CN113777411A - Method and device for measuring complex dielectric constant of terahertz waveband material - Google Patents
Method and device for measuring complex dielectric constant of terahertz waveband material Download PDFInfo
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Abstract
The invention provides a method and a device for measuring complex dielectric constant of a terahertz waveband material, which comprises the following steps: preparing a sample to be measured into a sample piece, and preparing a calibration piece according to the sample piece, wherein the thickness of the calibration piece is greater than or equal to that of the sample piece; the calibration piece is arranged between a second parabolic mirror and a third parabolic mirror, a first terahertz wave receiving and transmitting module transmits terahertz waves to the first parabolic mirror, a second terahertz wave receiving and transmitting module transmits terahertz waves to a fourth parabolic mirror, the left side surface and the right side surface of the calibration piece are calibration surfaces after calibration, and then the calibration piece is taken down; the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, the right side face of the sample piece is aligned to the right side calibration face, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, the second terahertz transceiver module receives the information carrying the sample and records the information carrying the sample as corresponding S parameters, and the complex dielectric constant can be calculated through the corresponding calculation method.
Description
Technical Field
The invention relates to the technical field of complex dielectric constant measurement, in particular to a method and a device for measuring a complex dielectric constant of a terahertz waveband material.
Background
Obtaining the complex dielectric constant of the material in the terahertz wave band is a basic requirement for designing and realizing various application systems and devices. Such as radar, remote sensing, spectrum, imaging, radio astronomy, wireless communication systems and the like, the complex dielectric constant of the material in the terahertz wave band needs to be obtained.
The existing method for acquiring the complex dielectric constant of the terahertz waveband mainly comprises a terahertz time-domain spectroscopy technology, a waveguide method based on a vector network analyzer, a resonant cavity method and the like. However, the problem of limited frequency resolution exists in the process of obtaining the material complex dielectric constant of the terahertz waveband by the terahertz time-domain spectroscopy technology; the method for obtaining the complex dielectric constant of the material of the terahertz waveband by the waveguide method based on the vector network analyzer has the problems of high requirement on a sample, difficulty in preparing the waveguide of a high frequency band, difficulty in popularization and use and the like; the complex dielectric constant of the material of the terahertz waveband obtained by the resonant cavity method can only be used for a single frequency point, so that the frequency band is greatly limited, and the accuracy of the final result is influenced by the size and the shape of a sample.
Disclosure of Invention
The invention provides a method and a device for measuring complex dielectric constant of a terahertz waveband material, which are used for solving the defects that the method for obtaining the complex dielectric constant of the terahertz waveband material in the prior art has high requirements on a sample and is difficult to realize measurement on a low-loss medium, can obtain terahertz waves with larger energy and more converged wave beams, realize effective measurement on the low-loss medium, reduce the preparation requirements on the sample, and have the advantages of more accurate measurement, simple operation and convenient use.
The invention provides a method for measuring complex dielectric constant of a terahertz waveband material, which comprises the following steps:
s101: preparing a sample to be measured into a sample piece, and preparing a calibration piece according to the sample piece, wherein the thickness of the calibration piece is greater than or equal to that of the sample piece;
s102: installing the calibration piece between the second parabolic mirror and the third parabolic mirror, enabling the first terahertz wave transceiver module to transmit terahertz waves to the first parabolic mirror, enabling the second terahertz wave transceiver module to transmit terahertz waves to the fourth parabolic mirror, then carrying out adaptive adjustment calibration, enabling the left side surface and the right side surface of the calibration piece to be calibration surfaces after calibration, and then taking down the calibration piece;
s103: the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned to the left calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, and the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
a sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned to the right side calibration surface, the second terahertz transceiver module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
s104: and the vector network analyzer processes the terahertz waves to obtain S parameters, stores the S parameters, and extracts the S parameters to obtain the complex dielectric constant.
According to the method for measuring the complex dielectric constant of the terahertz waveband material, provided by the invention, the step S103 can also be:
installing a sample piece between the second parabolic mirror and the third parabolic mirror, so that the sample piece is positioned between the left calibration surface and the right calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and the distance between the sample piece and the left calibration surface is measured at the same time;
or:
the method comprises the steps that a sample piece is arranged between a second parabolic mirror and a third parabolic mirror, so that the sample piece is located between a left calibration surface and a right calibration surface, a second terahertz transceiver module transmits terahertz waves to a fourth parabolic mirror, the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and the distance between the sample piece and the right calibration surface is measured simultaneously.
