Thickness detection method and device, storage medium and computer equipment

Abstract

The invention discloses a thickness detection method. The method comprises the following steps: acquiring a blank time-domain signal, a time-domain signal of a standard sample with known thickness and a time-domain signal of a sample to be detected based on a terahertz time-domain spectroscopy system; performing corresponding frequency domain transformation on the time domain signals, and calculating a refractive index corresponding to each frequency component in the terahertz pulse signal based on a result after the frequency domain transformation; performing signal energy weighted average on all refractive indexes to obtain an equivalent average refractive index; and calculating the thickness of the to-be-measured sample by using the equivalent average refractive index. According to the method, the time-domain signal is converted into the frequency-domain signal, corresponding calculation is carried out, the refractive indexes corresponding to different frequency components in the terahertz pulse signal are obtained, then energy weighted averaging is carried out on the refractive indexes, the more accurate equivalent average refractive index is obtained, and when the thickness is calculated on the basis of the equivalent average refractive index subsequently, the thickness of the terahertz pulse signal is calculated more accurately. The influence caused by the dispersion phenomenon is effectively eliminated, and a more accurate thickness detection effect is obtained.

Description

Technical Field

[0001] This application relates to the field of nondestructive testing technology, and in particular to a thickness testing method, apparatus, storage medium, and computer equipment. Background Technology

[0002] Non-destructive testing (NDT) is a widely used non-destructive analytical technique in the scientific and technological industries for evaluating the properties of materials, parts, or systems. This type of method does not alter the properties of the object being tested, saving time and money in product evaluation and troubleshooting, and has significant application value. NDT is commonly used in many fields such as medicine, machinery, electrical engineering, cultural relic inspection, and aerospace. Among these, the measurement of material thickness is the most basic and common requirement in NDT, such as the precise detection of the uniformity of material coating thickness and flaw detection of workpieces or cultural relics. Ultrasonic testing, as a common NDT thickness measurement technique, has been widely used. However, limited by the wavelength of sound waves and the minimum time sampling interval of electronic instruments, ultrasonic thickness measurement is only suitable for larger objects. It is inadequate for situations requiring precise thickness measurement (such as micrometer-level resolution). Therefore, time-domain terahertz spectroscopy has been used to develop a material thickness measurement method based on the time-of-flight principle. Terahertz waves, with frequencies ranging from 0.1 THz to 10 THz and wavelengths between far-infrared and microwaves, possess strong penetrating power through most non-polar materials. Compared to X-rays, which also have strong penetrating power, terahertz waves have only one millionth the energy. When applied to object inspection, they do not cause ionization and damage to objects during penetration due to excessive energy, and are virtually harmless to humans. Therefore, they have enormous potential for non-destructive testing applications. Furthermore, with the miniaturization and portability of femtosecond lasers used to generate terahertz radiation, the technology of using terahertz waves for non-destructive thickness measurement has become a subject of increasing research by scientists.

[0003] However, it is understandable that time-domain terahertz pulse signals are not ideal single-frequency electromagnetic waves. They are actually composed of multiple different terahertz frequencies superimposed together. Since the refractive index of the same material is not the same for electromagnetic waves of different frequencies, the propagation speed of terahertz waves of different frequencies in the material varies. After the terahertz wave passes through the material, the distance between each frequency component in spacetime increases, causing the originally compact terahertz pulse to broaden and produce dispersion, which in turn greatly reduces the reliability of the final thickness detection result. Summary of the Invention

[0004] Based on this, and in response to the above problems, this application provides a thickness detection method, apparatus, storage medium, and computer equipment to at least solve the problem of low reliability of current thickness detection results.

[0005] In a first aspect, this application provides a thickness detection method based on a terahertz time-domain spectroscopy system, the method comprising:

[0006] The first time-domain signal of the blank sample, the second time-domain signal of the standard sample, and the third time-domain signal of the sample to be tested are obtained based on the terahertz time-domain spectroscopy system; wherein the standard sample and the sample to be tested are made of the same material, and the thickness of the standard sample is a preset first thickness;

[0007] A first frequency domain signal is obtained by transforming the first time domain signal, and a second frequency domain signal is obtained by transforming the second time domain signal.

[0008] Based on the first frequency domain signal, the second frequency domain signal, and the first thickness, the refractive index corresponding to each frequency component in the terahertz pulse signal is calculated.

