A method and device for testing dielectric properties of materials under multi-physics field coupling

Abstract

The purpose of the present invention is to provide a method and device for testing the dielectric properties of materials under multi-physical field coupling, which belongs to the field of microwave testing technology. The test method uses the ideal quality factor Q corresponding to the imaginary material without time consumption. 0s The radiation loss and ohmic loss of the open coaxial cavity were corrected to improve the accuracy and stability of the complex dielectric constant test; at the same time, the test device was designed so that it can construct multiple physical fields such as force, heat, electricity, magnetism, and microwaves, and realize the dielectric properties test of the material to be tested under the coupling of multiple physical fields, providing important technical support for analyzing the evolution of the complex dielectric constant of functional materials with the loading of multiple physical fields.

Description

Technical Field

[0001] The present invention belongs to the field of microwave testing technology, and in particular relates to a method and device for testing dielectric properties of materials under multi-physical field coupling. Background Art

[0002] With the rapid development of electronic information technology, functional materials with electrical and magnetic properties, such as ferroelectric / ferromagnetic materials and semiconductors, are increasingly being used in engineering and technology, particularly in the manufacture of novel sensors, actuators, and electronic components. Research results have shown that ferroelectric / ferromagnetic materials, piezoelectric materials, and semiconductors exhibit complex multi-physics field coupled constitutive behaviors. Microwave fields, electrostatic fields, static magnetic fields, temperature, and stress can affect the constitutive electrical properties of certain functional materials. Consequently, testing the electrical properties of functional materials under multi-physics field coupling has garnered widespread attention, leading to an urgent need for relevant testing methods.

[0003] At present, the complex dielectric constant testing technology of materials based on the resonance method has been reported under high temperature, high pressure or microwave field coupling. In the patent "System and method for testing the dielectric properties of materials under high temperature and high pressure based on the coaxial cavity method" with publication number CN117388581A, it is proposed to place the absorbing material to be tested in a gradient coaxial resonant cavity, use a heating and pressurizing device to simultaneously construct a temperature field and a pressure field, and measure the dielectric properties of the material at different temperatures and pressures; in the patent "System and method for testing the dielectric properties of wave-transmitting materials under high temperature and high pressure" with publication number CN117630502A, it is proposed to add a heating and pressurizing device to a conventional quasi-optical cavity testing device, and use fused quartz as a standard sample for data correction to realize the dielectric property testing of wave-transmitting materials under high temperature and high pressure; in the patent "System and method for testing the dielectric properties of low-loss materials under the action of low-frequency microwave electric field" with publication number CN115932412A, it is proposed to load a rectangular resonant cavity in the quasi-optical cavity testing device, use the rectangular cavity to apply a microwave electric field to the low-loss material, and realize the dielectric property testing of the low-loss material under microwave electric field coupling. However, the above-mentioned test systems only measure the dielectric performance parameters of microwave materials under a single physical field or dual physical fields, and cannot fully evaluate the change law of the electrical performance of the material under simulated service conditions (in-situ conditions: simultaneous coupling of multiple physical fields such as force, heat, electricity, magnetism, and microwave).

[0004] In addition, the existing test method assumes that the quality factor corresponding to the radiation loss and conductor loss of the open coaxial resonant cavity remains unchanged when loading different samples. However, after the sample is actually loaded, the change in the relative dielectric constant of the sample in the opening area of ​​the resonant cavity will cause a change in the field distribution, thereby changing the radiation loss and ohmic loss, causing the corresponding quality factor to change accordingly. When the loaded sample is a medium-low dielectric (ε r<6) and medium-to-high loss (tanδ>0.002) materials, the error introduced by the above assumptions is negligible. However, when the loaded sample is a high-dielectric, low-loss sample, the quality factor corresponding to the coaxial resonant cavity's radiation loss and conductor loss varies significantly. The amount of change will be greater than the change in the quality factor caused by the sample's dielectric loss. This leads to inaccurate quality factors used to calculate dielectric loss in existing algorithms, and it is impossible to accurately calculate the sample's loss tangent. Therefore, it is necessary to improve the existing algorithm to take into account the changes in the quality factors corresponding to the open coaxial resonant cavity's radiation loss and conductor loss when loading different samples.

