CN111751314A - Terahertz-based coating thickness detection method and device - Google Patents
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- 239000011248 coating agent Substances 0.000 title claims abstract description 113
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- 238000001514 detection method Methods 0.000 title claims abstract description 44
- 238000001328 terahertz time-domain spectroscopy Methods 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 19
- 239000000523 sample Substances 0.000 claims description 127
- 238000012360 testing method Methods 0.000 claims description 15
- 239000010410 layer Substances 0.000 description 37
- 238000005259 measurement Methods 0.000 description 13
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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- 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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- G01B11/0625—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of absorption or reflection
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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Abstract
The invention provides a terahertz-based coating thickness detection method and device, and the method comprises the following steps: the method comprises the steps of detecting a sample to be measured at the junction of a coating by using a reflective terahertz time-domain spectroscopy detection system, simultaneously measuring an echo signal of terahertz waves which penetrate through air and penetrate through the detected coating and the surface of the coating and serve as a reference signal of the terahertz time-domain spectroscopy, establishing a terahertz thickness equation, and substituting two time differences of the echo signal obtained in the first step into the established equation respectively so as to obtain the thickness of the coating. The invention can provide a new detection method for high-precision and rapid detection of the thickness of the multi-layer coating.
Description
Technical Field
The invention relates to a nondestructive detection technology of a coating, in particular to a terahertz-based coating thickness detection method and device.
Background
The uniformity and the integrity of the coating are the key for ensuring the performance of the coating, so that the quantitative detection of key parameters such as the thickness of the coating is required in the preparation, use and maintenance processes of the coating.
At present, in the aspect of coating thickness detection, a 'contrast plate' method, an eddy current method and the like are mainly used. The comparison plate method is characterized in that the spraying time and the spraying amount are calculated by manufacturing a standard substrate, the coating thickness is estimated, and the precision cannot be guaranteed; the eddy current method can only detect metal materials or nonmetal materials on a metal substrate, can only detect a single layer, and cannot meet the detection requirement of a multi-layer coating on the surface of the nonmetal substrate. Terahertz (THz) is a novel technique for aerospace special coating thickness detection.
At present, the thickness of the coating is mostly detected by terahertz by adopting a flight time method, the refractive index of the material needs to be predicted in advance, then the thickness information is calculated according to the time difference between reflection echoes of different interfaces, and the measurement of the thickness of the coating with unclear refractive index cannot be realized.
Disclosure of Invention
The invention provides a terahertz-based coating thickness detection method and device, which solve the problem that the conventional method for detecting the coating thickness by utilizing terahertz cannot realize the measurement of the coating thickness with unclear refractive index.
The invention provides a terahertz-based coating thickness detection method on one hand, which adopts a reflective terahertz time-domain spectroscopy detection system, and the reflective terahertz time-domain spectroscopy detection system comprises: the device comprises a transmitting probe 1, a receiving probe 2 and an arc-shaped slide rail 3, wherein the transmitting probe 1 and the receiving probe 2 are arranged on the arc-shaped slide rail 3 and slide along the arc-shaped slide rail 3 to adjust a transmitting angle and a receiving angle; the method comprises the following steps:
acquiring a first time length, wherein the first time length is a time length T required for the transmitting probe 1 to transmit a first terahertz wave to a first measuring point of a sample to be measured 4 at a preset angle theta, and the receiving probe 2 receives a first echodown0(ii) a The first measuring point is positioned on the surface of the ith layer of coating on the sample to be measured 4; the first echo is a reflection echo of the first terahertz wave at the first measuring point;
acquiring a second time length and a third time length, wherein the second time length is a time length T required for the transmitting probe 1 to transmit a second terahertz wave to a second measuring point of the sample to be measured 4 at the preset angle theta, and the receiving probe 2 receives a second echoup1(ii) a The third time length is the time length T 'required by the receiving probe 2 to receive the third echo'down0(ii) a The second measuring point is positioned on the surface of the i +1 th coating on the sample to be measured 4, and the i +1 th coating covers the i th coating; the second echo is a reflection echo of the second terahertz wave at the second measuring point; the third echo is a reflection echo of the second terahertz wave on the surface of the ith layer of coating;
according to the first time difference Delta Ti1And a second time difference Δ Tr1The thickness d of the i +1 th layer coating on the sample 4 to be measured was obtained using the following formula (1)i；
Wherein n is0Is the refractive index of air, c is the speed of light, sin (theta) represents the sine value of the preset angle theta, delta Ti1＝T′down0-Tup1(ii) a And the value of i is a non-negative integer, and when i is 0, the coating surface of the i-th layer is the uncoated surface of the sample 4 to be measured.
