Terahertz thickness measuring method and system for soft solidified sample
By acquiring terahertz waveforms during the soft curing process and establishing the correspondence between refractive index and characteristics, the problem of large thickness assessment error in traditional methods is solved, and high-precision online thickness detection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-04-10
AI Technical Summary
Traditional terahertz measurement methods suffer from increasing thickness assessment errors due to dynamic refractive index drift during the spraying process, making it impossible to achieve high-precision online quality control.
By repeatedly acquiring the terahertz waveform of the reference sample during the soft curing process, extracting features, establishing the correspondence between the refractive index and the features, and calculating the refractive index and thickness of the sample under test in real time.
It enables high-precision detection of sample thickness during the spraying process, reduces measurement errors, and supports online quality control.
Smart Images
Figure CN121829339A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of measurement and analysis technology, and in particular to a terahertz thickness measurement method and system for soft-state solidified samples. Background Technology
[0002] Terahertz radiation, as a non-contact measurement method, reflects corresponding peaks at the interface of media with different refractive indices, and has been proven to be an effective means of thickness measurement. In the aerospace field, the thermal barrier effect of thermal barrier coatings is directly related to their thickness; therefore, online thickness measurement is necessary during production. Coatings are typically applied by spraying. During the coating curing process, solvent evaporation and cross-linking reactions cause the thickness and refractive index to exhibit time-varying characteristics. Traditional terahertz thickness measurement methods use a uniform refractive index for the entire calculation, which is difficult to adapt to dynamic refractive index drift. This leads to an increase in thickness assessment error as curing progresses, making it impossible to achieve high-precision in-situ quality control of time-varying refractive indices on spraying production lines. Summary of the Invention
[0003] In view of this, the purpose of this application is to propose a terahertz thickness measurement method and system for soft-state cured samples, which solves the problem of large measurement error when using terahertz with a uniform refractive index to measure the thickness of samples during the curing process.
[0004] To achieve one of the aforementioned objectives, this application provides a terahertz thickness measurement method for soft-state solidified samples, the method comprising: During the curing process of the soft reference sample, the terahertz waveform of the reference sample is acquired multiple times at preset intervals, and multiple reference features are extracted from the multiple terahertz waveforms of the reference sample. Based on the multiple reference features and the thickness of the reference sample, calculate multiple refractive indices of the reference sample during the curing process; Establish a correspondence between the multiple reference features and the multiple refractive indices; Measure the terahertz waveform of the sample under test and extract the test characteristics of the terahertz waveform of the sample under test; Based on the correspondence, determine the real-time refractive index corresponding to the test feature; The thickness of the sample under test is calculated based on the real-time refractive index.
[0005] As a further improvement to one embodiment of this application, the step of repeatedly acquiring the terahertz waveform of the reference sample at preset intervals and extracting multiple reference features from the multiple terahertz waveforms of the reference sample includes: The terahertz time-domain waveform of the reference sample is acquired multiple times at preset intervals; Perform a Fourier transform on the terahertz time-domain waveform to generate a frequency-domain waveform; The frequency, peak amplitude, and peak phase of the strongest absorption peak within a specific range of the frequency domain waveform are extracted as the reference features.
[0006] As a further improvement to one embodiment of this application, the calculation of multiple refractive indices of the reference sample during the curing process includes: The refractive index is calculated using the following formula: ; Where n is the refractive index, The peak phase is λ, the terahertz wavelength is d. ref The thickness of the reference sample.
[0007] As a further improvement to one embodiment of this application, establishing the correspondence between the plurality of reference features and the plurality of refractive indices includes: Establish a correspondence table between the multiple reference features and the multiple refractive indices; Determining the real-time refractive index corresponding to the test feature based on the correspondence includes: In the corresponding table, find the reference feature that is closest to the test feature, and the refractive index corresponding to the reference feature is the real-time refractive index.
