A device and method for testing shielding effectiveness in low-frequency and below frequency bands

Abstract

This invention relates to a shielding effectiveness testing device and method for low-frequency and below frequency bands, comprising: a shielded room and a control memory, a low-frequency signal generator, a spectrum analyzer, a loop antenna, and a shielded cabinet disposed within the shielded room; the control memory is connected to the low-frequency signal generator and the spectrum analyzer via shielded network cables and optical fibers, and is used to perform shielding effectiveness testing based on antennas selected for different frequency bands; the low-frequency signal generator generates signals of corresponding frequency bands based on control commands sent by the control memory and sends them to the loop antenna; the loop antenna includes a transmitting loop antenna and a receiving loop antenna disposed outside and inside the shielded cabinet, respectively, with the transmitting loop antenna connected to the low-frequency signal generator and the receiving loop antenna connected to the spectrum analyzer disposed within the shielded cabinet, the spectrum analyzer performing spectrum analysis on the signals received by the receiving loop antenna and sending the results to the control memory. This invention can be widely applied in the field of electromagnetic shielding effectiveness testing.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding effectiveness testing, and particularly relates to a shielding effectiveness testing device and method for low-frequency and below frequency bands, especially an electromagnetic shielding effectiveness testing device and method for electromagnetic shielding cabinets and electromagnetic shielding rooms with each side dimension not less than 1.2m. Background Technology

[0002] A charged particle accelerator is a device that artificially generates a beam of high-energy charged particles. This device involves many devices in the system and has a high level of electromagnetic emission. Some high-power devices can emit hundreds of millivolts, while the detection signals of ion beams or physical experiments are generally in the microampere or millivolt range. Electromagnetic noise can drown out useful signals and affect the detection of weak signals. In addition, strong electromagnetic interference can also cause equipment failures and abnormalities, affecting the reliability of the system.

[0003] To effectively address the aforementioned issues, electromagnetic compatibility engineers established an interference coupling path model based on weak signal detection equipment. They analyzed the main interference factors from the perspectives of field and path, and proposed a shielding scheme for relevant systems and equipment of the accelerator device. If a professional shielded cabinet is used, this scheme can greatly alleviate the problems of poor system stability and unsatisfactory observation data caused by electromagnetic interference. However, a cost-effectiveness contradiction will arise because while professional shielded cabinets ensure shielding effectiveness, they also increase costs. Since the shielding requirements of various systems in the accelerator device are not very high, the electromagnetic compatibility engineers proposed to independently develop a low-cost shielded cabinet suitable for the accelerator device.

[0004] Because accelerator systems are numerous and their operating frequencies vary widely, the design of low-cost shielded cabinets needs to consider the frequency range of DC to 1 GHz. However, existing shielding effectiveness testing standards only provide testing methods for the 9 kHz to 40 GHz range, such as GB / T12190, GJB5792, and GJB5240, and do not provide specific testing methods for low-frequency bands and below. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a shielding effectiveness testing device and method for low-frequency and below frequency bands, thereby solving the problem of insufficient shielding effectiveness testing capability of low-cost shielded cabinets in low-frequency and below frequency bands, and also providing a reference for the testing of shielding effectiveness in low-frequency and below frequency bands.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a shielding effectiveness testing device, comprising:

[0008] The shielded room, and the control storage, low-frequency signal generator, spectrum analyzer, loop antenna and shielded cabinet installed in the shielded room;

[0009] The control memory is connected to the low-frequency signal generator and the spectrum analyzer via a shielded network cable and an optical fiber, and is used to perform shielding effectiveness tests based on antennas selected in different frequency bands.

[0010] The low-frequency signal generating device generates a signal of the corresponding frequency band based on the control instructions sent by the control memory, and sends it to the loop antenna;

[0011] The loop antenna includes a transmitting loop antenna and a receiving loop antenna respectively disposed outside and inside the shielded cabinet. The transmitting loop antenna is connected to the low-frequency signal generating device, and the receiving loop antenna is connected to a spectrum analyzer disposed inside the shielded cabinet. The spectrum analyzer is used to perform spectrum analysis on the signal received by the receiving loop antenna and send it to the control memory.

