CN108020165A - The method and system measured using THz wave to the thickness of nonmetallic materials - Google Patents
The method and system measured using THz wave to the thickness of nonmetallic materials Download PDFInfo
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- CN108020165A CN108020165A CN201711233541.9A CN201711233541A CN108020165A CN 108020165 A CN108020165 A CN 108020165A CN 201711233541 A CN201711233541 A CN 201711233541A CN 108020165 A CN108020165 A CN 108020165A
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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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- 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 present invention provides a kind of method and system measured using THz wave to the thickness of nonmetallic materials.The method of the present invention includes：Make THz wave vertical incidence to the surface of nonmetallic materials, surface and bottom reflection of the THz wave through nonmetallic materials form the first and second reflected signals respectively, receive the first and second reflected signals, obtain the receiving time difference Δ T of reflected signal twice1；Make THz wave with angle, θiThe surface of nonmetallic materials is incident to, surface and bottom reflection of the THz wave through nonmetallic materials form the third and fourth reflected signal respectively, receive the third and fourth reflected signal, obtain the receiving time difference Δ T of reflected signal twice2, wherein 0 °<θi<90°；According to receiving time difference Δ T1With Δ T2, obtain the refractive index n of nonmetallic materials；According to the refractive index n of nonmetallic materials, the thickness d of nonmetallic materials is obtained.The method of the present invention can directly measure the refractive index and thickness of nonmetallic materials, and the error of measurement is small, and accuracy is high.
Description
Technical Field
The invention relates to a thickness measuring method, in particular to a method and a system for measuring the thickness of a non-metal material by utilizing terahertz waves.
Background
The terahertz wave is an electromagnetic wave with the frequency of 0.1 THz-10 THz, the wavelength of the terahertz wave is approximately 0.03 mm-3 mm, and the wave band is between the microwave and the infrared light. In recent years, the rapid development of the ultrafast laser technology provides a stable and reliable excitation light source for the generation of terahertz pulses, so that the mechanism research, detection technology and application technology of terahertz radiation are developed vigorously.
At present, a conventional thickness measurement method based on the terahertz principle is generally performed on the basis of a known refractive index of a sample, a material is measured once to obtain a receiving time difference between two reflected signals, and then the receiving time difference and the known refractive index are combined to calculate the thickness of the material, however, the method cannot measure the thickness of the material when the refractive index of the material is unknown.
In order to overcome the above-mentioned drawbacks, there is a method using inverse calculation, which obtains a receiving time difference between two reflected signals by performing one measurement on a standard sample having a known thickness, and inversely calculates a refractive index of the sample from the receiving time difference; subsequently, the thickness of the material is obtained by the receiving time difference between two reflected signals obtained by one measurement of the same sample material and the refractive index calculated reversely, however, the method has measurement errors caused by different materials having refractive index differences and the like.
Disclosure of Invention
The invention provides a method and a system for measuring the thickness of a non-metallic material by utilizing terahertz waves, which can directly measure the refractive index and the thickness of the non-metallic material, thereby avoiding measurement errors caused by different materials with refractive index differences and other factors and ensuring the accuracy of measurement results.
The invention provides a method for measuring the thickness of a non-metallic material by utilizing terahertz waves, wherein the non-metallic material is provided with a surface and a bottom surface, and the method comprises the following steps:
vertically irradiating the terahertz wave to the surface of the nonmetallic material, respectively reflecting the terahertz wave by the surface and the bottom of the nonmetallic material to form a first reflection signal and a second reflection signal, receiving the first reflection signal and the second reflection signal, and obtaining the receiving time difference delta T between the first reflection signal and the second reflection signal 1 ；
Making terahertz wave at angle theta i The terahertz waves are incident to the surface of the non-metallic material, the terahertz waves are reflected by the surface and the bottom surface of the non-metallic material to form a third reflection signal and a fourth reflection signal respectively, the third reflection signal and the fourth reflection signal are received, and the receiving time difference delta T between the third reflection signal and the fourth reflection signal is obtained 2 Wherein 0 degree<θ i <90°；
According to the difference of receiving time DeltaT 1 And a reception time difference Δ T 2 Obtaining the refractive index n of the non-metal material;
and obtaining the thickness d of the non-metal material according to the refractive index n of the non-metal material.