[0009] The equivalent average refractive index is obtained by taking a signal energy-weighted average of all refractive indices.

[0010] The thickness of the sample under test is calculated using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal.

[0011] Optionally, the acquisition of the blank first time-domain signal, the second time-domain signal of the standard sample, and the third time-domain signal of the sample to be tested based on the terahertz time-domain spectroscopy system specifically includes:

[0012] In the detection optical path of the terahertz time-domain spectroscopy system, without placing any sample, the terahertz pulse signal emitted by the system after passing through the air is collected, and a blank first time-domain signal is obtained based on it.

[0013] The standard sample is placed in the detection optical path so that the terahertz pulse signal emitted by the system passes perpendicularly through the standard sample. The terahertz pulse signal after passing through is collected and the second time-domain signal of the standard sample is obtained based on it.

[0014] The sample to be tested is placed in the detection optical path so that the terahertz pulse signal emitted by the system passes perpendicularly through the sample to be tested. The terahertz pulse signal after passing through is collected and the third time-domain signal of the sample to be tested is obtained based on it.

[0015] Optionally, the step of calculating the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first frequency domain signal, the second frequency domain signal, and the first thickness includes:

[0016] Calculate the ratio of the first frequency domain signal to the second frequency domain signal, substitute the ratio into the first calculation formula, and obtain the phase shift corresponding to each frequency component in the terahertz pulse signal;

[0017] Substituting the phase shift and the first thickness into the second calculation formula, the refractive index corresponding to each frequency component in the terahertz pulse signal is obtained.

[0018] Optionally, the first calculation formula is:

[0019]

[0020] Where A is the ratio of the first frequency domain signal to the second frequency domain signal; T(ω) is the transmittance corresponding to frequency ω in the terahertz pulse signal; and i is the imaginary unit. This represents the phase shift corresponding to frequency ω in a terahertz pulse signal.

[0021] Optionally, the second calculation formula is:

[0022]

[0023] in, ω represents the phase shift corresponding to frequency ω in the terahertz pulse signal; n(ω) represents the refractive index corresponding to frequency ω in the terahertz pulse signal; ω represents the frequency; d0 represents the first thickness; and c represents the speed of light.

[0024] Optionally, the step of performing a signal energy-weighted average of all refractive indices to obtain the equivalent average refractive index specifically includes:

[0025] According to the third calculation formula, the equivalent average refractive index is obtained by taking a signal energy weighted average of all refractive indices.

[0026] The third calculation formula is as follows:

[0027]

[0028] Where N is the equivalent average refractive index; n k The frequency ω in the terahertz pulse signal k Corresponding refractive index; is Planck's constant.

[0029] Optionally, calculating the thickness of the sample under test using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal specifically includes:

[0030] Obtain the time t1 corresponding to the peak value in the first time domain signal; obtain the time t3 corresponding to the peak value in the third time domain signal;

[0031] The equivalent average refractive index, the time t1 corresponding to the peak value in the first time domain signal, and the time t3 corresponding to the peak value in the third time domain signal are substituted into the optical path difference calculation formula to calculate the thickness of the sample to be tested.

[0032] The formula for calculating the optical path difference includes:

[0033] (N-1)d=c(t3-t1);

[0034] Where N is the equivalent average refractive index; d is the thickness of the sample to be tested; c is the speed of light; t3 is the time corresponding to the peak value in the third time domain signal; and t1 is the time corresponding to the peak value in the first time domain signal.

[0035] In a second aspect, the present invention provides a thickness detection device, the device comprising:

[0036] The acquisition module is used to acquire a blank first time-domain signal, a second time-domain signal of the standard sample, and a third time-domain signal of the sample to be tested based on the terahertz time-domain spectroscopy system; wherein the standard sample and the sample to be tested are made of the same material, the thickness of the standard sample is known and is a preset first thickness, and the thickness of the sample to be tested is unknown;

[0037] The transformation module is used to transform the first time-domain signal to obtain a first frequency-domain signal, and to transform the second time-domain signal to obtain a second frequency-domain signal.

[0038] The first calculation module is used to calculate the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first frequency domain signal, the second frequency domain signal, and the first thickness.

[0039] The weighted average module is used to perform a weighted average of the signal energy for all refractive indices to obtain the equivalent average refractive index.

[0040] The second calculation module is used to calculate the thickness of the sample under test using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal.