[0012] Furthermore, the low-frequency signal generating device includes a power divider, a current driver, a low-frequency function generator, and a signal source; the input terminals of the low-frequency function generator and the signal source are connected to the control memory via shielded mesh cables and a first photoelectric converter; the output terminals of the low-frequency function generator and the signal source are connected to the two input terminals of the power divider via shielded radio frequency cables, and the output terminal of the power divider is connected to the transmitting loop antenna via shielded radio frequency cables; the current driver is disposed between the output terminal of the low-frequency function generator and the input terminal of the power divider, and is used to increase the driving current of the low-frequency function generator.

[0013] Furthermore, the low-frequency function generator outputs a signal with a frequency of 20Hz to 100kHz; the signal source outputs a signal with a frequency of 100kHz to 30MHz.

[0014] Furthermore, the current driver includes a power supply, a low-impedance amplifier, a resistor, and an output port; the low-impedance amplifier is used to amplify the voltage signal output by the low-frequency function generator, so that its voltage amplitude remains unchanged and its internal resistance is reduced; the resistor is used to limit the current of the signal output by the low-impedance amplifier and output it through the output port; the power supply is used to power the current driver.

[0015] Furthermore, the spectrum analyzer is connected to the second photoelectric converter via a shielded network cable. The optical fiber of the second photoelectric converter passes through a waveguide installed on the wall of the shielded cabinet and then connects to the control memory via the first photoelectric converter.

[0016] Furthermore, the transmitting loop antenna and the receiving loop antenna are arranged in the same plane, and the line connecting the centers of the transmitting loop antenna and the receiving loop antenna should be perpendicular to the wall where the test point is located.

[0017] Furthermore, the shielded cabinet is insulated from the shielded room by an insulating support, and the thickness of the insulating support is at least 100mm.

[0018] Furthermore, the receiving loop antenna is supported by an antenna bracket and connected to the spectrum analyzer via a shielded RF cable.

[0019] Secondly, the present invention provides a shielding effectiveness testing method, which includes the following steps:

[0020] Connect the control memory, low-frequency signal generator, loop antenna and spectrum analyzer to form a test link and determine the test frequency.

[0021] The positions of the transmitting and receiving loop antennas are determined, and the background noise is tested to obtain the noise matrix;

[0022] Keeping the positions of the transmitting and receiving loop antennas unchanged, the data matrix of the shielded cabinet at each test frequency is detected;

[0023] Repeat the previous step, and based on the noise matrix and the data matrix of each test frequency, obtain the shielding effectiveness test results of the shielded cabinet at each test frequency.

[0024] Furthermore, the formula for calculating the shielding effectiveness test results at each test frequency is as follows:

[0025] SE = S SE -H SE

[0026] Among them, S SE H is a data matrix for a certain test point. SE This is the background noise matrix.

[0027] The present invention has the following advantages due to the adoption of the above technical solutions:

[0028] 1. The present invention incorporates a current driver in the low-frequency signal generator, which reduces the internal resistance of the low-frequency function generator to 0.2Ω without changing the voltage amplitude, thereby effectively improving the dynamic range of the low-frequency function generator;

[0029] 2. The present invention has a waveguide installed on the wall of the shielded cabinet. The connection between the spectrum analyzer and the control memory is realized through the waveguide, the first photoelectric converter and the second photoelectric converter, which effectively reduces the conduction leakage problem caused by directly using shielded network cable connection and improves the shielding effect.

