CN114487618A - Composite material low-frequency electromagnetic parameter equivalent extraction device and method - Google Patents
Composite material low-frequency electromagnetic parameter equivalent extraction device and method Download PDFInfo
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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 the low-frequency sweep frequency test result, and simultaneously reduces the influence of background noise on the test result and improves the test precision by increasing wave-absorbing materials, reducing fields and the like in the test environment.
Description
Technical Field
The invention relates to electromagnetic parameter extraction, in particular to a composite material low-frequency electromagnetic parameter equivalent extraction device and method.
Background
The weight reduction and efficiency increase requirements in the development process of various aircrafts make the use of composite materials in large quantities become a main trend. Foreign aircraft have largely used composite structures instead of metal structures. While aircraft use a large amount of composite materials, the increasingly complex electromagnetic environment within the flight space poses a serious threat to the operation of onboard electronic equipment. The fuselage outboard is a skin structure made of composite material. In the interior of the skin, cables on the aircraft are generally arranged closely to bulkhead structural members for convenience of fixation and the like, and routing lines are closely attached to the composite material skin. The electromagnetic shielding performance of the cable, in addition to its own shielding, is mainly derived from the composite material structure. Meanwhile, a large number of key electronic equipment in the aircraft is placed under the deck on the lower side in the cabin, and no other shielding structure is generally arranged between the equipment and the skin of the aircraft body. A large number of devices and components sensitive to low-frequency interference exist on the aircraft, and whether the devices and components can work normally or not has great influence on flight safety. Therefore, the fuselage composite material structure is used as a main electromagnetic shielding source for various electronic devices on the aircraft, the electromagnetic shielding performance of the fuselage composite material structure is subject to severe examination, and the analysis of the electromagnetic shielding performance of the fuselage composite material structure is urgently needed. The existing testing method is difficult to carry out comprehensive testing on the electromagnetic shielding performance of the composite material, and the electromagnetic parameters of the used composite material need to be tested comprehensively and thoroughly to obtain the complex dielectric constant and the complex magnetic permeability of the composite material.
The existing composite material electromagnetic parameter testing method comprises a resonant cavity method and a free space method. The resonant cavity method comprises the steps of utilizing a fixed resonator to measure electromagnetic parameters of materials, recording the change conditions of resonant frequency and quality factor Q of the resonant cavity after materials to be tested are not placed in the resonant cavity and the materials to be tested are placed in the resonant cavity in the testing process, obtaining the influence of the placement of the composite materials on the working state of the resonant cavity, and then utilizing the computational electromagnetism principle to calculate the electromagnetic parameters of the materials to be tested. On one hand, because the resonant frequency of the resonant cavity is related to the size of the cavity and is the inherent property of the resonant cavity, the test of different frequency points by using the resonant cavity method can only be completed by frequently replacing the resonant cavities with different sizes; on the other hand, the resonant frequency of the resonant cavity is reduced along with the increase of the size of the cavity, and the resonant cavity method is difficult to test the low-frequency electromagnetic parameters of the composite material. The free space method is an electromagnetic parameter testing method based on transmission line theory, the composite material is placed between testing clamps or antennas in free space in a microwave darkroom, complex reflection parameters and complex transmission parameters under a testing environment are obtained through measurement of a vector network analyzer, and then the electromagnetic parameters of the material are obtained through calculation on the basis.
When a frequency band (hereinafter referred to as high frequency) test of more than 1GHz is carried out, the frequency band is higher, the wavelength of electromagnetic waves is smaller, the width of a main lobe of an antenna is narrower, the wave beams are more concentrated, and the frequency sweep test can be carried out by using a smaller field. When the frequency band below 1GHz (hereinafter referred to as low frequency) is tested, on one hand, in order to ensure that a test antenna works in a far field range, a larger distance is required between the antenna and a material to be tested, so that the size of a field to be tested is larger, and the test is difficult to develop.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a composite material low-frequency electromagnetic parameter equivalent extraction device and method, which can equivalently extract a low-frequency sweep frequency test result, reduce the influence of background noise on the test result in a test environment by adding wave-absorbing materials, reducing the field and the like, and improve the test precision.
The purpose of the invention is realized by the following technical scheme: a 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.
Furthermore, the support module comprises a nonmetal support flat plate, and a square shielding window is arranged in the center of the nonmetal support flat plate;
one side of the nonmetal supporting flat plate faces the signal transceiving module, a flange clamp surrounding the square shielding window is arranged on the side, the flange clamp is made of nonmetal materials, the size of the flange clamp is larger than that of the square shielding window, and the flange clamp is used for adding a material to be detected onto the nonmetal supporting flat plate and enabling the material to be detected to be tightly attached to the flat plate;
the side, where the flange clamp is located, of the nonmetal supporting flat plate is fully paved with pyramid wave-absorbing materials, and the working frequency range of the pyramid wave-absorbing materials covers the test development frequency range, so that electromagnetic waves sent by the signal receiving and sending module cannot penetrate through the nonmetal supporting flat plate;
the nonmetal supporting flat plate is provided with two nonmetal beams at the bottom, and each nonmetal beam is connected with a group of universal wheels to be connected, so that the supporting module can move and rotate conveniently, and the device has the capacity of equivalently extracting low-frequency electromagnetic parameters of the material to be tested facing electromagnetic waves in different directions.
Furthermore, the supporting device further comprises a laser calibrator used for establishing a laser plane in space for calibration and ensuring that the center heights of the square shielding window and the receiving antenna and the transmitting antenna in the signal transceiving module are consistent.
