Array heat flow transverse heat flow diffusion suppression device and method based on feature iteration

Abstract

The invention provides an array heat flow transverse heat flow diffusion suppression device and method based on feature iteration, belongs to the technical field of nondestructive testing, and solves the problem of transverse heat flow diffusion in current active infrared thermal wave imaging detection. The suppression device comprises a computer, a USB (universal serial bus) data line, a data acquisition card, a first BNC (bayonet nut connector) data line, a laser power supply, a laser power line, a TEC (thermoelectric cooler) power line, a laser, a TEC, an optical fiber bundle, a collimating mirror, a first polarizer, a sample piece, a clamping frame, a mobile station, a motion driving line, a mobile station controller, a motion control line, a filter, a first fixed support and a second polarizer. The device comprises a first fixing support, a second fixing support, a magnetic base, a thermal infrared imager, an Ethernet cable, a second BNC data line, a third fixing support, a fourth fixing support, a third BNC data line and a temperature control feedback system.

Description

Technical Field

[0001] The invention relates to an array heat flow lateral heat flow diffusion suppression device and method based on feature iteration, belonging to the technical field of non-destructive testing. Background Art

[0002] Composite materials have been widely used in the automotive industry, aerospace, medical equipment, shipbuilding, power electronics and other fields due to their excellent mechanical properties, corrosion resistance and high specific strength, and have become an important material choice in the manufacture of key components. However, composite materials are prone to internal defects such as delamination, bubbles and cracks during manufacturing, processing and actual use. These defects can significantly weaken the structural integrity and mechanical properties of the material, thus seriously affecting its service life and may even lead to system-level failures and safety hazards. Therefore, accurately identifying and quantifying potential defects in composite materials is crucial to ensure their reliability in high-demand applications.

[0003] Traditional nondestructive testing methods, such as ultrasonic testing and radiographic testing, have been widely used to detect internal defects in materials, but they still have significant limitations in the nondestructive testing of composite materials. Ultrasonic testing has a certain sensitivity in the detection of delamination defects, but it is not able to identify tiny bubbles and cracks, and is easily affected by the complexity of the material structure, resulting in reduced detection signal resolution; radiographic testing relies on high-energy rays to penetrate materials, but it is often difficult to achieve ideal imaging resolution in the detection of thicker or complex composite materials. In addition, radiographic testing has high requirements for the operating environment and poses radiation safety risks. Therefore, in the field of nondestructive testing of complex composite materials, the detection sensitivity and resolution of traditional methods are difficult to meet the current high-precision detection needs, and it is urgent to explore new and more sensitive detection technologies to achieve accurate identification and reliable evaluation of internal defects in composite materials.

[0004] As a cutting-edge nondestructive testing method, infrared thermal wave imaging detection technology has become a powerful supplement to traditional ultrasonic testing and X-ray testing due to its high efficiency and non-contact detection method. Unlike these traditional detection methods, infrared thermal wave imaging detection technology achieves rapid and non-invasive detection of internal defects by capturing the material's response to thermal excitation, and has the advantages of high sensitivity and superior resolution. In particular, active infrared thermal wave imaging detection technology can effectively identify thermal conduction anomalies caused by internal defects by applying external thermal excitation to guide heat propagation inside the material. This technical principle makes it suitable for the detection of internal structures of various materials, especially the defect assessment of complex structures or heterogeneous materials.

[0005] Under thermal excitation conditions, defects inside the material, such as cracks, delamination and bubbles, will disturb the heat transfer process due to their different thermal conductivity from the surrounding materials, forming abnormal heat flow paths and temperature gradients. These defective areas will cause significant differences in the temperature distribution on the surface of the object, and infrared thermal imagers can capture and record these tiny temperature changes in real time, and reveal the defect information inside the object being tested through analysis of temperature distribution images and extraction of defect features. Compared with traditional methods, infrared thermal wave imaging detection technology can complete detection in a shorter time and maintain a higher detection accuracy for shallow surface defects, so it has significant advantages in the needs of precise detection and large-area detection.

