greatly improves the detection efficiency. The receiving system is carried on the aircraft and measures the magnetic field above the survey area. It can adapt to the environment with complex surface structure and weaken the static effect caused by the near-field influence, expanding the detection range of electromagnetic exploration. This method is suitable for deep detection in areas with harsh surface conditions, and has the characteristics of wide detection range, large detection depth and high detection efficiency.

[0004] Although the semi-aerial frequency domain electromagnetic exploration method can greatly improve the detection efficiency, the induction coil sensor in the existing receiving system can only receive the magnetic field signal of the vertical surface component, resulting in the loss of magnetic field signals of other components, forcing the detection area to be reduced. At the same time, the sensor sensitivity is insufficient and the detection ability of weak magnetic signals is limited. Moreover, due to the influence of electromagnetic noise and motion noise, high-sensitivity sensors are prone to saturation, and the detection area and detection accuracy need to be improved. Summary of the invention

[0005] A first aspect of the present invention provides a semi-aeronautical electromagnetic detection frequency domain receiving system for ground-to-air electromagnetic detection, which solves the problem of low-frequency data saturation caused by high-speed movement of traditional magnetic core coil sensors used for ground static or low-speed detection.

[0006] The invention also provides a design method for a semi-aeronautical electromagnetic detection frequency domain receiving system.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is:

[0008] A semi-aeronautical electromagnetic detection frequency domain receiving system comprises: an unmanned aerial vehicle, a three-component magnetic core coil sensor suspended by the unmanned aerial vehicle and performing dynamic flight detection in a detection area, a signal conditioning circuit for conditioning data received by the three-component magnetic core coil sensor, and a receiver carried on the top of the unmanned aerial vehicle for receiving signals conditioned by the signal conditioning circuit, wherein the three-component magnetic core coil sensor comprises three mutually orthogonal magnetic bars, which are magnetic cores and are fixed by a non-metallic cubic skeleton, on which a posture sensor is arranged, and the signal conditioning circuit comprises three groups, which respectively receive signals from the three magnetic bars, and by adjusting the time constant of a low-pass filter circuit in the signal conditioning circuit, the sensitivity corresponding to the frequency band that affects the saturation of the receiving signal of the receiving system is reduced.

[0009] Furthermore, the signal conditioning circuit includes a coil preamplifier circuit and an analog signal conditioning circuit, the coil preamplifier circuit is a pre-differential amplifier circuit, and the pre-differential amplifier circuit outputs a two-ended signal; the analog signal conditioning circuit includes: an operational amplifier, which is used to convert the two-ended signal into a single-ended signal and amplify it; a second-order low-pass filter circuit, which is connected to the output of the operational amplifier and is used to suppress environmental noise; a 50Hz industrial frequency band-stop filter circuit, which is connected to the output of the second-order low-pass filter circuit and is used to remove the industrial frequency interference signal of the ground-to-air electromagnetic detection work.

[0010] Furthermore, the second-order low-pass filter circuit includes: a first low-pass filter circuit and a second low-pass filter circuit with the same structure, the first low-pass filter circuit includes a first passive first-order low-pass filter circuit, a first inverting proportional operation circuit and a first first-order active low-pass filter circuit, and the second low-pass filter circuit includes a second passive first-order low-pass filter circuit, a second inverting proportional operation circuit and a second first-order active low-pass filter circuit;

[0011] Wherein, the first passive first-order low-pass filter circuit includes a resistor R1 and a capacitor C1, wherein the first end of the resistor R1 is connected to the input end, the second end is connected to the first end of the capacitor C1, and the second end of the capacitor C1 is grounded; the first inverting proportional operation circuit includes a resistor R3; the first first-order active low-pass filter circuit includes a resistor R2, a capacitor C2, a resistor R4 and an operational amplifier V1, wherein the first end of the resistor R2 is connected to the second end of the resistor R1, the second end of the resistor R2 is connected to the inverting input end of the operational amplifier V1, the first end of the resistor R3 is connected to the second end of the resistor R1, the second end of the resistor R3 is connected to the output end of the operational amplifier V1, the first end of the capacitor C2 is connected to the inverting input end of the operational amplifier V1, and the second end of the capacitor C2 is connected to the output end of the operational amplifier V1; the first end of the resistor R4 is connected to the non-inverting input end of the operational amplifier V1, and the second end of the resistor R4 is grounded;

