An array magnetic feedback coil system and its calibration method

Abstract

The present invention discloses an array magnetic feedback coil system, which includes a plurality of magnetic feedback coils for receiving magnetic field change signals; a programmable gain amplifier connected to each magnetic feedback coil one by one for eliminating the difference in coil gains; an analog-to-digital converter connected to each programmable gain amplifier one by one for performing analog-to-digital conversion; a fractional delay filter connected to each analog-to-digital converter one by one for correcting the group delay of the magnetic feedback coils; a gain compensation module for generating corresponding gains for each coil; and a multi-frequency data reconstruction module for generating a reconstructed signal. The present invention can improve the deficiencies of the prior art, broaden the amplitude-frequency response range of the array magnetic feedback coils, and at the same time has a relatively wide approximate linear phase range, and can effectively receive broadband multi-frequency signals.

Description

Technical Field

[0001] The present invention relates to the technical field of fixed-wing airborne physical exploration, and in particular to an array magnetic feedback coil system and a calibration method thereof. Background Art

[0002] Common transient electromagnetic induction receiving coils have two working modes: magnetic feedback and resistance matching. The coils in these two working modes have approximately ideal amplitude-frequency characteristics. However, the coils in these two working modes do not have linear phase characteristics within the passband, which causes serious phase distortion when receiving multi-frequency (multi-tone) signals (such as square waves, triangular waves, etc.). The effective frequency reception range of common transient electromagnetic induction coils is only near their own resonance points, which makes the effective working bandwidth of transient electromagnetic induction coils too narrow to be conducive to receiving broadband multi-tone signals. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an array magnetic feedback coil system and a calibration method thereof, which can solve the deficiencies of the prior art, broaden the amplitude-frequency response interval of the array magnetic feedback coil, and at the same time have a relatively wide approximate linear phase interval, and can effectively receive broadband multi-frequency signals.

[0004] To solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0005] An array magnetic feedback coil system includes:

[0006] A plurality of magnetic feedback coils for receiving magnetic field change signals;

[0007] Programmable gain amplifiers connected to the magnetic feedback coils one by one for eliminating the difference in coil gains;

[0008] Analog-to-digital converters connected to the programmable gain amplifiers one by one for performing analog-to-digital conversion;

[0009] Fractional delay filters connected to the analog-to-digital converters one by one for correcting the group delay of the magnetic feedback coils;

[0010] A gain compensation module for generating corresponding gains for each coil;

[0011] A multi-frequency data reconstruction module for generating a reconstructed signal.

[0012] Preferably, the magnetic feedback coils are arranged in a series arrangement or a matrix array arrangement.

[0013] Preferably, the magnetic feedback coil includes a first operational amplifier. The positive input terminal of the first operational amplifier is connected to a main coil and an adjustable capacitor which are arranged in parallel. The negative input terminal of the first operational amplifier is grounded through a second resistor. The negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier through a first resistor. The output terminal of the first operational amplifier is connected to an auxiliary coil through a feedback resistor.

[0014] Preferably, the input terminal of the fractional delay filter is connected to the positive input terminal of a second operational amplifier through a third resistor. The negative input terminal of the second operational amplifier is grounded through a fourth resistor. The negative input terminal of the second operational amplifier is connected to the output terminal of the second operational amplifier through a fifth resistor. The positive input terminal of the second operational amplifier is grounded through a first capacitor. The output terminal of the first operational amplifier is grounded through a series-connected sixth resistor and a second capacitor. The output terminal of the first operational amplifier is connected to the emitter of a first triode. The base of the first triode is connected between the sixth resistor and the second capacitor. The collector of the first triode is grounded through a seventh resistor. The collector of the first triode is connected to the positive input terminal of a third operational amplifier through an eighth resistor. The input terminal of the fractional delay filter is connected to the negative input terminal of a fourth operational amplifier through a series-connected ninth resistor and a tenth resistor. A third capacitor is grounded between the ninth resistor and the tenth resistor. The output terminal of the fourth operational amplifier is connected between the ninth resistor and the tenth resistor through an eleventh resistor. The negative input terminal of the fourth operational amplifier is connected to the base of a second triode through a twelfth resistor. The negative input terminal of the fourth operational amplifier is connected to the collector of the second triode. The emitter of the second triode is grounded through a fourth capacitor. The output terminal of the fourth operational amplifier is connected to the negative input terminal of the fourth operational amplifier through a fifth capacitor. The positive input terminal of the fourth operational amplifier is grounded through a thirteenth resistor. The output terminal of the fourth operational amplifier is connected to the positive input terminal of the third operational amplifier through a fourteenth resistor. The positive input terminal of the third operational amplifier is grounded through a fifteenth resistor. The negative input terminal of the third operational amplifier is grounded through a sixteenth resistor. The negative input terminal of the third operational amplifier is connected to the output terminal of the third operational amplifier through a seventeenth resistor. The output terminal of the third operational amplifier is connected to the input terminal of an FPGA module. The output terminal of the FPGA module serves as the output terminal of the fractional delay filter.