Optionally, the thickness d of the coating of the (i + 1) th layer on the sample 4 to be measured is obtainediThen, the method further comprises：
According to the thickness d of the (i + 1) th coatingiObtaining the refractive index n of the coating of the (i + 1) th layer by adopting the following formula (2)i+1；
Optionally, the transmitting probe 1 and the receiving probe 2 are synchronously adjusted on two sides of the symmetry axis of the arc-shaped slide rail 3.
Optionally, the reflective terahertz time-domain spectroscopy detection system further includes: the arc-shaped slide rail 3 is perpendicular to the test platform, and the sample to be measured 4 is horizontally placed on the test platform.
In another aspect, the present invention provides a terahertz-based coating thickness detection apparatus, which employs a reflective terahertz time-domain spectroscopy detection system, wherein the reflective terahertz time-domain spectroscopy detection system comprises: the device comprises a transmitting probe 1, a receiving probe 2 and an arc-shaped slide rail 3, wherein the transmitting probe 1 and the receiving probe 2 are arranged on the arc-shaped slide rail 3 and slide along the arc-shaped slide rail 3 to adjust a transmitting angle and a receiving angle; the device comprises:
a first measuring module, configured to obtain a first time length, where the first time length is a time length T required for the transmitting probe 1 to transmit a first terahertz wave to a first measuring point of the sample to be measured 4 at a preset angle θ, and the receiving probe 2 to receive a first echodown0(ii) a The first measuring point is positioned on the surface of the ith layer of coating on the sample to be measured 4; the first echo is a reflection echo of the first terahertz wave at the first measuring point;
a second measuring module, configured to obtain a second time duration and a third time duration, where the second time duration is a time duration T required for the transmitting probe 1 to transmit a second terahertz wave to a second measuring point of the sample to be measured 4 at the preset angle θ, and the time duration T required for the receiving probe 2 to receive a second echoup1(ii) a The third time length is the time length T 'required by the receiving probe 2 to receive the third echo'down0(ii) a The second measuring point is located atThe surface of the i +1 th coating on the sample to be measured 4, wherein the i +1 th coating covers the i th coating; the second echo is a reflection echo of the second terahertz wave at the second measuring point; the third echo is a reflection echo of the second terahertz wave on the surface of the ith layer of coating;
a thickness obtaining module for obtaining a thickness according to the first time difference Delta Ti1And a second time difference Δ Tr1The thickness d of the i +1 th layer coating on the sample 4 to be measured was obtained using the following formula (1)i；
Wherein n is0Is the refractive index of air, c is the speed of light, sin (theta) represents the sine value of the preset angle theta, delta Ti1＝T′down0-Tup1(ii) a And the value of i is a non-negative integer, and when i is 0, the coating surface of the i-th layer is the uncoated surface of the sample 4 to be measured.
Optionally, the apparatus further comprises:
a refractive index obtaining module for obtaining the thickness d of the (i + 1) th layer of coatingiObtaining the refractive index n of the coating of the (i + 1) th layer by adopting the following formula (2)i+1；
Optionally, the transmitting probe 1 and the receiving probe 2 are synchronously adjusted on two sides of the symmetry axis of the arc-shaped slide rail 3.
Optionally, the reflective terahertz time-domain spectroscopy detection system further includes: the arc-shaped slide rail 3 is perpendicular to the test platform, and the sample to be measured 4 is horizontally placed on the test platform.
In another aspect, the present invention further provides a reflective terahertz time-domain spectroscopy detection system, including: the device comprises a transmitting probe 1, a receiving probe 2 and an arc-shaped slide rail 3, wherein the transmitting probe 1 and the receiving probe 2 are arranged on the arc-shaped slide rail 3 and slide along the arc-shaped slide rail 3 to adjust a transmitting angle and a receiving angle;
the transmitting probe 1 and the receiving probe 2 are synchronously adjusted at two sides of the symmetry axis of the arc-shaped slide rail 3.
Optionally, the system further comprises: the arc-shaped slide rail 3 is perpendicular to the test platform, and the sample to be measured 4 is horizontally placed on the test platform.
According to the terahertz-based coating thickness detection method and device provided by the embodiment of the invention, the traditional detection probe with a fixed angle is improved, the angles of the transmitting end and the receiving end can be freely changed, and the variable-angle measurement of a terahertz system is realized. The method comprises the steps of utilizing a reflective terahertz time-domain spectroscopy detection system to simultaneously measure the junction of a sample to be measured, simultaneously measuring echo signals of terahertz waves which penetrate through air and penetrate through a coating to be detected and the surface of the coating to be reflected, using the echo signals as reference signals of terahertz time-domain spectroscopy to calculate the thickness of the coating and the refractive index of the material, needing no known refractive index of the material, needing no establishment of a complex thickness measurement algorithm, simultaneously measuring the thickness and the refractive index of the material, having a simple detection method, and avoiding measurement errors caused by position inconsistency when echo signals are extracted through multiple measurements.
