Thermal expansion coefficient measurement system and method based on light field regulation and control

Abstract

The invention provides a thermal expansion coefficient measurement system and method based on light field regulation, and the system comprises a light field generation module which comprises a light source and a spatial light modulator which is used for modulating a light beam generated by the light source to generate a structured light field containing orthogonal stripes; the temperature control module is used for controlling the temperature of the to-be-tested sample; the detection module comprises a 4f optical assembly and a camera, the 4f optical assembly is used for processing a reflected light field generated after the structured light field projects the surface of the to-be-detected sample and then enabling the reflected light field to enter the camera, and the camera is used for imaging; the data processing unit is used for processing imaging data of the camera and calculating to obtain the thermal expansion coefficient of the to-be-detected sample. The programmable measurement light field is dynamically generated by adopting the SLM, and sample surface treatment is not needed; the three-dimensional deformation of the sample is inverted through the phase change of the light field, the environmental disturbance can be effectively eliminated in combination with the multi-wavelength differential measurement technology, and the measurement precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal expansion coefficient measurement, and in particular relates to a thermal expansion coefficient measurement system and method based on light field regulation. Background Art

[0002] The coefficient of thermal expansion (CTE) is a key physical parameter that indicates the change in volume or length of a material when its temperature changes. It is crucial for engineering design, material selection, and structural stability analysis. Traditional CTE measurement methods fall into two categories: contact and non-contact.

[0003] Contact measurement typically uses strain gauges or displacement sensors, which directly contact the sample to measure deformation caused by thermal expansion. For example, patent application publication number CN117890418A discloses a method for measuring the thermal expansion coefficient of a material using strain gauges. Using a standard specimen as a reference, the method uses strain gauges and thermocouples connected to a corresponding data acquisition system to measure the strain and temperature of the standard specimen and the sample being tested. The thermal expansion coefficient of the sample being tested is then calculated by comparison.

[0004] However, this method has the following limitations: first, contact measurement may impose additional stress on the sample, affecting the accuracy of the measurement results; second, contact measurement is difficult to implement for high-temperature, corrosive or tiny samples; in addition, the installation and calibration process of contact sensors is complicated and easily affected by environmental interference.

[0005] Among non-contact measurement methods, digital image correlation (DIC) is currently the most widely used. DIC calculates the thermal expansion coefficient by pre-fabricating artificial speckles on the sample surface and analyzing the displacement changes of the speckles using an image matching algorithm.

[0006] For example, the patent application with publication number CN113030158A discloses a method for measuring the thermal expansion coefficient and stress of a thin film material, which includes the following steps: Step 1, first prepare a measurement sample and spray speckle, and then build a full-field deformation measurement platform in a high-temperature environment; Step 2, real-time measurement of the morphology and full-field deformation of the thin film sample, including: (1) real-time measurement of the in-plane deformation of the thin film sample; (2) real-time measurement of the three-dimensional thermal deformation of the thin film sample; (3) morphology measurement of the thin film sample before and after electroplating; Step 3, calculation of the thermal expansion coefficient of the thin film material: (1) using the digital image correlation method to calculate the thermal deformation image to obtain the deformation map; (2) obtaining the in-plane deformation through data analysis of the deformation map; (3) substituting the in-plane deformation into the formula based on the thermal expansion coefficient of the deformed film to obtain the thermal expansion coefficient of the thin film material; Step 4, calculation of the full-field thermal stress of the thin film at high temperature; Step 5, calculation of the full-field residual stress generated by the film preparation.

[0007] However, DIC technology also has some significant drawbacks:

[0008] 1. Limitations of 2D Image Analysis: DIC technology is primarily based on 2D image analysis, making it difficult to eliminate measurement errors caused by out-of-plane displacement (i.e., displacement perpendicular to the image plane). For complex shapes or anisotropic materials, 2D analysis can lead to large systematic errors.

[0009] 2. High computational complexity: DIC technology requires a large number of image correlation operations, which is computationally complex and has poor real-time performance. In high-precision measurement scenarios, data processing time may become a bottleneck.

