Method for researching influence of ablation on wave-transparent performance of antenna housing material

Abstract

The invention relates to a method for researching the influence of ablation on the wave-transparent performance of a radome material, which is used for researching the ablation wave-transparent performance of a radar radome material, and is used for designing a testing device at the downstream of an electric arc heater by taking electric arc heater ground testing equipment as a support and combining with special requirements of an antenna window ablation test, so that two test pieces are simultaneously ablated, and the wave-transparent performance of the radome material is improved. A microwave testing system is used for measuring microwave transmission performance change conditions before, during and after ablation of an antenna window material, rotating target X-ray diffraction analysis, atomic energy spectrum analysis and electrical performance measurement are carried out on a test piece before and after a test, and subsequently, reasons of wave transmission performance change of the material after ablation can be analyzed from a microscopic perspective; and support is provided for a material development department.

Description

Technical Field

[0001] The present invention belongs to the research field of wave - transmitting materials for aircraft antenna windows. Background Art

[0002] To improve the hitting accuracy and enhance the electronic counter - measure ability, advanced tactical aircraft will adopt various new terminal - guidance radar systems, such as millimeter - wave radar, frequency - agile radar, frequency - variable radar, etc. At the same time, dual - mode or multi - mode composite guidance is also adopted, such as passive radar / active radar, passive radar / infrared imaging, passive radar / TV imaging, etc., and image - matching technology is applied to achieve map / terrain - matching guidance. The radar seeker is located at the head of the aircraft. In order to protect the seeker antenna to work normally during flight, a radome that meets the usage requirements must be adopted. The radome is an important structural component of the seeker. It not only needs to ensure the necessary aerodynamic shape, withstand aerodynamic heating and various loads during flight, reduce the influence of the flight environment on the electronic equipment inside the radome, but also is the channel for transmitting and receiving electromagnetic waves. Therefore, it is required not only to have excellent environmental resistance and mechanical properties, but also to have excellent electromagnetic transmission characteristics and excellent high - temperature resistance. Thus, multifunctional structure - heat - resistant - wave - transmitting composite materials must be used. Over the years, scientific and technological workers at home and abroad have conducted relatively in - depth research on the selection and performance of radome materials, aiming to seek radome materials with excellent wave - transmitting performance, mechanical properties and moisture - heat resistance to meet the actual usage requirements. Since the radome technology is directly related to the working frequency and performance of the terminal - guidance radar, and the technical difficulty is high, the materials, processes, structures and performances of military aircraft and aircraft radomes have become very sensitive issues. At present, there are few detailed reports abroad, and even the information obtained occasionally is very discrete. The research results of wave - transmitting materials for radomes in China are occasionally published in magazines and periodicals. Generally, it is known through performance tests that they have good electromagnetic transmission performance. However, under the conditions of high - speed flight and re - entry aerodynamic heating, how the wave - transmitting performance of radome materials changes and why such changes occur have not been systematically and thoroughly studied in the currently published literature, and this is exactly what the material research department and the model development unit hope to understand. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a research method for the influence of ablation on the wave - transmitting performance of radome materials, conduct microscopic analysis on the samples before and after ablation, and explore the mechanism of the change in wave - transmitting performance.

[0004] The technical solution of the present invention: A research method for the influence of ablation on the wave - transmitting performance of radome materials, including:

[0005] Conduct microwave testing on the wave - transmitting material to obtain the change in wave - transmitting performance before and after ablation; the specific steps are as follows:

[0006] Set up a test device; the test device includes an arc heater, a mixing and stabilizing chamber, a diverging section, and a microwave experimental section; the inlet diameter of the mixing and stabilizing chamber is the same as the outlet diameter of the arc heater, its outlet diameter is the same as the inlet diameter of the diverging section, the diverging section is a circular-to-square structure for connection, and the microwave experimental section is a mounting and bearing component for the wave-transparent material. A pair of wave-transparent materials are symmetrically installed on the two side walls of the microwave experimental section to form a rectangular flow passage sealed on all sides, and the flow area of the rectangular flow passage is the same as the outlet of the diverging section;

[0007] On both sides of the wave-transparent material, through a microwave test system, the curve of the change in wave-transmission performance during the ablation process of the wave-transparent material is collected in real time to obtain the change in wave-transmission performance before and after ablation;

[0008] Obtain the powdery samples before and after ablation from the wave-transparent material after the test. Conduct rotating anode X-ray diffraction analysis on the samples respectively to obtain the diffraction peak distribution and obtain the change in the statistical atomic spacing; conduct energy spectrum analysis of atoms to obtain the material composition and the percentage content of various atoms; measure the dielectric constant ε and loss tangent tanδ by the waveguide short-circuit method for dielectric performance testing.