[0008] As a further improvement to one embodiment of this application, establishing the correspondence between the plurality of reference features and the plurality of refractive indices includes: The plurality of the reference features and the plurality of refractive indices are fitted into a curve formula; After finding the reference feature that is closest to the test feature in the corresponding table, the process includes: If the difference between the test feature and its closest reference feature is greater than the feature error threshold, the real-time refractive index is calculated using the curve formula.
[0009] As a further improvement to one embodiment of this application, the curve formula is: ; Where n is the refractive index, f peak R is the frequency of the strongest absorption peak. 2 The goodness of fit is represented by a0, a1, and a2, which are the coefficients after fitting. If the difference between the test feature and its closest reference feature is greater than the feature error threshold, the real-time refractive index is calculated using the curve formula, including: If the following formula is satisfied, the real-time refractive index is calculated using the curve formula: ; in, f is the frequency of the strongest absorption peak in the test characteristics. peak The frequency of the strongest absorption peak in the reference feature is given in THz, where THz is the unit of terahertz.
[0010] As a further improvement to one embodiment of this application, the step of calculating the thickness of the sample to be tested based on the real-time refractive index includes: The thickness of the sample to be tested is calculated using the following formula: ; Where d is the thickness of the sample to be tested, c is the speed of light in vacuum, and n real The real-time refractive index, t is the time delay between the air-to-sample interface echo and the base-to-bottom interface echo of the sample.
[0011] As a further improvement to one embodiment of this application, after calculating the thickness of the sample to be tested, the process includes: Randomly select the sample to be tested and destroy the selected sample; The actual thickness of the sampled specimen is measured. If the difference between the actual thickness and the calculated thickness is less than the thickness error threshold, the test feature and real-time refractive index are entered into the corresponding relationship.
[0012] Based on the same inventive concept, this application also provides a terahertz thickness measurement system for soft-state solidified samples, comprising: A terahertz spectrometer is used to acquire the terahertz waveform of a soft reference sample multiple times at preset intervals during the solidification process of the reference sample, and to extract multiple reference features from the multiple terahertz waveforms of the reference sample. A computing device for calculating multiple refractive indices of the reference sample during the curing process based on multiple reference features and the thickness of the reference sample; The computing device is also used to establish a correspondence between the plurality of the reference features and the plurality of the refractive indices; Terahertz spectrometers are also used to measure the terahertz waveform of a sample and extract the test characteristics of the terahertz waveform of the sample. The computing device is also used to determine the real-time refractive index corresponding to the test feature based on the correspondence; The computing device is also used to calculate the thickness of the sample under test based on the real-time refractive index.
[0013] As a further improvement of one embodiment of this application, it also includes: a thickness testing device for detecting the thickness of the reference sample, or for detecting the true thickness of the sample to be tested after extraction and destruction.
[0014] Compared to existing technologies, the technical advantages of this invention are as follows: the refractive index of a sample obtained by terahertz waves is an inherent characteristic of the sample itself, and this refractive index changes with the sample's state during the curing process. By testing a reference sample of known thickness, the correspondence between the terahertz-acquired features and the refractive index is obtained. When actually measuring the thickness of the sample to be tested, the characteristics of the sample obtained by terahertz waves are obtained, the refractive index in that state is determined, and the thickness of the sample to be tested is obtained based on this refractive index. This achieves thickness detection of samples during the curing process while ensuring detection accuracy. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the implementation methods or related technologies will be briefly introduced below. Obviously, the drawings described below are only the implementation methods of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 A flowchart of a terahertz thickness measurement method for a soft-state solidified sample provided in one embodiment of this application; Figure 2 This is a schematic diagram of a terahertz thickness measurement system for a soft-state cured sample provided in one embodiment of this application. Detailed Implementation
[0017] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.
[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by those skilled in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.
[0019] To address the aforementioned problems, this application provides a terahertz thickness measurement method for soft-state solidified samples, such as... Figure 1 As shown, it includes the following steps: In step S100, during the curing process of the soft reference sample, the terahertz waveform of the reference sample is acquired multiple times at preset intervals, and multiple reference features are extracted from the multiple terahertz waveforms of the reference sample.
