CN113777411B - Terahertz wave band material complex dielectric constant measuring method and device - Google Patents
Terahertz wave band material complex dielectric constant measuring method and device Download PDFInfo
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- CN113777411B CN113777411B CN202111101704.4A CN202111101704A CN113777411B CN 113777411 B CN113777411 B CN 113777411B CN 202111101704 A CN202111101704 A CN 202111101704A CN 113777411 B CN113777411 B CN 113777411B
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
- G01R27/2682—Measuring dielectric properties, e.g. constants using optical methods or electron beams
Abstract
The invention provides a method and a device for measuring complex dielectric constant of terahertz wave band materials, comprising 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 the second parabolic mirror and the third parabolic mirror, the first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, the left side surface and the right side surface of the calibration piece are the 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 surface of the sample piece is aligned with the right side calibration surface, the first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, the second terahertz receiving and transmitting module receives information carrying the sample and records the information as corresponding S parameters, and complex dielectric constants can be calculated through a 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 complex dielectric constant of terahertz wave band materials.
Background
Obtaining the complex dielectric constant of the material in the terahertz wave band is a basic requirement for the design and implementation of various application systems and devices. Such as radar, remote sensing, spectroscopy, imaging, radioastronomy, wireless communication systems, etc., all require acquisition of the complex dielectric constant of the material in the terahertz band.
The existing terahertz wave band complex dielectric constant acquisition method 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 acquiring the complex dielectric constant of a material in a terahertz wave band through a terahertz time-domain spectroscopy technology; the complex dielectric constant of the material for obtaining the terahertz wave band by a waveguide method based on a vector network analyzer has the problems that the requirement on a sample is high, the preparation of a high-frequency-band waveguide is difficult, the popularization and the use are not suitable, and the like; the complex dielectric constant of the material for obtaining the terahertz wave band by the resonant cavity method can only be used for a single frequency point, so that the material has a large limit on the frequency band, and the accuracy of a final result is influenced by the size and shape of a sample.
Disclosure of Invention
The invention provides a method and a device for measuring the complex dielectric constant of a terahertz wave band material, which are used for solving the defects that the sample requirement is high, and the measurement of a low-loss medium is difficult to realize in the method for acquiring the complex dielectric constant of the terahertz wave band material in the prior art, and can obtain the terahertz wave with larger energy and more convergent wave beams, so that the effective measurement of the low-loss medium is realized, the preparation requirement of the sample is reduced, the measurement is more accurate, the operation is simple, and the use is convenient.
The invention provides a method for measuring complex dielectric constant of terahertz wave band materials, 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: the calibration piece is arranged between the second parabolic mirror and the third parabolic mirror, the first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, then adaptive adjustment and calibration are carried out, the left side surface and the right side surface of the calibration piece are the calibration surfaces, and then the calibration piece is taken down;
s103: the sample piece is arranged 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 receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and the second terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned with the right calibration surface, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the 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 complex dielectric constants according to the S parameters.
According to the method for measuring the complex dielectric constant of the terahertz wave band material provided by the invention, the step S103 can be as follows:
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 positioned between a left calibration surface and a right calibration surface, a first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and a second terahertz receiving and transmitting module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and meanwhile the distance between the sample piece and the left calibration surface is measured;
or:
and the sample piece is arranged 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 second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and simultaneously measures the distance between the sample piece and the right calibration surface.
According to the method for measuring the complex dielectric constant of the terahertz wave band material provided by the invention, the method for measuring the complex dielectric constant of the terahertz wave band material further comprises the following steps: and selecting the parabolic mirror, wherein the size of the parabolic mirror is larger than the beam width of the terahertz wave according to the beam width of the terahertz wave irradiated on the parabolic mirror.
According to the method for measuring the complex dielectric constant of the terahertz wave band material, which is provided by the invention, the step of preparing the calibration piece according to the sample piece specifically comprises the following steps: and preparing the parallel plate metal calibration piece with a smooth surface by utilizing metal according to the shape thickness of the sample piece.
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 the 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 wave band material provided by the invention, the step of installing the calibration piece between the second parabolic mirror and the third parabolic mirror specifically comprises the following steps: and installing the calibration piece between the second parabolic mirror and the third parabolic mirror, and enabling the connecting line of the second parabolic mirror and the third parabolic mirror to be perpendicular to the calibration piece.