[0009] Preferably, the arc heater adopts a long-segment arc heater.

[0010] Preferably, the inlet diameter of the mixing and stabilizing chamber is the same as the outlet diameter of the arc heater, and then it expands to an equal-diameter section with a semi-cone angle of 70° - 80°. The diameter of the equal-diameter section is 80% - 90% of the effective side length of the wave-transparent material, and the aspect ratio of the inner cavity of the equal-diameter section ≥ 2.

[0011] Preferably, the diverging section (3) is a circular-to-square structure for connection, that is, it contracts from a circle to a rectangle, and the two half-cone angles of contraction are 70° - 75° and 20° - 30° respectively, and the inlet diameter is the same as that of the mixing and stabilizing chamber.

[0012] Preferably, the mixing and stabilizing chamber, the diverging section, and the microwave experimental section are all inner and outer sleeve sandwich water-cooled structures. The material of the inner sleeve is all copper, and the material of the outer sleeve is carbon steel.

[0013] Preferably, during the test, high-pressure water of 3 - 4 MPa is passed through each section for cooling, and the high-pressure water adopts a water flow direction of entering from the bottom and exiting from the top to improve the cooling effect.

[0014] Preferably, the material of the wave-transparent material is selected from non-metallic inorganic ceramics or composite ceramics, resin-based fiber composite materials.

[0015] Preferably, the thickness of the wave-transparent material test piece before the test is calculated and determined according to the following formula based on the measured dielectric constant of the test piece:

[0016]

[0017] Where: λ—the free wavelength of the radar;

[0018] ε—the dielectric constant of the material;

[0019] N—a positive integer, taking 3 - 5.

[0020] The beneficial effects of the present invention: The present invention closely combines the research and development requirements of radar radome materials, relies on the arc heating ground test equipment, develops a special test device for the ablation test of wave - transmitting materials, measures the change of the wave - transmitting performance of the material during the test, and then analyzes the composition of the material before and after ablation. Through the research results of the present invention, the mechanism of the influence of ablation on the wave - transmitting performance of the material can be explored from a microscopic perspective, which has positive reference significance for the model department to develop wave - transmitting materials for radar radomes. Brief Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the test device for the ablation test of wave - transmitting materials. Detailed Embodiments

[0022] During the re - entry flight of the aircraft, due to aerodynamic heating, the windward surface of the seeker radome will undergo high - temperature ablation, and the antenna starts to work after the radome ablation. Therefore, the ablation condition will affect the wave - transmitting performance of the radome. This method uses an arc heater to conduct the ablation test of radome materials, and uses multiple testing means to analyze the reasons for the change of the wave - transmitting performance of the radome material after ablation from the aspects of microscopic composition and structural changes, and draws a relatively systematic conclusion.

[0023] The present invention consists of a test device and testing and analysis means. The testing and analysis means include a microwave test system, rotating - target X - ray diffraction analysis, energy - dispersive X - ray spectroscopy analysis, dielectric property waveguide short - circuit method testing, etc.

[0024] The present invention uses the arc heater test device to simulate the aerodynamic heating environment of the radome, conducts the ablation test on the wave - transmitting material, samples the test pieces before and after the test, conducts rotating - target X - ray diffraction analysis, energy - dispersive X - ray spectroscopy analysis, dielectric property waveguide short - circuit method testing, etc. Subsequently, based on the above - mentioned test results, the microscopic mechanism of the change of the wave - transmitting performance of the material after ablation is given.

[0025] Embodiment

[0026] The following gives a specific and preferred example of the research method of the present invention. The method steps are as follows:

[0027] Build a test device, which consists of an arc heater 1, a mixing and stabilizing chamber 2, a diffuser section 3, a microwave test section 4, a wave-transparent material 5, etc. The arc heater 1 should be able to provide a high enthalpy value to achieve the aerodynamic heating conditions for the ablation of the wave-transparent material. The inlet diameter of the mixing and stabilizing chamber 2 is the same as the outlet diameter of the arc heater 1, and then it expands to the outlet diameter of Φ80mm with a semi-cone angle of 75°. The inner cavity aspect ratio of the large-diameter section is ≥2, and the larger the aspect ratio, the more beneficial it is to the stability and uniform mixing of the airflow. The diffuser section 3 is a circular-to-square structure for transition, with the inlet diameter the same as that of the mixing and stabilizing chamber, and the outlet section is a rectangle of 90mm×14mm. The microwave test section 4 is a mounting and bearing component for the wave-transparent material. The size of the wave-transparent material 5 is 95mmm×90mm, and one pair is used for each test. They are symmetrically installed on the two side walls of the microwave test section 4 as two side walls. 95mmm is in the height direction, and 2.5mm is provided at the top and bottom for clamping. After installation, a rectangular flow-through channel sealed on all sides is formed, and the flow-through area is the same as the outlet of the diffuser section 3, which is 90mm×14mm. The mixing and stabilizing chamber 2, the diffuser section 3, and the microwave test section 4 are all inner and outer sleeve sandwich water-cooled structures. The inner sleeve is made of good thermal conductivity copper, and the outer sleeve is made of high-quality carbon steel. During the test, high-pressure water of 3MPa is passed through each section for cooling, and the high-pressure water adopts the water flow direction of entering from the bottom and exiting from the top to improve the cooling effect. The wave-transparent material 5 is made of non-metallic inorganic ceramics or composite ceramics, resin-based fiber composite materials, etc. Its performance is relatively stable at high temperatures, has good dielectric properties, can obtain relatively ideal wave-transparent performance and small insertion loss;

