CN114487618B - Composite material low-frequency electromagnetic parameter equivalent extraction device and method - Google Patents

Abstract

The invention discloses a composite material low-frequency electromagnetic parameter equivalent extraction device and a method, and the composite material low-frequency electromagnetic parameter equivalent extraction device comprises a support module, a signal transceiving module and a data processing module; the supporting module is used for clamping the material to be detected; the signal receiving and transmitting module is used for transmitting electromagnetic wave signals for testing, the transmitted signals are received by the signal transmitting module after passing through a material to be tested clamped by the supporting module in a testing environment, and the received signals are used as testing results and transmitted to the data processing module; and the data processing module is used for calculating by using the data obtained by the test and converting the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be tested. The invention can equivalently extract a low-frequency sweep frequency test result, and simultaneously reduces the influence of background noise on the test result and improves the test precision by adding wave-absorbing materials, reducing fields and the like in a test environment.

Description

A device and method for equivalent extraction of low-frequency electromagnetic parameters of composite materials

technical field

The invention relates to electromagnetic parameter extraction, in particular to an equivalent extraction device and method for low-frequency electromagnetic parameters of composite materials.

Background technique

The demand for weight reduction and efficiency enhancement in the development of various types of aircraft has made the extensive use of composite materials a major trend. Foreign aircraft have used a large number of composite structures instead of metal structures. With the extensive use of composite materials in aircraft, the increasingly complex electromagnetic environment in the flight space poses a serious threat to the work of onboard electronic equipment. The outside of the fuselage is a skin structure made of composite materials. Inside the skin, the cables on the aircraft are generally laid close to the bulkhead structure for the convenience of fixing and other considerations, and the wiring is close to the composite material skin. In addition to its own shielding, the electromagnetic shielding performance of the cable mainly comes from the composite material structure. At the same time, a large number of key electronic equipment in the aircraft are placed under the deck on the lower side of the cabin, and there is generally no other shielding structure between the equipment and the fuselage skin. There are a large number of devices and components on the aircraft that are sensitive to low-frequency interference. Whether such devices and components can work normally will have a huge impact on flight safety. Therefore, the fuselage composite material structure is the main source of electromagnetic shielding for various electronic equipment on the aircraft, and its electromagnetic shielding performance is facing severe tests. It is urgent to carry out the electromagnetic shielding performance analysis of the fuselage composite material structure. It is difficult to comprehensively test the electromagnetic shielding performance of composite materials with the existing test methods. It is necessary to conduct comprehensive and detailed tests on the electromagnetic parameters of the composite materials used to obtain their complex permittivity and complex permeability.

Existing methods for measuring electromagnetic parameters of composite materials include resonant cavity method and free space method. The resonant cavity method uses a fixed resonator to measure the electromagnetic parameters of the material. During the test, the resonant frequency and quality factor Q of the resonant cavity are recorded without the material to be tested in the cavity resonator and after the material to be tested is placed, and the composite is obtained. The influence of the placement of the material on the working state of the resonator cavity, and then the electromagnetic parameters of the material to be measured are calculated by using the principle of computational electromagnetics. On the one hand, since the resonant frequency of the resonator is related to the size of the cavity, which is an inherent property of the resonator itself, testing at different frequencies using the resonator method can only be accomplished by frequently replacing resonators of different sizes; The resonant frequency of the cavity decreases with the increase of the cavity size, so it is difficult to test the low-frequency electromagnetic parameters of the composite material by the resonant cavity method. The free space method is an electromagnetic parameter testing method based on the transmission line theory. The composite material is placed in the test fixture or between the antennas in the free space of the microwave anechoic chamber, and the complex reflection parameters and complex transmission in the test environment are measured by the vector network analyzer. parameters, and then calculate the electromagnetic parameters of the material on this basis.

When carrying out the test in the frequency band above 1GHz (hereinafter referred to as high frequency), because the test frequency band is high, the electromagnetic wave wavelength is small, the antenna main lobe width is narrow, and the beam is more concentrated, so a smaller venue can be used to carry out the frequency sweep test. When testing the frequency band below 1GHz (hereinafter referred to as low frequency), on the one hand, in order to ensure that the test antenna works in the far-field range, it is necessary to have a large distance between the antenna and the material to be tested, resulting in a large test site size, and the test is carried out. It is more difficult. Although the traditional microwave anechoic chamber test method has a small site size, the frequency sweep test cost is relatively high when the frequency band below 1GHz is tested. Generally, the point frequency test is used for simple performance verification, and it is difficult to obtain the sweep frequency test results. Low-Frequency Electromagnetic Parameters Low-frequency testing brings many changes.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide an equivalent extraction device and method for low-frequency electromagnetic parameters of composite materials, which can equivalently extract low-frequency sweep test results, and at the same time, in the test environment by adding wave absorbing materials, Reducing the site and other methods reduces the influence of background noise on the test results and improves the test accuracy.

The object of the present invention is achieved through the following technical solutions: an equivalent extraction device for low-frequency electromagnetic parameters of composite materials, comprising a support module, a signal transceiver module and a data processing module;

The support module is used for clamping the material to be tested;

The signal transceiver module is used to transmit electromagnetic wave signals for testing. After the transmitted signal passes through the material to be tested clamped by the support module in the test environment, it is then received by the signal transceiver module, and the received signal is transmitted to the test result as the test result. data processing module;

The data processing module is used to perform calculation using the data obtained from the test, and convert the calculation result into an equivalent extraction result of low-frequency electromagnetic parameters of the material to be tested.

