Digital image correlation strain measurement system and method based on super-structure lens

Abstract

The invention provides a digital image correlation strain measurement system and method based on a super-structure lens. The system comprises the super-structure lens, a digital camera, an illumination light source and a computer. The super-structure lens comprises a plurality of super-structure lens units, light scattered or emitted by an object is imaged, and the formed image is located on the plane where a photosensitive chip of the digital camera is located. The digital camera is used for acquiring an image of a measured object formed by the super-structure lens; the computer is used for processing the calibration and experiment image data acquired by the digital camera, calculating camera parameters through the calibration image, and performing three-dimensional digital image analysis and calculation on the experiment image to obtain the three-dimensional shape, displacement and deformation data of the measured object; according to the invention, 3D-DIC measurement can be realized by only adopting single shooting of one camera, and a conventional lens is replaced by the metamaterial lens, so that a simpler and more compact optical structure can be obtained on the premise of keeping the imaging quality, and the 3D-DIC measurement device has the characteristics of high efficiency, no need of camera synchronization and the like.

Description

Technical Field

[0001] The present invention relates to the field of photomechanics, and in particular to a digital image correlation strain measurement system and method based on a meta-lens. Background Art

[0002] At present, the strain measurement of the surface of an object can be divided into contact measurement and non-contact measurement. Among them, non-contact measurement has attracted much attention due to its advantages such as no influence on the measured object, no contact interference, wide practicability, easy real-time operation, and high measurement accuracy. Non-contact strain measurement is mainly based on optical measurement methods, including laser speckle method, digital volume correlation, and digital image correlation.

[0003] Among them, digital image correlation continuously takes images of the surface of an object within a short time interval, calculates the displacement between images based on the cross-correlation algorithm, and thus obtains the displacement and strain of the surface of the object. It is widely used in the field of optical strain measurement. The three-dimensional digital image correlation method (3D Digital Image Correlation, 3D-DIC) uses two or more cameras for measurement, which can extract the three-dimensional morphology, displacement and strain information of the sample surface. However, since multiple cameras are required and the cameras need to be calibrated and synchronized, the system complexity and difficulty of this method are relatively high. Therefore, researchers began to study the method of using a single camera for 3D-DIC. Han et al. proposed a single-camera 3D-DIC system based on a fiber bundle (FB), which transmits images through a fiber bundle. Compared with traditional 3D-DIC, strict synchronization is not required; at the same time, a method of positioning and correcting misalignment that combines image acquisition and image processing is proposed to reduce the error during transmission. Pan et al. proposed a single-camera microscopic 3D-DIC method using a diffraction grating, which can measure the deformation of small-scale objects while reducing the overall size. Wu et al. proposed a 3D-DIC technology using a single camera and a double prism. By placing a double prism between the camera and the sample, the demand for cameras was reduced while maintaining a certain measurement accuracy. The above methods have solved the 3D-DIC system's demand for multiple cameras and the difficulty of multi-camera synchronous control to a certain extent. However, the above methods all have a shortcoming. While reducing the number of cameras, other optical components are added, and the overall complexity of the system has not been improved.

[0004] In order to reduce the overall size of digital image correlation optical equipment so that it can be applied to a wider range of places and can perform strain measurement on tiny areas, the patent of this invention utilizes the imaging characteristics of meta-lens and proposes a digital image correlation strain measurement method based on meta-lens. Meta-lens is used to replace traditional lenses, which reduces the number of cameras without adding unnecessary optical elements. Correspondingly, the time for camera calibration and synchronization is also reduced, which greatly increases the shooting efficiency and can complete high-precision three-dimensional measurement more conveniently and effectively. Summary of the invention

[0005] In view of the defects in the prior art, the purpose of the present invention is to provide a digital image correlation strain measurement system and system based on meta-lens.

[0006] A digital image correlation strain measurement system based on a meta-lens provided by the present invention comprises:

[0007] Meta-lenses, digital cameras, lighting sources and computers;

[0008] Wherein, the light intensity of the illumination light source can be adjusted;

[0009] The meta-lens comprises a plurality of meta-lens units, which images the light scattered or emitted by the object, and the formed image is located on the plane where the photosensitive chip of the digital camera is located;

[0010] The meta-lens unit is composed of a substrate and a nano-column array covering the substrate, which can adjust the phase of the incident light to achieve the imaging function; different phase compensations are designed for different situations;

[0011] The meta-lens is designed as a phase modulation with a spherical aberration. A single micron-thick meta-lens can accurately refract and focus light incident from different directions onto the focal plane. The focal spot size of the meta-lens is close to the diffraction limit, and has better imaging resolution at the same numerical aperture.

