Device and method for measuring lightning magnetic field shielding performance of Helmholtz coil material

Abstract

The invention discloses a Helmholtz coil material lightning magnetic field shielding performance measuring device, which comprises a magnetic field generation device, a shielding test box is arranged in a magnetic field coverage range of the magnetic field generation device, an open hole is formed in the shielding test box, and the open hole enables a magnetic line of force of the magnetic field generation device to transversely penetrate through the shielding test box. The shielding test box is internally provided with the signal measurement unit, the signal measurement unit measures the magnetic field in the shielding test box, the lightning stroke magnetic field environment is accurately simulated, and the repeatability and accuracy of the shielding performance test are improved. The invention further discloses a method for measuring the lightning magnetic field shielding performance of the Helmholtz coil material, the lightning magnetic field shielding performance of the measured shielding material is measured by applying the device for measuring the lightning magnetic field shielding performance of the Helmholtz coil material, and the problem that traditional measurement is poor in accuracy is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding performance testing technology, and relates to a device for measuring the electromagnetic shielding performance of Helmholtz coil materials in the event of lightning, as well as a method for measuring the electromagnetic shielding performance of Helmholtz coil materials in the event of lightning. Background Technology

[0002] Shielding is a crucial aspect of electromagnetic protection. Traditional shielding tests primarily focus on electric field shielding, lacking reliable methods for assessing the shielding effectiveness against transient, strong magnetic fields caused by lightning strikes. The magnetic shielding effectiveness of materials is a critical parameter in lightning protection structural design. Magnetic field shielding effectiveness testing is a vital component of lightning protection performance evaluation. Compared to structural effectiveness testing, testing the magnetic field shielding effectiveness of materials is extremely difficult for the following reasons: 1) Lightning electromagnetic fields are characterized by high intensity and wide bandwidth, making it difficult to construct a large-scale, high-intensity, controllable changing magnetic field environment. Traditional shielded room measurement methods are not applicable. 2) Traditional magnetic field excitation methods cannot simulate the actual distribution of lightning electromagnetic fields and lack standardized measurement schemes for lightning current waveform injection and magnetic field comparison. 3) Open testing environments are susceptible to external electromagnetic interference, and the magnetic field generated by ordinary coils is uneven, making it difficult to accurately compare the relative magnetic field strength before and after shielding, resulting in large measurement errors.

[0003] 4) Current magnetic field shielding effectiveness measurements, especially pulsed magnetic field shielding effectiveness assessments, only focus on comparing the peak magnetic field values. However, the magnetic field change rate (dH(t) / dt) is usually ignored. The magnetic field change rate reflects the shield's ability to suppress the steepest part of the magnetic field change. This is crucial for preventing electromagnetic interference and protecting sensitive equipment from transient impacts, such as transient magnetic fields formed by electrostatic discharge and lightning discharge. Summary of the Invention

[0004] The purpose of this invention is to provide a device for measuring the electromagnetic shielding performance of Helmholtz coil materials during lightning strikes, which accurately simulates the magnetic field environment of lightning strikes and improves the repeatability and accuracy of shielding performance testing.

[0005] Another objective of this invention is to provide a method for measuring the electromagnetic shielding performance of Helmholtz coil materials, using the electromagnetic shielding performance measuring device for Helmholtz coil materials of this invention for accurate measurement.

[0006] Another objective of this invention is to provide a method for comprehensively evaluating the shielding performance of materials by comparing the rate of change of electromagnetic field of lightning based on Helmholtz coils, and to apply the method for measuring the electromagnetic field shielding performance of materials using Helmholtz coils.

[0007] The first technical solution adopted in this invention is a lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials, including a magnetic field generating device. A shielding test box is set within the magnetic field coverage area of ​​the magnetic field generating device. An opening is provided on the shielding test box, allowing the magnetic field lines of the magnetic field generating device to pass through the shielding test box. A signal measuring unit is set inside the shielding test box, and the signal measuring unit measures the magnetic field inside the shielding test box. The magnetic field generating device is a Helmholtz coil, and the Helmholtz coil is connected to an impulse current generator.

[0008] The first technical solution of this invention is further characterized by: The Helmholtz coils are positioned on both sides of the shielded test box, with the Helmholtz coils located outside the openings.

[0009] The Helmholtz coil consists of two circular coils, one of which is located outside the opening. The diameter D of the circular coil satisfies: D≥3L or D≥4d, where L is the side length of the shielded test box, d is the diagonal length of the shielded test box, and the distance between the two circular coils is s=D / 2.

