Miniaturized wave-absorbing coating radar reflectivity in-situ detection probe

Abstract

The invention provides a miniaturized in-situ detection probe for radar reflectivity of a wave-absorbing coating, and belongs to the technical field of wave-absorbing performance testing of coating materials. The probe is based on a coaxial transmission line structure, a traditional uniform-section coaxial line is optimized into a gradient structure, and a step and ridge structure is introduced, so that the fringe effect introduced when the probe is loaded on the surface of a wave-absorbing coating to be detected is effectively reduced, that is, a microwave near field at the end face of the probe is corrected into a free space plane wave field distribution form through a physical structure; therefore, the test result of the vertical reflectivity of the coating can be compared with the reflectivity of the coating under the vertical incidence of free space waves. For a 2-18GHz test frequency band, the diameter of a testable coating area of the test probe can be 20mm to the minimum extent.

Description

Technical Field

[0001] The invention belongs to the technical field of coating material wave absorbing performance testing, and in particular relates to a miniaturized wave absorbing coating radar reflectivity in-situ detection probe. Background Art

[0002] With the rapid development of microwave technology, absorbing coating materials have gained widespread application. Accurate characterization of their absorbing properties is crucial for the in-depth research and widespread application of high-performance absorbing coatings. Radar reflectivity is a key parameter used to measure the absorbing performance of absorbing coatings. It is the reflectivity of electromagnetic waves incident on the coating surface under TEM mode. Currently, the main methods for measuring radar reflectivity are the bow method and the RCS method. Patent Publication No. CN214150491U, "An Ultra-Wideband, Wide-Angle Microwave Reflectivity Automatic Testing System," builds on the bow method by introducing an "X-shaped," retractable, wide-angle, automatically adjustable bracket and employing programmable stepper motors to precisely control system components. This enables stable and reliable testing of microwave reflectivity over a wide range of ultra-wideband frequencies. Patent Publication No. CN105352978A, "A Handheld Absorbing Material Reflectivity Measurement Device," builds on the dual-antenna reflection method by employing Vivaldi antennas as both the transmitting and receiving antennas to simulate a far-field radiation environment in the near field, shifting the test area from the far field to the near field, reducing the test space. In the patent "A system and method for testing the local reflectivity of flat-plate absorbing materials on site" with announcement number CN116429795A, based on the dual-antenna reflection method, a focusing lens antenna is used to greatly improve the antenna beam energy concentration, and a corrugated structure is used to reduce the sidelobe coupling between antennas, thereby achieving high-precision testing of the local reflectivity of the absorbing material.

[0003] Most existing radar reflectivity testing methods use antennas as transceiver sensors, and their electromagnetic wave irradiation area is usually large, which requires large lateral dimensions of the sample to be tested, making it difficult to test small samples. Although coaxial transmission lines can simulate TEM wave incidence to perform radar reflectivity tests on small samples, that is, the coaxial line uses the natural TEM mode inside the coaxial line, which is very similar to the free-space plane wave to complete the test. Therefore, the material to be tested can only be prepared and loaded into the coaxial line. This places high demands on sample preparation and cannot achieve non-destructive in-situ testing of the applied coating. In actual applications, the coating surface of the absorbing coating is complex. In addition to the large area measured outside the equipment, the coating area also includes some small internal areas, making the existing methods difficult to apply to in-situ testing scenarios for the radar reflectivity of coated small areas.

[0004] Therefore, how to design a detection device that can realize in-situ small area detection of the absorbing coating is an urgent problem to be solved. Summary of the Invention

[0005] In response to the problems presented by the prior art, the present invention aims to provide a miniaturized in-situ radar reflectivity detection probe for absorbing coatings. This probe, based on a coaxial transmission line structure, optimizes the traditional uniform-cross-section coaxial line into a tapered structure, incorporating steps and ridges. This effectively reduces the edge effects introduced when the probe is applied to the surface of the absorbing coating to be tested. Specifically, the microwave near-field at the probe's end face is physically corrected to resemble a free-space plane wave field distribution, enabling the probe's vertical reflectivity test results to be comparable to the coating's reflectivity under vertical free-space incidence.

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

[0007] A miniaturized radar reflectivity in-situ detection probe for an absorbing coating includes a coaxial connector, an inner conductor of the probe, and an outer conductor of the probe;

[0008] The coaxial connector is fixedly arranged on the upper surface of the probe outer conductor, the probe inner conductor is arranged inside the probe outer conductor, and the coaxial connector, the probe inner conductor and the probe outer conductor are coaxial;

[0009] The probe inner conductor consists of three sections: an upper section, a middle section, and a lower section connected in sequence. The upper and lower sections are uniform cylinders, and the diameter of the upper section is smaller than that of the lower section. The middle section is a frustum, and the diameter of its upper top surface is the same as that of the upper section, and the diameter of its lower bottom surface is the same as that of the lower section. The upper section of the probe inner conductor is located in the inner conductor hole of the coaxial connector, and the top of the middle section is flush with the upper surface of the probe outer conductor.

