A Dynamic Correction Method for Electromagnetic Response of Unmanned Aerial Vehicles Based on Residual Magnetic Field Injection

Abstract

This application belongs to the field of electromagnetic detection technology and provides a dynamic correction method for the electromagnetic response of a UAV based on residual magnetic field injection. The method includes: under no flux negative feedback, a receiving coil collects a first induced voltage, and a receiving system receives the first induced voltage to obtain a first measured voltage; a reverse magnetic field is generated through flux negative feedback, and the receiving coil collects a second induced voltage, which is then received by the receiving system to obtain a second measured voltage; the transfer function of the actual receiving system is calculated based on the relationships between the first and second measured voltages and the first and second induced voltages, respectively; the transfer function of the theoretical receiving system is calculated, and correction coefficients and the effective secondary field signal are calculated; the amplitude and phase information of the effective secondary field signal are calculated. By eliminating the residual primary field voltage, dynamic calibration of the receiving system is simultaneously achieved, thereby obtaining more accurate response voltage data from two aspects and improving flight detection accuracy.

Description

Technical Field

[0001] This application belongs to the field of electromagnetic detection technology, specifically a method for dynamic correction of the electromagnetic response of unmanned aerial vehicles based on residual magnetic field injection. Background Technology

[0002] In electromagnetic detection, UAV electromagnetic detection is widely used in mineral resource exploration, space hazard detection, environmental monitoring, and underground pipeline investigation due to its flexibility and adaptability. The primary field in electromagnetic detection affects the received signal, and there are generally two methods to eliminate it. First, removing the primary field based on coil structure. Bucking coils are commonly used to eliminate the primary field in electromagnetic detection; however, this cannot be completely eliminated when the bucking coil is not accurately modeled, the actual size differs from the theoretical value, or the coil deforms during movement. Second, removing the primary field during data processing based on the theoretical value of the primary field calculated numerically. However, the theoretical and actual values ​​may deviate due to on-site deployment issues. Therefore, the residual primary field and secondary field are mixed and collected in the receiving system, and the secondary field voltage cannot be accurately extracted. In electromagnetic detection, calibration is necessary because the measured value of the electromagnetic field response signal differs from the theoretical value; otherwise, the true secondary field response cannot be reflected. The most classic calibration method is to calibrate the receiving system using the uniform spatial magnetic field of an electromagnetic shielding room and perform on-site calibration on the ground. However, during flight, the magnetic field signal received by the coil is also affected by factors such as the metal shell of the UAV, the magnetic field of the rotor DC motor, environmental and human electromagnetic interference, and electromagnetic interference caused by the cutting of the geomagnetic field. These problems cannot be taken into account in electromagnetic shielding rooms and ground field calibration, and are difficult to model and quantify. Summary of the Invention

[0003] This application provides a dynamic correction method for the electromagnetic response of a UAV based on residual magnetic field injection, which solves the problem that existing calibration methods cannot eliminate measurement errors and noise effects, resulting in inaccurate secondary field signals.

[0004] A method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection, according to an embodiment of this application, includes:

[0005] Without magnetic flux negative feedback, the receiving coil collects the first induced voltage containing the residual primary field and secondary field, and the receiving system receives the first induced voltage to obtain the first measured voltage.

[0006] A reverse magnetic field is generated by magnetic flux negative feedback, and a voltage opposite to the direction of the residual primary field is injected into the receiving coil. The receiving coil collects the second induced voltage containing the secondary field, and the receiving system receives the second induced voltage to obtain the second measured voltage.

[0007] The transfer function of the actual receiving system is calculated by using the relationship between the first measured voltage and the second measured voltage and the first induced voltage and the second induced voltage, respectively.

[0008] Calculate the transfer function of the theoretical receiving system;

[0009] Correction coefficient for the ratio of the transfer function of the theoretical receiving system to the transfer function of the actual receiving system;

[0010] The induced voltage of the receiving system under magnetic flux negative feedback is corrected by a correction coefficient to obtain the effective signal of the secondary field.

[0011] Calculate the amplitude and phase information of the effective signal in the secondary field.

[0012] Furthermore, the magnetic flux negative feedback is achieved by winding a magnetic flux negative feedback coil around the outside of the receiving coil, thereby forming negative feedback on the measured magnetic field of the receiving coil through mutual inductance.