[0012] The digital camera is used to collect the image of the object under test formed by the meta-lens;

[0013] The computer is used to process calibration and experimental image data collected by the digital camera, calculate camera parameters through calibration images, perform three-dimensional digital image analysis and calculation on the experimental images, and obtain three-dimensional morphology, displacement and deformation data of the measured object;

[0014] The light emitted by the illumination light source has the working wavelength when designing the meta-lens; or the illumination light source is a white light source, and a frequency band filter corresponding to the working wavelength is placed when using the white light source; or a white light source without a filter and ambient light that meets the light intensity requirement for imaging are directly used.

[0015] Preferably, in the meta-lens:

[0016] The meta-lens comprises two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two meta-lens units can simultaneously image the object or area to be measured. The imaging areas of the two meta-lens units respectively cover the entire area to be measured.

[0017] Preferably, in the meta-lens:

[0018] The meta-lens comprises more than two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of meta-lens units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of meta-lens units, the imaging areas of the two meta-lens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of meta-lens units covers the entire area to be measured.

[0019] Preferably, in the digital camera:

[0020] The digital camera is a black and white camera or a color camera.

[0021] Preferably, in the metalens, different metalens units use different working wavelengths, but have the same focal length at different working wavelengths;

[0022] The illumination light source used has the ability to emit light of the above working wavelength, or is a white light source.

[0023] According to a digital image correlation strain measurement method based on a metalens provided by the present invention, the digital image correlation strain measurement system based on a metalens is used to perform the following steps:

[0024] Step S1: spraying speckles on the surface of the test piece and fixing the test piece according to the required measurement conditions;

[0025] Step S2: adjusting the meta-lens and the digital camera to make each meta-lens unit image clear;

[0026] Step S3: Perform the required measurement conditions and use a computer to control the camera to collect images;

[0027] Step S4: photographing a calibration image and obtaining calibration parameters;

[0028] Step S5: Separate the collected images and perform three-dimensional DIC analysis and calculation on the digital images.

[0029] Preferably, in the meta-lens:

[0030] The meta-lens comprises two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two meta-lens units can simultaneously image the object or area to be measured. The imaging areas of the two meta-lens units respectively cover the entire area to be measured.

[0031] Preferably, in the meta-lens:

[0032] The meta-lens comprises more than two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of meta-lens units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of meta-lens units, the imaging areas of the two meta-lens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of meta-lens units covers the entire area to be measured.

[0033] Preferably, in the digital camera:

[0034] The digital camera is a black and white camera or a color camera.

[0035] Preferably, in the metalens, different metalens units use different working wavelengths, but have the same focal length at different working wavelengths;

[0036] The illumination light source used has the ability to emit light of the above working wavelength, or is a white light source.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention can realize 3D-DIC measurement with only a single shot of a camera, and uses a meta-lens to replace the traditional lens, so that it can obtain a simpler and more compact optical structure while maintaining the imaging quality, with the characteristics of high efficiency and no need for camera synchronization. At the same time, the meta-lens is designed as a phase modulation with a spherical aberration, and only a single micron-level meta-lens is used to accurately refract and focus light incident from different directions to the focal plane. In addition, the focal spot size of the meta-lens is close to the diffraction limit, and has better imaging resolution at the same numerical aperture;

[0039] 2. The present invention realizes single-camera 3D imaging through binocular / multi-eye meta-lenses, and can optimize the depth of field and field of view of DIC measurement by designing meta-lenses with different focal lengths and apertures. Compared with traditional binocular 3D-DIC, multi-eye 3D-DIC can provide more viewing angle information and reduce the impact of occlusion for the same feature, so as to more accurately solve the parallax relationship, thereby accurately solving the deformation and displacement in the three-dimensional direction;

[0040] 3. The present invention can also be effectively extended to special measurement fields such as high speed and microscopy, thereby effectively reducing hardware costs and test space requirements;

[0041] 4. Thanks to the optical structure of the new system, the present invention can realize convenient adjustment of system parameters like traditional binocular 3D-DIC. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0043] Figure 1 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0044] Figure 2 Schematic diagram of binocular meta-lens according to embodiment 3 of the present invention;

[0045] Figure 3 Schematic diagram of a multi-eye meta-lens according to Embodiment 4 of the present invention;

[0046] Among them, 1 is the lighting source; 2 is the meta-lens; 3 is the computer; and 4 is the digital camera. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0048] Embodiment 1:

[0049] The present invention discloses a digital image correlation strain measurement system and method based on a meta-lens and a single digital camera, the method comprising the following steps: first, using a meta-lens 2 as the main optical element and integrating it with a digital camera 4 to form an image capture system; then, collecting images of the surface of a deformed object with speckles; finally, using a traditional digital image correlation algorithm based on the collected images to obtain the three-dimensional displacement and strain of the measured object. The present invention uses a meta-lens 2 to replace a traditional optical lens, has a compact structure, is easy to adjust system parameters, and can more conveniently and effectively complete high-precision three-dimensional measurements when conducting experiments on three-dimensional morphology and deformation in special fields such as microscopy and high speed.

