A ground-to-air frequency domain electromagnetic detection receiving system performance checking device and method

Abstract

The application provides a ground-to-air frequency domain electromagnetic detection receiving system performance verification device and method, belonging to the technical field of ground-to-air detection, comprising a transmitting link for generating a standardized single-frequency excitation magnetic field, comprising a reverse conversion and modulation module, a hybrid filtering module, a dynamic power supply power amplification module and a transmitting calibration coil module connected in sequence; a receiving and processing link for receiving the excitation magnetic field and evaluating the coil performance, comprising a receiving coil module, a posture correction and noise suppression module, a data processing module and a performance evaluation module; the application can quickly verify the receiving device, especially in high-altitude areas, potential problems of the equipment can be found in advance through an automatic process, and time and economic losses caused by equipment failure are reduced.

Description

Technical Field

[0001] This invention belongs to the field of ground-to-air detection technology, specifically a performance verification device and method for a ground-to-air frequency domain electromagnetic detection and receiving system. Background Technology

[0002] With the widespread application of ground-to-air frequency domain receivers in aerospace, meteorological monitoring, and radio communications, the stability and reliability of the receiving coil directly affect the overall system performance. In high-altitude areas and extreme environments, receiving coils typically face more demanding operating conditions, leading to wear and tear or damage during transportation, assembly, long-term storage, and actual use. The harsh climate of high-altitude regions, with extremely low temperatures and atmospheric pressure, poses significant challenges to the stability, reliability, and battery life of equipment. Receiving coils, in particular, need to maintain good performance during long-term transportation and assembly. However, the complex assembly and debugging processes often result in unnecessary damage to the equipment before actual operation, a problem exacerbated in extreme environments such as high altitudes.

[0003] Equipment failures, especially in high-altitude areas, often severely limit repair capabilities due to environmental constraints. Damage discovered in such environments is difficult to repair, time-consuming, and resource-intensive, hindering timely restoration of normal operation. This not only delays production schedules but also incurs significant economic losses. Furthermore, launch devices, as crucial system components, are typically large and complex, requiring substantial human intervention and technical support. The harsh conditions of high-altitude environments make commissioning, deployment, and maintenance of launch devices exceptionally challenging. In particular, prolonged exposure to harsh weather conditions can degrade stability. Precise adjustments and commissioning of launch devices necessitate a large number of technicians, increasing labor costs and complicating system deployment. Crucially, when equipment fails at high altitudes, the harsh environment significantly complicates repair and replacement, often requiring substantial logistical support, time, and financial investment. Equipment damage not only disrupts system operations but can also delay or prevent timely mission completion, resulting in significant resource waste. Therefore, in complex environments such as high altitudes, ensuring that the receiving coil is in good condition before use and avoiding irreparable damage has become a pressing technical challenge. Summary of the Invention

[0004] To address the shortcomings of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide a performance verification device and method for a ground-to-air frequency domain electromagnetic detection and receiving system.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system includes:

[0007] The transmit link, used to generate a standardized single-frequency excitation magnetic field, includes an inverter and modulation module, a hybrid filter module, a dynamic power supply amplifier module, and a transmit calibration coil module connected in sequence.

[0008] The hybrid filtering module is composed of a cascaded LC filter and an active second-order filter, and is used to filter the inverter output signal.

[0009] The dynamic power supply power amplifier module adopts an envelope tracking structure, which is used to adjust the power amplifier supply voltage in real time according to the excitation signal envelope to maintain a constant magnetic field amplitude.

[0010] The receiving and processing link is used to receive the excitation magnetic field and evaluate the coil performance, including a receiving coil module, an attitude correction and noise suppression module, a data processing module and a performance evaluation module;

[0011] The attitude correction and noise suppression module is configured to: predict the geomagnetic coupling noise voltage caused by attitude change by calculating the projection of the geomagnetic field on the sensitive axis of the receiving coil based on the attitude information obtained by the attitude sensor, and then subtract the predicted noise voltage from the actual induced voltage measured by the receiving coil module after synchronization.

[0012] As a further improvement, the inverter and modulation module adopts a space vector pulse width modulation strategy and includes a nanosecond-level time jitter correction unit for improving frequency resolution and a phase accumulation algorithm for maintaining phase continuity.

[0013] As a further improvement: the posture correction and noise suppression module includes:

[0014] Attitude sensor, used to measure roll, pitch and yaw angles of the receiving coil;

[0015] The installation error compensation unit is used to correct the measured attitude according to the installation error compensation matrix.

[0016] The noise prediction unit is used to predict attitude noise voltage based on the corrected attitude, geomagnetic field vector, and unit impulse response through convolution operations.

[0017] The cross-correlation synchronization unit is used to calculate the cross-correlation function between the predicted noise voltage and the measured induced voltage in order to determine the time delay and perform synchronization.

[0018] The noise reduction unit is used to subtract the synchronized predicted noise voltage from the measured induced voltage.

[0019] As a further improvement: the data processing module includes:

[0020] The center frequency of the bandpass filter unit is adjustable according to the current excitation frequency;

[0021] A windowing processing unit is used to apply a Hanning window to the signal to reduce spectral leakage;

[0022] The Fast Fourier Transform (FFT) unit is used to convert time-domain signals into frequency-domain signals.

[0023] Amplitude and frequency extraction unit, used to extract the signal amplitude and precise frequency at the excitation frequency point from the spectrum;

[0024] The signal-to-noise ratio (SNR) evaluation unit is used to calculate the SNR based on the peak power of the signal and the noise power in the neighborhood.

[0025] As a further improvement: the performance evaluation module is configured as follows:

[0026] The current sensitivity of the receiving coil is calculated based on the signal amplitude extracted by the data processing module, and the sensitivity deviation is obtained by comparing it with the sensitivity benchmark.

[0027] The frequency deviation is obtained by comparing the extracted signal frequency with the theoretical excitation frequency.

[0028] The sensitivity deviation, frequency deviation, and signal-to-noise ratio are combined with a preset threshold to generate a comprehensive judgment result regarding whether the receiving coil performance is qualified or abnormal.