[0012] The second passive first-order low-pass filter circuit includes a resistor R5 and a capacitor C3, wherein the first end of the resistor R5 is connected to the output end of the first passive first-order low-pass filter circuit, and the second end is connected to the first end of the capacitor C3, and the second end of the capacitor C3 is grounded; the second inverting proportional operation circuit includes a resistor R7; the second first-order active low-pass filter circuit includes a resistor R6, a capacitor C4, a resistor R8 and an operational amplifier V2, wherein the first end of the resistor R6 is connected to the second end of the resistor R5, and the second end of the resistor R6 is connected to the inverting input end of the operational amplifier V2; the first end of the resistor R7 is connected to the second end of the resistor R5, and the second end of the resistor R7 is connected to the output end of the operational amplifier V2; the first end of the capacitor C4 is connected to the inverting input end of the operational amplifier V2, and the second end of the capacitor C4 is connected to the output end of the operational amplifier V2; the first end of the resistor R8 is connected to the non-inverting input end of the operational amplifier V2, and the second end of the resistor R8 is grounded.

[0013] Furthermore, the resistance values ​​of the resistors R1, R2, R3, R5, R7 and R6 are set to be the same; the capacitors C2 and C4 are adjusted to change the time constant, and the capacitors C1 and C3 are adjusted to change the low-pass cutoff frequency.

[0014] Furthermore, the maximum value of the sensitivity in the frequency range of 10 Hz-100 Hz is adjusted to 40 mV / nT.

[0015] Another aspect of the present invention provides a method for designing a semi-aeronautical electromagnetic detection frequency domain receiving system, comprising:

[0016] Under static conditions, a semi-aeronautical electromagnetic detection frequency domain receiving system is used to detect in the detection area to obtain a received time domain signal;

[0017] Perform Fourier transformation on the time domain signal to obtain the frequency and the amplitude corresponding to the frequency, and obtain the frequency range that affects the signal saturation according to the frequency domain signal;

[0018] The semi-aeronautical electromagnetic detection frequency domain receiving system is placed in a shielded room and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer;

[0019] According to the frequency range that affects signal saturation and the sensitivity curve, the intersection of the high-sensitivity frequency range and the frequency range that affects signal saturation is determined as the sensitivity adjustment range;

[0020] The capacitor C2 and the capacitor C4 are continuously adjusted to change the time constant, and the semi-aeronautical electromagnetic detection frequency domain receiving system is used for dynamic flight detection each time after adjustment to obtain the received time domain signal, until the waveform of the time domain signal shows that the signal saturation no longer occurs, and the capacitor C2 and the capacitor C4 values ​​corresponding to the critical point where the signal saturation no longer occurs are determined;

[0021] The semi-aeronautical electromagnetic detection frequency domain receiving system with determined values ​​of capacitors C2 and C4 is placed in a shielded room, and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer, and the maximum sensitivity in the sensitivity adjustment range is found according to the sensitivity curve.

[0022] Compared with the prior art, the present invention has the beneficial effect that: the present invention can be used to prevent data saturation and avoid low-frequency noise caused by drastic attitude changes during flight by performing effective gain attenuation in the low-frequency part. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of a semi-aeronautical electromagnetic detection frequency domain receiving system provided by an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the structure of a vibration reduction system provided by an embodiment of the present invention;

[0025] Figure 3 A structural block diagram of a signal conditioning circuit provided by an embodiment of the present invention;

[0026] Figure 4 A circuit schematic diagram of a second-order low-pass filter circuit provided by an embodiment of the present invention;