[0005] In summary, if the non-destructive testing system for material dielectric properties can be improved and a multi-physics field coupling loading module can be integrated, it will be possible to simulate in-situ testing of the electrical properties of specific functional materials in a multi-physics field coupling environment. At the same time, by optimizing the test method to make the measurement results of the dielectric constant more accurate, it will provide a powerful testing method for the analysis of the aging process and damage mechanism of materials under service. Summary of the Invention

[0006] In view of the problems existing in the background technology, the purpose of the present invention is to provide a method and device for testing the dielectric properties of materials under multi-physical field coupling. The testing method uses the ideal quality factor Q corresponding to the imaginary material without time consumption. 0s The radiation loss and ohmic loss of the open coaxial cavity are corrected to improve the accuracy and stability of the complex dielectric constant test; at the same time, the test device is designed so that it can construct multiple physical fields such as force, heat, electricity, magnetism, and microwaves, and realize the dielectric performance test of the material to be tested under the coupling of multiple physical fields.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for testing dielectric properties of materials under multi-physics field coupling, comprising the following steps:

[0009] Step 1: Measure the resonant frequency f0 and quality factor Q0 of the TEM mode of the open coaxial cavity in the cavity state;

[0010] Step 2: Place a reference sample of the same thickness as the sample to be tested at the open end of the open coaxial cavity, measure the resonant frequency f1 and quality factor Q1 of the TEM mode of the open coaxial cavity when the reference sample k1 is loaded, and then replace the reference sample. Test the resonant frequency and quality factor of each reference sample until the mth reference sample k1 is loaded. m , measure the resonant frequency f m and quality factor Q m ;

[0011] Step 3: Place the sample under test at the open end of the open coaxial cavity and apply a multi-physics field to the sample. After the applied multi-physics field stabilizes, measure the resonant frequency f and quality factor Q of the TEM mode of the open coaxial cavity under the loaded sample.

[0012] Step 4: Based on the m+2 sets of measurement data obtained in steps 1, 2, and 3, calculate the relative complex dielectric constant ε of the sample to be tested. r , the calculation process is as follows:

[0013] Step 4.1. For the TEM mode, the following equation is obtained based on the perturbation method:

[0014]

[0015] Among them, ε r is the relative complex permittivity, ε' r is the relative dielectric constant, tanδ is the loss tangent, j is the imaginary part, ε0 is the vacuum dielectric constant, △f=f0-f s , f s f m or f, Q s Q m or Q, {a m} and {b m} is the calibration coefficient;

[0016] Step 4.2. Load the measurement data f0 under the cavity state and the measurement data {f m}, and the relative dielectric constant ε' of the reference sample rm Substituting into equation (2), we get m equations, which are solved together to obtain the calibration coefficients {a m};

[0017] Step 4.3. Load the measurement data of the reference sample state {f m} and {Q m}, relative dielectric constant ε' of the reference sample rm and loss tangent tanδ m , and the obtained calibration coefficient {a m Substituting into equation (3), we get m equations, which are solved together to obtain the ideal quality factor of the TEM mode {Q 0sm};

[0018] Step 4.4. Load the measured data f0 and Q0 in the cavity state with the measured data {f m}, and the ideal quality factor of the TEM mode obtained in step 4.3 {Q 0sm}Substitute into equation (4), and we get m+1 equations, which are solved together to obtain the calibration coefficients {b m};

[0019] Step 4.5. Load the measured data f0 in the cavity state with the resonant frequency f and quality factor Q of the sample to be tested, as well as the obtained calibration coefficient {a m} and {b m}, and substitute into equations (1) to (4), the relative complex dielectric constant ε of the sample to be tested can be calculated. r .

[0020] Furthermore, the relative dielectric constant and loss tangent of the reference samples are extracted using the high-Q cavity method. The number of reference samples is not less than 3, and their relative dielectric constants should be at least in the range of 2 to 4, 4 to 8, and 8 to 12, respectively, and their loss tangents should be at least in the range of 10 -4 , 10 -3 and 10 -2 order of magnitude to improve the calibration factor {a m} and {b m}reliability and applicability.

[0021] The present invention also provides a material dielectric property testing device under multi-physical field coupling suitable for the above-mentioned testing method, comprising a dielectric property testing module and a multi-physical field loading module;

[0022] The dielectric performance test module includes a first vector network analyzer and an open coaxial cavity; the multi-physics field loading module includes a microwave field loading submodule, an electrostatic field loading submodule, a static magnetic field loading submodule, a temperature field loading submodule and a pressure field loading submodule; wherein the microwave field loading submodule includes a second vector network analyzer, a power amplifier, a coupler, a DC block and a band-stop filter; the electrostatic field loading submodule includes a DC source and a metal sample stage; the static magnetic field loading submodule includes an electromagnet; the temperature field loading submodule includes a temperature controller, a heating element and a thermally conductive insulating box; the pressure field loading submodule includes a pressure gauge, a pressure sensor, a spring array, a transition support, a lifting platform, an insulating connecting column and a system bracket;