[0029] As a further improvement, a power supply module is also included, which employs a multi-phase interleaved parallel Buck converter structure to provide a low-ripple DC bus voltage for the inverter and modulation module.

[0030] This invention also provides a method for verifying the performance of a ground-to-air frequency domain electromagnetic detection and receiving system, the method comprising:

[0031] Through the transmission link, a standardized single-frequency excitation magnetic field with constant amplitude is generated sequentially at multiple discrete frequency points;

[0032] The receiving coil module receives the excitation magnetic field and outputs an induced voltage signal, while the attitude sensor collects the attitude angle data of the receiving coil.

[0033] Based on the attitude angle data, the attitude noise voltage generated by geomagnetic coupling is predicted, and the attitude noise voltage is subtracted after time synchronization with the induced voltage signal to obtain the purified signal.

[0034] The purified signal is filtered, windowed, and subjected to Fast Fourier Transform to extract the signal amplitude, precise frequency, and signal-to-noise ratio at the current excitation frequency.

[0035] The extracted signal amplitude, frequency, and signal-to-noise ratio are compared with preset sensitivity, frequency, and signal-to-noise ratio thresholds to comprehensively determine the performance status of the receiving coil.

[0036] As a further improvement: the step of predicting the attitude noise voltage generated by geomagnetic coupling based on the attitude angle data, and then subtracting it after time synchronization with the induced voltage signal, specifically includes:

[0037] Based on the attitude angle and the installation error compensation matrix, calculate the true orientation of the receiving coil's sensing axis in the geographic coordinate system;

[0038] Based on the true direction and the geomagnetic field vector, calculate the change of the projection component of the geomagnetic field on the sensitive axis over time;

[0039] The predicted attitude noise voltage is obtained by convolving the time rate of change of the projection component with the unit impulse response of the receiving coil.

[0040] Calculate the cross-correlation function between the predicted attitude noise voltage and the measured induced voltage, determine the time delay between the two, and perform synchronization alignment.

[0041] Subtract the predicted noise voltage after synchronization from the measured induced voltage.

[0042] Compared with existing technologies, the advantages of this invention are: it innovatively introduces an attitude noise prediction algorithm based on installation error compensation and unit impulse response convolution. By eliminating mechanical installation deviations through static calibration and using a cross-correlation algorithm to solve the multi-sensor time synchronization problem, it can accurately deduct low-frequency attitude noise generated by geomagnetic field coupling from the received signal, thereby improving the extraction accuracy of weak single-frequency verification signals by an order of magnitude under dynamic conditions such as wind swaying. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system.

[0044] Figure 2 This is a schematic diagram of the overall structural modules of a performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system.

[0045] Figure 3 A flowchart of a method for verifying the performance of a ground-to-air frequency domain electromagnetic detection and receiving system; Detailed Implementation

[0046] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0047] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0048] Please see Figure 1 , Figure 2 , Figure 3 In one embodiment, a performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system includes:

[0049] The transmit link, used to generate a standardized single-frequency excitation magnetic field, includes an inverter and modulation module, a hybrid filter module, a dynamic power supply amplifier module, and a transmit calibration coil module connected in sequence.

[0050] The hybrid filtering module is composed of a cascaded LC filter and an active second-order filter, and is used to filter the inverter output signal.

[0051] The dynamic power supply power amplifier module adopts an envelope tracking structure, which is used to adjust the power amplifier supply voltage in real time according to the excitation signal envelope to maintain a constant magnetic field amplitude.

[0052] The receiving and processing link is used to receive the excitation magnetic field and evaluate the coil performance, including a receiving coil module, an attitude correction and noise suppression module, a data processing module and a performance evaluation module;

[0053] The attitude correction and noise suppression module is configured to: predict the geomagnetic coupling noise voltage caused by attitude change by calculating the projection of the geomagnetic field on the sensitive axis of the receiving coil based on the attitude information obtained by the attitude sensor, and then subtract the predicted noise voltage from the actual induced voltage measured by the receiving coil module after synchronization.

[0054] In this embodiment, the rectifier module includes a full-bridge rectifier circuit and a large-capacity bus capacitor bank, which is used to rectify the input AC power into stable DC power and suppress voltage ripple through the bus capacitor, thereby reducing rectification ripple and improving the stability of DC bus voltage.

[0055] The hybrid filtering module, consisting of an LC filter and an active second-order filter, is used to reduce inverter switching harmonics and improve the waveform purity of the excitation signal.

[0056] The dynamic power supply power amplifier module adopts an envelope tracking structure and adjusts the power supply voltage based on real-time current sampling to keep the amplitude of the excitation magnetic field constant across the entire frequency band.

[0057] It also includes a transmitter calibration coil module for generating an experimentally calibrated standardized single-frequency magnetic field based on the excitation current;

[0058] The receiving coil module is used to receive the excitation magnetic field and output the induced voltage;

[0059] The attitude correction and noise suppression module compensates for the attitude changes of the receiving coil based on the attitude angle measured by the attitude sensor, and predicts and synchronously subtracts the geomagnetic coupling noise caused by the attitude.

[0060] The data processing module is used to filter, process window functions, perform fast Fourier transform, extract amplitude, estimate noise and identify frequency deviation of the induced voltage after attitude correction. The data processing module needs to perform attitude compensation and spectrum analysis on the output signal of the receiving coil, and also needs to perform comprehensive modeling of the sensitivity, phase, noise and frequency stability of the coil under frequency sweep conditions, so that the system can establish stable and repeatable performance evaluation results in multiple full-band verification processes.

[0061] The performance evaluation module is used to output the comprehensive performance judgment result of the receiving coil based on the multi-frequency amplitude sensitivity, signal-to-noise ratio, frequency deviation and phase stability.

