Space-time coding array differential eddy current probe and detection system and method thereof

Abstract

A space-time coding array differential eddy current probe and a detection system and method thereof belong to the technical field of nondestructive testing, and are characterized in that a differential detection module is provided with a flexible printed circuit (FPC), M miniature planar coils with independent channels are integrated on the surface of the FPC, the M miniature planar coils are distributed according to a regular triangle array, and M is an integer greater than or equal to 2. The coil surface of each miniature planar coil is attached to the surface of the flexible printed circuit board FPC; coil centers of any three adjacent miniature planar coils are used as three vertexes of a regular triangle to form a group of differential detection units, the M miniature planar coils form M-2 groups of differential detection units, and each group of differential detection units comprises an excitation coil and two receiving coils; and the micro planar coil is alternately used as an exciting coil or a receiving coil according to the conversion of the currently excited differential detection unit. The method has the effects that the detection efficiency, the resolution and the signal-to-noise ratio of the dense defects of the metal matrix can be improved.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a spatiotemporal encoded array differential eddy current probe and its testing system and method. Background Technology

[0002] Aerospace aluminum alloy components are prone to developing hidden shallow corrosion defects under organic coatings under long-term service conditions. In the early stages, this type of corrosion often presents as a microscale "near-surface-low contrast" morphology, and conventional ultrasonic, X-ray, or infrared detection methods are difficult to obtain effective signals in thick coatings and complex curved surface environments.

[0003] Current electromagnetic nondestructive testing (EMB) techniques still have limited resolution and sensitivity for shallow corrosion under organic coatings. Traditional simple array-type eddy current probes are insufficient for achieving fine imaging and quantitative identification of dense corrosion defects in metal substrates. There is an urgent need for an eddy current probe structure and detection method with high spatial sampling density, spatiotemporally adjustable excitation characteristics, and excellent common-mode suppression capabilities to achieve high-resolution detection of shallow corrosion in metal substrates under organic coatings.

[0004] The shortcomings of existing technologies: Existing research methods generally have many technical problems that need to be solved in terms of detection sensitivity, imaging resolution and noise suppression: low detection efficiency, low imaging resolution and low signal-to-noise ratio in large-area metal substrates. Summary of the Invention

[0005] The present invention provides a spatiotemporal encoded array differential eddy current probe and its detection system and method, which can improve the detection efficiency of dense defects in metal substrates.

[0006] To achieve the above objectives, the present invention provides a spatiotemporal encoded array differential eddy current probe, the key of which is: a differential detection module is provided, the differential detection module is provided with a flexible printed circuit board (FPC), the surface of the FPC is integrated with M independent channels of micro planar coils, the M micro planar coils are distributed in an equilateral triangle array, and the coil surface of each micro planar coil is attached to the surface of the FPC.

[0007] The coil centers of any three adjacent miniature planar coils form a set of differential detection units as the three vertices of an equilateral triangle. M miniature planar coils form M-2 sets of differential detection units. Each set of differential detection units includes one excitation coil and two receiving coils.

[0008] The miniature planar coil alternates between being an excitation coil and a receiving coil depending on the change of the differential detection unit currently being excited.

[0009] Through the above design, the differential eddy current probe constructs a multi-winding electromagnetic coupling relationship between the excitation winding, the receiving winding, and the induced eddy current loop based on an electromagnetic coupling equivalent transformer model. Abnormal internal structures of the metal matrix, such as corrosion, cause local permeability changes, resulting in abrupt changes in magnetic circuit reluctance and eddy current loop impedance. This disrupts the electromagnetic symmetry of the excitation-receiving path, causing changes in mutual inductance parameters and impedance matrix, and generating an unbalanced differential output voltage at the receiving end. The differential output voltage is used to reflect the disturbance of electromagnetic energy distribution by abnormal structures, achieving high-efficiency, high-resolution, and high signal-to-noise ratio detection of shallow corrosion defects in the metal matrix.

[0010] As a priority: the center distance between each miniature planar coil in each differential detection unit is 1-2 mm, and the number of turns of each miniature planar coil is 10-20.

[0011] As a preferred feature, the conductor material of the miniature planar coil is a high-conductivity copper conductor.

[0012] As a preference, the frequency range of the high-frequency sinusoidal current excitation signal is 1KHz-10MHz, and the amplitude range is 0.5V-10V.