According to the method for measuring the complex dielectric constant of the terahertz waveband material provided by the invention, the method for measuring the complex dielectric constant of the terahertz waveband material further comprises the following steps: and selecting the parabolic mirror, namely selecting the parabolic mirror with the mirror surface size larger than the terahertz wave beam width according to the terahertz wave beam width irradiated on the parabolic mirror.
According to the method for measuring the complex dielectric constant of the terahertz waveband material, the step of preparing the calibration piece according to the sample piece specifically comprises the following steps: and according to the shape and thickness of the sample piece, preparing a parallel plate metal calibration piece with a smooth surface by using metal.
According to the method for measuring the complex dielectric constant of the terahertz wave band material, provided by the invention, the sizes of the sample piece and the calibration piece are larger than the beam waist width of a terahertz wave focal plane between the second parabolic mirror and the third parabolic mirror.
According to the method for measuring the complex dielectric constant of the terahertz waveband material, the step of installing the calibration piece between the second parabolic mirror and the third parabolic mirror specifically comprises the following steps: and the calibration piece is arranged between the second parabolic mirror and the third parabolic mirror, and the connecting line of the second parabolic mirror and the third parabolic mirror is perpendicular to the calibration piece.
The invention also provides a device for measuring the complex dielectric constant of the terahertz waveband material, which comprises a vector network analyzer, a first terahertz transceiver module, a second terahertz transceiver module, a first paraboloidal mirror, a second paraboloidal mirror, a third paraboloidal mirror and a fourth paraboloidal mirror;
the first terahertz transceiver module and the second terahertz transceiver module are respectively connected with the vector network analyzer, the first parabolic mirror and the second parabolic mirror are located on the same straight line, the third parabolic mirror and the fourth parabolic mirror are located on the same straight line, the first parabolic mirror and the fourth parabolic mirror are symmetrical to each other, and the second parabolic mirror and the third parabolic mirror are symmetrical to each other.
According to the device for measuring the complex dielectric constant of the terahertz waveband material, provided by the invention, the first terahertz transceiver module and the second terahertz transceiver module respectively comprise terahertz spread spectrum modules, the ports of the terahertz spread spectrum modules are connected with antennas, and wave absorbing materials are arranged around the antennas.
According to the device for measuring the complex dielectric constant of the terahertz waveband material, provided by the invention, the phase center of the antenna of the first terahertz transceiver module is superposed with the focal plane of the first parabolic mirror, and the phase center of the antenna of the second terahertz transceiver module is superposed with the focal plane of the fourth parabolic mirror.
According to the device for measuring the complex dielectric constant of the terahertz waveband material, provided by the invention, the focal lengths of the first parabolic mirror, the second parabolic mirror, the third parabolic mirror and the fourth parabolic mirror are the same, and the distance between the second parabolic mirror and the third parabolic mirror is twice of the focal length of the parabolic mirror.
According to the method and the device for measuring the complex dielectric constant of the terahertz waveband material, provided by the invention, the terahertz waves are collected and then used for measuring the complex dielectric constant of the sample through the four parabolic mirrors, and the calibration is carried out through the calibration piece, so that the sample piece is ensured to be positioned on a focal plane, the optimal transflective signal can be obtained at the moment, a symmetrical transmission light path is formed, and the measurement accuracy and the measurement precision are ensured. The parabolic mirror collects terahertz waves and then penetrates through a sample, the terahertz waves carrying sample information are transmitted to the vector network analyzer, then after S parameters are obtained, the complex dielectric constant of the sample can be calculated according to the S parameters, terahertz waves with larger energy and more converged wave beams can be obtained, and the terahertz waves are ideal plane waves when reaching the surface of the sample to be measured, so that accurate measurement of samples with different loss media and thin and thick samples can be realized, the preparation requirements of the sample are reduced, particularly low-loss media are reduced, the measurement is more accurate, the operation is simple, and the use is convenient.
