Single-end measurement method for electromagnetic shielding effectiveness of metal mesh window

Abstract

A single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window, belonging to microwave measurement technology, is disclosed. The measurement device consists of a transceiver antenna, a vector network analyzer, an RF connection cable, a shielded cavity, and a computer. This method indirectly measures the electromagnetic shielding effectiveness of the metal mesh optical window by measuring its reflection amplitude and phase, combined with a two-port network transmission matrix calculation method. This method requires only one side of the metal mesh optical window to be equipped with a measurement antenna, making it suitable for applications where a receiving antenna cannot be placed inside the enclosed shielded cavity. It also offers high measurement accuracy, facilitating on-site measurement and evaluation of the electromagnetic shielding effectiveness of metal mesh optical windows.

Description

Technical Field

[0001] This invention pertains to microwave measurement, specifically a single-end measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window. Background Technology

[0002] With the increasing intensity of electromagnetic waves in space and the continuous expansion of application bands, the electromagnetic environment is becoming increasingly complex, thus requiring electromagnetic shielding in many fields. For optical instruments used in aerospace equipment for detection and observation, high light transmittance is required while ensuring strong electromagnetic shielding performance, rendering traditional electromagnetic shielding materials unsuitable. Metal mesh films, as transparent conductive films, have low production costs and simple fabrication processes, and are currently being used in transparent electromagnetic shielding in aerospace equipment and other fields.

[0003] Metal mesh optical windows are used in fields such as aerospace equipment. After prolonged use, they may crack, break, or even detach over large areas, leading to a decrease in electromagnetic shielding effectiveness or even complete failure. Therefore, there is an urgent need to develop electromagnetic shielding effectiveness measurement technology for metal mesh optical windows, especially single-end in-situ measurement technology without disassembling the metal mesh optical window.

[0004] Currently, depending on the testing object, there are multiple levels of shielding effectiveness testing standards and specifications in China, 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 shielding cavity and is not easily disassembled, the receiving antenna cannot be placed inside the cavity, thus making measurement impossible. Summary of the Invention

[0005] To address the limitation of traditional electromagnetic shielding effectiveness measurement methods when metal mesh optical windows form a closed cavity, this invention proposes a single-ended measurement method for the electromagnetic shielding effectiveness of metal mesh optical windows based on the principle of microwave two-port network cascading. This method indirectly measures the shielding effectiveness of the metal mesh optical window by measuring its reflection amplitude and phase, combined with transmission matrix calculation methods. It is suitable for applications where a receiving antenna cannot be placed inside a closed shielding cavity, enabling on-site measurement and evaluation of the electromagnetic shielding effectiveness of metal mesh optical windows.

[0006] The technical solution of the present invention is as follows:

[0007] A single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window includes a transceiver antenna, a vector network analyzer, an RF connection cable, a shielding 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 metal mesh optical window. The metal mesh optical window is fixed at the opening of the shielding cavity. After calibration, the vector network analyzer measures the reflection amplitude and phase and transmits this data to the computer. The computer calculates the electromagnetic shielding effectiveness of the metal mesh optical window using the numerical relationship between the reflection information and the electromagnetic shielding effectiveness. The numerical relationship between the reflection amplitude and phase of the metal mesh optical window and the shielding effectiveness is as follows:

[0008]

[0009] Where SE is the electromagnetic shielding effectiveness, r is the measured reflection amplitude of the metal mesh window, θ is the measured reflection phase of the metal mesh window, and d is the thickness of the substrate material of the metal mesh window. The characteristic impedance Z0 and the propagation constant γ are taken as follows:

[0010]

[0011]

[0012] μ r ε represents the complex permeability of the substrate material for the metal mesh window. r The complex permittivity of the substrate material for the metal mesh grating window is given. To measure the vacuum wavelength corresponding to the microwave frequency.

[0013] As a preferred method, the transceiver antenna is either a separate transceiver antenna or an integrated transceiver antenna, transmitting linearly polarized waves with a VSWR ≤ 2.5 within the measurement frequency band. The aperture plane of the integrated transceiver antenna is parallel to the optical window of the metal mesh grating under test, while the apertures of the separate transceiver antennas form a small angle with the optical window of the metal mesh grating under test, forming quasi-normal incidence. Within the plane of the optical window of the metal mesh grating under test, the electromagnetic wave path difference between the center and edge of the optical window is less than λ / 16, and the 3dB beamwidth of the antenna is less than 1 / 3 of the maximum inscribed circle diameter of the optical window.

[0014] Step 2: Connect end a of the RF cable to the vector network analyzer, and connect end b to the open-circuit, short-circuit, and matching calibration pieces respectively for calibration. After completion, remove the calibration pieces.

[0015] Step 3: Connect the b end of the RF connection cable to the transceiver antenna. Place the calibration metal plate (metal plate thickness greater than 1mm, side length not less than 3 times the 3dB beamwidth of the antenna) on the same measurement plane as the metal mesh window, and perform short-circuit frequency response calibration. After completion, remove the metal plate.

