A method for testing electromagnetic properties of a material by measuring backscattering

Abstract

The application discloses a kind of materials electromagnetic performance test methods of measuring reflection and transmission, belong to microwave measurement technology, and measurement system is formed by transceiver antenna, vector network analyzer, computer;The method comprises the following steps: installing the measurement system of measuring reflection and transmission based on space transmission line method;Four measurements are carried out in reflection area, respectively empty load test, reflection test, test piece test, test piece plus backplate test;According to the four groups of reflection coefficients measured, the transmission line parameters related to the transmission field of the material to be measured are calculated, and the transmission field size and phase of the transmission area are calculated according to the transmission line parameters.The application provides a kind of high-precision, non-destructive, easy-to-operate reflection measurement method, which can predict the transmission field distribution of the material to be measured under a specific incoming wave through reflection measurement.

Description

Technical Field

[0001] This technology relates to the fields of microwave and millimeter-wave shielding effectiveness measurement and free-space method technology, specifically to a method for testing the electromagnetic properties of materials by measuring reflection and penetration. Background Technology

[0002] With the continuous development of electronic science and technology, various electronic devices are becoming increasingly numerous, and electromagnetic interference between devices is also rapidly increasing. The increasingly complex electromagnetic environment places demands on the shielding of electronic device enclosures against external electromagnetic waves. Therefore, the technology for measuring the shielding effectiveness of material enclosures has become increasingly important. Currently, most shielding effectiveness measurements require measurement within the transmission region. However, it is difficult to place receiving antennas and data processing equipment inside some enclosures, causing measurement methods in the transmission region to fail. Compared to transmission measurement methods, the reflection-based free-space method offers advantages such as convenient testing, high degree of freedom in measurement, and no damage to the material under test, making it more suitable for practical application scenarios.

[0003] There are two major challenges in measurement methods for the electromagnetic properties of materials: first, how to obtain sufficient known information under the premise of placing a transmitting and receiving antenna at a single port; and second, to establish a model that is sufficiently effective in predicting shielding effectiveness, which requires effectively predicting the transmission field and shielding effectiveness under a specific incoming wave with the fewest possible parameters.

[0004] Currently, depending on the test object, there are various domestic standards for measuring shielding effectiveness, including GB / T12190-2021 "Measurement Method for Shielding Effectiveness of Electromagnetic Shielding Rooms" for shielding bodies, GB / T30142-2013 "Measurement Method for Shielding Effectiveness of Planar Electromagnetic Shielding Materials", GB / T25471-2010 "Test Method for Shielding Effectiveness of Electromagnetic Shielding Coatings", and GJB6190-2008 "Measurement Method for Shielding Effectiveness of Electromagnetic Shielding Materials" for shielding materials, and GJB 5185-2003 "Measurement Method for Shielding Effectiveness of Small Shielding Bodies" for special structures. However, these methods all require the transmitting and receiving antennas to be located on both sides of the shielding material. When the shielding material has formed a shielded enclosure, the receiving antenna cannot be placed inside the enclosure. In this case, the above measurement methods cannot be applied.

[0005] Patent No. CN 116626402 A, Patent Title: A Single-Ended Measurement Method for Electromagnetic Shielding Effectiveness of a Metal Mesh Window; This invention proposes a single-port method for measuring the electromagnetic shielding effectiveness of a metal mesh window. The metal mesh structure is equivalent to a cascaded microwave two-port network. The transmission matrix method is used to solve for the numerical relationship between the complex reflection coefficient and transmittance of the metal mesh, and then the shielding effectiveness is measured by measuring the complex reflection coefficient. This method has the advantages of simple operation and high measurement accuracy. Unfortunately, this method requires prior knowledge of the equivalent dielectric constant, equivalent permeability, and thickness of the metal mesh window under test, which has significant limitations for measuring materials with unknown electromagnetic parameters or unknown thickness. Summary of the Invention

[0006] To address the problem of reflective measurement of the shielding effectiveness of unknown materials, this invention proposes a method based on spatial transmission line theory.

[0007] A method for measuring the electromagnetic shielding effectiveness of unknown materials is proposed. This method constructs a spatial transmission line model for predicting shielding effectiveness and presents the relationships between impedance, electrical length, and transmission field in the transmission line model. By measuring the echo signal of the material under test (UTD) and the echo signal of the UTD with a backplate, a one-to-one correspondence between the measured signal and the transmission line parameters (impedance, electrical length) is established, achieving the goal of measuring the electromagnetic shielding effectiveness of unknown materials. This method is suitable for applications where a receiving antenna cannot be placed inside a closed shielded enclosure, enabling on-site measurement and evaluation of the electromagnetic shielding effectiveness of unknown materials.

