CN110068283A - A kind of digital speckle sensor-based system applied to face internal strain - Google Patents

Abstract

The invention relates to a digital speckle sensing system applied to in-plane strain, comprising a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, wherein the light source system includes two different wavelength laser light sources, It is used to emit different wavelength lasers to the detection sample on the electric loading device; the electric loading device is used to clamp the detection sample and can load the detection sample with pressure; the digital speckle interferometry system is used for detection when no pressure is loaded The reference speckle interference image of the sample and the test speckle interference image of the test sample when the pressure is loaded; the image acquisition system is used to obtain the reference speckle interference image and the test speckle interference image; The phase of the speckle interference image is obtained, and the in-plane strain information of the material is analyzed according to the phase. The invention does not need multiple CCDs to perform synchronous recording, and can greatly reduce the cost of the sensing system.

Description

A digital speckle sensing system for in-plane strain

technical field

The invention relates to the technical field of strain measurement, in particular to a digital speckle sensing system applied to in-plane strain.

Background technique

In order to eliminate the worries of amputees and help them return to normal lives, prostheses or total hip replacements need to be designed and fitted. For patients with lower extremity amputations and total joint replacement, there are still various difficulties in improving the performance of the prosthesis. Currently, the most important issue is the adaptation of the biointerfacial interaction forces between harder metals and softer bone surfaces. When a dynamic load is applied to such a structure, the structure not only has out-of-plane stress, but also may appear instantaneously sharp in-plane high strain force, which is very important for biological or biomimetic structural materials with low yield strength. very dangerous. The determination of the dynamic strain distribution at the biomaterial interface and the assessment of the potential pressure mismatch at the interface are critical to avoid loosening, misalignment, and potential infection of interface gaps. Although the current CAD software and finite element analysis play an important role in the estimation of strain, the establishment of these models requires the correct boundary conditions (constraints) and mechanical parameters of the material to be known in advance and verified by accurate measurements. Therefore, it is important to measure the strain induced by transient loads at the bone-implant interface. Bone is an anisotropic and heterogeneous biological material. In addition to the evaluation of out-of-plane stress at the material interface, the measurement of in-plane tension at the microscopic level is also crucial for understanding the biomechanical properties between bone and implants. However, in the existing strain testing methods, it is difficult to accurately identify and measure various strains caused by dynamic loads on bioactive materials. Especially due to the influence of unstructured test environment factors during the test process, so far, no ideal in-plane strain measurement sensing system can meet this detection requirement.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a digital speckle sensing system applied to the in-plane strain, which can realize convenient, accurate and rapid detection of the in-plane strain of the detected object.

The technical solution adopted by the present invention to solve the technical problem is to provide a digital speckle sensing system applied to in-plane strain, including a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, so The light source system includes two different wavelength laser light sources, which are used to emit different wavelength lasers to the detection sample on the electric loading device; the electric loading device is used to clamp the detection sample and can load pressure on the detection sample; The speckle interference system is used for generating a reference speckle interference image of the detection sample when no pressure is loaded and a test speckle interference image of the detection sample when the pressure is loaded; the image acquisition system is used for acquiring the reference speckle interference image and the test speckle interference image ; The computer calculates the phases of the two speckle interference images respectively through the spectrum separation technology, and resolves the in-plane strain information of the material according to the phases.

The digital speckle interference system includes an aperture diaphragm, an imaging lens, a half mirror and a half mirror, a first adjustable mirror and a second adjustable mirror; the diffuse reflection light on the surface of the detection sample is sequentially aperture diaphragm, imaging lens and a half mirror half mirror, the two sides of the half mirror half mirror are provided with a first adjustable mirror and a second adjustable mirror to form an interference system; the diffuse reflection light on the surface of the detection sample can be adjusted through the tilt angle respectively. After being reflected by the first reflecting mirror and the second reflecting mirror, they are sheared by the interference system, and the sheared interference images in both directions are simultaneously recorded in the same image acquisition system.

The computer calculates the phase of the two speckle interference images by using the different wavelengths of the two different wavelength laser sources and the different positions of the spectrograms of the speckle interference images sheared in the two directions. information, and perform complex operation to extract the phase information of the two shearing directions.