[0010] The shielding test box is a cubic iron shielding box. The opening is located at the center of one side of the shielding test box, and the opening and bottom of the opening are two symmetrical squares.

[0011] The signal measurement unit is a high-precision magnetic field probe with a frequency band coverage of 0.1kHz-30MHz.

[0012] The shielded test chamber is equipped with a plastic positioning bracket, on which a high-precision magnetic field probe is fixed. The high-precision magnetic field probe is located at the center of the opening.

[0013] The second technical solution adopted in this invention is a method for measuring the electromagnetic shielding performance of Helmholtz coil materials. The method utilizes a Helmholtz coil material electromagnetic shielding performance measuring device to measure the electromagnetic shielding performance of the shielding material under test. Specifically, it is implemented according to the following steps: Step 1: Calculate the waveform parameters of the Helmholtz coil injected current based on the lightning environment being measured; Step 2: Measure the reference magnetic field; Step 3: Measure the magnetic field after the shielding material under test is covered by the opening, and calculate the magnetic field shielding effectiveness based on the reference magnetic field and the magnetic field after the shielding material under test is covered.

[0014] The second technical solution of the present invention is further characterized by: Step 1 specifically involves calculating the waveform parameters of the injected current in the Helmholtz coil, including the peak magnetic field strength at the center of the Helmholtz coil, the rate of change of the magnetic field strength, the time corresponding to the peak magnetic field strength, and the time corresponding to the maximum rate of change of the magnetic field strength. The calculation process is as follows: Magnetic field strength at the center of a Helmholtz coil for:

[0015] In equation (11): Represents the permeability of free space. ; The radius of the Helmholtz coil; This represents the number of turns of the Helmholtz coil; This indicates the current passing through the Helmholtz coil. t Indicates time; For standard lightning current A-wave current :

[0016] In equation (12), Indicates the peak value of lightning current. This is the time constant during the rise phase of the lightning current. The time constant for the lightning current decay stage; Substituting equation (12) into equation (11), we get:

[0017] The rate of change of the magnetic field strength at the center of the Helmholtz coil is the first derivative of equation (13). :

[0018] When equation (14) is zero, the maximum magnetic field strength is obtained. At this time, t = :

[0019] The rate of change of the magnetic field strength at the center of the Helmholtz coil is monotonically decreasing during the rising phase. Considering the triggering range during experimental testing, we take... t = The rate of change of magnetic field strength at time t is the test benchmark. Substituting it into equation (14) yields...

[0020] because and Given a time constant, t = Substitution formula (13) t =0.2 The peak magnetic field strength and the rate of change of magnetic field strength at the center of the Helmholtz coil are obtained from equation (14); Select the control parameters for the injected lightning waveform according to the standard / test requirements.

[0021] Step 2 is as follows: Step 2.1: Place the Helmholtz coil on the insulating support; Step 2.2: Connect the output terminal and ground terminal of the impulse current generator to the input and output terminals of the Helmholtz coil, respectively. Step 2.3: Place the signal measurement unit at the measurement position inside the shielded test box; Step 2.4: Operate the impulse current generator and output the specified current waveform of the lightning electromagnetic field according to the Helmholtz coil injection current waveform parameters in Step 1. Adjust the waveform until the peak value and rate of change of the magnetic field strength meet the test requirements. Step 2.5: Record the output of the impulse current generator under the reference magnetic field condition, as well as the peak magnetic field strength when unshielded. The average rate of change of magnetic field strength when unshielded .

[0022] Step 3 specifically involves: Step 3.1: Place the shielding material plate to be tested over the opening, press it firmly, and seal the edges with copper foil to avoid the impact of edge leakage on the test results. Place the entire measuring device in the calibrated position. Step 3.2: Operate the impulse current generator, set the parameters to 100% of the value recorded by the reference magnetic field in Step 2, output pulse current, conduct the test at least 3 times, and take the average value; Step 3.3: Record the output of the impulse current generator under the magnetic field conditions after the shielding material is applied, as well as the peak value of the magnetic field strength after being shielded by the shielding material. and the average rate of change of magnetic field strength shielded by shielding material ; Step 3.4: Calculate the magnetic field shielding effectiveness of the shielding material under test in the time domain. Magnetic field shielding effectiveness, representing the efficiency of suppressing changes in field strength. : , .

[0023] The beneficial effects of this invention are: This invention relates to a lightning electromagnetic field shielding performance measurement device for Helmholtz coil materials. By setting up a magnetic field generator (Helmholtz coil) to generate a large-scale uniform strong magnetic field, it can accurately simulate the lightning magnetic field environment. A dedicated test chamber (shielding test chamber) is designed to achieve precise comparison of the magnetic field at the same point before and after shielding; thus achieving repeatability and accuracy of the measurement.