[0010] 3. Poor environmental adaptability: DIC technology has high requirements for ambient lighting conditions and sample surface conditions, and it is difficult to work stably in environments with strong light, weak light, or large changes in surface reflectivity.

[0011] While existing speckle field interferometry methods have improved measurement accuracy to a certain extent, they still fail to fundamentally resolve the aforementioned issues. Therefore, developing a method for measuring the coefficient of thermal expansion that requires no surface treatment, offers high accuracy, and is suitable for use in complex environments is of great scientific and engineering significance. Summary of the Invention

[0012] In order to solve the above technical problems existing in the prior art, the present invention provides a thermal expansion coefficient measurement system and method based on light field regulation.

[0013] The present invention provides a thermal expansion coefficient measurement system based on light field regulation, comprising:

[0014] A light field generation module includes a light source, a first beam splitter, and a spatial light modulator (SLM). The first beam splitter is used to decompose the light beam generated by the light source into two beams, one of which is incident on the spatial light modulator as a measurement beam and the other as a reference beam. The spatial light modulator is used to modulate the measurement beam to generate a structured light field containing orthogonal fringes to be measured.

[0015] Temperature control module, used to control the temperature of the sample to be tested;

[0016] The detection module includes a second beam splitter, a 4f optical component, and a camera. The second beam splitter is used to recombine the reference beam from the first beam splitter and the reflected light field of the sample to be measured into one beam, which is then incident on the 4f optical component. The 4f optical component is used to process the reflected light field generated after the structured light field is projected onto the surface of the sample to be measured, and then the reflected light field is incident on the camera. The camera is used for imaging.

[0017] The data processing unit processes the camera imaging data and calculates the thermal expansion coefficient of the sample to be tested.

[0018] Preferably, the light source is a multi-wavelength laser source, which provides a stable, high-brightness light source. The multi-wavelength laser source refers to a device that can output two or more lasers of different wavelengths. The wavelength of the laser source can be selected according to the optical properties of the sample and the measurement requirements.

[0019] Preferably, the spatial light modulator generates a structured light field containing orthogonal fringes by loading a Dammann grating phase pattern.

[0020] Preferably, the resolution of the spatial light modulator is not less than 1280×720, and can generate a high-precision structured light field.

[0021] Preferably, the camera is a high-speed CMOS camera, and the sampling frequency of the camera matches the refresh rate of the spatial light modulator to ensure data synchronization.

[0022] Further preferably, the sampling frequency of the camera is not less than 50 fps, and can record the thermal deformation process of the sample in real time.

[0023] Preferably, the temperature control module includes a temperature control furnace, the interior of which adopts a uniform heating design with a temperature control accuracy of ±0.1°C, which can meet the measurement requirements of 20-800°C.

[0024] Preferably, the temperature control module includes multiple temperature sensors, which are arranged inside the temperature control furnace and on the surface of the sample to be tested, and monitor the temperature changes of the sample in real time. They can provide temperature information and provide data support for measuring the thermal expansion coefficient of anisotropic materials.

[0025] Preferably, the data processing unit includes:

[0026] Phase solution algorithm module, used to convert the collected light field intensity distribution into phase distribution;

[0027] The thermal expansion coefficient calculation module calculates the thermal expansion coefficient of the sample to be tested based on the phase-displacement mapping relationship;

[0028] The error compensation module uses the least squares fitting method to correct system errors and environmental disturbances.

[0029] Preferably, the phase solution algorithm module adopts a five-step phase shift method, collects the light field intensity distribution of five different phases, calculates the phase change of each pixel point, and establishes a phase-displacement mapping relationship: Δφ(x,y)=(4π / λ)·[ΔL(x,y)+ɑ·L0·ΔT], wherein Δφ(x,y) represents the phase change, α is the thermal expansion coefficient, L0 is the initial length of the sample, ΔT is the temperature change, λ is the laser wavelength, and ΔL(x,y) represents the displacement field distributed on the surface of the material.