Further, the supporting module includes a non-metallic supporting plate, and a square shielding window is opened in the center of the non-metallic supporting plate;

One side of the non-metallic support plate faces the transmitting antenna of the signal transceiver module, and this side is provided with a flange clamp surrounding the square shielding window. The flange clamp is made of non-metallic material and has a size larger than a square The shielding window is used to attach the material to be tested to the non-metallic support plate and make the material to be tested closely fit the plane of the flat plate;

The side of the non-metallic support plate where the flange fixture is located is covered with pyramid wave absorbing material, and the working frequency range of the pyramid wave absorbing material covers the test frequency band, so that the electromagnetic wave emitted by the signal transceiver module cannot penetrate the non-metallic support plate ;

The bottom of the non-metallic supporting plate is provided with two non-metallic beams, and each non-metallic beam is connected with a set of universal wheels to facilitate the movement and rotation of the supporting module, so that the device has the ability to develop the material to be tested and face electromagnetic waves in different directions. The capability of equivalent extraction of low-frequency electromagnetic parameters under incident conditions.

Further, the support module further includes a laser collimator, which is used to establish a laser plane in space for calibration, so as to ensure that the square shielding window is consistent with the center height of the receiving antenna and the transmitting antenna in the signal transceiver module.

Further, the signal transceiver module includes a receiving antenna, a transmitting antenna and a vector network analyzer; the receiving antenna is in the form of a horn antenna, the transmitting antenna is used to transmit electromagnetic wave signals for testing, and the receiving antenna is used to receive the transmitted signal through the test environment. generated signal;

The vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display. The transmitting antenna and the receiving antenna are connected to the two ports of the dual-port vector network analyzer using coaxial cables, respectively. The transmitter port of the instrument is It is connected with the transmitting antenna to output the transmitting signal, and the receiving port is connected with the receiving antenna to measure the field strength and phase of the electromagnetic signal it receives, and at the same time, the vector network display screen is used to display the test results in real time;

When arranging the receiving antenna and the transmitting antenna, it is necessary to ensure that the center of the antenna is aligned with the center of the square shielding window, and adjust the layout position of the antenna and the distance between the antenna and the shielding window, so that the width of the main lobe of the antenna pattern in the test frequency band is kept within the shielding window. The side lobe radiation is not within the range of the shielding window and is absorbed by the corner cone absorbing material.

Further, the data processing module includes a data processing computer, and the data processing computer is connected to the vector network through a data transmission line, reads the test data therein, and uses the test data for calculation, and converts the calculation results into the low-frequency electromagnetic parameters of the material to be tested. Equivalent extraction results.

An equivalent extraction method for low-frequency electromagnetic parameters of composite materials, comprising the following steps:

S1. Complete the layout according to the test placement requirements of transmission parameters and reflection parameters;

S2. Start the test of the tested material;

S3. Carry out test data analysis; export the data obtained from the test to the data processing computer, and the data processing computer will analyze and process, and convert the calculation results into the equivalent extraction results of low-frequency electromagnetic parameters of the material to be tested.

Wherein, the step S1 includes:

When testing the reflection parameters, the transmitting antenna and the receiving antenna are arranged on the side of the flat support structure covering the wave absorbing material. The two antennas are arranged in mirror symmetry on the normal plane of the center of the flat support structure, and the center is at the same height as the center of the shielding window on the support structure. Working in the far-field range, the distance between the antenna and the shielding window is 0.6m; the vector network analyzer and the data processing computer are arranged behind the two antennas;

When testing transmission parameters, the transmitting antenna and the receiving antenna are arranged on both sides of the flat support structure, and the two antennas are placed opposite each other. It is arranged on the side of the flat support structure, and the distance from the edge of the flat support is not less than 0.3m to avoid the fluctuation of the test results caused by the electromagnetic emission of the vector network and the data processing computer itself and the movement of the testers during the test.

Wherein, the step S2 includes:

S201. Calibrate the test device: use the vector network analyzer calibration function to complete the dual-port open-circuit, short-circuit, and load calibration, and complete the path calibration between the two ports to eliminate the system error in the test process;

S202. Carry out the transmission parameter test between the two antenna ports when the shielding window is not equipped with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency transmission parameter test result is expressed as S21_W_H. The transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is installed. The low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The test result of the low-frequency transmission parameter is expressed as S21_W_L. Transmission parameters measured at each low frequency point and frequency point when the material to be tested is installed; the transmission parameter measurement results retain the amplitude and phase;

S203. Carry out the transmission parameter test between the two antenna ports when the material to be tested is installed on the shielding window. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency transmission parameter test result is expressed as S21_C_H. The transmission parameters measured at each high-frequency sweep frequency point when measuring materials; the low-frequency point-frequency test conducts point-frequency tests for the key working frequency points of the material to be tested, and the low-frequency transmission parameter test results are expressed as S21_C_L. Transmission parameters measured at each low frequency point and frequency points when measuring materials, among which, the transmission parameter measurement results retain the amplitude and phase;

S204. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with a metal plate. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency reflection parameter test result is expressed as S11_W_H. The test result includes the addition of the metal plate. The reflection parameters measured at each high-frequency sweep frequency point; the low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The low-frequency reflection parameter test result is expressed as S11_W_L, and the test result includes the installation of the metal plate. Reflection parameters measured at each low frequency point and frequency point, among which, the reflection parameter measurement results retain the amplitude and phase;

S205. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency reflection parameter test result is expressed as S11_C_H. The reflection parameters measured at each high-frequency sweep frequency point when measuring materials; the low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The reflection parameter measured at each low frequency point and frequent point of the material to be tested, wherein the reflection parameter measurement result retains the amplitude and phase.