[0024] The present invention relates to a lightning electromagnetic field shielding performance measurement device for Helmholtz coil materials, which is based on an impulse current generator and a Helmholtz coil. It accurately simulates the lightning magnetic field environment and improves the repeatability and accuracy of time-domain shielding performance testing.

[0025] This invention discloses a method for measuring the electromagnetic shielding performance of Helmholtz coil materials. The method utilizes the measuring device of this invention, standardizes the lightning current waveform injection process, and injects a lightning current conforming to standard specifications into the magnetic field generating device (Helmholtz coil). A specially designed test chamber (shielding test chamber) is used to construct a shielding structure that is only affected by the material under test. By comparing the precise peak magnetic field and average rate of change of the magnetic field before and after shielding, the shielding effectiveness can be calculated to evaluate the material's shielding performance, thus improving the repeatability and accuracy of the measurement. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of the Helmholtz coil material lightning electromagnetic field shielding performance measuring device of the present invention; Figure 2 This is a schematic diagram of the shielding test box in the lightning electromagnetic field shielding performance measurement device for Helmholtz coil materials of the present invention; Figure 3 This is a flowchart of the method for measuring the electromagnetic shielding performance of Helmholtz coil materials in this invention. Figure 4 This is a magnetic field measurement diagram of the shielding material being tested after being placed on the opening cover of the Helmholtz coil material lightning electromagnetic field shielding performance measuring device of the present invention.

[0028] In the diagram, 1. Shielded test box, 2. Opening, 3. Helmholtz coil, 4. Inrush current generator, 5. High-precision magnetic field probe, 6. Positioning bracket, 7. Insulation support, 8. Digital storage oscilloscope, 9. UPS power supply, 10. Electromagnetic shielding box. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0032] Example 1 This embodiment provides a device for measuring the electromagnetic shielding performance of Helmholtz coil materials, including a magnetic field generating device. A shielding test box 1 is set within the magnetic field coverage area of ​​the magnetic field generating device. An opening 2 is provided on the shielding test box 1, allowing the magnetic field lines of the magnetic field generating device to pass through the shielding test box 1. The magnetic field generating device is a Helmholtz coil 3. The Helmholtz coil 3 is a device that generates a uniform magnetic field in a small area. Because the Helmholtz coil has an open nature, it is easy to place or remove other instruments, and it can also be directly observed visually. Furthermore, using the Helmholtz coil 3, the peak magnetic field strength and the rate of change of magnetic field strength at its center can be accurately calculated and estimated.

[0033] Helmholtz coils 3 are set on both sides of the shielded test box 1. The Helmholtz coils 3 are located outside the opening 2 and are connected to the impulse current generator 4. The Helmholtz coils connected to the impulse current generator 4 can reverse the injection waveform to obtain the standard lightning electromagnetic field environment. A signal measurement unit is set inside the shielded test box 1 to measure the magnetic field inside the shielded test box 1.

[0034] This embodiment represents only a preferred implementation of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention. Any lightning electromagnetic field shielding performance measuring device designed with similar technical features to the present invention will fall within the protection scope of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention.

[0035] Example 2 This embodiment provides a device for measuring the electromagnetic shielding performance of Helmholtz coil materials, including a magnetic field generating device. A shielding test box 1 is set within the magnetic field coverage area of ​​the magnetic field generating device. An opening 2 is provided on the shielding test box 1, allowing the magnetic field lines of the magnetic field generating device to pass through the shielding test box 1. The magnetic field generating device is a Helmholtz coil 3, which is set on both sides of the shielding test box 1. The Helmholtz coil 3 is located outside the opening 2, and is connected to an impulse current generator 4. The Helmholtz coil connected to the impulse current generator 4 can reverse calculate the injected waveform to obtain a standard electromagnetic field environment. A signal measurement unit is set inside the shielding test box 1 to measure the magnetic field inside the shielding test box 1.

[0036] The Helmholtz coil 3 consists of two circular coils, one of which is located outside the opening 2. To ensure that the magnetic field uniformity in the central region is >95%, the diameter D of the circular coil satisfies: D≥3L or D≥4d, where L is the side length of the shielded test box 1, d is the diagonal length of the shielded test box 1, and the distance between the two circular coils is s=D / 2.

[0037] This embodiment represents only a preferred implementation of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention. Any lightning electromagnetic field shielding performance measuring device designed with similar technical features to the present invention will fall within the protection scope of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention.