[0013] As a priority: the spatiotemporal coding excitation control module is equipped with an FPGA controller, a multi-channel sine wave signal source and a time-division multiplexing switch connected in sequence;

[0014] The FPGA controller is used to dynamically adjust the phase and frequency of the signal generated by the multi-channel sine wave signal source;

[0015] The multi-channel sinusoidal signal source is used to generate a high-frequency sinusoidal current excitation signal;

[0016] The time-division multiplexing switcher is used to enable rapid switching of any excitation channel in the differential detection module.

[0017] The output of the multi-channel sine wave signal source is connected to the input of the time-division multiplexer via a first-stage voltage-controlled gain amplifier unit and a second-stage power gain amplifier unit.

[0018] The spatiotemporal coding excitation control module, with an FPGA controller at its core, generates programmable high-frequency sinusoidal excitation signals through a multi-channel sinusoidal signal source. A time-division multiplexing switch then sequentially selects and switches each excitation channel according to a preset spatiotemporal coding sequence. The synchronization control unit within the FPGA controller ensures strict timing alignment between the excitation switching process and the data acquisition process, thereby guaranteeing the temporal consistency and spatial matching of the multi-channel signals.

[0019] As a priority: the receiving coil is connected to the data acquisition and processing module via a differential signal conditioning circuit.

[0020] At the receiving end, the response signal from the array receiving coil is processed by signal conditioning circuits such as differential amplification, bandpass filtering, and impedance matching to suppress noise and enhance sensitivity characteristics. The conditioned analog signal is acquired in real time by a high-speed analog-to-digital converter (ADC) and transmitted to the host computer via a data interface for subsequent differential calculations, complex domain parameter extraction, and imaging processing.

[0021] A detection method for a spatiotemporally encoded array differential eddy current probe, the key of which includes the following steps:

[0022] S1: Probe positioning and lifting control: The differential detection module is fixed above the metal substrate to be measured by a mechanical clamp, and the vertical distance between the differential detection module and the surface of the metal substrate to be measured is adjusted to 1mm to 2mm to reduce the influence of mechanical vibration and environmental changes, and ensure the consistency of the excitation magnetic field and eddy current distribution measurement.

[0023] S2: Spatiotemporal coding excitation and signal acquisition: The spatiotemporal coding excitation control module drives each coil in the differential detection module in a time-division manner according to the set sequence, and adjacent coils are multiplexed as receiving coils;

[0024] The data acquisition and processing module synchronously acquires the response signals, i.e., the induced voltages, of each receiving coil in the same time and space, forming a coding sequence that matches the time and space domains, thereby improving signal acquisition efficiency.

[0025] S3: Complex domain signal processing: The data acquisition and processing module calculates the differential impedance data of the corresponding differential detection unit based on the acquired induced voltage, and then performs complex domain processing on the differential impedance data to extract its amplitude, phase and impedance change as feature values ​​to characterize the local permeability change and electromagnetic disturbance distribution law caused by shallow corrosion defects in the metal matrix.

[0026] S4: Spatial Domain Reconstruction and Imaging: The data acquisition and processing module reconstructs the response signals of each receiving coil in the spatial domain to form a high-resolution defect image; then, it performs spatial domain interpolation, mapping and reconstruction on the differential impedance data of all differential detection units, and realizes high-resolution visualization imaging of the corrosion area by constructing a two-dimensional amplitude and phase distribution map, characterizing the geometric contour and location features of the defect, and realizing quantitative detection.

[0027] As a priority: To further reveal the electromagnetic response characteristics of this probe structure under the induction of abnormal tissue structure, this invention establishes a multi-winding electromagnetic coupling model of the differential detection unit based on Faraday's law of electromagnetic induction and Kirchhoff's circuit laws. Its mathematical expression is as follows:

[0028] ;

[0029] in, The excitation voltage in the excitation coil, , The induced voltage in the two receiving coils; To excite the coil current, , For the current of the two receiving coils, The induced eddy current in the differential detection unit; This indicates the winding's own impedance. , ; Indicates the coil inductance value; Represents the imaginary unit, indicating a 90-degree phase difference; Represents angular frequency, i.e. ; This represents the complex impedance of an inductive element, i.e., its inductive reactance. , Subscript 1 refers to the excitation coil, and subscripts 2 and 3 refer to the receiving coil. It is an eddy current loop; These are the mutual inductance parameters between each coil and eddy current loop;