The step S3 includes:

S301. Carry out test data analysis; export the data obtained from the test to the data processing computer, use the time-domain gate method to filter out clutter, noise floor and the interference caused by the coupling between the transmitting and receiving antennas, and obtain the high-frequency transmission parameters of the material to be tested S _{21_H} , Measurement results of the high frequency reflection parameter S _{11_H} , the low frequency transmission parameter S _{21_L} and the low frequency reflection parameter S _{11_L} :

S _{21_H} =S _{21_W_H} -S _{21_C_H} , S _{11_H} =S _{11_W_H} -S _{11_C_H}

S _{21_L} =S _{21_W_L} -S _{21_C_L} , S _{11_L} =S _{11_W_L} -S _{11_C_L}

Among them, the subtraction in the calculation process of the measurement result refers to the subtraction of the corresponding test results under each frequency point;

S302. Derive the way to calculate the electromagnetic parameters of the material from the scattering parameters:

Suppose the scattering parameters of the material include the transmission parameter S ₂₁ and the reflection parameter S ₁₁ , and the relationship between the scattering parameter and the material reflection coefficient and transmission coefficient is expressed as follows:

where Γ and z are the reflection coefficient and transmission coefficient when the electromagnetic wave is incident on the surface of the material to be measured, respectively;

The equivalent electromagnetic parameters of the material in the corresponding frequency band are calculated based on the NRW method; the reflection coefficient and transmission coefficient in the scattering parameter expression are related to the electromagnetic parameters of the material, which are specifically expressed as:

where μ _r and ε _r are the relative permittivity and relative permeability of the material to be measured, respectively, and d is the thickness of the material to be measured, from which the equivalent electromagnetic parameters of the material are calculated:

in:

S303. Under each high-frequency sweep frequency point, take the corresponding measurement result in S _{21_H} as S ₂₁ , take the corresponding measurement result in S _{11_H} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate high-frequency sweep electromagnetic parameters μ _{r_H} , ε _{r_H} ; where μ _{r_H} includes the relative permittivity μ _r calculated at each high-frequency sweep frequency point; ε _{r_H} includes each high-frequency sweep frequency Calculated relative permeability ε _r under the point;

At the same time, at each low frequency point and frequency point, the corresponding measurement result in S _{21_L} is taken as S ₂₁ , and the corresponding measurement result in S _{11_L} is taken as S ₁₁ , and brought into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate low-frequency point-frequency electromagnetic parameters μ _{r_L} , ε _{r_L} ; where μ _{r_L} contains the relative permittivity μ _r calculated at each low-frequency point and frequency point; ε _{r_L} contains the calculated value at each low-frequency point and frequency point The relative permeability ε _r ;

S304. Carry out the calculation of the electromagnetic parameters of the material to be tested; pre-set the material, structure and laying method of each layer of the composite material to be tested, equate the constituent materials of the material to be tested individually into a uniform dielectric layer, and calculate the i-th layer when the electromagnetic wave is incident. The transfer matrix T _i of the medium:

In the formula, n _i and _zi are the refractive index and impedance of the material of the i-th layer under the incident electromagnetic wave; k is the known wave number; d is the thickness of the medium of the i-th layer; the overall transfer matrix T of the material to be tested can be used _Multiplying the transfer matrix of each layer of the medium itself and the interlayer loss Pi can be obtained:

T=∑T _i P _i

The interlayer loss is difficult to obtain directly by measurement, and itself changes with the frequency, which is represented by a frequency curve; therefore, it is first considered that the electromagnetic wave has no loss in the case of interlayer transmission, and P _i = 1 is used to substitute the following two formulas for preliminary calculation to obtain the material The pre-evaluated scattering parameters of :

S305. Take the corresponding measurement result in _{S21_forecast} as _S21 and the corresponding measurement result in _{S11_forecast} as _S11 at each frequency point above 1 GHz of the frequency change curve, and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated high-frequency swept electromagnetic parameters μ _{r_forecast_H} , ε _{r_forecast_H} ; where μ _{r_forecast_H} includes the relative permittivity μ _r calculated at each frequency point above 1 GHz of the frequency curve; ε _{r_forecast_H} Including the relative permeability ε _r calculated at each frequency point above 1GHz of the frequency curve;

At the same time, at each frequency point below 1 GHz of the frequency change curve, take the corresponding measurement result in S _{21_forecast} as S ₂₁ , take the corresponding measurement result in S _{11_forecast} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated low-frequency swept electromagnetic parameters μ _{r_forecast_L} , ε _{r_forecast_L} ; where μ _{r_forecast_L} includes the relative permittivity μ _r calculated at each frequency point below 1 GHz of the frequency curve; ε _{r_forecast_L} includes The relative permeability ε _r calculated at each frequency point below 1 GHz of the frequency curve;

The interlayer loss P _i curve is adjusted so that the calculation results μ _{r_forecast_H} and ε _{r_forecast_H} of the equivalent electromagnetic parameters of the high frequency sweep pre-evaluation are consistent with the test results μ _{r_H} and ε _{r_H} of the high frequency sweep equivalent electromagnetic parameters, and the low frequency sweep pre-evaluation The equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} are consistent with the low frequency point frequency equivalent electromagnetic parameter test results μ _{r_L} and ε _{r_L} at the low frequency test frequency; The difference is less than the set threshold;

The low-frequency sweep pre-evaluation equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} at this time are used as the equivalent extraction results of the low-frequency electromagnetic parameters.