[0023] The system bracket includes a bottom plate, a top plate, and a column fixedly connecting the bottom plate and the top plate; an insulating connecting column, an open coaxial cavity, a metal sample stage, a heating element, a spring array, a pressure sensor, and a lifting platform are arranged on the bottom plate in order from top to bottom, and the other end of the insulating connecting column is fixedly connected to the top plate; the sample to be tested is placed on the metal sample stage and is located at the open end of the open coaxial cavity; the pressure gauge is connected to the pressure sensor to display the loaded pressure value; the electromagnet is symmetrically placed on both sides of the sample to be tested so that the sample to be tested is located in the static magnetic field action area of ​​the electromagnet;

[0024] The open coaxial cavity includes an inner conductor and an outer conductor coaxially arranged with the inner conductor, one end of which is short-circuited and the other end is open-circuited. Two coupling ports are symmetrically arranged on the side wall of the outer conductor near the short-circuit surface of the open coaxial cavity, and a feed port is arranged near the middle of the outer conductor side wall. At the same time, four circumferentially symmetrical gaps are set through the side wall of the outer conductor. A first water cooling passage is provided on the side wall of the outer conductor near the open-circuit end to protect the open coaxial cavity.

[0025] The two ports of the first vector network analyzer are connected to the two coupling ports via a band-stop filter and a DC block, respectively; the first port of the second vector network analyzer is connected to a power amplifier, a coupler, and a first DC block in sequence, and then to the feed port of the open coaxial cavity, wherein the output end of the power amplifier is connected to the output end of the coupler, the first DC block is connected to the input end of the coupler, and the second port of the second vector network analyzer is connected to the coupling end of the coupler;

[0026] The positive pole of the DC source is connected to the metal sample stage, and the negative pole is grounded and connected to the outer conductor of the open coaxial cavity; the metal sample stage is embedded in the heating element, and a heat-conducting insulating box is provided between the metal sample stage and the heating element to insulate the metal sample stage and the heating element; a heating rod is embedded in the side of the heating element, and after the heating rod is heated, it heats the sample to be tested through heat conduction; a thermocouple is provided on the metal sample stage for detecting the temperature of the sample to be tested.

[0027] Furthermore, the coupling port adopts a circular weak coupling structure, and its coupling amount (S21) should be less than -50dB; the feeding port adopts a probe strong coupling structure, and its S11 should be less than -10dB.

[0028] Furthermore, the specific position of the feeding port is determined by the field distribution of the TEM resonance mode corresponding to the feeding frequency.

[0029] Furthermore, the metal sample table is made of a high-temperature alloy and is in a "T" shape as a whole, with the bottom embedded in a thermally conductive insulating box; the heating element is made of a high-temperature alloy and has a groove structure on the top for supporting the thermally conductive insulating box, and the bottom is connected and fixed to the transition support; the top of the transition support has a second water-cooling passage for thermally isolating the pressure loading submodule below.

[0030] Furthermore, the spring array is composed of six screws with springs and a chassis. The screws pass through the through holes at the bottom of the transition pillar from top to bottom and are fixed on the chassis.

[0031] Furthermore, the frequency of the output signal of the second vector network analyzer is within the stop band of the band-stop filter.

[0032] Furthermore, the DC block and the band-stop filter are only connected when the microwave field is loaded. At this time, the frequency of the output signal of the second vector network analyzer should be near the resonant frequency of one of the n TEM modes of the open coaxial cavity under the sample to be tested (depending on the microwave field loading frequency requirement). When a high-power microwave field is loaded, the first vector network analyzer test needs to skip this TEM mode to avoid the impact of the injected high-power signal on the test signal.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] The dielectric properties testing device designed in the present invention can test the dielectric properties of the material to be tested under multiple physical fields such as loading force, heat, electricity, magnetism, and microwaves; in addition, a test algorithm improved based on the perturbation method is established to improve the accuracy and test stability of the complex dielectric constant test; the testing device and method of the present invention provide important technical support for analyzing the evolution law of the complex dielectric constant of functional materials with the loading amount of multiple physical fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the material dielectric properties testing device under multi-physical field coupling of the present invention.

[0036] Figure 2 This is a schematic diagram of the open coaxial cavity and its cross-sectional structure of the present invention.

[0037] Figure 3 This is a diagram showing the positional relationship between the metal sample stage, the thermally conductive insulating box, and the heating element of the present invention.