When the computer extracts the phase information of the two shearing directions, it is specifically: if the shearing direction is along the x-axis direction, then the expressions of the measured wavefronts in the k ₁ and k ₂ directions are recorded as: Among them, u ₁₁ and u ₁₂ are the wave fronts in the sensitive direction k1 passing through the first adjustable mirror and the second adjustable mirror, respectively, and u ₂₁ and u ₂₂ are the wave fronts passing through the first adjustable mirror and the second adjustable mirror respectively. Two wavefronts on the tunable mirror in the sensitive direction k ₂ ; and is the phase _of the wavefront, while f1 and f2 are _two different spatial frequencies produced by shearing, expressed as: λ ₁ and λ ₂ are the wavelengths of two different-wavelength laser light sources, and β is the tilt angle of the second tunable mirror, then the obtained speckle interference image I is expressed as: I=(u ₁₁ u ₁₁ ^* +u ₁₂ u ₁₂ ^* )+(u ₂₁ u ₂₁ ^* +u ₂₂ u ₂₂ ^* )+(u ₁₁ u ₁₂ ^* +u ₁₂ u ₁₁ ^* )+(u ₂₁ u ₂₂ ^* +u ₂₂ u ₂₁ ^* ), where u ₁₁ ^* , u ₁₂ ^* , u ₂₁ ^* , u ₂₂ ^* are the wavefront conjugate terms of u ₁₁ , u ₁₂ , u ₂₁ , and u ₂₂ in the sensitive directions k ₁ and k ₂ respectively, which are obtained by Fourier transform in, Represents the convolution operation, let: U ₁₁ (f _x , f _y ) = FT(u ₁₁ ), U ₁₂ (f _x +f ₁ , f _y ) = FT(u ₁₂ ), U ₂₁ (f _x , f _y ) )=FT(u ₂₁ ), U ₂₂ (f _x +f ₂ ,f _y )=FT(u ₂₂ ), the Fourier spectrogram distribution of the recorded speckle image is obtained, in which 8 terms are divided into 5 parts , where (U ₁₁ +U ₁₁ ^* +U ₁₂ +U ₁₂ ^* ) and (U ₂₁ +U ₂₁ ^* +U ₂₂ +U ₂₂ ^* ) are low-frequency terms, occupying the center of the frequency domain respectively, and their widths are respectively are 2f _c1 and 2f _c2 ; (U ₁₂ +U ₁₁ ^* ) is located at the center of (f ₁ ,0), and (U ₁₁ +U ₁₂ ^* ) is located at the center of (-f ₁ ,0), they are in the spectrum The widths in are 2f _c1 , these two items contain the phase information sheared in the k ₁ direction; the (U ₂₂ +U ₂₁ ^* ) item is positioned at (f ₂ ,0) as the center, and the (U ₂₁ +U ₂₂ ^{* )} ) are located at (-f ₂ ,0), and their widths in the spectrum are both 2f _c2 , and these two terms record the phase information clipped in the k ₂ direction; where f _c1 and f _c2 are Slit size control, in the spectral regions (f ₁ ,0) and (f ₂ ,0), by applying the windowed inverse Fourier transform, the phase distribution is calculated using the complex amplitude, which is calculated as: where Im and Re represent the real and imaginary parts of the complex number, respectively, and φ ₁ and φ ₂ are the phase differences of the two oblique beams, respectively; after loading the sample for deformation, the same method can be used to obtain

The computer analyzes the in-plane strain information of the material according to the phase. Specifically, the phase distribution diagrams reflecting the out-of-plane strain in the two illumination directions are obtained by subtracting the phases before and after the deformation, and through the out-of-plane strain phase information in the two directions, Calculate the in-plane strain information of the inspection surface.

beneficial effect

Due to adopting the above-mentioned technical scheme, the present invention has the following advantages and positive effects compared with the prior art:

The present invention provides a simpler and faster method for measuring in-plane strain induced by dynamic loading. The traditional complex in-plane strain detection method to detect the strain process needs to capture 16 frames of time phase shift images and change the lens switch 4 times. However, with the spatial phase shift shearing system proposed now, the entire detection process is simplified to only need to acquire two frame interference images. Especially in the detection process, only one frame of image is needed to calculate the relative phase change after its deformation. Since the detection speed of the entire measurement system is only limited by the CCD frame rate, the current frame rate of advanced CCD cameras can reach 15,000 frames/second, which makes the proposed new sensor system ideal for those requiring dozens of microstrain levels. High sensitivity dynamic strain testing.

