A biaxial anisotropic material dielectric constant temperature variation test system and test method

Abstract

The application aims to provide a biaxial anisotropic material dielectric constant temperature variation test system and method, and belongs to the technical field of microwave and millimeter wave test. The system innovatively designs a free space terminal short circuit test system, realizes the acquisition of S21 parameters of microwave materials under high temperature through symmetrically arranging two antennas, and inversely obtains electromagnetic parameters based on the S21 parameters. Meanwhile, the test system can rotate the sample and rotate the antenna by 90 degrees, so as to realize the extraction of electromagnetic parameters of isotropic materials and biaxial anisotropic materials under high temperature in a wide frequency band, and has the advantages of large test range, simple detection mode, high measurement precision and the like.

Description

Technical Field

[0001] This invention belongs to the field of microwave and millimeter-wave testing technology, specifically relating to a temperature-dependent testing system and method for the dielectric constant of biaxial anisotropic materials. Background Technology

[0002] With the rapid development of science and technology, microwave materials have a wide range of applications, including aerospace, military equipment, medical devices, satellite communications, radar, and infrared remote sensing. In variable-temperature environments, accurately measuring the electromagnetic parameters of materials and evaluating their electromagnetic properties is particularly important. For example, high-speed aerospace equipment such as aircraft, missiles, and rockets widely use various anisotropic and isotropic electromagnetic materials. Friction between the air and the equipment causes a rapid rise in material temperature. Since the dielectric parameters of microwave materials change non-linearly at high temperatures, failure to evaluate their dielectric properties under high-temperature conditions will severely affect signal transmission and reception, and may even cause equipment malfunction. Furthermore, biaxial anisotropic materials can achieve different dielectric constants and permeabilities through different micro-unit structure designs, thereby enabling the manufacture of devices such as microwave absorbers, subwavelength resonators, and stealth materials. Therefore, the dielectric constant testing of biaxial anisotropic materials has significant practical implications.

[0003] To address the need for extracting electromagnetic parameters of microwave materials under varying temperatures, Li Jianqiao, in his paper "Research on Varying Temperature Testing Technology of Dielectric Properties of Materials Using Free-Space Termination Short-Circuit Method," achieved the measurement of electromagnetic parameters of microwave materials under temperature fields by measuring the S11 parameter using a metal ellipsoidal reflector, a feed antenna, and a metal reflector. This testing method offers advantages such as convenient installation, calibration, and testing; easy temperature control; and the ability to handle larger test samples, facilitating sample processing. However, compared to the S21 parameter, the S11 parameter of the vector network analyzer has lower measurement sensitivity and a smaller dynamic range. This means that the traditional free-space termination short-circuit method cannot measure electromagnetic materials with high dielectric constants and high losses, resulting in low measurement accuracy and limited measurement range. Furthermore, it presents difficulties in testing anisotropic materials.

[0004] Therefore, designing a testing system to measure the S21 parameter of biaxial anisotropic materials under varying temperatures and to obtain the dielectric constant based on the S21 parameter is of great practical significance. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a temperature-varying dielectric constant testing system and method for biaxial anisotropic materials. This system innovatively designs a free-space terminal short-circuit testing system. By symmetrically setting two antennas, it acquires the S21 parameters of microwave materials under varying temperatures and obtains electromagnetic parameters based on the S21 parameters. Simultaneously, this testing system can extract electromagnetic parameters of biaxial anisotropic materials over a wide bandwidth and under varying temperatures by rotating the sample and the antennas. It has advantages such as a large testing range, simple detection method, and high measurement accuracy.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A temperature-dependent dielectric constant testing system and method for biaxial anisotropic materials includes: a vector network analyzer 1, a transmitting antenna 2, a receiving antenna 3, a transmitting-end wave-to-single-channel converter 4, a receiving-end wave-to-single-channel converter 5, a transmitting-end plano-convex lens 6, a receiving-end plano-convex lens 7, an antenna mounting bracket 8, a metal short-circuit board 9, a heater 10, a temperature sensor 11, and a temperature controller 13.

[0008] The antenna mounting bracket 8 is a horizontally placed fan-shaped structure with a connecting section from its center to the center point of the arc. A metal short-circuit plate 9 is vertically fixed at the center of the arc of the antenna mounting bracket. A heater 10 is fixed on the rear surface of the metal short-circuit plate 9 and connected to a temperature controller 13. The temperature controller 13 is connected to the heater 10 via a cable for heating the material under test. The material under test 12 is positioned at the center of the front surface of the metal short-circuit plate 9. A transmitting antenna 2 and a receiving antenna 3 are mounted on the two arms of the antenna mounting bracket 8, with their illumination center lines pointing towards the center of the metal short-circuit plate 9. The transmitting antenna 2 is connected to the first port of the vector network analyzer 1 via a transmitting-end wave-to-wave converter 4, and the receiving antenna 2 is connected to the second port of the vector network analyzer 1 via a receiving-end wave-to-wave converter 4. A transmitting-end plano-convex lens is located between the transmitting antenna 2 and the material under test 12, and a receiving-end plano-convex lens is located between the receiving antenna 3 and the material under test 12, with the center points of the two plano-convex lenses located on the illumination center line of the antenna. A temperature sensor 11 is mounted on the connecting section and can move back and forth along the connecting section.