[0027] Figure 5 The embodiments of the present invention provide a diagram of the on-site preparation stage and the flight reception effect under artificial source conditions. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] See also Figure 1 Combination Figure 2 As shown, a semi-aeronautical electromagnetic detection frequency domain receiving system includes: a drone 9, a three-component magnetic core coil sensor suspended by the drone 9 and performing dynamic flight detection in the detection area, a signal conditioning circuit for conditioning the data received by the three-component magnetic core coil sensor, and a receiver 8 carried on the drone, which is used to receive the signal conditioned by the signal conditioning circuit. The three-component magnetic core coil sensor includes three mutually orthogonal magnetic bars, the magnetic bars have a magnetic core in the middle, and are fixed by a non-metallic cubic skeleton 4. A posture sensor 5 is arranged on the non-metallic cubic skeleton 4. The signal conditioning circuit is three groups, which receive the signals of the three magnetic bars respectively, and by adjusting the time constant of the low-pass filter circuit in the signal conditioning circuit, the sensitivity corresponding to the frequency band that affects the saturation of the receiving system is reduced. It also includes a vibration reduction system 6 and a suspension rope 7. One end of the suspension rope 7 is connected to the three-component magnetic core coil sensor through the vibration reduction system 6, and the other end is connected to the drone 9. In order to reduce electromagnetic interference and reduce the weight of the drone suspension, the receiver 8 is carried above the drone 9 so that the three-component magnetic core coil sensor can obtain a good electromagnetic environment and the flight state of the drone.

[0030] The three-component magnetic core coil sensor, specifically including an X-component magnetic core coil sensor 1, a Y-component magnetic core coil sensor 2 and a Z-component magnetic core coil sensor 3, are distributed in mutually orthogonal positions, respectively measuring magnetic field signals in three directions, and using a non-metallic skeleton 4 to orthogonally fix the position. At the same time, a posture sensor 5 is placed on the surface of the non-metallic skeleton 4 to measure the posture of the three-component magnetic core coil sensor.

[0031] In the embodiment of the present invention, three mutually orthogonal magnetic bars are used, and a magnetic core is provided in the middle of the magnetic bars. The magnetic conductive material used in the magnetic core can capture more magnetic field signals at the measurement position. The three-component magnetic core coil sensor with a magnetic core structure has higher sensitivity.

[0032] See also Figure 2The structure diagram of the vibration reduction system is shown. When the three-component magnetic core coil sensor is suspended, it will inevitably generate vibration. This vibration causes the three-component magnetic core coil to introduce electromagnetic noise after cutting the earth's magnetic field. The active vibration reduction method will inevitably use the electronic control system, and the electronic control system will generate electromagnetic interference when working. The present invention uses a passive vibration reduction method to weaken the vibration noise. The vibration reduction system is composed of a spring system 61 and a damping system 62. The spring system 61 reduces the vibration frequency of the three-component magnetic core coil sensor. At the same time, the damping system 62 absorbs part of the vibration energy, converts the kinetic energy of the three-component magnetic core coil sensor into heat energy and dissipates the heat energy through the air.

[0033] See also Figure 3 As shown, the signal conditioning circuit includes a coil preamplifier circuit and an analog signal conditioning circuit. The coil preamplifier circuit is a pre-differential amplifier circuit, and the pre-differential amplifier circuit outputs a two-end signal; the analog signal conditioning circuit includes: an operational amplifier, which is used to convert the two-end signal into a single-end signal and amplify it; a second-order low-pass filter circuit, which is connected to the output of the operational amplifier and is used to suppress environmental noise; a 50Hz power frequency band-stop filter circuit, which is connected to the output of the second-order low-pass filter circuit and is used to remove the power frequency interference signal of the ground-to-air electromagnetic detection work.

