CN107543970B - Dielectric constant measuring method based on database calibration method - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 39
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- -1 polytetrafluoroethylene Polymers 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
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Abstract
The invention belongs to the technical field of dielectric constant measurement, and provides a dielectric constant measurement method based on a database calibration method, which is used for measuring a dielectric material with a coaxial structure; the invention adopts a three-section type coaxial clamp which comprises a left section clamp, a middle section clamp and a right section clamp, which are all used for filling a medium to be tested, and the connection mode is as follows: the left section clamp is connected with the right section clamp, or the left section clamp, the middle section clamp and the right section clamp are sequentially connected; firstly, establishing a database by adopting a plurality of sample medium materials; then connecting the left section clamp filled with the dielectric material to be tested with the right section clamp, measuring an S parameter, and determining a clamp parameter; and finally, sequentially connecting the three sections of clamps after filling the dielectric material to be measured to measure the S parameter, and performing embedding treatment through the clamps to ensure that the calibration end surface of the clamp is positioned in the sample to be measured so as to accurately measure the dielectric constant of the dielectric material to be measured. The invention has the advantages of low cost, simple operation, low assembly requirement, high precision and the like.
Description
Technical Field
The invention belongs to the technical field of dielectric constant measurement, and particularly relates to a dielectric constant measurement method based on a database calibration method for a dielectric material with a coaxial structure.
Background
With the progress of science and technology, microwave technology is increasingly applied to production, life, national defense and military, and in the microwave technology, the transmission and emission of electromagnetic waves are the basis of the theory, so the research on microwave transmission lines is always a hot point of research, the microwave transmission lines are rapidly developed in the combination with material science, and the key point in the production process of the transmission lines is to grasp the electromagnetic characteristics of material media utilized by the transmission lines. At present, in the microwave field, a coaxial line is a transmission line widely applied, so that the dielectric constant of a coaxial structure material is measured quickly, accurately and at low cost, and the method has important significance in research and production processes.
At present, common dielectric constant measuring methods include a transmission \ reflection method, a resonant cavity method and a free space method. Among them, the free space method can realize the non-contact measurement of the medium, for example, the patent document with the application number of CN201410049841.1 entitled "a test system and method for accurately measuring dielectric constant" discloses a method for accurately measuring the electromagnetic parameters of the sample by using the change of the input impedance of the antenna and the radiation field; however, the method has high requirements for processing the dielectric material, is relatively complex, needs to design a complete set of T \ R components such as a low-noise amplifier, a mixer, a power amplifier and the like, a specially-made antenna and the like, has high cost and limited application range. Although the resonant cavity method has better measurement accuracy for low-loss materials, the resonant cavity method also has the defects of narrow measurement frequency band, complex measurement instrument and the like. The transmission/reflection method was first proposed by Nicolson, Ross and Weir et al in 1970, and is also called NRW method, which essentially determines the complex permittivity by using the relationship between the single reflection coefficient and the single transmission coefficient and permittivity; the method comprises the steps of placing a sample to be tested in an air transmission line, measuring S parameters of a double port, combining with de-embedding processing, and inverting to obtain the complex dielectric constant of the sample to be tested, wherein for the method, a certain application is obtained at present, and for example, a temperature-changing test method of the dielectric constant based on a transmission \ reflection method is disclosed in patent documents with the application number of CN201510305197.4 and the name of 'wide-band temperature-changing dielectric constant test system of solid and powder materials'; however, there are still some disadvantages to this approach: firstly, during measurement, as the sample is placed in the air transmission line, the assembly requirement of the system is higher, the sample to be measured needs to be accurately positioned, and otherwise, measurement errors are caused; secondly, for the measuring end face, de-embedding processing is needed, if a TRL de-embedding method is used, high calibration accuracy can be obtained, but the clamp is often a non-standard device, a calibration piece needs to be customized, the cost is high, and if only phase transformation is used for processing, a certain loss error is brought.
Disclosure of Invention
The invention aims to provide a dielectric constant measuring method based on a database calibration method aiming at the defects of the dielectric constant measuring method. The measuring object of the invention is a dielectric material for a coaxial structure, and compared with the traditional dielectric constant measuring method, the invention has the advantages of low cost, simple and convenient operation, lower assembly requirement, higher precision and the like.