[0062] To convert the PWM excitation waveform output by the inverter module into a sinusoidal current with extremely low harmonics, this invention employs a hybrid filtering structure consisting of an LC filter and an active second-order filter. The LC filter section, through the configuration of a series inductor and a parallel capacitor, effectively attenuates high-frequency switching harmonics without significantly affecting the principal components in the target frequency range of 1Hz to 10kHz. The transfer function of the active second-order filter section is:

[0063] ;

[0064] Where s is the complex frequency variable, w c The cutoff frequency, The damping ratio is denoted by . By adjusting the feedback parameters of the operational amplifier, a steep roll-off characteristic and a flatter passband response can be obtained, making the excitation waveform highly consistent with the ideal sine wave after filtering.

[0065] This invention employs a hybrid filtering structure consisting of a passive LC filter and an active second-order filter. The passive component reduces high-frequency harmonics generated by the inverter switching, while the active component refines the passband waveform to improve passband flatness and stopband roll-off performance, ensuring that the excitation current maintains low harmonics and high phase consistency across the entire frequency band. The filter parameters can be automatically adjusted according to the calibration frequency, enabling the system to achieve high waveform purity at different frequencies. This ensures that the transmitting coil generates a stable and calibrable sinusoidal magnetic field, guaranteeing accurate frequency, amplitude, and phase references for the receiving coil's FFT analysis.

[0066] To maintain the stability of the excitation magnetic field amplitude under different frequencies and amplitudes, this invention designs a dynamic power amplifier module with envelope tracking capability, and provides overcurrent, overvoltage, overtemperature, and short-circuit protection functions. The envelope of the excitation signal... Used to adjust the power amplifier supply voltage in real time to meet the following requirements:

[0067] ;

[0068] Where k e V is the envelope adjustment coefficient. min To maintain the minimum supply voltage for linear operation, the envelope tracking design automatically reduces the supply voltage when the power amplifier outputs a small-amplitude excitation signal, thereby reducing ineffective losses and improving overall efficiency. To ensure the consistency of the excitation magnetic field amplitude, this module employs a high-speed current sampling circuit. It obtains the real-time current value of the transmitting calibration coil through a current transformer and compares it with the target current reference. The DSP adjusts the drive waveform in real time based on the error, maintaining a constant proportional relationship between the output current and the input current.

[0069] Furthermore, this module features a temperature adaptive mechanism, automatically reducing the output amplitude or adjusting the bias level based on the temperature rise of the power amplifier components, ensuring system stability during long-term continuous operation. Simultaneously, the power amplifier module incorporates overcurrent, overvoltage, and short-circuit protection, along with a gradual recovery strategy, protecting the system from damage under extreme environments or sudden load changes. The dynamic power supply power amplifier module's function is to provide precise control over the excitation magnetic field amplitude, offering a constant and standardized magnetic field input for the receiving coil's amplitude response and SNR determination.

[0070] In a preferred embodiment of the present invention, the inverter and modulation module adopts a space vector pulse width modulation strategy and includes a nanosecond-level time jitter correction unit for improving frequency resolution and a phase accumulation algorithm for maintaining phase continuity.

[0071] In this embodiment, the inverter and modulation module includes a full-bridge or half-bridge IGBT or SiC MOSFET inverter circuit and an SVPWM modulation unit, used to generate a single-frequency excitation signal with accurate frequency, continuous phase and controllable amplitude.

[0072] To generate a sinusoidal excitation current with high frequency accuracy and extremely low distortion, this invention employs a full-bridge multi-level inverter topology. Compared to the traditional single H-bridge inverter structure, the multi-level inverter of this invention can achieve a near-analog multi-step waveform at the output. High-resolution SPWM is used to control each level, making the output waveform closer to an ideal sine wave, thereby significantly reducing the harmonic content in the coil excitation magnetic field. The inverter bridge arms are composed of SiC MOSFETs, and high-speed turn-on and turn-off are achieved through bidirectional high-voltage drivers. This circuit supports five-level cascaded output, achieving higher equivalent waveform accuracy without increasing the switching frequency, and reducing the design pressure on the output filter.

[0073] A carrier phase-shift based SVPWM (Space Vector Pulse Width Modulation) strategy is adopted. SVPWM maximizes the utilization of the DC bus, enabling the inverter bridge to achieve a higher equivalent voltage amplitude at the same duty cycle, and maintains phase continuity during frequency switching, avoiding transient changes in the transmitting magnetic field. The inverter output voltage can be expressed as:

[0074] ;

[0075] Where M is the modulation system, V dc φ0 represents the DC bus voltage output by the power module, w is the target excitation angular frequency, and φ0 is the initial modulation phase. A soft-switching ZVS / ZCS auxiliary network is added, utilizing resonant inductors and capacitors to achieve zero voltage or zero current at the switching nodes. This ensures that the SiC devices experience almost no transition losses during turn-on / turn-off, thus maintaining high efficiency and low temperature rise characteristics even in low-pressure environments. The inverter bridge has real-time fault detection capabilities, including short-circuit, overcurrent, and overtemperature protection. Synchronous adjustment with the power amplifier module via the control system ensures that the excitation signal maintains phase stability and amplitude consistency throughout the frequency sweep process, unaffected by load changes.

[0076] The IGBT inverter module converts direct current into a controllable alternating current signal, and is the core of signal generation; its performance directly determines the quality of the output signal. Modern IGBT devices combine the fast switching characteristics of MOSFETs with the low on-resistance advantage of bipolar transistors. The system uses seventh-generation trench gate IGBT technology, which improves the switching speed by 30% compared to traditional devices.

[0077] The current transport characteristics of an IGBT can be described by the following equation:

[0078] ;

[0079] Where: V GE V is the gate-emitter voltage of the IGBT. th V is the turn-on threshold voltage of the IGBT. CE,satV is the saturated collector-emitter voltage of the IGBT. CE This is the actual collector-emitter voltage of the IGBT. For electron mobility, C ox λ is the gate oxide capacitance, W / L is the width-to-length ratio of the device, and λ is the channel length modulation coefficient.

[0080] In practical applications, by precisely controlling V GE The rate of change of voltage (dV / dt) can optimize the switching performance of IGBTs and reduce switching losses and EMI.

