A large deformation displacement extensometer device based on complex field imaging of metalens array

Abstract

The present invention discloses a large deformation displacement extensometer device based on complex field of view imaging of a metalens array, comprising: a metalens array camera, which collects an image of a tensile specimen placed directly in front of the metalens array camera, and a light source is placed between the metalens array camera and the tensile specimen; a data processor receives image data transmitted by the metalens array camera, preprocesses the image data, and extracts feature information of marker points; a computer receives the processed feature information of the marker points, further analyzes the deformation and displacement of the tensile specimen, and generates a visualization result; the metalens array camera includes a metalens array lens and an image sensor, and the metalens array lens is fixed on the outside of the front cover of the camera chassis; the image sensor is fixed on the inside of the rear cover of the camera chassis; the present invention realizes synchronous measurement of W×N×H full-area coverage and W×H local resolution through multi-field coupling of the metalens array camera.

Description

Technical Field

[0001] The present invention belongs to the field of optical measurement technology, and in particular relates to a large deformation displacement extensometer device based on complex field imaging of a meta-lens array. Background Art

[0002] In the field of material mechanical property testing, displacement extensometers are key measuring devices. Their accuracy and range directly impact the accuracy of characterizing material deformation behavior. With the widespread application of new flexible and composite materials, the measured objects often exhibit extremely large strains (>100%) and non-uniform deformation, posing a severe challenge to traditional measurement techniques.

[0003] Currently, mainstream non-contact optical extensometers primarily utilize digital image correlation (DIC) or laser interferometry. DIC systems rely on high-resolution industrial cameras combined with speckle patterns. While capable of full-field measurement, they are limited by the conflicting field of view and resolution constraints of traditional optical systems. While maintaining micron-level resolution, a single-camera system typically has an effective field of view of less than 50 mm, making it difficult to capture the full deformation of large specimens. While multi-camera stitching can expand the field of view, it significantly increases system complexity and calibration difficulty. Laser interferometry, while offering submicron accuracy, is only suitable for measuring small deformations and is extremely sensitive to environmental vibrations.

[0004] In recent years, metalens technology has provided a new avenue for innovation in optical measurement systems. Compared to traditional refractive lenses, metalenses achieve wavefront control through subwavelength structures, offering unique advantages such as ultra-thin planarization, high multi-focal design freedom, and programmable chromatic aberration. However, existing research has primarily focused on single-lens imaging optimization, and a systematic solution for collaborative measurement of composite fields of view has yet to be developed. In particular, in large dynamic range displacement field measurements, the limited aperture of a single metalens still presents a technical bottleneck, making it difficult to achieve both effective field of view and spatial resolution. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a large deformation displacement extensometer device based on complex field of view imaging of a meta-lens array, so as to solve the problem of mutual constraint between the measurement field of view and the resolution in the large dynamic range displacement field measurement technology.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a large deformation displacement extensometer device based on metalens array complex field imaging, comprising: a computer, a data processor, a metalens array camera, a tripod, and a light source;

[0008] The metalens array camera is fixed on a tripod and is used to collect images of a tensile specimen placed directly in front of it. The light source is placed between the metalens array camera and the tensile specimen, and a marking point is set on the tensile specimen.

[0009] The data processor is connected to the metalens array camera data, receives image data transmitted by the metalens array camera, pre-processes the image data, and extracts feature information of the marker points;

[0010] The computer is connected to the data processor for receiving the processed feature information of the marking points, analyzing the deformation and displacement of the tensile specimen, generating visual results, and storing relevant data;

[0011] The meta-lens array camera includes a meta-lens array lens and an image sensor. The meta-lens array lens is fixed on the outside of the front cover of the camera chassis; the image sensor is fixed on the inside of the rear cover of the camera chassis; there are no other components between the meta-lens array lens and the image sensor.

[0012] Furthermore, the light source is a monochromatic light source with a wavelength of λ.

[0013] Furthermore, the baseline length of the tensile specimen is l ,and l ≤H, range of motion of tensile specimen l ’ Less than H×N, where H is the single field of view x The length of the direction, W is the length of the single field of view in y The length of the direction, N is the number of complex fields of view, N ≥ 2, and the size of a single field of view is H × W.

