Digital image correlation strain measurement system and method based on superlens

Abstract

The application provides a kind of digital image correlation strain measurement system and method based on super lens, comprising: super lens, digital camera, illumination light source and computer;The super lens contains a plurality of super lens units, the light scattered or emitted by object is imaged, and the image formed is located in the plane where the digital camera photosensitive chip is located;The digital camera is used to collect the image of the measured object formed by the super lens;The computer is used to process the calibration and experimental image data collected by the digital camera, 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 topography, displacement and deformation data of the measured object;The application can realize 3D-DIC measurement by single shooting of one camera, uses super lens to replace traditional lens, so that it can obtain simpler and more compact optical structure under the premise of maintaining imaging quality, and has the characteristics of high efficiency and no camera synchronization.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photomechanics, in particular, to a digital image correlation strain measurement system and method based on a superlens. BACKGROUND

[0002] At present, the strain measurement of the surface of an object can be divided into contact measurement and non-contact measurement. Among them, the non-contact measurement has the advantages of no influence on the measured object, no contact interference, wide practicality, easy real-time operation, high measurement accuracy, etc., and is concerned, and the non-contact strain measurement is mainly based on optical measurement methods, including laser speckle method, digital volume correlation and digital image correlation, etc.

[0003] Among them, the digital image correlation measures the surface images of the object in a short time interval by continuous shooting, calculates the displacement between the images according to the cross-correlation algorithm, and obtains the displacement and strain of the surface of the object, which is widely used in the field of optical strain measurement. The three-dimensional digital image correlation method (3D-DIC) uses two or more cameras for measurement, and can extract the three-dimensional topography, displacement and strain information of the surface of the sample, but due to the need to use multiple cameras and the need for camera calibration, synchronization and other processes, the system complexity and use difficulty of this method are relatively high, therefore researchers begin to study the method of using single camera for 3D-DIC. Han et al. proposed a single camera 3D-DIC system based on fiber bundle (FB), which transmits images through fiber bundle, compared with traditional 3D-DIC, which does not need to be strictly synchronized; At the same time, a positioning and correction method combining 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 diffraction grating, which can reduce the overall size while measuring the deformation of small scale objects. Wu et al. proposed a 3D-DIC technology using a single camera and a double prism, which reduces the demand for cameras while maintaining a certain measurement accuracy by placing a double prism between the camera and the sample. The above methods have solved the problem of the demand for multiple cameras and the difficulty of synchronization control of multiple cameras to a certain extent. However, the above methods all have a deficiency, that is, while reducing the number of cameras, additional optical elements 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 redundant optical elements. Correspondingly, it also reduces the time for camera calibration and synchronization, greatly increases shooting efficiency, and can more conveniently and effectively complete high-precision three-dimensional measurement. 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] According to the present invention, a digital image correlation strain measurement system based on a metalens is provided, comprising:

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

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

[0009] The meta-lens comprises a plurality of meta-lens units, which form an image of light scattered or emitted by an 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 consists of a substrate and a nano-pillar array covering the substrate, which can control the phase of the incident light to achieve imaging function; different phase compensation is designed for different situations;

[0011] The meta-lens is designed as a spherical aberration-free phase modulation. Using a single micron-thick meta-lens, light incident from different directions can be accurately refracted and focused onto the focal plane. The focal spot size of the meta-lens is close to the diffraction limit, achieving 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 shape, displacement and deformation data of the object under test;

[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 when using a white light source, a frequency band filter corresponding to the working wavelength is placed; or a white light source without a filter is directly used and ambient light that meets the light intensity requirements for imaging is used.

[0015] Preferably, in the metalens:

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

[0017] Preferably, in the metalens:

[0018] The metalens includes two or more metalens units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens units are capable of simultaneously imaging all or part of an object or area to be measured. In the multiple pairs of metalens units, the imaging areas of the two metalens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 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 operating wavelengths, but have the same focal length at different operating wavelengths;

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

[0023] According to the present invention, a digital image correlation strain measurement method based on a metalens is provided, which uses the digital image correlation strain measurement system based on a metalens and performs 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: Adjust 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 capture images;

[0027] Step S4: Capture the calibration image and obtain 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 metalens:

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

[0031] Preferably, in the metalens:

[0032] The metalens includes two or more metalens units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens units are capable of simultaneously imaging all or part of an object or area to be measured. In the multiple pairs of metalens units, the imaging areas of the two metalens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 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 operating wavelengths, but have the same focal length at different operating wavelengths;

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

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

[0038] 1. This invention achieves 3D-DIC measurement with a single camera shot. By replacing traditional lenses with meta-lenses, the method achieves a simpler and more compact optical structure while maintaining imaging quality. It boasts high efficiency and eliminates the need for camera synchronization. The meta-lens is designed as a phase-modulated lens with a spherical aberration. Using a single, micron-thick meta-lens, it accurately refracts and focuses incident light from different directions onto the focal plane. Furthermore, the focal spot size of the meta-lens approaches the diffraction limit, resulting in improved imaging resolution at the same numerical aperture.