[0081] The system employs adaptive gate drive technology, dynamically adjusting drive parameters based on device temperature and load current.

[0082] ;

[0083] Among them, V GE (t) represents the real-time gate-emitter drive voltage of the IGBT at time t, V GE,plateau k is the IGBT gate drive platform voltage. T T is the temperature regulation coefficient, and T is the real-time junction temperature of the IGBT. ref For reference temperature, k I I is the current regulation coefficient. C I represents the real-time collector current of the IGBT. ref This is the reference current.

[0084] The practical function of this adaptive drive is to optimize IGBT performance under different operating conditions. At high temperatures, it reduces the drive voltage to decrease losses, while at high currents, it increases the drive strength to ensure reliable switching.

[0085] The excitation signal of this invention needs to accurately generate a single-frequency sinusoidal voltage and current at any frequency point during the frequency sweep process, so that the transmitting calibration coil can generate a magnetic field with controllable amplitude and precise frequency. To achieve high frequency accuracy and low phase jitter, this invention adopts an SPWM modulation scheme based on a time fine-tuning mechanism. The modulator generates a basic PWM waveform through a high-precision timer in the system's main control chip, and adds a nanosecond-level time jitter correction unit on this basis. Time jitter correction improves the effective resolution of the PWM to:

[0086]

[0087] in Here, N represents the base time step of the timer, and N is the number of jitter bits. By changing the minute delay of the PWM edge, the modulation step size of the SPWM can be refined, making its output frequency and phase more precise. The modulator internally employs a phase accumulation algorithm to convert the target excitation frequency f0 into an equivalent phase increment. , where fclk The high-precision timer clock frequency of the main control chip is used to generate an approximately ideal sine reference in each PWM cycle, so that the phase change of the inverter remains continuous when switching between different sweep frequency points.

[0088] This structure further incorporates temperature compensation and distortion correction mechanisms, enabling SPWM to maintain frequency stability even under varying temperature conditions at high altitudes. This ensures that the receiving coil presents a clear single-frequency peak in the FFT, enabling functions such as frequency deviation judgment and phase stability judgment. The role of this module is to provide a highly linear and stable modulation reference for the inverter module, ensuring the excitation magnetic field is repeatable and calibrable throughout the entire scanning frequency band.

[0089] In a preferred embodiment of the present invention, the posture correction and noise suppression module includes:

[0090] Attitude sensor, used to measure roll, pitch and yaw angles of the receiving coil;

[0091] The installation error compensation unit is used to correct the measured attitude according to the installation error compensation matrix.

[0092] The noise prediction unit is used to predict attitude noise voltage based on the corrected attitude, geomagnetic field vector, and unit impulse response through convolution operations.

[0093] The cross-correlation synchronization unit is used to calculate the cross-correlation function between the predicted noise voltage and the measured induced voltage in order to determine the time delay and perform synchronization.

[0094] The noise reduction unit is used to subtract the synchronized predicted noise voltage from the measured induced voltage.

[0095] In this embodiment, the transmitting calibration coil is used to generate an excitation magnetic field with predictable spatial distribution, known direction, and calibrable amplitude for the triaxial receiving coil to measure during calibration. The transmitting calibration coil has an air-core structure, and its coil constant is determined through laboratory calibration. It is used to generate a standard magnetic field with known direction and controllable amplitude. The number of turns in the calibration coil is N. c The coil radius is r, and the effective area is A. c When an excitation current flows through it, its axial magnetic field can be approximated as:

[0096] ;

[0097] Where, k f is the magnetic field constant of the coil, which is related to the coil's geometry and material parameters, and i(t) is the excitation current flowing through the transmitting calibration coil at time t. This invention obtains k through a precise measurement and calibration process. fAccurate value: In the laboratory, the magnetic field generated by the calibration coil under different currents is measured using a standard magnetometer. The coil constant is determined by the least squares fitting method, so that the magnetic field amplitude can be directly calculated from the current in subsequent field verification.

[0098] In this system, the calibration coil maintains a fixed geometric relationship with the receiving coil, ensuring that the coil receives a stable magnetic field component under different orientation conditions. The magnetic field provided by this module is the basis for "amplitude judgment" and "frequency deviation judgment," enabling the entire system to test the performance of the receiving coil based on a standardized magnetic field.

[0099] The raw voltage data obtained from sampling by the receiving coil is analyzed, quantized, and time-synchronized to ensure the signal meets the accuracy requirements for subsequent frequency domain processing and performance analysis. The induced voltage of the receiving coil is then converted by an analog-to-digital converter at a sampling frequency f. s This is recorded as a digital quantity D(n), based on the quantization step size K of the ADC. lsb Convert it to physical voltage:

[0100] ;

[0101] Saturation detection, jump detection, and outlier repair are performed on all sampling points. The excitation frequency point and data segment are aligned using timestamp information so that each data segment corresponds to a single-frequency excitation of the corresponding frequency point.

[0102] The attitude correction and attitude noise suppression module is used to eliminate voltage disturbances introduced by attitude changes and installation angle errors in the receiving coil during calibration. The signal used for performance judgment only reflects the response of the calibration excitation magnetic field. In the air-to-ground frequency domain calibration environment, the receiving coil is in both the alternating magnetic field generated by the transmitting calibration coil and the geostatic magnetic field. When the coil undergoes attitude changes such as roll, pitch, and yaw, the projection of the geostatic magnetic field on the sensitive direction of the coil changes over time. Even if the transmitter output remains constant, an additional voltage that changes with attitude will be induced in the receiving coil. This module models and removes this type of attitude-related interference from the measured signal through steps such as attitude measurement, installation error compensation, attitude noise prediction and synchronization, and differential subtraction.