Furthermore, the signal transceiver module comprises a receiving antenna, a transmitting antenna and a vector network analyzer; the receiving antenna is in a horn antenna form, the transmitting antenna is used for transmitting electromagnetic wave signals for testing, and the receiving antenna is used for receiving signals generated by the transmitted signals passing through a testing environment;
the vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display, a transmitting antenna and a receiving antenna are respectively connected with two ports of the dual-port vector network analyzer by using coaxial cables, an instrument transmitting port is connected with the transmitting antenna and used for outputting a transmitting signal, a receiving port is connected with the receiving antenna to measure the field intensity and the phase of an electromagnetic signal received by the receiving antenna, and a vector network display screen is used for performing real-time display of a test result;
when the receiving antenna and the transmitting antenna are arranged, the center of the antenna needs to be aligned to the center of the square shielding window, and the arrangement position of the antenna and the distance between the antenna and the shielding window are adjusted, so that the width of a main lobe of an antenna directional pattern in a test frequency band is kept in the shielding window, and side lobe radiation is not in the range of the shielding window and is absorbed by the pyramid wave-absorbing material.
Furthermore, the data processing module comprises a data processing computer, the data processing computer is connected with the vector network through a data transmission line, reads the test data in the vector network, performs calculation by using the test data, and converts the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be measured.
A composite material low-frequency electromagnetic parameter equivalent extraction method comprises the following steps:
s1, arrangement is finished according to the test placement requirements of transmission parameters and reflection parameters;
s2, starting to test the tested material;
s3, carrying out test data analysis; and exporting the data obtained by the test to a data processing computer, analyzing and processing the data by the data processing computer, and converting the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be tested.
Wherein the step S1 includes:
when the reflection parameters are tested, the transmitting antenna and the receiving antenna are arranged on one side of the flat support structure, which covers the wave-absorbing material, the two antennas are arranged in a mirror symmetry mode by using the normal plane of the center of the flat support structure, the center is consistent with the center height of a shielding window on the support structure, and the distance between the antennas and the shielding window is 0.6m in order to ensure that the antennas work in a far field range; the vector network analyzer and the data processing computer are arranged at the rear sides of the two antennas;
when the transmission parameters are tested, the transmitting antenna and the receiving antenna are arranged on two sides of the flat support structure, the two antennas are oppositely arranged, the flat support plane is in mirror symmetry arrangement, and the center of the flat support plane is consistent with the center of the shielding window on the support structure in height; the vector network analyzer and the data processing computer are arranged on one side of the flat plate support structure, and the distance between the vector network analyzer and the data processing computer and the edge of the flat plate support is not less than 0.3m, so that the fluctuation of a test result caused by the electromagnetic emission of the vector network and the data processing computer and the walking of a tester in the test process is avoided.
Wherein the step S2 includes:
s201, calibrating the testing device: the calibration function of the vector network analyzer is used for completing calibration of a double-port open circuit, a short circuit and a load, and completing calibration of a path between two ports so as to eliminate system errors in the test process;
s202, carrying out transmission parameter testing between two antenna ports when a shielding window is not provided with a material to be tested, wherein the starting frequency of a high-frequency sweep testing frequency band is more than 1GHz, the high-frequency transmission parameter testing result is represented as S21_ W _ H, the testing result comprises transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is not provided, the low-frequency point frequency testing is carried out on key working frequency points of the material to be tested, the low-frequency transmission parameter testing result is represented as S21_ W _ L, and the testing result comprises transmission parameters measured at each low-frequency point when the material to be tested is not provided; wherein the transmission parameter measurement preserves amplitude and phase;
s203, carrying out transmission parameter test between two antenna ports when the shielding window is additionally provided with the material to be tested, wherein the starting frequency of a high-frequency sweep test frequency band is more than 1GHz, and a high-frequency transmission parameter test result is expressed as S21_ C _ H and comprises transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is additionally provided; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency transmission parameter test result is represented as S21_ C _ L, the test result comprises transmission parameters measured at each low-frequency point when the material to be tested is additionally installed, and the amplitude and the phase of the transmission parameter measurement result are reserved;
s204, carrying out reflection parameter test between two antenna ports when the metal plate is additionally arranged on the shielding window, wherein the starting frequency of a high-frequency sweep frequency test frequency band is more than 1GHz, and a high-frequency reflection parameter test result is expressed as S11_ W _ H and comprises a reflection parameter measured at each high-frequency sweep frequency point when the metal plate is additionally arranged; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency reflection parameter test result is expressed as S11_ W _ L, the test result comprises reflection parameters measured at each low-frequency point when a metal plate is additionally installed, and the amplitude and the phase of the reflection parameter measurement result are reserved;
s205, when the material to be tested is additionally installed on the shielding window, reflection parameter testing between two antenna ports is carried out, the starting frequency of a high-frequency sweep frequency testing frequency band is more than 1GHz, a high-frequency reflection parameter testing result is expressed as S11_ C _ H, and the testing result comprises reflection parameters measured at each high-frequency sweep frequency point when the material to be tested is additionally installed; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency reflection parameter test result is represented as S11_ C _ L, the test result comprises reflection parameters measured at each low-frequency point when the material to be tested is additionally installed, and the amplitude and the phase of the reflection parameter measurement result are reserved.