The beneficial effects of the present invention are as follows: the present invention can carry out tests without using a large-scale microwave anechoic chamber to obtain the frequency sweep test results of the low-frequency electromagnetic parameters of composite materials. The computational electromagnetic method realizes the equivalent extraction of low-frequency electromagnetic parameters of materials, which reduces the requirements for the test environment; at the same time, the test environment is optimized, and the background noise is reduced by adding absorbing materials and reducing the site in the test environment. The influence of the test results improves the test accuracy.

Description of drawings

Figure 1 is a schematic diagram of the arrangement of the device in the case of measuring the reflection parameters of the composite material;

Figure 2 is a schematic diagram of the arrangement of the device under the condition of measuring the transmission parameters of the composite material;

Figure 3 is a flowchart of the equivalent extraction of low-frequency electromagnetic parameters of composite materials.

Detailed ways

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

As shown in Figures 1-2, an equivalent extraction device for low-frequency electromagnetic parameters of composite materials includes a support module, a signal transceiver module and a data processing module;

The support module is used for clamping the material to be tested;

The signal transceiver module is used to transmit electromagnetic wave signals for testing. After the transmitted signal passes through the material to be tested clamped by the support module in the test environment, it is then received by the signal transceiver module, and the received signal is transmitted to the test result as the test result. data processing module;

The data processing module is used to perform calculation using the data obtained from the test, and convert the calculation result into an equivalent extraction result of low-frequency electromagnetic parameters of the material to be tested.

Further, the support module mainly includes a flat plate support structure covered with a wave absorbing material on one side, the module includes a non-metallic support plate 1, and a square shielding window 2 is opened in the center of the non-metallic support plate 1, the size of the window is greater than 0.6m, and the center of the window is away from the ground. 1m, and the window border is 0.5m away from the border of the plate support. One side of the non-metallic support plate faces the transmitting antenna of the signal transceiver module, and this side is provided with a flange clamp 3 surrounding the square shielding window, the clamp is made of non-metallic material, and the size is slightly larger than the square shielding window 2. It is used to add the material to be tested on the non-metallic support plate 1 and to make the material to be tested closely fit with the plane of the flat plate. The side of the non-metallic support plate where the flange fixture is located is covered with a pyramid wave absorbing material 4, and the working frequency range of the pyramid wave absorbing material covers the test development frequency band, so that the electromagnetic wave emitted by the signal transceiver module cannot penetrate the non-metallic support. Plate 1. Two non-metallic beams 5 are installed at the bottom of the non-metallic support plate 1, which are respectively connected with the two sets of universal wheels 6, so that the support module can be moved and rotated conveniently, so that the device can carry out the test material under the condition of electromagnetic waves incident in different directions. The capability of equivalent extraction of low-frequency electromagnetic parameters. A laser calibrator 7 is arranged outside the bracket. The instrument establishes a laser plane in space for calibration, so that the center height of the square shielding window 2 and the receiving antenna and the transmitting antenna in the signal transceiver module are consistent, so as to reduce the test caused by the dislocation of the antenna. Signal loss, improve test accuracy;

Further, the signal transceiver module includes a receiving antenna, a transmitting antenna and a vector network analyzer; the receiving antenna is in the form of a horn antenna, the transmitting antenna is used to transmit electromagnetic wave signals for testing, and the receiving antenna is used to receive the transmitted signal through the test environment. generated signal;

The vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display. The transmitting antenna and the receiving antenna are connected to the two ports of the dual-port vector network analyzer using coaxial cables, respectively. The transmitter port of the instrument is It is connected with the transmitting antenna to output the transmitting signal, and the receiving port is connected with the receiving antenna to measure the field strength and phase of the electromagnetic signal it receives, and at the same time, the vector network display screen is used to display the test results in real time;

When arranging the receiving antenna and the transmitting antenna, it is necessary to ensure that the center of the antenna is aligned with the center of the square shielding window, and adjust the layout position of the antenna and the distance between the antenna and the shielding window, so that the width of the main lobe of the antenna pattern in the test frequency band is kept within the shielding window. The side lobe radiation is not within the range of the shielding window and is absorbed by the corner cone absorbing material.

Further, the data processing module includes a data processing computer, and the data processing computer is connected to the vector network through a data transmission line, reads the test data therein, and uses the test data for calculation, and converts the calculation results into the low-frequency electromagnetic parameters of the material to be tested. Equivalent extraction results.

As shown in Figure 3, a method for equivalent extraction of low-frequency electromagnetic parameters of composite materials includes the following steps:

S1. Complete the layout according to the test placement requirements of transmission parameters and reflection parameters;

S2. Start the test of the tested material;

S3. Carry out test data analysis; export the data obtained from the test to the data processing computer, and the data processing computer will analyze and process, and convert the calculation results into the equivalent extraction results of low-frequency electromagnetic parameters of the material to be tested.