[0041] In a third aspect, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, causes the processor to perform the steps of the method as described in any of the preceding claims.

[0042] In a fourth aspect, the present invention provides a computer device including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the steps of the method as described in any of the preceding claims.

[0043] The embodiments of this application have the following advantages or beneficial effects:

[0044] This invention provides a thickness detection method based on a terahertz time-domain spectroscopy system. The method includes: acquiring a blank first time-domain signal, a standard sample's second time-domain signal, and a test sample's third time-domain signal based on the terahertz time-domain spectroscopy system; wherein the standard sample and the test sample are made of identical materials, and the thickness of the standard sample is a preset first thickness; transforming the first time-domain signal to obtain a first frequency-domain signal, and transforming the second time-domain signal to obtain a second frequency-domain signal; calculating the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first and second frequency-domain signals and the first thickness; performing a signal energy-weighted average of all refractive indices to obtain an equivalent average refractive index; and calculating the thickness of the test sample using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal. This invention converts a time-domain signal into a frequency-domain signal and obtains the refractive index corresponding to different frequency components in a terahertz pulse signal through corresponding calculations. Then, it performs an energy-weighted average of the refractive index to obtain a more accurate equivalent average refractive index. This effectively eliminates the influence of dispersion when calculating the thickness based on the equivalent average refractive index, resulting in a more accurate and reliable thickness detection effect. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] in:

[0047] Figure 1 This application provides a method for measuring sample thickness based on traditional terahertz spectroscopy.

[0048] Figure 2 A schematic diagram showing the broadening of a terahertz pulse signal due to dispersion effect after passing through a sample under test, as provided in an embodiment of this application.

[0049] Figure 3 This is a schematic flowchart of a thickness detection method provided in an embodiment of this application;

[0050] Figure 4 A schematic diagram illustrating the transformation of a paper sample's time-domain signal into a frequency-domain signal, as provided in an embodiment of this application;

[0051] Figure 5 A time-domain waveform diagram of a time difference provided in an embodiment of this application;

[0052] Figure 6 A schematic diagram illustrating the principle of thickness measurement in a terahertz time-domain spectroscopy detection system provided in this application embodiment;

[0053] Figure 7 This application provides a measurement result of sample thickness based on the thickness detection method provided by the present invention, which is an embodiment of the present application.

[0054] Figure 8 This is a schematic diagram of the structure of a thickness detection device according to an embodiment of this application;

[0055] Figure 9 An internal structural diagram of the device in one embodiment is shown. Detailed Implementation

[0056] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0057] Traditional time-of-flight thickness measurement methods based on time-domain projected terahertz spectroscopy include: applying a terahertz time-domain spectroscopy system to measure a standard sample and the sample to be measured, both made of the same material and with known thicknesses, to obtain their time-domain signals and the times corresponding to the peak values ​​in the time-domain signals; simultaneously measuring the terahertz wave passing through air (i.e., without any sample placed on it) to obtain a blank time-domain signal and the times corresponding to the peak values, which serve as a reference signal for the terahertz time-domain spectrum. An optical path difference formula is established, and the time difference between the times corresponding to the peak values ​​in the blank time-domain signal and the time corresponding to the peak values ​​in the time-domain signal of the standard sample is substituted into the formula to obtain the terahertz refractive index of the standard sample. Since the materials are identical, this refractive index is also the refractive index of the sample to be measured; finally, the time difference between the times corresponding to the peak values ​​in the blank time-domain signal and the time corresponding to the peak values ​​in the time-domain signal of the sample to be measured, along with the refractive index, is substituted into the optical path difference formula to calculate the thickness of the sample to be measured.

[0058] A typical terahertz time-domain spectroscopy system comprises a femtosecond laser, a terahertz radiation generator and corresponding detection device, a time delay control system, and a data acquisition and signal processing system. Its working principle is generally as follows: the instrument generates a laser pulse using the laser, then uses optical elements to convert the laser pulse into terahertz pulses. These pulses are emitted to the object under test through a terahertz detector. As the terahertz waves pass through the object, they interact with the object's internal structure. A portion of the terahertz waves is reflected back and received by the detector. The received terahertz wave signal is converted into an electrical signal and processed by the signal processing system. The processing system analyzes the propagation time and intensity of the terahertz waves and calculates the object's thickness based on this data. Generally, the electrical signal is presented in the form of a time-domain signal, which can intuitively reflect data such as peak times.