The step S3 includes:
s301, carrying out test data analysis; exporting the data obtained by the test to a data processing computer, filtering out clutter, bottom noise and interference generated by coupling between transmitting and receiving antennas by using a time domain gate method, and obtaining a high-frequency transmission parameter S of the material to be tested21_HHigh frequency reflection parameter S11_HLow frequency transmission parameter S21_LAnd a low frequency reflection parameter S11_LThe measurement results of (a):
S21_H＝S21_W_H-S21_C_H、S11_H＝S11_W_H-S11_C_H
S21_L＝S21_W_L-S21_C_L、S11_L＝S11_W_L-S11_C_L
the subtraction in the measurement result calculation process refers to subtraction of corresponding test results at each frequency point;
s302, deducing a mode of calculating electromagnetic parameters of the material by using scattering parameters:
the scattering parameter of the material comprises a transmission parameter S21And a reflection parameter S11The relationship between the scattering parameter and the reflection coefficient and transmission coefficient of the material is expressed as follows:
wherein gamma and z are respectively a reflection coefficient and a transmission coefficient when electromagnetic waves are normally incident to the surface of the material to be measured;
calculating to obtain equivalent electromagnetic parameters of the material in the corresponding frequency band based on an NRW method; the reflection coefficient and the transmission coefficient in the scattering parameter expression formula are related to the electromagnetic parameters of the material, and are specifically expressed as follows:
in the formula ofr、εrThe relative dielectric constant and the relative magnetic permeability of the material to be measured are respectively, d is the thickness of the material to be measured, and the equivalent electromagnetic parameter of the material is obtained by calculation:
wherein:
s303, under each high-frequency sweep frequency point, dividing S21_HAs S21Will S11_HAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining accurate high-frequency sweep frequency electromagnetic parameter mur_H、εr_H(ii) a Wherein, mur_HComprises a relative dielectric constant mu calculated under each high-frequency sweeping frequency pointr；εr_HComprises the relative magnetic permeability epsilon calculated under each high-frequency sweeping frequency pointr；
Meanwhile, at each low frequency point, S is added21_LAs S21Will S11_LAs S11In step S302, calculation is performedOut of corresponding mur，εrThereby obtaining accurate low-frequency point frequency electromagnetic parameter mur_L、εr_L(ii) a Wherein, mur_LComprises the relative dielectric constant mu calculated under each low frequency pointr；εr_LComprises the relative magnetic permeability epsilon calculated under each low-frequency pointr；
S304, calculating electromagnetic parameters of the material to be detected; presetting each layer material, structure and laying mode of the composite material to be detected, independently and equivalently forming each component material of the material to be detected into a uniform medium layer, and calculating to obtain a transmission matrix T of the ith layer medium when electromagnetic waves are incidenti：
In the formula ni、ziRespectively the refractive index and the impedance of the ith layer of material under the incident condition of electromagnetic waves; k is a known wavenumber; d thickness of ith layer medium; the whole transfer matrix T of the material to be tested can use the self transfer matrix of each layer of medium and the interlaminar loss PiMultiplication results in:
T＝∑TiPi
the interlayer loss is difficult to directly obtain through measurement, and the interlayer loss changes along with the frequency change and is represented by a frequency change curve; therefore, it is considered that the electromagnetic wave is not lost in the case of transmission between layers, and P is usediSubstituting 1 into the following two formulas to obtain the pre-estimated scattering parameter of the material by preliminary calculation:
s305, under each frequency point of the frequency conversion curve above 1GHz, S is processed21_forecastAs S21Will S11_forecastAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining pre-estimated high-frequency sweep electromagnetic parametersμr_forecast_H、εr_forecast_H(ii) a Wherein, mur_forecast_HThe relative dielectric constant mu calculated under each frequency point with the frequency change curve of more than 1GHzr；εr_forecast_HThe relative magnetic permeability epsilon calculated under each frequency point above 1GHz containing frequency-change curver；
Meanwhile, under each frequency point below the frequency conversion curve 1GHz, S is added21_forecastAs S21Will S11_forecastAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining the pre-estimated low-frequency sweep frequency electromagnetic parameter mur_forecast_L、εr_forecast_L(ii) a Wherein, mur_forecast_LContains the relative dielectric constant mu calculated under each frequency point below 1GHz of the frequency change curver；εr_forecast_LComprises the relative magnetic permeability epsilon calculated under each frequency point below the frequency variation curve 1GHzr；
Adjusting interlayer loss PiCurve, so that the calculation result mu of the equivalent electromagnetic parameter of the high-frequency sweep frequency pre-evaluationr_forecast_H、εr_forecast_HElectromagnetic parameter test result mu equivalent to high frequency sweep frequencyr_H、εr_HInosculating low-frequency sweep frequency pre-evaluation equivalent electromagnetic parameter calculation result mur_forecast_L、εr_forecast_LTesting result mu of equivalent electromagnetic parameter with low frequency point frequency on low frequency testing frequency pointr_L、εr_LInosculating; the coincidence here means that the difference value on each test frequency point is smaller than a set threshold value;
calculating the result mu of the equivalent electromagnetic parameter of the low-frequency sweep frequency pre-evaluation at the momentr_forecast_L、εr_forecast_LAs an equivalent extraction result of the low frequency electromagnetic parameters.
The invention has the beneficial effects that: the method can be used for testing without using a large-scale microwave darkroom to obtain the sweep frequency test result of the low-frequency electromagnetic parameters of the composite material, and compared with the existing electromagnetic parameter test method aiming at the composite material, the method realizes equivalent extraction of the low-frequency electromagnetic parameters of the material by using a computational electromagnetism method, thereby reducing the requirement on the test environment; meanwhile, the test environment is optimized, the influence of background noise on the test result is reduced by increasing wave-absorbing materials, reducing the field and the like in the test environment, and the test precision is improved.