[0039] 2. This invention achieves single-camera 3D imaging through binocular / multi-camera metalenses. Furthermore, the depth of field and field of view of DIC measurements can be optimized by designing metalenses with different focal lengths and apertures. Compared to traditional binocular 3D-DIC, multi-camera 3D-DIC provides more perspective information for the same feature and reduces the impact of occlusion, enabling more accurate calculation of parallax relationships and, consequently, deformation and displacement in three dimensions.

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

[0041] 4. Thanks to the new optical structure of the system, the present invention can achieve 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 upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

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

[0044] Figure 2 Schematic diagram of the binocular meta-lens according to Example 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 will be described in detail below with reference to specific embodiments. The following examples 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 skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0048] Example 1:

[0049] This invention discloses a digital image correlation strain measurement system and method based on a metalens and a single digital camera. The method comprises the following steps: first, using a metalens 2 as the primary optical element and integrating it with a digital camera 4 to form an image capture system; then, capturing images of the surface of a deformed object exhibiting speckle; and finally, applying a traditional digital image correlation algorithm based on the captured images to determine the three-dimensional displacement and strain of the measured object. By replacing traditional optical lenses with a metalens 2, the present invention boasts a compact structure and easily adjustable system parameters, enabling more convenient and efficient high-precision three-dimensional measurement for experiments on three-dimensional topography and deformation in specialized applications such as microscopy and high-speed imaging.

[0050] According to the present invention, a digital image correlation strain measurement method based on a metalens 2 is provided, which uses the digital image correlation strain measurement system based on a metalens 2 and performs 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: Adjust the meta-lens 2 and the digital camera 4 to make the image of each meta-lens 2 unit clear;

[0053] Step S3: performing the required measurement load and using the computer 3 to control the camera to capture images;

[0054] Step S4: Capture the calibration image and obtain 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 metalens 2:

[0057] The metalens 2 includes 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 each cover the entire area to be measured.

[0058] The MetaLens 2 is designed as a phase modulation lens with a spherical aberration. Using a single, micron-thick, two-dimensional MetaLens 2, incident light from all directions can be accurately refracted and focused onto the focal plane. The focal spot size of the MetaLens 2 approaches the diffraction limit, resulting in better imaging resolution at the same numerical aperture.

[0059] Specifically, in the metalens 2:

[0060] The metalens 2 includes two or more metalens 2 units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens 2 units are capable of simultaneously imaging all or part of an 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 operating wavelengths, but have the same focal length at different operating wavelengths;

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

[0065] Example 2:

[0066] Example 2 is a preferred example of Example 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 embodiment of the digital image correlation strain measurement system based on a metalens.

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

[0069] Metalens 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 image is located on the plane where the photosensitive chip of the digital camera 4 is located;

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

[0073] The digital camera 4 is used to capture the image of the object being measured 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, and perform three-dimensional digital image analysis and calculation on the experimental image to obtain the three-dimensional shape, displacement and deformation data of the object under test;

[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 when using a white light source, a frequency band filter corresponding to the working wavelength is placed; or a white light source without a filter and ambient light that meets the light intensity requirements for imaging are directly used.

[0076] Specifically, in the metalens 2:

[0077] The metalens 2 includes 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 each cover the entire area to be measured.

[0078] The MetaLens 2 is designed as a phase modulation lens with a spherical aberration. Using a single, micron-thick, two-dimensional MetaLens 2, incident light from all directions can be accurately refracted and focused onto the focal plane. The focal spot size of the MetaLens 2 approaches the diffraction limit, resulting in better imaging resolution at the same numerical aperture.

