CN102393490A - Device for measuring high-temperature complex dielectric constants of dielectric material - Google Patents

Abstract

A device for measuring high-temperature complex dielectric constants of dielectric material belongs to the technical field of microwave testing, and comprises a vector network analyzer and a rectangular waveguide resonant cavity, wherein the rectangular waveguide resonant cavity is formed by connecting a radiating waveguide, a thermal insulation waveguide, a high-temperature waveguide and a short-circuit flange plate in sequence; a structure of a groove with rectangular sections is arranged at one side of the short-circuit flange plate, facing to the interior of the rectangular resonant cavity and is used for bearing samples of detected media; and a choke type flange structure is formed at the connection part between the high-temperature waveguide and the short-circuit flange plate. In the device, a structure that a high-temperature waveguide is contacted with a metal short-circuit plat in the existing device for measuring the high-temperature complex dielectric constants of the dielectric material is changed to be the choke type flange structure that the high-temperature waveguide is connected with the short-circuit flange plate; and the device has the advantages that the operation is convenient, and the costs for use and maintenance are low, and simultaneously, can ensure the good electric contact between a terminal short circuit surface and the waveguides, thereby ensuring the accuracy of testing results.

Description

A kind of dielectric materials high-temperature complex dielectric constant measurement mechanism

Technical field

The invention belongs to the microwave testing field, relate to terminal short circuit dielectric material method for measuring complex dielectric constant and system, in particular for the system of dielectric materials high-temperature complex dielectric constant measurement.

Background technology

Along with the high-temperature medium material in Application for Field such as Aero-Space, military equipments more and more widely, also increasingly high to the requirement of its microwave property.Complex permittivity and temperature characterisitic thereof are to weigh a good and bad important parameter of high-temperature medium material microwave performance.Therefore, when research and application of high temperatures dielectric material, all need under hot environment, test the temperature characterisitic of material complex permittivity.

Terminal short circuit is a kind of common method of measuring media material complex permittivity.Its measuring principle is the transmission line that measured material is filled in terminal short circuit, through measuring the complex reflection coefficient of this transmission line, can calculate the complex permittivity of measured material.This method only need be measured the single port reflection coefficient, and has advantages such as simple in structure, that test frequency range is wide, volume is little, relatively is fit to high temperature measurement.The test philosophy of terminal short circuit is as shown in Figure 1.According to impedance principle, can obtain

$\frac{\tanh (\mathrm{\γ}\·d)}{\mathrm{\γ}\·d}=\frac{1}{j\·{\mathrm{\β}}_0\·d}\left(\frac{1-j\·\mathrm{\ρ}\·\tan \left({\mathrm{\θ}}_j\right)}{\mathrm{\ρ}-j\·\tan \left({\mathrm{\θ}}_j\right)}\right)---\left(1\right)$

Wherein, γ is the transmission coefficient that is filled with measured medium sample waveguide segment, and d is the measured medium thickness of sample.

$\mathrm{\ρ}=\frac{1+\left|S_{11}\right|}{1-\left|S_{11}\right|}---\left(2\right)$

${\mathrm{\θ}}_j=\frac{{\mathrm{\θ}}_{S11}-(2\·n+1)\·\mathrm{\π}}{2}+2\·{\mathrm{\β}}_0\·(L-d)---\left(3\right)$

${\mathrm{\β}}_0=\frac{2\·\mathrm{\π}}{{\mathrm{\λ}}_0}\·\sqrt{1-{\left(\frac{{\mathrm{\λ}}_0}{{\mathrm{\λ}}_c}\right)}^2}---\left(4\right)$

λ _c＝2·a (5)

${\mathrm{\λ}}_0=\frac{c}{f_0}---\left(6\right)$

γ＝α+jβ (7)

α is an attenuation constant, and β is a phase constant, and L is a waveguide length, and a is the long hem width degree of waveguide, S ₁₁Be complex reflection coefficient, θ _S11Be S ₁₁Angle.After trying to achieve the transmission coefficient γ that is filled with the measured material waveguide segment by formula (1), utilize equation for transmission line again, can try to achieve the complex permittivity of measured material.

${\mathrm{\ϵ}}_r^{\′}=\frac{{\mathrm{\λ}}_0}{2\·\mathrm{\π}}\·[{\left(\frac{2\·\mathrm{\π}}{{\mathrm{\λ}}_c}\right)}^2+{\mathrm{\β}}^2-{\mathrm{\α}}^2]---\left(8\right)$

$\tan {\mathrm{\δ}}_{\mathrm{\ϵ}}=\frac{2\·\mathrm{\α}\·\mathrm{\β}}{{\left(\frac{2\·\mathrm{\π}}{{\mathrm{\λ}}_c}\right)}^2+{\mathrm{\β}}^2-{\mathrm{\α}}^2}---\left(9\right)$

In the formula,

Be the relative dielectric constant of dielectric material, tan δ _εBe loss tangent.