[0014] Furthermore, the meta-lens array lens comprises N×2 meta-lenses in two directions, N≥2, and the focal length of each meta-lens is f, and the distance between adjacent meta-lenses in the x direction is d. x , the y-direction spacing is d y ; The meta-lens array lens is installed parallel to the image sensor, with a parallel distance of v.

[0015] Furthermore, the size of a single metalens in the metalens array is , the working wavelength is λ, and it is composed of a nanocolumn structure; the optical center coordinates of a single meta-lens are set to ( d x , d y ), then the first ( i,j ) The optical center coordinates of a single meta-lens are ( i × d x , j × dy ), , Taking the optical center of any single metalens as the origin of the local coordinate system, establish the local polar coordinates and design the phase of the nanopillars so that the phase φ(r) distribution of the nanopillars satisfies the following:

[0016] ;

[0017] Where, f is the focal length of the metalens, r is the local radial coordinate of the nanopillar structure in a single metalens.

[0018] Furthermore, the diameter of each nanopillar in a single metalens is simulated using COMSOL, and the one-to-one functional relationship between the nanopillar diameter D, the phase φ, and the local radial coordinate r is constructed as follows:

[0019] D=D(φ)= D(φ(r))

[0020] Where D(φ) represents the function equation of diameter D and phase φ, phase φ is a function of coordinate r, and D(φ(r)) is the function of diameter D with respect to coordinate r.

[0021] Furthermore, the physical spacing of the meta-lens array lenses needs to satisfy the following proportional relationship: the lateral physical spacing d x The image sensor's horizontal size x The ratio is: d x / s x =f / v, vertical physical distance d y The vertical dimension of the image sensor s y The ratio is: 2d y / s y =f / v.

[0022] Furthermore, the size of a single metalens in the metalens array is , the image sensor size is , the two must satisfy the following relationship: .

[0023] Furthermore, a T-shaped marking point is arranged at each end of the tensile specimen. After the T-shaped marking point is imaged by the complex field of view model, any single frame image has four T-shaped patterns on the image sensor.

[0024] Furthermore, a single-frame image reconstructs the three-dimensional displacement of two T-shaped markers, wherein the T-shaped markers include four identifiable markers, one of which is a main marker and three are auxiliary directional markers.

[0025] Beneficial effects of the present invention:

[0026] 1. Simultaneous measurement of high resolution and large field of view: Through the multi-field coupling of the metalens array, simultaneous measurement of full-area coverage (H×W×N) and local high resolution (H×W) is achieved. The theoretical resolution can reach N times that of a traditional single-lens system, solving the industry problem of the mutual restriction between field of view and resolution in large deformation measurement.

[0027] 2. System simplification and cost reduction: The integrated design of the metalens array camera reduces the number of cameras to 1 / (2×N) of a traditional multi-camera system, reducing power consumption while eliminating the complex spatial alignment operations required for multi-camera calibration. The traditional optical module (lens + CCD / CMOS) is reduced to a size close to that of a CCD / CMOS package, significantly reducing the quality of a single camera.

[0028] 3. Volume and weight optimization: The planar design of the metalens array camera significantly reduces the size of the optical module (lens + image sensor), approaching the package size of the image sensor, significantly reducing the mass and space occupied by a single camera.

[0029] 4. High-precision 3D displacement reconstruction: Multi-field imaging technology combined with triangulation method is used to achieve high-precision 3D displacement reconstruction of marker points.

[0030] 5. Strong Adaptability: The metalens array arrangement (N×2 metalenses in two directions, where N is adjustable) can be flexibly adjusted to accommodate the measurement needs of specimens of varying sizes, covering a wide range of deformation scenarios, from small to large. The combination of a monochromatic light source and nanopillar phase design enhances the system's adaptability to operating wavelengths.