[0016] Step 4: Orient the transceiver antennas toward free space and perform frequency response matching calibration.

[0017] As a preferred method, time-domain gating is applied to the reflection measurement results under non-anechoic conditions, and an appropriate gating time is selected to include the main peak of the reflection signal in the time domain and eliminate multipath interference signals.

[0018] As a preferred method, the metal mesh film that can be measured by the measurement method includes copper, aluminum, gold, and silver; the substrate material includes ordinary glass, quartz glass, infrared materials, and transparent resin materials; when the metal mesh is other transparent conductive films or semiconductor films, this method can also be used to measure electromagnetic shielding effectiveness.

[0019] This invention has the following advantages and outstanding effects:

[0020] This invention proposes a single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window. The metal mesh structure is equivalent to a cascaded microwave two-port network. The numerical relationship between the complex reflection coefficient and transmittance of the metal mesh is obtained by using the transmission matrix method. Then, the shielding effectiveness is measured by measuring the complex reflection coefficient. This method is suitable for measurement situations where the metal mesh optical window has formed a shielded cavity and is not easy to disassemble, and the receiving antenna cannot be placed inside the cavity. It also has high measurement accuracy. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the measuring device in Embodiment 1 of the present invention.

[0023] Figure 2 This is a schematic diagram of the equivalent two-port cascaded network of a metal mesh grid.

[0024] Figure 3 This is a comparison chart of the measurement results of the single-end measurement method and the transmission-type shielding effectiveness measurement method of this patent. In the chart, 1—point focusing lens antenna, 2—vector network analyzer, 3—RF connection line, 4—shielding cavity, and 5—computer. Detailed Implementation

[0025] The present invention will now be further described with reference to the accompanying drawings and preferred embodiments: as shown in the attached specification. Figure 2As shown, a two-layer metal mesh grid with a dielectric substrate can be equivalent to a cascaded microwave two-port network, where the upper metal mesh can be equivalent to an RLC lumped element, and the lower dielectric substrate can be equivalent to a uniform transmission line. Therefore, the overall transmission matrix of the metal mesh grid can be written as the product of the transmission matrices of the two microwave two-port networks:

[0026]

[0027] Where d, Z0, and γ are the thickness, characteristic impedance, and propagation constant of the metal mesh substrate, respectively, and are known quantities. Y is the equivalent admittance of the metal mesh portion, which is related to the actual shielding performance of the metal mesh and is an unknown quantity. By establishing the relationship between the reflection coefficient and transmission coefficient of the metal mesh through the above transmission matrix, and eliminating the unknown Y, we can obtain:

[0028]

[0029] To facilitate understanding of the present invention, the invention will be described more clearly and completely below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Example 1

[0031] A schematic diagram of a measuring device according to a preferred embodiment of the present invention is shown below. Figure 1 As shown, the system includes a transceiver antenna, a vector network analyzer, RF cables, a shielded cavity, and a computer. The transceiver antenna is a point-focusing lens antenna with an integrated transceiver capability, a VSWR ≤2.5, a 3dB focal spot size ≤3 cm, and a focal length of 5 cm in the 12-18 GHz frequency band. The shielded cavity is made of aluminum, 2 mm thick, with a circular window of 10 cm in diameter. The specific implementation steps of this single-ended measurement method for the electromagnetic shielding effectiveness of the metal mesh window are as follows:

[0032] Step 1: Power on and warm up, set the frequency range and the number of sweep points;

[0033] Step 2: Connect one end of the RF cable to the vector network analyzer, and connect the other end to the open circuit, short circuit, and matching calibration pieces respectively for calibration. After completion, remove the calibration pieces.

[0034] Step 3: Connect the RF connection cable to the point focusing lens antenna, place the calibration aluminum plate (2 mm thick, 10 cm side length) on the focal plane of the point focusing lens antenna, and perform short-circuit frequency response calibration. After completion, remove the aluminum plate.

[0035] Step 4: Orient the point-focusing lens antenna toward free space and perform frequency response matching calibration;

[0036] Step 5: Fix the metal mesh window to be tested at the opening of the shielding cavity, ensuring they are pressed tightly together. The surface of the metal mesh window should coincide with the focal plane of the point-focusing lens antenna. Keep the incident beam perpendicular to the metal mesh window and read the S value from the vector network analyzer. 11 Display number.

[0037] Step 6: Apply time-domain gating to the reflection measurement results, select an appropriate gating time, include the main peak of the reflection signal in the time domain, and eliminate multipath interference.