[0028] The thickness of the test piece of the wave-transparent material 5 before the test is calculated and determined according to the measured dielectric constant of the test piece by the following formula:

[0029]

[0030] In the formula: λ—the free wavelength of the radar; ε—the dielectric constant of the material; N—a positive integer, taking 3.

[0031] The arc heater 1 is an external device, and a long-segment arc heater that can provide a high enthalpy is selected. The mixing and stabilizing chamber 2 plays the role of adjusting the enthalpy value of the airflow and stabilizing the airflow. The diffuser section 3 completes the conversion from circular to square in terms of shape. The microwave test section 4 is a component for carrying the wave-transparent material for ablation. During the test, the arc heater 1 heats the air to form a high-temperature and high-speed airflow. After passing through the mixing and stabilizing chamber 2 to adjust the enthalpy and stabilize the pressure, it passes through the diffuser section 3 for rectification, and finally flows through the microwave test section 4 to ablate the wave-transparent material 5 bilaterally. The transmitting and receiving antennas of the microwave test system are placed on both sides of the wave-transparent material respectively to dynamically measure the change of the wave-transmission rate during the test in real time.

[0032] Take several grams of powdered samples from the front and back surfaces (ablated surface and non-ablated surface) of the test piece, scan the wavelength or angle on a rotating anode X-ray diffractometer, and the "statistical atomic spacing" can be obtained through the distribution law of diffraction peaks. Its physical principle is Bragg's law 2dsinθ = nλ, which is the result of the periodicity of the crystal lattice.

[0033] Perform an atomic energy spectrum experiment using an atomic energy spectrum analyzer to analyze the composition of the powdered samples before and after material ablation. Its physical principle is the photoelectric effect. Since different atomic nuclei have different abilities to bind electrons, the work function of electrons is also different, so the maximum initial kinetic energy is also different, and its motion trajectory in an external magnetic field is also different, thus realizing the separation of photoelectrons. After a series of processes such as counting, graphing, and calculating the photoelectrons, relevant information such as the composition of the material and the percentage content of various atoms can be obtained.

[0034] The dielectric constant ε and the loss tangent tanδ are the two most commonly used and important parameters to describe the electrical properties of materials. Whether the wave transmission performance of the material becomes better or worse after ablation is directly related to the changes in these two parameters. The waveguide short-circuit method is used to measure the test specimens before and after ablation: when a material sample of a specific size is placed at the end of the waveguide, it will cause a change in the position of the standing wave in the waveguide. By measuring the displacement of the standing wave node with a probe and substituting it into the relevant calculation formula, the corresponding ε and tanδ values of the material can be obtained.