Drawings
In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a device for measuring complex dielectric constant of a terahertz waveband material provided by the invention;
FIG. 2 is a flow chart of a method for measuring complex dielectric constant of a terahertz wave band material provided by the invention;
FIG. 3 is the measured S parameter of a 4mm air layer by applying the method for measuring the complex dielectric constant of the terahertz wave band material provided by the invention;
FIG. 4 is a complex dielectric constant of a 4mm air layer measured by applying a method for measuring a complex dielectric constant of a terahertz wave band material;
FIG. 5 is an S parameter of 10mm porous ceramics measured by a method of measuring a complex dielectric constant of a terahertz wave band material;
FIG. 6 is a complex dielectric constant of 10mm porous ceramic measured by a method of measuring the complex dielectric constant of a terahertz wave band material;
reference numerals:
1: a vector network analyzer; 2: a first terahertz transceiver module; 3: a second terahertz transceiver module;
4: a first parabolic mirror; 5: a second parabolic mirror; 6: a third parabolic mirror;
7: a fourth parabolic mirror; 8: a terahertz spread spectrum module; 9: an antenna.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. 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 following describes a method and an apparatus for measuring the complex dielectric constant of a terahertz wave band material according to the present invention with reference to fig. 1 to 6.
As shown in fig. 1, the device for measuring complex dielectric constant of terahertz waveband material includes a vector network analyzer 1, a first terahertz transceiver module 2, a second terahertz transceiver module 3, a first parabolic mirror 4, a second parabolic mirror 5, a third parabolic mirror 6 and a fourth parabolic mirror 7.
Specifically, the first terahertz transceiver module 2 and the second terahertz transceiver module 3 are respectively connected to the vector network analyzer 1, the first parabolic mirror 4 and the second parabolic mirror 5 are located on the same straight line, the third parabolic mirror 6 and the fourth parabolic mirror 7 are located on the same straight line, the first parabolic mirror 4 and the fourth parabolic mirror 7 are symmetrical to each other, and the second parabolic mirror 5 and the third parabolic mirror 6 are symmetrical to each other.
When the device is used, the measuring device is calibrated, the calibration piece is a metal piece thicker than the sample piece, a corresponding calibration piece is manufactured according to the sample piece to be measured actually before calibration, and then the calibration piece is fixed between the second parabolic mirror 5 and the third parabolic mirror 6. Then the first terahertz wave transceiver module 2 transmits terahertz waves to the first parabolic mirror 4, the first parabolic mirror 4 reflects the terahertz waves to the second parabolic mirror 5, the second parabolic mirror 5 collects the terahertz waves and then transmits the terahertz waves to the calibration piece, the calibration piece reflects the terahertz waves back to the second parabolic mirror 5, the terahertz waves are transmitted back to the first terahertz wave transceiver module through the first parabolic mirror 4, and the distance between the first terahertz wave transceiver module and the first parabolic mirror 4 is adjusted. Meanwhile, the second terahertz wave transceiver module transmits terahertz waves to the fourth parabolic mirror 7, and then the terahertz waves are transmitted to the calibration piece through the third parabolic mirror 6, the calibration piece reflects and transmits the terahertz waves back to the second terahertz wave transceiver module, and then the distance between the second terahertz wave transceiver module and the fourth parabolic mirror 7 is adjusted. The calibration of the measuring device is realized, symmetrical transmission light paths are formed, and further the subsequent measurement accuracy and measurement precision are ensured.
And after the calibration is finished, the measurement of the sample piece is started, the position of the calibration piece is recorded as a calibration area, the left side surface and the right side surface of the calibration piece are calibration surfaces, then the calibration piece is taken down, the sample piece is installed at the calibration area, and the left side surface of the sample piece is coincided with the left calibration surface. Then, the first terahertz transceiver module 2 transmits terahertz waves to the first parabolic mirror 4, the first parabolic mirror 4 reflects the terahertz waves to the second parabolic mirror 5, the second parabolic mirror 5 collects the terahertz waves and transmits the terahertz waves to the third parabolic mirror 6 after the terahertz waves pass through a sample piece, the third parabolic mirror 6 reflects the terahertz waves carrying sample information to the fourth parabolic mirror 7, and then the fourth parabolic mirror 7 transmits the terahertz waves to the second terahertz transceiver module 3. The second terahertz transceiving module 3 receives the terahertz waves carrying the sample information, transmits the terahertz waves to the vector network analyzer 1 and records the terahertz waves as S11 and S21, the vector network analyzer 1 analyzes the terahertz waves carrying the sample information to obtain S parameters, and then the complex dielectric constant of the sample can be calculated according to the S parameters.