[0015] A calibration method for the above array magnetic feedback coil system includes the following steps:

[0016] A. The magnetic feedback coil receives a magnetic field change signal;

[0017] B. The gain compensation module generates corresponding gain values for the signals received by each coil;

[0018] C. The analog-to-digital converter converts the received analog signal into a digital signal;

[0019] D. The fractional delay filter performs filtering and calibration on the digital signal;

[0020] E. The multi - frequency data reconstruction module reconstructs the signal for multi - frequency data to complete the reception of multi - tone signals.

[0021] Preferably, in step D, the correction of the digital signal includes the following steps:

[0022] D1. The FPGA module performs clustering processing on the filtered signal to obtain n classifications.

[0023] D2. Update the state according to the data of each classification and establish an update objective function for each type of data.

[0024] D3. Calculate the signal deviation correction value using the update objective function and correct the signal according to the signal deviation correction value.

[0025] Preferably, in step D2, establishing the update objective function for each type of data includes the following steps:

[0026] D21. Extract the eigenvalue of the data update state to form a feature set.

[0027] D22. Calculate the eigenfunction of the feature set.

[0028] D23. Perform iterative processing with convergence on the non - linear part of the eigenfunction, and perform linear transformation on the linear part of the eigenfunction to maximize the similarity between the linear part after linear transformation and the non - linear part after convergence processing.

[0029] D24. Use the minimum value function of the eigenfunction processed in step D23 as the update objective function.

[0030] The beneficial effects brought by adopting the above technical solutions are as follows: The present invention broadens the amplitude - frequency response interval of the array magnetic feedback coil, and at the same time has a relatively wide approximate linear phase interval, and can effectively receive broadband multi - frequency signals. The auxiliary coil in the magnetic feedback coil is used to provide negative feedback to the entire system. The auxiliary coil adjusts the amplitude - frequency response and phase - frequency response of the system. The first operational amplifier is used to amplify the signal received by the main coil and cooperate with the auxiliary coil to provide negative feedback to the system. The adjustment capacitor is used to further finely adjust the amplitude - frequency response and group delay of the magnetic feedback system. The fractional - delay filter adopts a dual - path parallel input structure to reduce the filtering distortion of the filter. A two - stage grounded filtering structure is adopted at the input end of the non - delay path, and the second - stage grounded filtering structure is an active control type, so as to realize the feedback control of the signal filtering process of this path and improve the filtering accuracy. The output signal of the fractional - delay filter is corrected through the processing of the FPGA module. By reasonably setting the update objective function, the operation amount of the FPGA module is reduced, and the real - time performance of the fractional - delay filter for signal processing is improved. Description of the Drawings

[0031] Figure 1It is the schematic diagram of a specific embodiment of the present invention.

[0032] Figure 2 It is the circuit diagram of the magnetic feedback coil in a specific embodiment of the present invention.

[0033] Figure 3 It is the circuit diagram of the fractional delay filter in a specific embodiment of the present invention. Specific embodiment

[0034] Refer to Figures 1-3 In a specific embodiment of the present invention, it includes

[0035] A plurality of magnetic feedback coils 1 for receiving magnetic field change signals;

[0036] A programmable gain amplifier 2 connected to the magnetic feedback coil 1 in one-to-one correspondence for eliminating the difference in coil gain;

[0037] An analog-to-digital converter 3 connected to the programmable gain amplifier 2 in one-to-one correspondence for performing analog-to-digital conversion;

[0038] A fractional delay filter 4 connected to the analog-to-digital converter 3 in one-to-one correspondence for correcting the group delay of the magnetic feedback coil 1;

[0039] A gain compensation module 5 for generating corresponding gain for each coil;

[0040] A multi-frequency data reconstruction module 6 for generating a reconstructed signal.