[0030] The receiving coil has a high input impedance and is considered an open circuit, i.e. The equation simplifies to:

[0031] ;

[0032] ;

[0033] Using eddy current loop Equation description and The relationships between them can be summarized as follows:

[0034] ;

[0035] In this case, and The relationship between them is:

[0036] ;

[0037] get , The induced voltage is:

[0038] ;

[0039] ;

[0040] Differential output voltage for:

[0041] ;

[0042] Current Extract it to obtain the impedance of the differential coil. The expression is:

[0043] ;

[0044] Further calculations yield the real and imaginary parts of the impedance:

[0045] ;

[0046] ;

[0047] Among them, the real part The resistive component reflects the energy loss of the eddy current and the conductivity of the metal. Related; Imaginary part The reactance component reflects the energy storage characteristics of the eddy current magnetic field and is related to the geometry of the eddy current path. , , This represents the self-impedance of the eddy current loop. This represents the equivalent resistance of the eddy current loop. The equivalent inductance of the eddy current loop is... The equivalent self-inductance of the eddy current loop;

[0048] As can be seen from the multi-winding electromagnetic coupling model, when there are shallow corrosion defects in the metal matrix, the mutual inductance... , , and eddy current loop impedance parameters , All of these will change, thus affecting the differential output voltage. This produces an observable offset; by measuring this offset, the differential impedance can be deduced. This enables the quantitative identification and inversion of shallow corrosion characteristics of metal substrates.

[0049] A detection system for a spatiotemporal encoded array differential eddy current probe, the key of which is: a spatiotemporal encoded excitation control module, a differential detection module and a data acquisition and processing module that are interconnected;

[0050] The excitation coils in the differential detection module are sequentially connected to the spatiotemporal coding excitation control module. The spatiotemporal coding excitation control module is used to apply high-frequency sinusoidal current excitation signals to each excitation coil in a predetermined timing sequence using a time-division multiplexing method. There are controllable phase delays and amplitude distributions between the excitation signals of different channels, realizing joint coding excitation in the time domain and spatial domain.

[0051] The receiving coil in the differential detection module is connected to the data acquisition and processing module. The data acquisition and processing module is used to acquire the electromagnetic induction voltage change in the receiving coil caused by the abnormal microstructure of the metal matrix in real time, and to calculate the differential impedance signal.

[0052] The beneficial effects of this invention are:

[0053] (1) High spatial resolution and sampling density: The differential coil array with equilateral triangular topology is used, and the units partially overlap to form a high-density spatial sampling network with a center distance as small as 1-2 mm, which can effectively distinguish densely distributed micro corrosion defects.

[0054] (2) It has a high signal-to-noise ratio and strong anti-interference capability: the differential detection unit design can effectively suppress common-mode interference, while the spatiotemporal coding excitation further improves the signal-to-noise ratio through signal processing gain;

[0055] (3) High detection efficiency: Through spatiotemporal coding and time-division multiplexing technology, a high-channel equivalent dense measurement is achieved using a small number of hardware channels, taking into account the needs of high resolution and large-area rapid detection.

[0056] (4) Excellent imaging quality and strong applicability: The imaging method based on multi-channel data spatial reconstruction can intuitively and clearly display the two-dimensional morphology, size and location of corrosion defects, which is convenient for quantitative evaluation. The flexible PCB substrate enables the probe to fit the curved surface component well, and it has strong applicability on complex structural components. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the spatiotemporal coding array differential eddy current probe in the embodiment;

[0058] Figure 2 This is a schematic diagram illustrating the working principle of the equilateral triangular topological arrangement of a single differential detection unit in the embodiment;

[0059] Figure 3 This is a system block diagram of the spatiotemporal coding excitation control module and the data acquisition and processing module in the embodiment;

[0060] Figure 4 This is a flowchart of the detection method in the embodiment;

[0061] Figure 5 This is an example of a high-resolution imaging effect of shallow corrosion defects obtained through spatial domain reconstruction in the embodiment. Detailed Implementation

[0062] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The following embodiments or drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0063] like Figure 1 As shown, a spatiotemporally encoded array differential eddy current probe includes a differential detection module. This module incorporates a flexible printed circuit board (FPC) with 64 independently channeled miniature planar coils integrated on its surface. These 64 miniature planar coils are arranged in a regular equilateral triangular topology, resulting in a high space fill rate and magnetic field uniformity. Any three adjacent miniature planar coils form a differential detection unit. The 64 miniature planar coils constitute 62 differential detection units. Each differential detection unit includes one excitation coil and two receiving coils.