[0059] In this embodiment, the thickness of paper, soda-lime glass, quartz, alumina ceramic, and zirconia ceramic samples was measured using the aforementioned conventional methods. Please refer to [link to relevant documentation]. Figure 1 This application provides a method for measuring sample thickness using traditional terahertz spectroscopy, where the calculated sample thickness is obtained using a traditional method, and the actual measured sample thickness is obtained using a micrometer. It can be observed that for soda-lime glass and paper samples, there is a significant difference between the thickness calculated using traditional terahertz spectroscopy and the actual thickness measured using a micrometer. The reasons for this are analyzed as follows:

[0060] Since time-domain terahertz pulse signals are composed of electromagnetic waves of various frequencies, these waves propagate at different speeds within materials. This speed difference is primarily determined by the material's refractive index. The refractive index refers to the degree to which an electromagnetic wave changes its propagation direction as it passes through a material. Different frequencies of electromagnetic waves will have different refractive indices within the same material, thus resulting in differences in their propagation distance and path. When a terahertz wave passes through a material, the spatial and temporal distances of its various frequency components change. This change depends on the aforementioned propagation speed and path. If a certain frequency propagates slowly within the material, its spatial and temporal distance will be relatively small; conversely, if a certain frequency propagates quickly, its spatial and temporal distance will be relatively large. Furthermore, the different dispersion effects of different materials also affect the propagation of terahertz waves. Dispersion refers to the changes in the frequency, direction, and speed of light during propagation. Generally, dispersion effects are related to the medium material; that is, different materials exhibit different dispersion effects in the terahertz frequency band.

[0061] In summary, for some materials, traditional terahertz spectroscopy methods for thickness measurement yield relatively accurate results; however, for other materials, due to dispersion effects and the inherent characteristics of terahertz pulse signals, these methods can lead to inaccurate results. In these other materials, the spatial and temporal distances of the electromagnetic waves at different frequency components of the terahertz pulse signal increase, causing the originally compact terahertz pulse to broaden—this is the so-called dispersion phenomenon. For details, please refer to [link to relevant documentation]. Figure 2 This diagram illustrates the broadening of a terahertz pulse signal after passing through a sample under test due to dispersion, as provided in an embodiment of this application. The waveform on the left broadens to the waveform on the right after a transmission time Δt due to the material's dispersion effect. Different materials exhibit varying dispersion effects in the terahertz band. The more pronounced the dispersion, the greater the discrepancy between the thickness obtained using traditional thickness measurement methods and the actual thickness (e.g., paper and soda-lime glass). Quartz and ceramics, however, exhibit weaker dispersion effects in the terahertz band, resulting in less significant differences between the measured results and the actual thickness.

[0062] Based on the above, this application proposes a thickness detection method, which is of great significance for measuring the thickness of materials with significant dispersion effects. Please refer to... Figure 3 This is a schematic diagram of a thickness detection method provided in an embodiment of this application. The method is based on the aforementioned terahertz time-domain spectroscopy system. Specifically:

[0063] Step 101: Obtain the first time-domain signal of the blank sample, the second time-domain signal of the standard sample, and the third time-domain signal of the sample to be tested based on the terahertz time-domain spectroscopy system; wherein the standard sample and the sample to be tested are made of the same material, and the thickness of the standard sample is the preset first thickness.

[0064] In this embodiment, based on the aforementioned terahertz time-domain spectroscopy system, no sample is placed in the detection optical path of the system. The terahertz pulse signal emitted by the system is collected after passing through the air, and converted into a time-domain signal by the signal processing module within the system, recorded as the blank first time-domain signal. Then, a pre-prepared standard sample with the same material as the sample to be tested and a thickness of a first thickness d0 is placed in the terahertz time-domain spectroscopy detection optical path, allowing the terahertz wave to pass perpendicularly through the standard sample. The terahertz pulse signal after passing through is collected, and converted into a time-domain signal by the signal processing module within the system, recorded as the second time-domain signal. Next, a sample of unknown thickness is placed in the detection optical path, allowing the terahertz wave to pass perpendicularly through the sample. The terahertz pulse signal after passing through is collected, and converted into a time-domain signal by the signal processing module within the system, recorded as the third time-domain signal. Here, the first thickness d0 is a known thickness.