[0050] According to a digital image correlation strain measurement method based on a metalens 2 provided by the present invention, the digital image correlation strain measurement system based on a metalens 2 is used to perform the following steps:

[0051] Step S1: spraying speckles on the surface of the test piece and fixing the test piece according to the required measurement conditions;

[0052] Step S2: adjusting the meta-lens 2 and the digital camera 4 to make each meta-lens 2 unit image clear;

[0053] Step S3: performing the required measurement conditions loading, and using the computer 3 to control the camera to collect images;

[0054] Step S4: photographing a calibration image and obtaining calibration parameters;

[0055] Step S5: Separate the collected images and perform three-dimensional DIC analysis and calculation on the digital images.

[0056] Specifically, in the meta-lens 2:

[0057] The metalens 2 comprises two metalens 2 units, which are located in the same plane and have the same focal length. Within the designed working distance, the two metalens 2 units can simultaneously image the object or area to be measured. The imaging areas of the two metalens 2 units respectively cover the entire area to be measured.

[0058] The meta-lens 2 is designed as a phase modulation with a spherical aberration. A single micron-thick two-dimensional meta-lens 2 is used to accurately refract and focus incident light from different directions onto the focal plane. The focal spot size of the meta-lens 2 is close to the diffraction limit, and has better imaging resolution at the same numerical aperture.

[0059] Specifically, in the meta-lens 2:

[0060] The metalens 2 comprises more than two metalens 2 units, and the metalens 2 units are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of metalens 2 units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of metalens 2 units, the imaging areas of the two metalens 2 units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 2 units covers the entire area to be measured.

[0061] Specifically, in the digital camera 4:

[0062] The digital camera 4 is a black and white camera or a color camera.

[0063] Specifically, in the metalens 2, different metalens 2 units use different working wavelengths, but have the same focal length at different working wavelengths;

[0064] The illumination light source 1 used has the ability to emit light of the above working wavelength, or is a white light source.

[0065] Embodiment 2:

[0066] Embodiment 2 is a preferred example of Embodiment 1, and is used to illustrate the present invention in more detail.

[0067] The present invention also provides a digital image correlation strain measurement system based on a metalens. The digital image correlation strain measurement system based on a metalens can be implemented by executing the process steps of the digital image correlation strain measurement method based on a metalens, that is, those skilled in the art can understand the digital image correlation strain measurement method based on a metalens as a preferred implementation of the digital image correlation strain measurement system based on a metalens.

[0068] According to a digital image correlation strain measurement system based on a meta-lens provided by the present invention, Figure 1-Figure 3 As shown, including:

[0069] Meta-lens 2, digital camera 4, lighting source 1 and computer 3;

[0070] Wherein, the light intensity of the illumination light source 1 can be adjusted;

[0071] The meta-lens 2 comprises a plurality of meta-lens 2 units, which images the light scattered or emitted by the object, and the formed image is located on the plane where the photosensitive chip of the digital camera 4 is located;

[0072] The meta-lens 2 unit is composed of a substrate and a nano-column array covered on the substrate, which can control the phase of the incident light to achieve the imaging function; different phase compensations are designed for different situations.

[0073] The digital camera 4 is used to collect the image of the object under test formed by the meta-lens 2;

[0074] The computer 3 is used to process the calibration and experimental image data collected by the digital camera 4, calculate the camera parameters through the calibration image, perform three-dimensional digital image analysis and calculation on the experimental image, and obtain the three-dimensional shape, displacement and deformation data of the measured object;

[0075] The light emitted by the illumination light source 1 has the working wavelength when designing the meta-lens 2; or the illumination light source 1 is a white light source, and a frequency band filter corresponding to the working wavelength is placed when using a white light source; or a white light source without a filter and ambient light that meets the light intensity requirement for imaging are directly used.

[0076] Specifically, in the meta-lens 2:

[0077] The metalens 2 comprises two metalens 2 units, which are located in the same plane and have the same focal length. Within the designed working distance, the two metalens 2 units can simultaneously image the object or area to be measured. The imaging areas of the two metalens 2 units respectively cover the entire area to be measured.