[0041] The magnetic feedback coils 1 are arranged in series.

[0042] The magnetic feedback coil 1 includes a first operational amplifier A1. The positive input terminal of the first operational amplifier A1 is connected to a main coil L1 and an adjustable capacitor C arranged in parallel. X , the negative input terminal of the first operational amplifier A1 is grounded through a second resistor R2, the negative input terminal of the first operational amplifier A1 is connected to the output terminal of the first operational amplifier A1 through a first resistor R1, and the output terminal of the first operational amplifier A1 is connected to an auxiliary coil L2 through a feedback resistor R. f connected to the auxiliary coil L2.

[0043] The input terminal IN of the fractional delay filter 4 is connected to the non-inverting input terminal of the second operational amplifier A2 through the third resistor R3. The inverting input terminal of the second operational amplifier A2 is grounded through the fourth resistor R4. The inverting input terminal of the second operational amplifier A2 is connected to the output terminal of the second operational amplifier A2 through the fifth resistor R5. The non-inverting input terminal of the second operational amplifier A2 is grounded through the first capacitor C1. The output terminal of the first operational amplifier A1 is grounded through the series-connected sixth resistor R6 and second capacitor C2. The output terminal of the first operational amplifier A1 is connected to the emitter of the first triode Q1. The base of the first triode Q1 is connected between the sixth resistor R6 and the second capacitor C2. The collector of the first triode Q1 is grounded through the seventh resistor R7. The collector of the first triode Q1 is connected to the non-inverting input terminal of the third operational amplifier A3 through the eighth resistor R8. The input terminal IN of the fractional delay filter 4 is connected to the inverting input terminal of the fourth operational amplifier A4 through the series-connected ninth resistor R9 and tenth resistor R10. A third capacitor C3 is grounded between the ninth resistor R9 and the tenth resistor R10. The output terminal of the fourth operational amplifier A4 is connected between the ninth resistor R9 and the tenth resistor R10 through the eleventh resistor R11. The inverting input terminal of the fourth operational amplifier A4 is connected to the base of the second triode Q2 through the twelfth resistor R12. The inverting input terminal of the fourth operational amplifier A4 is connected to the collector of the second triode Q2. The emitter of the second triode Q2 is grounded through the fourth capacitor C4. The output terminal of the fourth operational amplifier A4 is connected to the inverting input terminal of the fourth operational amplifier A4 through the fifth capacitor C5. The non-inverting input terminal of the fourth operational amplifier A4 is grounded through the thirteenth resistor R13. The output terminal of the fourth operational amplifier A4 is connected to the non-inverting input terminal of the third operational amplifier A3 through the fourteenth resistor R14. The non-inverting input terminal of the third operational amplifier A3 is grounded through the fifteenth resistor R15. The inverting input terminal of the third operational amplifier A3 is grounded through the sixteenth resistor R16. The inverting input terminal of the third operational amplifier A3 is connected to the output terminal of the third operational amplifier A3 through the seventeenth resistor R17. The output terminal of the third operational amplifier A3 is connected to the input terminal of the FPGA module. The output terminal of the FPGA module serves as the output terminal OUT of the fractional delay filter 4.

[0044] Among them, the first resistor R1 is 1.5 kΩ, the second resistor R2 is 5 kΩ, and the feedback resistor R fThe first resistor R1 is 0.35 kΩ, the third resistor R3 is 1 kΩ, the fourth resistor R4 is 2.5 kΩ, the fifth resistor R5 is 0.65 kΩ, the sixth resistor R6 is 1.3 kΩ, the seventh resistor R7 is 3 kΩ, the eighth resistor R8 is 4.5 kΩ, the ninth resistor R9 is 0.75 kΩ, the tenth resistor R10 is 1.5 kΩ, the eleventh resistor R11 is 5.5 kΩ, the twelfth resistor R12 is 6 kΩ, the thirteenth resistor R13 is 3.5 kΩ, the fourteenth resistor R14 is 1.75 kΩ, the fifteenth resistor R15 is 0.25 kΩ, the sixteenth resistor R16 is 1 kΩ, the seventeenth resistor R17 is 0.3 kΩ. The first capacitor C1 is 500 μF, the second capacitor C2 is 100 μF, the third capacitor C3 is 200 μF, the fourth capacitor C4 is 175 μF, the fifth capacitor C5 is 850 μF.