[0008] The technical solution of the present invention is as follows:

[0009] A method for testing the electromagnetic properties of materials by measuring reflection and penetration includes a transceiver antenna, a vector network analyzer, an RF connection cable, a shielded cavity, and a computer. The transceiver antenna is connected to the vector network analyzer via the RF connection cable and is located on one side of the material under test. After calibration, the vector network analyzer measures the reflection amplitude and phase and transmits this data to the computer. The computer then uses the reflection information to establish a model of the material's electromagnetic properties. Figure 3 The equivalent transmission line model is shown, and the transmission field of the material for a specific incoming wave is calculated based on the transmission line parameters. The relationship between the transmission field and the equivalent transmission line parameters is as follows:

[0010]

[0011] in Let Γ be the incident electric field amplitude, Θ be the equivalent electric length of the material, Z be the equivalent characteristic impedance of the material, Γ be the local reflection coefficient between the material and the air, and Z0 be the wave impedance of the air.

[0012] The shielding effectiveness is:

[0013]

[0014] To obtain the equivalent transmission line parameters of a material to predict the transmission field and shielding effectiveness, the following steps are included:

[0015] Step 1: Install the measurement system for the material's inverse-to-transmit measurement method. The signal source is a transceiver antenna with a VSWR of less than 2.5 and an aperture efficiency greater than 85% within the measurement frequency band. The aperture surface of the transceiver antenna is kept parallel to the plane of the material under test.

[0016] Step 2: Align the transmitting and receiving antennas with free space and perform matching calibration.

[0017] Step 3: Align the transceiver antenna with the reflector and perform reflection calibration.

[0018] Step 4: Point the transceiver antenna at the material to be measured and measure it. The material should be in the same position as the reflector in Step 3.

[0019] Step 5: Keeping the relative positions of the transmitting and receiving antennas and the material under test unchanged as in Step 3, place a metal plate behind the material under test for measurement.

[0020] Step 6: Transfer the data from the four measurements in Steps 2 to 5 back to the computer for processing with a time-domain window, select an appropriate gating time, and eliminate multipath interference.

[0021] Step 7: Establish the relationship between the measurement data and the transmission line parameters, and calculate the transmission field based on the transmission line parameters.

[0022] Furthermore, in step six, the measurement data S is transmitted back to the computer. 11 This includes denoising interference signals. The measurement data is subjected to inverse Fourier transform to obtain the time-domain echo signal. When electromagnetic waves are incident on the material under test, reflection peaks are generated. Taking the time when the reflection peak appears as the center, an appropriate gating time is selected, and the signal is multiplied with the original signal in the form of a window function and then subjected to Fourier transform to return to the frequency domain, thus completing the denoising process.

[0023] Furthermore, in step two, when the transmitting and receiving antennas are aligned with free space, the data obtained after calibration of the reflected signal is S. 11air In step three, when the transmitting and receiving antennas are aligned with the metal plate, the data obtained after calibration of the reflected signal is S. 11pec In S4, when the transmitting and receiving antennas are aligned with the material, the data obtained after calibration of the reflected signal is S. 11mut In S5, when the transmitting and receiving antennas are aligned with a material with a metal backplate, the reflected signal, after calibration, yields data as S. 11backp .

[0024] Furthermore, in S7, transmission line parameters can be calculated based on four measurement data:

[0025] Transmission line characteristic impedance

[0026] Where Z0 is the wave impedance in air.

[0027]

[0028] Where χ can be calculated based on the measurement data:

[0029]

[0030] in,

[0031] Transmission line electrical length

[0032] in

[0033]

[0034] b = 2ZZ0

[0035]

[0036] The transmission field can then be calculated from the transmission line parameters:

[0037]

[0038] The shielding effectiveness can be calculated from the transmission field:

[0039]

[0040] Compared with the prior art, the advantages of this invention are:

[0041] This invention relates to a method for testing the electromagnetic properties of materials by measuring both transmission and reception. For the material under test, only a transmitting and receiving antenna needs to be placed on one side to predict its transmission field. Furthermore, this method does not require any prior information about the material, such as its equivalent dielectric constant or thickness. This method is suitable for measurement situations where the material is already encased in a housing that cannot be damaged, and where it is impossible to place the receiving antenna inside the housing. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of four measurements in an embodiment of the present invention.

[0043] Figure 2 This is a material transport line model established in the embodiments of the present invention.

[0044] Figure 3 This is a schematic diagram of the structure of the measurement system for measuring back and through in an example of the present invention.

[0045] Figure 4This is the simulation environment for calculating the transmission coefficient under ideal plane wave illumination in this invention example.

[0046] Figure 5 This is a comparison chart of the real and imaginary parts of the transmission coefficient and the measured and theoretical values ​​of the real and imaginary parts of the transmission coefficient in the transmission coefficient measurement method of the present invention.