Can know by formula (1)～(9), behind the complex reflection coefficient of the known transmission line that is filled with measured material, can calculate the complex permittivity of material.Therefore have:

${\mathrm{\ϵ}}_r^{\′}=f(L,a,f_0,S_{11},d)---\left(10\right)$

2002, the U.S. formulated ASTM standard " D2520-01 ".In this standard, adopt the rectangular waveguide transmission line, to carry out the alternating temperature of dielectric material performance with terminal short circuit and measure, the maximum temperature of measurement is 1650 ℃, the material that transmission line adopts is a platinum-rhodium alloy; When probe temperature is low, but the other materials that can adopt satisfied temperature to measure.

(application number: the test waveguide of adopting 200910059213.0) is the waveguide of high temperature test rectangle, is made up of heat radiation waveguide, heat insulation waveguide, high temperature waveguide and short board in its patented claim " a kind of method for measuring high-temperature complex dielectric based on terminal short circuit " in University of Electronic Science and Technology.Total two-way, one tunnel load sample, the one tunnel is used for error correction.During test; The measured medium sample is close to short board and is positioned in wherein one road high temperature waveguide; Reflection coefficient when measuring WAVEGUIDE LOADED measured medium sample, and utilize the reflection coefficient of the unloaded waveguide in another road to revise, calculate the complex permittivity of tested ring material then.

Because some dielectric material at high temperature can melt, in addition with short board and high temperature waveguide generation chemical reaction, thereby pollution short board and high temperature waveguide.This thing happens, and back short board and high temperature waveguide can't be reused.Common way is thoroughly to change short board and high temperature waveguide, because short board and high temperature waveguide material and processing cost are very high, thoroughly changes short board and high temperature waveguide meeting causes the too high and inconvenient operation of testing cost; In addition, under hot conditions, deformation can take place owing to be heated inhomogeneously in waveguide, even can clean the short circuit face that can not guarantee and waveguide has good electrical contact all the time to short board and high temperature waveguide, thereby influences precision of test result.

Summary of the invention

The present invention is directed to the above-mentioned defective that exists in the existing dielectric materials high-temperature complex dielectric constant measurement mechanism, a kind of new dielectric materials high-temperature complex dielectric constant measurement mechanism is provided.This measurement mechanism improves the sample test anchor clamps (bearing structure) that are made up of short board and high temperature waveguide in the existing dielectric materials high-temperature complex dielectric constant measurement mechanism; Increase a choke flange structure that constitutes by high temperature waveguide and short circuit flange in high temperature waveguide rear end, and adopt the short circuit ring flange to carry the measured medium sample.Adopt dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention, in measuring process, have characteristics easy to operate, that the operation and maintenance cost is low; Dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention can guarantee good electrical contact between terminal short circuit face and the waveguide, thereby can guarantee precision of test result owing to adopted the choke flange structure simultaneously.

Technical scheme of the present invention is following:

A kind of dielectric materials high-temperature complex dielectric constant measurement mechanism, as shown in Figure 2, comprise vector network analyzer and rectangular-wave resonant cavity, said rectangular-wave resonant cavity links to each other with said vector network analyzer with coaxial cable through waveguide-coaxial X-over; Said rectangular-wave resonant cavity is linked in sequence by the heat radiation waveguide of same size, heat insulation waveguide and high temperature waveguide and a short circuit ring flange and forms, and the rectangular-wave resonant cavity wall is done metalized.Said short circuit ring flange adopts high temperature resistant conductive material to make, and it has the square-section groove structure towards the inner side of rectangular cavity, in order to carry the measured medium sample; The square-section size of said groove structure is consistent with the sectional dimension of rectangular-wave resonant cavity.The junction of said high temperature waveguide and short circuit ring flange forms chokes formula flange arrangement.

Above-mentioned dielectric materials high-temperature complex dielectric constant measurement mechanism also can comprise a high temperature furnace, and said high temperature furnace used to be opposite to the high temperature section of the rectangular-wave resonant cavity in the stove, i.e. high temperature waveguide and short circuit ring flange heat to realize high temperature measurement.