[0038] Figure numerals: 1 is the first vector network analyzer, 2 is the open coaxial cavity, 3 is the second vector network analyzer, 4 is the power amplifier, 5 is the coupler, 6 is the DC block, 7 is the band-stop filter, 8 is the DC source, 9 is the metal sample stage, 10 is the electromagnet, 11 is the temperature controller, 12 is the heating element, 13 is the thermal insulation box, 14 is the pressure gauge, 15 is the pressure sensor, 16 is the spring array, 17 is the transition support, 18 is the lifting platform, 19 is the insulating connecting column, 20 is the system bracket, 21 and 22 are the coupling ports of the open coaxial cavity, 23 is the feeding port of the open coaxial cavity, 24 is the gap, 25 is the first water-cooling passage, 26 is the sample to be tested, 27 is the thermocouple, 28 is the heating rod, and 29 is the second water-cooling passage. DETAILED DESCRIPTION

[0039] 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.

[0040] A device for testing dielectric properties of materials under multi-physical field coupling, the structural diagram of which is shown in FIG. Figure 1 As shown, it includes dielectric performance test module and multi-physics field loading module;

[0041] The dielectric performance test module includes a first vector network analyzer 1 and an open coaxial cavity 2; the multi-physics field loading module includes a microwave field loading submodule, an electrostatic field loading submodule, a static magnetic field loading submodule, a temperature field loading submodule and a pressure field loading submodule; wherein the microwave field loading submodule includes a second vector network analyzer 3, a power amplifier 4, a coupler 5, a DC block 6 and a band-stop filter 7; the electrostatic field loading submodule includes a DC source 8 and a metal sample stage 9; the static magnetic field loading submodule includes an electromagnet 10; the temperature field loading submodule includes a temperature controller 11, a heating element 12 and a thermally conductive insulating box 13; the pressure field loading submodule includes a pressure gauge 14, a pressure sensor 15, a spring array 16, a transition support 17, a lifting platform 18, an insulating connecting column 19 and a system bracket 20;

[0042] The system bracket 20 includes a bottom plate, a top plate, and a column fixedly connecting the bottom plate and the top plate; an insulating connecting column 19, an open coaxial cavity 2, a metal sample stage 9, a heating element 12, a spring array 16, a pressure sensor 15 and a lifting platform 18 are arranged on the bottom plate from top to bottom, one end of the insulating connecting column 19 is fixedly connected to the top plate, and the other end is connected to the short-circuit end of the open coaxial cavity 2; the sample to be tested 26 is set on the metal sample stage 9 and is located at the open-circuit end of the open coaxial cavity 2; the pressure gauge 14 is connected to the pressure sensor 15 to display the loaded pressure value; the electromagnet 10 is symmetrically placed on both sides of the sample to be tested so that the sample to be tested is located in the static magnetic field action area of ​​the electromagnet; in order to facilitate the clear view of the positional relationship of the various components in the figure, only half of the electromagnet is drawn, and the other half is mirrored and located on the other side of the system bracket;

[0043] The open coaxial cavity adopts a gradient open coaxial cavity, and its overall and cross-sectional structure diagram is shown as follows Figure 2 As shown, the overall structure diagram is as follows Figure 2 As shown in the left figure, the cross-sectional structure is as follows Figure 2 As shown in the figure on the right, the open coaxial cavity includes an inner conductor and an outer conductor coaxially arranged with the inner conductor. One end of the outer conductor is short-circuited and the other end is open-circuited. A section of the cavity near the open end is gradually changed so that the opening diameter of the cavity is smaller than the diameter of the cavity body. Two coupling ports 21 and 22 are symmetrically arranged on the side wall of the open coaxial cavity near the short-circuit surface. A feeding port 23 is also arranged on the side wall of the open coaxial cavity. Four circumferentially symmetrical gaps are also provided. A first water cooling passage 25 is provided near the open end of the outer conductor to protect the open coaxial cavity.

[0044] The two ports of the first vector network analyzer 1 are connected to the two coupling ports 21 and 22 respectively through the band-stop filter 7 and the second DC block 6; the first port of the second vector network analyzer 3 is connected to the power amplifier 4, the coupler 5 and the first DC block 6 in sequence, and then connected to the feeding port 23 of the open coaxial cavity 2, wherein the output end of the power amplifier 4 is connected to the output end of the coupler 5, and the first DC block 6 is connected to the input end of the coupler 5; the second port of the second vector network analyzer 3 is connected to the coupling end of the coupler 5;

[0045] The positive electrode of the DC source 8 is connected to the metal sample stage 9, and the negative electrode is connected to the outer conductor of the open coaxial cavity 2 after being grounded; the positional relationship between the metal sample stage 9, the thermally conductive insulating box 13 and the heating element 12 is shown in the figure. Figure 3 As shown, the metal sample stage 9 is in a "T" shape as a whole, with the bottom embedded in the thermally conductive insulating box 13, and the thermally conductive insulating box 13 embedded in the heating element to insulate the metal sample stage and the heating element; the top of the heating element 12 has a groove structure for supporting the thermally conductive insulating box 13, and a heating rod 28 is embedded in the side. After the heating rod 28 is heated, the sample to be tested 26 is heated by thermal radiation, and the bottom is fixed to the transition support 17; the top of the transition support 17 has a second water-cooling passage 29 for thermally isolating the pressure loading submodule below; a thermocouple 27 is provided on the metal sample stage 9 for detecting the temperature of the sample to be tested.