In addition, the current spatially phase-shifted digital shearing system for in-plane strain measurement is generally realized through dual information channels and dual beams. However, the inventor of the present application found in experiments that by using laser illumination with different wavelengths, the positions of the two sheared speckle spectra obtained on the frequency domain image will be different. Therefore, the laser speckle interferometry system of different wavelengths and dual light sources in the present application can realize the simultaneous recording of two shear speckle patterns by a single channel, and it is possible to realize the separation of the two shear spectrograms by selecting appropriate system parameters. Since the entire sensing system only needs one CCD camera for image recording, not only can the system cost be greatly reduced, but the measurement process can also be made simpler, since pixel registration and pixel registration of images from multiple channels are no longer required Sync trigger recording, etc.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the flow chart of in-plane strain detection in the present invention;

3 is a schematic diagram of the speckle interference spectrum recorded by the interference system in the present invention;

In the figure: the first laser 1, the second laser 2, the first beam expander 3, the second beam expander 4, the aperture stop 5, the imaging lens 6, the half mirror half mirror 7, the first adjustable mirror 8, The second adjustable mirror 9 , the loading bracket 10 , the voice coil motor 11 , the CCD camera 12 , the display 13 , the computer 14 , and the test sample 15 .

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Embodiments of the present invention relate to a digital speckle sensing system applied to in-plane strain, including a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, wherein the light source system includes two different wavelengths The laser light source is used to emit different wavelength lasers to the detection sample on the electric loading device; the electric loading device is used to clamp the detection sample and can load the detection sample with pressure; the digital speckle interferometry system is used to generate unloaded The reference speckle interference image of the detection sample under pressure and the test speckle interference image of the detection sample when the pressure is loaded; the image acquisition system is used to obtain the reference speckle interference image and the test speckle interference image; the computer adopts the spectrum separation technology Calculate the phase of the two speckle interference images respectively, and resolve the in-plane strain information of the material according to the phase.

During the detection process, two different wavelength lasers project laser light and irradiate the surface of the object at the same time, and generate two frames of speckle interferogram in the improved Michelson interferometry system, which are simultaneously recorded to the same CCD imaging array through different channels Then, through the spectrum separation technology, the phase of the speckle interferogram in the two shear directions is calculated respectively, and finally the in-plane strain information of the material is analyzed.

As shown in FIG. 1, the light source system includes a different wavelength laser 1, a laser 2, a beam expander 3 and a beam expander 4; the digital speckle interference system is an improved Michelson speckle interference device, which mainly includes aperture light A stop 5, an imaging lens 6, a half mirror half mirror 7, an adjustable mirror 8 and an adjustable mirror 9, the image acquisition system includes a CCD camera 12 and other devices, the electric loading system includes a loading bracket 10, a voice coil motor 11 and so on.

The electric loading system is used to realize the installation and loading of the detection sample 15; the digital speckle interference system and the image acquisition system are placed in front of the detection area of the detection sample 15; the two different wavelength laser light sources 1 and 2 The laser beam is projected, and after being expanded by the beam expander 3 and the beam expander 4 respectively, it is irradiated to the surface of the detection sample 15 at the same time; the diffuse reflection beam on the surface of the detection sample 15 passes through the aperture diaphragm 5, the imaging lens 6, the half mirror The lens 7, the adjustable mirror 8 and the adjustable mirror 9 finally form shearing speckles and image them on the front surface of the CCD camera 12, and the CCD camera 12 performs image acquisition control through the computer 14; the CCD imaging front 12 Acquire a speckle image, perform spectrum separation and complex number operation by the computer 14, respectively calculate the phase of the sheared speckle images in two directions, and finally analyze the in-plane strain of the material. The two lasers illuminate the object to be detected, respectively, and the reflected light is reflected by the adjustable mirror 8 and the adjustable mirror 9 with adjustable tilt angle, and then sheared by the Michelson interference device, and the sheared interference images in two directions. Simultaneously recorded into the image sensor.

This embodiment can use the following equipment:

(1) Computer: The model is Advantech IPC-610L-701VG, the processor is inter i5-2400, supports JPEG hardware codec, and the memory is 4Gbits DDR3. Support RGB 24Bit interface and TVOUT video output;

(2) Display: model Samsung C27F390FHC, resolution 1920*1080;

(3) Laser light source 1: wavelength 532nm, 200mw solid-state laser, single longitudinal mode;

(4) Laser light source 2: wavelength 632nm, 200mw solid-state laser, single longitudinal mode;

(5) Beam expander 3: f=16mm, φ=20.4mm;

(6) Beam expander 4: f=16mm, φ=20.4mm;