[0103] The system first acquires the roll, pitch, and yaw angles of the receiving coil during the calibration process using an inertial measurement unit (IMU). Then, it employs interpolation to upscale the low-sampling-rate attitude data to a time resolution consistent with the coil voltage sampling. Based on these attitude angles, a global rotation matrix R(t) is constructed to describe the rotation relationship from the geographic reference coordinate system to the coil mounting coordinate system. The system also considers potential fixed assembly deviations R between the coil axis and the attitude sensor coordinate axes. mThe physical axis of the coil and the measurement axis of the attitude sensor inevitably deviate during mechanical installation. This invention obtains the installation error compensation matrix R through static calibration experiments before shipment. m .

[0104] Static calibration method: The receiving coil assembly is fixed on a non-magnetic three-axis precision turntable. Given the geomagnetic vector B... s In this environment, the turntable is controlled to rotate to multiple known attitude positions, and the output matrix R of the attitude sensor is recorded. sensor The physical pointing vector derived from the coil induced voltage.

[0105] R m It is a 3×3 orthogonal rotation matrix, stored in the system's non-volatile memory. During real-time computation, the corrected rotation matrix is... .

[0106] Obtain the unit vector of the coil's true sensing direction in the geographic coordinate system. Given the local geomagnetic field vector Under the premise that the effective projection of the geomagnetic field on the sensitive direction of the coil can be calculated at any time:

[0107] ;

[0108] The effective projection of the geomagnetic field on the sensitive direction of the coil at any given time characterizes the equivalent magnetic field component generated by the coupling between the coil attitude change and the static magnetic field, which is the magnetic field source of the so-called attitude noise.

[0109] Local geomagnetic field vector Measurements can be performed using a static measurement method (preferred): before the calibration system initiates dynamic frequency sweeping, the system enters a static initialization mode. Using a triaxial fluxgate magnetometer or high-precision magnetic compass integrated into the attitude sensor assembly, environmental magnetic field data for at least N cycles (e.g., the average over 1 second) are collected while the system is stationary. Since the coils are not moving, the collected magnetic field data represents the projection of the Earth's magnetic field onto the sensor coordinate system. After coordinate transformation, the local geomagnetic field vector is obtained. This method can effectively capture local magnetic anomalies present at the verification site, achieving the highest accuracy.

[0110] If sensor accuracy is limited, the system can read the longitude, latitude, and altitude information of the calibration location obtained by the GPS module, and call the pre-stored International Geomagnetic Reference Field (IGRF) or World Magnetic Model (WMM) database to calculate the theoretical geomagnetic field strength, dip angle, and declination angle under that spatiotemporal coordinates, thereby reconstructing the geomagnetic vector. .

[0111] To obtain the corresponding attitude noise voltage, this invention utilizes the unit impulse response h of the coil and the front-end amplifier circuit. c (t) Establish the equivalent transmission relationship of the coil, and transfer B... att (t) is used as input for convolution to obtain the predicted attitude noise voltage:

[0112] ;

[0113] Method for obtaining the unit impulse response: The step response test method is used. In a shielded laboratory environment, a step current with an extremely steep edge is injected into the transmitting coil, and the step response voltage output by the receiving coil is measured. Mathematical processing: The unit impulse response can be obtained by differentiating the step response voltage. In actual calculations, h is... c (t) with h c Substitute the form (τ) into the convolution integral.

[0114] In discrete implementation, this corresponds to a convolution of the sampled sequence. Since the attitude measurement channel and the voltage sampling channel have different clocks and fixed delays, this invention uses a cross-correlation method to align the predicted attitude noise with the measured voltage in time, calculating their cross-correlation function. This is used to find the optimal time alignment point between the predicted noise and the measured voltage.

[0115] ;

[0116] Find the time delay with the highest relevance within a given search range. And based on this, By performing a time shift, the predicted attitude noise voltage after synchronization is obtained. Finally, the coil output voltage after attitude correction is expressed as:

[0117] ;

[0118] Where v meas (t) represents the original measured voltage of the receiving coil. After the above processing, the low-frequency disturbance component generated by the coupling between the geomagnetic static field and attitude change in the signal is significantly suppressed, while the single-frequency response caused by the transmitting calibration magnetic field is basically preserved. The output v of the attitude correction and attitude noise suppression module corr (t) serves as the input for subsequent bandpass filtering, fast Fourier transform, amplitude calculation, signal-to-noise ratio calculation, and frequency deviation judgment, thereby improving the stability and repeatability of the receiving coil performance test results under different attitude conditions.

[0119] The cross-correlation search range depends on the maximum hardware delay difference between the attitude sensor data transmission link and the ADC sampling link. In practice, the maximum clock deviation between the two links is typically within ±10ms. If the system sampling rate is 1kHz, the search range is set to ±10 sampling points, within which the cross-correlation peak value is searched. It can ensure synchronization accuracy while reducing the amount of computation.

[0120] In a preferred embodiment of the present invention, the data processing module includes:

[0121] The center frequency of the bandpass filter unit is adjustable according to the current excitation frequency;

[0122] A windowing processing unit is used to apply a Hanning window to the signal to reduce spectral leakage;

[0123] The Fast Fourier Transform (FFT) unit is used to convert time-domain signals into frequency-domain signals.

[0124] Amplitude and frequency extraction unit, used to extract the signal amplitude and precise frequency at the excitation frequency point from the spectrum;

[0125] The signal-to-noise ratio (SNR) evaluation unit is used to calculate the SNR based on the peak power of the signal and the noise power in the neighborhood.

[0126] In this embodiment, since the excitation signal is a narrowband single-frequency magnetic field, the filtering module is used to filter out DC drift, low-frequency noise, and high-frequency interference unrelated to the excitation from the received signal, concentrating the signal energy near the transmission frequency. The bandpass filter is composed of a cascaded high-pass and low-pass filter, and its equivalent transfer function is:

[0127] ;

[0128] Wherein: H bp (s) is the complex frequency domain equivalent transfer function of the bandpass filter, H hp (s) is the transfer function of the high-pass filter, H lp (s) is the transfer function of the low-pass filter.

[0129] The center frequency of the bandpass filter is automatically updated based on the current calibration frequency, and its bandwidth is dynamically adjusted according to the FFT resolution, ensuring that each frequency point has matched filtering characteristics. This module makes the spectrum of the received signal more concentrated, improves the peak resolution of the FFT, and provides a clean signal for subsequent amplitude, signal-to-noise ratio, and frequency deviation extraction.