[0006] However, the current traditional active infrared thermal wave imaging detection technology mainly relies on surface source heat flow excitation, and its inevitable lateral heat flow diffusion phenomenon has become a bottleneck for infrared thermal wave imaging detection technology to achieve accurate detection of material defects. The lateral heat flow diffusion will affect the clarity of the edge area of ​​the defect feature and blur the identification of the defect boundary, thereby weakening the image resolution and the boundary accuracy of the detection, resulting in a significant decrease in the measurement accuracy of the defect morphology. Especially in the detection of composite materials with large size and complex structure, the influence of lateral heat flow diffusion is more prominent. The heat flow diffusion in complex material structures will not only produce "artifacts" around the defect area, interfering with the accurate identification of the defect boundary, but also make it difficult to effectively distinguish deeper defects from the background area. In order to achieve higher resolution and higher precision defect detection, it is urgent to develop new excitation and detection methods that can suppress lateral heat flow diffusion to ensure that infrared thermal wave imaging technology can be applied to non-destructive testing of complex and large-sized composite materials, thereby improving the recognition of internal defects and morphology recognition capabilities.

[0007] In order to solve the problem of heat flux diffusion, the similar optical flow method was proposed as a new method to suppress heat flux diffusion. This method analyzes the gradient diffusion behavior of heat flux inside the material and reversely suppresses the interference of the lateral heat diffusion effect on the detection results. However, the accuracy of the similar optical flow method is easily affected by factors such as noise and the complexity of the internal structure of the material, resulting in insufficient robustness of signal interpretation. Therefore, when detecting small or complex defects, the analytical accuracy of these methods is still limited and the true size and shape of the defects cannot be fully restored. With the widespread application of composite materials in aerospace, automobiles and high-end manufacturing, the requirements for detection technology have also increased. The shortcomings of traditional active infrared thermal wave imaging technology in suppressing lateral heat flux diffusion have gradually become a technical obstacle to achieving high-precision detection. In the field of high-end manufacturing, the complexity and size diversity of material components are constantly increasing, which requires the detection method to have not only higher accuracy and reliability, but also to adapt to the fine detection of various defect morphologies. To this end, it is urgent to further develop new methods that can effectively suppress lateral heat flux diffusion to break through the limitations of traditional infrared thermal wave imaging technology, so as to meet the needs of higher accuracy and more complex defect morphology detection in the future. Summary of the invention

[0008] The present invention aims to solve the problem of lateral heat flow diffusion in the current active infrared thermal wave imaging detection, and further proposes an array heat flow lateral heat flow diffusion suppression device and method based on feature iteration, wherein the diffusion suppression device includes:

[0009] Computer (1), USB data cable (2), data acquisition card (3), first BNC data cable (4), laser power supply (5), laser power cable (6), TEC refrigerator power cable (7), laser (8), TEC refrigerator (9), optical fiber bundle (10), collimator (11), first polarizer (12), sample (13), clamping frame (14), mobile stage (15), motion drive cable (16), mobile stage controller (17), motion control cable (18), filter (19), first fixed support (20), second polarizer (21), second fixed support (22), magnetic base (23), infrared thermal imager (24), Ethernet cable (25), second BNC data cable (26), third fixed support (27), fourth fixed support (28), third BNC data cable (29) and temperature control feedback system (30);

[0010] The computer (1) is provided with three signal output terminals, wherein the first signal output terminal of the computer is connected to the signal input terminal of the data acquisition card (3) via a USB data line (2), the second signal output terminal of the computer is connected to the signal output terminal of the infrared thermal imager (24) via an Ethernet line (25), and the third signal output terminal of the computer is connected to the signal input terminal of the mobile station controller (17) via a motion drive line (16).

[0011] Preferably, the data acquisition card (3) is provided with two signal output terminals, the first signal output terminal of the data acquisition card is connected to the input terminal of the laser power supply (5) via a first BNC data line (4), and the second signal output terminal of the data acquisition card is connected to the signal input terminal of the infrared thermal imager (24) via a second BNC data line (26).

[0012] Preferably, the output end of the laser power supply (5) is connected to the laser (8) via a laser power supply line (6), the output end of the laser (8) is connected to the collimator (11) via an optical fiber bundle (10), the collimator (11) is fixed on a fourth fixed support (28), and the signal input end of the TEC cooler (9) is connected to the temperature control feedback system (30) via a third BNC data line (29).

[0013] Preferably, the first polarizer (12) is fixed on a third fixed support (27), the sample (13) is fixed on a clamping frame (14), the clamping frame (14) is placed on a moving platform (15), the moving platform (15) is connected to a moving platform controller (17) via a motion drive line (16), and the infrared thermal imager (24) is fixed on a magnetic base (23).

