Material testing device and system for testing dielectric constant of wave-transmitting material

Abstract

The present invention provides a material testing device, comprising: a waveguide mounting member, a sleeve, and a shielding cap; the waveguide mounting member comprises a waveguide column and a cover; a transmission cavity is provided in the waveguide column and the cover; the waveguide columns of the two waveguide mounting members are respectively inserted into the inner hole of the sleeve from the left and right ends of the sleeve; an air cavity is left in the middle of the sleeve; the covers of the two waveguide mounting members are respectively connected to the two ends of the sleeve; two shielding caps are respectively screwed on the sleeve from the left and right ends of the sleeve; the inner shrinkage edge of the shielding cap contacts the cover of the waveguide mounting member, and the edge of the cover is completely pressed into the shielding cap. The present invention also proposes a system for testing the dielectric constant of a wave-transmitting material comprising the above-mentioned material testing device. The present invention can measure the dielectric constant of a wave-transmitting material by comparative testing with an air cavity under the same environment.

Description

Technical Field

[0001] The invention relates to the technical field of material testing, in particular to a system for testing the dielectric constant of a wave-transmitting material. Background Art

[0002] With the widespread use of millimeter-wave radar in autonomous driving, the testing of millimeter-wave radar radome materials is a prerequisite for the development of millimeter-wave radar. For the testing of millimeter-wave radar radome wave-transparent materials, the measurement of its complex dielectric constant is particularly important.

[0003] At present, there are many kinds of test methods that can be used to measure the complex dielectric constant of microwave dielectric materials at home and abroad. There are different methods according to the parameter range of the material to be tested and the test frequency band. In the frequency range of microwave and millimeter waves, they can be divided into two categories according to the different test principles: network parameter method and resonance method. In the current technical solution, the two methods have their own advantages and disadvantages. The biggest advantage of the network parameter method is that it can realize continuous frequency sweep test. In theory, data of each frequency point in the test frequency range can be obtained. At the same time, it can realize the complex dielectric constant and complex magnetic permeability test of high-loss materials. In addition, the test fixture processing is relatively simple and the cost is low. The disadvantage is that the loss measurement accuracy of low-loss materials is not high. The resonance method is very suitable for the test of the complex dielectric constant of low-loss materials. If a suitable cavity is selected, as long as the quality factor is high enough, the test results can be very accurate. However, its test frequency is limited by the resonance frequency of the cavity. If a wide-band test is to be achieved, multi-mode testing must be used, and the frequency interval between adjacent resonance modes cannot be too large. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a material testing device and a system for testing the dielectric constant of a wave-transmitting material, which can measure the dielectric constant of the wave-transmitting material by comparing the test with an air cavity under the same environment.

[0005] In a first aspect, an embodiment of the present invention provides a material testing device, comprising: two waveguide mounting members, a sleeve, and two shielding caps;

[0006] The waveguide mounting part includes a waveguide column and a cover connected to one end of the waveguide column; a transmission cavity is provided in the waveguide column and the cover; the waveguide column is adapted to the inner hole of the sleeve;

[0007] The waveguide columns of the two waveguide mounting parts are respectively inserted into the inner hole of the sleeve from the left and right ends of the sleeve; an air cavity is left in the middle of the sleeve; the covers of the two waveguide mounting parts are respectively connected to the two ends of the sleeve; the radial dimension of the cover of the waveguide mounting part is larger than the radial dimension of the inner hole of the sleeve;

[0008] External threads are arranged on the circumference of both ends of the sleeve; the shielding cap is a cylinder with an inwardly contracted edge at one end; an internal thread is arranged on the other end of the shielding cap away from the inwardly contracted edge; two shielding caps are respectively screwed on the sleeve from the left and right ends of the sleeve; the inwardly contracted edge of the shielding cap contacts the cover body of the waveguide mounting piece, and the edge of the cover body is completely pressed into the shielding cap;

[0009] The outer end surfaces of the cover bodies of the two waveguide mounting parts are used to respectively connect with the waveguide end of the spread spectrum transmitting module and the waveguide end of the spread spectrum receiving module.

[0010] Furthermore, a positioning pin is connected to the inner side of the cover of the waveguide mounting piece, and the waveguide mounting piece is positioned by the positioning pin and the sleeve.

[0011] Furthermore, the cover of the waveguide mounting piece is connected to the end surface of the sleeve via a set screw, and the thickness of the air cavity can be adjusted by adjusting the set screw.

[0012] Furthermore, the waveguide column and the cover are integrally constructed.