[0065] In one feasible implementation, the first time t1 corresponding to the peak value in the first time domain signal, the second time t2 corresponding to the peak value in the second time domain signal, and the third time t3 corresponding to the peak value in the third time domain signal are recorded respectively.

[0066] Step 102: Obtain the first frequency domain signal by transforming the first time domain signal, and obtain the second frequency domain signal by transforming the second time domain signal.

[0067] In this embodiment of the application, the first time-domain signal E obtained above is... ref Fast Fourier transforms are performed on the second time-domain signal E0(t) and the second time-domain signal E0(t) respectively, and then the first frequency-domain signal E0(t) is obtained. ref (ω) and the second frequency domain signal E0(ω). For an example using a paper sample, please refer to [link / reference]. Figure 4 This is a schematic diagram illustrating the time-domain signal transformation of a paper sample into a frequency-domain signal according to an embodiment of this application. Figure 4 The left image in the diagram is the time-domain signal, and the right image is the frequency-domain signal obtained through Fast Fourier Transform.

[0068] Step 103: Based on the first frequency domain signal, the second frequency domain signal, and the first thickness, calculate the refractive index corresponding to each frequency component in the terahertz pulse signal.

[0069] In one feasible implementation, the first frequency domain signal E is calculated. ref The ratio A of ω to the second frequency domain signal E0(ω) is substituted into the first calculation formula to obtain the phase shift corresponding to each frequency component in the terahertz pulse signal. Phase shift Substituting the first thickness d0 into the second calculation formula, we obtain the refractive index n(ω) corresponding to each frequency component in the terahertz pulse signal. Here, each frequency component refers to the signal of each frequency contained in the terahertz pulse signal.

[0070] Among them, the first frequency domain signal E ref The ratio of (ω) to the second frequency domain signal E0(ω) is

[0071] The first calculation formula is: Where A is the ratio of the first frequency domain signal to the second frequency domain signal; T(ω) is the transmittance corresponding to frequency ω in the terahertz pulse signal; and i is the imaginary unit. This represents the phase shift corresponding to frequency ω in a terahertz pulse signal.

[0072] The second calculation formula is: in, ω represents the phase shift corresponding to frequency ω in the terahertz pulse signal; n(ω) represents the refractive index corresponding to frequency ω in the terahertz pulse signal; ω represents the frequency; d0 represents the first thickness; and c represents the speed of light.

[0073] It is understandable that, since terahertz pulse signals are composed of electromagnetic waves with multiple frequency components, converting them from a time-domain signal to a frequency-domain signal will yield frequency-domain signals corresponding to different frequencies ω. Then, based on these frequency-domain signals, the refractive index n(ω) at each frequency ω can be calculated according to the steps described above, thus obtaining the functional relationship between the refractive index and frequency. The terahertz time-domain spectrometer used in the experiment can be the TPF15K model from Diertech (Tianjin) Technology Co., Ltd. Considering the signal-to-noise ratio, the effective signal is typically taken within the range of 0.2–2.5 THz. The choice of spectrometer model here is merely an optimal method provided for the experiment and is not intended to impose excessive restrictions.

[0074] Step 104: Perform a signal energy weighted average on all refractive indices to obtain the equivalent average refractive index.

[0075] In one feasible implementation, the different refractive indices n(ω) corresponding to each frequency component obtained in step 103 are weighted by the corresponding signal energy to obtain an equivalent average refractive index N. The equivalent average refractive index N is then used as the corrected refractive index to reduce the influence of dispersion. Specifically, according to the third calculation formula, a weighted average of the signal energy is performed on all refractive indices to obtain the equivalent average refractive index N.

[0076] The third calculation formula is: Where N is the equivalent average refractive index; n k The frequency ω in the terahertz pulse signal k Corresponding refractive index; is Planck's constant.

[0077] It should be noted that ω k (k = 1, 2, 3...) represent the frequencies in step 103, n k (k = 1, 2, 3...) represents the refractive index n(ω) corresponding to each frequency ω in step 103; that is, assuming the fourth frequency ω = 1.5Thz obtained in step 103 has a corresponding refractive index n(ω) = n(1.5Thz) = 1.838; then ω here... k =1.5Thz, where k=4; and its corresponding n k =1.838. Introducing Planck's constant here transforms the refractive index calculation formula into an energy calculation formula, thereby achieving an energy-weighted average of the signal.