[0014] Preferably, the filter (19) is fixed on the first fixed support (20), and the second polarizer (21) is fixed on the second fixed support (22), and the infrared thermal radiation signal radiated by the sample (13) is transmitted to the infrared thermal imager (24) through the filter (19) and the second polarizer (21).

[0015] Preferably, the lasers (8) are arranged in a 7×7 matrix, all laser beams are Gaussian light sources, and the lasers (8) are controlled by emitting analog signals via the data acquisition card (3).

[0016] The array heat flow lateral heat flow diffusion suppression method based on feature iteration includes:

[0017] Step 1: Fix the sample (13) on the clamping frame (14), turn on the computer (1), data acquisition card (3), laser power supply (5), TEC cooler (9) and temperature control feedback system (30), and set the operating temperature of the laser power supply (5) to 25°C;

[0018] Step 2: Turn on the infrared thermal imager (24), adjust the magnetic base (23), the first fixed support (20) and the second fixed support (22), and confirm that the imaging field of view of the infrared thermal imager (24) can completely cover the sample;

[0019] Step 3: The data acquisition card (3) transmits an analog signal to start the array laser (8) to irradiate the sample (13), and adjusts the positions of the third fixed support (27) and the fourth fixed support (28) so that the spacing and size of the array light spots irradiated to the sample (13) meet the preset range;

[0020] Step 4: Use a dual-channel digital orthogonal demodulation algorithm based on feature iteration to extract the defect features of the sample and obtain the laser point excitation amplitude and phase after iteration;

[0021] Step 5: Repeat steps 3-4 according to the excitation amplitude and phase of the laser point after iteration until a defect feature phase map based on feature iteration is obtained to achieve defect feature extraction;

[0022] Step 6: After the defect feature extraction is completed, turn off the computer (1), the data acquisition card (3), the laser power supply (5), the TEC cooler (9), the temperature control feedback system (30), the infrared thermal imager (24), the data acquisition card (3) and the laser (8).

[0023] Preferably, the excitation intensity expression of a single laser beam of the laser (8) in step 3 is:

[0024]

[0025] In formula (1), I(i,j,t) is the laser intensity, i,j=1,2,…,7,I max is the peak light intensity, I max =1000W / m 2 , f is the excitation frequency, f=0.05Hz.

[0026] Preferably, the expression of the two-way digital orthogonal demodulation algorithm based on feature iteration in step 4 is:

[0027]

[0028] Ph ex,k+1 =Ph ex,k -Ph meas,k

[0029]

[0030] In formula (2) to formula (6), F n (x, y) is the thermal wave signal image, N is the number of frames, Am is the characteristic amplitude, Ph is the characteristic phase, Am ex,k+1 is the laser point excitation amplitude after iteration, Ph ex,k+1 is the laser point excitation phase after iteration, Amp ex,k+1 is the laser point excitation amplitude before iteration, is the laser spot excitation phase before iteration, Ammeas,k is the characteristic amplitude of the central pixel of the laser point excitation in the amplitude characteristic map, Ph meas,k is the characteristic phase value of the central pixel excited by the laser point in the phase characteristic map.

[0031] The beneficial effects of the present invention are:

[0032] 1. Compared with the traditional active infrared thermal wave imaging detection technology, the present invention can effectively suppress the lateral heat flow diffusion and improve the accuracy of material defect morphology feature extraction, especially for the accurate and efficient detection of shallow surface defects (<5mm, diameter / depth ratio>1.5) of composite materials;

[0033] 2. The lateral heat flux diffusion suppression device designed in the present invention uses array lasers to actively excite the sample, and realizes excitation parameter regulation through excitation phase feature iteration, thereby suppressing lateral heat flux diffusion, so that the defect morphology feature extraction deviation is controlled within 3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The schematic diagram of the structure of the array heat flow lateral heat flow diffusion suppression device based on feature iteration provided by the present invention is as follows: Figure 1 Among them, 1-computer, 2-USB data cable, 3-data acquisition card, 4-first BNC data cable, 5-laser power supply, 6-laser power cable, 7-TEC refrigerator power cable, 8-laser, 9-TEC refrigerator, 10-optical fiber bundle, 11-collimator, 12-first polarizer, 13-sample, 14-clamping frame, 15-mobile stage, 16-motion drive line, 17-mobile stage controller, 18-motion control line, 19-filter, 20-first fixed support, 21-second polarizer, 22-second fixed support, 23-magnetic base, 24-infrared thermal imager, 25-Ethernet cable, 26-second BNC data cable, 27-third fixed support, 28-fourth fixed support, 29-third BNC data cable, 30-temperature control feedback system.