[0031] 6. Technological advancement: The sub-wavelength structure of the meta-lens is used to control the wavefront, achieving multi-focal design freedom and chromatic aberration programmability that are difficult to achieve with traditional refractive lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the device of the present invention;

[0033] Figure 2 for Figure 1 Internal view of the middle M section;

[0034] Figure 3a Schematic diagram of the field of view of the metalens array lens of the present invention;

[0035] Figure 3b Schematic diagram of the arrangement of metalenses on a metalens array lens;

[0036] Figure 3c Schematic diagram of the image sensor on the meta-lens array camera;

[0037] Figure 4a Schematic diagram of imaging of the field of view on an image sensor through two adjacent meta-lenses in the x-direction in the present invention;

[0038] Figure 4b Schematic diagram of imaging of the field of view on an image sensor through two adjacent meta-lenses in the y direction in the present invention;

[0039] Figure 5a Schematic diagram of the geometric configuration of the T-shaped marking point on the tensile specimen of the present invention;

[0040] Figure 5b Schematic diagram of the position change relationship of the T-shaped marking point before and after the force is applied on the tensile specimen and the single field of view;

[0041] Figure 5c Schematic diagram of the typical positional relationship of the marking points after coincident imaging of a single field of view in preferred example 1;

[0042] Figure 5d Schematic diagram of the typical positional relationship of the marking points after coincident imaging of a single field of view in preferred example 2;

[0043] Figure 6 Schematic diagram of the size and phase distribution of nanopillars in the present invention;

[0044] Figure 7 Schematic diagram of the principle of three-dimensional displacement reconstruction in the present invention;

[0045] In the figure: 1-computer, 2-data processor, 3-meta-lens array camera, 4-tripod, 5-tensile specimen, 6-light source, 10-complex field of view, 20-meta-lens array lens, 201-optical center of a single meta-lens, 30-image sensor. DETAILED DESCRIPTION

[0046] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and drawings. The contents mentioned in the embodiments are not intended to limit the present invention.

[0047] Reference Figure 1 、 Figure 2 As shown, a large deformation displacement extensometer device based on metalens array complex field imaging of the present invention includes: a computer 1, a data processor 2, a metalens array camera 3, a tripod 4 and a light source 6;

[0048] The metalens array camera 3 is fixed on a tripod 4 and is used to capture an image of a tensile specimen 5 placed directly in front of it. A light source 6 is placed between the metalens array camera 3 and the tensile specimen 5. Marking points are set on the tensile specimen 5.

[0049] The data processor 2 is data-connected to the metalens array camera 3, receives image data transmitted by the metalens array camera, pre-processes the image data (such as denoising, contrast enhancement, etc.), and extracts feature information of the markers (such as position, displacement, deformation, etc.);

[0050] The computer 1 is data-connected to the data processor 2, and is used to receive the processed feature information of the marking points, further analyze the deformation and displacement of the tensile specimen 5, generate visual results (such as displacement curves, deformation cloud maps, etc.), and store relevant data;

[0051] The metalens array camera 3 includes a metalens array lens 20 and an image sensor 30. The metalens array lens is fixed on the outside of the front cover of the camera chassis; the image sensor is fixed on the inside of the rear cover of the camera chassis; there are no other components between the metalens array lens and the image sensor.

[0052] Specifically, the light source 6 is a monochromatic light source with a wavelength of λ.

[0053] Specifically, the baseline length of the tensile specimen 5 is l ,and l ≤H, range of motion of tensile specimen 5 l ’ Less than H×N, where H is the single field of view x The length of the direction, W is the length of the single field of view in y The length of the direction, N is the number of complex fields of view 10, N ≥ 2, the size of a single field of view is H × W. Figure 3a shown.

[0054] Specifically, the meta-lens array lens 20 includes N×2 meta-lenses in two directions, N≥2, and the focal length of each meta-lens is f, and the distance between adjacent meta-lenses in the x direction is d. x , the y-direction spacing is d y ; Meta-lens array lens 20 and image sensor (image sensor size s x ×s y , with a resolution of P × Q pixels) are mounted in parallel with a parallel distance of v, see Figure 3b As shown;

[0055] Specifically, the size of a single meta-lens in the meta-lens array lens 20 is m x ×m y , the working wavelength is λ, and it is composed of a nanocolumn structure; the optical center 201 coordinates of a single meta-lens are set to (d x ,d y ), then the optical center coordinates of the (i, j)th single meta-lens are (i×d x ,j×d y ), , Taking the optical center of any single metalens as the origin of the local coordinate system, establish the local polar coordinates and design the phase of the nanopillars so that the phase φ(r) distribution of the nanopillars satisfies the following:

[0056]

[0057] Where f is the focal length of the metalens, and r is the local radial coordinate of the nanopillar structure in a single metalens.

