CN114894105B - Method and system for measuring thickness of nonmetallic material in atmospheric environment - Google Patents
Method and system for measuring thickness of nonmetallic material in atmospheric environment Download PDFInfo
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- 239000000463 material Substances 0.000 title claims abstract description 37
- 238000000034 method Methods 0.000 title claims abstract description 26
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 60
- 238000005516 engineering process Methods 0.000 claims abstract description 38
- 238000001328 terahertz time-domain spectroscopy Methods 0.000 claims abstract description 36
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- 239000004810 polytetrafluoroethylene Substances 0.000 description 11
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 11
- 238000001228 spectrum Methods 0.000 description 5
- 239000007769 metal material Substances 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- -1 coatings Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000011152 fibreglass Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
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- 238000000691 measurement method Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
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- 239000010703 silicon Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
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- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
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Abstract
The invention relates to a method and a system for measuring the thickness of a nonmetallic material in an atmospheric environment, and belongs to the technical field of thickness measurement. Firstly, measuring time domain signals of air in a dry environment or in a nitrogen environment and an atmospheric environment respectively, and carrying out Fourier transform on the time domain signals in the two environments to determine the propagation function of terahertz waves in humid air. And then measuring a time domain signal of the sample to be measured in an atmospheric environment, carrying out Fourier transform on the time domain signal of the sample to obtain a frequency domain signal of the sample, and carrying out reconstruction and inverse Fourier transform on the frequency domain signal of the sample by using a propagation function to obtain a reconstructed time domain signal of the sample to be measured in a dry environment or a nitrogen environment. And finally, calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal, so that the thickness of the nonmetallic material can be accurately measured by using the terahertz time-domain spectroscopy technology in the atmospheric environment without measuring in a dry environment.
Description
Technical Field
The invention relates to the technical field of thickness measurement, in particular to a method and a system for measuring the thickness of a nonmetallic material in an atmospheric environment by using a terahertz time-domain spectroscopy technology.
Background
Nonmetallic materials including ceramics, coatings, paper, plastic pipes and the like are basic materials necessary for industrial production and people's life. Among them, the thickness is the most important index of non-metallic material products, concerning reliability in use and maintenance. Therefore, the high-precision detection technology of the thickness has important significance for the quality control and the use process monitoring of nonmetallic material products.
The frequency of the terahertz wave is 0.1-10 THz, and the wavelength is 0.03-3 mm. The terahertz time-domain spectroscopy technology is a non-metal material thickness measurement technology with great potential, has the characteristics of no damage, rapidness, non-contact and high precision, and calculates the thickness of a measured sample according to the delay time of a echo peak and a main peak in the measured sample. However, moisture in the air has strong absorption to terahertz waves, and the terahertz time-domain signal tail section in the atmospheric environment generates stray oscillation due to the absorption of water vapor, so that an echo peak of a nonmetallic material is covered, and the phenomenon enables the terahertz time-domain spectroscopy technology to be only applied to thickness measurement of nonmetallic materials in special environments such as dry air, nitrogen and the like, and limits the application of the terahertz time-domain spectroscopy technology to industrial sites.
Therefore, a method and system for measuring the thickness of a non-metallic material in an atmospheric environment by using terahertz time-domain spectroscopy are needed.
Disclosure of Invention
The invention aims to provide a method and a system for measuring the thickness of a nonmetallic material in an atmospheric environment, which can realize the accurate measurement of the thickness of the nonmetallic material by utilizing a terahertz time-domain spectroscopy technology in the atmospheric environment.
In order to achieve the above object, the present invention provides the following solutions:
a method of measuring the thickness of a nonmetallic material in an atmospheric environment, the method comprising:
in a dry environment or a nitrogen environment, measuring a time domain signal of dry air by using a terahertz time domain spectroscopy technology to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
in the atmospheric environment, measuring a time domain signal of a sample to be measured by using a terahertz time domain spectroscopy technology to obtain a sample time domain signal; the material of the sample to be detected is a nonmetallic material;
performing Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
and calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal.