[0046] Example 1

[0047] The open coaxial cavity is designed to operate in the P, L, and S bands, and the inner cavity walls are silver-plated. The total cavity length (L) is 152 mm, with a 120 mm long constant-diameter section, a 4.3 mm inner conductor radius, and a 15 mm inner outer conductor radius. The tapered section is 32 mm long, with a 1 mm open-circuit end radius for the inner conductor, a 3.5 mm inner radius for the outer conductor, and a 14 mm outer radius. A step is provided on the sidewall of the open end of the outer conductor, with a diameter smaller than the outer conductor's outer radius. This allows the two electromagnets to directly contact the step, providing a stronger magnetic field within a smaller area.

[0048] The reference sample and the sample to be tested are both cylindrical sheets (diameter d = 50 mm, thickness h = 2 mm). The reference sample is made of three materials: fused quartz, fiberglass, and alumina. Their relative dielectric constants ε' rm and loss tangent tanδ m The extraction was performed by the perturbation test system, and the values ​​are shown in Table 1.

[0049] Table 1 Relative dielectric constant and loss tangent of reference samples

[0050] Material name <![CDATA[Relative permittivity ε' rm > <![CDATA[Loss tangent tanδ m > Fused Silica 3.83 0.0005 fiberglass 5.23 0.0198 Alumina 9.12 0.0016

[0051] Combined with the size of the open coaxial cavity and the material selection of the reference sample, the test system operates in the P, L, and S frequency bands. The test range of its material dielectric performance parameters is: relative dielectric constant of 1 to 12, loss tangent of 1×10 -4 ~5×10 -2 .

[0052] The microwave field loading submodule output signal frequency covers P, L, and S frequency bands, with an output power of 0 to 20W; the electrostatic field loading submodule can apply a DC voltage of 0 to 1kV; the static magnetic field loading submodule can apply a static magnetic field of 0 to 1.2T; the temperature field loading submodule can heat the sample in the range of room temperature to 600°C; the pressure field loading submodule can apply a pressure field of 0 to 50kN / m to the sample 2 .

[0053] The test is performed based on the material dielectric properties testing device under the above multi-physics field coupling, including the following steps:

[0054] Step 1: Adjust the lifting platform so that the metal sample stage slowly approaches the open end of the open coaxial cavity. When the distance is consistent with the thickness of the sample to be measured, fix the height of the lifting platform;

[0055] Step 2: Without connecting the DC block and the band-stop filter, measure and record the resonant frequency f of the nth TE M mode of the open coaxial cavity in the cavity state. 0n and quality factor Q 0n , the measured data are shown in Table 2, n is 1, 2, 3, 4:

[0056] Table 2 Resonant frequency and quality factor of TEM mode in cavity state

[0057] Mode number n 1 2 3 4 <![CDATA[Resonant frequency f 0n / GHz]]> 0.4838 1.4569 2.4355 3.4128 <![CDATA[Quality factor Q 0n > 2360.2 3483.6 3181.5 3945.1

[0058] Step 3: Place the fused quartz, fiberglass, and alumina samples as samples 1, 2, and 3, and place them on the sample stage. Adjust the lifting platform so that the reference sample is in close contact with the open end of the open coaxial cavity. Measure and record the resonant frequency f of the nth TEM mode of the open coaxial cavity under the mth reference sample. mn and quality factor Q mn , a total of 3 groups of data, as shown in Table 3;

[0059] Table 3 Resonant frequency and quality factor of TEM mode under the reference sample loading state

[0060] serial number <![CDATA[f m1 / GHz]]> <![CDATA[Q m1 ]]> <![CDATA[f m2 / GHz]]> <![CDATA[Q m2 ]]> <![CDATA[f m3 / GHz]]> <![CDATA[Q m3 ]]> <![CDATA[f m4 / GHz]]> <![CDATA[Q m4 ]]> 1 0.4758 2166.5 1.4336 2781.4 2.3965 3417.0 3.3554 2546.2 2 0.4723 617.0 1.4237 705.8 2.3804 553.8 3.3316 645.6 3 0.4650 1998.3 1.4012 2553.0 2.3425 2103.8 3.2795 1374.3