[0058] Specifically, the diameter of each nanopillar in a single metalens is simulated using COMSOL, and the one-to-one functional relationship between the nanopillar diameter D, the phase φ, and the local radial coordinate r is constructed as follows:

[0059] D = D(φ) = D(φ(r))

[0060] Where D(φ) represents the function equation of diameter D and phase φ, phase φ is a function of coordinate r, and D(φ(r)) is the function of diameter D with respect to coordinate r; see Figure 6 As shown, the nanocolumn size and phase distribution meet the requirements of the present invention.

[0061] Specifically, the physical spacing of the meta-lens array lens 20 needs to satisfy the following proportional relationship: the lateral physical spacing d x The image sensor's horizontal size x The ratio is: d x / s x =f / v, vertical physical distance d y The vertical dimension of the image sensor s y The ratio is: 2d y / s y =f / v, see Figure 4a and 4b shown.

[0062] Specifically, the size of a single meta-lens in the meta-lens array lens 20 is , the image sensor size is , the two must satisfy the following relationship: , see Figure 3c shown.

[0063] Specifically, a T-shaped marking point is arranged at each end of the tensile specimen. After the T-shaped marking point is imaged by the complex field of view model, any single frame image has four T-shaped patterns on the image sensor. Figure 5a and 5b As shown;

[0064] Specifically, a single-frame image reconstructs the three-dimensional displacement of two T-shaped markers, wherein the T-shaped markers include four identifiable markers, one of which is a main marker and three are auxiliary directional markers.

[0065] Specifically, the meta-lens array lens 20 performs three-dimensional displacement reconstruction on the marking point, see Figure 7 As shown;

[0066] The specific steps are as follows:

[0067] First, a single metalens is calibrated to obtain the intrinsic parameters of each camera. A high-precision checkerboard calibration plate with known dimensions and pattern spacing is used. A monochromatic light source with a wavelength of λ is used to ensure uniform and stable illumination. The metalens array camera is fixed on a tripod, ensuring that it is parallel to the calibration plate. The calibration plate's posture (translation, rotation, tilt, etc.) is adjusted to ensure that the calibration plate covers the entire field of view. At least 10 sets of calibration plate images with different postures are collected for each metalens. For each calibration plate image, the pixel coordinates of the corner points or dot centers are extracted. ; Calculation of internal parameters of a single meta-lens: Using Zhang Zhengyou calibration method, calculate the internal parameter matrix K and distortion coefficient D by minimizing the reprojection error; The internal parameter matrix of each meta-lens is , ,in, , To change the physical focal length f Converted to the equivalent focal length in the image sensor pixel coordinate system, are the coordinates of the principal point at the center of the image, , , is the radial distortion coefficient, , is the tangential distortion coefficient; then perform distortion correction on each meta-lens: dedistort the image, and the corrected coordinates Calculated by the following formula:

[0068]

[0069]

[0070] in, ;

[0071] Next, we perform metalens array calibration to determine the relative positional relationships (extrinsic parameters) between all metalenses in the array. We then perform feature point matching: for multiple metalens images under the same calibration plate pose, we match the corresponding feature points. Finally, we calculate the relative poses between the metalenses (rotation matrix R and translation vector t), as follows:

[0072] ,

[0073] The nine computational elements in the rotation matrix R represent the projections of the new directions of the three basis vectors in the original coordinate system when the coordinate system rotates about the x, y, and z axes; the three computational elements in the translation vector t represent the translation amounts along the three coordinate axes. Marker point detection and matching: Identify T-shaped marker points in the image, ensure that all marker points detected by the meta-lens are consistent, and extract the corresponding pixel coordinates;

[0074] Finally, the three-dimensional displacement reconstruction of the marker point is performed: a projection matrix is constructed based on the internal and external parameters of the meta-lens, and the three-dimensional coordinates of the T-shaped marker point are calculated using triangulation. The marker point displacement reconstruction includes computational imaging and three-dimensional reconstruction of N×2 sub-images in the x and y directions; the sub-image computational imaging is characterized by decomposing the P×Q pixel image of any instantaneous image sensor into N×2 P×Q pixel images based on the displacement at the previous moment t0 of the sample stretching, for three-dimensional reconstruction at the current moment t1; let the coordinates of the marker points corresponding to two adjacent meta-lenses be , , first eliminate the distortion, apply distortion correction (coordinate normalization) to the two coordinates, the formula is:

[0075]

[0076]

[0077] in, 、 After distortion correction 、 The corresponding coordinates; 、 is the internal parameter matrix, 、 is the distortion coefficient.