[0035] Figure 2 A flow chart of a method for suppressing lateral heat flow diffusion of array heat flow based on feature iteration provided by the present invention;

[0036] Figure 3 Schematic diagram of the experimental results of suppressing the lateral heat flow diffusion of array heat flow based on feature iteration provided by the present invention. DETAILED DESCRIPTION

[0037] Specific implementation method 1: Combination Figure 1 To illustrate this embodiment, Figure 1As shown, the structure of the array heat flow lateral heat flow diffusion suppression device based on feature iteration described in this embodiment includes: 1-computer, 2-USB data cable, 3-data acquisition card, 4-first BNC data cable, 5-laser power supply, 6-laser power supply cable, 7-TEC refrigerator power supply cable, 8-laser, 9-TEC refrigerator, 10-optical fiber bundle, 11-collimator, 12-first polarizer, 13-sample, 14-clamping frame, 15-moving stage, 16-motion drive line, 17-moving stage control Device, 18-motion control line, 19-filter, 20-first fixed support, 21-second polarizer, 22-second fixed support, 23-magnetic base, 24-infrared thermal imager, 25-Ethernet cable, 26-second BNC data cable, 27-third fixed support, 28-fourth fixed support, 29-third BNC data cable, 30-temperature control feedback system, wherein 8-lasers are arranged in a 7×7 matrix, all laser beams are Gaussian light sources, and 8-lasers are controlled by emitting analog signals through 3-data acquisition cards.

[0038] The lateral heat flux diffusion suppression device designed in this embodiment uses array laser to actively excite the sample, and realizes excitation parameter regulation through excitation phase feature iteration, thereby suppressing lateral heat flux diffusion, so that the defect morphology feature extraction deviation is controlled within 3%.

[0039] 1-the computer is provided with three signal output terminals, the first signal output terminal of the computer is connected to the signal input terminal of 3-the data acquisition card through 2-a USB data cable, 3-the data acquisition card is provided with two signal output terminals, the first signal output terminal of the data acquisition card is connected to the input terminal of 5-the laser power supply through 4-a first BNC data cable, 5-the laser power supply output terminal is connected to 8-the laser through 6-the laser power supply cable, 8-the laser output terminal is connected to 11-the collimator through 10-the optical fiber bundle, 11-the collimator is fixed on 28-the fourth fixed support, 9-the signal input terminal of the TEC refrigerator is connected to 30-the temperature control feedback system through 29-the third BNC data cable, and the second signal output terminal of the data acquisition card is connected to 24-the signal input terminal of the infrared thermal imager through 26-the second BNC data cable.

[0040] The second signal output terminal of the computer is connected to the signal output terminal of the infrared thermal imager 24 through an Ethernet cable 25, 12-a first polarizer is fixed on a third fixed support 27, 13-a sample is fixed on a clamping frame 14, 14-a clamping frame is placed on a moving table 15, 15-moving table is connected to a moving table controller 17 through a motion drive line 16, and 24-an infrared thermal imager is fixed on a magnetic base 23.

[0041] The third signal output terminal of the computer is connected to the signal input terminal of the mobile stage controller 17 through the motion drive line 16, the first polarizer 12 is fixed on the third fixed support 27, the sample is fixed on the clamping frame 14, the clamping frame 14 is placed on the mobile stage 15, the mobile stage 15 is connected to the mobile stage controller 17 through the motion drive line 16, and the infrared thermal imager 24 is fixed on the magnetic base 23.