Drawings
FIG. 1 is a schematic view of an apparatus for measuring a reflection parameter of a composite material;
FIG. 2 is a schematic view of the arrangement of the apparatus for measuring the transmission parameter of the composite material;
FIG. 3 is a flow chart of equivalent extraction of low-frequency electromagnetic parameters of composite materials.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
As shown in fig. 1-2, a composite material low-frequency electromagnetic parameter equivalent extraction device comprises a support module, a signal transceiver 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.
Furthermore, the supporting module mainly comprises a flat plate support structure, one surface of the flat plate support structure is covered with the wave-absorbing material, the module comprises a nonmetal supporting flat plate 1, a square shielding window 2 is arranged in the center of the nonmetal supporting flat plate 1, the size of the window is larger than 0.6m, the center distance of the window is 1m, and the distance of the window boundary to the flat plate support boundary is 0.5 m. One side of the nonmetal support plate faces the signal transceiving module, the flange clamp 3 surrounding the square shielding window is arranged on the side, the clamp is made of nonmetal materials, the size of the clamp is slightly larger than that of the square shielding window 2, and the clamp is used for installing materials to be tested on the nonmetal support plate 1 and enabling the materials to be tested to be tightly attached to the plane of the plate. The use pyramid wave-absorbing material 4 on one side of the non-metal supporting flat plate where the flange clamp is located is fully paved, and the working frequency range of the pyramid wave-absorbing material covers the test development frequency range, so that the electromagnetic waves sent by the signal receiving and transmitting module cannot penetrate through the non-metal supporting flat plate 1. Two nonmetal crossbeams 5 are installed additional to nonmetal support flat board 1 bottom, are connected with two sets of universal wheels 6 respectively for support module can be convenient removal and rotation, make the device possess the ability of developing the low frequency electromagnetic parameter equivalence extraction of the material that awaits measuring under the circumstances of the incident of equidirectional electromagnetic wave. A laser calibrator 7 is arranged outside the bracket, and a laser plane is established in the instrument in space for calibration, so that the center heights of the square shielding window 2 and the receiving antenna and the transmitting antenna in the signal receiving and transmitting module are consistent, the loss of test signals caused by the dislocation of the antennas is reduced, and the test precision is improved;
furthermore, the signal transceiver module comprises a receiving antenna, a transmitting antenna and a vector network analyzer; the receiving antenna is in a horn antenna form, the transmitting antenna is used for transmitting electromagnetic wave signals for testing, and the receiving antenna is used for receiving signals generated by the transmitted signals passing through a testing environment;
the vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display, a transmitting antenna and a receiving antenna are respectively connected with two ports of the dual-port vector network analyzer by using coaxial cables, an instrument transmitting port is connected with the transmitting antenna and used for outputting a transmitting signal, a receiving port is connected with the receiving antenna to measure the field intensity and the phase of an electromagnetic signal received by the receiving antenna, and a vector network display screen is used for performing real-time display of a test result;
when the receiving antenna and the transmitting antenna are arranged, the center of the antenna needs to be aligned to the center of the square shielding window, and the arrangement position of the antenna and the distance between the antenna and the shielding window are adjusted, so that the width of a main lobe of an antenna directional pattern in a test frequency band is kept in the shielding window, and side lobe radiation is not in the range of the shielding window and is absorbed by the pyramid wave-absorbing material.
Furthermore, the data processing module comprises a data processing computer, the data processing computer is connected with the vector network through a data transmission line, reads the test data in the vector network, performs calculation by using the test data, and converts the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be measured.
As shown in fig. 3, a method for equivalently extracting low-frequency electromagnetic parameters of a composite material comprises the following steps:
s1, arrangement is finished according to the test placement requirements of transmission parameters and reflection parameters;
s2, starting to test the tested material;
s3, carrying out test data analysis; and exporting the data obtained by the test to a data processing computer, analyzing and processing the data by the data processing computer, and converting the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be tested.
Wherein the step S1 includes:
when the reflection parameters are tested, the transmitting antenna and the receiving antenna are arranged on one side of the flat support structure, which covers the wave-absorbing material, the two antennas are arranged in a mirror symmetry mode by using the normal plane of the center of the flat support structure, the center is consistent with the center height of a shielding window on the support structure, and the distance between the antennas and the shielding window is 0.6m in order to ensure that the antennas work in a far field range; the vector network analyzer and the data processing computer are arranged at the rear sides of the two antennas;
when the transmission parameters are tested, the transmitting antenna and the receiving antenna are arranged on two sides of the flat support structure, the two antennas are oppositely arranged, the flat support plane is in mirror symmetry arrangement, and the center of the flat support plane is consistent with the center of the shielding window on the support structure in height; the vector network analyzer and the data processing computer are arranged on one side of the flat plate support structure, and the distance between the vector network analyzer and the data processing computer and the edge of the flat plate support is not less than 0.3m, so that the fluctuation of a test result caused by the electromagnetic emission of the vector network and the data processing computer and the walking of a tester in the test process is avoided.