[0030] In summary, the shielding effectiveness testing device for low-frequency and below frequencies proposed in this invention can meet the shielding effectiveness testing requirements of 20Hz to 30MHz. Through specific test link design, its dynamic range can be improved by up to approximately 21dB, meeting the broadband electromagnetic shielding effectiveness testing requirements of accelerator facilities. This is of great significance for the development and optimization of low-cost shielded cabinets, and also provides important evidence for suppressing electronic equipment radiation, improving the electromagnetic environment, and increasing the system signal-to-noise ratio, thus possessing significant engineering value. Therefore, this invention can be widely applied in the field of electromagnetic shielding effectiveness testing. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0032] Figure 1 This is a schematic diagram of the shielding effectiveness testing device provided in an embodiment of the present invention;

[0033] Figure 2 This is a block diagram of the current driver principle provided in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the ring antenna arrangement provided in an embodiment of the present invention;

[0035] Figure 4 This is a flowchart of the shielding effectiveness test provided in an embodiment of the present invention;

[0036] Figure 5 This is the dynamic range curve provided in the embodiments of the present invention;

[0037] The markings in the attached diagram are as follows:

[0038] 1. Control memory; 2. Power divider; 3. Current driver; 31. Power supply; 32. Low internal resistance amplifier; 33. Resistor; 34. Output port; 4. Low frequency function generator; 5. Signal source; 6. Photoelectric converter; 61. First photoelectric converter; 62. Second photoelectric converter; 7. Waveguide; 8. Spectrum analyzer; 9. Loop antenna; 91. Transmitting loop antenna; 92. Receiving loop antenna; 10. Shielded cabinet; 11. Insulating support; 12. Shielded room. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0040] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0041] Accelerator facilities have proposed a low-cost shielded cabinet development solution to address electromagnetic interference issues. However, existing shielding effectiveness testing methods only cover the frequency range of 9kHz to 40GHz, which cannot meet the testing requirements for the shielding effectiveness of low-cost shielded cabinets. Therefore, to address this problem, some embodiments of this invention propose a shielding effectiveness testing device for low-frequency and below frequency bands. This device aims to solve the problem of insufficient shielding effectiveness testing capability for low-cost shielded cabinets in low-frequency and below frequency bands, and also provides a reference for the testing of shielding effectiveness in low-frequency and below frequency bands.

[0042] Correspondingly, some embodiments of the present invention also provide a method for testing shielding effectiveness.

[0043] Example 1

[0044] It should be noted that the shielding effectiveness testing device provided by this invention has a frequency range of 20Hz to 4GHz. The focus is on the testing device and method for shielding effectiveness in the low frequency band of 20Hz to 30MHz and below. The shielding effectiveness testing device and method for 30MHz to 4GHz are not the focus of this invention.

[0045] like Figure 1As shown, this embodiment provides a shielding effectiveness testing device for low-frequency and below frequency bands, comprising: a shielded chamber 12, and a control memory 1, a low-frequency signal generator, a spectrum analyzer 8, a loop antenna 9, and a shielded cabinet 10 disposed within the shielded chamber 12. The control memory 1 is connected to the low-frequency signal generator and the spectrum analyzer 8 via shielded network cables and optical fibers, and is used to perform shielding effectiveness testing based on antennas selected for different frequency bands. The low-frequency signal generator generates signals of corresponding frequency bands based on control commands sent by the control memory 1 and sends them to the loop antenna 9. The loop antenna 9 includes a transmitting loop antenna 91 and a receiving loop antenna 92 ​​disposed outside and inside the shielded cabinet 10, respectively. The transmitting loop antenna 91 is connected to the low-frequency signal generator, and the receiving loop antenna 92 ​​is connected to the spectrum analyzer 8 disposed within the shielded cabinet 10. The spectrum analyzer 8 performs spectrum analysis on the signals received by the receiving loop antenna 92 ​​and sends the results to the control memory 1.

[0046] Preferably, the low-frequency signal generating device includes a power divider 2, a current driver 3, a low-frequency function generator 4, and a signal source 5. The input terminals of the low-frequency function generator 4 and the signal source 5 are connected to the control memory 1 via shielded wire mesh and a first photoelectric converter 61; the output terminals of the low-frequency function generator 4 and the signal source 5 are connected to the two input terminals of the power divider 2 via shielded radio frequency cables, and the output terminal of the power divider 2 is connected to the transmitting loop antenna 91 via a shielded radio frequency cable; the current driver 3 is disposed between the output terminal of the low-frequency function generator 4 and the input terminal of the power divider 2, and is used to increase the driving current of the low-frequency function generator 4.

