Free space complex dielectric constant high-temperature testing device

Abstract

The utility model provides a high-temperature testing device for a complex dielectric constant in a free space. The high-temperature testing device comprises a dielectric lens, a transmitting antenna, a receiving antenna, a sample bracket, a high-temperature furnace and a vector network analyzer, the vector network analyzer is connected with the transmitting antenna and the receiving antenna through a microwave cable, the phase center of the transmitting antenna / receiving antenna is located at one focus of the dielectric lens, and the sample frame center of the sample support is located at the other focus of the dielectric lens; the two faces, facing the dielectric lens, of the high-temperature furnace are heat insulation flat plates, and heating resistance wires are arranged on the other four faces. According to the testing method, based on the complex dielectric constant and the thickness of the heat insulation flat plate, de-embedding is carried out on the influence of the heat insulation flat plate by adopting a network cascading method. The device has the characteristics of good heating uniformity and high test precision, and can effectively deduct system errors introduced by the heat insulation flat plate of the high-temperature furnace, so that the accuracy of a test result is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave and millimeter-wave material complex permittivity testing, and particularly relates to a high-temperature testing device and method for complex permittivity in free space. Background Technique

[0002] High-temperature dielectric materials are widely used in fields such as aerospace and microwave metallurgy. With the development of material technology, the working temperature of high-temperature dielectric materials is getting higher and higher, and the variation law of their dielectric properties with temperature is also more complex. These variations will affect the microwave properties of high-temperature dielectric materials and have an impact on the transmission, reflection, and scattering of electromagnetic waves. Therefore, accurately testing and analyzing the variation of the dielectric properties of high-temperature dielectric materials with temperature is crucial for the design and application of radomes, stealth components, etc.

[0003] The free space method is a commonly used method for measuring the dielectric properties of materials and has the advantage of non-contact non-destructive measurement. When using the free space method for high-temperature testing, the sample to be measured needs to be placed in a high-temperature furnace. In the patent of "A high-temperature furnace for testing the high-temperature dielectric properties of materials by the free space method" with the publication number CN210569967U, it is proposed to heat the sample by surrounding it with electric heating wires, and at the same time, use polycrystalline mullite fiber boards for heat insulation, but how to deduct the influence of the polycrystalline mullite fiber boards is not mentioned in this patent. In the patent of "A system and method for obtaining the dielectric constant of materials in a high-temperature environment" with the publication number CN105388363A, a spatial calibration method for the dielectric constant in a high-temperature environment is provided, but its calibration is relatively complicated and requires SOLT or TRL calibration first, and then GRL calibration. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-temperature testing device and method for complex permittivity in free space, which insulates and preserves the sample to be measured by introducing heat-insulating plates, and based on the electrical properties and size parameters of the heat-insulating plates, quickly de-embeds their influence through one-time calibration.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A high-temperature testing device for complex permittivity in free space includes: dielectric lenses 1 and 2, transmitting antenna 3, receiving antenna 4, sample holder 5, high-temperature furnace 6, and vector network analyzer 7. The vector network analyzer is connected to the transmitting antenna and the receiving antenna through a microwave cable. The phase centers of the transmitting antenna / receiving antenna are located at one focus of the dielectric lens, and the center of the sample frame of the sample holder is located at the other focus of the dielectric lens; the two sides of the high-temperature furnace facing the dielectric lens are heat-insulating plates 8 and 9, and heating resistance wires 10 are arranged on the other four sides.

[0007] As a preferred embodiment, the transmitting antenna and the receiving antenna are the same, and are a double-ridge horn antenna or a double-ridge conical horn antenna.

[0008] As a preferred embodiment, the sample holder includes a sample frame 11 and a base 12, which are processed from high-temperature resistant metal materials and are sprayed with a high-temperature oxidation-resistant coating on their surfaces. A thermocouple is installed at the center of each of the four sides of the sample frame, and a water-cooling groove is opened at the base away from the sample frame for water cooling.

[0009] As a preferred embodiment, the heat-insulating flat plate can be quickly disassembled and assembled, and the thickness of the air gap between the heat-insulating flat plate and the sample to be measured 13 d a1 and d a2 do not exceed 10 mm; the heating resistance wires are arranged at equal intervals along the sample frame.

[0010] As a preferred embodiment, the heat-insulating flat plate is made of a thermal wave-transparent material with a low dielectric constant and a low loss tangent, and its relative complex dielectric constant at different temperatures ε rg ( t ) is known; the transverse length and width of the heat-insulating flat plate are not less than 1.25 times the transverse length and width of the sample to be measured, and its thickness d g1 and d g2 do not exceed 10 mm. [[ID=??]]