[0064] The miniature planar coil alternates between being the excitation coil and the receiving coil depending on the change of the currently excited differential detection unit. The differential detection units are closely arranged in the plane and have partially overlapping areas, thus forming a high-density spatial sampling network with no detection blind spots.

[0065] In this example, the center-to-center distance between the miniature planar coils in each differential detection unit is designed to be 1.5 mm. Each coil is wound with 15 turns of high-conductivity copper wire to balance spatial resolution, sensitivity, and manufacturing feasibility. The probe has a total of 64 channels; the coils are arranged to form a multi-layered overlapping sampling area to enhance the uniformity of the planar electromagnetic field.

[0066] like Figure 2 As shown, when the differential detection unit is an equilateral triangle, the coil at its lower left corner... For the excitation coil, there are two other adjacent coils. , For receiving coils; when the differential detection unit is an inverted triangle, the coil in its upper left corner... For the excitation coil, there are two other adjacent coils. , This is a receiving coil. In this embodiment, , .

[0067] according to Figure 2 The positional relationship between the excitation coil and the receiving coil in the middle, Figure 1 In the first differential detection unit, a coil is included. , where the coil It can only be used as an excitation coil. This is the receiving coil. The second differential detection unit contains a coil. , where the coil To excite the coil, the coil This is the receiving coil. The excitation coil, receiving coil, and so on are repeated. The last differential detection unit contains a coil. , where the coil To excite the coil, the coil It can only be used as a receiving coil. Therefore, the 64 miniature planar coils together form 62 differential detection units.

[0068] In this example, within a single differential detection unit, when a high-frequency AC sinusoidal signal is applied to the excitation coil, a closed eddy current loop, constrained by the material properties, is generated within the metal substrate. When there are no defects in the measured area, because the metal substrate exhibits symmetrical overall electromagnetic properties under the excitation field, the voltage amplitudes induced by the receiving coils arranged on both sides of the excitation coil are equal and their phases are opposite, resulting in a differential output close to zero or exhibiting a stable reference value.

[0069] like Figure 3 As shown, a detection system for a spatiotemporal coded array differential eddy current probe is provided with a spatiotemporal coded excitation control module, a differential detection module and a data acquisition and processing module that are interconnected.

[0070] The spatiotemporal coding excitation control module is equipped with an FPGA controller, a multi-channel sine wave signal source, a first-stage voltage-controlled gain amplifier unit, a second-stage power gain amplifier unit, and a time-division multiplexing switch connected in sequence.

[0071] The FPGA controller is used to dynamically adjust the phase and frequency of the signal generated by the multi-channel sine wave signal source;

[0072] The multi-channel sinusoidal signal source is used to generate a high-frequency sinusoidal current excitation signal;

[0073] The time-division multiplexing switcher is used to enable rapid switching of any excitation channel in the differential detection module.

[0074] The spatiotemporal coding excitation control module, with an FPGA controller at its core, generates programmable high-frequency sinusoidal excitation signals through a multi-channel sinusoidal signal source. A time-division multiplexing switch then sequentially selects and switches each excitation channel according to a preset spatiotemporal coding sequence. The synchronization control unit within the FPGA controller ensures strict timing alignment between the excitation switching process and the data acquisition process, thereby guaranteeing the temporal consistency and spatial matching of the multi-channel signals.

[0075] The excitation coils are sequentially connected to a spatiotemporal encoded excitation control module, which uses a time-division multiplexing method to apply high-frequency sinusoidal current excitation signals to each excitation coil in a predetermined timing sequence. The excitation signals from different channels have controllable phase delays and amplitude distributions, achieving joint encoding excitation in both the time and spatial domains.

[0076] The frequency range of the high-frequency sinusoidal current excitation signal is 1KHz-10MHz, and the amplitude range is 0.5V-10V.