[0061] Step 4: Place the sample to be tested on the sample table, and adjust the lifting platform so that it is in close contact with the open end of the open coaxial cavity; select the microwave field (need to be connected to a DC block and a band-stop filter), electrostatic field, static magnetic field, temperature field, and pressure field loading sub-modules according to the test requirements: If five physical fields are required to be applied simultaneously, the following configurations can be performed in sequence: 1) Adjust the height of the lifting platform so that the pressure gauge reads 10N; 2) Set the sweep range of the second vector network analyzer to be near the resonant frequency of the third TEM mode of the open coaxial cavity, and use the second vector network analyzer to find the reflection concave peak of the feed port of the open coaxial cavity to determine the strongest coupling. ), set the frequency point as the sweep center frequency of the second vector network analyzer, set the sweep bandwidth to 5MHz, and then adjust the power amplifier gain to make the output power 10W; 3) adjust the electromagnet and use a Gauss meter to measure its static magnetic field strength so that its output static magnetic field strength is 0.1T; 4) adjust the temperature controller so that the thermocouple meter reading is stable at 100℃; 5) adjust the DC source so that its output voltage is 500V; after the parameter configuration is completed, wait for the system to stabilize, and then use the first vector network analyzer to measure the resonant frequency f of the nth (except the third) TEM mode of the open coaxial cavity when the sample to be tested is loaded. n and quality factor Q n ;

[0062] Step 5: Based on the five sets of measurement data obtained in each TEM mode in the previous steps, calculate the relative complex dielectric constant ε of the sample to be tested in the nth TEM mode rn ;

[0063] Step 5.1. Taking the second TEM mode as an example, the relative complex dielectric constant ε of the sample to be measured r2 The calculation process is as follows:

[0064] According to the perturbation method, the following equation is obtained:

[0065]

[0066] Among them, ε r is the relative complex permittivity, ε' r is the relative dielectric constant, tanδ is the loss tangent, j is the imaginary part, ε0 is the vacuum dielectric constant, △f=f0-f s , f s f m or f, Q s Q m or Q, {a m} and {b m} is the calibration coefficient;

[0067] Since three materials are used as reference samples, that is, m = 3, the above equation can be simplified to:

[0068]

[0069] Step 5.2. Load the measurement data f0 under the cavity state and the measurement data {f m}, and the relative dielectric constant ε' of the reference sample rm Substituting into equation (6), we get three equations, which can be solved simultaneously to obtain the calibration coefficients {a1 a2 a3} of the second TEM mode;

[0070] Step 5.3. Load the measurement data of the reference sample state {f m} and {Q m}, relative dielectric constant ε' of the reference sample rm and loss tangent tanδ m , and the obtained calibration coefficients {a1 a2 a3} are substituted into formula (7) to obtain three equations, which are solved together to obtain the ideal quality factor of the second TEM mode {Q 0s1 Q 0s2 Q 0s3};

[0071] Step 5.4. Load the measured data f0 and Q0 in the cavity state with the measured data {f m}, and the ideal quality factor of the second TEM mode obtained in step 4.3 {Q 0s1 Q 0s2 Q 0s3}Substitute into formula (8) to obtain four equations, which are solved simultaneously to obtain the calibration coefficients {b1 ​​b2 b3 b4} of the second TEM mode;

[0072] Step 5.5. Substitute the measured data f0 in the cavity state, the resonant frequency f2 and quality factor Q2 in the state of the sample to be tested, and the obtained calibration coefficients {a1 a2 a3} and {b1 b2 b3 b4} into equations (5) to (8) to calculate the relative complex dielectric constant ε of the sample to be tested in the second TEM mode. r2 .

[0073] The complex dielectric constants of the different test samples calculated in step 5 at room temperature and under the test conditions specified in step 4 are shown in Table 4. It can be seen that, compared to the test results at room temperature, the relative dielectric constants and loss tangents obtained for the different test samples under the test conditions specified in step 4 vary differently; these variations are also related to the properties of the test samples themselves. This demonstrates that the testing apparatus and method of the present invention can perform complex dielectric constant testing of materials under multi-physics field coupling, and the results are reliable.

[0074] Table 4 Complex dielectric constant test results of the tested samples before and after multi-physics field coupling

[0075]

[0076] In addition, the present invention can also obtain the relative complex dielectric constant ε of the sample to be tested r The relationship curve with the change of multi-physical field loading, that is, according to the needs, the loaded physical field is set, and one of the required physical fields is adjusted in a certain step, while the other physical fields remain unchanged. The corresponding relative complex dielectric constant value is calculated using the above test method, and the relationship curve of the relative complex dielectric constant of the sample to be tested with the change of multi-physical field loading can be obtained.