Certainly, in actual use, when a sample piece is installed, the right side surface of the sample piece can be coincided with the right calibration surface, terahertz waves are emitted to the fourth parabolic mirror 7 through the second terahertz transceiver module 3, the fourth parabolic mirror 7 reflects the terahertz waves to the third parabolic mirror 6, the third parabolic mirror 6 collects the terahertz waves and transmits the terahertz waves to the second parabolic mirror 5 after passing through the sample piece, and the terahertz waves carrying sample information are reflected to the first parabolic mirror 4 by the parabolic mirrors. The first parabolic mirror 4 transmits terahertz waves to the first terahertz transceiver module 2, the first terahertz transceiver module 2 transmits terahertz waves carrying sample information to the vector network analyzer 1 and records the terahertz waves as S22 and S12, and then the complex dielectric constant of the sample can be obtained. The left-right symmetry of the test device is further verified by the complete agreement between the complex dielectric constants calculated by the first set of S parameters S11 and S21 and the second set of S parameters S22 and S12.
The terahertz waves with larger energy and more converged wave beams are obtained after being converged, and then the terahertz waves are incident on the sample piece, so that the requirement on the sample is reduced, and the sample with the thickness of 10mm can be measured. The effective measurement of low-loss medium is realized, and the loss tangent is 10-3The low-loss material of the magnitude is still very effective, and even the loss tangent of the air under different conditions can be calibrated, and the effective extraction of the loss tangent reaches 10-4Magnitude. And because the terahertz wave beam incident on the sample piece is more concentrated, the area of the terahertz wave beam incident on the sample piece is reduced, the measurement accuracy can be ensured only by ensuring the uniform thickness of the part of the sample piece in contact with the terahertz wave beam, and the sample piece is simpler to manufacture. And the whole measuring device has simple structure, is more convenient to use and simpler to operate, and ensures the measuring accuracy.
In alternative embodiments of the present invention, any suitable mirror surface such as a convex lens may be used instead of the first parabolic mirror 4, the second parabolic mirror 5, the third parabolic mirror 6 and the fourth parabolic mirror 7.
In an alternative embodiment of the present invention, the first parabolic mirror 4, the second parabolic mirror 5, the third parabolic mirror 6, and the fourth parabolic mirror 7 are all 4-inch off-axis parabolic mirrors, and the focal length f is 101.6 mm. It should be understood that any other suitable size parabolic mirrors may be used as the first parabolic mirror 4, the second parabolic mirror 5, the third parabolic mirror 6 and the fourth parabolic mirror 7.
Further, as shown in fig. 1, the first terahertz transceiver module 2 and the second terahertz transceiver module 3 both include a terahertz spread spectrum module 8, a port of the terahertz spread spectrum module 8 is connected with an antenna 9, and a wave-absorbing material is arranged around the antenna 9. When the terahertz frequency spreading module 8 is used, terahertz waves are transmitted or received through the antenna 9, and when the terahertz waves pass through the antenna 9, the wave absorbing material can absorb stray waves, so that the influence of the stray waves on measurement is reduced, and the accuracy of the measurement is further ensured.
Further, as shown in fig. 1, a phase center of the antenna 9 of the first terahertz transceiver module 2 coincides with a focal plane of the first parabolic mirror 4, and a phase center of the antenna 9 of the second terahertz transceiver module 3 coincides with a focal plane of the fourth parabolic mirror 7. When the terahertz wave transmitter-receiver module is used, when the terahertz wave is transmitted by the first terahertz wave transceiver module through the antenna 9, the terahertz wave transmitted by the antenna 9 is reflected by the first parabolic mirror 4 to become a plane terahertz wave, the plane terahertz wave is incident on the second parabolic mirror 5, and the second parabolic mirror 5 converges the terahertz wave to a focal plane to become a beam waist beam. In the same way, the terahertz wave is reflected by the fourth parabolic mirror 7 to become a planar terahertz wave, the planar terahertz wave is incident on the third parabolic mirror 6, the third parabolic mirror 6 converges the terahertz wave to the focal plane to form a beam waist beam, and the beam waist beams converged by the second parabolic mirror 5 and the third parabolic mirror 6 are overlapped at the focal plane, so that the measuring device for the complex dielectric constant of the terahertz wave band material is completely symmetrical left and right, the measuring device for the complex dielectric constant of the terahertz wave band material is convenient to calibrate, the terahertz wave is an ideal planar wave when reaching the surface of a calibration piece or a sample piece, the calibration and measurement accuracy is ensured, the accurate measurement of low-loss dielectric samples and thin and thick samples can be realized, and the preparation requirement of the samples is reduced.