[0045] A calibration method for the above-mentioned array magnetic feedback coil system includes the following steps:

[0046] A. The magnetic feedback coil 1 receives the magnetic field change signal;

[0047] B. The gain compensation module 5 generates corresponding gain values for the signals received by each coil;

[0048] C. The analog-to-digital converter 3 converts the received analog signal into a digital signal;

[0049] D. The fractional delay filter 4 performs filter calibration on the digital signal;

[0050] E. The multi-frequency data reconstruction module 6 performs multi-frequency data reconstruction on the signal to complete the reception of the multi-tone signal.

[0051] In step D, calibrating the digital signal includes the following steps:

[0052] D1. The FPGA module performs clustering processing on the filtered signal to obtain n classifications;

[0053] D2. Update the state according to the data of each classification, and establish an update objective function for each class of data;

[0054] D3. Use the update objective function to calculate the signal deviation correction value, and correct the signal according to the signal deviation correction value.

[0055] In step D2, establishing the update objective function for each class of data includes the following steps:

[0056] D21. Extract the eigenvalue of the data update state to form an eigenvalue set;

[0057] D22. Calculate the eigenfunction of the eigenvalue set;

[0058] D23. Perform iterative processing with convergence on the non-linear part of the eigenfunction, and perform linear transformation on the linear part of the eigenfunction to maximize the similarity between the linear part after the linear transformation and the non-linear part after the convergence processing;

[0059] D24. Use the minimum value function of the eigenfunction after being processed in step D23 as the updated objective function.

[0060] The principle analysis of the present invention is as follows:

[0061] The amplitude-frequency response and group delay of the transient electromagnetic signal acquisition system based on magnetic feedback can be approximated as:

[0062]

[0063]

[0064] The gain inherent in each coil is A i , i ∈ [1, N], the inherent group delay of each coil is τ i , i ∈ [1, N], each coil is approximately linear-phase in the frequency interval i.e., τ i ≈ k i , i ∈ [1, N]. Assume that the operating frequency band range of the array coil is [f L , f H . Then the superposition sum of the approximately linear-phase regions of each coil must cover and exceed the operating frequency band range of the array coil.

[0065]

[0066] The gain compensation circuit generates different gains G i = 1 / A i , i ∈ [1, N]. Under the excitation of the same excitation field, the input matrix composed of the analog signals received by each magnetic feedback coil is

[0067]

[0068] The programmable gain amplifier cancels out the difference in coil gains. The signal after passing through the programmable gain amplifier is

[0069]

[0070] The signal after passing through the programmable gain amplifier is then quantized by the analog-to-digital converter to obtain Use a fractional delay filter to correct the group delay of each coil. The i-th fractional delay filter is

[0071]

[0072] Perform multi-frequency data reconstruction on the corrected data, and the reception of multi-tone signals can be completed.

[0073]