The invention also provides a device for measuring the complex dielectric constant of the terahertz wave band material, which comprises a vector network analyzer, a first terahertz receiving and transmitting module, a second terahertz receiving and transmitting module, a first parabolic mirror, a second parabolic mirror, a third parabolic mirror and a fourth parabolic mirror;
the first terahertz receiving and transmitting module and the second terahertz receiving and transmitting module are respectively connected with the vector network analyzer, the first parabolic mirror and the second parabolic mirror are positioned on the same straight line, the third parabolic mirror and the fourth parabolic mirror are positioned on the same straight line, the first parabolic mirror and the fourth parabolic mirror are mutually symmetrical, and the second parabolic mirror and the third parabolic mirror are mutually symmetrical.
According to the device for measuring the complex dielectric constant of the terahertz wave band material, which is provided by the invention, the first terahertz receiving and transmitting module and the second terahertz receiving and transmitting module both comprise terahertz spread spectrum modules, ports of the terahertz spread spectrum modules are connected with antennas, and wave absorbing materials are arranged around the antennas.
According to the measuring device for the complex dielectric constant of the terahertz wave band material, the phase center of the antenna of the first terahertz receiving and transmitting module coincides with the focal plane of the first parabolic mirror, and the phase center of the antenna of the second terahertz receiving and transmitting module coincides with the focal plane of the fourth parabolic mirror.
According to the terahertz wave band material complex dielectric constant measuring device 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 the focal length of the parabolic mirror.
According to the method and the device for measuring the complex dielectric constant of the terahertz wave band material, provided by the invention, the four parabolic mirrors are arranged, the terahertz waves are collected and then used for measuring the complex dielectric constant of the sample, the calibration is performed through the calibration piece, the sample piece is ensured to be positioned on the focal plane, the optimal transmission and reflection signal can be obtained at the moment, a symmetrical transmission light path is formed, and the measurement accuracy are ensured. The parabolic mirror gathers terahertz waves and passes through the 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, the terahertz waves with larger energy and more converged beams can be obtained, and the electric 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 samples with different thicknesses can be realized, the preparation requirements of the samples are reduced, particularly, the low-loss media are more accurate in measurement, the operation is simple, and the use is convenient.
Drawings
In order to more clearly illustrate the invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic structural diagram of a device for measuring complex dielectric constant of terahertz wave band materials;
FIG. 2 is a flow chart of a method for measuring complex dielectric constant of terahertz wave band materials provided by the invention;
FIG. 3 shows the S parameter of a 4mm air layer obtained by measurement of the terahertz wave band material complex dielectric constant measurement method;
FIG. 4 is a complex permittivity of a 4mm air layer measured using a method for measuring complex permittivity of terahertz band materials;
FIG. 5 is a S parameter of a 10mm porous ceramic measured using a terahertz band material complex permittivity measurement method;
FIG. 6 is a complex dielectric constant of 10mm porous ceramics measured using a method for measuring complex dielectric constant of terahertz band materials;
reference numerals:
1: a vector network analyzer; 2: the first terahertz transceiver module; 3: the second terahertz receiving and transmitting 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
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The method and apparatus for measuring complex dielectric constants of terahertz band materials according to the present invention are described below with reference to fig. 1 to 6.
As shown in fig. 1, the measuring device for the complex dielectric constant of the terahertz wave band material comprises a vector network analyzer 1, a first terahertz receiving and transmitting module 2, a second terahertz receiving and transmitting 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 with 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 measuring device is used, the measuring device is calibrated, the calibration piece is a metal piece thicker than the sample piece, the corresponding calibration piece is manufactured according to the sample piece which is measured according to actual needs before the calibration, and then the calibration piece is fixed between the second parabolic mirror 5 and the third parabolic mirror 6. 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 gathers the terahertz waves and transmits the terahertz waves to the calibration piece, the calibration piece reflects the terahertz waves back to the second parabolic mirror 5, and then the terahertz waves are transmitted back to the first terahertz transceiver module through the first parabolic mirror 4, and the distance between the first terahertz 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, and the calibration piece transmits the terahertz waves back to the second terahertz wave transceiver module in a reflection manner, so that 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, a symmetrical transmission light path is formed, and further the subsequent measurement accuracy and measurement precision are ensured.
And after the calibration is finished, starting to measure the sample piece, marking the position of the calibration piece as a calibration area, taking the left side surface and the right side surface of the calibration piece as calibration surfaces, taking down the calibration piece, installing the sample piece at the calibration area, and enabling the left side surface of the sample piece to coincide 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 gathers the terahertz waves and transmits the terahertz waves to the third parabolic mirror 6 after passing through the sample piece, the third parabolic mirror 6 reflects the terahertz waves carrying the 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 receiving and transmitting module 3 receives the terahertz wave carrying the sample information, transmits the terahertz wave to the vector network analyzer 1 and records the terahertz wave as S11 and S21, the vector network analyzer 1 analyzes the terahertz wave carrying the sample information to obtain an S parameter, and then the complex dielectric constant of the sample can be obtained according to the S parameter.