[0077] The receiving coil is connected to the data acquisition and processing module via a differential signal conditioning circuit. The data acquisition and processing module is used to acquire the electromagnetic induction voltage change in the receiving coil caused by the abnormal microstructure of the metal matrix in real time, and to calculate the differential impedance signal.

[0078] like Figure 4 As shown, a detection method for a spatiotemporally encoded array differential eddy current probe includes the following steps:

[0079] S1: Probe Positioning and Lifting Control: The differential detection module is fixed on the eddy current transient experimental platform using a mechanical clamp, and the vertical distance between the probe and the surface of the coated metal specimen is adjusted using a high-precision robotic arm to ensure stable probe lifting within 1.0 mm. This step ensures consistency between the excitation magnetic field distribution and the eddy current coupling conditions, reducing test errors caused by mechanical vibration.

[0080] S2: Spatiotemporal Encoding Excitation and Signal Acquisition: Upon system startup, the spatiotemporal encoding excitation control module drives each coil in the differential detection module in a time-division multiplexing manner according to a set sequence, with adjacent coils multiplexed as receiving coils. For example, at time t1, excitation channel 1 operates, and its two adjacent receiving channels synchronously acquire signals; at time t2, it switches to excitation channel 2 and acquires signals again... This cycle continues until the excitation states of all differential detection units have been traversed. This process is completed within milliseconds, achieving rapid spatial scanning.

[0081] The data acquisition and processing module synchronously acquires the response signals, i.e., the induced voltages, of each receiving coil in the same time and space, forming a coding sequence that matches the time and space domains, thereby improving signal acquisition efficiency.

[0082] S3: Complex Domain Signal Processing: The data acquisition and processing module calculates the differential impedance data of the corresponding differential detection unit based on the acquired induced voltage, and then performs complex domain processing on the differential impedance data to extract its amplitude, phase, and impedance change as feature values ​​to characterize the local permeability change and electromagnetic disturbance distribution law caused by shallow corrosion defects in the metal matrix; these feature values ​​are directly related to the electromagnetic disturbance caused by shallow corrosion of the metal matrix.

[0083] S4: Spatial Domain Reconstruction and Imaging: The data acquisition and processing module reconstructs the response signals of each receiving coil in the spatial domain to form a high-resolution defect image; then, it performs spatial domain interpolation, mapping and reconstruction on the differential impedance data of all differential detection units, and realizes high-resolution visualization imaging of the corrosion area by constructing a two-dimensional amplitude and phase distribution map, characterizing the geometric contour and location features of the defect, and realizing quantitative detection.

[0084] The data acquisition and processing module uses the feature values ​​extracted from all channels as pixel values, and generates a high-resolution two-dimensional amplitude and phase distribution map based on the actual physical coordinates of each unit on the probe using algorithms such as bilinear interpolation. Figure 5 As shown, this reconstructed image of corrosion defects clearly reveals the distribution, shape, and relative severity of dense shallow corrosion beneath the coating.

[0085] To further reveal the electromagnetic response characteristics of the probe structure under the induction of abnormal tissue structure, this invention establishes a multi-winding electromagnetic coupling model of the differential detection unit based on Faraday's law of electromagnetic induction and Kirchhoff's circuit laws. Its mathematical expression is as follows:

[0086] ;

[0087] in, The excitation voltage in the excitation coil, , The induced voltage in the two receiving coils; To excite the coil current, , For the current of the two receiving coils, The induced eddy current in the differential detection unit; This indicates the winding's own impedance. , ; Indicates the coil inductance value; Represents the imaginary unit, indicating a 90-degree phase difference; Represents angular frequency, i.e. ; This represents the complex impedance of an inductive element, i.e., its inductive reactance. , Subscript 1 refers to the excitation coil, and subscripts 2 and 3 refer to the receiving coil. It is an eddy current loop; These are the mutual inductance parameters between each coil and eddy current loop;

[0088] The receiving coil has a high input impedance and can be considered an open circuit, i.e. The equation simplifies to:

[0089] ;

[0090] ;

[0091] Using eddy current loop Equation description and The relationships between them can be summarized as follows:

[0092] ;

[0093] In this case, and The relationship between them is:

[0094] ;

[0095] get , The induced voltage is:

[0096] ;

[0097] ;

[0098] Differential output voltage for:

[0099] ;

[0100] Current Extract it to obtain the impedance of the differential coil. The expression is:

[0101] ;