[0047] Preferably, the low-frequency function generator 4 outputs a signal with a frequency of 20Hz to 100kHz; the signal source 5 outputs a signal with a frequency of 100kHz to 30MHz.

[0048] Preferably, such as Figure 2 As shown, the current driver 3 includes a power supply 31, a low-impedance amplifier 32, a resistor 33, and an output port 34. The low-impedance amplifier 32 amplifies the voltage signal output from the low-frequency function generator 4, keeping its voltage amplitude constant while reducing its internal resistance. The resistor 33 limits the current output of the low-impedance amplifier 32 and outputs the signal through the output port 34. The power supply 31 provides AC power to other components.

[0049] In practice, existing standards lack specific testing methods for shielding effectiveness in low-frequency and lower frequency bands due to significant attenuation. Most standards employ a 30cm diameter loop antenna as both the transmitting and receiving antennas, resulting in a system dynamic range that fails to meet shielding effectiveness testing requirements. To address this issue, this invention improves the system dynamic range by increasing the drive current, without significantly increasing the antenna turns.

[0050] The voltage signal output from the low-frequency function generator 4 with an internal resistance of 50Ω is passed through a low-impedance amplifier 32 with a gain of 1. The voltage amplitude remains unchanged, but the internal resistance decreases from 50Ω to 0.2Ω. The signal output from the low-impedance amplifier 32 is then current-limited by resistor 33 and input to the transmitting loop antenna 91. When the output of the low-frequency function generator 4 is 18V Vpp and the resistance is 4Ω, the loop current is approximately 1.59A rms. Compared to the 0.014A rms generated when only the low-frequency function generator 4 outputs 20V Vpp, the dynamic range is improved by approximately 21dB.

[0051] Preferably, the gain of the low internal resistance amplifier 32 is 1.

[0052] Preferably, the spectrum analyzer 8 is connected to the second photoelectric converter 62 via a shielded network cable. The optical fiber of the second photoelectric converter 62 passes through the waveguide 7 installed on the wall of the shielded cabinet 10 and then connects to the control memory 1 via the first photoelectric converter 61. The control memory 1 controls the spectrum analyzer 8 using a combination of shielded network cable and optical fiber. Since conduction leakage may occur when the shielded network cable passes through the shielded cabinet 10, adding a network port to the interface board would affect the shielding effectiveness of the shielded cabinet 10. Therefore, in this embodiment, the shielded network cable is connected to the second photoelectric converter 62, and the optical fiber is connected to the first photoelectric converter 61 through the waveguide 7 to achieve shielding.

[0053] Preferably, the diameter and length of the waveguide 7 are determined according to the shielding effectiveness requirements and the cutoff frequency, as shown in Equations (1), (2) and (3), which are calculated based on the fact that the waveguide 7 is filled with a non-air medium.

[0054]

[0055]

[0056] In the formula, f εc f is the cutoff frequency when the waveguide is filled with other media, in GHz; c d is the cutoff frequency when the circular cutoff waveguide contains only air, in GHz; d is the inner diameter of the circular cutoff waveguide, in cm; ε r is the relative permittivity of the medium.

[0057]

[0058] In the formula, W SE ρ represents the shielding effectiveness of the waveguide; f represents the electromagnetic wave frequency in GHz; l represents the waveguide length in meters; μ represents the shielding effectiveness of the waveguide. r The relative permeability of a medium is generally considered to be the magnetic permeability of other media, except for ferromagnetic materials.

[0059] Preferably, the transmitting loop antenna 91 and the receiving loop antenna 92 ​​are arranged in the same plane, and the line connecting the centers of the transmitting loop antenna 91 and the receiving loop antenna 92 ​​should be perpendicular to the wall surface where the test point is located. The test points should be arranged at the seams of weak points such as doors, panels, and interface boards. For each seam, test points should be arranged as needed, but the distance between two adjacent test points on each seam should not exceed 0.4m.