Of course, in actual use, the right side surface of the sample piece may be overlapped with the right calibration surface when the sample piece is mounted, and then the terahertz wave is sent to the fourth parabolic mirror 7 through the second terahertz receiving and sending module 3, the terahertz wave is reflected to the third parabolic mirror 6 by the fourth parabolic mirror 7, the terahertz wave is collected by the third parabolic mirror 6 and transmitted to the second parabolic mirror 5 after passing through the sample piece, and the terahertz wave carrying the sample information is reflected to the first parabolic mirror 4 by the parabolic mirror. The first parabolic mirror 4 transmits terahertz waves to the first terahertz transceiver module 2, and 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, so that complex dielectric constants of samples can be obtained. The complex dielectric constants obtained by calculation of the first set of S parameters S11 and S21 and the second set of S parameters S22 and S12 are completely consistent, so that the bilateral symmetry of the testing device is further verified.
The terahertz waves are collected to obtain terahertz waves with larger energy and more collected wave beams, and then the terahertz waves are incident on a sample piece, so that the requirements on samples are reduced, and samples with the thickness of 10mm can be measured. Realize the alignment ofEffective measurement of low loss dielectric at loss tangent of 10 -3 Low loss materials of the order of magnitude are still very effective, and even the loss tangent of air under different conditions can be calibrated, and the loss tangent can be effectively extracted to reach 10 -4 Magnitude. 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 also reduced along with the reduction, and the measurement accuracy can be ensured only by ensuring that the thickness of the component contacted by the sample piece and the terahertz wave beam is uniform, so that the sample piece is simpler to manufacture. And the whole measuring device has simple structure, is more convenient to use, is simpler to operate, and ensures the accuracy of measurement.
In alternative embodiments of the invention, any suitable mirror surface such as convex lenses 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 invention, the first parabolic mirror 4, the second parabolic mirror 5, the third parabolic mirror 6 and the fourth parabolic mirror 7 are each 4 inch off-axis parabolic mirrors with a focal length f=101.6 mm. It should be appreciated that any other parabolic mirror of suitable dimensions 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 each include a terahertz spread spectrum module 8, ports of the terahertz spread spectrum modules 8 are connected with an antenna 9, and wave absorbing materials are disposed 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 measurement accuracy is further ensured.
Further, as shown in fig. 1, the phase center of the antenna 9 of the first terahertz transceiver module 2 coincides with the focal plane of the first parabolic mirror 4, and the phase center of the antenna 9 of the second terahertz transceiver module 3 coincides with the focal plane of the fourth parabolic mirror 7. When the terahertz wave transmitting and receiving module is used, the terahertz wave transmitted by the antenna 9 is reflected by the first parabolic mirror 4 and then becomes a planar terahertz wave, the planar terahertz wave is incident on the second parabolic mirror 5, and the second parabolic mirror 5 converges the terahertz wave at a focal plane to form a beam waist beam. In the same way, the terahertz wave becomes a planar terahertz wave after being reflected by the fourth parabolic mirror 7, the planar terahertz wave is incident on the third parabolic mirror 6, the terahertz wave is converged at the focal plane by the third parabolic mirror 6 to become a beam waist beam, 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 of the complex dielectric constant of the terahertz wave band material is completely symmetrical left and right, the measuring device of the complex dielectric constant of the terahertz wave band material is convenient to calibrate, the terahertz wave is ensured to be a more ideal planar wave when reaching the surface of a calibration piece or a sample piece, the accuracy of calibration and measurement is ensured, the accurate measurement of a low-loss medium sample and a thin and thick sample can be realized, and the preparation requirement of the sample is reduced.
The gain and 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.
The phase center of the antenna is the co-phase plane of the antenna. In practical situations, since there is no ideal antenna, the phase center of the antenna is a plane, but the implementation of the technical scheme 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 second parabolic mirror 5 collects terahertz waves and transmits the terahertz waves to the third parabolic mirror 6 or the third parabolic mirror 6 collects terahertz waves and transmits the terahertz waves to the second parabolic mirror 5, the sample piece is just positioned at the focus, the collected terahertz waves are incident on the sample piece, the terahertz waves incident on the sample piece are the largest in energy, the wave beams are the smallest in the convergence, 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 wave band material, as shown in the attached figure 2, 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;
when the device is used, after the 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, the part of the structure of the sample piece is prevented from being located outside the calibration area, and the measurement accuracy is ensured.