[0078] Construct the projection equation. The coordinate system of the meta-lens on the left is the world coordinate system, and the relative position of the meta-lens on the right is ,but:

[0079] ;

[0080] ;

[0081] in, 、 is the scale factor (proportional coefficient), is the projection matrix of the metalens on the left (identity matrix + zero translation vector), is the external parameter matrix of the metalens on the right (rotation matrix + translation vector), represents the i-th row of the internal parameter matrix K; X, Y, Z are the three-dimensional coordinates of the marker point to be solved;

[0082] After expansion, we get a system of linear equations (eliminating the scale factor , ):

[0083]

[0084] in, is the homogeneous coordinate of the marked point;

[0085] Solve the system of equations using the least squares method, expressing it as AP=0, and find the least squares solution through SVD decomposition as follows:

[0086]

[0087] Among them, the matrix A represents the linear relationship matrix between the observations and the parameters; the solution is the column of the right singular vector of A corresponding to the minimum singular value.

[0088] Solving for 3D coordinates :

[0089] = .

[0090] Preferred Example 1: The present invention is used in the case of traditional small deformation stretching, where the tensile deformation of the sample is less than 50%.

[0091] Place the T-shaped mark point near the middle of the tensile specimen;

[0092] The focal length of a single meta-lens is f=10mm. The number of meta-lenses arranged on the meta-lens array is 2×2. The image sensor 30 is a common industrial camera image sensor with a size of s. x × s y 8.32mm×6.96mm, with a resolution of 2448×2048 pixels;

[0093] By d x / s x =f / v, sensor s x × s y 8.32mm×6.96mm, with a resolution of 2448×2048 pixels;

[0094] The parallel image distance between the meta-lens array lens 20 and the image sensor 30 is v = 10.5 mm;

[0095] By d x / s x =f / v to get d x=7.92mm; by 2d y / s y =f / v, get d y =3.31mm;

[0096] Design a single meta-lens size m x ×m y 7.89mm× 3.30mm.

[0097] The test field of view is W×2×H=66.2mm×2×158mm.

[0098] According to this embodiment, due to the expected small deformation, the two T-shaped marking points on the tensile specimen are placed close to the middle of the tensile specimen, that is, the lower marking point is placed near the middle of the field of view (W×H)1, and the upper marking point is placed near the middle of (W×H)2; since the tensile deformation of the specimen is less than 50%, the overlapping method of the marking points after the coincident imaging of a single field of view is shown in Figure 5c .

[0099] According to this embodiment, the test is carried out to reconstruct the three-dimensional coordinates of the two marking points. Calculate the deformation of the specimen in real time.

[0100] Preferred Example 2: The present invention is used for a large deformation tensile specimen, where the tensile deformation of the specimen is 200%.

[0101] The focal length of a single meta-lens is f=10mm. The number of meta-lenses arranged on the meta-lens array is 2×3. The image sensor 30 is a common industrial camera image sensor with a size of s. x × s y It is 8.32mm×6.96mm and has a resolution of 2448×2048 pixels.

[0102] By d x / s x =f / v, sensor s x × s y It is 8.32mm×6.96mm and has a resolution of 2448×2048 pixels.

[0103] The parallel image distance between the meta-lens array lens 20 and the image sensor 30 is v = 10.5 mm;

[0104] By d x / s x =f / v to get d x =7.92mm; by 2d y / s y =f / v, get dy =3.31mm;

[0105] Design a single meta-lens size m x ×m y 7.89mm× 3.30mm;

[0106] The test field of view is W×3×H=66.2mm×3×158mm.

[0107] According to this embodiment, the test is carried out by placing the two T-shaped marking points on the tensile specimen close to the middle of the image, that is, the lower marking point is placed near the bottom of the field of view (W×H)1, and the upper marking point is placed near the top of (W×H)1; due to the large tensile deformation of the specimen, the overlapping mode of the marking points after the re-imaging of a single field of view may be Figure 5d In any way, the upper marking point passes through (W×H)1, (W×H)2, and (W×H)3. According to this embodiment, the test is carried out to reconstruct the three-dimensional coordinates of the two marking points. Calculate the deformation of the specimen in real time.