Wherein, the gain and the divergence angle parameters of the antenna 9 of the first terahertz transceiver module 2 are the same as those of the antenna 9 of the second terahertz transceiver module 3.
Wherein, the phase center of the antenna is the common phase plane of the antenna. In practical situations, the phase center of the antenna is a plane because there is no ideal antenna, but the implementation of the technical solution of the present invention is not affected.
Further, as shown in fig. 1, the focal lengths of the first parabolic mirror 4, the second parabolic mirror 5, the third parabolic mirror 6 and the fourth parabolic mirror 7 are the same, and the distance between the second parabolic mirror 5 and the third parabolic mirror 6 is twice the focal length of the parabolic mirrors. When the terahertz wave measuring device is used, a sample piece is arranged between the second parabolic mirror 5 and the third parabolic mirror 6, namely the sample piece is positioned at the focus of the second parabolic mirror 5 and the third parabolic mirror 6, when the terahertz waves are collected by the second parabolic mirror 5 and transmitted to the third parabolic mirror 6, or when the terahertz waves are collected by the third parabolic mirror 6 and transmitted to the second parabolic mirror 5, the sample piece is just at the focus, the collected terahertz waves are incident on the sample piece, the terahertz waves incident on the sample piece have the largest energy and the smallest wave beam is collected, and at the moment, the contact area between the terahertz waves and the sample piece is the smallest, so that the effective measurement of a low-loss medium is realized, the preparation requirement of the sample is reduced, and the sample with the thickness of 10mm can be measured.
The invention also provides a method for measuring the complex dielectric constant of the terahertz waveband material, which comprises the following steps of:
s101: preparing a sample to be measured into a sample piece, and preparing a calibration piece according to the sample piece, wherein the thickness of the calibration piece is greater than or equal to that of the sample piece;
when the calibration device is used, after calibration is carried out through the calibration piece, the area where the calibration piece is located is the calibration area, the thickness of the sample piece is smaller than that of the calibration piece, namely the thickness of the sample piece is also smaller than that of the calibration area, the sample piece can be completely placed in the calibration area, partial structure of the sample piece is prevented from being located outside the calibration area, and the measurement accuracy is guaranteed.
S102: installing a calibration piece between the second parabolic mirror and the third parabolic mirror, enabling the first terahertz wave transceiver module to transmit terahertz waves to the first parabolic mirror, enabling the second terahertz wave transceiver module to transmit terahertz waves to the fourth parabolic mirror, then carrying out adaptive adjustment calibration, enabling the left side surface and the right side surface of the calibration piece to be calibration surfaces after calibration, and then taking down the calibration piece;
when the terahertz wave calibration device is used, the calibration piece is installed at a focal plane between the second parabolic mirror and the third parabolic mirror and is bilaterally symmetrical with the focal plane as a center, the terahertz wave can be reflected to the second parabolic mirror by the first parabolic mirror, the terahertz wave is collected by the second parabolic mirror and then is incident on the surface of the calibration piece, the terahertz wave is reflected back to the second parabolic mirror by the calibration piece, the terahertz wave is reflected to the first parabolic mirror by the second parabolic mirror, the terahertz wave is reflected to the first terahertz wave transceiver module by the first parabolic mirror, and adaptive adjustment and calibration are performed according to the terahertz wave received by the first terahertz wave transceiver module. Similarly, adaptive adjustment and calibration can be performed according to the terahertz waves received by the second terahertz wave receiving module, so that the focal planes of the second parabolic mirror and the third parabolic mirror are overlapped, and further, when a sample piece is placed between the second parabolic mirror and the third parabolic mirror, namely, the sample piece is located on the focal plane, an optimal transflective signal can be obtained at the moment, a symmetric transmission light path is formed, and the accuracy of measurement and the measurement precision are ensured.