[0011] To achieve the above-mentioned invention purpose, the present invention also provides a method for high-temperature testing of the complex dielectric constant of materials by using the above device, including the following steps:

[0012] Step 1: Connect the transmitting antenna and the receiving antenna to a vector network analyzer respectively;

[0013] Step 2: Adjust the positions of the transmitting antenna, the receiving antenna, the dielectric lens and the sample holder so that the phase center of the transmitting antenna / receiving antenna is located at one focus of the dielectric lens, and the center of the sample frame of the sample holder is located at the other focus of the dielectric lens;

[0014] Step 3: Without installing the heat-insulating flat plate, perform a room-temperature TRL (Through-Reflect-Line) calibration on the test system;

[0015] Step 4: Place the sample to be measured with a thickness of d in the sample frame, install the heat-insulating flat plate, and move the receiving antenna in the direction away from the transmitting antenna. The moving distance is the sum of the thicknesses of the heat-insulating flat plate, the air gap and the sample to be measured, that is d g1 + d a1 + d + It should be noted that there seems to be some missing or unclear information in the original text, especially in the part about "the thickness of d ", which makes the translation a bit difficult to be completely accurate in this regard. If you can provide more complete information, it will be helpful for a more accurate translation.d a2 + d g2 ;

[0016] Step 5: Heat the sample to be tested, record the temperature measurement values of the four thermocouples on the sample frame, and take their average value as the test temperature; after reaching the required test temperature, keep it at a constant temperature for at least 10 min, and measure the temperature of the heat insulation plate t ; Record the scattering parameters S 11T 、S 21T 、S 12T and S 22T ;

[0017] Step 6: Calculate the relative complex permittivity of the sample to be tested at the required test temperature according to the inversion formula , specifically:

[0018]

[0019] In the formula:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027] The plus or minus sign in the Γ expression is determined by the condition |Γ| < 1. λ 0 is the free space wavelength corresponding to the test frequency, Z 0 = 120π is the free space wave impedance, is the transmission matrix of the sample to be tested, which is calculated by the following formula:

[0028]

[0029] where 、 、 、 are the transmission matrices of the left air gap, left heat insulation plate, right heat insulation plate, and right air gap respectively, and the expressions are as follows:

[0030]

[0031]

[0032]

[0033]

[0034] is the transfer matrix of the overall 5-layer material composed of a heat-insulating flat plate, an air gap, and the sample to be measured, and the expressions of each item are as follows:

[0035]

[0036]

[0037]

[0038]

[0039] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0040] The high-temperature test device for complex permittivity in free space provided by the present invention has the characteristics of high heating efficiency, good heating uniformity, and high test accuracy. By introducing a heat-insulating flat plate on the high-temperature furnace, heat can be insulated, reducing the heat diffusion of the sample to be measured, thereby improving the heating efficiency and temperature distribution uniformity of the sample to be measured; in addition, the test method provided by the present invention is based on the microwave network cascade theory of multi-layer materials. By calculating by substituting parameters such as the complex permittivity, thickness of the heat-insulating flat plate, and thickness of the air gap, the influence of the heat-insulating flat plate can be de-embedded, thereby ensuring the accuracy of the test results at high temperatures. Description of the Drawings

[0041] Figure 1 is a schematic structural diagram of the high-temperature test device for complex permittivity in free space provided by the present invention.

[0042] Figure 2 is a schematic diagram of the high-temperature furnace and the sample to be measured provided by the present invention.

[0043] Among them, 1 and 2 are dielectric lenses, 3 is a transmitting antenna, 4 is a receiving antenna, 5 is a sample holder, 6 is a high-temperature furnace, 7 is a vector network analyzer, 8 and 9 are heat-insulating flat plates, 10 is a heating resistance wire, 11 is a sample frame, 12 is a base, and 13 is the sample to be measured. Detailed Embodiments

[0044] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0045] AsFigure 1 As shown in the figure, a high-temperature test device for the complex permittivity of free space includes: dielectric lenses 1 and 2, transmitting antenna 3, receiving antenna 4, sample holder 5, high-temperature furnace 6, and vector network analyzer 7. The vector network analyzer is connected to the transmitting antenna and the receiving antenna through a microwave cable. The phase centers of the transmitting antenna / receiving antenna are located at one focus of the dielectric lens, and the center of the sample frame of the sample holder is located at the other focus of the dielectric lens. The two sides of the high-temperature furnace facing the dielectric lens are heat-insulating plates 8 and 9, and heating resistance wires 10 are arranged on the other four sides.

[0046] Preferably, the transmitting antenna and the receiving antenna are the same and are dual-ridge horn antennas.

[0047] Preferably, the sample holder includes a sample frame 11 and a base 12, which are processed from high-temperature-resistant metal materials and are sprayed with a high-temperature oxidation-resistant coating on their surfaces. A thermocouple is installed at the center of each of the four sides of the sample frame, and a water-cooling groove is opened at the base away from the sample frame for water cooling.