[0030] Preferably, the data processing unit adopts dual-wavelength differential interference technology to calculate the thermal expansion coefficient by the formula a=(Δφ1λ2-Δφ2λ1) / [4πL0ΔT(λ2-λ1)], wherein α is the thermal expansion coefficient, λ1 and λ2 are the laser wavelengths, Δφ1 and Δφ2 are the phase changes corresponding to the two wavelengths, L0 is the initial length of the sample, and ΔT is the temperature change.

[0031] Preferably, the first beam splitter and the second beam splitter are polarization beam splitting prisms.

[0032] Preferably, the light field generation module further includes a beam expansion and collimation unit, which is located between the light source and the first beam splitter and is used to expand and collimate the light beam generated by the light source before the light beam is incident on the first beam splitter.

[0033] The present invention also provides a method for measuring thermal expansion coefficient based on light field regulation, using the above-mentioned thermal expansion coefficient measurement system based on light field regulation, comprising the following steps:

[0034] (1) A structured light field containing orthogonal stripes is generated by a light field generation module. The structured light field is projected onto the surface of the sample to be tested, and the reflected light field carries the deformation information of the sample;

[0035] (2) The temperature of the sample to be tested is adjusted by the temperature control module, and the intensity distribution of the reflected light field is collected by the detection module simultaneously to obtain the deformation information of the sample to be tested at different temperatures;

[0036] (3) The thermal expansion coefficient of the sample to be tested is calculated by the data processing unit based on the deformation information of the sample to be tested at different temperatures.

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

[0038] The SLM dynamically generates a programmable measurement light field, eliminating the need for sample surface preparation. The three-dimensional sample deformation is inverted through phase changes in the light field. Combined with multi-wavelength differential measurement technology, this method effectively eliminates environmental disturbances and improves measurement accuracy. This method supports reflective operation and is applicable to a wide range of materials. It is suitable for measuring the thermal expansion coefficient of isotropic and anisotropic materials such as metals, ceramics, and composite materials. It performs particularly well in harsh environments such as high temperatures and corrosive environments, and has important scientific and engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the structure of the thermal expansion coefficient measurement system based on light field regulation in Example 1.

[0040] Figure 2 Schematic diagram of the structure of a structured light field containing orthogonal stripes generated by a spatial light modulator in Example 2.

[0041] Figure 3 Schematic diagram of phase solution in Example 2.

[0042] Figure 4 This is a flow chart of the thermal expansion coefficient measurement method based on light field regulation in Example 2.

[0043] Reference numerals:

[0044] Light source 1, first lens 2, second lens 3, first beam splitter 4, spatial light modulator 5, first reflector 6, sample to be tested 7, temperature control module 8, second beam splitter 9, third lens 10, fourth lens 11, camera 12, second reflector 13, data processing unit 14. DETAILED DESCRIPTION

[0045] Example 1

[0046] The present invention provides a thermal expansion coefficient measurement system based on light field regulation, which includes a light field generation module, a temperature control module 8, a detection module and a data processing unit 14.

[0047] The light field generation module includes a light source 1 and a spatial light modulator 5 (SLM). The spatial light modulator 5 is used to modulate the light beam generated by the light source 1 to generate a structured light field containing orthogonal fringes.

[0048] Light source 1 is preferably a multi-wavelength laser source that provides a stable, high-brightness light source. The wavelength of the laser source can be selected based on the optical properties of the sample and the measurement requirements. The resolution of spatial light modulator 5 is not less than 1280×720 to generate a high-precision structured light field.

[0049] Temperature control module 8 is used to control the temperature of the test sample 7. It can be equipped with a temperature-controlled furnace and multiple temperature sensors. The furnace's internal uniform heating design allows for temperature control accuracy of ±0.1°C, meeting measurement requirements from 0 to 1000°C. Temperature sensors are located inside the furnace and on the surface of the test sample 7 to monitor sample temperature changes in real time, providing temperature information and supporting data for measuring the thermal expansion coefficient of anisotropic materials.

[0050] The detection module includes a 4f optical assembly and a camera 12. The 4f optical assembly is used to process the reflected light field generated by projecting the structured light field onto the surface of the sample 7 before it is incident on the camera 12. The 4f optical assembly includes a third lens 10 and a fourth lens 11. The camera 12 is used to form an image and collect the intensity distribution of the reflected light field.