A system for measuring the thickness of a nonmetallic material in an atmospheric environment, the system comprising:
the propagation function determining module is used for measuring a time domain signal of the dry air by using a terahertz time domain spectroscopy technology in a dry environment or a nitrogen environment to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
the sample time domain signal acquisition module is used for measuring time domain signals of a sample to be measured by using a terahertz time domain spectroscopy technology under the atmospheric environment to obtain sample time domain signals; the material of the sample to be detected is a nonmetallic material;
the reconstruction module is used for carrying out Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
and the thickness calculation module is used for calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a method and a system for measuring the thickness of a nonmetallic material in an atmospheric environment, which are characterized in that a terahertz time-domain spectroscopy technology is utilized to measure a time-domain signal of dry air in a dry environment or a nitrogen environment to obtain a first time-domain signal, a terahertz time-domain spectroscopy technology is utilized to measure a time-domain signal of humid air in the atmospheric environment to obtain a second time-domain signal, fourier transformation is respectively carried out on the first time-domain signal and the second time-domain signal to obtain a first frequency-domain signal and a second frequency-domain signal, and a propagation function of terahertz waves in the humid air is determined according to the first frequency-domain signal and the second frequency-domain signal. And then in the atmospheric environment, measuring a time domain signal of a sample to be measured by using a terahertz time-domain spectroscopy technology to obtain a sample time domain signal, carrying out Fourier transform on the sample time domain signal to obtain a sample frequency domain signal, reconstructing the sample frequency domain signal by using a propagation function to obtain a reconstructed frequency domain signal of the sample to be measured in a dry environment or a nitrogen environment, and carrying out Fourier inverse transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be measured in the dry environment or the nitrogen environment. And finally, calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal, so that the thickness of the nonmetallic material can be accurately measured by using the terahertz time-domain spectroscopy technology in the atmospheric environment without measuring in a dry environment.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a measurement method according to embodiment 1 of the present invention;
FIG. 2 is a spectrum of a first time domain signal in a dry environment according to embodiment 1 of the present invention;
FIG. 3 is a graph showing the amplitude and frequency of the first frequency domain signal in the dry environment according to embodiment 1 of the present invention;
fig. 4 is a phase frequency diagram of a first frequency domain signal in a dry environment according to embodiment 1 of the present invention;
FIG. 5 is a spectrum of a second time domain signal in an atmospheric environment according to embodiment 1 of the present invention;
FIG. 6 is a graph showing the amplitude and frequency of the second frequency domain signal in the atmospheric environment according to embodiment 1 of the present invention;
FIG. 7 is a phase frequency diagram of a second frequency domain signal in an atmospheric environment according to embodiment 1 of the present invention;
FIG. 8 is a graph of the amplitude-frequency of the propagation function provided in embodiment 1 of the present invention;
FIG. 9 is a spectrum of the sample time domain signal of PTFE plate sample in the atmospheric environment according to example 1 of the present invention;
FIG. 10 is a graph showing the frequency domain signal of PTFE sheet sample in the atmospheric environment according to example 1 of the present invention;
FIG. 11 is a phase frequency plot of the sample frequency domain signal of a PTFE plate sample in an atmospheric environment according to example 1 of the present invention;
FIG. 12 is a graph showing the frequency of the reconstructed frequency domain signal according to embodiment 1 of the present invention;
fig. 13 is a phase-frequency diagram of a reconstructed frequency domain signal according to embodiment 1 of the present invention;
FIG. 14 is a spectrum chart of a reconstructed time domain signal according to embodiment 1 of the present invention;
fig. 15 is a system block diagram of a measurement system according to embodiment 2 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a method and a system for measuring the thickness of a nonmetallic material in an atmospheric environment, which can realize the accurate measurement of the thickness of the nonmetallic material by utilizing a terahertz time-domain spectroscopy technology in the atmospheric environment.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1:
the embodiment is used for providing a method for measuring the thickness of a nonmetallic material in an atmospheric environment, as shown in fig. 1, the method includes:
s1: in a dry environment or a nitrogen environment, measuring a time domain signal of dry air by using a terahertz time domain spectroscopy technology to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
s1, measuring a time domain signal of dry air in a dry environment or a nitrogen environment by adopting a terahertz time domain spectroscopy technology to obtain a first time domain signal f dry-air (t) performing Fourier transform on the first time domain signal of the dry air to obtain a first frequency domain signal E of the dry air in a dry environment or a nitrogen environment dry-air (omega). Measuring a time domain signal of humid air in an atmospheric environment by adopting a terahertz time-domain spectroscopy technology to obtain a second time domain signal f wet-air (t) performing Fourier transform on the second time domain signal of the humid air to obtain a second frequency domain signal E of the humid air in the atmospheric environment wet-air (ω)。
The first time domain signal of the dry air according to this embodiment may be measured in an experimental environment without being measured in a field environment.