[0078] The meta-lens 2 is designed as a phase modulation with a spherical aberration. A single micron-thick two-dimensional meta-lens 2 is used to accurately refract and focus incident light from different directions onto the focal plane. The focal spot size of the meta-lens 2 is close to the diffraction limit, and has better imaging resolution at the same numerical aperture.

[0079] Specifically, in the meta-lens 2:

[0080] The metalens 2 comprises more than two metalens 2 units, and the metalens 2 units are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of metalens 2 units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of metalens 2 units, the imaging areas of the two metalens 2 units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 2 units covers the entire area to be measured.

[0081] Specifically, in the digital camera 4:

[0082] The digital camera 4 is a black and white camera or a color camera.

[0083] Specifically, in the metalens 2, different metalens 2 units use different working wavelengths, but have the same focal length at different working wavelengths;

[0084] The illumination light source 1 used has the ability to emit light of the above working wavelength, or is a white light source.

[0085] Embodiment 3:

[0086] Embodiment 3 is a preferred example of Embodiment 1, and is used to illustrate the present invention in more detail.

[0087] This patent proposes a digital image correlation strain measurement method for meta-lens. Considering the imaging characteristics of meta-lens, a digital image correlation strain measurement method based on meta-lens is proposed. After obtaining the speckle image, the cross-correlation algorithm is used to calculate the displacement field, and then the surface strain field of the object is calculated through the displacement field. Solve the core problem of single-camera strain measurement and promote the development of digital image correlation strain measurement technology.

[0088] A digital image correlation strain measurement system based on a meta-lens 2 and a single digital camera 4 comprises a meta-lens 2, a digital camera 4, an illumination light source 1 and a computer 3; the light source is used to provide illumination so that the camera can conveniently collect images with suitable grayscale values, and the light intensity is adjustable; the meta-lens 2 comprises two meta-lens 2 units ( Figure 2 ), which is used to image the light scattered or emitted by the object on the photosensitive chip; the meta-lens 2 unit is composed of a substrate and a nano-column array covered on the substrate, which realizes the regulation of the phase of the incident light to achieve the imaging function; the digital camera 4 is used to collect the image of the object under test formed by the meta-lens 2; the computer 3 is used to process the calibration and experimental image data collected by the digital camera 4, calculate the camera parameters through the calibration image, and then perform 3D-DIC calculation on the image to obtain the three-dimensional morphology, displacement and deformation data of the object under test.

[0089] When in use, spray the speckle on the surface of the test piece, and fix the test piece according to the required measurement conditions; set the camera and the meta-lens 2 at the same height through optical elements, adjust the parallelism of the meta-lens 2 and the camera through the pitch mechanism, and adjust the rotation mechanism to make the meta-lens 2 imaging system parallel to the surface to be measured; place the meta-lens 2 measurement system in front of the test piece; adjust the image distance and object distance by adjusting the displacement mechanism at the bottom of the meta-lens 2, so that the image of the plane to be measured on the camera photosensitive chip is clear; adjust the intensity of the white light source so that the camera can easily collect images with suitable grayscale values. Perform the required rigid body displacement measurement, and use the computer 3 to control the camera to collect images; perform DIC analysis and calculation on the collected images to calculate the corresponding displacement field and strain field.

[0090] Embodiment 4:

[0091] Embodiment 4 is a preferred example of Embodiment 1, and is used to illustrate the present invention in more detail.

[0092] A digital image correlation strain measurement system based on a metalens and a single digital camera comprises a metalens 2, a digital camera 4, an illumination light source 1 and a computer 3; the light source is used to provide illumination so that the camera can conveniently collect images with suitable grayscale values, and the light intensity is adjustable; the metalens 2 comprises four metalens 2 units, which are used to image the light scattered or emitted by the object on a photosensitive chip; the metalens 2 unit is composed of a substrate and a nanocolumn array covered on the substrate, so as to achieve the regulation of the phase of the incident light to realize the imaging function; the digital camera 4 is used to collect the image of the measured object formed by the metalens 2 units; the computer 3 is used to process the calibration and experimental image data collected by the digital camera 4, calculate the camera parameters through the calibration image, and then perform DIC calculation on the image to obtain the three-dimensional morphology, displacement and deformation data of the measured object.