[0102] Further calculations yield the real and imaginary parts of the impedance:

[0103] ;

[0104] ;

[0105] Among them, the real part The resistive component reflects the energy loss of the eddy current and the conductivity of the metal. Related; Imaginary part The reactance component reflects the energy storage characteristics of the eddy current magnetic field and is related to the geometry of the eddy current path. , , This represents the self-impedance of the eddy current loop. This represents the equivalent resistance of the eddy current loop. The equivalent inductance of the eddy current loop is... The equivalent self-inductance of the eddy current loop;

[0106] As can be seen from the multi-winding electromagnetic coupling model, when there are shallow corrosion defects in the metal matrix, the mutual inductance... , , and eddy current loop impedance parameters , All of these will change, thus affecting the differential output voltage. This produces an observable offset; by measuring this offset, the differential impedance can be deduced. This enables the quantitative identification and inversion of shallow corrosion characteristics of metal substrates.

[0107] When shallow corrosion defects exist on the surface of a metal substrate, its local conductivity and permeability change, causing disturbances in the eddy current distribution and magnetic field coupling paths, thereby disrupting the original electromagnetic symmetry. As a result, the induced voltage in the receiving coil... , The amplitude or phase will be inconsistent, and the differential circuit will output a distinct non-zero differential voltage signal. This signal can be used as a sensitive characterization of the existence and influence of shallow corrosion defects.

[0108] This invention effectively solves the problem of detecting dense shallow corrosion in metal substrates through innovative probe structure design, high-resolution spatiotemporal coding excitation strategy and signal processing method, providing a reliable technical means for realizing high-precision non-destructive testing of key structural components in aerospace and other fields.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A spatiotemporal coded array differential eddy current probe, characterized in that: A differential detection module is provided, which is equipped with a flexible printed circuit board (FPC). The surface of the FPC is integrated with M independent channels of micro planar coils. The M micro planar coils are distributed in an equilateral triangle array, and the coil surface of each micro planar coil is attached to the surface of the FPC. The coil centers of any three adjacent miniature planar coils form a set of differential detection units as the three vertices of an equilateral triangle. M miniature planar coils form M-2 sets of differential detection units. Each set of differential detection units includes one excitation coil and two receiving coils. The miniature planar coil alternates between being an excitation coil and a receiving coil depending on the change of the differential detection unit currently being excited.

2. The spatiotemporal coded array differential eddy current probe according to claim 1, characterized in that: The differential impedance calculation expression for each differential detection unit is as follows: ； in, This represents differential impedance data. , These represent the mutual inductance parameters between receiving coils 2 and 3 and excitation coil 1, respectively. Represents an eddy current loop The mutual inductance parameters between the excitation coil 1 and the excitation coil 2. Indicates receiving coil 2 and eddy current circuit Mutual inductance parameters between them Indicates receiving coil 3 and eddy current circuit Mutual inductance parameters between them Represents an eddy current loop Self-impedance, Represents the imaginary unit; It represents angular frequency.

3. The spatiotemporal coded array differential eddy current probe according to claim 1, characterized in that: The center distance between each miniature planar coil in each differential detection unit is 1-2 mm, and the number of turns of each miniature planar coil is 10-20.

4. The spatiotemporal coded array differential eddy current probe according to claim 1, characterized in that: The conductor of the miniature planar coil is made of copper.

5. The detection system of a spatiotemporal coded array differential eddy current probe according to claim 1, characterized in that: It is equipped with an interconnected spatiotemporal coding excitation control module, differential detection module and data acquisition and processing module; The excitation coils in the differential detection module are sequentially connected to the spatiotemporal coding excitation control module. The spatiotemporal coding excitation control module is used to apply high-frequency sinusoidal current excitation signals to each excitation coil in a predetermined timing sequence using a time-division multiplexing method. The receiving coil in the differential detection module is connected to the data acquisition and processing module. The data acquisition and processing module is used to acquire the electromagnetic induction voltage change in the receiving coil caused by the abnormal microstructure of the metal matrix in real time, and to calculate the differential impedance signal.

6. The detection system of a spatiotemporal coded array differential eddy current probe according to claim 5, characterized in that: The frequency range of the high-frequency sinusoidal current excitation signal is 1KHz-10MHz, and the amplitude range is 0.5V-10V.