According to the first frequency domain signal E of the dry air dry-air (omega) and second frequency domain signal E of humid air wet-air (ω), a propagation function T (ω, L) of the terahertz wave in the humid air is calculated. Specifically, a first ratio of the second frequency domain signal to the first frequency domain signal is calculated, wherein the first ratio is a propagation function of the terahertz wave in humid air.
The propagation function is as follows:
in the formula (1), T (omega, L) is a propagation function; e (E) wet-air (ω) is a second frequency domain signal; e (E) dry-air (ω) is a first frequency domain signal; j is the imaginary part;is the complex refractive index of moist air; />Is the complex refractive index of dry air; omega is the angular frequency; l is the transmission distance.
S2: in the atmospheric environment, measuring a time domain signal of a sample to be measured by using a terahertz time domain spectroscopy technology to obtain a sample time domain signal; the material of the sample to be detected is a nonmetallic material;
measuring a time domain signal of a sample to be measured in an atmospheric environment by adopting a terahertz time domain spectroscopy technology to obtain a sample time domain signal f wet-sam (t). The nonmetallic material in this embodiment may be any one of plastic, rubber, fiberglass, silicon wafer, glue layer and cardboard. The sample to be measured has a certain thickness which can be 1mm-110mm.
S3: performing Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
performing Fourier transform on the sample time domain signal to obtain a sample frequency domain signal E wet-sam (ω)。
S2, calculating a sample frequency domain signal of the sample to be measured in the atmospheric environment by using a propagation function of the terahertz wave in the humid air, and reconstructing to obtain a reconstructed frequency domain signal E of the sample to be measured in the dry environment or the nitrogen environment dry-sam (ω)。
Specifically, the sample frequency domain signal of the sample to be measured in the atmospheric environment can be described as:
in the formula (2), E wet-sam (ω) is the sample frequency domain signal; e (E) wet-air (ω) is a second frequency domain signal of humid air;the complex refractive index of the sample to be measured is represented by omega, and the angular frequency is represented by omega; d is the thickness of the sample to be measured; c is the propagation speed of the terahertz wave in vacuum.
Combining the formula (1) and the formula (2) to obtain a sample frequency domain signal E of the sample to be tested in the atmospheric environment wet-sam (omega) and first frequency domain signal E of drying air dry-aie The relationship of (ω) is:
the frequency domain expression of the sample to be measured in the dry environment is:
the terahertz frequency domain relation of the sample to be measured in the dry environment and the atmospheric environment can be obtained by combining the formula (3) and the formula (4):
in the formula (5), E dry-sam (ω) reconstructing the frequency domain signal; e (E) wet-sam (ω) is the sample frequency domain signal; t (ω, L-d) is a propagation function.
Typically, the transmission distance L of the terahertz wave is far greater than the thickness d of the sample to be measured, and T (ω, L-d) may be approximated as T (ω, L). The reconstruction method is: and calculating a second ratio of the sample frequency domain signal and the propagation function, wherein the second ratio is a reconstructed frequency domain signal of the sample to be measured in a dry environment or a nitrogen environment, and the reconstructed frequency domain signal is shown in the following formula (6).
Reconstructing a frequency domain signal E of a sample to be measured in a dry environment calculated by using the formula (6) dry-sam (omega) performing inverse Fourier transform to obtain a reconstructed time domain signal f of the sample to be measured in a dry environment dry-sam (t)。
S4: and calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal.