The method of the invention passes through different incident angles theta i The method can measure the refractive index and the thickness of the same non-metal material under the condition that the refractive index of the material is unknown, can avoid measurement errors caused by the fact that different materials have refractive index differences and the like, and ensures the accuracy of a measurement result.
Specifically, at the time of the first measurement, the terahertz wave is perpendicularly incident to the surface of the non-metallic material (i.e., the angle θ) i =0 °), at this time, the terahertz wave is reflected by the surface of the non-metallic material to form a first reflected signal; meanwhile, the terahertz wave penetrates through the surface of the non-metallic material and is reflected at the bottom surface of the non-metallic material so as to form a second reflection signal; receiving the first reflected signal and the second reflected signal and obtaining a first reflectionReceiving time difference delta T between the transmitted signal and the second reflected signal 1 Then, the thickness of the first measurement can be obtained according to the terahertz wave propagation theory, namely:
in equation (1): d is the thickness of the non-metallic material; c is the speed of light in vacuum (i.e., the speed of the terahertz wave in vacuum); n is the refractive index, Δ T, of the non-metallic material 1 The difference in reception time measured for the first time.
At the time of the second measurement, the terahertz wave is at an angle θ i (0°<θ i &The terahertz wave is incident to the surface of the non-metal material at the angle of (lt) 90 DEG, and at the moment, the terahertz wave is reflected by the surface of the non-metal material to form a third reflection signal; meanwhile, the terahertz waves are refracted by the surface of the non-metallic material and then reflected by the bottom surface of the non-metallic material to form a fourth reflection signal; receiving the third reflected signal and the fourth reflected signal and obtaining the receiving time difference Delta T of the third reflected signal and the fourth reflected signal 2 Then, a second measured thickness can be obtained according to the terahertz wave propagation theory, namely:
in equation (2): d is the thickness of the non-metallic material; c is the speed of light in vacuum; n is the refractive index of the non-metallic material, theta i For the second measured angle of incidence, Δ T 2 The difference in reception time for the second measurement.
In view of the fact that the first and second measurements are performed on the same non-metallic material, i.e. the thickness of the first measurement is the same as the thickness of the second measurement, the refractive index n of the non-metallic material can be obtained by the above equations (1) and (2), i.e.:
further, substituting the above equation (3) into equation (1) can obtain the thickness d of the non-metallic material, that is:
in the present invention, it is understood that the non-metallic material to be measured is a material having a certain thickness; the method of the present invention has no strict requirement on the thickness uniformity of the non-metal material, and can measure the thickness of the non-metal material with uniform thickness and the thickness of a certain position on the non-metal material with non-uniform thickness.
Specifically, in determining the thickness of a non-metallic material of uniform thickness, the present invention measures the thickness at normal incidence (i.e., the first measurement) and at an angle θ i The emission distance of the terahertz wave (namely the distance between the terahertz wave emission source and the incident point) and the position (namely the incident point) of the terahertz wave incident to the surface of the nonmetallic material are not strictly limited during incidence (namely the second measurement); preferably, the terahertz waves can be made to be incident to the same position on the surface of the non-metal material at the same emission distance, and the measurement result is more accurate.
In determining the thickness of a certain position on a non-metallic material having a non-uniform thickness, terahertz waves should be made to be incident on the same position on the surface of the non-metallic material at the same emission distance at the first measurement and the second measurement in order to accurately measure the thickness of the non-metallic material at the position.
The terahertz wave used for measurement is not strictly limited, can be conventional terahertz wave, the frequency of the terahertz wave can be 0.1 THz-10 THz, and the wavelength of the terahertz wave can be 0.03 mm-3 mm.
The thickness of the non-metal material is not strictly limited, and the thickness of the non-metal material can be 0.5 mm-50 mm.
The invention can measure the incident angle theta of the terahertz wave in the second measurement i Is not strictly limited as long as it is 0 °<θ i < at 90 deg. i.eCan be prepared; further, the angle θ i Can be 30-60 degrees.