Wherein the step S2 includes:
s201, calibrating the testing device: the calibration function of the vector network analyzer is used for completing calibration of a double-port open circuit, a short circuit and a load, and completing calibration of a path between two ports so as to eliminate system errors in the test process;
s202, carrying out transmission parameter test between two antenna ports when a shielding window is not additionally provided with a material to be tested, wherein the starting frequency of a high-frequency sweep frequency test frequency band is more than 1GHz (currently, the actual test frequency band can be adjusted according to user requirements and test environments, but is ensured to be more than 1GHz, for example, a specific test frequency band adopts a continuous frequency of 1GHz-8GHz for testing), the test result of the high-frequency transmission parameter is expressed as S21_ W _ H, the low-frequency point frequency test is carried out on key working frequency points of the material to be tested (in the test process, the low-frequency test point frequency covers 1MHz-1GHz, 20 test frequency points are distributed in equal step length in the middle), the test result of the low-frequency transmission parameter is expressed as S21_ W _ L, and the amplitude and the phase of the transmission parameter are reserved;
s203, carrying out transmission parameter test between two antenna ports when the shielding window is additionally provided with the material to be tested, wherein the starting frequency of a high-frequency sweep frequency test frequency band is more than 1GHz, the high-frequency transmission parameter test result is expressed as S21_ C _ H, the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, the low-frequency transmission parameter test result is expressed as S21_ C _ L, and the amplitude and the phase of the transmission parameter measurement result are reserved;
s204, carrying out reflection parameter testing between two antenna ports when a metal plate is additionally arranged on the shielding window, wherein the starting frequency of a high-frequency sweep frequency testing frequency band is more than 1GHz, the high-frequency reflection parameter testing result is expressed as S11_ W _ H, the low-frequency point frequency testing is carried out on key working frequency points of the material to be tested, the low-frequency reflection parameter testing result is expressed as S11_ W _ L, and the amplitude and the phase of the reflection parameter measuring result are reserved;
s205, when the shielding window is additionally provided with the material to be tested, reflection parameter testing between two antenna ports is carried out, the starting frequency of a high-frequency sweep frequency testing frequency band is more than 1GHz, the high-frequency reflection parameter testing result is represented as S11_ C _ H, the low-frequency point frequency testing is carried out on the key working frequency point of the material to be tested, the low-frequency reflection parameter testing result is represented as S11_ C _ L, and the amplitude and the phase of the reflection parameter measuring result are reserved.
The step S3 includes:
s301, carrying out testAnalyzing data; exporting the data obtained by the test to a data processing computer, filtering out clutter, bottom noise and interference generated by coupling between transmitting and receiving antennas by using a time domain gate method, and obtaining a high-frequency transmission parameter S of the material to be tested21_HHigh frequency reflection parameter S11_HLow frequency transmission parameter S21_LAnd a low frequency reflection parameter S11_LThe measurement results of (a):
S21_H＝S21_W_H-S21_C_H、S11_H＝S11_W_H-S11_C_H
S21_L＝S21_W_L-S21_C_L、S11_L＝S11_W_L-S11_C_L
the subtraction in the measurement result calculation process refers to subtracting the corresponding test results under each frequency point;
s302, deducing a mode of calculating electromagnetic parameters of the material by using scattering parameters:
the scattering parameter of the material comprises a transmission parameter S21And a reflection parameter S11The relationship between the scattering parameter and the reflection coefficient and transmission coefficient of the material is expressed as follows:
wherein gamma and z are respectively a reflection coefficient and a transmission coefficient when electromagnetic waves are normally incident to the surface of the material to be measured;
calculating to obtain equivalent electromagnetic parameters of the material in the corresponding frequency band based on an NRW method; the reflection coefficient and the transmission coefficient in the scattering parameter expression formula are related to the electromagnetic parameters of the material, and are specifically expressed as follows:
in the formula ofr、εrThe relative dielectric constant and the relative magnetic permeability of the material to be measured are respectively, d is the thickness of the material to be measured, and the equivalent electromagnetic parameter of the material is obtained by calculation:
wherein:
s303, under each high-frequency sweep frequency point, dividing S21_HAs S21Will S11_HAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining accurate high-frequency sweep frequency electromagnetic parameter mur_H、εr_H(ii) a Wherein, mur_HComprises a relative dielectric constant mu calculated under each high-frequency sweeping frequency pointr；εr_HComprises the relative magnetic permeability epsilon calculated under each high-frequency sweeping frequency pointr；
Meanwhile, at each low frequency point, S is added21_LAs S21Will S11_LAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining accurate low-frequency point frequency electromagnetic parameter mur_L、εr_L(ii) a Wherein, mur_LComprises the relative dielectric constant mu calculated under each low frequency pointr；εr_LComprises the relative magnetic permeability epsilon calculated under each low-frequency pointr；
S304, carrying out electromagnetic parameter calculation on the material to be detected; presetting each layer material, structure and laying mode of the composite material to be detected, independently and equivalently forming each component material of the material to be detected into a uniform medium layer, and calculating to obtain a transmission matrix T of the ith layer medium when electromagnetic waves are incidenti：
In the formula ni、ziRespectively the refractive index and the impedance of the ith layer of material under the incident condition of electromagnetic waves; k is a known wavenumber; d thickness of ith layer medium; the whole transfer matrix T of the material to be tested can use the self transfer matrix of each layer of medium and the interlaminar loss PiMultiplication results in:
T＝∑TiPi