Specifically, S4 may include:
(1) Determining a first point in time of a dominant wave of a first time domain signal; determining a second point in time of the main wave of the reconstructed time-domain signal and a third point in time of the first echo;
the main wave is the peak point of the main pulse, and the first echo is the peak point of the first echo.
(2) Calculating the time difference between the first time point and the second time point to obtain a first delay time; calculating the time difference between the second time point and the third time point to obtain a second delay time;
the first delay time is the time difference Deltat between the main wave of the first time domain signal of the dry air and the main wave of the reconstructed time domain signal of the sample to be tested 1 The second delay time is the time difference delta t between the main wave of the reconstructed time domain signal of the sample to be detected and the first echo 2 . It should be noted that, subtracting the second time point from the first time point, and taking the absolute value to obtain the first delay time; and subtracting the third time point from the second time point, and taking the absolute value to obtain the second delay time.
(3) And calculating the thickness of the sample to be measured according to the first delay time and the second delay time.
Specifically, the first delay time and the second delay time are taken as inputs, and the average refractive index is calculated by using a refractive index calculation formula; and calculating the thickness of the sample to be measured by using the thickness calculation formula by taking the average refractive index as input.
The refractive index calculation formula used in this embodiment is:
in the formula (7), n is an average refractive index; Δt (delta t) 1 Is a first delay time; Δt (delta t) 2 Is the second delay time.
The thickness calculation formula used in this embodiment is:
in the formula (8), d is the thickness of the sample to be detected; c is the propagation speed of terahertz waves in vacuum; Δt (delta t) 1 Is a first delay time; n is the average refractive index.
The method for measuring the thickness of the nonmetallic material by using the terahertz time-domain spectroscopy technology in the atmospheric environment provided by the embodiment comprises the following steps: and measuring dry air by using a terahertz time-domain spectroscopy technology in a dry environment to obtain a first time-domain signal, and measuring humid air and a sample to be measured by using the terahertz time-domain spectroscopy technology in an atmospheric environment to obtain a second time-domain signal and a sample time-domain signal, wherein the first echo waveform of the sample is covered by moisture oscillation. Carrying out Fourier transform on air time domain signals measured under different environments to obtain a propagation function, carrying the propagation function into a sample frequency domain signal obtained by carrying out Fourier transform on the sample time domain signal, carrying out inverse Fourier transform to obtain a reconstructed time domain signal of a sample to be measured under a dry environment, and finally obtaining the refractive index of the sample to be measured by calculating the position relationship between a first time domain signal of dry air and a main wave and a first echo of the reconstructed time domain signal in a time domain spectrum and further calculating the thickness according to the refractive index. The method of the embodiment does not need to measure in a dry environment, can measure the thickness of the sample by reconstructing the time domain signal of the sample in the atmospheric environment, and has convenient measurement and high accuracy. The method of the embodiment can directly measure the refractive index and thickness information of the nonmetallic material in the atmosphere environment, and has important practical significance for the application of the terahertz technology in thickness measurement.
Here, the method of this example will be further described by taking a PTFE sheet sample (thickness measurement value of about 3.50 cm) whose refractive index and thickness are unknown as an example, and the specific method is as follows:
(1) First measurement
Introducing dry air into the experimental device, and starting to measure the dry air when the hygrometer displays humidity of about 1% to obtain a first dry airTime domain signals, as shown in fig. 2, and stores the obtained data. The main wave peak position of the dry air obtained at this time is t 0 I.e. a first point in time t of the main wave of the first time domain signal can be determined 0 。
(2) Second measurement
After the dry air is detected, the air supply to the experimental device is stopped, after the humidity displayed by the hygrometer is stable, the measurement of the humid air is started, a second time domain signal of the humid air is obtained, as shown in fig. 5, and the obtained data are stored.
(3) Third measurement
After the humid air is measured, a PTFE plate-shaped sample is put into the experimental device, the PTFE plate-shaped sample is measured, a sample time domain signal of the PTFE plate-shaped sample is obtained, as shown in fig. 9, and the obtained data are stored.