The transmission distance of the terahertz waves is not strictly limited, and can be set to be a conventional transmission distance, for example, 10 cm-30 cm.
The invention does not strictly limit the nonmetal materials to be measured, and can be polyethylene, glass fiber, carbon fiber, silicon chip, glue layer, rubber, paperboard and the like; in addition, the present invention does not strictly limit the shape of the non-metallic material to be measured, and the non-metallic material may be in the form of a tube, a sheet, a layer, or the like.
The invention also provides a system for measuring the thickness of the non-metallic material by utilizing the terahertz waves, which comprises a terahertz wave transmitting device, a terahertz wave receiving device, a sample fixing table and a track,
the terahertz wave transmitting device is arranged on the track in a sliding mode and can transmit terahertz waves to the non-metal material arranged on the sample fixing table,
the terahertz wave receiving device is arranged on the track in a sliding mode and can receive terahertz wave signals reflected by the non-metal materials.
In the present invention, the terahertz-wave emitting device is used to emit terahertz waves, which may be a conventional device in the art; it is understood that the emission source of the terahertz-wave emitting device should be directed toward the sample holding stage so as to facilitate the incidence of the terahertz waves emitted by the terahertz-wave emitting device on the surface of the non-metallic material placed on the sample holding stage.
In the present invention, the terahertz wave receiving device is used for receiving a terahertz wave signal reflected from a non-metallic material to obtain a reception time difference between different reflected signals, which may be a conventional device in the art.
The arrangement modes of the terahertz wave transmitting device and the terahertz wave receiving device are not strictly limited; the terahertz wave transmitting device and the terahertz wave receiving device can be arranged into two independent devices or can be arranged into one integrated device; under the premise of realizing respective functions, the functions can be reasonably set according to actual conditions.
In the present invention, the sample holding stage is used to hold the non-metallic material to be measured, which may be of conventional construction in the art.
In the invention, the track is used for supporting the sliding of the terahertz wave transmitting device and the terahertz wave receiving device, thereby facilitating the terahertz waves transmitted by the terahertz wave transmitting device to be at different angles theta i The terahertz wave signal is incident to the surface of the non-metallic material, and meanwhile, the terahertz wave signal reflected by the non-metallic material can be well received by the terahertz wave receiving device.
It can be understood that, at the time of the first measurement, the terahertz wave transmitting device and the terahertz wave receiving device may be respectively disposed at normal positions of the non-metallic material, and at this time, the terahertz wave transmitted by the terahertz wave transmitting device can be vertically incident on the surface of the non-metallic material.
During the second measurement, the terahertz wave transmitting device and the terahertz wave receiving device can be respectively arranged on two sides of the normal of the non-metal material; in particular, the terahertz-wave receiving device can be disposed between the third reflected signal and the fourth reflected signal, thereby facilitating good reception of the third reflected signal and the fourth reflected signal at the same time.
The invention does not strictly limit the shape of the track; preferably, the track may be a circular arc track centered on the sample fixing stage. The arc-shaped track can enable terahertz waves to be incident to the same position on the surface of the non-metal material at the same emission distance during the first measurement and the second measurement, so that the thickness of the non-metal material can be measured more accurately.
Further, the arc radius (i.e., the emission distance) of the circular arc track may be set to 10cm to 30cm.
The implementation of the invention has at least the following advantages:
1. the method disclosed by the invention is used for measuring the thickness and the refractive index of the non-metallic material based on the terahertz detection principle, and is different from the traditional terahertz thickness measurement principle that the thickness measurement can be carried out only by knowing the refractive index of the measured material.
2. The method can directly measure the refractive index and thickness information of the non-metal material, thereby avoiding the measurement error caused by the factors of different materials such as refractive index difference and the like, and having high accuracy of the measurement result.
3. The system has simple structure, can obtain the refractive index information and the thickness information of the measured material by measuring the receiving time difference twice, has simple operation of measuring twice, can avoid human errors, and has more rigorous and accurate measurement on the material.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention in a first measurement;
fig. 2 is a schematic diagram of the system of the present invention in a second measurement.