7. The detection system of a spatiotemporal coded array differential eddy current probe according to claim 5, characterized in that: The spatiotemporal coding excitation control module is equipped with an FPGA controller, a multi-channel sine wave signal source, and a time-division multiplexing switch connected in sequence. The FPGA controller is used to dynamically adjust the phase and frequency of the signal generated by the multi-channel sine wave signal source; The multi-channel sinusoidal signal source is used to generate a high-frequency sinusoidal current excitation signal; The time-division multiplexing switcher is used to enable rapid switching of any excitation channel in the differential detection module; The output of the multi-channel sine wave signal source is connected to the input of the time-division multiplexer via a first-stage voltage-controlled gain amplifier unit and a second-stage power gain amplifier unit.

8. The detection system of a spatiotemporal coded array differential eddy current probe according to claim 5, characterized in that: The receiving coil is connected to the data acquisition and processing module via a differential signal conditioning circuit.

9. A detection method for a spatiotemporally encoded array differential eddy current probe according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Probe positioning and lifting control: The differential detection module is fixed above the metal substrate to be tested by a mechanical clamp, and the vertical distance between the differential detection module and the surface of the metal substrate to be tested is adjusted to 1mm to 2mm. S2: Spatiotemporal coding excitation and signal acquisition: The spatiotemporal coding excitation control module drives each coil in the differential detection module in a time-division manner according to the set sequence, and adjacent coils are multiplexed as receiving coils; The data acquisition and processing module synchronously acquires the response signals, i.e., the induced voltages, of each receiving coil in the same time and space, forming a coding sequence that matches the time and space domains; S3: Complex domain signal processing: The data acquisition and processing module calculates the differential impedance data of the corresponding differential detection unit based on the acquired induced voltage, and then performs complex domain processing on the differential impedance data to extract its amplitude, phase and impedance change as feature values ​​to characterize the local permeability change and electromagnetic disturbance distribution law caused by shallow corrosion defects in the metal matrix. S4: Spatial Domain Reconstruction and Imaging: The data acquisition and processing module reconstructs the response signals of each receiving coil in the spatial domain to form a defect image; then, it performs spatial domain interpolation, mapping and reconstruction on the differential impedance data of all differential detection units, and realizes the visualization imaging of the corrosion area by constructing a two-dimensional amplitude and phase distribution map, characterizing the geometric contour and location features of the defect, and realizing quantitative detection.

10. The detection method of a spatiotemporally encoded array differential eddy current probe according to claim 9, characterized in that: In step S3, the data acquisition and processing module calculates the differential impedance data by establishing a multi-winding electromagnetic coupling model of the differential detection unit; the mathematical expression of the multi-winding electromagnetic coupling model is: ； in, The excitation voltage in the excitation coil, , The induced voltage in the two receiving coils; To excite the coil current, , For the current of the two receiving coils, The induced eddy current in the differential detection unit; This indicates the winding's own impedance. , ; Indicates the coil inductance value; Represents the imaginary unit, indicating a 90-degree phase difference; Represents angular frequency, i.e. ; This represents the complex impedance of an inductive element, i.e., its inductive reactance. , Subscript 1 refers to the excitation coil, and subscripts 2 and 3 refer to the receiving coil. It is an eddy current loop; These are the mutual inductance parameters between each coil and eddy current loop; The receiving coil has a high input impedance and is considered an open circuit, i.e. The equation is: ； ； Using eddy current loop Equation description and The relationships between them can be summarized as follows: ； In this case, and The relationship between them is: ； get , The induced voltage is: ； ； Differential output voltage for: ； Current Extract it to obtain the impedance of the differential coil. The expression is: ； Further calculations yield the real and imaginary parts of the impedance: ； ； Among them, the real part For the resistive component; imaginary part This is the reactance component; , , This represents the self-impedance of the eddy current loop. This represents the equivalent resistance of the eddy current loop. The equivalent inductance of the eddy current loop is... The equivalent self-inductance of the eddy current loop; As can be seen from the multi-winding electromagnetic coupling model, when there are shallow corrosion defects in the metal matrix, the mutual inductance... , , and eddy current loop impedance parameters , All of these will change, thus affecting the differential output voltage. An offset is generated; this offset is measured and the differential impedance is derived. This enables the quantitative identification and inversion of shallow corrosion characteristics of metal substrates.

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