S103: installing a sample piece between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned with the left calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, and the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
a sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned to the right side calibration surface, the second terahertz transceiver module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
when the terahertz wave vector network analyzer is used, when a sample piece is aligned with the left calibration surface, the first terahertz wave transceiver module is used for transmitting terahertz waves, the second terahertz wave transceiver module is used for receiving terahertz waves, the first parabolic mirror is used for reflecting the terahertz waves to the second parabolic mirror, the second parabolic mirror collects the terahertz waves, the terahertz waves penetrate through the sample piece and then are incident on the third parabolic mirror, the third parabolic mirror transmits the terahertz waves carrying sample information to the fourth parabolic mirror, then the fourth parabolic mirror reflects the terahertz waves to the second terahertz wave transceiver module, and the second terahertz wave transceiver module receives the terahertz waves carrying the sample information and transmits the terahertz waves to the vector network analyzer and records the terahertz waves as S11 and S21.
When a sample piece is aligned with the right side calibration surface, the second terahertz wave transceiver module is used for transmitting terahertz waves, the first terahertz wave transceiver module is used for receiving terahertz waves, the terahertz waves are transmitted to the third parabolic mirror through the fourth parabolic mirror, the third parabolic mirror collects the terahertz waves, the terahertz waves penetrate through the sample piece and then enter the second parabolic mirror, the terahertz waves are transmitted to the first terahertz wave transceiver module through the first parabolic mirror, and the terahertz waves carrying sample information are received by the first terahertz wave transceiver module and transmitted to the vector network analyzer and recorded as S22 and S12. The complex dielectric constant calculated by the first set of S-parameters S11 and S21 and the second set of S-parameters S22 and S12 are completely consistent.
S104: and processing the terahertz waves by the vector network analyzer to obtain S parameters, and extracting to obtain the complex dielectric constant according to the S parameters.
When the terahertz wave detector is used, after S parameters are obtained through the vector network analyzer, the complex dielectric constant of a sample can be calculated according to the S parameters, terahertz waves with larger energy and more converged wave beams are obtained, and the terahertz waves are ideal plane wave conditions when reaching the surface of a sample to be measured, so that accurate measurement of low-loss dielectric samples and thin and thick samples can be realized, the preparation requirements of the sample are reduced, the measurement is more accurate, the operation is simple, and the use is convenient.
Further, step S103 may also be:
installing a sample piece between the second parabolic mirror and the third parabolic mirror, so that the sample piece is positioned between the left calibration surface and the right calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and the distance between the sample piece and the left calibration surface is measured at the same time;
or:
the method comprises the steps that a sample piece is arranged between a second parabolic mirror and a third parabolic mirror, so that the sample piece is located between a left calibration surface and a right calibration surface, a second terahertz transceiver module transmits terahertz waves to a fourth parabolic mirror, the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and the distance between the sample piece and the right calibration surface is measured simultaneously.
When the device is used, the sample piece is arranged between the two calibration surfaces, the S parameter of the surface of the sample can be obtained through calculation by measuring the distance between the sample piece and the calibration surfaces, and then the complex dielectric constant of the sample piece can also be obtained.
Further, the method for measuring the complex dielectric constant of the terahertz wave band material further comprises the following steps: and selecting the parabolic mirror, namely selecting the parabolic mirror with the mirror surface size larger than the terahertz wave beam width according to the terahertz wave beam width irradiated on the parabolic mirror. When the terahertz wave beam measuring device is used, the parabolic mirror with the mirror surface size larger than the beam width is selected, the fact that the parabolic mirror can completely reflect and collect terahertz wave beams is guaranteed, the situation that the parabolic mirror cannot receive all terahertz wave beams and therefore partial terahertz wave beams leak is avoided, the fact that all terahertz waves can be collected is guaranteed, the terahertz wave beams with the maximum energy can be obtained, and effective measurement on low-loss media is achieved.
Further, the step of preparing the sample to be measured into the sample piece comprises the step of preparing the sample to be measured into a parallel plate sample piece with a smooth surface, wherein the surface roughness of the sample piece is less than 0.1 lambda. When the terahertz wave beam detector is used, when a sample to be detected is manufactured into a sample piece, the surface roughness of the sample piece is controlled, so that the surface of the sample piece is smooth as much as possible, the error influence of the surface roughness of the sample piece on measurement is reduced, the measurement accuracy is further ensured, the parallelism of the sample piece is ensured, when the terahertz wave beam is incident on the surface of the sample piece, the contact part of the terahertz wave beam and the sample piece is parallel, and the inaccuracy of a detection result caused by the fact that the surface of the sample piece is uneven is further avoided.