[0009] Furthermore, the polarization directions of the transmitting antenna 2 and the receiving antenna 3 are the same, meaning that the transmitting antenna 2 and the receiving antenna 3 are either vertically polarized or parallelly polarized relative to the reflection of the metal short-circuit plate.

[0010] Furthermore, both the transmitting antenna and the receiving antenna are double-ridged horn antennas.

[0011] Furthermore, the arc of the antenna mounting bracket 8 is 90°; the angle between the illumination center lines of the transmitting end double-ridged horn antenna 2 and the receiving end double-ridged horn antenna 3 is preferably 90°; the transmitting end double-ridged horn antenna 2 and the receiving end double-ridged horn antenna 3 are symmetrically distributed with the line connecting the center of the metal short-circuit board and the temperature sensor 11 as the axis of symmetry.

[0012] Furthermore, the metal short-circuit board 9 is made of high-temperature metal, which ensures that it will not undergo significant oxidation when heated to above 1000°C.

[0013] Furthermore, the heater 10 is formed by wrapping an induction coil around a metal rod and is used to heat the sample 12 to be tested.

[0014] Furthermore, the temperature sensor 11 is an infrared temperature sensor.

[0015] This invention also provides a method for testing the dielectric properties of high-temperature biaxial anisotropic materials based on the above-mentioned testing system, comprising the following steps:

[0016] Step 1. Calibrate the test system, including port calibration and response calibration at room temperature;

[0017] Step 2. Place a rectangular sample to be tested, heat the sample, and hold it at the test temperature for a period of time before testing to obtain the S21 parameter in the direction parallel to the short side of the sample.

[0018] Step 3. Keep the test temperature constant, rotate the sample to be tested 90° clockwise, and then perform the test to obtain the S21 parameter in the direction parallel to the long side of the material to be tested;

[0019] Step 4. Keep the test temperature constant, rotate the antenna 90° clockwise around the illumination center line, and then perform the test to obtain the S21 parameter in the thickness direction of the material under test;

[0020] Step 5. Obtain the biaxial anisotropic dielectric parameters of the material under test at high temperature based on the S21 parameter inversion. The specific calculation method is as follows:

[0021] First, the relationship between the S21 parameter and the reflectivity Γ is:

[0022] S 21 =10lg(Γ) (1)

[0023] The dielectric constants for the short-side parallel direction and the long-side parallel direction are calculated using the relationship between the reflection coefficient of the vertically polarized antenna and the incident angle of the electromagnetic wave:

[0024]

[0025] Wherein, the subscript S indicates the direction of parallelism between the short side and the long side, and ΓS To measure the reflectivity when the dielectric constant is parallel to the short side or parallel to the long side, θ is the incident angle of the electromagnetic wave, and ε is... S The relative permittivity is the direction in which the short side is parallel or the long side is parallel.

[0026] After obtaining the relative permittivity in the direction parallel to the short side and the direction parallel to the long side, it is easy to obtain the average permittivity ε in the direction parallel to the short side and the direction parallel to the long side. A Therefore, by solving equations (3) and (4) simultaneously, the relative permittivity ε in the thickness direction can be obtained. z :

[0027]

[0028]

[0029] Where p=k0ε A cosθ+k z ;q=k0ε A cosθ-k z d is the thickness of the sample to be tested, and k0 is the free space wavenumber; thus, the dielectric constants of the biaxial anisotropic material in three directions are obtained.

[0030] Furthermore, the response calibration includes horizontal polarization direction calibration and vertical polarization direction calibration.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] This invention innovatively designs a testing device for the free-space terminal short-circuit method, overcoming the shortcomings of existing free-space short-circuit methods that conventionally use a single antenna for testing, which can only obtain S11 parameters and thus has low testing accuracy. This invention uses dual antennas for testing, obtaining S21 parameters. Simultaneously, the device can measure the electromagnetic parameters of anisotropic materials in three directions by rotating the sample and changing the antenna polarization direction, and an inversion algorithm is designed to extract the dielectric constant of biaxial anisotropic materials. Furthermore, this invention uses infrared thermometry perpendicular to the temperature measurement area, making temperature measurement more accurate and thus more accurately reflecting the corresponding electromagnetic parameters of microwave materials under high-temperature environments. The testing device of this invention features improved measurement sensitivity and the ability to measure microwave materials with high dielectric constants and high losses. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the high-temperature dielectric performance testing system of the present invention;