In order to achieve the purpose, the invention adopts the following solution:
the dielectric constant measuring method based on the database calibration method is characterized in that a three-section type coaxial clamp is adopted, the three-section type coaxial clamp comprises a left section clamp, a middle section clamp and a right section clamp, the three-section type coaxial clamp is used for filling a medium to be measured, and the connection mode is as follows: the left section clamp is connected with the right section clamp, or the left section clamp, the middle section clamp and the right section clamp are sequentially connected; the method specifically comprises the following steps:
step 1, establishing a database: filling N sample medium materials into the left section fixture and the right section fixture respectively, and measuring S parameters of the left section fixture and the right section fixture respectively through electromagnetic simulation software:
left segment clamp Sl：
Right section fixture Sr：
And the S parameters of the left section fixture and the right section fixture are respectively converted into T parameters:
left segment clamp Tl：
Right section anchor clamps Tr：
Calculating T parameter T of cascade connection of the left section clamp and the right section clampa：
T parameter T of left section clamp and right section clamp in cascade connectionaConversion to S parameter Sa：
A parameter Tl、Tr、Ta、SaStoring the data into a database, namely establishing a parameter database for embedding the clamp;
step 2, filling the dielectric material to be measured into the left section fixture, the middle section fixture and the right section fixture respectively, connecting the left section fixture and the right section fixture into a vector network analyzer, and measuring to obtain S parameter Ss：
Calculating the parameter S in the databaseaAnd SsError value:
finding S of minimum error valueaParameter, label
It corresponds to Tl、TrThe parameters are identified as T parameters of the left section clamp and the right section clamp after being filled with the medium to be measured and are respectively marked as
Step 3, embedding the clamp: connecting the left section clamp, the middle section clamp and the right section clamp in sequence, connecting the left section clamp, the middle section clamp and the right section clamp into a vector network analyzer, and measuring to obtain an S parameter SzAnd converted into T parameter Tz：
Calculating to obtain T parameter T of middle fixture after filling medium to be measuredx：
And converted into S parameter Sx：
Calculating to obtain the dielectric constant epsilon of the dielectric material to be measuredr：Wherein T is Sx21C is the speed of light, ω is 2 π f, f is the frequency, and d is the length of the medium to be measured in the middle section.
In the invention, the interconversion formula of the S parameter and the T parameter is as follows:
The invention has the beneficial effects that:
the invention provides a dielectric constant measuring method based on a database calibration method, which adopts a three-section coaxial clamp, medium materials to be measured are filled in a left, a middle and a right three-section clamps, and because the medium materials of samples to be measured are identical, namely continuous, in the clamps at the left and the right ends, the obtained S parameter is the single transmission coefficient of the samples to be measured, and further the complex dielectric constant to be measured is obtained according to the relation between the single transmission coefficient and the complex dielectric constant; meanwhile, the medium material to be measured is used as a part of the clamp, discontinuity does not exist between the calibration end surface and the clamp end surface, and after the clamp is subjected to embedding treatment, the calibration end surface is positioned in the sample to be measured, so that the measurement precision is greatly improved; meanwhile, the error caused by inaccurate positioning of the sample can be reduced as much as possible in the transferring and matching process of the clamp; in conclusion, the invention has the advantages of low cost, simple operation, lower assembly requirement, higher precision and the like.
Drawings
FIG. 1 is a cross-sectional view of a three-segment coaxial fixture of the present invention taken along the vertical axis; wherein, 1 is a metal thread, 2 is an outer conductor, 3 is an SMA adapter supporting medium (usually polytetrafluoroethylene), 4 is an SMA inner conductor, 5 is air, 6 and 7 are pin holes, and A-F represent an end surface A to an end surface F.
FIG. 2 is an assembly diagram of the dielectric material to be measured according to the present invention.
FIG. 3 is a three-dimensional schematic view of a three-segment coaxial fixture of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and examples, which should not be construed as limiting the invention.
The embodiment provides a dielectric constant measuring method based on a database calibration method, the structure of a three-section coaxial clamp adopted by the method is shown in fig. 1, the clamps are connected by using pins or screws, particularly, a left section clamp can be directly connected with a right section clamp as shown in fig. 3(b), or can be sequentially connected with a left section, a middle section and a right section as shown in fig. 3 (a); the left and right clamps are used for converting nonstandard coaxial media into the size of the SMA connector so as to be connected with a vector network analyzer to measure S parameters, and the left and right ports of the clamps are designed by SMA adapters and can be directly connected with the coaxial lines through SMA and further connected with the vector network. As shown in fig. 1 and 2, the length of the left clamp, i.e., the end face A, C, is L1, the length of the middle sample clamp, i.e., the end face C, D, is L2, and the length of the right clamp, i.e., the end face D, F, is L3, where L1 is L3.