[0078] It is understandable that the refractive index is a function of the electromagnetic wave frequency, and it changes with the electromagnetic wave frequency. Therefore, in this embodiment of the application, the collected discrete terahertz time-domain pulse transmission signal is converted into a frequency-domain signal by the fast Fourier transform in step 102, thereby obtaining the transmittance at different terahertz frequencies. Then, the relationship between the refractive index and the frequency is calculated by the phase shift of the terahertz wave at each frequency. Finally, the equivalent average refractive index N is obtained by the weighted average N of the refractive index on the energy (the energy of the electromagnetic wave is proportional to its frequency), which provides a more accurate refractive index for subsequent calculation of the thickness of the object under test.

[0079] Step 105: Calculate the thickness of the sample under test using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal.

[0080] In this embodiment of the application, an optical path difference calculation formula is established based on the first time t1 corresponding to the peak value in the first time-domain signal obtained in step 101 and the second time t2 corresponding to the peak value in the second time-domain signal. Specifically, the "detection of the first time-domain signal" is named "blank detection," and the "detection of the second time-domain signal" is named "standard sample detection."

[0081] i. Calculate the time difference between the blank test and the standard sample test, i.e., calculate the time difference between the first and second time points as Δt0 = t2 - t1. (See also...) Figure 5 This is a schematic diagram of the time-domain waveform of a time difference Δt0 provided in an embodiment of this application.

[0082] ii. Calculate the optical path difference between the blank test and the standard sample test. See also... Figure 6 This is a schematic diagram illustrating the principle of thickness measurement in a terahertz time-domain spectroscopy detection system according to an embodiment of this application. In this system, a terahertz pulse signal is emitted from the transmitter, passes through the sample to be measured, and reaches the receiver. The receiver receives the terahertz pulse signal after it has passed through the sample. It can be observed that the optical path length of the terahertz pulse signal through air is L; while the optical path length of the terahertz pulse signal through a standard sample (with a thickness of d0) is L - d0 + nd0, where n is the terahertz refractive index of the standard sample. Therefore, the formula for calculating the optical path difference is: (n-1)d0 = cΔt0; where c is the speed of light.

[0083] iii. Further, the general form of the formula for calculating the optical path difference is obtained: (refractive index - 1) sample thickness = c * time difference; where c is the speed of light.

[0084] In one feasible implementation, based on the first time t1 corresponding to the peak value in the first time-domain signal obtained in step 101, the third time t3 corresponding to the peak value in the third time-domain signal, and the equivalent average refractive index N obtained in step 104, the thickness of the sample to be measured can be calculated by substituting these values ​​into the optical path difference calculation formula. Specifically: the time difference between the first and third times is calculated as t3-t1. The optical path difference calculation formula, including the thickness of the sample to be measured, is: (N-1)d=c(t3-t1); where N is the equivalent average refractive index; d is the thickness of the sample to be measured; c is the speed of light; t3 is the time corresponding to the peak value in the third time-domain signal; and t1 is the time corresponding to the peak value in the first time-domain signal.

[0085] In this embodiment, the thickness of paper, soda-lime glass, quartz, alumina ceramic, and zirconia ceramic samples was remeasured using the thickness measurement method provided in this embodiment. Please refer to [link to relevant documentation]. Figure 7 This application provides a method for measuring sample thickness based on the thickness detection method provided by the present invention. Similarly, the calculated sample thickness is the thickness calculated using the method proposed in this application, and the actual measured sample thickness is the actual thickness measured using a micrometer. Please refer to [reference needed]. Figure 1 and Figure 7 It can be clearly seen that by introducing the equivalent average refractive index N to correct the original refractive index and re-estimating the thickness based on the equivalent average refractive index, the estimated thickness of soda-lime glass and paper samples is closer to the actual thickness. In other words, for these materials with more obvious dispersion effects, the thickness calculated by the method proposed in the embodiments of this application is more accurate and reliable than the result of traditional terahertz spectroscopy thickness measurement.

[0086] This application embodiment converts the time-domain signal into a frequency-domain signal and obtains the refractive index corresponding to different frequency components in the terahertz pulse signal through corresponding calculations. Then, it performs energy-weighted averaging on the refractive index to obtain a more accurate equivalent average refractive index. This effectively eliminates the influence of dispersion when the thickness is subsequently calculated based on the equivalent average refractive index, thereby obtaining a more accurate thickness detection effect.