[0013] Furthermore, the waveguide mounting member, the sleeve, and the shielding cap are all made of metal.

[0014] In a second aspect, an embodiment of the present invention provides a system for testing the dielectric constant of a wave-transmitting material, comprising: a vector network analyzer, a spread spectrum transmitting module, any of the material testing devices described above, and a spread spectrum receiving module;

[0015] The waveguide end of the spread spectrum transmitting module and the waveguide end of the spread spectrum receiving module are respectively connected to the material testing device; the tail end of the spread spectrum transmitting module and the tail end of the spread spectrum receiving module are respectively connected to the vector network analyzer through coaxial cables.

[0016] The advantages of the present invention are:

[0017] 1) Use a shielded cavity to ensure that there are no other objects around the dielectric material to be tested that may cause unnecessary reflection and diffraction.

[0018] 2) The dielectric constant of the wave-transmitting material is measured by comparison test with the air cavity. Compared with the traditional network parameter method, it has higher measurement accuracy while having broadband scanning test capability.

[0019] 3) Simple assembly, good material repeatability, and simpler processing requirements for the medium material to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a system for testing the dielectric constant of a wave-transmitting material in an embodiment of the present invention.

[0021] Figure 2 1 is an exploded view of a material testing device in an embodiment of the present invention.

[0022] Figure 3a and Figure 3b Schematic diagram of the structure of a waveguide mounting member in an embodiment of the present invention.

[0023] Figure 4 Schematic diagram of the sleeve structure in an embodiment of the present invention.

[0024] Figure 5a and Figure 5b Schematic diagram of the shielding cap structure in an embodiment of the present invention.

[0025] Figure 6 It is a schematic diagram of a test state in which the air cavity is filled with air medium in an embodiment of the present invention.

[0026] Figure 7 Schematic diagram of the test state of the dielectric material in the air cavity in the embodiment of the present invention.

[0027] Figure 8 4 is a flow chart of the measurement process in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The embodiment of the present invention provides a system for testing the dielectric constant of a wave-transmitting material (hereinafter referred to as the testing system), such as Figure 1 As shown, it includes: a vector network analyzer 1, a spread spectrum transmitting module 2, a material testing device 3 and a spread spectrum receiving module 4; the waveguide end 201 of the spread spectrum transmitting module 2 and the waveguide end 401 of the spread spectrum receiving module 4 are respectively connected to the material testing device 3; the tail end of the spread spectrum transmitting module 2 and the tail end of the spread spectrum receiving module 4 are respectively connected to the vector network analyzer 1 through a coaxial cable;

[0030] The present application focuses on the structure of the material testing device 3, and the vector network analyzer 1, the spread spectrum transmitting module 2 and the spread spectrum receiving module 4 are only briefly introduced;

[0031] The vector network analyzer 1 is composed of a signal source, a receiver and a display; the signal source sends a single frequency signal to the material testing device 3 via the spread spectrum transmitting module 2, and the transmitted wave signal passing through the material testing device 3 is transmitted to the receiver via the spread spectrum receiving module 4 to be tuned to the frequency and detect the transmitted wave signal and the reflected wave signal of the dielectric material (received from the spread spectrum transmitting module 2 and sent to the receiver of the vector network analyzer 1); the amplitude and phase data at the frequency can be obtained according to the measured response, and the parameters of the complex reflection coefficient and the complex scattering parameter network characteristics can be obtained, and then the parameter changes of the air cavity before and after the dielectric material to be tested is loaded on the material testing device 3 are compared, and the complex dielectric constant and complex magnetic permeability of the dielectric material to be tested are calculated and measured;

[0032] like Figure 2 As shown, the material testing device 3 includes two waveguide mounting members 302, a sleeve 304, and two shielding caps 306; the waveguide mounting member 302 is as shown in FIG. Figure 3a , Figure 3b As shown, the sleeve 304 is Figure 4 As shown, the shielding cap 306 is Figure 5a , Figure 5b As shown; the waveguide mounting member 302, the sleeve 304, and the shielding cap 306 are all made of aluminum;

[0033] The waveguide mounting member 302 includes a waveguide column 3021 and a cover 3022 connected to one end of the waveguide column 3021; ​​the waveguide column 3021 and the cover 3022 can be integrally constructed; a transmission cavity 3023 is provided in the waveguide column 3021 and the cover 3022; the waveguide column 3021 is adapted to the inner hole 3041 of the sleeve 304;