[0020] Specifically, during the curing process of the soft reference sample, the inherent characteristics of the reference sample are constantly changing. Reference samples collected at preset intervals are at different degrees of curing, i.e., terahertz waveforms of reference samples at different degrees of curing are collected, thereby extracting reference features of reference samples at different degrees of curing.
[0021] In one possible implementation of this application, step S100 includes: Step S110: Acquire the terahertz time-domain waveform of the reference sample multiple times at preset intervals; Step S120: Perform a Fourier transform on the terahertz time-domain waveform to generate a frequency-domain waveform; Step S130: Extract the frequency, peak amplitude, and peak phase of the strongest absorption peak within a specific range of the frequency domain waveform as reference features.
[0022] Specifically, the terahertz time-domain waveforms of the soft sample are first recorded throughout the entire process from fluidity to complete hardening. Fourier transforms are then performed on the curves of each terahertz time-domain waveform to convert them into frequency-domain waveforms. The frequency, peak amplitude, and peak phase of the strongest absorption peak are extracted from the frequency-domain waveforms. These characteristics can reflect the reflectivity of the reference sample at a certain degree of hardening.
[0023] Step S200: Calculate multiple refractive indices of the reference sample during the curing process based on multiple reference features and the thickness of the reference sample.
[0024] Specifically, the refractive index of the reference sample and subsequent test samples is a property of the material itself, which changes only with the evolution of its curing degree and when the sample deteriorates. The reference feature and thickness are not variables that affect the refractive index, but the specific value of the refractive index can be calculated by the reference feature and the thickness of the sample. Therefore, the specific value of the refractive index can be calculated by obtaining the terahertz waveform and measuring the thickness of the reference feature.
[0025] It should be noted that the reference sample is a part used to test the material properties, and can be any structure that facilitates direct thickness measurement, while the sample to be tested is a complete product that is difficult to measure directly.
[0026] In one possible implementation of this application, step S200, calculating multiple refractive indices of the reference sample during the curing process, includes: Calculate the refractive index using the following formula: ; Where n is the refractive index, λ is the peak phase, λ is the terahertz wavelength, and d ref The thickness is for reference samples.
[0027] Step S300: Establish the correspondence between multiple reference features and multiple refractive indices.
[0028] Specifically, using a reference sample of known thickness, the correspondence between reference characteristics and refractive index is established at different degrees of curing. When measuring the sample to be tested, the refractive index at that curing degree can be obtained using only the terahertz waveform, thus allowing the thickness of the sample to be deduced. This enables experimental-level modeling of the refractive index evolution curve throughout the curing process, providing a searchable and updatable physical database for instantaneous refractive index inversion at any intermediate state.
[0029] In one possible implementation of this application, step S300 includes: Step S310: Establish a corresponding table for multiple reference features and multiple refractive indices.
[0030] Specifically, the curing of the reference sample is a linear process, but data needs to be collected at preset intervals in the preceding steps. Therefore, the recorded degree of curing and its corresponding reference characteristics and refractive index are data points at the collection time points. The independent corresponding data are represented in tabular form for easy reference.
[0031] In one possible implementation of this application, step S300 includes: fitting multiple reference features and multiple refractive indices into a curve formula.
[0032] Specifically, the collected data points are fitted into a curve to simulate the linear curing process of the reference sample. This makes it easier to identify the data that was not collected between preset time intervals and their corresponding relationships, thereby obtaining a more accurate thickness in subsequent steps.
[0033] In the feasible implementation of this application, the curve formula is: ; Where n is the refractive index, f peak R is the frequency of the strongest absorption peak. 2 The goodness of fit is represented by a0, a1, and a2, which are the coefficients after fitting.
[0034] Step S400: Measure the terahertz waveform of the sample to be tested and extract the test features of the terahertz waveform of the sample to be tested.
[0035] Specifically, when measuring the sample to be tested, the degree of curing and thickness of the sample are unknown. Terahertz wave detection is used to obtain the terahertz waveform, and then the test features are extracted to obtain the characteristics of the sample at this time.