[0034] In the figure, 1 is a vector network analyzer, 2 is a transmitting linearly polarized antenna, 3 is a receiving linearly polarized antenna, 4 is a transmitting waveform converter, 5 is a receiving waveform converter, 6 is a transmitting plano-convex lens, 7 is a receiving plano-convex lens, 8 is an antenna mount, 9 is a metal shorting board, 10 is a heater, 11 is an infrared temperature sensor, 12 is the sample to be tested, and 13 is a temperature controller. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0036] A temperature-dependent dielectric constant testing system and method for biaxial anisotropic materials, the schematic diagram of which is shown below. Figure 1 As shown, it includes a vector network analyzer 1, a transmitting antenna 2, a receiving antenna 3, a transmitting-end wave-to-same converter 4, a receiving-end wave-to-same converter 5, a transmitting-end plano-convex lens 6, a receiving-end plano-convex lens 7, an antenna mounting bracket 8, a metal short-circuit board 9, a heater 10, a temperature sensor 11, and a temperature controller 13.

[0037] The antenna mounting bracket 8 is a horizontally placed fan-shaped structure with a central angle of 90°, and a connecting section is provided from the center of the circle to the center point of the arc. The metal short-circuit plate 9 is vertically fixed at the center of the arc of the antenna mounting bracket. The metal short-circuit plate 9 is made of high-temperature metal and can ensure that it will not oxidize significantly when heated to above 1000°C. The heater 10 is fixed on the rear surface of the metal short-circuit plate 9 and connected to the temperature controller 13. The heater 10 is obtained by wrapping an induction coil around a metal rod and is used to heat the material to be tested.

[0038] The material under test 12 is positioned at the center of the front surface of the metal short-circuit plate 9; the transmitting antenna 2 and the receiving antenna 3 are mounted on the two arms of the antenna mounting bracket 8, with the illumination center lines of the transmitting antenna 2 and the receiving antenna 3 pointing towards the center of the metal short-circuit plate 9, and the polarization directions of the transmitting antenna 2 and the receiving antenna 3 are the same, either vertically polarized or parallelly polarized; the transmitting antenna 2 is connected to the first port of the vector network analyzer 1 through the transmitting-end wave-to-wave converter 4, and the receiving antenna 2 is connected to the second port of the vector network analyzer 1 through the receiving-end wave-to-wave converter 4; the transmitting-end plano-convex lens is located between the transmitting antenna 2 and the material under test 12, and the receiving-end plano-convex lens is located between the receiving antenna 3 and the material under test 12, with the center points of the two plano-convex lenses located on the illumination center line of the antenna, so that the electromagnetic waves emitted by the transmitting antenna or the battery waves received by the receiving antenna are approximately plane waves; the temperature sensor 11 is mounted on the connecting section and can move back and forth along the connecting section, used to measure the surface temperature of the material under test in real time during temperature changes.

[0039] Example 1

[0040] This invention also provides a method for testing the dielectric properties of high-temperature biaxial anisotropic materials based on the above-mentioned testing system, comprising the following steps:

[0041] Step 1. Calibrate the test system, including port calibration and response calibration at room temperature;

[0042] Step 2. Place a rectangular sample to be tested, heat the sample, and hold it at the test temperature for a period of time before testing to obtain the S21 parameter in the direction parallel to the short side of the sample.

[0043] Step 3. Keep the test temperature constant, rotate the sample to be tested 90° clockwise, and then perform the test to obtain the S21 parameter in the direction parallel to the long side of the material to be tested;

[0044] Step 4. Keep the test temperature constant, rotate the antenna 90° clockwise around the illumination center line, and then perform the test to obtain the S21 parameter in the thickness direction of the material under test;

[0045] Step 5. Obtain the biaxial anisotropic dielectric parameters of the material under test at high temperature based on the S21 parameter inversion. The specific calculation method is as follows:

[0046] First, the relationship between the S21 parameter and the reflectivity Γ is:

[0047] S 21 =10lg(Γ) (1)

[0048] The dielectric constants for the short-side parallel direction and the long-side parallel direction are calculated using the relationship between the reflection coefficient of the vertically polarized antenna and the incident angle of the electromagnetic wave:

[0049]

[0050] Where the subscript S represents the x-direction or y-direction, Γ S To measure the reflectivity when the dielectric constant is in the x or y direction, θ is the incident angle of the electromagnetic wave, and ε is the reflectivity. S The relative permittivity is the direction in which the short side is parallel or the long side is parallel.