[0013] Furthermore, the relationships between the first measured voltage and the second measured voltage and the first induced voltage and the second induced voltage, respectively, are expressed as follows: ,in, The first induced voltage, This is the second induced voltage. The first induced voltage, This is the second induced voltage. For a voltage opposite to the direction of the residual primary field, This is the transfer function of the actual receiving system.

[0014] Furthermore, correcting the induced voltage of the receiving system under magnetic flux negative feedback by means of the correction coefficient refers to multiplying the induced voltage of the receiving system under magnetic flux negative feedback by the correction coefficient.

[0015] Furthermore, the transfer function of the theoretical receiving system is calculated, including:

[0016] Establish an equivalent second-order system model for the receiving system, wherein the second-order system model includes equivalent to... In the series resistance-inductance model, the receiving coil is often connected in parallel with a matching resistor and a distributed capacitor in parallel with the matching resistor. A programmable amplifier is set at the output of the receiving coil.

[0017] The output voltage expression is obtained from the second-order system model: ,

[0018] For output voltage, This represents the induced voltage collected by the receiving coil. To match the resistor, Let be the angular frequency, and A be the gain of the programmable amplifier. R These are the inductance of the receiving coil, the resistance of the receiving coil, and the matching capacitor, respectively.

[0019] Furthermore, the amplitude and phase information of the effective signal of the secondary field are calculated, including:

[0020] Calculate the cross-power spectrum between the complex conjugate of the reference signal and the response signal, wherein the reference signal is the transmitted current and the response signal is the effective signal of the second field;

[0021] Calculate the self-power spectrum between the reference signal and its complex conjugate;

[0022] The amplitude ratio of the reference signal to the response signal is obtained by the ratio of the cross power spectrum to the self power spectrum.

[0023] The effective signal amplitude of the secondary field is obtained by multiplying the amplitude ratio of the reference signal and the response signal by the amplitude of the reference signal.

[0024] Calculate the phase difference between the reference signal and the response signal based on the amplitude ratio of the reference signal and the response signal, and compare it with the reference signal at a frequency... The phase information at the point is superimposed to obtain the effective phase information of the secondary field signal.

[0025] Furthermore, both the reference signal and the response signal are in frequency domain form obtained through fast Fourier transform.

[0026] Compared with existing technologies, the advantages of this application are as follows: the method of this application is applicable to dynamic signal correction during on-site flight testing. After eliminating residual primary field voltage, dynamic calibration of the receiving system is simultaneously achieved, thereby obtaining more accurate response voltage data from two aspects and improving flight detection accuracy. Attached Figure Description

[0027] Figure 1 The equivalent circuit model circuit diagram of the flux negative feedback coil and the receiving coil provided in the embodiments of this application;

[0028] Figure 2 A flowchart illustrating the method provided in the embodiments of this application;

[0029] Figure 3 The circuit diagram is an equivalent second-order system model of the receiving system provided in the embodiments of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] In UAV electromagnetic detection, the UAV tows three concentric coils, arranged from largest to smallest in diameter: a transmitting coil, a bucking coil, and a receiving coil. The transmitting coil generates a primary field, which in turn induces eddy currents in the subsurface anomaly, thus generating a secondary field. The bucking coil carries a current in the opposite direction to the transmitting coil to cancel the primary field in the receiving coil. The receiving coil receives the secondary field signal, obtaining the induced voltage of the anomaly. After subsequent data processing and interpretation, the distribution of subsurface anomalies can be determined, achieving the goal of acquiring stratigraphic information.

[0032] Since the buckling coil cannot completely eliminate the primary field during actual detection, the received induced voltage includes the remaining portion of the primary field and the response of the secondary field. To remove the remaining primary field, a magnetic flux negative feedback method is proposed. The structure of the magnetic flux negative feedback coil sensor involves winding the negative feedback coil outside the receiving coil, typically with a small number of turns. It uses mutual inductance to create negative feedback on the measured magnetic field of the receiving coil. The equivalent circuit structure is as follows: Figure 1 As shown. Figure 1 It includes a receiving coil, a magnetic flux negative feedback coil, and a feedback channel. R These are the inductance of the receiving coil, the resistance of the receiving coil, and the matching capacitor, respectively. It is the received induced voltage input, which includes the induced voltage of the two parts of the residual primary field. and the induced voltage of the secondary field . It is a programmable amplifier; the input is connected to the receiving coil, and the output passes through a feedback resistor. Connected to the flux negative feedback coil, , These are the inductance and resistance of the flux negative feedback coil, respectively. It is the mutual inductance between the negative feedback coil and the receiving coil. The induced voltage in the receiving coil is amplified by an amplifier and then... Converted into electric current It is then fed into the magnetic flux negative feedback coil, which in turn generates a reverse magnetic field, forming negative feedback on the measured magnetic field of the receiving coil and removing the influence of the residual primary field voltage.