the interlayer loss is difficult to directly obtain through measurement, and the interlayer loss changes along with the frequency change and is represented by a frequency change curve; therefore, it is considered that the electromagnetic wave is not lost in the case of transmission between layers, and P is usediSubstituting 1 into the following two formulas to obtain the pre-estimated scattering parameter of the material by preliminary calculation:
s305, under each frequency point of the frequency conversion curve above 1GHz, S is processed21_forecastAs S21Will S11_forecastAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining the pre-estimated high-frequency sweep frequency electromagnetic parameter mur_forecast_H、εr_forecast_H(ii) a Wherein, mur_forecast_HThe relative dielectric constant mu calculated under each frequency point with the frequency change curve of more than 1GHzr；εr_forecast_HThe relative magnetic permeability epsilon calculated under each frequency point above 1GHz containing frequency-change curver；
Meanwhile, under each frequency point below 1GHz of the frequency-dependent curve, S is measured21_forecastAs S21Will S11_forecastAs S11In the substituting step S302, the corresponding μ is calculatedr，εrThereby obtaining the pre-estimated low-frequency sweep frequency electromagnetic parameter mur_forecast_L、εr_forecast_L(ii) a Wherein, mur_forecast_LComprises relative medium obtained by calculation under each frequency point below 1GHz of frequency-dependent curveElectric constant mur；εr_forecast_LComprises the relative magnetic permeability epsilon calculated under each frequency point below the frequency variation curve 1GHzr；
Adjusting interlayer loss PiCurve, so that the calculation result mu of the equivalent electromagnetic parameter of the high-frequency sweep frequency pre-evaluationr_forecast_H、εr_forecast_HElectromagnetic parameter test result mu equivalent to high frequency sweep frequencyr_H、εr_HInosculating low-frequency sweep frequency pre-evaluation equivalent electromagnetic parameter calculation result mur_forecast_L、εr_forecast_LTesting result mu of equivalent electromagnetic parameter with low frequency point frequency on low frequency testing frequency pointr_L、εr_LInosculating; the coincidence here means that the difference value on each test frequency point is smaller than a set threshold value;
calculating the result mu of the equivalent electromagnetic parameter of the low-frequency sweep frequency pre-evaluation at the momentr_forecast_L、εr_forecast_LAs an equivalent extraction result of the low frequency electromagnetic parameters.
In summary, the invention simplifies the testing environment by using the flat plate support structure with the wave-absorbing material, performs the test to obtain the transmission and reflection parameter testing results of the high-frequency sweep and the low-frequency point frequency of the material to be tested, outputs the results to the data processing module, combines the known information of the structure, the composition material and the like of the composite material to be tested, performs the electromagnetic parameter calculation by using the electromagnetic calculation method to obtain the calculation result of the electromagnetic shielding effectiveness of the full frequency band of the material to be tested, compares whether the calculation result is matched with the high-frequency sweep testing result and the low-frequency point frequency testing result, performs the correction, and obtains the equivalent extraction result of the low-frequency electromagnetic parameter frequency sweep test after the matching. Compared with the existing device and method for testing the electromagnetic performance of the composite material, the device provided by the invention has the advantages that the requirement on the testing environment is reduced, the testing environment for testing the low-frequency electromagnetic parameters of the composite material can be simplified, and the influence of environmental interference on the testing precision is effectively reduced.
While the foregoing description shows and describes a preferred embodiment of the invention, it is to be understood, as noted above, that the invention is not limited to the form disclosed herein, but is not intended to be exhaustive or to exclude other embodiments and may be used in various other combinations, modifications, and environments and may be modified within the scope of the inventive concept described herein by the above teachings or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The utility model provides a combined material low frequency electromagnetic parameter equivalence extraction element which characterized in that: the device comprises a supporting 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 an electromagnetic wave signal for testing, the transmitted signal is 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 signal is used as a testing result 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.
2. The composite material low-frequency electromagnetic parameter equivalent extraction device according to claim 1, characterized in that: the support module comprises a nonmetal support flat plate (1), and a square shielding window (2) is arranged in the center of the nonmetal support flat plate (1);
one side of the nonmetal supporting flat plate (1) faces the signal transceiving module, a flange clamp (3) surrounding the square shielding window (2) is arranged on the side, the flange clamp (3) is made of nonmetal materials, the size of the flange clamp is larger than that of the square shielding window (2), and the flange clamp is used for adding a material to be tested to the nonmetal supporting flat plate (1) and enabling the material to be tested to be tightly attached to the flat plate plane;
the non-metal supporting flat plate (1) is fully paved with pyramid wave-absorbing materials (4) on one side of the non-metal supporting flat plate (1) where the flange clamp (3) is located, and the working frequency range of the pyramid wave-absorbing materials covers the test development frequency range, so that electromagnetic waves emitted by the signal receiving and transmitting module cannot penetrate through the non-metal supporting flat plate (1);
nonmetal support flat board (1) bottom is provided with two nonmetal crossbeams (5), and every nonmetal crossbeam (5) all is connected with a set of universal wheel (6) and connects to in the removal and the rotation that the support module goes on, make the device possess the ability of developing the low frequency electromagnetic parameter equivalence extraction of the material that awaits measuring under the circumstances of the not equidirectional electromagnetic wave incidence.
3. The composite material low-frequency electromagnetic parameter equivalent extraction device according to claim 1, characterized in that: the supporting device further comprises a laser calibrator (7) which is used for establishing a laser plane in space for calibration and ensuring that the center heights of the square shielding window (2) and the receiving antenna and the transmitting antenna in the signal transceiving module are consistent.