[0010] The inner cavity of the probe outer conductor consists of two sections, the upper section's inner cavity radially expanding from top to bottom, and the lower section's inner cavity being a ridged cylindrical cavity. A step is provided at the junction of the upper and lower sections. The inner cavity wall of the lower section is uniformly distributed circumferentially with four identical square ridges protruding from the circumference toward the central axis. The depth of the square ridges should be less than the depth of the step.

[0011] The length of the middle section of the inner conductor of the probe is consistent with the length of the upper section of the inner cavity of the outer conductor of the probe, together forming a gradual coaxial line; the length of the lower section of the inner conductor of the probe is consistent with the length of the lower section of the inner cavity of the outer conductor of the probe, and the bottom surfaces of the lower sections of the two are flush, together forming a coaxial line with equal cross-section.

[0012] Furthermore, a medium is filled between the inner conductor of the probe and the inner wall of the outer conductor of the probe, and the medium is air or a low dielectric constant and low loss material.

[0013] Furthermore, the low dielectric constant and low loss material is preferably polytetrafluoroethylene (PTFE), cross-linked polyethylene (XLPE) or polypropylene (PP).

[0014] Furthermore, the depth of the square ridge is preferably 0.4 to 0.6 times the step depth.

[0015] Furthermore, the diameter of the cylindrical inner wall of the lower section of the inner cavity of the outer conductor of the probe is d, and the radial protrusion depth of the square ridge is t. Then the spacing between the two axially symmetrical square ridges is d-2t, and the spacing between the two square ridges should be greater than the bottom diameter of the upper section of the inner cavity of the outer conductor of the probe.

[0016] Furthermore, the height of the lower cavity of the inner cavity of the outer conductor of the probe is determined according to the test frequency band and the thickness of the absorbing coating to be tested.

[0017] Furthermore, for a test frequency band of 2-18 GHz and a thickness of the absorbing coating to be measured of less than 1.5 mm, the length of the lower cavity of the inner cavity of the outer conductor of the probe is between 2-4 mm.

[0018] Furthermore, the design of the length and diameter of the middle section of the conductor inside the probe and the diameter of the cavity above the middle section of the conductor inside the probe makes the characteristic impedance gradually change, so that the characteristic impedance of the probe end is closer to the wave impedance of the absorbing coating to be measured, which can effectively improve the dynamic range of the probe reflection measurement.

[0019] The mechanism of the present invention is:

[0020] The present invention sets an in-situ detection probe with a specific structure, so that after the microwave near-field generated at the probe end face interacts with the material to be tested and the metal substrate, the electromagnetic field distribution form is similar to that of a plane wave. As a result, the reflectivity generated is also similar to the reflectivity of the plane wave after perpendicular incidence on the material to be tested. Therefore, the test efficiency of the coaxial connector can be compared with the test efficiency of the free space method. That is, during the test process, the radiation near-field (TM mode) plus the edge effect is equivalent to the TEM mode, thereby realizing the test.

[0021] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0022] The proposed detection probe utilizes a coaxial structure, featuring a stepped and square base at the contact point between the probe and the absorbing coating to be tested. This gives the probe the broadband and compact design of a coaxial transmission line, making it suitable for in-situ radar reflectivity testing of small areas of absorbing coatings applied to metal surfaces in confined spaces. For the 2-18 GHz test frequency range, the diameter of the measurable coating area can be as small as 20 mm, and the vertical reflectivity test results are comparable to the coating's reflectivity under normal free-space incidence. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the three-dimensional structure of the in-situ detection probe of the present invention.

[0024] Figure 2 It is a longitudinal cross-sectional view of the in-situ detection probe of the present invention.

[0025] Figure 3 It is a transverse cross-sectional view of the opening end of the in-situ detection probe of the present invention.

[0026] Figure 4 Schematic diagram of the field distribution of the in-situ detection probe of the present invention.

[0027] Figure 5 Schematic diagram of the simulation model of the in-situ detection probe of the present invention.

[0028] Figure 6 The following are the reflectivity simulation curves of the detection probe of the present invention for two absorbing coatings and their comparison with the reference radar reflectivity curves.

[0029] Reference numerals: 1 is a coaxial connector, 2 is an inner conductor of the probe, 3 is an outer conductor of the probe, 4 is a filling medium, 5 is a step, 6 is a square ridge, 7 is an absorbing coating to be tested, and 8 is a metal substrate. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation methods and drawings.