[0038] Step 7: Import the measured reflection amplitude and phase information into the computer, and calculate the electromagnetic shielding effectiveness of the metal mesh window using a preset program. The numerical relationship between the reflection amplitude and phase of the metal mesh window and the shielding effectiveness is as follows:

[0039]

[0040] Where SE is the electromagnetic shielding effectiveness, r is the measured reflection amplitude of the metal mesh window, θ is the measured reflection phase of the metal mesh window, and d is the thickness of the substrate material of the metal mesh window. The characteristic impedance Z0 and the propagation constant γ are taken as follows:

[0041]

[0042]

[0043] μ r ε represents the complex permeability of the substrate material for the metal mesh window. r The complex permittivity of the substrate material for the metal mesh grating window is given. The vacuum wavelength corresponds to the test frequency.

[0044] The effects of this invention can be achieved through Figure 3 Further explanation:

[0045] As shown in the figure, in the 12-18 GHz range, the measurement results obtained by the shielding effectiveness measurement method proposed in this patent have a maximum deviation of less than 0.95 dB from the standard transmission electromagnetic shielding effectiveness measurement results, indicating that the proposed measurement method has high accuracy.

[0046] The above description is only one 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 single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window, the measuring device comprising a transceiver antenna (1), a vector network analyzer (2), an RF connection line (3), a shielding cavity (4), and a computer (5), characterized in that: The transceiver antenna (1) is connected to the vector network analyzer (2) via the radio frequency connection line (3) and is located on one side of the optical window to be tested. The optical window to be tested is fixed on the opening (4) of the shielding cavity. After calibration, the vector network analyzer (2) measures the microwave reflection amplitude and phase of the optical window to be tested and transmits them to the computer (5). The computer (5) calculates the shielding effectiveness of the optical window to be tested by the numerical relationship between the reflection amplitude and phase and the shielding effectiveness. The specific calculation method is as follows: The metal grid with a double-layer structure of metal grid-dielectric substrate can be equivalent to a cascaded microwave two-port network. The upper metal grid can be equivalent to an RLC lumped element, and the lower dielectric substrate can be equivalent to a uniform transmission line. Then the overall transmission matrix of the metal grid can be written as the product of the transmission matrices of two microwave two-port networks: Where d, Z0, and γ are the thickness, characteristic impedance, and propagation constant of the metal mesh dielectric substrate, respectively, and are known quantities; Y is the equivalent admittance of the metal mesh portion, which is related to the actual shielding performance of the metal mesh and is an unknown quantity. The values ​​of characteristic impedance Z0 and propagation constant γ are as follows: Where, μ r ε represents the complex permeability of the substrate material for the metal mesh window. r The complex permittivity of the substrate material for the metal mesh grating window is given. To measure the vacuum wavelength corresponding to the microwave frequency, the relationship between the reflection coefficient and transmission coefficient of the metal mesh grating is established using the aforementioned transmission matrix. After eliminating the unknown Y, the numerical relationship between the reflection amplitude and phase of the metal mesh grating window and its shielding effectiveness can be obtained as follows: 。 2. The single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window as described in claim 1, characterized in that: The transceiver antenna (1) is either a separate transceiver antenna or a combined transceiver antenna, transmitting linearly polarized waves. The standing wave ratio is ≤2.5 in the measured microwave frequency band. The aperture surface of the combined transceiver antenna is parallel to the optical window of the metal mesh grating under test. The aperture surfaces of the separate transceiver antennas form quasi-normal incidence with the optical window of the metal mesh grating under test. In the plane of the optical window of the metal mesh grating under test, the electromagnetic wave path difference between the center and the edge of the optical window is less than λ / 16, and the 3dB beamwidth of the antenna is less than 1 / 3 of the maximum inscribed circle diameter of the optical window.

3. The single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window as described in claim 1, characterized in that: The calibration steps for the vector network analyzer (2) include: Step 1: Power on and warm up, set the frequency range and the number of sweep points; Step 2: Connect end a of the RF connection cable (3) to the vector network analyzer (2), and connect end b to the open-circuit calibrator, short-circuit calibrator, and matching calibrator respectively for calibration. After completion, remove the calibrators. Step 3: Connect the b end of the RF connection line (3) to the transceiver antenna (1), place the calibration metal plate on the same measurement plane as the optical window, perform short-circuit frequency response calibration, and remove the calibration metal plate after completion. The calibration metal plate has a thickness greater than 1 mm and its side length is not less than 3 times the 3dB beamwidth of the antenna. Step 4: Orient the transceiver antenna (1) toward free space and perform frequency response matching calibration.

4. The single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window as described in claim 1, characterized in that: In non-microwave anechoic chamber conditions, time-domain gating is required to process the reflection measurement results. The gating time is selected to include the main peak of the reflection signal in the time domain and to eliminate multipath interference signals.

5. The single-ended measurement method for the electromagnetic shielding effectiveness of a metal mesh optical window as described in claim 1, characterized in that: The measurement method can detect metal mesh window materials including copper, aluminum, gold, and silver; substrate materials include ordinary glass, quartz glass, infrared materials, and transparent resin materials.

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