Further, the step of preparing the calibration piece according to the sample piece specifically includes: according to the shape and thickness of the sample piece, a parallel plate metal calibration piece with a smooth surface is prepared by using metal. When the terahertz wave calibrating device is used, the metal calibrating piece can carry out total reflection on terahertz waves, so that the terahertz waves can return along the original path, and then calibration is realized.
Further, the sizes of the sample piece and the calibration piece are larger than the beam waist width of a terahertz wave focal plane between the second parabolic mirror and the third parabolic mirror. When the terahertz wave calibration device is used, the collected terahertz waves can be enabled to be totally incident on the sample piece or the calibration piece, the calibration accuracy is guaranteed, the terahertz wave energy can be enabled to be incident on the sample piece, and then the measurement of the low-loss medium is achieved.
Further, the thickness of the sample piece and the thickness of the calibration piece are both smaller than the focal depth of the parabolic mirror. When the terahertz wave beam measuring device is used, the sample piece or the calibration piece is arranged between the second parabolic mirror and the third parabolic mirror, namely the sample piece or the calibration piece is positioned at the focus of the second parabolic mirror and the third parabolic mirror, so that the energy of the terahertz wave beam which is incident to and penetrates through the sample piece is maximized, the energy of the terahertz wave beam which is incident to the surface of the calibration piece is also maximized, and the measurement of a low-loss medium is further ensured.
Further, the step of installing the calibration piece between the second parabolic mirror and the third parabolic mirror specifically includes: and vertically installing a calibration piece between the second parabolic mirror and the third parabolic mirror, wherein a connecting line of the second parabolic mirror and the third parabolic mirror is perpendicular to the calibration piece. When the terahertz wave calibrating device is used, the left side surface and the right side surface of the calibrating piece are perpendicular to the transmission path of the terahertz wave, the terahertz wave can be vertically incident to the surface of the calibrating piece, the calibrating accuracy is guaranteed, one side surface of the sample piece is aligned to one calibrating surface when a sample is measured, the sample piece is also guaranteed to be perpendicular to the transmission path of the terahertz wave, the terahertz wave can be vertically incident to the surface of the sample piece, and the detecting accuracy is guaranteed.
Further, step S104 specifically includes:
firstly, obtaining the accurate S parameter of a material to be measured through a vector network analyzer, and then calculating the complex dielectric constant of a sample through two modes:
the method comprises the following steps: the complex dielectric constant can be calculated by using a numerical solution method according to the following formula.
Wherein Γ is the reflection coefficient, T is the transmission coefficient, γ is the propagation constant in the sample, d is the sample thickness, c is the speed of light, and f is the frequency.
The second method comprises the following steps: the complex permittivity can also be calculated using an iterative method.
First, a complex dielectric constant ε'rAnd the step size is set, for example to 0.001. Then, calculating the corresponding loss tangent by using the set real part and the measured S parameter:
and then calculating the complete complex dielectric constant:
εr＝(1-jtanδ) (8)
and calculating theoretical S parameters of the sample by using the generated complex dielectric constant, comparing the theoretical S parameters with the actually measured S parameters, and obtaining a result which is the dielectric constant corresponding to the sample when the difference is minimum:
wherein is epsilon'rIs the real part of the complex dielectric constant, Γ is the reflection coefficient, T is the transmission coefficient, L is the sample thickness, c is the speed of light, and f is the frequency.
As shown in fig. 3 and fig. 4, the S parameter and the complex dielectric constant of the 4mm air layer calculated by the method and the device for measuring the complex dielectric constant of the terahertz wave band material can be obtained.