[0060] Preferably, such as Figure 3 As shown, the distance D1 between the transmitting ring antenna 91 and the outer wall of the shielded cabinet 10 is 60mm, and the distance D2 between the receiving ring antenna 92 ​​and the inner wall of the shielded cabinet 10 is 70mm.

[0061] Preferably, the receiving loop antenna 92 ​​is connected to the spectrum analyzer 8 via a shielded RF cable, which should be as short as possible. Since the shielded RF cable has some loss, especially at low frequencies, the length of the shielded RF cable needs to be minimized to reduce the loss caused by the cable; generally, it should be around 1.5-2m.

[0062] Preferably, the receiving loop antenna 92 ​​is supported by an antenna bracket, the height of which is determined according to the test point.

[0063] Preferably, the shielded cabinet 10 is insulated from the shielded chamber 12 by an insulating support 11. More preferably, the thickness of the insulating support 11 is at least 100 mm.

[0064] Example 2

[0065] like Figure 4 As shown, based on the low-frequency and below frequency band shielding effectiveness testing device provided in Embodiment 1, this embodiment provides a low-frequency and below frequency band shielding effectiveness testing method, including the following steps:

[0066] 1) Establish the test link and determine the test frequency;

[0067] 2) Determine the positions of the transmitting and receiving loop antennas, and test the background noise to obtain the noise matrix;

[0068] 3) Keep the positions of the transmitting and receiving loop antennas unchanged, and test the data matrix of the shielded cabinet at each test frequency;

[0069] 4) Repeat step 3), and based on the noise matrix and the data matrix of each test frequency, obtain the shielding effectiveness test results of the shielded cabinet at each test frequency.

[0070] Preferably, in step 1) above, when determining the test frequency, this embodiment of the invention mainly refers to the frequency list provided by the national or military radio management agency. The principle is to avoid protected civilian public wireless services, military and emergency management frequencies as much as possible, while also avoiding broadcasting, television, communications, wireless navigation, etc., so as not to interfere with the operation of other wireless services.

[0071] In addition, the test frequency should be selected to avoid the resonant frequency of the shielding body, because the resonant frequency will seriously affect the test results of the shielding effectiveness. The resonant frequency is related to the geometric dimensions of the shielding body. For shielded cabinets, the calculation of its resonant shielding is shown in Equation (4).

[0072]

[0073] In the formula, f mnk The resonant frequency is in MHz; m, n, k = 0, 1, 2..., are positive integers, and only one of them can be 0; a, b, c are the length, width, and height of the shielded cabinet, with the relationship a>b>c, and the unit is m.

[0074] Preferably, in step 4) above, the calculation formula for the shielding effectiveness test results at each test frequency point is as follows:

[0075] SE = S SE -H SE (dB)

[0076] Among them, S SE H is a data matrix for a certain test frequency point. SE Let be the background noise matrix, and the two matrices are represented as follows:

[0077]

[0078]

[0079] Where f1, f2, and f3 are different signal frequencies, H1, H2, and H3 are the signal amplitudes of different frequencies in the background noise, and S1, S2, and S3 are the signal amplitudes of different frequencies.

[0080] Example 3

[0081] To effectively validate this method, a verification hardware link was constructed based on the shielding effectiveness testing device, including a spectrum analyzer, a low-frequency function signal generator, a current driver, RF cables, and a control and storage unit. The main purpose is to verify the impact of connecting a current driver between the low-frequency function signal generator and the spectrum analyzer on the signal amplitude, thereby demonstrating the feasibility of this method.

[0082] Set the low-frequency function signal generator output amplitude to 10dBm, and select the test frequency band as shown in the table below.