[0033] In a concentric coil structure, the magnetic flux density generated by the transmitting coil with respect to the receiving coil is:

[0034] ,

[0035] in, It is the vacuum permeability. It is the number of turns of the transmitting coil. It is the emission current. It is the radius of the transmitting coil;

[0036] According to Faraday's law of electromagnetic induction, the primary field induced voltage of the receiving coil can be obtained:

[0037] ,

[0038] in, It is the magnetic flux passing through the receiving coil. It is the magnetic flux density passing through the receiving coil, N is the number of turns of the receiving coil, and S is the area of ​​the receiving coil.

[0039] It is the residual voltage of the primary field in the receiving coil, therefore It can be represented as:

[0040] ,

[0041] in, It is the residual coefficient. It is the residual voltage of the primary field in the receiving coil. It is the primary field-induced voltage of the receiving coil. It is the residual coefficient.

[0042] To ensure that the induced voltage generated by the feedback coil is equal in amplitude and opposite in phase to cancel the voltage generated by the residual primary field in the receiving coil, it is necessary to: ,

[0043] in, It is angular frequency. It is the mutual inductance between the negative feedback coil and the receiving coil. It is the feedback branch current. It is the imaginary unit.

[0044] Assuming the amplifier input impedance is sufficiently large, the expression for the feedback branch current is as follows: , It is the output voltage of the amplifier circuit. It is a feedback resistor.

[0045] The final frequency response function of the receiving system is: ,

[0046] in, It is the secondary field induced voltage. It is the imaginary unit.

[0047] Therefore, the residual primary field can be eliminated by adjusting the feedback resistor, as shown in the following equation:

[0048] .

[0049] The magnetic field in space is converted into an induced voltage signal through the receiving coil. Due to internal errors in the receiving system, there is a difference between the measured signal and the theoretical response signal, so calibration is required.

[0050] To enable dynamic calibration at the testing site, this application proposes a dynamic correction method for the electromagnetic response of unmanned aerial vehicles (UAVs) based on residual magnetic field injection.

[0051] See Figure 2 As shown, it includes: under the condition of no magnetic flux negative feedback, the receiving coil collects a first induced voltage containing residual primary field and secondary field, and the receiving system receives the first induced voltage to obtain a first measured voltage;

[0052] A reverse magnetic field is generated by magnetic flux negative feedback, and a voltage opposite to the direction of the residual primary field is injected into the receiving coil. The receiving coil collects the second induced voltage containing the secondary field, and the receiving system receives the second induced voltage to obtain the second measured voltage.

[0053] The transfer function of the actual receiving system is calculated by using the relationship between the first measured voltage and the second measured voltage and the first induced voltage and the second induced voltage, respectively.

[0054] Calculate the transfer function of the theoretical receiving system;

[0055] Correction coefficient for the ratio of the transfer function of the theoretical receiving system to the transfer function of the actual receiving system;

[0056] The induced voltage of the receiving system under magnetic flux negative feedback is corrected by a correction coefficient to obtain the effective signal of the secondary field.

[0057] Calculate the amplitude and phase information of the effective signal in the secondary field.

[0058] When the electromagnetic field in space changes, according to Faraday's law of electromagnetic induction, the receiving coil collects an induced voltage containing residual primary and secondary fields. Let this voltage be... The first induced voltage is obtained through the receiving system. Then, a known voltage signal opposite to the direction of the residual primary field is generated through magnetic flux negative feedback and injected into the receiving coil, making it... Theoretically, at this time the receiving coil only contains the secondary field induced voltage, i.e. The measured second induced voltage is obtained through the receiving system. The system of equations can be expressed using the method described above: ,

[0059] In the formula, It is the transfer function of the actual receiving system.