[0093] When in use, spray the speckle on the surface of the tested object, and clamp the tested object at a fixed position by a carrier; set the camera and the meta-lens 2 at the same height by optical elements, and adjust the rotation mechanism to make the meta-lens 2 imaging system parallel to the tested surface by the pitch mechanism of the meta-lens 2 and the camera; adjust the positional relationship between the meta-lens 2 and the camera to make the image of the tested plane clear; place the meta-lens 2 measurement system in front of the tested object; adjust the image distance and object distance by adjusting the displacement mechanism at the bottom of the meta-lens 2 to make the image of the tested plane on the camera photosensitive chip clear; adjust the intensity of the white light source so that the camera can easily collect images with suitable grayscale values. Load the required measurement conditions, and use the computer 3 to control the camera to collect images; perform 3D-DIC calculation on the collected images to obtain the three-dimensional morphology, displacement and deformation data of the tested object.

[0094] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0095] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A digital image correlation strain measurement system based on metalens, characterized in that: include: Meta-lenses, digital cameras, lighting sources and computers; Wherein, the light intensity of the illumination light source can be adjusted; The meta-lens comprises a plurality of meta-lens units, which images the light scattered or emitted by the object, and the formed image is located on the plane where the photosensitive chip of the digital camera is located; The meta-lens unit is composed of a substrate and a nano-column array covering the substrate, which can adjust the phase of the incident light to achieve the imaging function; different phase compensations are designed for different situations; The meta-lens is designed as a phase modulation with a spherical aberration. A single micron-thick meta-lens can accurately refract and focus light incident from different directions onto the focal plane. The difference between the focal spot size and the diffraction limit of the meta-lens is smaller than the preset standard, and it has better imaging resolution at the same numerical aperture. The digital camera is used to collect the image of the object under test formed by the meta-lens; The computer is used to process calibration and experimental image data collected by the digital camera, calculate camera parameters through calibration images, perform three-dimensional digital image analysis and calculation on the experimental images, and obtain three-dimensional morphology, displacement and deformation data of the measured object; The light emitted by the illumination light source has the working wavelength when designing the meta-lens; or the illumination light source is a white light source, and a frequency band filter corresponding to the working wavelength is placed when using the white light source; or a white light source without a filter and ambient light that meets the light intensity requirement for imaging are directly used.

2. The digital image correlation strain measurement system based on metalens according to claim 1, characterized in that: In the metalens: The meta-lens comprises two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two meta-lens units can simultaneously image the object or area to be measured. The imaging areas of the two meta-lens units respectively cover the entire area to be measured.

3. The digital image correlation strain measurement system based on metalens according to claim 1, characterized in that: In the metalens: The meta-lens comprises more than two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of meta-lens units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of meta-lens units, the imaging areas of the two meta-lens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of meta-lens units covers the entire area to be measured.

4. The digital image correlation strain measurement system based on metalens according to claim 1, characterized in that: In the digital camera: The digital camera is a black and white camera or a color camera.

5. The digital image correlation strain measurement system based on metalens according to claim 1, characterized in that: In the meta-lens, different meta-lens units use different working wavelengths, but have the same focal length at different working wavelengths; The illumination light source used has the ability to emit light of the above working wavelength, or is a white light source.

6. A digital image correlation strain measurement method based on metalens, characterized in that: The digital image correlation strain measurement system based on a metalens according to any one of claims 1 to 5 is used to perform the following steps: Step S1: spraying speckles on the surface of the test piece and fixing the test piece according to the required measurement conditions; Step S2: adjusting the meta-lens and the digital camera to make each meta-lens unit image clear; Step S3: Perform the required measurement conditions and use a computer to control the camera to collect images; Step S4: photographing a calibration image and obtaining calibration parameters; Step S5: Separate the collected images and perform three-dimensional DIC analysis and calculation on the digital images.

7. The digital image correlation strain measurement method based on metalens according to claim 6, characterized in that: In the metalens: The meta-lens comprises two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two meta-lens units can simultaneously image the object or area to be measured. The imaging areas of the two meta-lens units respectively cover the entire area to be measured.

8. The digital image correlation strain measurement method based on metalens according to claim 6, characterized in that: In the metalens: The meta-lens comprises more than two meta-lens units, which are located in the same plane and have the same focal length. Within the designed working distance, there are multiple pairs of meta-lens units that can simultaneously image all or part of the object or area to be measured. In the multiple pairs of meta-lens units, the imaging areas of the two meta-lens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of meta-lens units covers the entire area to be measured.

9. The digital image correlation strain measurement method based on metalens according to claim 6, characterized in that: In the digital camera: The digital camera is a black and white camera or a color camera.

10. The digital image correlation strain measurement method based on metalens according to claim 6, characterized in that: In the meta-lens, different meta-lens units use different working wavelengths, but have the same focal length at different working wavelengths; The illumination light source used has the ability to emit light of the above working wavelength, or is a white light source.

Images