S102: installing a calibration piece between the second parabolic mirror and the third parabolic mirror, transmitting terahertz waves to the first parabolic mirror by the first terahertz receiving and transmitting module, transmitting terahertz waves to the fourth parabolic mirror by the second terahertz receiving and transmitting module, performing adaptive adjustment and 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 arranged at the focal plane between the second parabolic mirror and the third parabolic mirror, the focal plane is used as the center to be bilaterally symmetrical, the first parabolic mirror reflects the terahertz wave to the second parabolic mirror, the second parabolic mirror gathers the terahertz wave and then enters the surface of the calibration piece, the calibration piece reflects the terahertz wave back to the second parabolic mirror, the second parabolic mirror reflects the terahertz wave to the first parabolic mirror, the first parabolic mirror reflects the terahertz wave to the first terahertz wave receiving and transmitting module, and the terahertz wave received by the first terahertz wave receiving and transmitting module is subjected to adaptive adjustment and calibration. And similarly, the terahertz wave receiving module can carry out adaptive adjustment and calibration according to the terahertz wave received by the second terahertz wave receiving module, so that focal planes of the second parabolic mirror and the third parabolic mirror coincide, and further, when a sample piece is placed between the second parabolic mirror and the third parabolic mirror, namely the sample piece is positioned on the focal plane, an optimal transmission signal can be obtained at the moment, a symmetrical transmission light path is formed, and the measurement accuracy are ensured.
S103: the sample piece is arranged 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 receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and the second terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned with the right calibration surface, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
when the sample piece is aligned with the left calibration surface, at this time, the first terahertz wave receiving and transmitting module is used for transmitting terahertz waves, the second terahertz wave receiving and transmitting module is used for receiving the 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 and passes through the sample piece to be 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 receiving and transmitting module, and the second terahertz receiving 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 the sample piece is aligned with the right calibration surface, the second terahertz wave receiving and transmitting module is used for transmitting terahertz waves, the first terahertz wave receiving and transmitting module is used for receiving the 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 and passes through the sample piece and then enters the second parabolic mirror, then the terahertz waves are transmitted to the first terahertz wave receiving and transmitting module through the first parabolic mirror, and the terahertz waves carrying sample information are received by the first terahertz receiving and transmitting module and transmitted to the vector network analyzer and recorded as S22 and S12. The complex permittivity calculated by the first set of S parameters S11 and S21 and the second set of S parameters S22 and S12 are identical.
S104: and the vector network analyzer processes the terahertz waves to obtain S parameters, and complex dielectric constants are obtained through extraction according to the S parameters.
When the device is used, after the S parameter is obtained through the vector network analyzer, the complex dielectric constant of the sample can be calculated according to the S parameter, terahertz waves with larger energy and more converged wave beams are obtained, and the electric terahertz waves reach the surface of the sample to be measured under ideal plane wave conditions, so that the device can accurately measure the low-loss dielectric sample and the thin and thick sample, reduce the preparation requirement of the sample, and has the advantages of more accurate measurement, simple operation and convenient use.
Further, step S103 may further be:
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 positioned between a left calibration surface and a right calibration surface, a first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and a second terahertz receiving and transmitting module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and meanwhile the distance between the sample piece and the left calibration surface is measured;
or:
and the sample piece is arranged 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 second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and simultaneously measures the distance between the sample piece and the right calibration surface.
When the device is used, the sample piece is arranged between the two calibration surfaces, the S parameter of the sample surface 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 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, wherein the size of the parabolic mirror is larger than the beam width of the terahertz wave according to the beam width of the terahertz wave irradiated on the parabolic mirror. When the terahertz wave measuring device is used, the parabolic mirror with the mirror surface size larger than the beam width is selected, so that the parabolic mirror is guaranteed to reflect and collect all terahertz wave beams, the fact that the parabolic mirror cannot receive all terahertz wave beams to cause part of terahertz wave beams to leak is prevented, the fact that all terahertz waves can be collected is guaranteed, the terahertz wave beams with the maximized energy can be obtained, and further effective measurement of low-loss media is achieved.