[0042] Specific implementation method 2: Combination Figure 2 and Figure 3 This embodiment is described as follows. Figure 2 As shown, the method for suppressing lateral heat flow diffusion of array heat flow based on feature iteration described in this embodiment includes the following steps:

[0043] S1: Fix the sample 13 on the clamping frame 14, turn on the computer 1, the data acquisition card 3, the laser power supply 5, the TEC cooler 9 and the temperature control feedback system 30, set the working temperature of the laser power supply 5 to 25°C to ensure the normal operation of the laser;

[0044] S2: Turn on 24-infrared thermal imager, adjust 23-magnetic base, 20-first fixed support and 22-second fixed support, and confirm that the imaging field of view of 24-infrared thermal imager can completely cover the sample;

[0045] S3: emitting an analog signal through the 3-data acquisition card to turn on the array 8-laser to irradiate the 13-sample, and adjusting the positions of the 27-third fixed support and the 28-fourth fixed support so that the spacing and size of the array light spots irradiated to the 13-sample are within the preset range;

[0046] The excitation intensity expression of a single laser beam of a laser is:

[0047]

[0048] In formula (1), I(i,j,t) is the laser intensity, i,j=1,2,…,7,I max is the peak light intensity, I max =1000W / m 2 , f is the excitation frequency, f = 0.05Hz;

[0049] S4: A dual-channel digital orthogonal demodulation algorithm based on feature iteration is used to extract the defect features of the sample and obtain the excitation amplitude and phase of the laser point after iteration;

[0050] The expression of the dual-path digital orthogonal demodulation algorithm based on feature iteration is:

[0051]

[0052] Phex,k+1 =Ph ex,k -Ph meas,k

[0053]

[0054] In formula (2) to formula (6), F n (x, y) is the thermal wave signal image, N is the number of frames, Am is the characteristic amplitude, Ph is the characteristic phase, Am ex,k+1 is the laser point excitation amplitude after iteration, Ph ex,k+1 is the laser point excitation phase after iteration, Amp ex,k+1 is the laser point excitation amplitude before iteration, is the laser spot excitation phase before iteration, Am meas,k is the characteristic amplitude of the central pixel of the laser point excitation in the amplitude characteristic map, Ph meas,k is the characteristic phase value of the central pixel excited by the laser point in the phase characteristic diagram;

[0055] S5: Repeat S3-S4 according to the excitation amplitude and phase of the laser point after iteration until the following is obtained: Figure 3 The defect feature phase diagram based on feature iteration shown in the figure realizes defect feature extraction;

[0056] S7: After the defect feature extraction is completed, turn off 1-computer, 3-data acquisition card, 5-laser power supply, 9-TEC refrigerator, 30-temperature control feedback system, 24-infrared thermal imager, 3-data acquisition card and 8-laser.

[0057] In summary, compared with the traditional active infrared thermal wave imaging detection technology, the present invention can effectively suppress the lateral heat flow diffusion and improve the accuracy of material defect morphology feature extraction, especially for the accurate and efficient detection of shallow surface defects of composite materials (<5mm, diameter / depth ratio>1.5).

[0058] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. An array heat flow lateral heat flow diffusion suppression device based on feature iteration, characterized in that: The array heat flow lateral heat flow diffusion suppression device based on feature iteration includes: Computer (1), USB data cable (2), data acquisition card (3), first BNC data cable (4), laser power supply (5), laser power cable (6), TEC refrigerator power cable (7), laser (8), TEC refrigerator (9), optical fiber bundle (10), collimator (11), first polarizer (12), sample (13), clamping frame (14), mobile stage (15), motion drive cable (16), mobile stage controller (17), motion control cable (18), filter (19), first fixed support (20), second polarizer (21), second fixed support (22), magnetic base (23), infrared thermal imager (24), Ethernet cable (25), second BNC data cable (26), third fixed support (27), fourth fixed support (28), third BNC data cable (29) and temperature control feedback system (30); The computer (1) is provided with three signal output terminals, wherein the first signal output terminal of the computer is connected to the signal input terminal of the data acquisition card (3) via a USB data line (2), the second signal output terminal of the computer is connected to the signal output terminal of the infrared thermal imager (24) via an Ethernet line (25), and the third signal output terminal of the computer is connected to the signal input terminal of the mobile station controller (17) via a motion drive line (16).

2. The array heat flow lateral heat flow diffusion suppression device based on feature iteration according to claim 1 is characterized in that: The data acquisition card (3) is provided with two signal output ends, the first signal output end of the data acquisition card is connected to the input end of the laser power supply (5) via a first BNC data line (4), and the second signal output end of the data acquisition card is connected to the signal input end of the infrared thermal imager (24) via a second BNC data line (26).