In the embodiment, a plurality of sample medium materials are firstly adopted to establish a database, for example, for a polytetrafluoroethylene foam material, a database with a dielectric constant of 1.0-2.1 and an imaginary part of 0.002-0.02 can be established, and the more accurate the selection of the stepping value is, the more accurate the measurement result is; cutting a section of coaxial cable to be tested with the length of 2 × L1+ L2+2 × L3, firstly cutting the cable into three parts with the lengths of L1, L3, L1+ L2+ L3, respectively filling L1 and L3 into a left section clamp and a right section clamp, and specially, cutting the coaxial cable to be tested into a section with the length of 2 × L1+ L2+2 × L3, and respectively filling the section with the lengths of L1 and L3 intoL ═ L3; the left and right clamps are butted and connected into a vector network analyzer, and S parameter Ss(ii) a Comparing the S parameters with the S parameters in the database, and selecting the S parameter with the minimum error between actual measurement and the model as the S parameter of the clamp; sequentially connecting the three sections of clamps, loading the medium to be tested with the length of L1+ L2+ L3, and connecting a vector network analyzer to measure the S parameter of the medium; substituting the obtained medium S parameter into a de-embedding algorithm written by matlab, and converting the measured medium S parameter from an A, F end face to a C, D end face by the two-port network matrix cascade method, as shown in FIG. 1; and finally, substituting the obtained S parameter of the C, D end face into a designed matlab program, calculating to obtain the complex dielectric constant of the medium to be measured, and calculating the S parameter of the C, D end face according to the microwave network and transmission line theory21I.e. the single transmission coefficient T in the sample, for non-magnetic materials there is the formula:
from this formula, one can obtain:
wherein T is S21ω is 2 pi f, c is the speed of light, f is the frequency, and d is the length between the end faces C, D, i.e., the length L2 of the medium to be measured.
While the invention has been described with reference to specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise; all of the disclosed features, or all of the method or process steps, may be combined in any combination, except mutually exclusive features and/or steps.
Claims (1)
1. A dielectric constant measuring method based on a database calibration method is characterized in that a three-section type coaxial clamp is adopted, and the three-section type coaxial clamp comprises a left section clamp, a middle section clamp and a right section clamp which are all used for filling a medium to be measured; the method specifically comprises the following steps:
step 1, establishing a database: filling N sample medium materials into the left section fixture and the right section fixture respectively, and measuring S parameters of the left section fixture and the right section fixture respectively through electromagnetic simulation software:
left segment clamp Sl：
Right section fixture Sr：
And the S parameters of the left section fixture and the right section fixture are respectively converted into T parameters:
left segment clamp Tl：
Right section anchor clamps Tr：
Calculating T parameter T of cascade connection of the left section clamp and the right section clampa：
T parameter T for cascading a left section clamp and a right section clampaConversion to S parameter Sa：
A parameter Tl、Tr、Ta、SaStoring the data into a database, namely establishing a parameter database for embedding the clamp;
step 2, filling the dielectric material to be measured into the left section fixture, the middle section fixture and the right section fixture respectively, connecting the left section fixture and the right section fixture into a vector network analyzer, and measuring to obtain S parameter Ss：
Calculating the parameter S in the databaseaAnd SsError value:
finding S of minimum error valueaParameter, label
It corresponds to Tl、TrThe parameters are identified as T parameters of the left section clamp and the right section clamp after being filled with the medium to be measured and are respectively marked as
Step 3, embedding the clamp: connecting the left section clamp, the middle section clamp and the right section clamp in sequence, connecting the left section clamp, the middle section clamp and the right section clamp into a vector network analyzer, and measuring to obtain an S parameter SzAnd converted into T parameter Tz：
Calculating to obtain T parameter T of middle fixture after filling medium to be measuredx：
And converted into S parameter Sx：
Calculating to obtain the dielectric constant epsilon of the dielectric material to be measuredr：
Wherein T is Sx21C is the speed of light, ω is 2 π f, f is the frequency, and d is the length of the medium to be measured in the middle section.
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| CN108318746A (en) * | 2018-04-10 | 2018-07-24 | 四川聚强创新科技有限公司 | A kind of VHF frequency ranges complex dielectric constant measuring apparatus |
| CN109444174B (en) * | 2018-08-20 | 2021-08-31 | 中国石油天然气集团有限公司 | High-frequency rock dielectric constant measuring method and measuring clamp |
| CN109270479B (en) * | 2018-09-21 | 2021-03-19 | 临海市云谱光电有限公司 | Multi-line TRL calibration method based on tensor decomposition |
| CN110048769B (en) * | 2019-04-29 | 2021-01-22 | 中国电子科技集团公司第四十一研究所 | Self-adaptive frequency response characteristic testing device and method |
| CN110361685B (en) * | 2019-07-01 | 2021-07-30 | 北京无线电计量测试研究所 | Broadband oscilloscope probe transmission characteristic calibration method and system |
| CN110596463B (en) * | 2019-09-20 | 2020-06-09 | 电子科技大学 | Coaxial measuring device, testing system and method for measuring dielectric constant of medium |
| CN110703054B (en) * | 2019-10-29 | 2022-12-20 | 山东省科学院自动化研究所 | Sample dielectric property testing device and method based on terahertz free space method |
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