[0130] ;

[0131] Where: P xx (f) represents the power spectral density of the received signal, f sLet U be the signal sampling frequency, U be the window function normalization factor, and X(f) be the frequency domain amplitude complex spectrum of the received signal after FFT transformation. Given its modulus, when using a window function w(n) of length N, U can be expressed as... .

[0132] The windowing and Fast Fourier Transform (FFT) module is used to extract the frequency domain features of a single-frequency excitation in the receiving coil output from the time-domain signal. The bandpass-filtered signal is first multiplied by a Hanning window to reduce energy dispersion caused by spectral leakage in the FFT. .

[0133] Then, a discrete Fourier transform is performed:

[0134]

[0135] Where V(n) is the signal value of the nth sampling point, w(n) is the window function weight corresponding to the nth sampling point, n is the sampling point number, N is the total number of sampling points in the current data segment, and j is the imaginary unit.

[0136] As a key module of the verification system, the amplitude spectrum, phase spectrum, and noise background output of the FFT provide fundamental data for subsequent performance evaluation. The frequency at the peak is compared with the theoretical excitation frequency to determine the frequency deviation, and the peak amplitude is used to calculate the sensitivity.

[0137] The amplitude response module is used to obtain the response intensity of the receiving coil at the current frequency. In the amplitude spectrum obtained by FFT, at the excitation frequency... Extract the signal amplitude A, where A represents the amplitude of the main peak at the current excitation frequency.

[0138] ;

[0139] The amplitude B0 of the excitation magnetic field is calculated from the transmitting current and the coil constant; therefore, the coil sensitivity can be expressed as:

[0140] ;

[0141] By comparing the current sensitivity with the coil's calibrated sensitivity, it can be determined whether the coil's sensitivity has decreased, such as due to winding breakage, changes in core parameters, or coil damage. This module is one of the core bases for determining whether the coil is damaged.

[0142] Frequency deviation reflects the receiving coil's ability to follow changes in the phase of the excitation magnetic field. This module obtains the measured frequency by performing parabolic fitting on three amplitude points near the FFT peak. And calculate the deviation based on the excitation frequency:

[0143] ;

[0144] If the parasitic parameters inside the coil change or the coil inductance shifts, the phase and effective frequency of the received signal will change. The frequency deviation module can determine whether the coil is in a healthy state by monitoring frequency by frequency.

[0145] In a preferred embodiment of the present invention, the performance evaluation module is configured as follows:

[0146] The current sensitivity of the receiving coil is calculated based on the signal amplitude extracted by the data processing module, and the sensitivity deviation is obtained by comparing it with the sensitivity benchmark.

[0147] The frequency deviation is obtained by comparing the extracted signal frequency with the theoretical excitation frequency.

[0148] The sensitivity deviation, frequency deviation, and signal-to-noise ratio are combined with a preset threshold to generate a comprehensive judgment result regarding whether the receiving coil performance is qualified or abnormal.

[0149] In this embodiment, the SNR module is used to evaluate the noise environment and output stability of the receiving coil at the current operating frequency. The system calculates the noise power P using the neighborhood frequency components after removing the main peak from the FFT spectrum. n The signal-to-noise ratio is obtained based on the signal amplitude A at the excitation frequency point:

[0150] ;

[0151] Finally, the coil performance is judged based on three indicators: amplitude, SNR, and frequency deviation. The system summarizes the criteria for each frequency point into a frequency response curve, an SNR curve, and a frequency deviation curve. If the following conditions are met throughout the entire scanning frequency band:

[0152] , , ;

[0153] If the coil deviates from its normal performance, it is automatically marked as an abnormal range, indicating potential coil damage. This module implements automated evaluation of the coil's performance across the entire frequency band, outputting the final verification results.

[0154] Sensitivity reference K ref And the judgment threshold:

[0155] Sensitivity reference K ref The data can be obtained from the factory certificate of conformity of the receiving coil, or from the multi-frequency sensitivity curve obtained through laboratory standard magnetic field calibration.

[0156] The measured sensitivity of the receiving coil is denoted as K. meas K refUsing the sensitivity benchmark, the relative error of sensitivity is... The calculation is as follows:

[0157] ;

[0158] To account for the relative error of sensitivity, a threshold of 5% or 10% is typically set based on the accuracy requirements of the detection mission. If If so, it is determined that the coil parameters have drifted or are damaged.

[0159] Minimum Signal-to-Noise Ratio (SNR) min Method of determination: Deduced backwards from the effective exploration depth requirements of the ground-to-space frequency domain detection system. To ensure the accuracy of weak secondary field signal extraction, the signal-to-noise ratio during calibration must be higher than the minimum requirement during actual operation.

[0160] SNR is usually set. min =20dB. A value lower than this indicates excessive environmental interference or excessive internal noise in the coil.

[0161] Maximum frequency deviation Depends on the frequency resolution of the FFT in the data processing module ;

[0162] Threshold setting: The deviation threshold is typically set to ±1 frequency resolution unit. For example, if the frequency resolution is 0.5Hz, then... Exceeding this range means that the transmitter frequency is out of lock or the receiver sampling rate is abnormal.

[0163] As a preferred embodiment of the present invention, it further includes a power supply module, which adopts a multi-phase interleaved parallel Buck converter structure to provide a low-ripple DC bus voltage for the inverter and modulation module.

[0164] In this embodiment, the power supply module provides a stable DC bus voltage to the inverter and modulation module. This invention employs a four-phase interleaved parallel Buck converter power supply architecture, where the switching signals of each phase are sequentially staggered by 90°, causing the ripples of each phase to cancel each other out. The output voltage of this four-phase interleaved parallel Buck converter still satisfies:

[0165] ;

[0166] Among them, V O V is the output voltage. in denoted as input voltage, and D as duty cycle.