Drawings
FIG. 1 is a schematic flow chart of a terahertz-based coating thickness detection method provided by the invention;
FIG. 2 is a schematic structural diagram of a reflective terahertz time-domain spectroscopy detection system provided by the present invention;
FIG. 3 is a schematic view of the interaction of terahertz waves with a coated substrate provided by the present invention;
FIG. 4 is a timing diagram of an echo of a terahertz wave provided by the present invention;
description of reference numerals:
1-a transmitting probe; 2-receiving the probe; 3-arc slide rail; 4-sample to be measured.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a terahertz-based coating thickness detection method. Fig. 1 is a schematic flow diagram of a terahertz-based coating thickness detection method provided by the present invention, fig. 2 is a schematic structural diagram of a reflective terahertz time-domain spectroscopy detection system provided by the present invention, and referring to fig. 2, the reflective terahertz time-domain spectroscopy detection system includes: the device comprises a transmitting probe 1, a receiving probe 2 and an arc-shaped slide rail 3, wherein the transmitting probe 1 and the receiving probe 2 are arranged on the arc-shaped slide rail 3 and slide along the arc-shaped slide rail 3 to adjust a transmitting angle and a receiving angle. Referring to fig. 1, the terahertz-based coating thickness detection method includes:
step 1, obtaining a first duration.
Wherein the first time length is a time length T required for the transmitting probe 1 to transmit a first terahertz wave to a first measuring point of the sample 4 to be measured at a preset angle theta, and the receiving probe 2 to receive a first echodown0(ii) a The first measuring point is positioned on the surface of the ith coating on the sample to be measured 4; the first echo is a reflected echo of the first terahertz wave at the first measurement point.
Optionally, the transmitting probe 1 and the receiving probe 2 are synchronously adjusted on two sides of the symmetry axis of the arc-shaped slide rail 3. Optionally, the reflective terahertz time-domain spectroscopy detection system further includes: the test platform, arc slide rail 3 is placed perpendicularly test platform, and the measuring sample 4 level is placed on test platform.
Illustratively, the transmitting probe 1 and the receiving probe 2 are fixed on an arc-shaped slide rail 3 with symmetrical angles and realize multi-angle measurement, a terahertz signal is emitted from the transmitting probe 1 and is incident on a sample 4 to be measured, and the terahertz signal can be reflected on the sample 4 to be measured and received by the receiving probe 2.
And 2, acquiring a second duration and a third duration.
Wherein, the second timeThe length of the time T required for the transmitting probe 1 to transmit the second terahertz wave to the second measuring point of the sample 4 to be measured at the preset angle theta and the receiving probe 2 to receive the second echoup1(ii) a The third time length is the time length T 'required by the receiving probe 2 to receive the third echo'down0(ii) a The second measuring point is positioned on the surface of the (i + 1) th coating on the sample to be measured, and the (i + 1) th coating covers the (i) th coating; the second echo is a reflection echo of the second terahertz wave at a second measuring point; the third echo is a reflection echo of the second terahertz wave on the surface of the ith layer of coating;
Wherein n is0Is the refractive index of air, c is the speed of light, sin (theta) represents the sine value of a preset angle theta, delta Ti1＝T′down0-Tup1(ii) a And the value of i is a non-negative integer, and when i is 0, the coating surface of the i-th layer is the uncoated surface of the sample to be measured.
Optionally, after the step 3, the method for detecting the coating thickness based on terahertz further includes:
Fig. 4 is an echo timing chart of a terahertz wave provided by the present invention, and with reference to fig. 4, a thickness measurement method provided by the present invention is exemplarily described below by taking i as 0, that is, by taking the measurement of the thickness of the 1 st layer coating of the sample to be measured as an example.