[0031] A miniaturized radar reflectivity in-situ detection probe for absorbing coatings, the three-dimensional structure of which is shown in the figure Figure 1 As shown, the longitudinal section is as Figure 2 As shown, it includes a coaxial connector 1, a probe inner conductor 2, and a probe outer conductor 3;

[0032] The coaxial connector 1 is fixedly mounted on the upper surface of the probe outer conductor 3 through two threaded holes. The probe inner conductor 2 is disposed inside the probe outer conductor 3. A filling medium 4 is filled between the probe inner conductor 2 and the probe outer conductor 3. The filling medium is made of polytetrafluoroethylene with a low dielectric constant and low loss, and is used to make the coaxial connector 1, the probe inner conductor 2, and the probe outer conductor 3 coaxial.

[0033] The probe inner conductor 2 is made of brass with a gold-plated surface and consists of three sections connected in sequence: upper, middle, and lower. The upper and lower sections are uniform cylinders. The upper section is 2.2 mm long and 0.91 mm in diameter, while the lower section is 4 mm long and 3.08 mm in diameter. The middle section is a tapered frustum with the same diameter on its top surface and the same diameter on its bottom surface. It is 15 mm long and its diameter is reduced from 3.08 mm to 0.91 mm. The upper section of the probe inner conductor 2 is located in the inner conductor hole of the coaxial connector, and the top of the middle section is flush with the upper surface of the probe outer conductor.

[0034] The probe outer conductor 3 is made of stainless steel, with a cylindrical outer surface, an outer diameter D = 15 mm, and a total height H = 19 mm. Its inner cavity consists of an upper and a lower section. The upper inner cavity gradually expands radially from top to bottom, and the lower inner cavity is a ridged cylindrical cavity. The connection between the upper and lower inner cavities has a step, and the step depth is the distance from the edge of the step to the circumference toward the central axis. The inner cavity wall of the lower inner cavity is uniformly distributed around the circumference with four identical square ridges protruding from the circumference toward the central axis. The transverse cross-sectional view of the probe opening end is shown in FIG. Figure 3 As shown in the figure, the depth of the square ridge should be less than the depth of the step; the length of the upper cavity is 15mm, the top diameter is 3mm, and the bottom diameter is 11.2mm; the length of the lower cavity is 4mm, and the inner diameter of the cylinder is 14mm; the radial protrusion depth of the square ridge is 1mm, and the distance between the two axially symmetrical square ridges is 12mm;

[0035] The middle section of the probe's inner conductor matches the upper section of the probe's outer conductor, forming a tapered coaxial line. The lower section of the probe's inner conductor matches the lower section of the probe's outer conductor, and their bottoms are flush, forming a uniform-section coaxial line. From the top of the tapered coaxial line to its bottom, the characteristic impedance gradually changes from 50Ω to approximately 70Ω. This impedance gradient design brings the characteristic impedance of the probe's tip closer to the impedance of the absorbing coating being measured, effectively improving the dynamic range of the probe's reflection measurement.

[0036] Figure 4 This is a schematic diagram of the field distribution of the in-situ detection probe of the present invention. As can be seen from the figure, the square ridges make the electromagnetic field energy in the probe more concentrated near the probe needle, suppressing the electromagnetic field energy in the area around the opening, that is, suppressing the edge effect of the probe.

[0037] Example 1

[0038] A testing method for in-situ detection of radar reflectivity of a small area absorbing coating based on the probe of the present invention comprises the following steps:

[0039] Step 1: Configure the vector network analyzer parameters according to the test requirements and perform a single-port calibration on the vector network analyzer and RF cable using a SOLT calibration kit compatible with the adapter. This shifts the S-parameter measurement reference plane to the top end face of coaxial connector 1. At this point, the S-parameters measured by the vector network analyzer are the target reflectivity required by the test probe.

[0040] Step 2: Connect the single port of the vector network analyzer to the detection probe through the RF cable, and then attach the detection probe to the reference absorbing coating with a thickness of 1mm coated on the metal plate, and record the reflection coefficient S at this time. 11 , and the reflectivity of the reference absorbing coating has been known by the standard bow method test, set as Γref ;

[0041] Step 3: Attach the detection probe to the absorbing coating to be tested on the metal plate, and record the reflection coefficient at this time, which is recorded as Γ x ;

[0042] Step 4: Based on the test data obtained in steps 2 and 3, calculate the reflectivity Γ of the absorbing coating to be tested. test , the calculation process is as follows:

[0043]

[0044] Γ test =k·Γ x (2)

[0045] Among them, Γ ref With S 11 All are linear values, k is the calibration factor, which is related to the frequency;

[0046] By solving formulas (1) to (2) and substituting the test data, the reflectivity Γ of the absorbing coating to be tested can be calculated. test .