(4) Signal reconstruction
Carrying out Fourier transform on the three obtained signals by using software, wherein the amplitude-frequency diagram of the first frequency domain signal in a dry environment is shown in figure 3, and the phase-frequency diagram is shown in figure 4; the amplitude-frequency diagram of the second frequency domain signal in the atmospheric environment is shown in fig. 6, and the phase-frequency diagram is shown in fig. 7; the amplitude-frequency diagram of the sample frequency domain signal of the PTFE sheet sample in the atmospheric environment is shown in fig. 10, and the phase-frequency diagram is shown in fig. 11. The signal reconstruction is performed according to the following formula to obtain a reconstructed frequency domain signal, the amplitude-frequency diagram of the propagation function is shown in fig. 8, the amplitude-frequency diagram of the reconstructed frequency domain signal is shown in fig. 12, and the phase-frequency diagram is shown in fig. 13. Then the reconstructed frequency domain signal is subjected to inverse Fourier transform to obtain a reconstructed time domain signal, as shown in FIG. 14, the main wave peak position of the reconstructed time domain signal of the PTFE plate-shaped sample obtained at the moment is t 1 Echo wave crest position t 2 Determining a second point in time t of the main wave of the reconstructed time-domain signal 1 And a third point in time t of the first echo 2 。
In the formula (9), E rec Is a reconstructed frequency domain signal after fourier transformation; e (E) r，n Is a first frequency domain signal of the dry air after fourier transform in a dry environment; e (E) r，at Is a second frequency domain signal of the humid air after fourier transformation in the atmospheric environment; e (E) s，at Is a sample frequency domain signal of a PTFE plate sample after Fourier transform in an atmospheric environment.
(5) Calculating refractive index
The refractive index of the PDFE plate-like sample was calculated using formula (7).
(6) Calculating thickness
The thickness of the PTFE sheet sample was calculated using the formula (8).
Example 2:
the present embodiment is used to provide a system for measuring the thickness of a nonmetallic material in an atmospheric environment, as shown in fig. 15, including:
the propagation function determining module M1 is used for measuring a time domain signal of the dry air by using a terahertz time domain spectroscopy technology in a dry environment or a nitrogen environment to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
the sample time domain signal acquisition module M2 is used for measuring a time domain signal of a sample to be measured by using a terahertz time domain spectroscopy technology in an atmospheric environment to obtain a sample time domain signal; the material of the sample to be detected is a nonmetallic material;
the reconstruction module M3 is used for carrying out Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
and the thickness calculation module M4 is used for calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal.
In this specification, each embodiment is mainly described in the specification as a difference from other embodiments, and the same similar parts between the embodiments are referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (4)
1. A method of measuring the thickness of a nonmetallic material in an atmospheric environment, the method comprising:
in a dry environment or a nitrogen environment, measuring a time domain signal of dry air by using a terahertz time domain spectroscopy technology to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
in the atmospheric environment, measuring a time domain signal of a sample to be measured by using a terahertz time domain spectroscopy technology to obtain a sample time domain signal; the material of the sample to be detected is a nonmetallic material;
performing Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
calculating the thickness of the sample to be measured according to the first time domain signal and the reconstruction time domain signal;
the determining a propagation function of the terahertz wave in the humid air according to the first frequency domain signal and the second frequency domain signal specifically comprises: calculating a first ratio of the second frequency domain signal to the first frequency domain signal, wherein the first ratio is a propagation function of terahertz waves in humid air;
the propagation function includes:
wherein T (ω, L) is a propagation function; e (E) wet-air (ω) is a second frequency domain signal; e (E) dry-air (ω) is a first frequency domain signal;is the complex refractive index of moist air; />Is the complex refractive index of dry air; omega is the angular frequency; l is the transmission distance;
the calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal specifically includes:
determining a first point in time of a dominant wave of the first time domain signal;
determining a second point in time of the main wave of the reconstructed time domain signal and a third point in time of the first echo;
calculating the time difference between the first time point and the second time point to obtain a first delay time; calculating the time difference between the second time point and the third time point to obtain a second delay time;
calculating the thickness of the sample to be measured according to the first delay time and the second delay time;
the calculating the thickness of the sample to be measured according to the first delay time and the second delay time specifically includes:
taking the first delay time and the second delay time as inputs, and calculating an average refractive index by using a refractive index calculation formula;
calculating the thickness of the sample to be measured by using the average refractive index as input and a thickness calculation formula;
the refractive index calculation formula includes:
wherein n is the average refractive index; Δt (delta t) 1 Is a first delay time; Δt (delta t) 2 Is a second delay time;
the thickness calculation formula includes:
wherein d is the thickness of the sample to be measured; c is the propagation speed of terahertz waves in vacuum; Δt (delta t) 1 Is a first delay time; n is the average refractive index.