[0034] The waveguide columns 3021 of the two waveguide mounting members 302 are respectively inserted into the inner hole 3041 of the sleeve 304 from the left and right ends of the sleeve 304; an air cavity 307 is left in the middle of the sleeve 304; the covers 3022 of the two waveguide mounting members 302 are respectively connected to the two ends of the sleeve 304; the radial dimension of the covers 3022 of the waveguide mounting members 302 is larger than the radial dimension of the inner hole 3041 of the sleeve 304;

[0035] The meaning of "connected" in this article includes the direct connection between two objects or the indirect connection between two objects through a third object;

[0036] In some embodiments, a positioning pin 303 is connected to the inner side of the cover 3022 of the waveguide mounting member 302, and the waveguide mounting member 302 is positioned by the positioning pin 303 and the sleeve 304;

[0037] In some embodiments, the cover 3022 of the waveguide mounting member 302 is connected to the end surface of the sleeve 30 via a set screw 305, and the thickness of the air cavity 307 can be adjusted by adjusting the set screw 305;

[0038] exist Figure 3a and Figure 3b Among the four holes on the cover 3022 of the waveguide mounting member 302 near the edge, two holes are pin holes, and the other two holes are set screw holes. These four holes are used for positioning and connecting the cover 3022 and the sleeve 304; among the four holes near the port of the middle transmission cavity 3023, two holes are pin holes, and the other two holes are set screw holes. These four holes are used for positioning and fixing the cover 3022 and the waveguide end 201 of the spread spectrum transmitting module 2 or the waveguide end 401 of the spread spectrum receiving module 4;

[0039] External threads are provided on the circumferential surfaces of both ends of the sleeve 304; the shielding cap 306 is a cylinder with an inwardly contracted edge 3061 at one end; the other end of the shielding cap 306 away from the inwardly contracted edge 3061 is provided with an internal thread; two shielding caps 306 are respectively screwed on the sleeve 304 from the left and right ends of the sleeve 304; the inwardly contracted edge 3061 of the shielding cap 306 contacts the cover 3022 of the waveguide mounting member 302, and the edge of the cover 3022 is completely pressed into the shielding cap 306, so that the shielding cavity in the material testing device 3, that is, the air cavity 307, is electromagnetically shielded from the outside world; when the dielectric material to be tested is placed in the air cavity 307, it is isolated from the outside world; the thickness of the air cavity is consistent with the thickness of the dielectric material to be tested;

[0040] The outer end surfaces of the covers 3022 of the two waveguide mounting members 302 are respectively connected to the waveguide end 201 of the spread spectrum transmitting module 2 and the waveguide end 401 of the spread spectrum receiving module 4; they can be positioned and fixed by positioning pins and fixing screws;

[0041] Remove the shielding cap 306 and the waveguide mounting member 302 at one end of the sleeve 304, and place the dielectric material 301 in the air cavity 307 in the sleeve; then assemble the material testing device 3;

[0042] The first and third test status are as follows Figure 6 As shown, the second and fourth test status are as follows Figure 7 As shown; the first and third measurements are air medium measurements, the second and fourth measurements are dielectric material measurements, the air cavity of the first measurement has the same physical dimensions as the dielectric material of the second measurement, and the dielectric constant and magnetic permeability parameters of the dielectric material are known, and the air cavity of the third measurement has the same physical dimensions as the dielectric material of the fourth measurement;

[0043] The thickness of the dielectric material 301 is consistent with the thickness of the air cavity; the measurement process is as follows Figure 7 As shown;

[0044] Step S1: Assemble the material testing device 3, connect the two ports of the vector network analyzer 1 to the spread spectrum transmitting module 2 and the spread spectrum receiving module 4 respectively, and start the test system;

[0045] Step S2: Initialize the vector network analyzer and set basic parameters, including the start frequency, end frequency, number of points, and calibration type;

[0046] Step S3: measuring and calibrating the vector network analyzer. After the calibration is completed, the spread spectrum transmitting module and the spread spectrum receiving module are respectively connected to the two ends of the material testing device 3 to enter the measurement phase;

[0047] Step S4: input the measured air cavity thickness and measure the two ports of the air cavity;

[0048] Step S5: loading a dielectric material with known measurement parameters, wherein the dielectric material has a size and thickness that is the same as the thickness of the air cavity, and measuring the dielectric material with known measurement parameters;

[0049] Step S6: Calculate the measurement results of two different dielectric materials (the medium in S4 is regarded as air) in S4 and S5, and calibrate the test system through the two measurements;

[0050] Step S7: input the measured air cavity thickness and measure the two ends of the air cavity;

[0051] Step S8: loading the dielectric material to be tested, the dielectric material size and thickness being the same as the thickness set for the air cavity, and measuring the dielectric material to be tested;

[0052] Step S9: According to the measurement results of two different dielectric materials (the medium is regarded as air in S7) in S7 and S8, the complex dielectric constant and complex magnetic permeability of the sample are analyzed and calculated, and the accuracy of the calculation results is determined by the verification results of S6;

[0053] Step S10: Display and output the measurement results of S9;

[0054] Step S11: confirm whether to continue the frequency sweep measurement of the test material at other frequencies. If so, proceed to step S2; if not, proceed to step S12 to terminate the measurement.