Wherein, the step S1 includes:

When testing the reflection parameters, the transmitting antenna and the receiving antenna are arranged on the side of the flat support structure covering the wave absorbing material. The two antennas are arranged in mirror symmetry on the normal plane of the center of the flat support structure, and the center is at the same height as the center of the shielding window on the support structure. Working in the far-field range, the distance between the antenna and the shielding window is 0.6m; the vector network analyzer and the data processing computer are arranged behind the two antennas;

When testing transmission parameters, the transmitting antenna and the receiving antenna are arranged on both sides of the flat support structure, and the two antennas are placed opposite each other. It is arranged on the side of the flat support structure, and the distance from the edge of the flat support is not less than 0.3m to avoid the fluctuation of the test results caused by the electromagnetic emission of the vector network and the data processing computer itself and the movement of the testers during the test.

Wherein, the step S2 includes:

S201. Calibrate the test device: use the vector network analyzer calibration function to complete the dual-port open-circuit, short-circuit, and load calibration, and complete the path calibration between the two ports to eliminate the system error in the test process;

S202. Carry out the transmission parameter test between the two antenna ports when the shielding window is not installed with the material to be tested, and the starting frequency of the high-frequency sweep test frequency band is above 1GHz (currently, it is considered that the actual test frequency band can be adjusted according to user needs and test environment, but To ensure that it is above 1GHz, for example, the specific test frequency band is tested with a continuous frequency of 1GHz-8GHz). During the process, the frequency of the low frequency test points covers 1MHz-1GHz, and 20 test frequency points are distributed with equal steps in the middle), the low frequency transmission parameter test result is expressed as S21_W_L, and the transmission parameter measurement result retains the amplitude and phase;

S203. Carry out the transmission parameter test between the two antenna ports when the shielding window is installed with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the test result of the high-frequency transmission parameter is expressed as S21_C_H. The low-frequency point-frequency test is for the material to be tested. The key working frequency points carry out point frequency test, the low frequency transmission parameter test result is expressed as S21_C_L, and the transmission parameter measurement result retains the amplitude and phase;

S204. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with a metal plate. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency reflection parameter test result is expressed as S11_W_H. The low-frequency point-frequency test focuses on the material to be tested. The point-frequency test is carried out at the working frequency, the low-frequency reflection parameter test result is expressed as S11_W_L, and the reflection parameter measurement result retains the amplitude and phase;

S205. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the test result of the high-frequency reflection parameter is expressed as S11_C_H. The low-frequency point-frequency test is for the material to be tested. The key working frequency points carry out point-frequency test, the low-frequency reflection parameter test result is expressed as S11_C_L, and the reflection parameter measurement result retains the amplitude and phase.

The step S3 includes:

S301. Carry out test data analysis; export the data obtained from the test to the data processing computer, use the time-domain gate method to filter out clutter, noise floor and the interference caused by the coupling between the transmitting and receiving antennas, and obtain the high-frequency transmission parameters of the material to be tested S _{21_H} , Measurement results of the high frequency reflection parameter S _{11_H} , the low frequency transmission parameter S _{21_L} and the low frequency reflection parameter S _{11_L} :

S _{21_H} =S _{21_W_H} -S _{21_C_H} , S _{11_H} =S _{11_W_H} -S _{11_C_H}

S _{21_L} =S _{21_W_L} -S _{21_C_L} , S _{11_L} =S _{11_W_L} -S _{11_C_L}

Among them, the subtraction in the calculation process of the measurement result refers to the subtraction of the corresponding test results under each frequency point;

S302. Derive the way to calculate the electromagnetic parameters of the material from the scattering parameters:

Suppose the scattering parameters of the material include the transmission parameter S ₂₁ and the reflection parameter S ₁₁ , and the relationship between the scattering parameter and the material reflection coefficient and transmission coefficient is expressed as follows:

where Γ and z are the reflection coefficient and transmission coefficient when the electromagnetic wave is incident on the surface of the material to be measured, respectively;

The equivalent electromagnetic parameters of the material in the corresponding frequency band are calculated based on the NRW method; the reflection coefficient and transmission coefficient in the scattering parameter expression are related to the electromagnetic parameters of the material, which are specifically expressed as:

where μ _r and ε _r are the relative permittivity and relative permeability of the material to be measured, respectively, and d is the thickness of the material to be measured, from which the equivalent electromagnetic parameters of the material are calculated:

in:

S303. Under each high-frequency sweep frequency point, take the corresponding measurement result in S _{21_H} as S ₂₁ , take the corresponding measurement result in S _{11_H} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate high-frequency sweep electromagnetic parameters μ _{r_H} , ε _{r_H} ; where μ _{r_H} includes the relative permittivity μ _r calculated at each high-frequency sweep frequency point; ε _{r_H} includes each high-frequency sweep frequency Calculated relative permeability ε _r under the point;

At the same time, at each low frequency point and frequency point, the corresponding measurement result in S _{21_L} is taken as S ₂₁ , and the corresponding measurement result in S _{11_L} is taken as S ₁₁ , and brought into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate low-frequency point-frequency electromagnetic parameters μ _{r_L} , ε _{r_L} ; where μ _{r_L} contains the relative permittivity μ _r calculated at each low-frequency point and frequency point; ε _{r_L} contains the calculated value at each low-frequency point and frequency point The relative permeability ε _r ;

S304. Carry out the calculation of the electromagnetic parameters of the material to be tested; pre-set the material, structure and laying method of each layer of the composite material to be tested, equate the constituent materials of the material to be tested individually into a uniform dielectric layer, and calculate the i-th layer when the electromagnetic wave is incident. The transfer matrix T _i of the medium:

In the formula, n _i and _zi are the refractive index and impedance of the material of the i-th layer under the incident electromagnetic wave; k is the known wave number; d is the thickness of the medium of the i-th layer; the overall transfer matrix T of the material to be tested can be used _Multiplying the transfer matrix of each layer of the medium itself and the interlayer loss Pi can be obtained:

T=ΣT _i P _i

The interlayer loss is difficult to obtain directly by measurement, and itself changes with the frequency, which is represented by a frequency curve; therefore, it is first considered that the electromagnetic wave has no loss in the case of interlayer transmission, and P _i = 1 is used to substitute the following two formulas for preliminary calculation to obtain the material The pre-evaluated scattering parameters of :

S305. Take the corresponding measurement result in _{S21_forecast} as _S21 and the corresponding measurement result in _{S11_forecast} as _S11 at each frequency point above 1 GHz of the frequency change curve, and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated high-frequency swept electromagnetic parameters μ _{r_forecast_H} , ε _{r_forecast_H} ; where μ _{r_forecast_H} includes the relative permittivity μ _r calculated at each frequency point above 1 GHz of the frequency curve; ε _{r_forecast_H} Including the relative permeability ε _r calculated at each frequency point above 1GHz of the frequency curve;

At the same time, at each frequency point below 1 GHz of the frequency change curve, take the corresponding measurement result in S _{21_forecast} as S ₂₁ , take the corresponding measurement result in S _{11_forecast} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated low-frequency swept electromagnetic parameters μ _{r_forecast_L} , ε _{r_forecast_L} ; where μ _{r_forecast_L} includes the relative permittivity μ _r calculated at each frequency point below 1 GHz of the frequency curve; ε _{r_forecast_L} includes The relative permeability ε _r calculated at each frequency point below 1 GHz of the frequency curve;

The interlayer loss P _i curve is adjusted so that the calculation results μ _{r_forecast_H} and ε _{r_forecast_H} of the equivalent electromagnetic parameters of the high frequency sweep pre-evaluation are consistent with the test results μ _{r_H} and ε _{r_H} of the high frequency sweep equivalent electromagnetic parameters, and the low frequency sweep pre-evaluation The equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} are consistent with the low frequency point frequency equivalent electromagnetic parameter test results μ _{r_L} and ε _{r_L} at the low frequency test frequency; The difference is less than the set threshold;

The low-frequency sweep pre-evaluation equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} at this time are used as the equivalent extraction results of the low-frequency electromagnetic parameters.

To sum up, the present invention utilizes the flat support structure with absorbing material to simplify the test environment, and carries out the test to obtain the transmission and reflection parameter test results of the high-frequency sweep frequency and low-frequency point frequency of the material to be tested, and then outputs the test results to the data processing module. With known information such as composite material structure and composition material, use computational electromagnetics to calculate electromagnetic parameters to obtain the full-frequency electromagnetic shielding effectiveness calculation results of the material to be tested. After matching, the correction is carried out, and the equivalent extraction results of the low-frequency electromagnetic parameter sweep frequency test are obtained after matching. Compared with the existing device and method for testing the electromagnetic properties of composite materials, the device proposed by the present invention reduces the requirements for the testing environment, can simplify the testing environment for low-frequency electromagnetic parameter testing of composite materials, and effectively reduce the environmental interference for testing. The effect of precision.

The foregoing description shows and describes a preferred embodiment of the present invention, but as previously mentioned, it should be understood that the present invention is not limited to the form disclosed herein, and should not be construed as an exclusion of other embodiments, but may be used in various and other combinations, modifications and environments, and can be modified within the scope of the inventive concepts described herein, from the above teachings or from skill or knowledge in the relevant art. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all fall within the protection scope of the appended claims of the present invention.

Claims (9)