[0167] The multiphase structure not only reduces ripple, resulting in a cleaner DC bus for the inverter, but also reduces inductor size, significantly lightening the overall system structure and making it more suitable for high-altitude field deployment. Simultaneously, the power supply of this invention employs an adaptive operating mode. Under light loads, it reduces switching losses through a pulse-skipping mode, while under heavy loads, it enters a continuous conduction mode to maintain output stability. Furthermore, it uses a temperature sensor to adjust the switching frequency in real time, ensuring reliability even under high-altitude and low-temperature conditions, providing a highly controllable and low-noise voltage foundation for subsequent inverters.

[0168] The calibration device of this invention can quickly calibrate receiving devices, especially in high-altitude areas. Through automated processes, it can proactively identify potential equipment problems, reducing time and economic losses due to equipment failure. During equipment transportation, assembly, and debugging, the calibration device ensures the equipment remains in good working order, preventing situations where equipment failures are discovered on-site and cannot be repaired. Furthermore, the calibration device uses efficient algorithms such as frequency domain analysis and amplitude and phase analysis to accurately evaluate the performance of the receiving device, effectively avoiding errors caused by human error or equipment damage. Compared to existing traditional testing equipment, the calibration device of this invention has advantages such as small size, simple operation, and high degree of automation, making it particularly suitable for applications in extreme environments such as high altitudes. It can complete rapid and accurate equipment calibration without relying on extensive manual intervention.

[0169] This invention exhibits excellent adaptability to high-altitude environments: for the low air pressure and low temperature environments of high altitudes, the power module adopts a multi-phase interleaved parallel Buck architecture combined with adaptive frequency conversion control, which effectively reduces switching losses and disperses thermal stress; at the same time, the gate drive of the inverter module adopts an adaptive adjustment strategy based on temperature and load current, avoiding the risk of insulation breakdown caused by excessively high dV / dt in thin air, ensuring that the equipment can still work stably at altitudes above 4000 meters.

[0170] This invention features high-precision attitude noise removal capabilities: it innovatively introduces an attitude noise prediction algorithm based on installation error compensation and unit impulse response convolution. By eliminating mechanical installation deviations through static calibration and utilizing a cross-correlation algorithm to solve the multi-sensor time synchronization problem, it can accurately subtract low-frequency attitude noise generated by geomagnetic field coupling from the received signal. This improves the extraction accuracy of weak single-frequency verification signals by an order of magnitude under dynamic conditions such as wind swaying.

[0171] Fully automated intelligent verification process: The system integrates the entire process from automatic frequency scanning excitation and data synchronization to health status determination. By using preset sensitivity, signal-to-noise ratio, and frequency offset thresholds, it automatically generates an intuitive "pass / fail" conclusion, solving the pain points of traditional manual verification that rely on expert experience, are time-consuming, and are difficult to operate in high-altitude environments.

[0172] Please see Figure 1 , Figure 2 , Figure 3 The present invention also provides a performance verification method for a ground-to-air frequency domain electromagnetic detection and receiving system, the method comprising:

[0173] Through the transmission link, a standardized single-frequency excitation magnetic field with constant amplitude is generated sequentially at multiple discrete frequency points;

[0174] The receiving coil module receives the excitation magnetic field and outputs an induced voltage signal, while the attitude sensor collects the attitude angle data of the receiving coil.

[0175] Based on the attitude angle data, the attitude noise voltage generated by geomagnetic coupling is predicted, and the attitude noise voltage is subtracted after time synchronization with the induced voltage signal to obtain the purified signal.

[0176] The purified signal is filtered, windowed, and subjected to Fast Fourier Transform to extract the signal amplitude, precise frequency, and signal-to-noise ratio at the current excitation frequency.

[0177] The extracted signal amplitude, frequency, and signal-to-noise ratio are compared with preset sensitivity, frequency, and signal-to-noise ratio thresholds to comprehensively determine the performance status of the receiving coil.

[0178] In this embodiment, system initialization and self-test: The operator deploys the calibration device on the ground, and the receiving coil is mounted under the drone. After the system is powered on, the power module first monitors the ambient temperature and air pressure, and automatically adjusts the switching frequency to a mode suitable for the current altitude (e.g., appropriately reducing the frequency at low temperatures to reduce switching stress).

[0179] Establishing a reference magnetic field: The system's main control unit controls the inverter and modulation module to initiate frequency sweep mode. The transmitting calibration coil sequentially generates discrete single-frequency magnetic fields from 1Hz, 10Hz... up to 10kHz. At this time, the dynamic power supply amplifier module adjusts the supply voltage in real time based on current sampling feedback to ensure that the magnetic field amplitude remains constant at different frequencies.

[0180] Dynamic data acquisition and synchronization: When the UAV is hovering or in a micro-motion state, the receiving coil module acquires the induced voltage signal. At the same time, the inertial measurement unit (IMU) records the roll, pitch and yaw angles of the coil at a frequency of 200Hz. The data processing module uses timestamps to align the voltage data with the attitude data.

[0181] Real-time noise suppression and feature extraction: The data processing module calls the pre-stored installation error compensation matrix and unit impulse response to calculate the geomagnetic coupling noise under the current attitude. The signal is then subtracted from the original signal. Subsequently, bandpass filtering and FFT transformation are performed on the purified signal to extract the signal amplitude and phase at each frequency point.

[0182] Comprehensive health status assessment: The performance evaluation module compares the measured amplitude with the factory calibration value to calculate the sensitivity deviation K, and combines this with the signal-to-noise ratio (SNR) and frequency deviation. .

[0183] If it meets the requirements across the entire frequency band and The system displays a green light, indicating "Verification passed".

[0184] If the sensitivity attenuation exceeds the threshold in a specific frequency band (such as 500Hz), the system will display a red light and generate a report: "Sensitivity abnormal at 500Hz frequency point, it is recommended to check the coil winding insulation."