As shown in fig. 5 and fig. 6, it can be known that the S parameter and the complex dielectric constant of the 10mm porous ceramic obtained by calculation after applying the method and the device for measuring the complex dielectric constant of the terahertz wave band material realize the measurement of the low-loss medium.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for measuring complex dielectric constant of a terahertz waveband material is characterized by comprising the following steps:
s101: preparing a sample to be measured into a sample piece, and preparing a calibration piece according to the sample piece, wherein the thickness of the calibration piece is greater than or equal to that of the sample piece;
s102: installing the calibration piece between the second parabolic mirror and the third parabolic mirror, enabling the first terahertz wave transceiver module to transmit terahertz waves to the first parabolic mirror, enabling the second terahertz wave transceiver module to transmit terahertz waves to the fourth parabolic mirror, then carrying out adaptive adjustment calibration, enabling the left side surface and the right side surface of the calibration piece to be calibration surfaces after calibration, and then taking down the calibration piece;
s103: the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned to the left calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, and the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
a sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned to the right side calibration surface, the second terahertz transceiver module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
s104: and the vector network analyzer processes the terahertz waves to obtain S parameters, stores the S parameters, and extracts the S parameters to obtain the complex dielectric constant.
2. The method for measuring the complex dielectric constant of the terahertz wave band material as claimed in claim 1, wherein step S103 is further:
installing a sample piece between the second parabolic mirror and the third parabolic mirror, so that the sample piece is positioned between the left calibration surface and the right calibration surface, the first terahertz transceiver module transmits terahertz waves to the first parabolic mirror, the second terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and the distance between the sample piece and the left calibration surface is measured at the same time;
or:
the method comprises the steps that a sample piece is arranged between a second parabolic mirror and a third parabolic mirror, so that the sample piece is located between a left calibration surface and a right calibration surface, a second terahertz transceiver module transmits terahertz waves to a fourth parabolic mirror, the first terahertz transceiver module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and the distance between the sample piece and the right calibration surface is measured simultaneously.
3. The method of measuring the complex permittivity of the terahertz wave-band material as claimed in claim 1, further comprising: and selecting the parabolic mirror, namely selecting the parabolic mirror with the mirror surface size larger than the terahertz wave beam width according to the terahertz wave beam width irradiated on the parabolic mirror.
4. The method for measuring the complex dielectric constant of the terahertz wave band material according to any one of claims 1 to 3, wherein the step of preparing the calibration piece according to the sample piece specifically comprises: and according to the shape and thickness of the sample piece, preparing a parallel plate metal calibration piece with a smooth surface by using metal.
5. The method for measuring complex dielectric constant of terahertz waveband material according to any one of claims 1 to 3, wherein the size of the sample piece and the calibration piece is larger than the beam waist width of the terahertz wave focal plane between the second parabolic mirror and the third parabolic mirror.
6. The method for measuring complex permittivity of a terahertz wave band material as claimed in any one of claims 1 to 3, wherein the step of mounting the calibration piece between the second parabolic mirror and the third parabolic mirror specifically includes: and the calibration piece is arranged between the second parabolic mirror and the third parabolic mirror, and the connecting line of the second parabolic mirror and the third parabolic mirror is perpendicular to the calibration piece.
7. A measuring device for complex dielectric constant of a terahertz waveband material is characterized by comprising a vector network analyzer, a first terahertz transceiver module, a second terahertz transceiver module, a first paraboloidal mirror, a second paraboloidal mirror, a third paraboloidal mirror and a fourth paraboloidal mirror;
the first terahertz transceiver module and the second terahertz transceiver module are respectively connected with the vector network analyzer, the first parabolic mirror and the second parabolic mirror are located on the same straight line, the third parabolic mirror and the fourth parabolic mirror are located on the same straight line, the first parabolic mirror and the fourth parabolic mirror are symmetrical to each other, and the second parabolic mirror and the third parabolic mirror are symmetrical to each other.
8. The device for measuring the complex dielectric constant of the terahertz waveband material as claimed in claim 7, wherein the first terahertz transceiver module and the second terahertz transceiver module both comprise terahertz spread spectrum modules, the ports of the terahertz spread spectrum modules are connected with antennas, and the antennas are provided with wave-absorbing materials around.
9. The apparatus of claim 8, wherein a phase center of the antenna of the first terahertz transceiver module coincides with a focal plane of the first parabolic mirror, and a phase center of the antenna of the second terahertz transceiver module coincides with a focal plane of the fourth parabolic mirror.
10. The device for measuring complex dielectric constant of terahertz waveband material according to any one of claims 7-9, characterized in that the focal lengths of the first parabolic mirror, the second parabolic mirror, the third parabolic mirror and the fourth parabolic mirror are the same, and the distance between the second parabolic mirror and the third parabolic mirror is twice the focal length of the parabolic mirror.
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