Further, the step of preparing the sample to be tested into a sample piece comprises the step of preparing the sample to be tested 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 sample to be measured is manufactured into a sample piece in use, 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, the contact part of the terahertz wave beam and the sample piece is parallel when the terahertz wave beam is incident on the surface of the sample piece, and inaccurate detection results caused by uneven surface of the sample piece are avoided.
Further, the step of preparing the calibration piece according to the sample piece specifically includes: a smooth-surfaced parallel plate metal calibrator was prepared from metal based on the shape thickness of the sample piece. When the terahertz wave calibration device is used, the metal calibration piece can conduct total reflection on the terahertz wave, so that the terahertz wave can return along an original path, and further calibration is achieved.
Further, the dimensions of the sample piece and the calibration piece are greater than the beam waist width of the terahertz focal plane between the second parabolic mirror and the third parabolic mirror. When the terahertz wave measuring device is used, the collected terahertz waves can be enabled to be totally incident on a sample piece or a calibration piece, the calibration accuracy is guaranteed, the total terahertz wave energy can be enabled to be incident on the sample piece, and then the low-loss medium is measured.
Further, the thickness of the sample piece and the thickness of the calibration piece are smaller than the focal depth of the parabolic mirror. When the 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 incident through the sample piece is maximized, the energy of the terahertz wave beam incident on the surface of the calibration piece is maximized, and the measurement of a low-loss medium is 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, and enabling a connecting line of the second parabolic mirror and the third parabolic mirror to be perpendicular to the calibration piece. When the terahertz wave calibration device is used, the left side surface and the right side surface of the calibration piece are perpendicular to the transmission path of the terahertz wave, the fact that the terahertz wave can vertically enter the surface of the calibration piece is achieved, calibration accuracy is guaranteed, when a sample is measured, one side surface of the sample piece is aligned with one of the calibration surfaces, the fact that the sample piece is perpendicular to the transmission path of the terahertz wave is guaranteed, the fact that the terahertz wave can vertically enter the surface of the sample piece is guaranteed, and detection accuracy is guaranteed.
Further, step S104 specifically includes:
firstly, obtaining accurate S parameters of a material to be measured through a vector network analyzer, and then calculating complex dielectric constants of samples in two ways:
the method comprises the following steps: the complex permittivity can be calculated by the following formula by using a numerical solution method.
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 is as follows: complex dielectric constants can also be calculated using iterative methods.
First, the complex dielectric constant epsilon 'is set' r And a step size is set, for example, to 0.001. The corresponding loss tangent is then calculated using the set real part and the measured S parameter:
and then the complete complex dielectric constant is calculated:
ε r ＝(1-jtanδ) (8)
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 selecting the result with the smallest difference value as the dielectric constant corresponding to the sample:
wherein ε' r Is 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 complex dielectric constant of the air layer of 4mm calculated after the terahertz wave band material complex dielectric constant measuring method and device are applied can be known.
As shown in the accompanying drawings 5 and 6, the S parameter and the complex dielectric constant of the 10mm porous ceramic obtained by calculation after the terahertz wave band material complex dielectric constant measuring method and the device are used can be known, and the low-loss medium is measured.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the 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 scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The method for measuring the complex dielectric constant of the terahertz wave band material is used for a measuring device of the complex dielectric constant of the terahertz wave band material and is characterized by comprising a vector network analyzer, a first terahertz receiving and transmitting module, a second terahertz receiving and transmitting module, a first parabolic mirror, a second parabolic mirror, a third parabolic mirror and a fourth parabolic mirror; the first terahertz receiving and transmitting module and the second terahertz receiving and transmitting module are respectively connected with the vector network analyzer, the first parabolic mirror and the second parabolic mirror are positioned on the same straight line, the third parabolic mirror and the fourth parabolic mirror are positioned on the same straight line, the first parabolic mirror and the fourth parabolic mirror are mutually symmetrical, the second parabolic mirror and the third parabolic mirror are mutually symmetrical, and the measuring method of the complex dielectric constant of the terahertz wave band material 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: the calibration piece is arranged between the second parabolic mirror and the third parabolic mirror, the first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, then adaptive adjustment and calibration are carried out, the left side surface and the right side surface of the calibration piece are the calibration surfaces, and then the calibration piece is taken down;
s103: the sample piece is arranged 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 receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and the second terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer;
or:
the sample piece is arranged between the second parabolic mirror and the third parabolic mirror, so that the sample piece is aligned with the right calibration surface, the second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the 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 complex dielectric constants according to the S parameters.