2. The method according to claim 1, wherein reconstructing the sample frequency domain signal using the propagation function to obtain a reconstructed frequency domain signal of the sample under a dry environment or a nitrogen environment specifically comprises:
and calculating a second ratio of the sample frequency domain signal to the propagation function, wherein the second ratio is a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment.
3. The method of claim 2, wherein the reconstructed frequency domain signal is:
wherein E is dry-sam (ω) reconstructing the frequency domain signal; e (E) wet-sam (ω) is the sample frequency domain signal; t (ω, L) is a propagation function.
4. A system for measuring the thickness of a nonmetallic material in an atmospheric environment, the system comprising:
the propagation function determining module is used for measuring a time domain signal of the dry air by using a terahertz time domain spectroscopy technology in a dry environment or a nitrogen environment to obtain a first time domain signal; in the atmospheric environment, measuring a time domain signal of humid air by using a terahertz time-domain spectroscopy technology to obtain a second time domain signal; performing Fourier transform on the first time domain signal and the second time domain signal respectively to obtain a first frequency domain signal and a second frequency domain signal; determining a propagation function of terahertz waves in humid air according to the first frequency domain signal and the second frequency domain signal;
the sample time domain signal acquisition module is used for measuring time domain signals of a sample to be measured by using a terahertz time domain spectroscopy technology under the atmospheric environment to obtain sample time domain signals; the material of the sample to be detected is a nonmetallic material;
the reconstruction module is used for carrying out Fourier transform on the sample time domain signal to obtain a sample frequency domain signal; reconstructing the sample frequency domain signal by using the propagation function to obtain a reconstructed frequency domain signal of the sample to be detected in a dry environment or a nitrogen environment; performing inverse Fourier transform on the reconstructed frequency domain signal to obtain a reconstructed time domain signal of the sample to be detected in a dry environment or a nitrogen environment;
the thickness calculation module is used for calculating the thickness of the sample to be measured according to the first time domain signal and the reconstruction time domain signal;
the determining a propagation function of the terahertz wave in the humid air according to the first frequency domain signal and the second frequency domain signal specifically comprises: calculating a first ratio of the second frequency domain signal to the first frequency domain signal, wherein the first ratio is a propagation function of terahertz waves in humid air;
the propagation function includes:
wherein T (ω, L) is a propagation function; e (E) wet-air (ω) is a second frequency domain signal; e (E) dry-air (ω) is a first frequency domain signal;is the complex refractive index of moist air; />Is the complex refractive index of dry air; omega is the angular frequency; l is the transmission distance;
the calculating the thickness of the sample to be measured according to the first time domain signal and the reconstructed time domain signal specifically includes:
determining a first point in time of a dominant wave of the first time domain signal;
determining a second point in time of the main wave of the reconstructed time domain signal and a third point in time of the first echo;
calculating the time difference between the first time point and the second time point to obtain a first delay time; calculating the time difference between the second time point and the third time point to obtain a second delay time;
calculating the thickness of the sample to be measured according to the first delay time and the second delay time;
the calculating the thickness of the sample to be measured according to the first delay time and the second delay time specifically includes:
taking the first delay time and the second delay time as inputs, and calculating an average refractive index by using a refractive index calculation formula;
calculating the thickness of the sample to be measured by using the average refractive index as input and a thickness calculation formula;
the refractive index calculation formula includes:
wherein n is the average refractive index; Δt (delta t) 1 Is a first delay time; Δt (delta t) 2 Is a second delay time;
the thickness calculation formula includes:
wherein d is the thickness of the sample to be measured; c is the propagation speed of terahertz waves in vacuum; Δt (delta t) 1 Is a first delay time; n is the average refractive index.
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