(7) Aperture diaphragm 5: electric adjustable aperture diaphragm HGEMD52, aperture change 3-52mm;

(8) CCD camera 12: Basler acA2400-50gm area array CCD, 2048*1536 pixels, imaging area size of 3626μm x 2709μm, pixel size of 1.75μm x 1.75μm, maximum speed up to 50 frames per second;

(9) Imaging lens 6: brand Daheng, Φ25.4K9 biconvex lens, f=100mm, clear aperture: 90%;

(10) Semi-reflective semi-mirror 7: Brand Daheng, GCC-4011 series broadband beamsplitter prism, transmittance/reflectivity: 50/50; material K9; dimension: 25.4mm*25.4mm*25.4mm;

(11) Voice coil motor 11: SMAC voice coil motor LAL series, rated power 10-50 (kW), rated voltage 24-48 (V), stroke 15mm, displacement resolution 5μm;

(12) Reflectors 8 and 9, loading bracket 10, and the like.

As shown in Figure 2, the described in-plane strain detection process is as follows: the CCD imaging front obtains the speckle interference images I ₁ and I ₂ before and after deformation respectively, and performs Fourier transform (FFT) respectively to obtain the images before loading. and the loaded spectrum images F(I ₁ ) and F(I ₂ ); because the wavelengths of the two laser light sources are different, the positions of the speckle images obtained by them are also different (as shown in Figure 3). Perform windowing (WIFT) and complex number operations on the frequency spectrum bands of the fixed neighborhood of frequencies f ₁ and f ₂ before and after deformation, and obtain phase information φ ₁ , φ ₂ , and φ in two illumination directions before and after deformation in turn ₁ ', φ ₂ '; phase distribution diagrams △ ₁ and △ ₂ reflecting out-of-plane strain in _two illumination directions are obtained by phase subtraction _; The in-plane strain information of the inspection surface is obtained.

It can be seen that, in this embodiment, the phase evaluation of the sheared speckle patterns of the two laser light sources is realized by performing spectral separation and correlation operation on the speckle interference images simultaneously recorded in the same image sensor. Using the different wavelengths of the two laser light sources, the positions of the spectrograms of the sheared speckle interference images in the two directions are also different. By intercepting the window spectral information at different positions, and performing complex operations, the phase information of the two shearing directions can be extracted. . details as follows:

If the shearing direction is along the x-axis, the expressions of the measured wavefront in the k ₁ and k ₂ directions can be written as:

u ₁₁ and u ₁₂ are the wavefronts in the sensitive direction k1 through the adjustable mirror 8 and the adjustable mirror 9 respectively, while u ₂₁ and u ₂₂ are the wave fronts in the sensitive direction through the adjustable mirror 8 and the adjustable mirror 9 respectively. The wavefront of k ₂ ; and is the phase of the wavefront, while f ₁ and f ₂ are two different spatial frequencies produced by shearing and can be expressed as:

f ₁ =(sinβ/λ ₁ ) (5)

f ₂ =(sinβ/λ ₂ ) (6)

λ ₁ and λ ₂ are the wavelengths of the two light sources, respectively, and β is the tilt angle of the tunable mirror 9; therefore, the speckle image I recorded on the CCD can be expressed as:

I=(u ₁₁ +u ₁₂ )(u ₁₁ ^* +u ₁₂ ^* )+(u ₂₁ +u ₂₂ )(u ₂₁ ^* +u ₂₂ ^* )

=(u ₁₁ u ₁₁ ^* +u ₁₂ u ₁₂ ^* +u ₁₁ u ₁₂ ^* +u ₁₂ u ₁₁ ^* )+(u ₂₁ u ₂₁ ^* +u ₂₂ u ₂₂ ^* )(u ₂₁ u ₂₂ ^* +u ₂₂ u ₂₁ ^* )

=(u ₁₁ u ₁₁ ^* +u ₁₂ u ₁₂ ^* )+(u ₂₁ u ₂₁ ^* +u ₂₂ u ₂₂ ^* )+(u ₁₁ u ₁₂ ^* +u ₁₂ u ₁₁ ^* )+(u ₂₁ u ₂₂ ^* + u ₂₂ u ₂₁ ^* ) (7)

By Fourier transform, we can get:

in Represents the convolution operation, let: U ₁₁ (f _x , f _y ) = FT(u ₁₁ ), U ₁₂ (f _x +f ₁ , f _y ) = FT(u ₁₂ ), U ₂₁ (f _x , f _y ) )=FT(u ₂₁ ), U ₂₂ (f _x +f ₂ , f _y )=FT(u ₂₂ ), then FIG. 3 shows the Fourier spectrogram distribution of the speckle image recorded under ideal conditions.