[0036] In a specific implementable manner, step S400 includes: Step S410: Acquire the terahertz time-domain waveform of the sample to be tested.
[0037] Step S420: Perform Fourier transform on the terahertz time-domain waveform of the sample to be tested to generate the frequency-domain waveform of the sample to be tested.
[0038] Step S430: Extract the frequency, peak amplitude, and peak phase of the strongest absorption peak within a specific range of the frequency domain waveform of the sample to be tested as test features.
[0039] Specifically, features identical to those in the reference sample are extracted from the sample to be tested, which facilitates subsequent comparison and calculation.
[0040] Step S500: Determine the real-time refractive index corresponding to the test feature based on the correspondence.
[0041] Specifically, after obtaining the same features in the test sample as the reference sample, the test features of the test sample can be substituted into the correspondence of the reference sample. The reflectance corresponding to the reference feature is the real-time reflectance of the same test feature.
[0042] In one of the possible implementations of this application, step 500 further includes: Step S510: In the corresponding table, find the reference feature that is closest to the test feature. The refractive index corresponding to the reference feature is the real-time refractive index.
[0043] Specifically, the test features detected in real time on the sample under test may not be exactly the same as the reference features detected at intervals in the corresponding table. The curing degree of the closest reference feature found in the corresponding table can represent the curing degree of the sample under test at the time of testing. The thickness is calculated using the reflectivity in this set of correspondences. Compared with the fixed and uniform reflectivity in the existing technology, the detection accuracy is greatly improved.
[0044] In the possible implementation of this application, step S510 is followed by: Step S520: If the difference between the test feature and its closest reference feature is greater than the feature error threshold, then the real-time refractive index is calculated using the curve formula.
[0045] Specifically, based on the actual situation and the acceptable level of error, a feature error threshold is set. When the difference between the test feature and the selected closest reference feature exceeds the feature error threshold, the real-time refractive index is calculated using the fitted curve formula. By changing to a comparison method with lower error, the detection error is further reduced.
[0046] In one possible implementation of this application, if the following formula is satisfied in step S520, the real-time refractive index is calculated using the curve formula: ; in, To test the frequency of the strongest absorption peak in the characteristic, f peak THz is the frequency of the strongest absorption peak in the reference characteristic, and is the unit of terahertz.
[0047] Step S600: Calculate the thickness of the sample to be tested based on the real-time refractive index.
[0048] In one possible implementation of this application, step S600 includes: The thickness of the sample to be tested is calculated using the following formula: ; Where d is the thickness of the sample to be measured, c is the speed of light in vacuum, and n real For real-time refractive index, t is the time delay between the air-to-sample interface echo and the base-to-bottom interface echo of the sample.
[0049] Specifically, the thickness is calculated by determining the refractive index and the interface echo time difference, thus achieving synchronous model-free extraction of thickness and refractive index during the curing process.
[0050] In a specific implementation method, steps S400-S600 are repeated to obtain the thickness of multiple samples to be tested, and the average value is calculated. The average thickness is then used as the final thickness.
[0051] In one possible implementation of this application, the method further includes the following after step S600: Step S700: Randomly select a sample to be tested and destroy the selected sample. Step S800: Measure the actual thickness of the sample to be tested. If the difference between the actual thickness and the calculated thickness is less than the thickness error threshold, then record the test features and real-time refractive index into the corresponding relationship.
[0052] Specifically, in order to improve the accuracy of the correspondence between reference features and reflectivity, after obtaining the final thickness, a small number of test samples are extracted from the batch of test samples, and the actual thickness is measured using a destructive method. The actual thickness is then compared with the calculated thickness. If the error between the calculated thickness and the actual thickness is extremely small, it can be used as a correspondence to provide a reference value for the next measurement.
[0053] Specifically, the actual thickness and measurement characteristics can be incorporated into the fitted curve to improve the curve's realism and accuracy.
[0054] In a specific feasible implementation, if the following formula is satisfied, the test characteristics and real-time refractive index will be entered into the corresponding relationship: ; Where, d messFor the final thickness, d true This represents the actual thickness.