For example, the terahertz pulse reflects echoes on the front surface and the back surface of the coating, and the time difference of the echoes is measuredAnd obtaining the thickness information of the sample to be measured. Referring to FIGS. 3 and 4, EinitialIs terahertz original incident signal with an incident angle of thetai，Edown0The method is characterized in that a first time length corresponding to a reflected signal of the surface of a terahertz sample metal substrate layer to be measured (namely, the uncoated substrate and the coating of the 0 th layer) is recorded as Tdown0；Eup1For the surface echo signal of the terahertz wave on the first layer of coating (namely the coating 1 in FIG. 3 and the single layer of coating in FIG. 4), the corresponding second time length is denoted as Tup1，E′down0Is the echo signal of the terahertz wave at the surface of the substrate at the first layer coating (namely the bottom of the first layer coating), and the corresponding third time length is recorded as T'down0。
Obtaining a thickness model according to the terahertz electromagnetic transmission characteristics:
wherein d is1Is the thickness of the first layer coating, n1For the refractive index of the first layer coating, n0Is refractive index of air, sin θiMeasuring the angle of incidence, Δ T, of the coating for terahertzr1Uncoated echo T of a sample substrate to be measureddown0And time difference T 'of echo of sample substrate to be measured containing coating'down0，ΔTi1Echo T of the surface of a coating containing a sample to be measuredup1And a substrate echo T'down0The time difference of (a). By the equations (3) and (4), a system of equations with the coating thickness and the refractive index of the coating material is established by measuring the time difference Δ Tr1And Δ Ti1The thickness d of the first layer coating is calculated by using the formula (4)1Then d is added1Substituting into formula (3) to obtain the refractive index n of the first coating1。
For example, the thickness measurement method provided by the present invention is exemplified by adding 1 to the value of i, where i is 1, and further taking the measurement of the thickness of the 2 nd coating of the sample to be measured as an example.
The thickness measurement of the second layer is carried out in accordance with the thickness measurement of the first layer, whereby the echo signal E of the surface of the first layer on the sample to be measured is extractedup1And the surface echo signal E 'of the first layer coating at the second layer coating of the sample to be measured'up1Time difference of (T'up1-Tup1) And surface echo signal E 'of the top surface of the first layer coating at the second layer coating of the sample to be measured'up1Echo signal E of the upper surface of the second coating (i.e. coating 2 in FIG. 3, the two-layer coating in FIG. 4)up2Time difference of (T'up1-Tup2)。E″down0The third time length is marked as T ″, which is an echo signal of the terahertz wave on the surface of the substrate at the second layer of coatingdown0. Obtaining a thickness model according to a terahertz electromagnetic transmission theory:
wherein d is2Thickness of the second layer coating, n2For the refractive index of the second layer, n0Is refractive index of air, sin θiThe incident angle of the coating is measured for terahertz.
The terahertz-based coating thickness detection method provided by the embodiment of the invention can realize measurement of the thickness and the refractive index of the multilayer coating.
Claims (10)
1. A terahertz-based coating thickness detection method is characterized in that a reflective terahertz time-domain spectroscopy detection system is adopted, and the reflective terahertz time-domain spectroscopy detection system comprises: the device comprises a transmitting probe (1), a receiving probe (2) and an arc-shaped sliding rail (3), wherein the transmitting probe (1) and the receiving probe (2) are arranged on the arc-shaped sliding rail (3) and slide along the arc-shaped sliding rail (3) to adjust a transmitting angle and a receiving angle; the method comprises the following steps:
obtaining a first time length, the second time lengthThe time length is the time length T required for the transmitting probe (1) to transmit a first terahertz wave to a first measuring point of a sample (4) to be measured at a preset angle theta, and the receiving probe (2) receives a first echodown0(ii) a The first measuring point is positioned on the surface of the ith layer of coating on the sample (4) to be measured; the first echo is a reflection echo of the first terahertz wave at the first measuring point;
acquiring a second time length and a third time length, wherein the second time length is the time length T required for the transmitting probe (1) to transmit a second terahertz wave to a second measuring point of the sample to be measured (4) at the preset angle theta, and the receiving probe (2) receives a second echoup1(ii) a The third time length is the time length T 'required by the receiving probe (2) to receive a third echo'down0(ii) a The second measuring point is positioned on the surface of the i +1 th coating on the sample (4) to be measured, and the i +1 th coating covers the i th coating; the second echo is a reflection echo of the second terahertz wave at the second measuring point; the third echo is a reflection echo of the second terahertz wave on the surface of the ith layer of coating;
according to the first time difference Delta Ti1And a second time difference Δ Tr1Obtaining the thickness d of the i +1 th layer of the coating on the sample (4) to be measured by using the following formula (1)i；
Wherein n is0Is the refractive index of air, c is the speed of light, sin (theta) represents the sine value of the preset angle theta, delta Ti1＝T′down0-Tup1(ii) a And the value of i is a non-negative integer, and when i is 0, the coating surface of the i-th layer is the uncoated surface of the sample (4) to be measured.