[0034] See also Figure 4 As shown, the second-order low-pass filter circuit includes: a first low-pass filter circuit and a second low-pass filter circuit with the same structure, the first low-pass filter circuit includes a first passive first-order low-pass filter circuit, a first inverting proportional operation circuit and a first first-order active low-pass filter circuit, and the second low-pass filter circuit includes a second passive first-order low-pass filter circuit, a second inverting proportional operation circuit and a second first-order active low-pass filter circuit;

[0035] Wherein, the first passive first-order low-pass filter circuit includes a resistor R1 and a capacitor C1, wherein the first end of the resistor R1 is connected to the input end, the second end is connected to the first end of the capacitor C1, and the second end of the capacitor C1 is grounded; the first inverting proportional operation circuit includes a resistor R3; the first first-order active low-pass filter circuit includes a resistor R2, a capacitor C2, a resistor R4 and an operational amplifier V1, wherein the first end of the resistor R2 is connected to the second end of the resistor R1, the second end of the resistor R2 is connected to the inverting input end of the operational amplifier V1, the first end of the resistor R3 is connected to the second end of the resistor R1, the second end of the resistor R3 is connected to the output end of the operational amplifier V1, the first end of the capacitor C2 is connected to the inverting input end of the operational amplifier V1, and the second end of the capacitor C2 is connected to the output end of the operational amplifier V1; the first end of the resistor R4 is connected to the non-inverting input end of the operational amplifier V1, and the second end of the resistor R4 is grounded;

[0036] The second passive first-order low-pass filter circuit includes a resistor R5 and a capacitor C3, wherein the first end of the resistor R5 is connected to the output end of the first passive first-order low-pass filter circuit, and the second end is connected to the first end of the capacitor C3, and the second end of the capacitor C3 is grounded; the second inverting proportional operation circuit includes a resistor R7; the second first-order active low-pass filter circuit includes a resistor R6, a capacitor C4, a resistor R8 and an operational amplifier V2, wherein the first end of the resistor R6 is connected to the second end of the resistor R5, and the second end of the resistor R6 is connected to the inverting input end of the operational amplifier V2; the first end of the resistor R7 is connected to the second end of the resistor R5, and the second end of the resistor R7 is connected to the output end of the operational amplifier V2; the first end of the capacitor C4 is connected to the inverting input end of the operational amplifier V2, and the second end of the capacitor C4 is connected to the output end of the operational amplifier V2; the first end of the resistor R8 is connected to the non-inverting input end of the operational amplifier V2, and the second end of the resistor R8 is grounded.

[0037] The operational amplifier V1 and the operational amplifier V2 are both LT1352, and include five terminals, including a non-inverting input terminal, an inverting input terminal, an output terminal, a power supply terminal connected to +5V, and a power supply terminal connected to -5V.

[0038] In this embodiment, the resistance values ​​of resistors R1, R2, R3, R5, R7 and R6 are set to be the same; the capacitors C2 and C4 are adjusted to change the time constant, and the capacitors C1 and C3 are adjusted to change the low-pass cutoff frequency.

[0039] In another embodiment, the present invention further provides a method for designing a semi-aeronautical electromagnetic detection frequency domain receiving system, comprising:

[0040] Under static conditions, a semi-aeronautical electromagnetic detection frequency domain receiving system is used to detect in the detection area to obtain a received time domain signal;

[0041] Perform Fourier transformation on the time domain signal to obtain the frequency and the amplitude corresponding to the frequency, and obtain the frequency range that affects the signal saturation according to the frequency domain signal;

[0042] The semi-aeronautical electromagnetic detection frequency domain receiving system is placed in a shielded room and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer;

[0043] According to the frequency range that affects signal saturation and the sensitivity curve, the intersection of the high-sensitivity frequency range and the frequency range that affects signal saturation is determined as the sensitivity adjustment range;

[0044] The capacitor C2 and the capacitor C4 are continuously adjusted to change the time constant, and the semi-aeronautical electromagnetic detection frequency domain receiving system is used for dynamic flight detection each time after adjustment to obtain the received time domain signal, until the waveform of the time domain signal shows that the signal saturation no longer occurs, and the capacitor C2 and the capacitor C4 values ​​corresponding to the critical point where the signal saturation no longer occurs are determined;

[0045] The semi-aeronautical electromagnetic detection frequency domain receiving system with determined values ​​of capacitors C2 and C4 is placed in a shielded room, and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer, and the maximum sensitivity in the sensitivity adjustment range is found according to the sensitivity curve.