[0051] The camera 12 can be a high-speed CMOS camera. The sampling frequency of the camera 12 matches the refresh rate of the spatial light modulator 5 to ensure data synchronization. The sampling frequency of the camera 12 is not less than 50 fps to record the thermal deformation process of the sample in real time.

[0052] The data processing unit 14 processes the imaging data of the camera 12 and calculates the thermal expansion coefficient of the sample 7 to be tested.

[0053] The data processing unit 14 includes a phase resolution algorithm module, which converts the collected light field intensity distribution into a phase distribution. The data processing unit 14 also includes a thermal expansion coefficient calculation model, which calculates the thermal expansion coefficient of the sample 7 to be tested based on the phase-displacement mapping relationship.

[0054] In order to improve the measurement accuracy, the data processing unit 14 further includes an error compensation module, which uses the least squares fitting method to correct system errors and environmental disturbances.

[0055] The phase solution algorithm module can adopt a five-step phase shift method to collect the light field intensity distribution at five different phases, calculate the phase change of each pixel point, and establish a phase-displacement mapping relationship: Δφ(x,y)=(4π / λ)·[ΔL(x,y)+ɑ·L0·ΔT], where α is the thermal expansion coefficient, L0 is the initial length of the sample, ΔT is the temperature change, λ is the laser wavelength, and ΔL(x,y) represents the displacement field distributed on the material surface.

[0056] The data processing unit 14 uses dual-wavelength differential interference technology to calculate the thermal expansion coefficient through the formula a=(Δφ1λ2-Δφ2λ1) / [4πL0ΔT(λ2-λ1)], where α is the thermal expansion coefficient, λ1 and λ2 are the laser wavelengths, Δφ1 and Δφ2 are the phase changes corresponding to the two wavelengths, L0 is the initial length of the sample, and ΔT is the temperature change.

[0057] The light field generation module also includes a first beam splitter 4, and the detection module includes a second beam splitter 9. The first beam splitter 4 is used to split the light beam generated by the light source 1 into two beams. One beam is incident on the spatial light modulator 5 as the measurement beam, and the other beam is incident on the second beam splitter 9 as the reference beam. The second beam splitter 9 is used to recombine the reference beam from the first beam splitter 4 and the reflected light field of the sample to be measured 7 into a single beam, which is then incident on the 4f optical component. The design of the first beam splitter 4 and the second beam splitter 9 can decompose the light field into two beams for phase resolution, thereby reducing ambient light interference and noise effects and improving measurement accuracy.

[0058] To optimize beam quality and light field distribution, the light field generation module is further provided with a beam expansion and collimation unit. The beam expansion and collimation unit is located between the light source 1 and the first beam splitter 4 and is used to expand and collimate the light beam generated by the light source 1 before it is incident on the first beam splitter 4. The beam expansion and collimation unit includes a first lens 2 and a second lens 3.

[0059] Reflectors can be added to adjust and control the direction and path of the light beam. Figure 1 As shown, a first reflector 6 is provided between the spatial light modulator 5 and the sample to be measured 7 to reflect the light beam reflected by the spatial light modulator 5 to the surface of the sample to be measured 7 which is not in the path of the light beam reflected by the spatial light modulator 5; a second reflector 13 is provided between the first beam splitter 4 and the second beam splitter 9 to reflect one of the beams decomposed by the first beam splitter 4 directly to the second beam splitter 9.

[0060] Working principle: Through Figure 1 The optical path shown will create a structured light field with orthogonal stripes ( Figure 2 The light intensity distribution is captured by the camera. The data processing unit uses the phase shift algorithm to convert the light intensity into phase difference ( Figure 3 As shown), and combined with the temperature information, the thermal expansion coefficient of the sample is calculated through the established phase-displacement-thermal expansion relationship model (the overall process is as shown in Figure 4 shown).

[0061] Example 2

[0062] This embodiment uses the thermal expansion coefficient measurement system based on light field control in Example 1 to measure the thermal expansion coefficient. The measurement process is as follows: Figure 4 shown.