2. Method according to claim 1, characterized in that the acquisition of the thickness d of the (i + 1) th coating on the sample (4) to be measurediThereafter, the method further comprises:
according to the thickness d of the (i + 1) th coatingiObtaining the refractive index n of the coating of the (i + 1) th layer by adopting the following formula (2)i+1；
3. Method according to claim 1, characterized in that the transmitting probe (1) and the receiving probe (2) are adjusted synchronously on both sides of the axis of symmetry of the curved slide (3).
4. The method of claim 1, wherein the reflective terahertz time-domain spectroscopy detection system further comprises: the arc-shaped sliding rail (3) is perpendicular to the test platform, and the sample to be measured (4) is horizontally placed on the test platform.
5. The utility model provides a coating thickness detection device based on terahertz, its characterized in that adopts reflective terahertz time-domain spectroscopy detection system now, reflective terahertz time-domain spectroscopy detection system includes: the device comprises a transmitting probe (1), a receiving probe (2) and an arc-shaped sliding rail (3), wherein the transmitting probe (1) and the receiving probe (2) are arranged on the arc-shaped sliding rail (3) and slide along the arc-shaped sliding rail (3) to adjust a transmitting angle and a receiving angle; the device comprises:
the first measuring module is used for acquiring a first time length, the first time length is that the transmitting probe (1) transmits a first terahertz wave to a first measuring point of a sample (4) to be measured at a preset angle theta, and the receiving probe (2) receives the required time length T of a first echodown0(ii) a The first measuring point is positioned on the surface of the ith layer of coating on the sample (4) to be measured; the first echo is a reflection echo of the first terahertz wave at the first measuring point;
a second measuring module for obtaining a second time length and a third time length, wherein the second time length is that the transmitting probe (1) uses the preset angle theta to the sample (4) to be measured) The second measuring point emits a second terahertz wave, and the receiving probe (2) receives the required time length T of a second echoup1(ii) a The third time length is the time length T 'required by the receiving probe (2) to receive a third echo'down0(ii) a The second measuring point is positioned on the surface of the i +1 th coating on the sample (4) to be measured, and the i +1 th coating covers the i th coating; the second echo is a reflection echo of the second terahertz wave at the second measuring point; the third echo is a reflection echo of the second terahertz wave on the surface of the ith layer of coating;
a thickness obtaining module for obtaining a thickness according to the first time difference Delta Ti1And a second time difference Δ Tr1Obtaining the thickness d of the i +1 th layer of the coating on the sample (4) to be measured by using the following formula (1)i；
Wherein n is0Is the refractive index of air, c is the speed of light, sin (theta) represents the sine value of the preset angle theta, delta Ti1＝T′down0-Tup1(ii) a And the value of i is a non-negative integer, and when i is 0, the coating surface of the i-th layer is the uncoated surface of the sample (4) to be measured.
6. The apparatus of claim 5, further comprising:
a refractive index obtaining module for obtaining the thickness d of the (i + 1) th layer of coatingiObtaining the refractive index n of the coating of the (i + 1) th layer by adopting the following formula (2)i+1；
7. The device according to claim 5, characterized in that the transmitting probe (1) and the receiving probe (2) are adjusted synchronously on both sides of the axis of symmetry of the curved slide (3).
8. The apparatus of claim 5, wherein the reflective terahertz time-domain spectroscopy detection system further comprises: the arc-shaped sliding rail (3) is perpendicular to the test platform, and the sample to be measured (4) is horizontally placed on the test platform.
9. A reflective terahertz time-domain spectroscopy detection system, comprising: the device comprises a transmitting probe (1), a receiving probe (2) and an arc-shaped sliding rail (3), wherein the transmitting probe (1) and the receiving probe (2) are arranged on the arc-shaped sliding rail (3) and slide along the arc-shaped sliding rail (3) to adjust a transmitting angle and a receiving angle;
the transmitting probe (1) and the receiving probe (2) are synchronously adjusted on two sides of the symmetry axis of the arc-shaped sliding rail (3).
10. The system of claim 9, further comprising: the arc-shaped sliding rail (3) is perpendicular to the test platform, and the sample to be measured (4) is horizontally placed on the test platform.
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| CN114199811A (en) * | 2021-11-25 | 2022-03-18 | 北京金轮坤天特种机械有限公司 | Method and device for characterizing microstructure of ceramic layer of thermal barrier coating of turbine blade |
| CN114403089A (en) * | 2021-12-20 | 2022-04-29 | 北京市农林科学院智能装备技术研究中心 | Laying poultry feeding method, device and system based on terahertz eggshell thickness measurement |
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| CN115435696A (en) * | 2022-07-12 | 2022-12-06 | 福州大学 | Method for detecting thickness of shaft sleeve self-lubricating coating based on terahertz time-domain spectroscopy |
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