[0047] Figure 6 This is a comparison chart of the predicted shielding effectiveness test value and the theoretical value in the measurement method of reverse penetration in the example of this invention. Detailed Implementation

[0048] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0049] Example 1:

[0050] Figure 1 This diagram illustrates the four measurements mentioned in the background section, including no-load testing, reflection testing, DUT testing, and DUT with metal backplate testing. The feasibility of the method is verified using full-wave simulation in CST Studio Suite 2021. The specific simulation steps are as follows:

[0051] Step 1, create the following in CST: Figure 1 The model of the measurement system includes the transmitting and receiving antennas and the sample.

[0052] Step 2: Create four project files, setting the material of the flat plate to air, metal plate, test plate, and test plate with a metal backplate attached, respectively. The test plate is set to a relative permittivity of 5 and a thickness of d = 2mm.

[0053] Step 3: Establish a wave port feed at port 1 of the transceiver antenna, correctly set the simulation frequency range and wave port settings, and ensure that the transceiver antenna operates in master mode.

[0054] Step four: Export the four simulation data in S1P format and import them into Matlab for noise reduction, and further establish a transmission line model to calculate the transmission field distribution.

[0055] Step 5: To verify the correctness of the obtained transmission field, calculate the transmission field under ideal conditions using the simulation software CST Studio Suite 2021. For example... Figure 4As shown, the parameters of the uniform plate and the test plate are set to be the same, and the transmission field is calculated under the floquet port. Unit cell boundary conditions are set around the test plate, and open boundary conditions are set at the top and bottom respectively, and the test plate is excited by the floquet port. At the background, the distance between the top and bottom ports and the surface of the test plate is set to Zmax = 10mm respectively, and the reference plane is set to -Zmax in the floquet port to obtain the transmission coefficient with the top and bottom surfaces of the test plate as reference planes.

[0056] Step six: Import the ideal transmission field into MATLAB and compare it with the transmission field distribution calculated in step four based on the four reflection measurements.

[0057] The effects of the present invention are as follows Figure 5 , Figure 6 As shown, within the measurement range of 12.5-16.5 GHz, the real part error of the transmission coefficient is no greater than 0.02, the imaginary part error of the transmission coefficient is no greater than 0.06, and the shielding effectiveness error is no greater than 0.4 dB.

[0058] The above description is merely a specific example of the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A method for testing the electromagnetic properties of materials by measuring their transparency, characterized in that, Includes the following steps: Step 1: Install a material-specific measurement system; Step 2: Perform four measurements within the reflection area: no-load test, reflection test, test device under test (DUT) test, and test device under test with metal backplate. Step 3: Denoise the four sets of measured reflection coefficients, use the denoised data to calculate the transmission line parameters of the transmission field of the material under test, and calculate the magnitude and phase of the transmission field in the transmission region based on the transmission line parameters. In step one, the measurement system based on the spatial transmission line method includes a transceiver antenna, a vector network analyzer, and a computer. The transceiver antenna is positioned directly over the material under test. The transceiver antenna is connected to the vector network analyzer and emits a detection signal that interacts with the material under test. The reflected wave is received again by the transceiver antenna and displayed and recorded as S-parameters by the vector network analyzer. Finally, the S-parameters are transmitted back to the computer in S1P file format. The transmission line parameters of the material are calculated using an algorithm, and the transmission coefficient is predicted. In step two, no-load testing, reflection testing, DUT testing, and DUT with backplane testing are performed. Noise interference is removed from the four sets of measurement data by applying a time-domain window. After noise reduction, the echo information of the transmitting and receiving antennas under free-space radiation conditions is obtained from the no-load testing. The reflection test obtained the echo information when the reflector was placed at a distance L behind the radiating surface of the transmitting and receiving antenna. The test device obtains the echo information when the reflector is replaced with the test material. The echo information of the test material after adding a backplate and then connecting a reflector is obtained during the test. ; In step three, transmission line parameters can be calculated based on the four sets of reflection measurements. The reflection coefficient of the material under test is: The reflection coefficient of the test piece with a backplate is: The transmission line impedance Z is calculated as follows: ; Γ is defined as the local reflection coefficient between the material and the air; , The wave impedance in air; The method for calculating the electrical length of a transmission line is as follows: ; Θ is defined as the equivalent electrical length of the material; Based on the basic parameters of the transmission line The transmission field of the material under test can then be calculated: , The amplitude of the incident electric field; The shielding effectiveness can be calculated based on the transmission field: 。 2. The method for testing the electromagnetic properties of materials based on reflection and penetration according to claim 1, characterized in that, In step one, the transmitting and receiving antennas include a horn antenna and a dielectric surface for phase control.

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