Description of reference numerals:
1: a terahertz wave emitting device; 2: a terahertz wave receiving device; 3: a track; 4: a non-metallic material; 41: a surface; 42: a bottom surface.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings and the embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1
In this example, a polyethylene pipe (thickness of about 3 cm) with unknown refractive index and unknown thickness is measured by the following specific method:
1. first measurement
The terahertz wave is made perpendicular (theta) at a transmission distance of 30cm i The terahertz wave is incident to the surface of the polyethylene pipe, the terahertz wave is reflected by the surface of the polyethylene pipe (namely, the outer wall of the pipe) to form a first reflection signal, and meanwhile, the terahertz wave penetrates through the surface of the polyethylene pipe and is reflected by the bottom surface of the polyethylene pipe (namely, the inner wall of the pipe) to form a second reflection signal.
Receiving the first reflected signal and the second reflected signal to obtain a receiving time difference delta T between the first reflected signal and the second reflected signal 1 。
2. Second measurement
The same terahertz wave is emitted at a distance of 30cm and an incident angle of 60 degrees (theta) i The terahertz waves are incident to the same position on the surface of the polyethylene pipe, and the terahertz waves are reflected by the surface of the polyethylene pipe to form a third reflection signal; meanwhile, the terahertz waves are refracted by the surface of the polyethylene pipe and then reflected by the bottom surface of the polyethylene pipe to form a fourth reflection signal.
Receiving the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the polyethylene pipe is calculated according to the following formula:
wherein: n: a refractive index; theta i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in reception time of the second measurement.
4. Calculating the thickness
The thickness of the polyethylene pipe is calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in reception time of the second measurement.
Example 2
In this example, the measurement of a glass fiber sheet (thickness of about 2.5 mm) with unknown refractive index and thickness is carried out by the following method:
1. first measurement
The terahertz wave is made perpendicular (theta) at a transmission distance of 20cm i And =0 °) is incident on the surface of the glass fiber plate, the terahertz wave is reflected by the surface of the glass fiber plate to form a first reflected signal, and meanwhile, the terahertz wave is transmitted through the surface of the glass fiber plate and is reflected at the bottom surface of the glass fiber plate to form a second reflected signal.
Receiving the first reflected signal and the second reflected signal to obtain a receiving time difference delta T between the first reflected signal and the second reflected signal 1 。
2. Second measurement
The same terahertz wave is emitted at a distance of 20cm and an incident angle of 30 degrees (theta) i =30 °) is incident on the same position on the surface of the glass fiber plate, and the terahertz wave is reflected by the surface of the glass fiber plate to form a third reflected signal; meanwhile, the terahertz waves are refracted by the surface of the glass fiber plate and then reflected by the bottom surface of the glass fiber plate to form a fourth reflection signal.
Receiving the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the glass fiber sheet was calculated according to the following formula:
wherein: n: a refractive index; theta i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in reception time of the second measurement.
4. Calculating the thickness
The thickness of the glass fiber sheet was calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in reception time of the second measurement.
Example 3
In this example, a silicon wafer (with a thickness of about 0.5 mm) with unknown refractive index and unknown thickness is measured by the following specific method:
1. first measurement
The terahertz wave is made perpendicular (theta) at a transmission distance of 10cm i And (= 0 °) the terahertz waves are incident to the surface of the silicon wafer, the terahertz waves are reflected by the surface of the silicon wafer to form a first reflection signal, and meanwhile, the terahertz waves penetrate through the surface of the silicon wafer and are reflected at the bottom surface of the silicon wafer to form a second reflection signal.
Receiving the first reflected signal and the second reflected signal to obtain a receiving time difference delta T between the first reflected signal and the second reflected signal 1 。
2. Second measurement
The same terahertz wave is emitted by a distance of 10cm and an incident angle of 55 degrees (theta) i The terahertz waves are incident to the same position on the surface of the silicon wafer in a angle of =55 DEG, and the terahertz waves are reflected by the surface of the silicon wafer to form a third reflection signal; meanwhile, the terahertz wave is refracted by the surface of the silicon wafer and then reflected by the bottom surface of the silicon wafer to form a fourth reflection signal.