[0060] in, and It can be measured. Since the given signal is known, solving the system of equations yields the transfer function of the actual receiving system. .

[0061] However, the transfer function of the actual receiving system It is obtained through measured parameters and is related to the transfer function of the theoretical receiving system. Measurement errors still exist. An equivalent second-order system model of the receiving system is established, such as... Figure 3 As shown. The receiving coil is equivalent to... The resistance-inductance series model exists, and the distributed capacitance is present. A matching resistor is often connected in parallel across the receiving coil. The back-end programmable amplifier amplifies the weak signal and inputs it to the ADC module for acquisition. The receiving system operates in mode 1 without additional voltage injection and in mode 2 with additional voltage injection. In mode 1, the programmable amplifier has high gain, while in mode 2, it has low gain. Therefore, a receiving system with a smaller dynamic range can be used, resulting in more accurate secondary field voltage reception.

[0062] Assuming the gain of the programmable amplifier at the back end is A, the output voltage can be obtained. expression:

[0063] ;

[0064] in, This represents the induced voltage collected by the receiving coil. To match the resistor, Angular frequency, It is the imaginary unit.

[0065] Therefore, the transfer function of the ideal receiving system can be obtained as follows:

[0066] ,

[0067] The correction coefficient can then be obtained. .

[0068] Correcting the induced voltage of the receiving system under magnetic flux negative feedback by using a correction factor refers to multiplying the induced voltage of the receiving system under magnetic flux negative feedback by the correction factor.

[0069] In the actual measurement process, the induced voltage measured by the receiving system under magnetic flux negative feedback is corrected using a correction coefficient. This yields an ideal induced voltage, which eliminates the primary field and internal errors of the receiving system. Combined with the transfer function of the actual receiving system, this results in a theoretical induced voltage containing only the secondary field, i.e., the effective secondary field signal.

[0070] To accurately extract the amplitude and phase of the effective secondary field signal under strong background noise, it is necessary to address the issue that directly using the FFT (Fast Fourier Transform) method to extract amplitude and phase under low signal-to-noise ratio conditions would severely reduce accuracy. The cross-power spectrum method can suppress uncorrelated noise and amplify components related to the reference signal, thus enabling precise and effective extraction of amplitude and phase.

[0071] Calculate the amplitude and phase information of the effective signal in the secondary field, including:

[0072] Calculate the cross-power spectrum between the complex conjugate of the reference signal and the response signal, wherein the reference signal is the transmitted current and the response signal is the effective signal of the second field;

[0073] Calculate the self-power spectrum between the reference signal and its complex conjugate;

[0074] The amplitude ratio of the reference signal to the response signal is obtained by the ratio of the cross power spectrum to the self power spectrum.

[0075] The effective signal amplitude of the secondary field is obtained by multiplying the amplitude ratio of the reference signal and the response signal by the amplitude of the reference signal.

[0076] Calculate the phase difference between the reference signal and the response signal based on the amplitude ratio of the reference signal and the response signal, and compare it with the reference signal at a frequency... The phase information at the point is superimposed to obtain the effective phase information of the secondary field signal.

[0077] Reference signal of cross power spectrum method Select the transmitted current as the record, and respond to the signal. It is a secondary field effective signal. Cross-power spectrum. and self-power spectrum The calculation formula is shown below.

[0078] ,

[0079] In the formula, It is the frequency domain representation of the reference signal. It is the frequency domain representation of the response signal. It is the frequency domain representation of the reference signal. The complex conjugate, It is the frequency domain representation of the response signal. . It is a reference signal The amplitude spectrum at frequency f It is a response signal In frequency Amplitude spectrum at that location, It is a reference signal In frequency Phase information at the location, It is a response signal In frequency Phase information at the location, It is the imaginary unit.

[0080] From this, the amplitude ratio and phase difference can be obtained, and thus the accurate amplitude of the secondary field voltage can be obtained. and secondary field voltage phase information .

[0081] According to the cross power spectrum and self-power spectrum The ratio of the reference signal to the response signal is used to obtain the amplitude ratio of the reference signal to the response signal; and the effective amplitude of the secondary field signal is obtained by multiplying the amplitude ratio of the reference signal to the response signal by the amplitude of the reference signal.