[0055] In the feasible implementation of this application, the beneficial effects of the terahertz thickness measurement method for soft-state cured samples are as follows: Firstly, it innovatively discretizes the continuous curing trajectory of soft samples from the fluid state to the hardened state into time-degree-of-curing nodes. Through high-density terahertz time-domain sampling and multi-dimensional feature extraction, a gradual change state correspondence table with a one-to-one correspondence of "degree of curing-feature-refractive index" is constructed. This achieves experimental-level modeling of the refractive index evolution curve throughout the curing process for the first time, providing a searchable and updatable physical database for instantaneous refractive index inversion of any intermediate state. Secondly, for non-constant samples where the refractive index continuously changes within a range, a feature matching mechanism is used to collect data at any moment during solidification and compare it in real time with the gradual change state lookup table to directly output the current refractive index. Combined with interface echo time difference analysis, synchronous in-situ acquisition of thickness and refractive index is achieved.
[0056] In one possible implementation of this application, such as Figure 2 As shown, a terahertz thickness measurement system for soft-state solidified samples is also proposed, including a terahertz spectrometer and a computing device. The terahertz spectrometer is used to acquire the terahertz waveform of the reference sample multiple times at preset intervals during the solidification process of the soft-state reference sample, and extract multiple reference features from the multiple terahertz waveforms of the reference sample. The computing device is used to calculate multiple refractive indices of a reference sample during the curing process based on multiple reference features and the thickness of the reference sample; The computing device is also used to establish the correspondence between multiple reference features and multiple refractive indices; Terahertz spectrometers are also used to measure the terahertz waveform of a sample and extract the test characteristics of the terahertz waveform of the sample. The computing device is also used to determine the real-time refractive index corresponding to the test feature based on the correspondence. The computing device is also used to calculate the thickness of the sample under test based on the real-time refractive index.
[0057] In one possible implementation of this application, the terahertz spectrometer is also used to acquire the terahertz time-domain waveform of the reference sample multiple times at preset intervals. The computing device is also used to perform Fourier transform on terahertz time-domain waveforms to generate frequency-domain waveforms; The computing device is also used to extract the frequency, peak amplitude, and peak phase of the strongest absorption peak within a specific range of the frequency domain waveform as reference features.
[0058] In one possible implementation of this application, the computing device is further configured to calculate the refractive index according to the following formula: ; Where n is the refractive index, λ is the peak phase, λ is the terahertz wavelength, and d ref The thickness is for reference samples.
[0059] In one possible implementation of this application, the computing device is further configured to establish a correspondence table of multiple reference features and multiple refractive indices; the computing device is further configured to find the reference feature that is closest to the test feature in the correspondence table, and the refractive index corresponding to the reference feature is the real-time refractive index.
[0060] In one possible implementation of this application, the computing device is further configured to fit multiple reference features and multiple refractive indices into a curve formula; the computing device is further configured to calculate the real-time refractive index using the curve formula if the difference between the test feature and its closest reference feature is greater than the feature error threshold.
[0061] In one possible implementation of this application, the curve formula in the computing device is: ; Where n is the refractive index, f peak R is the frequency of the strongest absorption peak. 2 The goodness of fit is represented by a0, a1, and a2, which are the coefficients after fitting. The computing device is also used to calculate the real-time refractive index using a curve formula if the following formula is satisfied: ; in, To test the frequency of the strongest absorption peak in the characteristic, f peak THz is the frequency of the strongest absorption peak in the reference characteristic, and is the unit of terahertz.
[0062] In one possible implementation of this application, the computing device is further configured to calculate the thickness of the sample to be tested according to the following formula: ; Where d is the thickness of the sample to be measured, c is the speed of light in vacuum, and n real For real-time refractive index, t is the time delay between the air-to-sample interface echo and the base-to-bottom interface echo of the sample.
[0063] In one possible implementation of this application, the terahertz thickness measurement system for soft-state solidified samples further includes a thickness testing device for detecting the thickness of a reference sample or for detecting the true thickness of a sample to be tested that has been extracted and destroyed.