1. a composite material low-frequency electromagnetic parameter equivalent extraction device, is characterized in that: comprise support module, signal transceiver module and data processing module; The support module is used for clamping the material to be tested; The signal transceiver module is used to transmit electromagnetic wave signals for testing. After the transmitted signal passes through the material to be tested clamped by the support module in the test environment, it is then received by the signal transceiver module, and the received signal is transmitted to the test result as the test result. data processing module; The data processing module is used to perform calculation using the data obtained by the test, and convert the calculation result into the equivalent extraction result of low-frequency electromagnetic parameters of the material to be tested; The supporting module comprises a non-metallic supporting plate (1), and a square shielding window (2) is opened in the center of the non-metallic supporting plate (1); One side of the non-metallic supporting plate (1) faces the transmitting antenna of the signal transceiver module, and a flange clamp (3) surrounding the square shielding window (2) is arranged on the side, and the flange clamp ( 3) It is made of non-metallic material, and its size is larger than the square shielding window (2), which is used to add the material to be tested on the non-metallic support plate (1) and to make the material to be tested closely fit with the plane of the flat plate; The side where the flange fixture (3) of the non-metallic support plate (1) is located is covered with a pyramid wave absorbing material (4), and the working frequency range of the pyramid wave absorbing material covers the frequency range of the test, so that the signal transceiver module sends out The electromagnetic wave cannot penetrate the non-metallic supporting plate (1); The signal transceiver module includes a receiving antenna, a transmitting antenna and a vector network analyzer; when the receiving antenna and the transmitting antenna are arranged, it is necessary to ensure that the center of the antenna is aligned with the center of the square shielding window, and the layout position of the antenna and the distance from the shielding window are adjusted. , so that the main lobe width of the antenna pattern remains within the shielding window in the test frequency band, and the side lobe radiation is not within the shielding window and is absorbed by the corner cone absorbing material. 2. An equivalent extraction device for low-frequency electromagnetic parameters of composite materials according to claim 1, characterized in that: the bottom of the non-metallic support plate (1) is provided with two non-metallic beams (5), each non-metallic beam (5). The beams (5) are connected with a set of universal wheels (6) to facilitate the movement and rotation of the support module, so that the device has the ability to carry out the equivalent extraction of low-frequency electromagnetic parameters when the material to be tested faces the incidence of electromagnetic waves in different directions. 3. An equivalent extraction device for low-frequency electromagnetic parameters of composite materials according to claim 1, characterized in that: the support module further comprises a laser collimator (7) for establishing a laser plane in space for calibration, Make sure that the square shielding window (2) is at the same height as the center of the receiving antenna and the transmitting antenna in the signal transceiver module. 4. a kind of composite material low frequency electromagnetic parameter equivalent extraction device according to claim 1, is characterized in that: The receiving antenna is in the form of a horn antenna, the transmitting antenna is used to transmit the electromagnetic wave signal used for testing, and the receiving antenna is used to receive the signal generated by the transmitting signal through the test environment; The vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display. The transmitting antenna and the receiving antenna are connected to the two ports of the dual-port vector network analyzer using coaxial cables, respectively. The transmitter port of the instrument is It is connected to the transmitting antenna to output the transmitting signal, and the receiving port is connected to the receiving antenna to measure the field strength and phase of the electromagnetic signal it receives. At the same time, the vector network display screen is used to display the test results in real time. 5. The device for equivalent extraction of low-frequency electromagnetic parameters of composite materials according to claim 1, wherein the data processing module comprises a data processing computer, and the data processing computer is connected with a vector network analyzer through a data transmission line, and reads Take the test data, and use the test data to calculate, and convert the calculation results into the equivalent extraction results of low-frequency electromagnetic parameters of the material to be tested. 6. A method for equivalent extraction of low-frequency electromagnetic parameters of composite materials, based on the device according to any one of claims 1 to 5, characterized in that: comprising the following steps: S1. Complete the layout according to the test placement requirements of transmission parameters and reflection parameters; S2. Start the test of the tested material; S3. Carry out test data analysis; export the data obtained from the test to the data processing computer, and the data processing computer will analyze and process, and convert the calculation results into the equivalent extraction results of low-frequency electromagnetic parameters of the material to be tested. 7. The method for equivalent extraction of low-frequency electromagnetic parameters of composite materials according to claim 6, wherein the step S1 comprises: When testing the reflection parameters, the transmitting antenna and the receiving antenna are arranged on the side of the flat support structure covering the wave absorbing material. The two antennas are arranged in mirror symmetry on the normal plane of the center of the flat support structure, and the center is at the same height as the center of the shielding window on the support structure. Working in the far-field range, the distance between the antenna and the shielding window is 0.6m; the vector network analyzer and the data processing computer are arranged behind the two antennas; When testing transmission parameters, the transmitting antenna and the receiving antenna are arranged on both sides of the flat support structure, and the two antennas are placed opposite each other. It is arranged on the side of the flat support structure, and the distance from the edge of the flat support is not less than 0.3m to avoid the fluctuation of the test results caused by the electromagnetic emission of the vector network and the data processing computer itself and the movement of the testers during the test. 8 . The method for equivalently extracting low-frequency electromagnetic parameters of composite materials according to claim 6 , wherein the step S2 comprises: S201. Calibrate the test device; S202. Carry out the transmission parameter test between the two antenna ports when the shielding window is not equipped with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency transmission parameter test result is expressed as S21_W_H. The transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is installed. The low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The test result of the low-frequency transmission parameter is expressed as S21_W_L. Transmission parameters measured at each low frequency point and frequency point when the material to be tested is installed; the transmission parameter measurement results retain the amplitude and phase; S203. Carry out the transmission parameter test between the two antenna ports when the material to be tested is installed on the shielding window. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency transmission parameter test result is expressed as S21_C_H. The transmission parameters measured at each high-frequency sweep frequency point when measuring materials; the low-frequency point-frequency test conducts point-frequency tests for the key working frequency points of the material to be tested, and the low-frequency transmission parameter test results are expressed as S21_C_L. Transmission parameters measured at each low frequency point and frequency points when measuring materials, among which, the transmission parameter measurement results retain the amplitude and phase; S204. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with a metal plate. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency reflection parameter test result is expressed as S11_W_H. The test result includes the addition of the metal plate. The reflection parameters measured at each high-frequency sweep frequency point; the low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The low-frequency reflection parameter test result is expressed as S11_W_L, and the test result includes the installation of the metal plate. Reflection parameters measured at each low frequency point and frequency point, among which, the reflection parameter measurement results retain the amplitude and phase; S205. Carry out the reflection parameter test between the two antenna ports when the shielding window is equipped with the material to be tested. The starting frequency of the high-frequency sweep test frequency band is above 1GHz, and the high-frequency reflection parameter test result is expressed as S11_C_H. The reflection parameters measured at each high-frequency sweep frequency point when measuring materials; the low-frequency point-frequency test is carried out for the key working frequency points of the material to be tested. The reflection parameter measured at each low frequency point and frequent point of the material to be tested, wherein the reflection parameter measurement result retains the amplitude and phase. 9 . The method for equivalently extracting low-frequency electromagnetic parameters of composite materials according to claim 6 , wherein the step S3 comprises: S301. Carry out test data analysis; export the data obtained from the test to the data processing computer, use the time-domain gate method to filter out clutter, noise floor and the interference caused by the coupling between the transmitting and receiving antennas, and obtain the high-frequency transmission parameters of the material to be tested S _{21_H} , Measurement results of the high frequency reflection parameter S _{11_H} , the low frequency transmission parameter S _{21_L} and the low frequency reflection parameter S _{11_L} : S _{21_H} =S _{21_W_H} -S _{21_C_H} , S _{11_H} =S _{11_W_H} -S _{11_C_H} S _{21_L} =S _{21_W_L} -S _{21_C_L} , S _{11_L} =S _{11_W_L} -S _{11_C_L} Among them, the subtraction in the calculation process of the measurement result refers to the subtraction of the corresponding test results under each frequency point; S302. Derive the way to calculate the electromagnetic parameters of the material from the scattering parameters: Suppose the scattering parameters of the material include the transmission parameter S ₂₁ and the reflection parameter S ₁₁ , and the relationship between the scattering parameter and the material reflection coefficient and transmission coefficient is expressed as follows:

where Γ and z are the reflection coefficient and transmission coefficient when the electromagnetic wave is incident on the surface of the material to be measured, respectively; The equivalent electromagnetic parameters of the material in the corresponding frequency band are calculated based on the NRW method; the reflection coefficient and transmission coefficient in the scattering parameter expression are related to the electromagnetic parameters of the material, which are specifically expressed as:

where μ _r and ε _r are the relative permittivity and relative permeability of the material to be measured, respectively, and d is the thickness of the material to be measured, from which the equivalent electromagnetic parameters of the material are calculated:

in:

S303. Under each high-frequency sweep frequency point, take the corresponding measurement result in S _{21_H} as S ₂₁ , take the corresponding measurement result in S _{11_H} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate high-frequency sweep electromagnetic parameters μ _{r_H} , ε _{r_H} ; where μ _{r_H} includes the relative permittivity μ _r calculated at each high-frequency sweep frequency point; ε _{r_H} includes each high-frequency sweep frequency Calculated relative permeability ε _r under the point; At the same time, at each low frequency point and frequency point, the corresponding measurement result in S _{21_L} is taken as S ₂₁ , and the corresponding measurement result in S _{11_L} is taken as S ₁₁ , and brought into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain accurate low-frequency point-frequency electromagnetic parameters μ _{r_L} , ε _{r_L} ; where μ _{r_L} contains the relative permittivity μ _r calculated at each low-frequency point and frequency point; ε _{r_L} contains the calculated value at each low-frequency point and frequency point The relative permeability ε _r ; S304. Carry out the calculation of the electromagnetic parameters of the material to be tested; pre-set the material, structure and laying method of each layer of the composite material to be tested, equate the constituent materials of the material to be tested individually into a uniform dielectric layer, and calculate the i-th layer when the electromagnetic wave is incident. The transfer matrix T _i of the medium:

In the formula, n _i and _zi are the refractive index and impedance of the material of the i-th layer under the incident electromagnetic wave, respectively; k is the known wave number; d is the thickness of the medium of the i-th layer; the overall transfer matrix T of the material to be tested uses each _Multiplying the transfer matrix of the layer medium itself and the interlayer loss Pi can be obtained: T=ΣT _i P _i The interlayer loss is difficult to obtain directly by measurement, and itself changes with the frequency, which is represented by a frequency curve; therefore, it is first considered that the electromagnetic wave has no loss in the case of interlayer transmission, and P _i = 1 is used to substitute the following two formulas for preliminary calculation to obtain the material The pre-evaluated scattering parameters of :

S305. Take the corresponding measurement result in _{S21_forecast} as _S21 and the corresponding measurement result in _{S11_forecast} as _S11 at each frequency point above 1 GHz of the frequency change curve, and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated high-frequency swept electromagnetic parameters μ _{r_forecast_H} , ε _{r_forecast_H} ; where μ _{r_forecast_H} includes the relative permittivity μ _r calculated at each frequency point above 1 GHz of the frequency curve; ε _{r_forecast_H} Including the relative permeability ε _r calculated at each frequency point above 1GHz of the frequency curve; At the same time, at each frequency point below 1 GHz of the frequency change curve, take the corresponding measurement result in S _{21_forecast} as S ₂₁ , take the corresponding measurement result in S _{11_forecast} as S ₁₁ , and bring it into step S302 to calculate the corresponding μ _r , ε _r , so as to obtain the pre-evaluated low-frequency swept electromagnetic parameters μ _{r_forecast_L} , ε _{r_forecast_L} ; where μ _{r_forecast_L} includes the relative permittivity μ _r calculated at each frequency point below 1 GHz of the frequency curve; ε _{r_forecast_L} includes The relative permeability ε _r calculated at each frequency point below 1 GHz of the frequency curve; The interlayer loss P _i curve is adjusted so that the calculation results μ _{r_forecast_H} and ε _{r_forecast_H} of the equivalent electromagnetic parameters of the high frequency sweep pre-evaluation are consistent with the test results μ _{r_H} and ε _{r_H} of the high frequency sweep equivalent electromagnetic parameters, and the low frequency sweep pre-evaluation The equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} are consistent with the low frequency point frequency equivalent electromagnetic parameter test results μ _{r_L} and ε _{r_L} at the low frequency test frequency; The difference is less than the set threshold; The low-frequency sweep pre-evaluation equivalent electromagnetic parameter calculation results μ _{r_forecast_L} and ε _{r_forecast_L} at this time are used as the equivalent extraction results of the low-frequency electromagnetic parameters.

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