[0055] Principle of measurement: When a TEM wave (transverse electromagnetic wave) propagates normally in free space and is incident on the surface of a dielectric material, an impedance mismatch will occur due to the difference (lower) between the wave impedance in the dielectric material and the impedance of free space, generating a reflected wave. At the same time, a portion of the energy will pass through the dielectric material to form a transmitted wave. Once the wave enters the dielectric material, the wave speed will become slower than the speed of light. Since the dielectric material always produces certain losses, the wave will attenuate or have insertion losses. This application is to load a dielectric material of known physical dimensions into a material testing device, treat it as a two-port network during testing, and measure the changes in reflection and transmission responses of the two ports. The complex reflection coefficient and complex scattering parameters, which characterize the network characteristics, are measured using an instrument. Then, the complex dielectric constant and complex magnetic permeability of the dielectric material to be tested are inferred using a calculation model of air and dielectric materials with known measurement parameters under the same state combined with electromagnetic field theory.

[0056] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A material testing device (3), characterized in that: include: Two waveguide mounting parts (302), a sleeve (304), and two shielding caps (306); The waveguide mounting member (302) comprises a waveguide column (3021) and a cover (3022) connected to one end of the waveguide column (3021); a transmission cavity (3023) is provided in the waveguide column (3021) and the cover (3022); the waveguide column (3021) is adapted to the inner hole (3041) of the sleeve (304); The waveguide columns (3021) of the two waveguide mounting members (302) are respectively inserted into the inner hole (3041) of the sleeve (304) from the left and right ends of the sleeve (304); an air cavity (307) is left in the middle of the sleeve (304); the covers (3022) of the two waveguide mounting members (302) are respectively connected to the two ends of the sleeve (304); the radial dimension of the covers (3022) of the waveguide mounting members (302) is greater than the radial dimension of the inner hole (3041) of the sleeve (304); External threads are provided on the circumferential surfaces of both ends of the sleeve (304); the shielding cap (306) is a cylindrical body having an inwardly contracted edge (3061) at one end; an internal thread is provided on the other end of the shielding cap (306) away from the inwardly contracted edge (3061); the two shielding caps (306) are respectively screwed onto the sleeve (304) from the left and right ends of the sleeve (304); the inwardly contracted edge (3061) of the shielding cap (306) contacts the cover body (3022) of the waveguide mounting member (302), and the edge of the cover body (3022) is completely pressed into the shielding cap (306); The outer end surfaces of the covers (3022) of the two waveguide mounting members (302) are used to respectively dock with the waveguide end (201) of the spread spectrum transmitting module (2) and the waveguide end (401) of the spread spectrum receiving module (4).

2. The material testing device (3) according to claim 1, characterized in that: The inner side of the cover body (3022) of the waveguide mounting piece (302) is connected with a positioning pin (303), and the waveguide mounting piece (302) is positioned by the positioning pin (303) and the sleeve (304).

3. The material testing device (3) according to claim 1, characterized in that: The cover body (3022) of the waveguide mounting member (302) is connected to the end surface of the sleeve (304) via a set screw (305), and the thickness of the air cavity (307) can be adjusted by adjusting the set screw (305).

4. The material testing device (3) according to claim 1, characterized in that: The waveguide column (3021) and the cover body (3022) are integrally constructed.

5. The material testing device (3) according to claim 1, characterized in that: The waveguide mounting part (302), the sleeve (304) and the shielding cap (306) are all made of metal.

6. A system for testing the dielectric constant of a wave-transmitting material, characterized in that: include: A vector network analyzer (1), a spread spectrum transmitting module (2), a material testing device (3) according to any one of claims 1 to 5, and a spread spectrum receiving module (4); The waveguide end (201) of the spread spectrum transmission module (2) and the waveguide end (401) of the spread spectrum reception module (4) are respectively connected to the material testing device (3); the tail end of the spread spectrum transmission module (2) and the tail end of the spread spectrum reception module (4) are respectively connected to the vector network analyzer (1) via a coaxial cable.

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