[0046] The three-component magnetic core coil sensor of the present invention can only be used for static ground measurement when the signal conditioning circuit of the present invention is not used. Once the magnetic rod moves, the closed coil cuts the geomagnetic field and generates huge low-frequency motion noise, causing data saturation. The state is good during static ground measurement, but if the detection system is suspended in mid-air, the data will be saturated and unusable just by the influence of ordinary wind. Such a three-component magnetic core coil sensor cannot be used in ground-to-air electromagnetic detection.

[0047] The method of the present invention uses a semi-aeronautical electromagnetic detection frequency domain receiving system to detect in the detection area in a static state to obtain a received time domain signal; the time domain signal is subjected to Fourier transformation to obtain a frequency domain signal of the frequency and the amplitude corresponding to the frequency, and the frequency range affecting the signal saturation is obtained according to the frequency domain signal. In the analysis process, it can be known that the amplitude is high on the left and low on the right, that is, the low-frequency part is greatly affected by the geomagnetic field and approaches saturation. Once saturated, the collected data will lose its meaning.

[0048] For example, in one embodiment, in a time domain waveform formed by a saturated time domain signal, the maximum signal voltage exceeds the measurement range, and the time domain signal is Fourier expanded to find out which frequency has the highest amplitude, and to find out that the main reason for low-frequency saturation is below 0-100 Hz.

[0049] The semi-aeronautical electromagnetic detection frequency domain receiving system was placed in a shielded room and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency change was measured by a dynamic analyzer; combined with the sensitivity curve, for example, the sensitivity of 0-10Hz gradually increased, but the overall sensitivity was low, indicating that the receiving system was not sensitive to the frequency change of 0-10Hz, which was not the main cause of saturation. However, the sensitivity of 10-100Hz was close to the maximum value of 150mV / nT.

[0050] Therefore, according to the frequency range that affects signal saturation and the sensitivity curve, the intersection of the high-sensitivity frequency range and the frequency range that affects signal saturation is determined as the sensitivity adjustment range, that is, the frequency range of 10-100 Hz. The sensitivity within the frequency range of 10-100 Hz is adjusted.

[0051] The method used to adjust the sensitivity within the frequency range of 10-100 Hz is: continuously adjust capacitor C2 and capacitor C4 to change the time constant, and perform dynamic flight detection on the semi-aeronautical electromagnetic detection frequency domain receiving system after each adjustment to obtain the received time domain signal until the waveform of the time domain signal shows that signal saturation no longer occurs, and determine the capacitor C2 and capacitor C4 values ​​corresponding to the critical point where signal saturation no longer occurs.

[0052] The principle in the above process is:

[0053] The first low-pass filter circuit and the second low-pass filter circuit have the same structure. Taking one of them as an example, the first low-pass filter circuit includes a first passive first-order low-pass filter circuit, a first inverting proportional operation circuit and a first first-order active low-pass filter circuit. The first passive first-order low-pass filter circuit, the first inverting proportional operation circuit and the first first-order active low-pass filter circuit are analyzed separately. Finally, the overall transfer function H(s) is obtained.

[0054] The transfer function of the first passive first-order low-pass filter circuit ,in, is the Laplace operator;

[0055] The transfer function of the first inverting proportional circuit is: ;

[0056] The transfer function of the first-order active low-pass filter circuit is ;

[0057] The overall transfer function of the first low-pass filter circuit is: ;

[0058] Here we take R 1 =R 2 =R 3 =R, simplifying the transfer function, we get: ;

[0059] Assume that the transfer function of the first low-pass filter circuit is expressed as: ;

[0060] The transfer function of the second low-pass filter circuit is expressed as: ;

[0061] Then the transfer function of the second-order low-pass filter circuit is:

[0062] ;

[0063] Compare with the standard second-order active LPF: , ;

[0064] in, is the standard transfer function of the second-order filter, is the second-order filter gain, is the quality factor, is the center angular frequency,

[0065] Take R 1 =R 2 =R,C 1 =C 3 =C, the cut-off frequency is: .