Because when adopting terminal short circuit measuring media material at high temperature dielectric properties (complex permittivity) usually; Need to measure rectangular-wave resonant cavity zero load at high temperature and a year reflection coefficient is arranged; Therefore dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention can comprise two identical rectangular-wave resonant cavities; Two rectangular-wave resonant cavities link to each other through waveguide-coaxial X-over and the coaxial cable passage different with said vector network analyzer respectively; Make that when high temperature measurement with the high temperature section of two rectangular-wave resonant cavities, promptly the high temperature waveguide of two rectangular-wave resonant cavities and short circuit ring flange place high temperature furnace simultaneously; One of them rectangular-wave resonant cavity has year (the short circuit ring flange that is rectangular-wave resonant cavity carries the measured medium sample); And another rectangular-wave resonant cavity is unloaded, can measure rectangular-wave resonant cavity zero load at high temperature so simultaneously and a year reflection coefficient is arranged, thereby can improve efficiency of measurement greatly.

Need to prove:

One, making flange material is high temperature resistant conductive material, and like molybdenum, tungsten, tantalum, graphite etc., practical implementation can be according to probe temperature, measured material characteristic and processing cost decision.The tungsten material hardness is high, and difficulty of processing is big, and Mo can only be used for 1300 ℃ of following temperature environments to be tested.

Two, in the dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention, the length L 2 of the length L 1 of radial transmission line A and coaxial waveguide section B should be 1/4 waveguide wavelength in the said chokes formula flange arrangement.And the width of radial transmission line A (being chokes formula flange slot width) d should be the gap width of standard flange joint; Consider material thermal expansion effects at high temperature; Also can chokes formula flange slot width d be designed to be slightly larger than the gap width of standard flange joint, be an equivalent short circuit face with the interface that guarantees high temperature lower flange slit and rectangular-wave resonant cavity chamber wall.Because the interface of flange slot and rectangular-wave resonant cavity chamber wall is an equivalent short circuit face; Agingly certain deformation takes place and can't realize still can guaranteeing good electrical contact between terminal short circuit plate (short circuit flange) and the rectangular waveguide under the situation that favorable mechanical contacts with the high temperature waveguide even make to use at the short circuit ring flange; Thereby can guarantee measuring accuracy for a long time, avoid existing based on the measuring error that causes owing to short board and waveguide loose contact in the terminal short circuit dielectric materials high-temperature complex dielectric constant measuring system.

Three, when test, the measured medium material sample is put into the rectangular recess of short circuit ring flange, the rectangular recess cross section of measured material lateral dimension and short circuit ring flange adapts, and closely contacts with the short circuit face of short circuit ring flange; With short circuit ring flange and high temperature waveguide aligned, be connected with screw again through tommy; Increase temperature then and test.But short circuit ring flange unified manufacture is overlapped more, to reduce cost of manufacture.Even the situation of measured medium sample contamination or aging distortion occurs receiving; Also only needing to change the short circuit ring flange gets final product; Waveguide can't be polluted and damaged, and is reusable, and therefore dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the present invention has lower operation and maintenance cost.

In sum, dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention has characteristics easy to operate, that the operation and maintenance cost is low; Dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention can guarantee good electrical contact between terminal short circuit face and the waveguide, thereby can guarantee precision of test result owing to adopted the choke flange structure simultaneously.

Description of drawings

Fig. 1 is the measurement mechanism structural representation of conventional terminal short-circuit method measuring media material high temperature complex dielectric constant.

Fig. 2 is a dielectric materials high-temperature complex dielectric constant measurement mechanism basic structure synoptic diagram provided by the invention.

Fig. 3 is in the dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention, the schematic cross-section of chokes formula flange arrangement junction.

Fig. 4 is another structural representation of dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention.

Embodiment

Embodiment one

A kind of dielectric materials high-temperature complex dielectric constant measurement mechanism, as shown in Figure 2, comprise vector network analyzer and rectangular-wave resonant cavity, said rectangular-wave resonant cavity links to each other with said vector network analyzer with coaxial cable through waveguide-coaxial X-over; Said rectangular-wave resonant cavity is linked in sequence by the heat radiation waveguide of same size, heat insulation waveguide and high temperature waveguide and a short circuit ring flange and forms, and the rectangular-wave resonant cavity wall is done metalized.Said short circuit ring flange adopts high temperature resistant conductive material to make, and it has the square-section groove structure towards the inner side of rectangular cavity, in order to carry the measured medium sample; The square-section size of said groove structure is consistent with the sectional dimension of rectangular-wave resonant cavity.The junction of said high temperature waveguide and short circuit ring flange forms chokes formula flange arrangement.

Above-mentioned dielectric materials high-temperature complex dielectric constant measurement mechanism also can comprise a high temperature furnace, and said high temperature furnace used to be opposite to the high temperature section of the rectangular-wave resonant cavity in the stove, i.e. high temperature waveguide and short circuit ring flange heat to realize high temperature measurement.

During use; At first confirm rectangular-wave resonant cavity microwave reflection coefficient at normal temperatures described in the measurement mechanism; Measure said rectangular-wave resonant cavity again the microwave reflection coefficient that carries with no-load is at high temperature arranged; And combine various known conditions (comprising size, test frequency, material heat expansion characteristic etc.), adopt terminal short circuit can calculate the high-temperature complex dielectric of measured medium sample.