[0083] Table 1 Test Frequency Band Selection

[0084] frequency band frequency Hz 20 100 500 kHz 1 5 10 50 80

[0085] like Figure 5 The results shown are from two comparisons. The comparison reveals that the method proposed in this invention can improve the dynamic range of low-frequency and lower frequency bands, providing a reference for shielding effectiveness testing in low-frequency and lower frequency bands.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A shielding effectiveness testing device for low-frequency and below frequency bands, characterized in that, include: The shielded room, and the control storage, low-frequency signal generator, spectrum analyzer, loop antenna and shielded cabinet installed in the shielded room; The control memory is connected to the low-frequency signal generator and the spectrum analyzer via a shielded network cable and an optical fiber, and is used to perform shielding effectiveness tests based on antennas selected in different frequency bands. The low-frequency signal generating device generates a signal of the corresponding frequency band based on the control instructions sent by the control memory, and sends it to the loop antenna; The loop antenna includes a transmitting loop antenna and a receiving loop antenna respectively disposed outside and inside the shielded cabinet. The transmitting loop antenna is connected to the low-frequency signal generating device, and the receiving loop antenna is connected to a spectrum analyzer disposed inside the shielded cabinet. The spectrum analyzer is used to perform spectrum analysis on the signal received by the receiving loop antenna and send it to the control memory. The low-frequency signal generating device includes a power divider, a current driver, a low-frequency function generator, and a signal source; The input terminals of the low-frequency function generator and signal source are connected to the control memory via a shielded mesh cable and a first photoelectric converter; the output terminals of the low-frequency function generator and signal source are connected to the two input terminals of the power divider via a shielded radio frequency cable, and the output terminal of the power divider is connected to the transmitting loop antenna via a shielded radio frequency cable; the current driver is disposed between the output terminal of the low-frequency function generator and the input terminal of the power divider, and is used to increase the driving current of the low-frequency function generator; The low-frequency function generator outputs a signal with a frequency of 20Hz to 100kHz; the signal source outputs a signal with a frequency of 100kHz to 30MHz. The current driver includes a power supply, a low-impedance amplifier, a resistor, and an output port; the low-impedance amplifier amplifies the voltage signal output by the low-frequency function generator, keeping its voltage amplitude constant while reducing its internal resistance; the resistor limits the current output of the low-impedance amplifier and outputs it through the output port; the power supply powers the current driver.

2. The shielding effectiveness testing device for low-frequency and below frequency bands as described in claim 1, characterized in that, The spectrum analyzer is connected to the second photoelectric converter via a shielded network cable. The optical fiber of the second photoelectric converter passes through a waveguide installed on the wall of the shielded cabinet and then connects to the control memory via the first photoelectric converter.

3. The shielding effectiveness testing device for low-frequency and below frequency bands as described in claim 1, characterized in that, The transmitting loop antenna and the receiving loop antenna are set in the same plane, and the line connecting the centers of the transmitting loop antenna and the receiving loop antenna should be perpendicular to the wall where the test point is located.

4. The shielding effectiveness testing device for low-frequency and below frequency bands as described in claim 1, characterized in that, The shielded cabinet is insulated from the shielded room by an insulating support, and the thickness of the insulating support is at least 100mm.

5. The shielding effectiveness testing device for low-frequency and below frequency bands as described in claim 1, characterized in that, The receiving loop antenna is supported by an antenna bracket and connected to the spectrum analyzer via a shielded RF cable.

6. A method for testing shielding effectiveness using the shielding effectiveness testing device for low-frequency and below frequency bands as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Connect the control memory, low-frequency signal generator, loop antenna and spectrum analyzer to form a test link and determine the test frequency. The positions of the transmitting and receiving loop antennas are determined, and the background noise is tested to obtain the noise matrix; Keeping the positions of the transmitting and receiving loop antennas unchanged, the data matrix of the shielded cabinet at each test frequency is detected; Repeat the previous step, and based on the noise matrix and the data matrix of each test frequency, obtain the shielding effectiveness test results of the shielded cabinet at each test frequency.

7. The shielding effectiveness testing method as described in claim 6, characterized in that, The formula for calculating the shielding effectiveness test results at each test frequency is as follows: in, For a certain test point, This is the background noise matrix.

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