[0064] In one possible implementation of this application, a specific method for failure localization of a terahertz thickness measurement system for soft-state solidified samples is proposed, including: S1, a soft sample is coated on a metal or carbon fiber substrate to create reference samples of different thicknesses.
[0065] S2. Place the reference sample in the same environment as the sample to be tested, and collect the time-domain waveform every 15 minutes using a terahertz time-domain spectrometer until it is completely solidified.
[0066] S3, Simultaneously measure the mechanical thickness d of the same area using instruments such as a white light interferometer, and record it as d. ref .
[0067] S4. Perform a Fourier transform on each time-domain waveform curve to extract the frequency f of the strongest absorption peak within the range of 0.2–2 THz in the frequency-domain waveform. peak Peak amplitude A peak and peak phase .
[0068] S5. Calculate the refractive index n using the following formula: .
[0069] S6, establish "f" peak - -A peak The "-n" four-dimensional lookup table serves as the benchmark for subsequent compensation.
[0070] S7, with f in each terahertz time-domain waveform peak With n as the independent variable and the refractive index n as the dependent variable, the following formula is obtained by fitting a quadratic polynomial: .
[0071] S8 writes the fitting coefficients a0, a1, and a2 into the configuration file and embeds them into the measurement software.
[0072] S9 uses a terahertz time-domain spectrometer to measure the time-domain waveform of the sample under test.
[0073] S10 performs a Fourier transform on each time-domain waveform curve to obtain the terahertz frequency-domain waveform.
[0074] S11 automatically identifies the strongest absorption peak and records its frequency. Peak amplitude A' peak and peak phase .
[0075] S12, with frequency Using the index, perform nearest neighbor matching in the lookup table and read the corresponding refractive index n. table .
[0076] S13, if Then the fitting model is enabled. Calculate the real-time refractive index n real .
[0077] S14, Read the time delay between the air-sample interface echo and the sample-substrate interface echo in the time-domain waveform. t.
[0078] S15, calculate the thickness using the following formula, where c is the speed of light in a vacuum: .
[0079] S16, repeat the measurement and take the average value to obtain the final thickness d. mess .
[0080] S17, then 10% of the sample to be tested was randomly selected, and d was measured using a destructive method. true .
[0081] S18, if |d mess -d true If |>1μm, then write the data back to the lookup table, update the fitting coefficients a0, a1, a2, and achieve self-learning correction.
[0082] S19 replaces the old configuration file with the corrected model.
[0083] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; this manner of description is merely for clarity, and those skilled in the art should consider the specification as a whole. Within the framework of this application, the above embodiments or the technical features of different embodiments can also be appropriately combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.
[0084] Additionally, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, the well-known power / ground connections to integrated circuit (IC) chips and other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be shown in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of the implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be entirely within the understanding of those skilled in the art). While specific details (e.g., circuits) are set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application can be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.
[0085] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may use the embodiments discussed.
[0086] The embodiments described herein are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and principles of the embodiments described herein should be included within the protection scope of this application.
Claims
1. A terahertz thickness measurement method for soft-state solidified samples, characterized in that, The method includes: During the curing process of the soft reference sample, the terahertz waveform of the reference sample is acquired multiple times at preset intervals, and multiple reference features are extracted from the multiple terahertz waveforms of the reference sample. Based on the multiple reference features and the thickness of the reference sample, calculate multiple refractive indices of the reference sample during the curing process; Establish a correspondence between the multiple reference features and the multiple refractive indices; Measure the terahertz waveform of the sample under test and extract the test characteristics of the terahertz waveform of the sample under test; Based on the correspondence, determine the real-time refractive index corresponding to the test feature; The thickness of the sample under test is calculated based on the real-time refractive index.
2. The terahertz thickness measurement method for soft-state solidified samples according to claim 1, characterized in that, The step of repeatedly acquiring the terahertz waveform of the reference sample at preset intervals and extracting multiple reference features from the multiple terahertz waveforms of the reference sample includes: The terahertz time-domain waveform of the reference sample is acquired multiple times at preset intervals; Perform a Fourier transform on the terahertz time-domain waveform to generate a frequency-domain waveform; The frequency, peak amplitude, and peak phase of the strongest absorption peak within a specific range of the frequency domain waveform are extracted as the reference features.