[0063] (1) System configuration

[0064] Using a dual-wavelength laser source of 532nm and 635nm, the SLM has a resolution of 1920×1080, capable of generating high-precision structured light fields. The temperature control range is 20-800°C, and the heating and cooling rates are adjustable from 0.1°C / min to 10°C / min, meeting the measurement requirements of a variety of materials. A high-speed CMOS camera with a sampling rate of 100fps is used to record the thermal deformation process of the sample in real time.

[0065] (2) Measurement process

[0066] First, the quartz glass (sample to be tested) deposited with a chromium film is firmly mounted on a special sample fixture in a temperature-controlled furnace to ensure that the test surface (chromium film surface) is flat and there is no rigid body displacement during the entire temperature change process. Subsequently, a specially designed Dammann grating phase image is loaded through the SLM to accurately project a structured light field containing spatially orthogonal sinusoidal stripes onto the sample surface. Start the temperature control program and heat it to 800°C at a set constant rate (for example, 5°C / min). At the same time, start the high-speed CMOS camera to synchronously capture the intensity distribution image sequence of the structured light field at a frequency of 100fps. In the data processing unit, the five-step phase shift method (phase shift step angle π / 2) is applied to the acquired image sequence to solve the dynamic phase change Δφ of each object point in the X and Y directions respectively. x (x,y,t) and φ γ (x, y, t). According to the pre-calibrated phase-displacement mapping relationship Δφ(x, y) = (4π / λ) · [ΔL(x, y) + α·L0·ΔT], the phase change is converted into the instantaneous in-plane displacement of each point on the sample surface in the X and Y directions, and the out-of-plane displacement information can be obtained by analysis. The specific characteristic reference length L0 of the sample is selected (precisely measured and calibrated at the reference temperature T0), and the thermal expansion ΔL(T) = L(T)-L0 along the measurement direction (such as the main direction of the material) as a function of temperature is extracted from the displacement field. Using dual-wavelength differential interference technology, the displacements calculated independently at the two wavelengths are differentially processed to effectively suppress environmental noise. Finally, combined with the real-time recorded sample temperature T(t), the relationship between ΔL(T) and the corresponding temperature change ΔT = T-T0 is linearly fitted by the least squares method to obtain the slope k, and the linear thermal expansion coefficient α of the material is calculated according to the formula ɑ = k / L0. For anisotropic materials, the thermal expansion coefficient α in the main axis directions of different materials can be measured and calculated simultaneously. ++ and α ⊥ .

[0067] (3) Result analysis

[0068] The system can achieve high-precision measurement of the thermal expansion coefficient of the sample, and the measurement results are expressed as the average linear thermal expansion coefficient. For anisotropic materials, the isotropic thermal expansion coefficient α can be obtained simultaneously. ++ and α ⊥ The system's measurement accuracy of α is better than 10 -7 K -1Order of magnitude. This high precision comes from: 1) High-resolution displacement measurement: The five-step phase shift method combined with the application of high sampling rate and high-resolution camera makes the in-plane single-point displacement resolution better than δd_min≈1nm; dual-wavelength differential interference technology significantly suppresses common mode noise, further improving the signal-to-noise ratio of small displacement detection; 2) Precision temperature control: ±0.1℃ temperature control accuracy ensures the accuracy of ΔT measurement; 3) Accurate calibration of reference length: The measurement uncertainty of L0 is better than 0.5μm; 4) Algorithm optimization: Least squares fitting and dual-wavelength difference effectively reduce random errors. The main contributions to the system uncertainty are: length calibration error δL0 / L0≈0.1%, thermal expansion measurement error δ(ΔL) / ΔL≈0.1% (with ΔT=100℃, L0=10mm, α≈10 -6 K -1 The temperature measurement error is δ(ΔT) / ΔT≈0.1% (ΔT=100°C). The relative uncertainty of α is about 0.1%-0.2%, and the absolute uncertainty δɑ≈(1-2)×10 -9 K -1 The standard deviation of repeated measurements is stable at ±5×10 -8 K -1 level, verified that the system reaches 10 -7 K -1 The measurement accuracy is higher than that of traditional digital image correlation method (DIC, which is usually accurate within 10 -5 K -1 This technology offers significant advantages: it requires no sample surface pretreatment, thus avoiding potential damage or impact of coatings on the material; it is suitable for harsh environments such as high temperatures (>600°C) and corrosive environments; it can simultaneously acquire a three-dimensional displacement field, enabling precise characterization of the three-dimensional thermal expansion behavior of anisotropic materials; and it provides more comprehensive and reliable data support for the study of the thermodynamic properties of complex materials.