In the Fourier domain, there are 6 spectral segments corresponding to the 8 sub-terms in the above equation. As you can see from the spectrogram, these 8 terms can be divided into 5 parts. Among them, the terms (U ₁₁ +U ₁₁ ^* +U ₁₂ +U ₁₂ ^* ) and (U ₂₁ +U ₂₁ ^* +U ₂₂ +U ₂₂ ^* ) are low-frequency terms, mainly background light, which occupy the center of the frequency domain respectively , whose widths are 2f _c1 and 2f _c2 , respectively. (U ₁₂ +U ₁₁ ^* ) is located at the center of (f ₁ ,0), and (U ₁₁ +U ₁₂ ^* ) is located at the center of (-f ₁ ,0), both of which have a width of 2f _c1 in the spectrum , these two terms contain the phase information of the shearing in the k ₁ direction. The (U ₂₂ +U ₂₁ ^* ) term is positioned at (f ₂ ,0) as the center, and the (U ₂₁ +U ₂₂ ^* ) is positioned at (-f ₂ ,0), both of which have a width of 2f _c2 in the spectrum, These two terms record phase information clipped in the _k direction. Among them, f _c1 and f _c2 can be controlled by choosing the appropriate slit size. In the spectral regions (f ₁ ,0) and (f ₂ ,0), by applying the Windowed Inverse Fourier Transform (WIFT), the phase distribution can be calculated using the complex amplitude. Its calculation formula is as follows:

[φ ₁ +2πxf ₁ ]=arctan{Im[u ₁₂ u ₁₁ *]/Re[u ₁₂ u ₁₁ *]} (9)

[φ ₂ +2πxf ₂ ]=arctan{Im[u ₂₂ u ₂₁ *]/Re[u ₂₂ u ₂₁ *]} (10)

where Im and Re represent the real and imaginary parts of the complex number, respectively, and _φ1 and φ2 are the phase differences of the _two oblique beams, respectively, After loading the sample deformation, by using the same method we can get:

[φ ₁ ′+2πxf ₁ ]=arctan{Im[u ₁₂ u ₁₁ ^* ]/Re[u ₁₂ u ₁₁ ^* ]} (11)

[φ ₂ ′+2πxf ₂ ]=arctan{Im[u ₂₂ u ₁₁ ^* ]/Re[u ₂₂ u ₂₁ ^* ]} (12)

Therefore, the relative phase difference caused by deformation can be calculated by the following formulas:

Δ ₁ =φ ₁ ′-φ ₁ (13)

Δ ₂ =φ ₂ ′-φ ₂ (14)

Thereby, the phase distribution diagrams △ ₁ and △ ₂ reflecting the out-of-plane strain information are obtained.

The calculation of the in-plane strain of the biomaterial is obtained by calculating the phase information Δ ₁ and Δ ₂ of the out-of-plane strain in two directions, and the calculation process is as follows:

Based on the relationship between the phase difference and the in-plane strain, we can get:

Combine and simplify to get:

Similarly, the in-plane strain components in other directions can be expressed in the same way as:

Thus, the in-plane strain information of the detection surface is finally obtained.

The invention can be applied to the in-plane strain detection of biological materials, so as to facilitate the detection of potential stress mismatch, uneven distribution of pressure or stress on the contact interface of the prosthesis, etc. The stress distribution and matching of the bone-implant interface provide the most direct information for patient diagnosis, treatment and recovery.

Claims (5)

1. A digital speckle sensing system applied to in-plane strain comprises a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, and is characterized in that the light source system comprises two different-wavelength laser light sources which are used for emitting different-wavelength laser to a detection sample on the electric loading device; the electric loading device is used for clamping a detection sample and loading pressure to the detection sample; the digital speckle interference system is used for generating a reference speckle interference image of a detection sample when pressure is not loaded and a test speckle interference image of the detection sample when pressure is loaded; the image acquisition system is used for acquiring a reference speckle interference image and a test speckle interference image; the computer respectively calculates the phases of the two speckle interference images through a frequency spectrum separation technology, and analyzes strain information in the material surface according to the phases.