Receiving the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the silicon wafer is calculated according to the following formula:
wherein: n: a refractive index; theta i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in the time of receipt of the second measurement.
4. Calculating the thickness
The thickness of the silicon wafer is calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta.theta. i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in reception time of the second measurement.
Example 4
In this embodiment, a rubber sheet (with a thickness of about 1 mm) with unknown refractive index and unknown thickness is measured by the following specific method:
1. first measurement
The terahertz wave is made perpendicular (theta) at a transmission distance of 20cm i And the terahertz waves are incident to the surface of the rubber sheet, the terahertz waves are reflected by the surface of the rubber sheet to form a first reflection signal, and meanwhile, the terahertz waves penetrate through the surface of the rubber sheet and are reflected at the bottom surface of the rubber sheet to form a second reflection signal.
Receiving the first reflected signal and the second reflected signal to obtain a first reflected signal and a second reflected signalReception time difference Δ T of reflected signal 1 。
2. Second measurement
The same terahertz wave is emitted at a distance of 20cm and an incident angle of 45 degrees (theta) i The terahertz waves are incident to the same position on the surface of the rubber sheet at an angle of 45 DEG, and the terahertz waves are reflected by the surface of the rubber sheet to form a third reflection signal; meanwhile, the terahertz wave is refracted by the surface of the rubber sheet and then reflected by the bottom surface of the rubber sheet to form a fourth reflection signal.
Receiving the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the rubber sheet was calculated according to the following formula:
wherein: n: a refractive index; theta i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in the time of receipt of the second measurement.
4. Calculating the thickness
The thickness of the rubber sheet was calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in the time of receipt of the second measurement.
Example 5
In this example, the refractive index and thickness of a cardboard (about 10 mm) are unknown, and the specific method is as follows:
1. first measurement
The terahertz wave is made perpendicular (theta) at a transmission distance of 25cm i And (= 0 °) the terahertz waves are incident to the surface of the paperboard, the terahertz waves are reflected by the surface of the paperboard to form a first reflection signal, and meanwhile, the terahertz waves penetrate through the surface of the paperboard and are reflected at the bottom surface of the paperboard to form a second reflection signal.
Receiving the first reflected signal and the second reflected signal to obtain a receiving time difference delta T between the first reflected signal and the second reflected signal 1 。
2. Second measurement
The same terahertz wave is emitted at a distance of 25cm and an incident angle of 35 degrees (theta) i =35 °) the terahertz waves are incident to the same position on the surface of the paperboard, and the terahertz waves are reflected by the surface of the paperboard to form a third reflected signal; meanwhile, the terahertz wave is refracted by the surface of the paperboard and then reflected by the bottom surface of the paperboard to form a fourth reflection signal.
Receiving the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the paperboard was calculated according to the following formula:
wherein: n: a refractive index; theta i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in reception time of the second measurement.
4. Calculating the thickness
The thickness of the paperboard is calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in reception time of the second measurement.
Example 6
Referring to fig. 1 and 2, the system for measuring the thickness of a nonmetallic material by using terahertz waves of the present invention includes a terahertz wave transmitting device 1, a terahertz wave receiving device 2, a sample fixing table (not shown), and a rail 3, wherein the terahertz wave transmitting device 1 is slidably disposed on the rail 3 and is capable of transmitting terahertz waves to the nonmetallic material 4 disposed on the sample fixing table, and the terahertz wave receiving device 2 is slidably disposed on the rail 3 and is capable of receiving terahertz wave signals reflected from the nonmetallic material 4.
In the present invention, the terahertz-wave transmitting device 1 is for transmitting terahertz waves, which may be a conventional device in the art; it is understood that the emission source of the terahertz-wave emitting device 1 should be directed toward the sample holding stage so as to facilitate the incidence of the terahertz waves emitted by the terahertz-wave emitting device 1 on the surface 41 of the non-metallic material 4 placed on the sample holding stage.
In the present invention, the terahertz-wave receiving device 2 is for receiving a terahertz-wave signal reflected from the non-metallic material 4 and acquiring a reception time difference between the two reflected signals, which may be a conventional device in the art.