[0035] The purpose of the research method of the present invention is to obtain the results corresponding to the above test means. Subsequently, all measurement results can be comprehensively analyzed to specifically analyze the reasons for the change in the wave transmission performance of the antenna window material before and after ablation from a microscopic level. The analysis results can be used for the research and development or improvement of new and old wave transmission functional materials. For example, in one embodiment, an 8s ablation test was carried out on a 2.5D quartz braid + 20% silicone resin reinforced material. After the test, the wave transmission attenuation increased suddenly from 19.5 dB before the test to 34.1 dB, and gradually stabilized at 31.8 dB after the test, which was 12.3 dB greater than before ablation, and the wave transmission performance deteriorated significantly. Using the waveguide short-circuit method, the dielectric constant ε of the material before the test was 3.18, and after the test was 3.33; the loss tangent tanδ before the test was 16×10 -3 , and after the test was 16.5×10 -3 , both increased. Calculating from the scanning atomic energy spectrum analysis diagram, the percentage content of each element, Si 2+ (silicone) was all converted to Si 4+(Silicon dioxide), the C-C bond is reduced by 23% and the C-O bond is increased by 106%. SiO2 is a non-polar molecule. This change can make the dielectric constant ε smaller, but the two changes of the relatively reduced content of non-polar C-C bonds and the relatively large increase in the content of polar C-O bonds will both increase the dielectric constant ε. The combined effect of the three finally makes the ε of the material increase from 3.18 to 3.33. From the results of rotating anode X-ray diffraction, the statistical atomic spacing d value of the material increases by 0.053 Å after ablation compared with that before ablation. This is because the surface fiber bundle of the material changes from the oriented state to the non-oriented state after ablation, and the molecular arrangement changes from ordered to disordered, resulting in a relatively loose surface, so the statistical d value increases; macroscopically, the mass of the material does not change after ablation but the thickness increases by 0.3 mm. Both microscopically and macroscopically, it shows that the material becomes loose after ablation, which will directly lead to an increase in structural loss, making the loss tangent tanδ of the material change from 16×10 -3 to 16.5×10 -3 an increase of 0.5×10 -3 . The increase in the dielectric constant ε indicates that the potential energy stored due to polarization of the material increases, and the increase in the loss tangent tanδ indicates that the ability of the material to absorb microwave energy and convert it into its own internal energy increases. It is the increase of both after ablation that causes serious attenuation of the microwave energy passing through it.

[0036] The un-disclosed technology of the present invention belongs to the common general knowledge of those skilled in the art.

Claims

1. A research method for the influence of ablation on the wave transmission performance of radome materials, characterized in that Including: Performing microwave tests on the wave-transparent material to obtain the change in wave-transmission performance before and after ablation; the specific steps are as follows: Constructing a test device; the test device includes an arc heater, a mixing and stabilizing chamber, a divergent section, and a microwave test section; the inlet diameter of the mixing and stabilizing chamber is the same as the outlet diameter of the arc heater, its outlet diameter is the same as the inlet diameter of the divergent section, the divergent section is a circular-to-square structure for transition, and the microwave test section is a mounting and bearing component for the wave-transparent material. A pair of wave-transparent materials are symmetrically installed on the two side walls of the microwave test section to form a rectangular flow channel sealed on all sides, and the flow area of the rectangular flow channel is the same as the outlet of the divergent section; On both sides of the wave-transparent material, through a microwave test system, the change curve of the wave-transmission performance during the ablation process of the wave-transparent material is collected in real time to obtain the change in wave-transmission performance before and after ablation; Obtaining powdery samples before and after ablation from the tested wave-transparent material, respectively performing rotating anode X-ray diffraction analysis on the samples to obtain the diffraction peak distribution, and obtaining the change in the statistical atomic spacing; performing energy spectrum analysis of atoms to obtain the material composition and the percentage content of various atoms; measuring the dielectric constant ε and the loss tangent tanδ by the waveguide short-circuit method for dielectric properties.

2. The research method for the influence of ablation on the wave transmission performance of radome materials according to claim 1, characterized in that: The arc heater used is a long-segment arc heater.

3. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 1, characterized in that: The inlet diameter of the mixing and stabilizing chamber is the same as the outlet diameter of the arc heater, and then it expands to a straight section with a semi-cone angle of 70° - 80°, and the diameter of the straight section is 80% - 90% of the effective side length of the wave-transparent material, and the aspect ratio of the inner cavity of the straight section ≥ 2.

4. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 1, characterized in that: The divergent section (3) is a circular-to-square structure for transition, that is, it contracts from a circle to a rectangle, and the two semi-cone angles of contraction are 70° - 75° and 20° - 30° respectively, and the inlet diameter is the same as that of the mixing and stabilizing chamber.

5. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 1, characterized in that: The mixing and stabilizing chamber, the divergent section, and the microwave test section are all water-cooled structures with inner and outer jacket layers. The material of the inner jacket is all copper, and the material of the outer jacket is carbon steel.

6. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 5, characterized in that: During the test, high-pressure water of 3 - 4 MPa is passed through each section for cooling, and the high-pressure water adopts a water flow direction of entering from the bottom and exiting from the top to improve the cooling effect.

7. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 1, characterized in that: The material of the wave-transparent material is selected from non-metallic inorganic ceramics or composite ceramics, resin-based fiber composites.

8. A research method for the influence of ablation on the wave transmission performance of radome materials according to claim 7, characterized in that The thickness of the wave-transparent material specimen before the test is calculated and determined according to the following formula based on the measured dielectric constant of the specimen: Where: λ—the free wavelength of the radar; ε—the dielectric constant of the material; N—a positive integer, taking 3 - 5.

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