4. The composite material low-frequency electromagnetic parameter equivalent extraction device according to claim 1, characterized in that: the signal transceiving module comprises a receiving antenna, a transmitting antenna and a vector network analyzer; the receiving antenna is in a horn antenna form, the transmitting antenna is used for transmitting electromagnetic wave signals for testing, and the receiving antenna is used for receiving signals generated by the transmitted signals passing through a testing environment;
the vector network analyzer adopts a vector dual-port vector network analyzer as a signal source and performs data display, a transmitting antenna and a receiving antenna are respectively connected with two ports of the dual-port vector network analyzer by using coaxial cables, an instrument transmitting port is connected with the transmitting antenna and used for outputting a transmitting signal, a receiving port is connected with the receiving antenna to measure the field intensity and the phase of an electromagnetic signal received by the receiving antenna, and a vector network display screen is used for performing real-time display of a test result;
when the receiving antenna and the transmitting antenna are arranged, the center of the antenna needs to be aligned to the center of the square shielding window, and the arrangement position of the antenna and the distance between the antenna and the shielding window are adjusted, so that the width of a main lobe of an antenna directional pattern in a test frequency band is kept in the shielding window, and side lobe radiation is not in the range of the shielding window and is absorbed by the pyramid wave-absorbing material.
5. The composite material low-frequency electromagnetic parameter equivalent extraction device according to claim 1, characterized in that: the data processing module comprises a data processing computer, the data processing computer is connected with the vector network analyzer through a data transmission line, reads test data in the vector network analyzer, calculates by using the test data, and converts a calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be detected.
6. A composite material low-frequency electromagnetic parameter equivalent extraction method is based on the device of any one of claims 1-5, and is characterized in that: the method comprises the following steps:
s1, arrangement is finished according to the test placement requirements of transmission parameters and reflection parameters;
s2, starting to test the tested material;
s3, carrying out test data analysis; and exporting the data obtained by the test to a data processing computer, analyzing and processing the data by the data processing computer, and converting the calculation result into a low-frequency electromagnetic parameter equivalent extraction result of the material to be tested.
7. The method for equivalently extracting the low-frequency electromagnetic parameters of the composite material as claimed in claim 6, wherein the method comprises the following steps: the step S1 includes:
when the reflection parameters are tested, the transmitting antenna and the receiving antenna are arranged on one side of the flat support structure, which covers the wave-absorbing material, the two antennas are arranged in a mirror symmetry mode by using the normal plane of the center of the flat support structure, the center is consistent with the center height of a shielding window on the support structure, and the distance between the antennas and the shielding window is 0.6m in order to ensure that the antennas work in a far field range; the vector network analyzer and the data processing computer are arranged at the rear sides of the two antennas;
when the transmission parameters are tested, the transmitting antenna and the receiving antenna are arranged on two sides of the flat support structure, the two antennas are oppositely arranged, the flat support plane is in mirror symmetry arrangement, and the center of the flat support plane is consistent with the center of the shielding window on the support structure in height; the vector network analyzer and the data processing computer are arranged on one side of the flat plate support structure, and the distance between the vector network analyzer and the data processing computer and the edge of the flat plate support is not less than 0.3m, so that the fluctuation of a test result caused by the electromagnetic emission of the vector network and the data processing computer and the walking of a tester in the test process is avoided.
8. The method for equivalently extracting the low-frequency electromagnetic parameters of the composite material as claimed in claim 6, wherein the method comprises the following steps: the step S2 includes:
s201, calibrating a testing device;
s202, carrying out transmission parameter testing between two antenna ports when a shielding window is not provided with a material to be tested, wherein the starting frequency of a high-frequency sweep testing frequency band is more than 1GHz, the high-frequency transmission parameter testing result is represented as S21_ W _ H, the testing result comprises transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is not provided, the low-frequency point frequency testing is carried out on key working frequency points of the material to be tested, the low-frequency transmission parameter testing result is represented as S21_ W _ L, and the testing result comprises transmission parameters measured at each low-frequency point when the material to be tested is not provided; wherein the transmission parameter measurement preserves amplitude and phase;
s203, carrying out transmission parameter test between two antenna ports when the shielding window is additionally provided with the material to be tested, wherein the starting frequency of a high-frequency sweep test frequency band is more than 1GHz, and a high-frequency transmission parameter test result is expressed as S21_ C _ H and comprises transmission parameters measured at each high-frequency sweep frequency point when the material to be tested is additionally provided; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency transmission parameter test result is represented as S21_ C _ L, the test result comprises transmission parameters measured at each low-frequency point when the material to be tested is additionally installed, and the amplitude and the phase of the transmission parameter measurement result are reserved;
s204, carrying out reflection parameter test between two antenna ports when the metal plate is additionally arranged on the shielding window, wherein the starting frequency of a high-frequency sweep frequency test frequency band is more than 1GHz, and a high-frequency reflection parameter test result is expressed as S11_ W _ H and comprises a reflection parameter measured at each high-frequency sweep frequency point when the metal plate is additionally arranged; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency reflection parameter test result is expressed as S11_ W _ L, the test result comprises reflection parameters measured at each low-frequency point when a metal plate is additionally installed, and the amplitude and the phase of the reflection parameter measurement result are reserved;
s205, when the material to be tested is additionally installed on the shielding window, reflection parameter testing between two antenna ports is carried out, the starting frequency of a high-frequency sweep frequency testing frequency band is more than 1GHz, a high-frequency reflection parameter testing result is expressed as S11_ C _ H, and the testing result comprises reflection parameters measured at each high-frequency sweep frequency point when the material to be tested is additionally installed; the low-frequency point frequency test is carried out on key working frequency points of the material to be tested, a low-frequency reflection parameter test result is represented as S11_ C _ L, the test result comprises reflection parameters measured at each low-frequency point when the material to be tested is additionally installed, and the amplitude and the phase of the reflection parameter measurement result are reserved.