Claims

1. A thermal expansion coefficient measurement system based on light field control, characterized in that: include: A light field generation module includes a light source, a first beam splitter, and a spatial light modulator. The first beam splitter is used to decompose the light beam generated by the light source into two beams, one of which is incident on the spatial light modulator as a measurement beam and the other as a reference beam. The spatial light modulator is used to modulate the measurement beam to generate a structured light field containing orthogonal fringes to be measured. Temperature control module, used to control the temperature of the sample to be tested; The detection module includes a second beam splitter, a 4f optical component, and a camera. The second beam splitter is used to recombine the reference beam from the first beam splitter and the reflected light field of the sample to be measured into one beam, which is then incident on the 4f optical component. The 4f optical component is used to process the reflected light field generated after the structured light field is projected onto the surface of the sample to be measured, and then the reflected light field is incident on the camera. The camera is used for imaging. The data processing unit processes the camera imaging data and calculates the thermal expansion coefficient of the sample to be tested.

2. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The light source is a multi-wavelength laser source.

3. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The spatial light modulator generates a structured light field containing orthogonal fringes by loading a Dammann grating phase pattern.

4. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The resolution of the spatial light modulator is not less than 1280×720; The camera is a high-speed CMOS camera. The sampling frequency of the camera matches the refresh rate of the spatial light modulator, and the sampling frequency of the camera is not less than 50 fps.

5. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The data processing unit includes: Phase solution algorithm module, used to convert the collected light field intensity distribution into phase distribution; The thermal expansion coefficient calculation module calculates the thermal expansion coefficient of the sample to be tested based on the phase-displacement mapping relationship; The error compensation module uses the least squares fitting method to correct system errors and environmental disturbances.

6. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The phase solution algorithm module adopts a five-step phase shift method. By collecting the light field intensity distribution at five different phases, the phase change of each pixel is calculated and a phase-displacement mapping relationship is established: Δφ(x,y)=(4π / λ)·[ΔL(x,y)+ɑ·L0·ΔT], where Δφ(x,y) represents the phase change, α is the thermal expansion coefficient, L0 is the initial length of the sample, ΔT is the temperature change, λ is the laser wavelength, and ΔL(x,y) represents the displacement field distributed on the material surface.

7. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The data processing unit adopts dual-wavelength differential interference technology to calculate the thermal expansion coefficient through the formula a=(Δφ1λ2-Δφ2λ1) / [4πL0ΔT(λ2-λ1)], where α is the thermal expansion coefficient, λ1 and λ2 are the laser wavelengths, Δφ1 and Δφ2 are the phase changes corresponding to the two wavelengths, L0 is the initial length of the sample, and ΔT is the temperature change.

8. The thermal expansion coefficient measurement system based on light field control according to claim 1, characterized in that: The light field generation module further includes a beam expansion and collimation unit, which is located between the light source and the first beam splitter and is used to expand and collimate the light beam generated by the light source before it is incident on the first beam splitter.

9. A method for measuring thermal expansion coefficient based on light field regulation, characterized in that: The thermal expansion coefficient measurement system based on light field control according to any one of claims 1 to 8 comprises the following steps: (1) A structured light field containing orthogonal stripes is generated by a light field generation module. The structured light field is projected onto the surface of the sample to be tested, and the reflected light field carries the deformation information of the sample; (2) The temperature of the sample to be tested is adjusted by the temperature control module, and the intensity distribution of the reflected light field is collected by the detection module simultaneously to obtain the deformation information of the sample to be tested at different temperatures; (3) The thermal expansion coefficient of the sample to be tested is calculated by the data processing unit based on the deformation information of the sample to be tested at different temperatures.

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