[0066] Then, the cut-off frequency is only related to the capacitance C 1 , capacitor C 3 The time constant τ is only related to capacitor C2 and capacitor C4. Extending the time constant will not affect the low-pass performance of the system, but it can reduce the sensitivity of the system.

[0067] The present invention evaluates the semi-aeronautical electromagnetic detection frequency domain receiving system through the signal-to-noise ratio.

[0068] The signal-to-noise ratio is calculated as:

[0069] , , ,

[0070] is the signal-to-noise ratio, is the signal voltage, is the noise voltage, represents the static Earth magnetic field strength, represents the rotation matrix in the carrier coordinate system, represents the Fourier transform, is the angular frequency. The higher the signal-to-noise ratio, the stronger the anti-interference ability and the collection ability of the semi-aeronautical electromagnetic detection frequency domain receiving system.

[0071] ,

[0072] Among them, α is the rotation angle around the X axis in the carrier coordinate system; β is the rotation angle around the Y axis; γ is the rotation angle around the Z axis, is the rotation matrix when the coordinate system rotates around the X axis alone, is the rotation matrix when the coordinate system rotates around the Y axis alone, It is the rotation matrix when the coordinate system rotates around the Z axis alone.

[0073] In order to further verify the effectiveness of the semi-aeronautical electromagnetic detection frequency domain receiving system of the present invention, we participated in the tunnel exploration project of Batang Deda section of Sichuan-Tibet Railway project. Figure 5 The following are the reception effects during the preparation phase of the site and under artificial source conditions. Figure 5 It can be seen that under the flight condition with drastic attitude changes, the X-axis frequency, Y-axis frequency and Z-axis frequency obtained have good data reception effects without unsaturation, indicating that the receiving system of the present invention can be stably used for measurements under flight conditions.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A semi-aeronautical electromagnetic detection frequency domain receiving system, characterized in that: include: An unmanned aerial vehicle, a three-component magnetic core coil sensor that is suspended by the unmanned aerial vehicle and performs dynamic flight detection in a detection area, a signal conditioning circuit that conditions data received by the three-component magnetic core coil sensor, and a receiver carried on the top of the unmanned aerial vehicle, which is used to receive the signal conditioned by the signal conditioning circuit, wherein the three-component magnetic core coil sensor includes three mutually orthogonal magnetic bars, which are magnetic cores and are fixed by a non-metallic cubic skeleton, on which a posture sensor is arranged, and the signal conditioning circuit includes three groups, which receive signals from the three magnetic bars respectively, and by adjusting the time constant of the low-pass filter circuit in the signal conditioning circuit, the sensitivity corresponding to the frequency band that affects the saturation of the receiving signal of the receiving system is reduced; The signal conditioning circuit includes a coil preamplifier circuit and an analog signal conditioning circuit. The coil preamplifier circuit is a pre-differential amplifier circuit, and the pre-differential amplifier circuit outputs a two-end signal; the analog signal conditioning circuit includes: an operational amplifier, which is used to convert the two-end signal into a single-end signal and amplify it; a second-order low-pass filter circuit, which is connected to the output of the operational amplifier and is used to suppress environmental noise; a 50Hz power frequency band-stop filter circuit, which is connected to the output of the second-order low-pass filter circuit and is used to remove the power frequency interference signal of the ground-to-air electromagnetic detection work; The second-order low-pass filter circuit comprises: a first low-pass filter circuit and a second low-pass filter circuit of the same structure, the first low-pass filter circuit comprises a first passive first-order low-pass filter circuit, a first inverting proportional operation circuit and a first first-order active low-pass filter circuit, and the second low-pass filter circuit comprises a second passive first-order low-pass filter circuit, a second inverting proportional operation circuit and a second first-order active low-pass filter circuit; Wherein, the first passive first-order low-pass filter circuit includes a resistor R1 and a capacitor C1, wherein the first end of the resistor R1 is connected to the input end, the second end is connected to the first end of the capacitor C1, and the second end of the capacitor C1 is grounded; the first inverting proportional operation circuit includes a resistor R3; the first first-order active low-pass filter circuit includes a resistor R2, a capacitor C2, a resistor R4 and an operational amplifier V1, wherein the first end of the resistor R2 is connected to the second end of the resistor R1, the second end of the resistor R2 is connected to the inverting input end of the operational amplifier V1, the first end of the resistor R3 is connected to the second end of the resistor R1, the second end of the resistor R3 is connected to the output end of the operational amplifier V1, the first end of the capacitor C2 is connected to the inverting input end of the operational amplifier V1, and the second end of the capacitor C2 is connected to the output end of the operational amplifier V1; the first end of the resistor R4 is connected to the non-inverting input end of the operational amplifier V1, and the second end of the resistor R4 is grounded; The second passive first-order low-pass filter circuit includes a resistor R5 and a capacitor C3, wherein the first end of the resistor R5 is connected to the output end of the first passive first-order low-pass filter circuit, and the second end is connected to the first end of the capacitor C3, and the second end of the capacitor C3 is grounded; the second inverting proportional operation circuit includes a resistor R7; the second first-order active low-pass filter circuit includes a resistor R6, a capacitor C4, a resistor R8 and an operational amplifier V2, wherein the first end of the resistor R6 is connected to the second end of the resistor R5, and the second end of the resistor R6 is connected to the inverting input end of the operational amplifier V2; the first end of the resistor R7 is connected to the second end of the resistor R5, and the second end of the resistor R7 is connected to the output end of the operational amplifier V2; the first end of the capacitor C4 is connected to the inverting input end of the operational amplifier V2, and the second end of the capacitor C4 is connected to the output end of the operational amplifier V2; the first end of the resistor R8 is connected to the non-inverting input end of the operational amplifier V2, and the second end of the resistor R8 is grounded; The resistance values ​​of resistors R1, R2, R3, R5, R7 and R6 are set to be the same; the capacitors C2 and C4 are adjusted to change the time constant; and the capacitors C1 and C3 are adjusted to change the low-pass cutoff frequency.