[0077] Example 2

[0078] Different dielectric materials were tested. The cavity structure, reference samples, and test steps used were consistent with those in Example 1. Only the multi-physics field loading in step 4 was adjusted to room temperature (no physical field coupling). At the second TEM mode, different algorithms were used to calculate the test data of different samples to be tested. The calculation results are shown in Table 5.

[0079] Table 5 Processing results of different algorithms

[0080] Samples to be tested <![CDATA[f2 / GHz]]> <![CDATA[ε′ r ]]> <![CDATA[tanδ1]]> <![CDATA[tanδ2]]> cavity 1.4569 1.02 0.0002 0.0015 Fused Silica 1.4335 3.86 0.0005 0.0008 Boron nitride 1.4269 4.23 0.0018 0.0003 fiberglass 1.4232 5.30 0.0204 0.0205 Alumina 1.3999 9.38 0.0016 0.0019 sapphire 1.3927 10.12 0.0006 0.0012

[0081] Where tan δ1 is the test result obtained using the improved algorithm proposed in this invention, and tan δ2 is the test result obtained using the perturbation algorithm used in the existing test method. The three test samples, fused quartz, fiberglass, and alumina, were also used as reference samples. Their reference values ​​are given in Table 1 in Example 1.

[0082] From the data in the comparison table, it can be seen that for an open coaxial resonant cavity, the perturbation algorithm used in the existing test method only has a certain accuracy for the loss tangent near the dielectric constant of the reference sample. If the dielectric constant of the material to be tested deviates from the reference sample, the test accuracy of the loss tangent will also decrease accordingly; the improved algorithm proposed in the present invention has a better test range for material loss than the existing algorithm, and its loss tangent test results are more accurate.

[0083] 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 method for testing dielectric properties of materials under multi-physical field coupling, characterized in that: The following steps are involved: Step 1: Measure the resonant frequency f0 and quality factor Q0 of the TEM mode of the open coaxial cavity in the cavity state; Step 2: Place a reference sample of the same thickness as the sample to be tested at the open end of the open coaxial cavity, measure the resonant frequency f1 and quality factor Q1 of the TEM mode of the open coaxial cavity when the reference sample k1 is loaded, and then replace the reference sample. Test the resonant frequency and quality factor of each reference sample until the mth reference sample k1 is loaded. m , measure the resonant frequency f m and quality factor Q m ; Step 3: Place the sample under test at the open end of the open coaxial cavity and apply a multi-physics field to the sample. After the applied multi-physics field stabilizes, measure the resonant frequency f and quality factor Q of the TEM mode of the open coaxial cavity under the loaded sample. Step 4: Based on the m+2 sets of measurement data obtained in steps 1, 2, and 3, calculate the relative complex dielectric constant ε of the sample to be tested. r , the calculation process is as follows: Step 4.

1. For the TEM mode, the following equation is obtained based on the perturbation method: Among them, ε r is the relative complex permittivity, ε' r is the relative dielectric constant, tanδ is the loss tangent, j is the imaginary part, ε0 is the vacuum dielectric constant, △f=f0-f s , f s f m or f, Q s Q m or Q, {a m } and {b m } is the calibration coefficient; Step 4.

2. Load the measurement data f0 under the cavity state and the measurement data {f m }, and the relative dielectric constant ε' of the reference sample rm Substituting into equation (2), we get m equations, which are solved together to obtain the calibration coefficients {a m }; Step 4.

3. Load the measurement data of the reference sample state {f m } and {Q m }, relative dielectric constant ε' of the reference sample rm and loss tangent tanδ m , and the obtained calibration coefficient {a m Substituting into equation (3), we get m equations, which are solved together to obtain the ideal quality factor of the TEM mode {Q 0sm }; Step 4.

4. Load the measured data f0 and Q0 in the cavity state with the measured data {f m }, and the ideal quality factor of the TEM mode obtained in step 4.3 {Q 0sm }Substitute into equation (4), and we get m+1 equations, which are solved together to obtain the calibration coefficients {b m }; Step 4.

5. Load the measured data f0 in the cavity state with the resonant frequency f and quality factor Q of the sample to be tested, as well as the obtained calibration coefficient {a m } and {b m }, and substitute into equations (1) to (4), the relative complex dielectric constant ε of the sample to be tested can be calculated. r .

2. The material dielectric property testing method under multi-physical field coupling according to claim 1, characterized in that: The relative permittivity and loss tangent of the reference sample were extracted using the high-Q cavity method.

3. The material dielectric property testing method under multi-physical field coupling according to claim 2, characterized in that: The number of reference samples should be no less than 3, and their relative dielectric constants should be at least in the range of 2 to 4, 4 to 8, and 8 to 12, respectively, and their loss tangents should be at least in the range of 10 -4 , 10 -3 and 10 -2 Magnitude.