9. The composite material low-frequency electromagnetic parameter equivalent extraction method as claimed in claim 6, characterized in that: the step S3 includes:
s301, carrying out test data analysis; exporting the data obtained by the test to a data processing computer, filtering out clutter, bottom noise and interference generated by coupling between transmitting and receiving antennas by using a time domain gate method, and obtaining a high-frequency transmission parameter S of the material to be tested21_HHigh frequency reflection parameter S11_HLow frequency transmission parameter S21_LAnd a low frequency reflection parameter S11_LThe measurement results of (a):
S21_H＝S21_W_H-S21_C_H、S11_H＝S11_W_H-S11_C_H
S21_L＝S21_W_L-S21_C_L、S11_L＝S11_W_L-S11_C_L
the subtraction in the measurement result calculation process refers to subtracting the corresponding test results under each frequency point;
s302, deducing a mode of calculating electromagnetic parameters of the material by using scattering parameters:
the scattering parameter of the material comprises a transmission parameter S21And a reflection parameter S11Between scattering parameter and reflection coefficient and transmission coefficient of materialThe relationship is represented by the following formula:
wherein gamma and z are respectively a reflection coefficient and a transmission coefficient when electromagnetic waves are normally incident to the surface of the material to be measured;
calculating to obtain equivalent electromagnetic parameters of the material in the corresponding frequency band based on an NRW method; the reflection coefficient and the transmission coefficient in the scattering parameter expression formula are related to the electromagnetic parameters of the material, and are specifically expressed as follows:
in the formula ofr、εrThe relative dielectric constant and the relative magnetic permeability of the material to be measured are respectively, d is the thickness of the material to be measured, and the equivalent electromagnetic parameter of the material is obtained by calculation:
wherein:
s303, under each high-frequency sweep frequency point, dividing S21_HAs S21Will S11_HAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining accurate high-frequency sweep frequency electromagnetic parameter mur_H、εr_H(ii) a Wherein, mur_HComprises a relative dielectric constant mu calculated under each high-frequency sweeping frequency pointr；εr_HComprises the relative magnetic permeability epsilon calculated under each high-frequency sweeping frequency pointr；
Meanwhile, at each low frequency point, S is added21_LAs S21Will S11_LAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining accurate low-frequency point frequency electromagnetic parameter mur_L、εr_L(ii) a Wherein, mur_LComprises the relative dielectric constant mu calculated under each low frequency pointr；εr_LComprises the relative magnetic permeability epsilon calculated under each low-frequency pointr；
S304, carrying out electromagnetic parameter calculation on the material to be detected; presetting each layer material, structure and laying mode of the composite material to be detected, independently and equivalently forming each component material of the material to be detected into a uniform medium layer, and calculating to obtain a transmission matrix T of the ith layer medium when electromagnetic waves are incidenti：
In the formula ni、ziRespectively the refractive index and the impedance of the ith layer of material under the incident condition of electromagnetic waves; k is a known wavenumber; d thickness of ith layer medium; the whole transfer matrix T of the material to be tested can use the self transfer matrix of each layer of medium and the interlaminar loss PiMultiplication results in:
T＝∑TiPi
the interlayer loss is difficult to directly obtain through measurement, and the interlayer loss changes along with the frequency change and is represented by a frequency change curve; therefore, it is considered that the electromagnetic wave is not lost in the case of transmission between layers, and P is usediSubstituting 1 into the following two formulas to obtain the pre-estimated scattering parameter of the material by preliminary calculation:
s305, under each frequency point of the frequency conversion curve above 1GHz, S is processed21_forecastIn (1) correspond toThe measurement result is taken as S21Will S11_forecastAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining the pre-estimated high-frequency sweep frequency electromagnetic parameter mur_forecast_H、εr_forecast_H(ii) a Wherein, mur_forecast_HThe relative dielectric constant mu calculated under each frequency point with the frequency change curve of more than 1GHzr；εr_forecast_HThe relative magnetic permeability epsilon calculated under each frequency point above 1GHz containing frequency-change curver；
Meanwhile, under each frequency point below 1GHz of the frequency-dependent curve, S is measured21_forecastAs S21Will S11_forecastAs S11Alternatively, in step S302, the corresponding μ is calculatedr，εrThereby obtaining the pre-estimated low-frequency sweep frequency electromagnetic parameter mur_forecast_L、εr_forecast_L(ii) a Wherein, mur_forecast_LContains the relative dielectric constant mu calculated under each frequency point below 1GHz of the frequency change curver；εr_forecast_LComprises the relative magnetic permeability epsilon calculated under each frequency point below the frequency variation curve 1GHzr；
Adjusting interlayer loss PiCurve, so that the calculation result mu of the equivalent electromagnetic parameter of the high-frequency sweep frequency pre-evaluationr_forecast_H、εr_forecast_HElectromagnetic parameter test result mu equivalent to high frequency sweep frequencyr_H、εr_HInosculating low-frequency sweep frequency pre-evaluation equivalent electromagnetic parameter calculation result mur_forecast_L、εr_forecast_LTesting result mu of equivalent electromagnetic parameter with low frequency point frequency on low frequency testing frequency pointr_L、εr_LInosculating; the coincidence here means that the difference value on each test frequency point is smaller than a set threshold value;
calculating the result mu of the equivalent electromagnetic parameter of the low-frequency sweep frequency pre-evaluation at the momentr_forecast_L、εr_forecast_LAs an equivalent extraction result of the low frequency electromagnetic parameters.
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