2. The digital speckle sensing system applied to in-plane strain of claim 1, wherein the digital speckle interference system comprises an aperture stop, an imaging lens, a semi-reflective semi-transparent mirror, a first adjustable mirror and a second adjustable mirror; the diffuse reflection light on the surface of the detection sample sequentially comprises an aperture diaphragm, an imaging lens and a semi-reflecting and semi-transmitting lens, and a first adjustable reflective mirror and a second adjustable reflective mirror are arranged on two sides of the semi-reflecting and semi-transmitting lens to form an interference system; and after the diffuse reflection light on the surface of the detection sample is reflected by the first reflector and the second reflector with adjustable inclination angles, the diffuse reflection light is sheared by the interference system, and sheared interference images in two directions are recorded in the same image acquisition system at the same time.

3. The digital speckle sensing system applied to in-plane strain according to claim 1, wherein the computer extracts the phase information of the two shearing directions by intercepting the window spectrum information of different positions and performing complex operation by using the characteristics that the two different wavelength laser sources have different wavelengths and the positions of the spectral patterns shearing the speckle interference images in the two directions are different when calculating the phases of the two speckle interference images.

4. The digital speckle sensing system applied to in-plane strain according to claim 3, wherein the computer extracts the phase information of two shearing directions specifically as follows: if the shear direction is along the x-axis, then the measured wavefront is at k₁And k is₂The expression in direction is noted as:wherein, therein，u₁₁、u₁₂Is the wavefront, u, through the first and second adjustable mirrors in the sensitive direction k1, respectively₂₁And u₂₂Respectively passing through the first adjustable reflector and the second adjustable reflector in the sensitive direction k₂The wavefront of (a);andis the phase of the wavefront, and f₁And f₂Then two different spatial frequencies are generated by clipping, denoted as:λ₁and λ₂The obtained speckle interference image I is expressed as I ═ u (u) by the wavelength of the two different-wavelength laser light sources and the inclination angle of the second adjustable reflector β₁₁u₁₁ ^*+u₁₂u₁₂ ^*)+(u₂₁u₂₁ ^*+u₂₂u₂₂ ^*)+(u₁₁u₁₂ ^*+u₁₂u₁₁ ^*)+(u₂₁u₂₂ ^*+u₂₂u₂₁ ^*) Wherein u is₁₁ ^*、u₁₂ ^*、u₂₁ ^*、u₂₂ ^*Are each u₁₁、u₁₂、u₂₁、u₂₂In the sensitive direction k₁And k is₂The wave front conjugate term of (2) is obtained by Fourier transformWherein,representing a convolution operation, let: u shape₁₁(f_x,f_y)＝FT(u₁₁)，U₁₂(f_x+f₁,f_y)＝FT(u₁₂)，U₂₁(f_x,f_y)＝FT(u₂₁)，U₂₂(f_x+f₂,f_y)＝FT(u₂₂) A fourier spectrogram distribution in which speckle images are recorded is obtained, wherein the 8 terms are divided into 5 parts, wherein (U)₁₁+U₁₁ ^*+U₁₂+U₁₂ ^*) And (U)₂₁+U₂₁ ^*+U₂₂+U₂₂ ^*) The terms are low-frequency terms, respectively occupying the center of the frequency domain and having a width of 2f_c1And 2f_c2；(U₁₂+U₁₁ ^*) Is positioned at (f)₁0) is central, and (U)₁₁+U₁₂ ^*) Is positioned at (-f)₁0) as centers, they are all 2f wide in the frequency spectrum_c1The two terms comprise k₁Phase information of direction shearing; (U)₂₂+U₂₁ ^*) The item is located at (f)₂0) is central, and (U)₂₁+U₂₂ ^*) Is positioned at (-f)₂0), their widths in the spectrum are all 2f_c2The two items are recorded at k₂Phase information of the directional shear; wherein f is_c1And f_c2By selecting appropriate slit size control, in the spectral region (f)₁0) and (f)₂0), by applying a windowed inverse fourier transform, the phase distribution is calculated using the complex amplitude, which is calculated by the formula:where Im and Re represent the real and imaginary parts of the complex number, respectively, and phi₁And phi₂The phase difference of the two oblique beams respectively; after deformation of the loaded sample, it can be obtained by using the same method

5. The digital speckle sensing system applied to in-plane strain according to claim 1, wherein the computer analyzes the strain information in the material plane according to the phase specifically as follows: and subtracting the phase before and after deformation to obtain a phase distribution diagram reflecting the out-of-plane strain in the two illumination directions, and calculating the in-plane strain information of the detection surface according to the out-of-plane strain phase information in the two directions.