3. The array heat flow lateral heat flow diffusion suppression device based on feature iteration according to claim 1 is characterized in that: The output end of the laser power supply (5) is connected to the laser (8) via a laser power supply line (6), the output end of the laser (8) is connected to a collimator (11) via an optical fiber bundle (10), the collimator (11) is fixed on a fourth fixed support (28), and the signal input end of the TEC refrigerator (9) is connected to a temperature control feedback system (30) via a third BNC data line (29).

4. The array heat flow lateral heat flow diffusion suppression device based on feature iteration according to claim 1, characterized in that: The first polarizing plate (12) is fixed on a third fixed support (27), the sample (13) is fixed on a clamping frame (14), the clamping frame (14) is placed on a moving platform (15), the moving platform (15) is connected to a moving platform controller (17) via a motion driving line (16), and the infrared thermal imager (24) is fixed on a magnetic base (23).

5. The array heat flow lateral heat flow diffusion suppression device based on feature iteration according to claim 1, characterized in that: The filter (19) is fixed on a first fixed support (20), the second polarizer (21) is fixed on a second fixed support (22), and the infrared heat radiation signal radiated by the sample (13) is transmitted to the infrared thermal imager (24) through the filter (19) and the second polarizer (21).

6. The array heat flow lateral heat flow diffusion suppression device based on feature iteration according to claim 1, characterized in that: The lasers (8) are arranged in a 7×7 matrix, and all laser beams are Gaussian light sources. The lasers (8) are controlled by transmitting analog signals through a data acquisition card (3).

7. A method for suppressing lateral heat flow diffusion in an array heat flow based on feature iteration, applied to a device for suppressing lateral heat flow diffusion in an array heat flow based on feature iteration according to any one of claims 1 to 6, characterized in that: include: Step 1: Fix the sample (13) on the clamping frame (14), turn on the computer (1), data acquisition card (3), laser power supply (5), TEC cooler (9) and temperature control feedback system (30), and set the operating temperature of the laser power supply (5) to 25°C; Step 2: Turn on the infrared thermal imager (24), adjust the magnetic base (23), the first fixed support (20) and the second fixed support (22), and confirm that the imaging field of view of the infrared thermal imager (24) can completely cover the sample; Step 3: The data acquisition card (3) transmits an analog signal to start the array laser (8) to irradiate the sample (13), and adjusts the positions of the third fixed support (27) and the fourth fixed support (28) so that the spacing and size of the array light spots irradiated to the sample (13) meet the preset range; Step 4: Use a dual-channel digital orthogonal demodulation algorithm based on feature iteration to extract the defect features of the sample and obtain the laser point excitation amplitude and phase after iteration; Step 5: Repeat steps 3-4 according to the laser point excitation amplitude and phase after the iteration until a defect feature phase map based on feature iteration is obtained to achieve defect feature extraction; Step 6: After the defect feature extraction is completed, turn off the computer (1), the data acquisition card (3), the laser power supply (5), the TEC cooler (9), the temperature control feedback system (30), the infrared thermal imager (24), the data acquisition card (3) and the laser (8).

8. The array heat flow lateral heat flow diffusion suppression method based on feature iteration according to claim 7 is characterized in that: The excitation intensity expression of a single laser beam of the laser (8) in step 3 is: In formula (1), I(i,j,t) is the laser intensity, i,j=1,2,…,7,I max is the peak light intensity, I max =1000W / m 2 , f is the excitation frequency, f=0.05Hz.

9. The method for suppressing lateral heat flow diffusion of array heat flow based on feature iteration according to claim 7, characterized in that: The expression of the two-way digital orthogonal demodulation algorithm based on feature iteration in step 4 is: Ph ex,k+1 =Ph ex,k -P meas,k In formula (2) to formula (6), F n (x, y) is the thermal wave signal image, N is the number of frames, Am is the characteristic amplitude, Ph is the characteristic phase, Am ex,k+1 is the laser point excitation amplitude after iteration, Ph ex,k+1 is the laser point excitation phase after iteration, Amp ex,k+1 is the laser point excitation amplitude before iteration, is the laser spot excitation phase before iteration, Am meas,k is the characteristic amplitude of the central pixel of the laser point excitation in the amplitude characteristic map, Ph meas,k is the characteristic phase value of the central pixel excited by the laser point in the phase characteristic map.

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