2. The semi-aeronautical electromagnetic detection frequency domain receiving system according to claim 1, characterized in that: The maximum value of the sensitivity in the frequency range of 10Hz-100Hz is adjusted to 40mV / nT.

3. A method for designing a semi-aeronautical electromagnetic detection frequency domain receiving system according to any one of claims 1-2, characterized in that: include: Under static conditions, a semi-aeronautical electromagnetic detection frequency domain receiving system is used to detect in the detection area to obtain a received time domain signal; Perform Fourier transformation on the time domain signal to obtain the frequency and the amplitude corresponding to the frequency, and obtain the frequency range that affects the signal saturation according to the frequency domain signal; The semi-aeronautical electromagnetic detection frequency domain receiving system is placed in a shielded room and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer; According to the frequency range that affects signal saturation and the sensitivity curve, the intersection of the high-sensitivity frequency range and the frequency range that affects signal saturation is determined as the sensitivity adjustment range; The capacitor C2 and the capacitor C4 are continuously adjusted to change the time constant, and the semi-aeronautical electromagnetic detection frequency domain receiving system is used for dynamic flight detection each time after adjustment to obtain the received time domain signal, until the waveform of the time domain signal shows that the signal saturation no longer occurs, and the capacitor C2 and the capacitor C4 values ​​corresponding to the critical point where the signal saturation no longer occurs are determined; The semi-aeronautical electromagnetic detection frequency domain receiving system with determined values ​​of capacitors C2 and C4 is placed in a shielded room, and the sensitivity curve of the semi-aeronautical electromagnetic detection frequency domain receiving system with frequency variation is measured by a dynamic analyzer, and the maximum sensitivity in the sensitivity adjustment range is found according to the sensitivity curve.

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