[0185] In a preferred embodiment of the present invention, the step of predicting the attitude noise voltage generated by geomagnetic coupling based on the attitude angle data, and subtracting the attitude noise voltage after time synchronization with the induced voltage signal, specifically includes:

[0186] Based on the attitude angle and the installation error compensation matrix, calculate the true orientation of the receiving coil's sensing axis in the geographic coordinate system;

[0187] Based on the true direction and the geomagnetic field vector, calculate the change of the projection component of the geomagnetic field on the sensitive axis over time;

[0188] The predicted attitude noise voltage is obtained by convolving the time rate of change of the projection component with the unit impulse response of the receiving coil.

[0189] Calculate the cross-correlation function between the predicted attitude noise voltage and the measured induced voltage, determine the time delay between the two, and perform synchronization alignment.

[0190] Subtract the predicted noise voltage after synchronization from the measured induced voltage.

[0191] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0192] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A device for calibrating the performance of a ground-to-air frequency domain electromagnetic sounding receiving system, characterized in that, include: The transmit link, used to generate a standardized single-frequency excitation magnetic field, includes an inverter and modulation module, a hybrid filter module, a dynamic power supply amplifier module, and a transmit calibration coil module connected in sequence. The hybrid filtering module is composed of a cascaded LC filter and an active second-order filter, and is used to filter the inverter output signal. The dynamic power supply power amplifier module adopts an envelope tracking structure to adjust the power amplifier supply voltage in real time according to the excitation signal envelope in order to maintain a constant magnetic field amplitude. The receiving and processing link is used to receive the excitation magnetic field and evaluate the coil performance, including a receiving coil module, an attitude correction and noise suppression module, a data processing module and a performance evaluation module; The attitude correction and noise suppression module is configured to: predict the geomagnetic coupling noise voltage caused by attitude change by calculating the projection of the geomagnetic field on the sensitive axis of the receiving coil based on the attitude information obtained by the attitude sensor; and then subtract the predicted noise voltage from the induced voltage measured by the receiving coil module after synchronizing the predicted noise voltage with the induced voltage measured by the receiving coil module. The posture correction and noise suppression module includes: Attitude sensor, used to measure roll, pitch and yaw angles of the receiving coil; The installation error compensation unit is used to correct the measured attitude according to the installation error compensation matrix. The noise prediction unit is used to predict attitude noise voltage based on the corrected attitude, geomagnetic field vector, and unit impulse response through convolution operations. The cross-correlation synchronization unit is used to calculate the cross-correlation function between the predicted noise voltage and the measured induced voltage in order to determine the time delay and perform synchronization. The noise reduction unit is used to subtract the synchronized predicted noise voltage from the measured induced voltage.

2. The performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system according to claim 1, characterized in that, The inverter and modulation module employs a space vector pulse width modulation strategy and includes a nanosecond-level time jitter correction unit for improving frequency resolution and a phase accumulation algorithm for maintaining phase continuity.

3. The performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system according to claim 1, characterized in that, The data processing module includes: The center frequency of the bandpass filter unit is adjustable according to the current excitation frequency; A windowing processing unit is used to apply a Hanning window to the signal to reduce spectral leakage; The Fast Fourier Transform (FFT) unit is used to convert time-domain signals into frequency-domain signals. Amplitude and frequency extraction unit, used to extract the signal amplitude and precise frequency at the excitation frequency point from the spectrum; The signal-to-noise ratio (SNR) evaluation unit is used to calculate the SNR based on the peak power of the signal and the noise power in the neighborhood.

4. The performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system according to claim 1, characterized in that, The performance evaluation module is configured as follows: The current sensitivity of the receiving coil is calculated based on the signal amplitude extracted by the data processing module, and the sensitivity deviation is obtained by comparing it with the sensitivity benchmark. The frequency deviation is obtained by comparing the extracted signal frequency with the theoretical excitation frequency. The sensitivity deviation, frequency deviation, and signal-to-noise ratio are combined with a preset threshold to generate a comprehensive judgment result regarding whether the receiving coil performance is qualified or abnormal.

5. The performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system according to claim 1, characterized in that, It also includes a power supply module, which adopts a multi-phase interleaved parallel Buck converter structure to provide a low-ripple DC bus voltage for the inverter and modulation module.

6. A method for verifying the performance of a ground-to-space frequency domain electromagnetic detection and receiving system, characterized in that, The method is implemented based on the performance verification device for a ground-to-air frequency domain electromagnetic detection and receiving system as described in any one of claims 1-5, and the method includes: Through the transmission link, a standardized single-frequency excitation magnetic field with constant amplitude is generated sequentially at multiple discrete frequency points; The receiving coil module receives the excitation magnetic field and outputs an induced voltage signal, while the attitude sensor collects the attitude angle data of the receiving coil. Based on the attitude angle data, the attitude noise voltage generated by geomagnetic coupling is predicted, and the attitude noise voltage is subtracted after time synchronization with the induced voltage signal to obtain the purified signal. The purified signal is filtered, windowed, and subjected to Fast Fourier Transform to extract the signal amplitude, precise frequency, and signal-to-noise ratio at the current excitation frequency. The extracted signal amplitude, frequency, and signal-to-noise ratio are compared with preset sensitivity, frequency, and signal-to-noise ratio thresholds to comprehensively determine the performance status of the receiving coil.

7. The method for performance verification of a ground-to-air frequency domain electromagnetic detection and receiving system according to claim 6, characterized in that, The step of predicting the attitude noise voltage generated by geomagnetic coupling based on the attitude angle data, and then subtracting the attitude noise voltage after time synchronization with the induced voltage signal, specifically includes: Based on the attitude angle and the installation error compensation matrix, calculate the true orientation of the receiving coil's sensing axis in the geographic coordinate system; Based on the true direction and the geomagnetic field vector, calculate the change of the projection component of the geomagnetic field on the sensitive axis over time; The predicted attitude noise voltage is obtained by convolving the time rate of change of the projection component with the unit impulse response of the receiving coil. Calculate the cross-correlation function between the predicted attitude noise voltage and the measured induced voltage, determine the time delay between the two, and perform synchronization alignment. Subtract the predicted noise voltage after synchronization from the measured induced voltage.

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