The arrangement modes of the terahertz wave transmitting device 1 and the terahertz wave receiving device 2 are not strictly limited, and the terahertz wave transmitting device can be arranged as two independent devices or can be arranged as an integrated device; under the premise of realizing respective functions, the functions can be reasonably set according to actual conditions.
In the present invention, the sample holding stage is used to hold the non-metallic material 4 to be measured, which may be of conventional construction in the art. It is understood that the non-metallic material 4 is a material having a certain thickness, which has a surface 41 and a bottom surface 42, and the thickness and material are not limited strictly; the thickness of the non-metallic material 4 can be 0.5 mm-50 mm, and the non-metallic material 4 can be polyethylene, glass fiber, carbon fiber, silicon chip, colloid, rubber, paperboard and the like.
In the present invention, the rail 3 is used for supporting the terahertz wave transmitting device 1 and the terahertz wave receiving device 2 to slide, so that the terahertz waves transmitted by the terahertz wave transmitting device 1 can be conveniently emitted at different angles θ i Incident to the surface 41 of the non-metallic material 4, while facilitating the terahertz-wave receiving device 2 to satisfactorily receive the terahertz-wave signal reflected from the non-metallic material 4.
As shown in fig. 1, at the time of the first measurement, the terahertz-wave transmitting device 1 and the terahertz-wave receiving device 2 may be respectively disposed at normal positions of the non-metallic material 4, and the terahertz wave transmitted by the terahertz-wave transmitting device 1 can be vertically incident on the surface 41 of the non-metallic material 4.
As shown in fig. 2, at the time of the second measurement, the terahertz-wave transmitting device 1 and the terahertz-wave receiving device 2 may be respectively disposed on both sides of the normal line of the non-metallic material 4; specifically, the angle between the terahertz wave emitting device 1 and the normal of the nonmetal material 4 is the incident angle θ i The terahertz-wave receiving device 2 can be disposed between the third reflected signal and the fourth reflected signal, thereby facilitating the simultaneous good reception of the third reflected signal and the fourth reflected signal.
The invention does not impose strict restrictions on the shape of the track 3; preferably, the track 3 may be a circular arc track centered on the sample holding stage. The circular arc-shaped track enables terahertz waves to be incident to the same position on the surface 41 of the non-metallic material 4 at the same emission distance during the first measurement and the second measurement, so that the thickness of the non-metallic material 4 can be accurately measured.
Further, the arc radius (i.e., the launch distance) of the circular arc orbit may be set to 10cm to 30cm.
The method for measuring the thickness of the non-metallic material 4 by using the system is as follows:
1. first measurement
As shown in fig. 1, after the non-metallic material 4 is fixed on the sample fixing table, the terahertz wave transmitting device 1 and the terahertz wave receiving device 2 are disposed at or near the normal position of the non-metallic material 4, wherein the distance (i.e., the transmission distance) between the transmission source of the terahertz wave transmitting device 1 and the position of incidence on the surface 41 of the non-metallic material 4 can be set to 10cm to 30cm.
The terahertz wave emitted by the terahertz wave emitting device 1 is perpendicular (θ) i =0 °) is incident on the surface 41 of the non-metallic material 4, the terahertz wave is reflected by the surface 41 of the non-metallic material 4 to form a first reflection signal, and meanwhile, the terahertz wave is transmitted through the surface 41 of the non-metallic material 4 and is reflected at the bottom surface 42 thereof to form a second reflection signal.
The terahertz wave receiving device 2 receives the first reflected signal and the second reflected signal to obtain a receiving time difference Δ T between the first reflected signal and the second reflected signal 1 。
2. Second measurement
Subsequently, the terahertz-wave transmitting device 1 and the terahertz-wave receiving device 2 are slid on the rail 3, whereby the positions of the terahertz-wave transmitting device 1 and the terahertz-wave receiving device 2 are adjusted to both sides of the normal position of the nonmetallic material 4, respectively, wherein the angle between the set position of the terahertz-wave transmitting device 1 and the normal position of the nonmetallic material 4 is an incident angle θ i (0°<θ i <90°)。
The terahertz wave emitted by the terahertz wave emitting device 1 is at an incident angle θ i The terahertz waves are incident to the surface 41 of the nonmetal material 4, and the terahertz waves are reflected by the surface 41 of the nonmetal material 4 to form a third reflection signal; meanwhile, the terahertz wave is refracted by the surface 41 of the non-metallic material 4 and then reflected by the bottom surface 42 thereof to form a fourth reflection signal.