4. A testing device suitable for the material dielectric property testing method under multi-physical field coupling according to any one of claims 1 to 3, characterized in that: Includes dielectric performance test module and multi-physics field loading module; The dielectric performance test module includes a first vector network analyzer and an open coaxial cavity; the multi-physics field loading module includes a microwave field loading submodule, an electrostatic field loading submodule, a static magnetic field loading submodule, a temperature field loading submodule and a pressure field loading submodule; wherein the microwave field loading submodule includes a second vector network analyzer, a power amplifier, a coupler, a DC block and a band-stop filter; the electrostatic field loading submodule includes a DC source and a metal sample stage; the static magnetic field loading submodule includes an electromagnet; the temperature field loading submodule includes a temperature controller, a heating element and a thermally conductive insulating box; the pressure field loading submodule includes a pressure gauge, a pressure sensor, a spring array, a transition support, a lifting platform, an insulating connecting column and a system bracket; The system bracket includes a bottom plate, a top plate, and a column fixedly connecting the bottom plate and the top plate; an insulating connecting column, an open coaxial cavity, a metal sample stage, a heating element, a spring array, a pressure sensor, and a lifting platform are arranged on the bottom plate in order from top to bottom, and the other end of the insulating connecting column is fixedly connected to the top plate; the sample to be tested is placed on the metal sample stage and is located at the open end of the open coaxial cavity; the pressure gauge is connected to the pressure sensor to display the loaded pressure value; the electromagnet is symmetrically placed on both sides of the sample to be tested so that the sample to be tested is located in the static magnetic field action area of ​​the electromagnet; The open coaxial cavity includes an inner conductor and an outer conductor coaxially arranged with the inner conductor, one end of which is short-circuited and the other end is open-circuited. Two coupling ports are symmetrically arranged on the side wall of the outer conductor near the short-circuit surface of the open coaxial cavity, and a feed port is arranged near the middle of the outer conductor side wall. At the same time, four circumferentially symmetrical gaps are set through the side wall of the outer conductor. A first water cooling passage is provided on the side wall of the outer conductor near the open-circuit end to protect the open coaxial cavity. The two ports of the first vector network analyzer are connected to the two coupling ports via a band-stop filter and a DC block, respectively; the first port of the second vector network analyzer is connected to a power amplifier, a coupler, and a first DC block in sequence, and then to the feed port of the open coaxial cavity, wherein the output end of the power amplifier is connected to the output end of the coupler, the first DC block is connected to the input end of the coupler, and the second port of the second vector network analyzer is connected to the coupling end of the coupler; The positive pole of the DC source is connected to the metal sample stage, and the negative pole is grounded and connected to the outer conductor of the open coaxial cavity; the metal sample stage is embedded in the heating element, and a heat-conducting insulating box is provided between the metal sample stage and the heating element to insulate the metal sample stage and the heating element; a heating rod is embedded in the side of the heating element, and after the heating rod is heated, it heats the sample to be tested through heat conduction; a thermocouple is provided on the metal sample stage for detecting the temperature of the sample to be tested.

5. The testing device according to claim 4, wherein: The coupling port adopts a ring weak coupling structure, and its S21 should be less than -50dB; the feeding port adopts a probe strong coupling structure, and its S11 should be less than -10dB.

6. The testing device according to claim 4, wherein: The specific location of the feeding port is determined by the field distribution of the TEM resonance mode corresponding to the feeding frequency.

7. The testing device according to claim 4, wherein: The metal sample table is made of high-temperature alloy and is "T"-shaped as a whole, with the bottom embedded in a thermally conductive insulating box; the heating element is made of high-temperature alloy and has a groove structure on the top for supporting the thermally conductive insulating box, and the bottom is connected and fixed to the transition support; the top of the transition support has a second water-cooling passage for thermally isolating the pressure-loading submodule below.

8. The testing device according to claim 4, wherein: The spring array consists of six screws with springs and a chassis. The screws pass through the through holes at the bottom of the transition pillar from top to bottom and are fixed on the chassis.

9. The testing device according to claim 4, wherein: The frequency of the output signal of the second vector network analyzer is within the stop band of the band stop filter.

10. The testing device according to claim 4, wherein: The DC block and band-stop filter are only connected when the microwave field is loaded. At this time, the frequency of the output signal of the second vector network analyzer should be near the resonant frequency of one of the n TEM modes of the open coaxial cavity under the load of the sample to be tested. When a high-power microwave field is loaded, the first vector network analyzer test needs to skip this TEM mode to avoid the impact of the injected high-power signal on the test signal. Among them, a certain mode depends on the microwave field loading frequency requirements.

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