[0079] Specifically, in the metalens 2:

[0080] The metalens 2 includes two or more metalens 2 units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens 2 units are capable of simultaneously imaging all or part of an 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 operating wavelengths, but have the same focal length at different operating wavelengths;

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

[0085] Example 3:

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

[0087] This patent proposes a digital image correlation strain measurement method based on a metalens. Taking into account the imaging characteristics of metalenses, this method uses a cross-correlation algorithm to calculate the displacement field after obtaining a speckle image. This displacement field is then used to calculate the surface strain field. This method addresses the core issues of single-camera strain measurement and promotes 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 capture 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 can control 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] During use, a speckle pattern is sprayed onto the surface of the test piece and the test piece is fixed according to the desired measurement conditions. Optical components are used to set the camera and metalens 2 at the same height. The pitch mechanism ensures parallelism between the metalens 2 and the camera, and the rotation mechanism is adjusted to parallelize the metalens 2 imaging system with the surface to be measured. The metalens 2 measurement system is placed in front of the test piece. The image distance and object distance are adjusted by adjusting the displacement mechanism at the bottom of the metalens 2 to ensure a clear image of the surface to be measured on the camera's photosensitive chip. The intensity of the white light source is adjusted to ensure the camera can easily capture images with appropriate grayscale values. The desired rigid body displacement is measured, and computer 3 is used to control the camera to capture images. DIC analysis is performed on the captured images to calculate the corresponding displacement and strain fields.

[0090] Example 4:

[0091] Example 4 is a preferred example of Example 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 includes 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 easily capture images with suitable grayscale values, and the light intensity is adjustable. The metalens 2 includes four metalens 2 units, which are used to image light scattered or emitted by an object on a photosensitive chip. The metalens 2 units are composed of a substrate and a nanopillar array covering the substrate, which can control the phase of the incident light to achieve the imaging function. The digital camera 4 is used to capture the image of the object under test 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 images, and then perform DIC calculations on the images to obtain the three-dimensional morphology, displacement, and deformation data of the object under test.

[0093] During use, a speckle pattern is sprayed on the surface of the test object, and the test object is clamped in a fixed position by a carrier. Optical elements are used to set the camera and metalens 2 at the same height. The pitch mechanism ensures parallelism between the metalens 2 and the camera, and the rotation mechanism is adjusted to parallelize the metalens 2 imaging system with the test surface. The positional relationship between the metalens 2 and the camera is adjusted to ensure a clear image of the test surface. The metalens 2 measurement system is placed in front of the test object. The image distance and object distance are adjusted by adjusting the displacement mechanism at the bottom of the metalens 2 to ensure a clear image of the test surface on the camera's photosensitive chip. The intensity of the white light source is adjusted to ensure the camera can easily capture images with appropriate grayscale values. The required measurement conditions are loaded, and the camera is controlled by a computer 3 to capture images. 3D-DIC calculations are performed on the captured images to obtain the three-dimensional shape, displacement, and deformation data of the test object.

[0094] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention 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 a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0095] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

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 form an image of light scattered or emitted by an object, and the formed image is located on the plane where the photosensitive chip of the digital camera is located; The meta-lens unit consists of a substrate and a nano-pillar array covering the substrate, which can control the phase of the incident light to achieve imaging function; different phase compensation is designed for different situations; The metalens is designed as a spherical aberration-free phase modulation lens. Using a single, micron-thick metalens, it accurately refracts and focuses incident light from all directions onto the focal plane. The difference between the focal spot size and the diffraction limit is smaller than the preset standard, resulting in 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 shape, displacement and deformation data of the object under test; 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 when using a white light source, a frequency band filter corresponding to the working wavelength is placed; or a white light source without a filter is directly used and ambient light that meets the light intensity requirements for imaging is used.

2. The digital image correlation strain measurement system based on metalens according to claim 1, characterized in that: In the metalens: The metalens includes two metalens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two metalens units can simultaneously image the object or area to be measured. The imaging areas of the two metalens units each 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 metalens includes two or more metalens units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens units are capable of simultaneously imaging all or part of an object or area to be measured. In the multiple pairs of metalens units, the imaging areas of the two metalens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 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 a metalens according to claim 1, characterized in that: In the metalens, different metalens units use different operating wavelengths, but have the same focal length at different operating wavelengths; The lighting source used has the ability to emit light of the above-mentioned 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: Adjust 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 capture images; Step S4: Capture the calibration image and obtain 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 metalens includes two metalens units, which are located in the same plane and have the same focal length. Within the designed working distance, the two metalens units can simultaneously image the object or area to be measured. The imaging areas of the two metalens units each 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 metalens includes two or more metalens units, which are located in the same plane and have the same focal length. Within a designed working distance, multiple pairs of metalens units are capable of simultaneously imaging all or part of an object or area to be measured. In the multiple pairs of metalens units, the imaging areas of the two metalens units in each pair include the same area to be measured. The sum of the imaging areas of the multiple pairs of metalens 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 metalens, different metalens units use different operating wavelengths, but have the same focal length at different operating wavelengths; The lighting source used has the ability to emit light of the above-mentioned working wavelength, or is a white light source.

Images