3. The terahertz thickness measurement method for soft-state solidified samples according to claim 2, characterized in that, The calculation of multiple refractive indices of the reference sample during the curing process includes: The refractive index is calculated using the following formula: ； Where n is the refractive index, The peak phase is λ, the terahertz wavelength is d. ref The thickness of the reference sample.
4. The terahertz thickness measurement method for soft-state solidified samples according to claim 2, characterized in that, Establishing the correspondence between the multiple reference features and the multiple refractive indices includes: Establish a correspondence table between the multiple reference features and the multiple refractive indices; Determining the real-time refractive index corresponding to the test feature based on the correspondence includes: In the corresponding table, find the reference feature that is closest to the test feature, and the refractive index corresponding to the reference feature is the real-time refractive index.
5. The terahertz thickness measurement method for soft-state solidified samples according to claim 4, characterized in that, Establishing the correspondence between the multiple reference features and the multiple refractive indices includes: The plurality of the reference features and the plurality of refractive indices are fitted into a curve formula; After finding the reference feature that is closest to the test feature in the corresponding table, the process includes: If the difference between the test feature and its closest reference feature is greater than the feature error threshold, the real-time refractive index is calculated using the curve formula.
6. The terahertz thickness measurement method for soft-state solidified samples according to claim 5, characterized in that, The formula for the curve is: ； Where n is the refractive index, f peak R is the frequency of the strongest absorption peak. 2 The goodness of fit is represented by a0, a1, and a2, which are the coefficients after fitting. If the difference between the test feature and its closest reference feature is greater than the feature error threshold, the real-time refractive index is calculated using the curve formula, including: If the following formula is satisfied, the real-time refractive index is calculated using the curve formula: ； in, f is the frequency of the strongest absorption peak in the test characteristics. peak The frequency of the strongest absorption peak in the reference feature is given in THz, where THz is the unit of terahertz.
7. The terahertz thickness measurement method for soft-state solidified samples according to claim 1, characterized in that, The step of calculating the thickness of the sample to be tested based on the real-time refractive index includes: The thickness of the sample to be tested is calculated using the following formula: ； Where d is the thickness of the sample to be tested, c is the speed of light in vacuum, and n real The real-time refractive index, t is the time delay between the air-to-sample interface echo and the base-to-bottom interface echo of the sample.
8. The terahertz thickness measurement method for soft-state solidified samples according to claim 1, characterized in that, After calculating the thickness of the sample to be tested, the following steps are included: Randomly select the sample to be tested and destroy the selected sample; The actual thickness of the sampled specimen is measured. If the difference between the actual thickness and the calculated thickness is less than the thickness error threshold, the test feature and real-time refractive index are entered into the corresponding relationship.
9. A terahertz thickness measurement system for soft-state solidified samples, characterized in that, The system includes: A terahertz spectrometer is used to acquire the terahertz waveform of a soft reference sample multiple times at preset intervals during the solidification process of the reference sample, and to extract multiple reference features from the multiple terahertz waveforms of the reference sample. A computing device for calculating multiple refractive indices of the reference sample during the curing process based on multiple reference features and the thickness of the reference sample; The computing device is also used to establish a correspondence between the plurality of the reference features and the plurality of the refractive indices; The terahertz spectrometer is also used to measure the terahertz waveform of the sample under test and extract the test characteristics of the terahertz waveform of the sample under test. The computing device is also used to determine the real-time refractive index corresponding to the test feature based on the correspondence. The computing device is also used to calculate the thickness of the sample under test based on the real-time refractive index.
10. The terahertz thickness measurement system for soft-state solidified samples according to claim 9, characterized in that, include: A thickness testing device is used to detect the thickness of the reference sample, or to detect the true thickness of the sample to be tested after extraction and destruction.