[0087] Understandably, compared to micrometers and vernier calipers, which are only suitable for measuring regularly shaped objects, this thickness measurement method can also be used to measure irregularly shaped objects with a certain internal spatial structure. Furthermore, because terahertz time-domain spectroscopy thickness measurement achieves micrometer-level accuracy, it is more accurate than conventional ultrasonic thickness measurement methods. While optical equal-inclination interferometry and equal-thickness interferometry can also achieve micrometer-level accuracy due to the high penetration characteristics of terahertz waves, their applicability is limited to transparent objects. Terahertz waves, however, can be used to measure the thickness of many opaque, non-polar dielectrics (such as ceramics, glass, textiles, and paper), offering a wider range of applications. Moreover, because this thickness measurement method is essentially a non-destructive testing technique, it can perform real-time, non-contact measurements on charged, high-temperature objects, or valuable artifacts, posing virtually no harm to the object being measured or the personnel performing the measurement, making it safe and reliable.

[0088] In this embodiment, based on traditional terahertz time-domain spectroscopy for thickness measurement, the influence of dispersion factors caused by the propagation of time-domain terahertz pulses within an object on thickness measurement is considered. An equivalent refractive index is introduced to correct the thickness calculation, effectively eliminating the influence of dispersion effects and achieving better results. Furthermore, different models of terahertz time-domain spectrometers have varying parameters such as response bandwidth (terahertz emission spectrum range), dynamic range, and spectral resolution. When using this invention to measure thickness, the narrower the response bandwidth, the higher the spectral resolution, and the larger the dynamic range of the instrument, the better the estimation effect.

[0089] Please see Figure 8 The diagram below shows a thickness detection device according to an embodiment of this application. The device includes:

[0090] The acquisition module 801 is used to acquire a blank first time-domain signal, a standard sample second time-domain signal, and a test sample third time-domain signal based on a terahertz time-domain spectroscopy system; wherein the standard sample and the test sample are made of the same material, the thickness of the standard sample is known and is a preset first thickness, and the thickness of the test sample is unknown.

[0091] The transformation module 802 is used to transform the first time-domain signal to obtain a first frequency-domain signal, and to transform the second time-domain signal to obtain a second frequency-domain signal.

[0092] The first calculation module 803 is used to calculate the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first frequency domain signal, the second frequency domain signal, and the first thickness.

[0093] The weighted average module 804 is used to perform a signal energy weighted average on all refractive indices to obtain the equivalent average refractive index.

[0094] The second calculation module 805 is used to calculate the thickness of the sample under test using the equivalent average refractive index, the first time domain signal, and the third time domain signal.

[0095] In this embodiment, the relevant contents of the acquisition module 801, transformation module 802, first calculation module 803, weighted average module 804, and second calculation module 805 can be found in the following references. Figures 1 to 7 The contents of the illustrated embodiments will not be repeated here.

[0096] In this application embodiment, a computer-readable storage medium is provided, which stores a computer program. When the computer program is executed by a processor, the processor performs any one of the methods described in the above method embodiments.

[0097] In one embodiment, an apparatus is provided, including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform any of the methods described in the above method embodiments.

[0098] Figure 9 An internal structural diagram of a device in one embodiment is shown. This computer device can specifically be a terminal, a server, or a gateway. Figure 9 As shown, the computer device includes a processor, memory, and network interface connected via a system bus. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and may also store a computer program. When executed by the processor, this computer program causes the processor to perform the steps in the above-described method embodiments. The internal memory may also store a computer program, which, when executed by the processor, causes the processor to perform the steps in the above-described method embodiments. Those skilled in the art will understand that... Figure 9 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0099] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A thickness detection method, said method being based on a terahertz time-domain spectroscopy system, characterized in that, The method includes: The first time-domain signal of the blank sample, the second time-domain signal of the standard sample, and the third time-domain signal of the sample to be tested are obtained based on the terahertz time-domain spectroscopy system; wherein the standard sample and the sample to be tested are made of the same material, and the thickness of the standard sample is a preset first thickness; A first frequency domain signal is obtained by transforming the first time domain signal, and a second frequency domain signal is obtained by transforming the second time domain signal. Based on the first frequency domain signal, the second frequency domain signal, and the first thickness, the refractive index corresponding to each frequency component in the terahertz pulse signal is calculated. The equivalent average refractive index is obtained by taking a signal energy-weighted average of all refractive indices. The thickness of the sample under test is calculated using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal.