2. The method for measuring complex permittivity of terahertz wave band material according to claim 1, wherein step S103 further comprises:
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 positioned between a left calibration surface and a right calibration surface, a first terahertz receiving and transmitting module transmits terahertz waves to the first parabolic mirror, and a second terahertz receiving and transmitting module receives terahertz waves carrying sample information and transmits the terahertz waves to a vector network analyzer, and meanwhile the distance between the sample piece and the left calibration surface is measured;
or:
and the sample piece is arranged 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 second terahertz receiving and transmitting module transmits terahertz waves to the fourth parabolic mirror, and the first terahertz receiving and transmitting module receives the terahertz waves carrying sample information and transmits the terahertz waves to the vector network analyzer, and simultaneously measures the distance between the sample piece and the right calibration surface.
3. The method for measuring the complex permittivity of a terahertz-band material according to claim 1, characterized in that the method for measuring the complex permittivity of a terahertz-band material further comprises: and selecting the parabolic mirror, wherein the size of the parabolic mirror is larger than the beam width of the terahertz wave according to the beam width of the terahertz wave irradiated on the parabolic mirror.
4. A method for measuring complex permittivity of terahertz wave band material according to any one of claims 1 to 3, wherein the step of preparing a calibration piece from the sample piece specifically includes: and preparing the parallel plate metal calibration piece with a smooth surface by utilizing metal according to the shape thickness of the sample piece.
5. The method for measuring complex permittivity of terahertz-band material according to any one of claims 1 to 3, wherein the dimensions of the sample member and the calibration member are larger than a beam waist width of a terahertz-wave focal plane between the second parabolic mirror and the third parabolic mirror.
6. A method for measuring complex permittivity of terahertz-band material according to any one of claims 1 to 3, characterized in that the step of mounting the calibration member between the second parabolic mirror and the third parabolic mirror specifically comprises: and installing the calibration piece between the second parabolic mirror and the third parabolic mirror, and enabling the connecting line of the second parabolic mirror and the third parabolic mirror to be perpendicular to the calibration piece.
7. The device for measuring the complex dielectric constant of the terahertz wave band material is characterized by comprising a vector network analyzer, a first terahertz receiving and transmitting module, a second terahertz receiving and transmitting module, a first parabolic mirror, a second parabolic mirror, a third parabolic mirror and a fourth parabolic mirror;
the first terahertz receiving and transmitting module and the second terahertz receiving and transmitting module are respectively connected with the vector network analyzer, the first parabolic mirror and the second parabolic mirror are positioned on the same straight line, the third parabolic mirror and the fourth parabolic mirror are positioned on the same straight line, the first parabolic mirror and the fourth parabolic mirror are mutually symmetrical, and the second parabolic mirror and the third parabolic mirror are mutually symmetrical.
8. The device for measuring the complex dielectric constant of the terahertz wave band material according to claim 7, wherein the first terahertz receiving and transmitting module and the second terahertz receiving and transmitting module both comprise a terahertz spread spectrum module, a port of the terahertz spread spectrum module is connected with an antenna, and wave absorbing materials are arranged around the antenna.
9. The device for measuring complex permittivity of a terahertz-band material according to 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 permittivity of terahertz-band material according to any one of claims 7 to 9, wherein focal lengths of the first parabolic mirror, the second parabolic mirror, the third parabolic mirror, and the fourth parabolic mirror are the same, and a distance between the second parabolic mirror and the third parabolic mirror is twice a focal length of the parabolic mirrors.
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| JP2001021503A (en) * | 1999-07-09 | 2001-01-26 | Japan Science & Technology Corp | Terahertz band complex dielectric constant measuring system |
| CN105548722A (en) * | 2015-12-08 | 2016-05-04 | 华东师范大学 | Measuring system of ferromagnetic material terahertz dielectric constant |
| JP2017003341A (en) * | 2015-06-08 | 2017-01-05 | 日本電信電話株式会社 | Dielectric spectroscopic apparatus |
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| CN109632694A (en) * | 2018-12-26 | 2019-04-16 | 深圳市太赫兹科技创新研究院有限公司 | Tera-hertz spectra test equipment and system |
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| JP2001021503A (en) * | 1999-07-09 | 2001-01-26 | Japan Science & Technology Corp | Terahertz band complex dielectric constant measuring system |
| JP2017003341A (en) * | 2015-06-08 | 2017-01-05 | 日本電信電話株式会社 | Dielectric spectroscopic apparatus |
| CN105548722A (en) * | 2015-12-08 | 2016-05-04 | 华东师范大学 | Measuring system of ferromagnetic material terahertz dielectric constant |
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