[0074] The above has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An array magnetic feedback coil system, characterized in that: including a plurality of magnetic feedback coils (1) for receiving magnetic field change signals; programmable gain amplifiers (2) connected in one-to-one correspondence with the magnetic feedback coils (1) for eliminating the difference in coil gains; analog-to-digital converters (3) connected in one-to-one correspondence with the programmable gain amplifiers (2) for performing analog-to-digital conversion; fractional delay filters (4) connected in one-to-one correspondence with the analog-to-digital converters (3) for correcting the group delay of the magnetic feedback coils (1); a gain compensation module (5) for generating corresponding gains for each coil; a multi-frequency data reconstruction module (6) for generating a reconstructed signal; The magnetic feedback coil (1) includes a first operational amplifier (A1). The positive input terminal of the first operational amplifier (A1) is connected to a main coil (L1) and a tuning capacitor (C X ) that are connected in parallel. The negative input terminal of the first operational amplifier (A1) is grounded through a second resistor (R2). The negative input terminal of the first operational amplifier (A1) is connected to the output terminal of the first operational amplifier (A1) through a first resistor (R1). The output terminal of the first operational amplifier (A1) is connected to an auxiliary coil (L2) through a feedback resistor (Rf); The input terminal (IN) of the fractional delay filter (4) is connected to the non-inverting input terminal of the second operational amplifier (A2) through the third resistor (R3). The inverting input terminal of the second operational amplifier (A2) is grounded through the fourth resistor (R4). The inverting input terminal of the second operational amplifier (A2) is connected to the output terminal of the second operational amplifier (A2) through the fifth resistor (R5). The non-inverting input terminal of the second operational amplifier (A2) is grounded through the first capacitor (C1). The output terminal of the second operational amplifier (A2) is grounded through the series-connected sixth resistor (R6) and second capacitor (C2). The output terminal of the second operational amplifier (A2) is connected to the emitter of the first triode (Q1). The base of the first triode (Q1) is connected between the sixth resistor (R6) and the second capacitor (C2). The collector of the first triode (Q1) is grounded through the seventh resistor (R7). The collector of the first triode (Q1) is connected to the non-inverting input terminal of the third operational amplifier (A3) through the eighth resistor (R8). The input terminal (IN) of the fractional delay filter (4) is connected to the inverting input terminal of the fourth operational amplifier (A4) through the series-connected ninth resistor (R9) and tenth resistor (R10). A third capacitor (C3) is grounded between the ninth resistor (R9) and the tenth resistor (R10). The output terminal of the fourth operational amplifier (A4) is connected between the ninth resistor (R9) and the tenth resistor (R10) through the eleventh resistor (R11). The inverting input terminal of the fourth operational amplifier (A4) is connected to the base of the second triode (Q2) through the twelfth resistor (R12). The inverting input terminal of the fourth operational amplifier (A4) is connected to the collector of the second triode (Q2). The emitter of the second triode (Q2) is grounded through the fourth capacitor (C4). The output terminal of the fourth operational amplifier (A4) is connected to the inverting input terminal of the fourth operational amplifier (A4) through the fifth capacitor (C5). The non-inverting input terminal of the fourth operational amplifier (A4) is grounded through the thirteenth resistor (R13). The output terminal of the fourth operational amplifier (A4) is connected to the non-inverting input terminal of the third operational amplifier (A3) through the fourteenth resistor (R14). The non-inverting input terminal of the third operational amplifier (A3) is grounded through the fifteenth resistor (R15). The inverting input terminal of the third operational amplifier (A3) is grounded through the sixteenth resistor (R16). The inverting input terminal of the third operational amplifier (A3) is connected to the output terminal of the third operational amplifier (A3) through the seventeenth resistor (R17). The output terminal of the third operational amplifier (A3) is connected to the input terminal of the FPGA module. The output terminal of the FPGA module serves as the output terminal (OUT) of the fractional delay filter (4).

2. The array magnetic feedback coil system according to claim 1, wherein: The magnetic feedback coils (1) are arranged in a series arrangement or a matrix array arrangement.

3. A calibration method for the array magnetic feedback coil system according to claim 2, characterized in that It includes the following steps: A. The magnetic feedback coil (1) receives a magnetic field change signal; B. The gain compensation module (5) generates a corresponding gain value for the signal received by each coil; C. The analog-to-digital converter (3) converts the received analog signal into a digital signal; D. The fractional delay filter (4) performs filtering and correction on the digital signal; E. The multi-frequency data reconstruction module (6) performs multi-frequency data reconstruction on the signal to complete the reception of the multi-tone signal.

4. The calibration method of the array magnetic feedback coil system according to claim 3, characterized in that: In step D, the correction of the digital signal includes the following steps: D1. The FPGA module performs clustering processing on the filtered signal to obtain n classifications; D2. Update the state according to the data of each classification, and establish an update objective function for each class of data; D3. Use the update objective function to calculate the signal deviation correction value, and correct the signal according to the signal deviation correction value.

5. The calibration method of the array magnetic feedback coil system according to claim 4, characterized in that: In step D2, establishing the update objective function for each class of data includes the following steps: D21. Extract the eigenvalue of the data update state, to form an eigenvalue set; D22. Calculate the eigenfunction of the eigenvalue set; D23. Perform iterative processing with convergence on the non-linear part of the eigenfunction, and perform linear transformation on the linear part of the eigenfunction to maximize the similarity between the linear part after linear transformation and the non-linear part after convergence processing; D24. Use the minimum value function of the eigenfunction after being processed in step D23 as the update objective function.

Images