[0051] After obtaining the relative permittivity in the direction parallel to the short side and the direction parallel to the long side, it is easy to obtain the average permittivity ε in the direction parallel to the short side and the direction parallel to the long side. A Therefore, by solving equations (3) and (4) simultaneously, the relative permittivity ε in the thickness direction can be obtained. z :

[0052]

[0053]

[0054] Where p=k0εA cosθ+k z ;q=k0ε A cosθ-k z d is the thickness of the sample to be tested, and k0 is the free space wavenumber; thus, the dielectric constants of the biaxial anisotropic material in three directions are obtained.

[0055] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A temperature-dependent testing system for the dielectric constant of biaxial anisotropic materials, characterized in that, Includes a vector network analyzer, transmitting antenna, receiving antenna, transmitting-end waveform converter, receiving-end waveform converter, transmitting-end plano-convex lens, receiving-end plano-convex lens, antenna mount, metal shorting board, heater, temperature sensor, and temperature controller; The antenna mounting bracket is horizontally placed in a fan shape, with a connecting section from the center of the circle to the center point of the arc. A metal short-circuit plate is vertically fixed at the center of the arc of the antenna mounting bracket. A heater is fixed on the rear surface of the metal short-circuit plate and connected to a temperature controller. The temperature controller is connected to the heater via a cable for heating the material under test. The material under test is positioned at the center of the front surface of the metal short-circuit plate. The transmitting and receiving antennas are mounted on the two arms of the antenna mounting bracket, with their illumination center lines pointing towards the center of the metal short-circuit plate. The transmitting and receiving antennas have the same polarization direction and are both double-ridged horn antennas. The arc of the antenna mounting bracket is 90°. The transmitting and receiving double-ridged horn antennas are symmetrically distributed with the line connecting the metal short-circuit board and the center of the temperature sensor as the axis of symmetry. The angle between the illumination center lines of the transmitting and receiving double-ridged horn antennas is 90°. The transmitting antenna is connected to the first port of the vector network analyzer through the transmitting-end wave-to-same converter, and the receiving antenna is connected to the second port of the vector network analyzer through the receiving-end wave-to-same converter. The transmitting-end plano-convex lens is located between the transmitting antenna and the material under test, and the receiving-end plano-convex lens is located between the receiving antenna and the material under test, with the center points of the two plano-convex lenses located on the illumination center line of the antennas. The temperature sensor is mounted on the connecting section and can move back and forth along the connecting section.

2. The temperature-dependent dielectric constant testing system for biaxial anisotropic materials as described in claim 1, characterized in that, The metal short-circuit board is made of high-temperature metal, which ensures that it will not oxidize significantly when heated to above 1000°C.

3. The temperature-varying dielectric constant testing system for biaxial anisotropic materials as described in claim 1, characterized in that, The heater is formed by wrapping an induction coil around a metal rod and is used to heat the sample to be tested.

4. The temperature-dependent dielectric constant testing system for biaxial anisotropic materials as described in claim 1, characterized in that, The temperature sensor is an infrared temperature sensor.

5. A test method based on the temperature-varying dielectric constant testing system for biaxial anisotropic materials as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1. Calibrate the test system, including port calibration and response calibration at room temperature. Response calibration includes horizontal polarization direction calibration and vertical polarization direction calibration. Step 2. Place a rectangular sample to be tested, heat the sample, and hold it at the test temperature for a period of time before testing to obtain the S21 parameter which is parallel to the short side of the material to be tested. Step 3. Keep the test temperature constant, rotate the sample to be tested 90° clockwise, and then perform the test to obtain the S21 parameter that is parallel to the long side of the material to be tested; Step 4. Keep the test temperature constant, rotate the antenna 90° clockwise around the illumination center line, and then perform the test to obtain the S21 parameter in the thickness direction of the material under test; Step 5. Obtain the biaxial anisotropic dielectric parameters of the material under test at high temperature based on the S21 parameter inversion. The specific calculation method is as follows: S21 parameters and reflectivity The relationship is: (1) The dielectric constants for the short-side parallel direction and the long-side parallel direction are calculated using the relationship between the reflection coefficient of the vertically polarized antenna and the incident angle of the electromagnetic wave: (2) Wherein, the subscript S indicates the direction of parallelism between the short side and the long side. To measure the reflectivity when the dielectric constant is parallel to the short side or parallel to the long side, θ is the incident angle of the electromagnetic wave. The relative permittivity is the direction in which the short side is parallel or the long side is parallel. The average of the relative permittivity in the short-side parallel direction and the long-side parallel direction is used as the average permittivity. ; By solving equations (3) and (4) simultaneously, the relative permittivity in the thickness direction can be obtained. : (3) (4) in, ; d is the thickness of the sample to be tested. The free space wavenumber is given; thus, the dielectric constants of the biaxial anisotropic material in three directions are obtained.

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