2. The method according to claim 1, characterized in that, The acquisition of the blank first time-domain signal, the second time-domain signal of the standard sample, and the third time-domain signal of the sample to be tested based on the terahertz time-domain spectroscopy system specifically includes: In the detection optical path of the terahertz time-domain spectroscopy system, without placing any sample, the terahertz pulse signal emitted by the system after passing through the air is collected, and a blank first time-domain signal is obtained based on it. The standard sample is placed in the detection optical path so that the terahertz pulse signal emitted by the system passes perpendicularly through the standard sample. The terahertz pulse signal after passing through is collected and the second time-domain signal of the standard sample is obtained based on it. The sample to be tested is placed in the detection optical path so that the terahertz pulse signal emitted by the system passes perpendicularly through the sample to be tested. The terahertz pulse signal after passing through is collected and the third time-domain signal of the sample to be tested is obtained based on it.

3. The method according to claim 1, characterized in that, The calculation of the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first frequency domain signal, the second frequency domain signal, and the first thickness includes: Calculate the ratio of the first frequency domain signal to the second frequency domain signal, substitute the ratio into the first calculation formula, and obtain the phase shift corresponding to each frequency component in the terahertz pulse signal; Substituting the phase shift and the first thickness into the second calculation formula, the refractive index corresponding to each frequency component in the terahertz pulse signal is obtained.

4. The method according to claim 3, characterized in that, The first calculation formula is: Where A is the ratio of the first frequency domain signal to the second frequency domain signal; T(ω) is the transmittance corresponding to frequency ω in the terahertz pulse signal; and i is the imaginary unit. This represents the phase shift corresponding to frequency ω in a terahertz pulse signal.

5. The method according to claim 4, characterized in that, The second calculation formula is: in, ω represents the phase shift corresponding to frequency ω in the terahertz pulse signal; n(ω) represents the refractive index corresponding to frequency ω in the terahertz pulse signal; ω represents the frequency; d0 represents the first thickness; and c represents the speed of light.

6. The method according to claim 1, characterized in that, The process of taking a signal energy-weighted average of all refractive indices to obtain the equivalent average refractive index specifically includes: According to the third calculation formula, the equivalent average refractive index is obtained by taking a signal energy weighted average of all refractive indices. The third calculation formula is as follows: Where N is the equivalent average refractive index; n k The frequency ω in the terahertz pulse signal k Corresponding refractive index; is Planck's constant.

7. The method according to claim 1, characterized in that, The calculation of the thickness of the sample under test using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal specifically includes: Obtain the time t1 corresponding to the peak value in the first time domain signal; obtain the time t3 corresponding to the peak value in the third time domain signal; The equivalent average refractive index, the time t1 corresponding to the peak value in the first time domain signal, and the time t3 corresponding to the peak value in the third time domain signal are substituted into the optical path difference calculation formula to calculate the thickness of the sample to be tested. The formula for calculating the optical path difference includes: (N-1)d=c(t3-t1); Where N is the equivalent average refractive index; d is the thickness of the sample to be tested; c is the speed of light; t3 is the time corresponding to the peak value in the third time domain signal; and t1 is the time corresponding to the peak value in the first time domain signal.

8. A thickness detection device, characterized in that, The device includes: The acquisition module is used to acquire a blank first time-domain signal, a second time-domain signal of the standard sample, and a third time-domain signal of the sample to be tested based on the terahertz time-domain spectroscopy system; wherein the standard sample and the sample to be tested are made of the same material, the thickness of the standard sample is known and is a preset first thickness, and the thickness of the sample to be tested is unknown; The transformation module is used to transform the first time-domain signal to obtain a first frequency-domain signal, and to transform the second time-domain signal to obtain a second frequency-domain signal. The first calculation module is used to calculate the refractive index corresponding to each frequency component in the terahertz pulse signal based on the first frequency domain signal, the second frequency domain signal, and the first thickness. The weighted average module is used to perform a weighted average of the signal energy for all refractive indices to obtain the equivalent average refractive index. The second calculation module is used to calculate the thickness of the sample under test using the equivalent average refractive index, the first time-domain signal, and the third time-domain signal.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

10. A computer device, comprising a memory and a processor, characterized in that, The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

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