[0048] Preferably, the heat-insulating plate can be quickly disassembled and assembled. The thickness of the air gap between the heat-insulating plate and the sample to be measured 13 d a1 and d a2 are both not more than 10 mm; the heating resistance wires are arranged at equal intervals along the sample frame.

[0049] Preferably, the heat-insulating plate is made of a heat-transparent wave material with low permittivity and low loss tangent, and its relative complex permittivity ε rg ( t ) is known; the transverse length and width of the heat-insulating plate are not less than 1.25 times the transverse length and width of the sample to be measured, and its thickness d g1 and d g2 are both not more than 10 mm.

[0050] A method for high-temperature testing of the complex permittivity of materials using the above device includes the following steps:

[0051] Step 1: Connect the transmitting antenna and the receiving antenna to the vector network analyzer respectively;

[0052] Step 2: Adjust the positions of the transmitting antenna, receiving antenna, dielectric lens, and sample holder so that the phase centers of the transmitting antenna / receiving antenna are located at one focus of the dielectric lens, and the center of the sample frame of the sample holder is located at the other focus of the dielectric lens;

[0053] Step 3: Without installing the heat-insulating plate, perform room-temperature TRL (Through-Reflect-Line) calibration on the test system;

[0054] Step 4: Place the sample to be measured with a thickness of d in the sample frame, install the heat insulation plate, and move the receiving antenna away from the transmitting antenna by a distance equal to the sum of the thicknesses of the heat insulation plate, air gap, and the sample to be measured, i.e., d g1 + d a1 + d + d a2 + d g2 ;

[0055] Step 5: Heat the sample to be measured, record the temperature measurement values of the four thermocouples on the sample frame, and take their average as the test temperature; after reaching the required test temperature, keep it at a constant temperature for at least 10 min, and measure the temperature of the heat insulation plate t ; Record the scattering parameters S 11T , S 21T , S 12T and S 22T measured by the vector network analyzer;

[0056] Step 6: Calculate the relative complex permittivity of the sample to be measured at the required test temperature according to the inversion formula , specifically:

[0057]

[0058] where:

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] The plus or minus sign in the Γ expression is determined by the condition |Γ| < 1. λ 0 is the free space wavelength corresponding to the test frequency, Z 0 = 120π is the free space wave impedance, is the transmission matrix of the sample to be measured, which is calculated by the following formula:

[0067]

[0068] Among them 、 、 、 are the transfer matrices of the left air gap, the left heat-insulating flat plate, the right heat-insulating flat plate, and the right air gap respectively, and the expressions are as follows:

[0069]

[0070]

[0071]

[0072]

[0073] is the transfer matrix of the overall 5-layer material composed of the heat-insulating flat plate, the air gap, and the sample to be measured, and the expressions of each item are:

[0074]

[0075]

[0076]

[0077]

[0078] As described above, it is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in all the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A high-temperature test device for the complex permittivity in free space, comprising: Dielectric lenses (1) and (2), transmitting antenna (3), receiving antenna (4), sample holder (5), high-temperature furnace (6) and vector network analyzer (7); characterized in that the vector network analyzer (7) is connected to the transmitting antenna (3) and the receiving antenna (4) through a microwave cable, the phase centers of the transmitting antenna (3) and the receiving antenna (4) are located at one focus of the dielectric lens, and the center of the sample frame of the sample holder (5) is located at the other focus of the dielectric lenses (1) and (2); the two sides of the high-temperature furnace (6) facing the dielectric lenses (1) and (2) are heat-insulating flat plates (8) and (9), and heating resistance wires (10) are arranged on the other four sides.

2. The high-temperature test device for complex permittivity in free space according to claim 1, wherein: The transmitting antenna (3) and the receiving antenna (4) are the same, and are double-ridge pyramidal horn antennas or double-ridge conical horn antennas.

3. The high-temperature test device for complex permittivity in free space according to claim 1, wherein: The sample holder (5) includes a sample frame (11) and a base (12), which are processed from high-temperature-resistant metal materials and are sprayed with a high-temperature oxidation-resistant coating on their surfaces; a thermocouple is installed at the center of each of the four sides of the sample frame (11), and a water-cooling groove is opened at a position on the base far from the sample frame for water cooling.

4. A free-space complex permittivity high-temperature testing device according to claim 1, characterized in that: The heat-insulating flat plates can be quickly disassembled and assembled, and the thicknesses da1 and da2 of the air gaps between the heat-insulating flat plates and the sample to be measured (13) do not exceed 10 mm; the heating resistance wires are arranged at equal intervals along the sample frame.

5. A free-space complex permittivity high-temperature test device according to claim 1, characterized in that: The heat-insulating flat plates are made of heat-transmitting wave materials with low dielectric constant and low loss tangent, and their relative complex dielectric constants εrg(t) at different temperatures are known; the transverse length and width of the heat-insulating flat plates are not less than 1.25 times the transverse length and width of the sample to be measured, and their thicknesses dg1 and dg2 do not exceed 10 mm.

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