The terahertz wave receiving device 2 is arranged between the third reflected signal and the fourth reflected signal, and the terahertz wave receiving device 2 receives the third reflected signal and the fourth reflected signal to obtain a receiving time difference delta T between the third reflected signal and the fourth reflected signal 2 。
3. Calculating refractive index
The refractive index of the non-metallic material 4 is calculated according to the following formula:
wherein: n: a refractive index; theta.theta. i : a second measured angle of incidence; delta T 1 : a reception time difference of the first measurement; delta T 2 : the difference in the time of receipt of the second measurement.
4. Calculating the thickness
The thickness of the non-metallic material 4 is calculated according to the following formula:
wherein: d: thickness; c: speed of light in vacuum; theta.theta. i : a second measured angle of incidence; delta T 1 : the difference in the time of receipt of the first measurement; delta T 2 : the difference in the time of receipt of the second measurement.
The system has simple structure, can obtain the refractive index information and the thickness information of the measured material by measuring the receiving time difference twice, has simple operation of measuring twice, can avoid personal errors, and has more rigorous and accurate measurement on the material.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for measuring a thickness of a non-metallic material using terahertz waves, the non-metallic material having a surface and a bottom surface, the method comprising the steps of:
with terahertz waves incident perpendicularly to the non-metallic materialThe terahertz wave is reflected by the surface and the bottom surface of the non-metallic material to form a first reflection signal and a second reflection signal respectively, the first reflection signal and the second reflection signal are received, and the receiving time difference delta T between the first reflection signal and the second reflection signal is obtained 1 ；
Making terahertz wave at angle theta i The terahertz waves are incident to the surface of the non-metallic material, the terahertz waves are reflected by the surface and the bottom surface of the non-metallic material to form a third reflection signal and a fourth reflection signal respectively, the third reflection signal and the fourth reflection signal are received, and the receiving time difference delta T between the third reflection signal and the fourth reflection signal is obtained 2 Wherein 0 degree<θ i <90°；
According to the difference of receiving time DeltaT 1 And a reception time difference Δ T 2 Obtaining the refractive index n of the non-metal material;
and obtaining the thickness d of the non-metal material according to the refractive index n of the non-metal material.
2. The method of claim 1, wherein the refractive index n of the non-metallic material is obtained according to the following formula,
3. the method of claim 1, wherein the thickness d of the non-metallic material is obtained according to the following formula,
where c is the speed of light in vacuum.
4. A method according to any one of claims 1 to 3, wherein at said normal incidence and at an angle θ i When the terahertz waves are incident, the terahertz waves are made to be incident to the nonmetal in the same emission distanceThe same location on the surface of the material.
5. A method according to any of claims 1 to 3, wherein the thickness of the non-metallic material is between 0.5mm and 50mm.
6. A method according to any one of claims 1 to 3, wherein said angle θ is i Is 30-60 degrees.
7. The method according to any one of claims 1 to 3, wherein the non-metallic material is selected from any one of polyethylene, glass fiber, carbon fiber, silicon wafer, glue layer, rubber and cardboard.
8. A system for measuring the thickness of a non-metallic material by using terahertz waves is characterized by comprising a terahertz wave transmitting device, a terahertz wave receiving device, a sample fixing table and a track,
the terahertz wave transmitting device is arranged on the track in a sliding mode and can transmit terahertz waves to the non-metal material arranged on the sample fixing table,
the terahertz wave receiving device is arranged on the track in a sliding mode and can receive terahertz wave signals reflected by the non-metal materials.
9. The system of claim 8, wherein the track is a circular arc track centered on the sample holding stage.
10. The system of claim 9, wherein the circular arc track has a circular arc radius of 10cm to 30cm.
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