[0047] Firstly, the reference absorbing coating was sampled, and the relative complex permittivity and relative complex permeability of the sample were measured by coaxial transmission reflection method. Finally, the relative complex permittivity and relative complex permeability were imported into HFSS and MATLAB respectively.

[0048] According to the model size parameters provided in the above content of this embodiment, 3D modeling is performed in HFSS, such as Figure 5 As shown. The thickness of the absorbing material to be tested is 0.5mm and 1.5mm respectively, and it is coated on the metal. The reflectivity of the absorbing material is obtained by simulation. Then, based on the principle of free space plane wave incidence, an algorithm is written in MATLAB according to the free space plane wave incidence formula, and the thickness of the absorbing material is set to 0.5mm and 1.5mm respectively, and the reflectivity of the absorbing material backed by the metal is calculated. Finally, the reflectivities obtained by the two methods are compared, as shown in the figure. Figure 6 It can be seen that the reflectivity of the two absorbing materials extracted by the detection probe of the present invention is well consistent with the reflection of the two absorbing materials under vertical incidence of free space waves, with a deviation of less than 2dB.

[0049] In summary, the invention of this embodiment can effectively characterize the relationship between the reflectivity of the absorbing material and its thickness, and its test performance is comparable to the free space method test results at a normal incidence angle.

[0050] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A miniaturized radar reflectivity in-situ detection probe for absorbing coatings, characterized in that: Including coaxial connector, probe inner conductor, probe outer conductor; The coaxial connector is fixedly arranged on the upper surface of the probe outer conductor, the probe inner conductor is arranged inside the probe outer conductor, and the coaxial connector, the probe inner conductor and the probe outer conductor are coaxial; The probe inner conductor consists of three sections: an upper section, a middle section, and a lower section connected in sequence. The upper and lower sections are uniform cylinders, and the diameter of the upper section is smaller than that of the lower section. The middle section is a frustum, and the diameter of its upper top surface is the same as that of the upper section, and the diameter of its lower bottom surface is the same as that of the lower section. The upper section of the probe inner conductor is located in the inner conductor hole of the coaxial connector, and the top of the middle section is flush with the upper surface of the probe outer conductor. The inner cavity of the probe outer conductor consists of two sections, the upper section's inner cavity radially expanding from top to bottom, and the lower section's inner cavity being a ridged cylindrical cavity. A step is provided at the junction of the upper and lower sections. Four identical square ridges protruding from the circumference toward the central axis are evenly distributed on the inner wall of the lower section's inner cavity. The depth of the square ridges should be less than the depth of the step. The length of the middle section of the inner conductor of the probe is consistent with the length of the upper section of the inner cavity of the outer conductor of the probe, together forming a gradual coaxial line; the length of the lower section of the inner conductor of the probe is consistent with the length of the lower section of the inner cavity of the outer conductor of the probe, and the bottom surfaces of the lower sections of the two are flush, together forming a coaxial line with equal cross-section.

2. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 1, characterized in that: A medium is filled between the inner conductor of the probe and the inner wall of the outer conductor of the probe. The medium is air or a low dielectric constant and low loss material.

3. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 2, characterized in that: The low dielectric constant and low loss material is polytetrafluoroethylene, cross-linked polyethylene or polypropylene.

4. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 1, characterized in that: The depth of the square ridge is 0.4 to 0.6 times the depth of the step.

5. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 1, characterized in that: The diameter of the cylindrical inner wall of the lower section of the probe outer conductor cavity is d, and the radial protrusion depth of the square ridge is t. Then the distance between the two axisymmetric square ridges is d-2t, and the distance between the two square ridges should be greater than the bottom diameter of the upper section of the probe outer conductor cavity.

6. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 1, characterized in that: The height of the lower cavity of the probe outer conductor is determined according to the test frequency band and the thickness of the absorbing coating to be tested.

7. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 6, characterized in that: For the 2-18 GHz test frequency band and the absorbing coating thickness to be measured below 1.5 mm, the length of the lower cavity of the probe outer conductor is between 2-4 mm.

8. The miniaturized radar reflectivity in-situ detection probe for absorbing coatings according to claim 1, characterized in that: The length and diameter of the middle section of the probe's inner conductor and the diameter of the cavity above the middle section of the probe's inner conductor are designed to gradually change the characteristic impedance, thereby making the characteristic impedance at the probe end closer to the wave impedance of the absorbing coating to be measured, thereby improving the dynamic range of the probe's reflection measurement.

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