[0108] In the preferred examples 1 and 2, the relationship between the distribution size and phase of the nanopillars of a single meta-lens is simulated by COMSOL and satisfies Figure 6 In this example, the wavelength of the light source is selected as 532nm. Design the distribution of nanopillars.

[0109] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be considered as the scope of protection of the present invention.

Claims

1. A large deformation displacement extensometer device based on complex field imaging of a metalens array, characterized in that: include: Computer, data processor, meta-lens array camera, tripod and light source; The metalens array camera is fixed on a tripod and is used to collect images of a tensile specimen placed directly in front of it. The light source is placed between the metalens array camera and the tensile specimen, and a marking point is set on the tensile specimen. The data processor is connected to the metalens array camera data, receives image data transmitted by the metalens array camera, pre-processes the image data, and extracts feature information of the marker points; The computer is connected to the data processor for receiving the processed characteristic information of the marking points, analyzing the deformation and displacement of the tensile specimen, generating visual results, and storing relevant data; The meta-lens array camera includes a meta-lens array lens and an image sensor, wherein the meta-lens array lens is fixed on the outside of the front cover of the camera chassis; and the image sensor is fixed on the inside of the rear cover of the camera chassis; The baseline length of the tensile specimen is l, and l≤H, and the range of motion of the tensile specimen is l ’ Less than H×N, where H is the length of the single field of view in the x-direction, W is the length of the single field of view in the y-direction, and N is the number of complex fields of view, N ≥ 2, and the size of a single field of view is H×W; The meta-lens array lens comprises N×2 meta-lenses in two directions, and the focal length of each meta-lens is f, and the distance between adjacent meta-lenses in the x direction is d x , the y-direction spacing is d y The meta-lens array lens is installed parallel to the image sensor, with a parallel distance of v. The physical spacing of the meta-lens array lenses needs to meet the following proportional relationship: the horizontal physical spacing d x The image sensor's horizontal size x The ratio is: d x / s x =f / v, vertical physical spacing d y The vertical dimension of the image sensor s y The ratio is: 2d y / s y =f / v,d x is the x-direction spacing between adjacent meta-lenses, d y is the y-direction spacing between adjacent metalenses, f is the focal length of the metalens, and v is the parallel distance between the metalens array lens and the image sensor.

2. The large deformation displacement extensometer device based on metalens array complex field imaging according to claim 1, characterized in that: The size of a single meta-lens in the meta-lens array is m x ×m y , the working wavelength is λ, and it is composed of nanocolumn structure; the optical center coordinates of a single meta-lens are set to (d x ,d y ), then the optical center coordinates of the (i,j)th single meta-lens are (i×d x ,j×d y ), i∈{1,2,…,N}, j∈{1,2}; take the optical center of any single meta-lens as the origin of the local coordinate system, establish the local polar coordinates, and design the phase of the nanocolumn so that the phase of the nanocolumn The distribution satisfies the following: Where f is the focal length of the metalens, and r is the local radial coordinate of the nanopillar structure in a single metalens.

3. The large deformation displacement extensometer device based on metalens array complex field imaging according to claim 1, characterized in that: The diameter of each nanopillar in a single meta-lens is simulated using COMSOL to construct the relationship between the nanopillar diameter D and the phase The one-to-one functional relationship of the local radial coordinate r is as follows: in, Indicates diameter D and phase Function equation, phase is a function of the coordinate r, is a function of the diameter D with respect to the coordinate r.

4. The large deformation displacement extensometer device based on metalens array complex field imaging according to claim 1, characterized in that: A T-shaped marking point is arranged at each end of the tensile specimen. After the T-shaped marking point is imaged by the complex field of view model, any single frame image has four T-shaped patterns on the image sensor.

5. The large deformation displacement extensometer device based on metalens array complex field imaging according to claim 1, characterized in that: The three-dimensional displacement of two T-shaped markers is reconstructed from a single frame image. The T-shaped marker contains four identifiable markers, one of which is the main marker and three are auxiliary direction markers.

Images