Embodiment two

Because when adopting terminal short circuit measuring media material at high temperature dielectric properties (complex permittivity) usually; Need to measure rectangular-wave resonant cavity zero load at high temperature and a year reflection coefficient is arranged; Therefore dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention can comprise two identical rectangular-wave resonant cavities, and two rectangular-wave resonant cavities link to each other through waveguide-coaxial X-over and the coaxial cable passage different with said vector network analyzer respectively.The material and the size of two huge waveguide resonant cavities are identical, and being linked in sequence by the heat radiation waveguide of same size, heat insulation waveguide and high temperature waveguide and a short circuit ring flange forms, and the rectangular-wave resonant cavity wall is done metalized; Said short circuit ring flange adopts high temperature resistant conductive material to make, and it has the square-section groove structure towards the inner side of rectangular cavity, in order to carry the measured medium sample; The square-section size of said groove structure is consistent with the sectional dimension of rectangular-wave resonant cavity; The junction of said high temperature waveguide and short circuit ring flange forms chokes formula flange arrangement.

During high temperature measurement; High temperature section with two rectangular-wave resonant cavities; Promptly the high temperature waveguide of two rectangular-wave resonant cavities and short circuit ring flange place high temperature furnace simultaneously, and one of them rectangular-wave resonant cavity has year (the short circuit ring flange that is rectangular-wave resonant cavity carries the measured medium sample), and another rectangular-wave resonant cavity is unloaded; Can measure simultaneously like this rectangular-wave resonant cavity at high temperature zero load and have and carry a reflection coefficient, thereby can improve efficiency of measurement greatly.

When adopting dielectric materials high-temperature complex dielectric constant measurement mechanism provided by the invention that dielectric material is carried out the high-temperature complex dielectric measurement; The terminal short circuit of basic step and computation process and routine measurement dielectric materials high-temperature complex dielectric constant is the same, repeats no more at this.What should be noted that the present invention adopts is the rectangular-wave resonant cavity structure, and for the transmission line of circular waveguide, coaxial waveguide and other types, design philosophy of the present invention stands good.

Claims (5)

1. a dielectric materials high-temperature complex dielectric constant measurement mechanism comprises vector network analyzer and rectangular-wave resonant cavity, and said rectangular-wave resonant cavity links to each other with said vector network analyzer with coaxial cable through waveguide-coaxial X-over; It is characterized in that said rectangular-wave resonant cavity is linked in sequence by the heat radiation waveguide of same size, heat insulation waveguide and high temperature waveguide and a short circuit ring flange and forms, the rectangular-wave resonant cavity wall is done metalized; Said short circuit ring flange adopts high temperature resistant conductive material to make, and it has the square-section groove structure towards the inner side of rectangular cavity, in order to carry the measured medium sample; The square-section size of said groove structure is consistent with the sectional dimension of rectangular-wave resonant cavity; The junction of said high temperature waveguide and short circuit ring flange forms chokes formula flange arrangement.

2. dielectric materials high-temperature complex dielectric constant measurement mechanism according to claim 1 is characterized in that, the length L 2 of the length L 1 of radial transmission line (A) and coaxial waveguide section (B) is 1/4 waveguide wavelength in the said chokes formula flange arrangement; And the width of radial transmission line A, be that chokes formula flange slot width d is the gap width of standard flange joint or the gap width that is slightly larger than the standard flange joint.

3. dielectric materials high-temperature complex dielectric constant measurement mechanism according to claim 1 and 2 is characterized in that, said dielectric materials high-temperature complex dielectric constant measurement mechanism also comprises a high temperature furnace; Said high temperature furnace used to be opposite to the high temperature section of the rectangular-wave resonant cavity in the stove, i.e. high temperature waveguide and short circuit ring flange heat to realize high temperature measurement.

4. dielectric materials high-temperature complex dielectric constant measurement mechanism according to claim 1 and 2; It is characterized in that; Said dielectric materials high-temperature complex dielectric constant measurement mechanism also comprises the identical rectangular-wave resonant cavity of another one, and said another one rectangular-wave resonant cavity links to each other with another path of said vector network analyzer with coaxial cable through waveguide-coaxial X-over equally.

5. dielectric materials high-temperature complex dielectric constant measurement mechanism according to claim 4 is characterized in that, said dielectric materials high-temperature complex dielectric constant measurement mechanism also comprises a high temperature furnace; Said high temperature furnace used to be opposite to the high temperature section of two rectangular-wave resonant cavities in the stove, i.e. high temperature waveguide and short circuit ring flange heat to realize high temperature measurement.

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