[0082] Calculate the phase difference between the reference signal and the response signal based on the amplitude ratio of the reference signal and the response signal, and compare it with the reference signal at a frequency... The phase information at the point is superimposed to obtain the effective phase information of the secondary field signal;

[0083] The calculation formula is as follows: It is the virtual part. It is the real part. It is the ratio of the amplitude of the reference signal to the amplitude of the response signal. It is the phase difference between the reference signal and the response signal.

[0084] ,

[0085] ,

[0086] ,

[0087] .

[0088] This application applies to a dynamic signal correction method for on-site flight testing. After eliminating residual primary field voltage, a smaller dynamic range acquisition system can be used, while simultaneously achieving dynamic calibration of the receiving system. This results in more accurate response voltage data from two aspects, improving flight detection accuracy.

[0089] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection, characterized in that, include: Without magnetic flux negative feedback, the receiving coil collects the first induced voltage containing the residual primary field and secondary field, and the receiving system receives the first induced voltage to obtain the first measured voltage. A reverse magnetic field is generated by magnetic flux negative feedback, and a voltage opposite to the direction of the residual primary field is injected into the receiving coil. The receiving coil collects the second induced voltage containing the secondary field, and the receiving system receives the second induced voltage to obtain the second measured voltage. The transfer function of the actual receiving system is calculated by using the relationship between the first measured voltage and the second measured voltage and the first induced voltage and the second induced voltage, respectively. Calculate the transfer function of the theoretical receiving system; Correction coefficient for the ratio of the transfer function of the theoretical receiving system to the transfer function of the actual receiving system; The induced voltage of the receiving system under magnetic flux negative feedback is corrected by a correction coefficient to obtain the effective signal of the secondary field. Calculate the amplitude and phase information of the effective signal in the secondary field.

2. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 1, characterized in that, The magnetic flux negative feedback is achieved by winding a magnetic flux negative feedback coil around the outside of the receiving coil, and forming negative feedback on the measured magnetic field of the receiving coil through mutual inductance.

3. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 1, characterized in that, The relationships between the first measured voltage and the second measured voltage and the first induced voltage and the second induced voltage, respectively, are expressed as follows: ,in, The first measured voltage, For the second measured voltage, The first induced voltage, This is the second induced voltage. For a voltage opposite to the direction of the residual primary field, This is the transfer function of the actual receiving system.

4. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 1, characterized in that, Correcting the induced voltage of the receiving system under magnetic flux negative feedback by using a correction factor refers to multiplying the induced voltage of the receiving system under magnetic flux negative feedback by the correction factor.

5. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 1, characterized in that, The transfer function of a theoretical receiving system is calculated, including: Establish an equivalent second-order system model for the receiving system, wherein the second-order system model includes equivalent to... The receiving coil of the series resistive-inductive model has a matching resistor connected in parallel across its two ends, and a distributed capacitor connected in parallel with the matching resistor. A programmable amplifier is set at the output of the receiving coil. The output voltage expression is obtained from the second-order system model: , For output voltage, This represents the induced voltage collected by the receiving coil. To match the resistor, Let be the angular frequency, and A be the gain of the programmable amplifier. R These are the inductance of the receiving coil, the resistance of the receiving coil, and the matching capacitor, respectively.

6. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 1, characterized in that, Calculate the amplitude and phase information of the effective signal in the secondary field, including: Calculate the cross-power spectrum between the complex conjugate of the reference signal and the response signal, wherein the reference signal is the transmitted current and the response signal is the effective signal of the second field; Calculate the self-power spectrum between the reference signal and its complex conjugate; The amplitude ratio of the reference signal to the response signal is obtained by the ratio of the cross power spectrum to the self power spectrum. The effective signal amplitude of the secondary field is obtained by multiplying the amplitude ratio of the reference signal and the response signal by the amplitude of the reference signal. Calculate the phase difference between the reference signal and the response signal based on the amplitude ratio of the reference signal and the response signal, and compare it with the reference signal at a frequency... The phase information at the point is superimposed to obtain the effective phase information of the secondary field signal.

7. The method for dynamic correction of the electromagnetic response of a UAV based on residual magnetic field injection according to claim 6, characterized in that, Both the reference signal and the response signal are in frequency domain form obtained through Fast Fourier Transform.

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