[0038] Example 3 This embodiment provides a device for measuring the electromagnetic shielding performance of Helmholtz coil materials, including a magnetic field generating device. A shielding test box 1 is set within the magnetic field coverage area of ​​the magnetic field generating device. The shielding test box 1 is an iron cube shielding box. An opening 2 is set at the center of one side of the shielding test box 1, and the opening and bottom of the opening 2 are two symmetrical squares. The opening 2 allows the magnetic field lines of the magnetic field generating device to pass through the shielding test box 1. The magnetic field generating device is a Helmholtz coil 3, which is set on both sides of the shielding test box 1. The Helmholtz coil 3 is located outside the opening 2 and is connected to an impulse current generator 4. The Helmholtz coil connected to the impulse current generator 4 can reverse calculate the injected waveform to obtain a standard lightning electromagnetic field environment. A signal measurement unit is set inside the shielding test box 1 to measure the magnetic field inside the shielding test box 1.

[0039] This embodiment represents only a preferred implementation of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention. Any lightning electromagnetic field shielding performance measuring device designed with similar technical features to the present invention will fall within the protection scope of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention.

[0040] Example 4 This embodiment provides a device for measuring the electromagnetic shielding performance of Helmholtz coil materials, including a magnetic field generating device. A shielding test box 1, an iron cube shielding box, is positioned within the magnetic field coverage area of ​​the magnetic field generating device. An opening 2 is located at the center of one side of the shielding test box 1, with the opening and bottom of the opening 2 being two symmetrical squares. The opening 2 allows the magnetic field lines of the magnetic field generating device to traverse the shielding test box 1. The magnetic field generating device is a Helmholtz coil 3, which is positioned on both sides of the shielding test box 1, located outside the opening 2. The Helmholtz coil 3 is connected to an impulse current generator 4. The Helmholtz coil connected to the impulse current generator 4 can reverse-calculate the injected waveform to obtain a standard lightning electromagnetic field environment. A high-precision magnetic field probe 5 is installed inside the shielding test box 1, with a frequency band coverage range of 0.1kHz-30MHz. The high-precision magnetic field probe 5 measures the magnetic field inside the shielding test box 1 and is connected to an oscilloscope to record the time-domain waveform and peak value of the magnetic field.

[0041] This embodiment represents only a preferred implementation of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention. Any lightning electromagnetic field shielding performance measuring device designed with similar technical features to the present invention will fall within the protection scope of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention.

[0042] Example 5 This embodiment provides a device for measuring the electromagnetic shielding performance of Helmholtz coil materials, such as... Figure 1 As shown, it includes a magnetic field generating device, and an iron cube-shaped shielded test box 1 with a side length of 1m is set within the magnetic field coverage area of ​​the magnetic field generating device, as shown. Figure 2 As shown, the shielding test box 1 is an iron cube shielding box. An opening 2 is provided at the center of one side of the shielding test box 1. The opening and bottom of the opening 2 are two symmetrical squares with a side length of 30cm. The opening 2 allows the magnetic field lines of the magnetic field generating device to pass through the shielding test box 1.

[0043] The magnetic field generating device is a Helmholtz coil 3, which consists of two circular coils. The two circular coils are respectively set on both sides of the shielded test box 1, with one of the circular coils located outside the opening 2. The number of turns of the circular coil is N, which can be adjusted as needed. The diameter of the circular coil is 3m, and the distance between the two circular coils is 1.5m. The Helmholtz coil 3 is connected to an impulse current generator 4. The Helmholtz coil connected to the impulse current generator 4 can reverse calculate the injected waveform to obtain a standard lightning electromagnetic field environment.

[0044] A plastic positioning bracket 6 is installed 5cm away from the surface where the opening 2 is located inside the shielded test box 1. A high-precision magnetic field probe 5 is fixed on the positioning bracket 6. The high-precision magnetic field probe 5 is located at the center of the opening 2. The frequency band coverage of the high-precision magnetic field probe 5 is 0.1kHz-30MHz. The high-precision magnetic field probe 5 measures the magnetic field inside the shielded test box 1. The high-precision magnetic field probe 5 is connected in sequence to a digital storage oscilloscope 8 and a UPS (Uninterruptible Power Supply) power supply 9. The digital storage oscilloscope 8 and the UPS power supply 9 are both placed in the electromagnetic shielding box 10 for the instrument.

[0045] The Helmholtz coil material lightning electromagnetic field shielding performance measurement device in this embodiment can measure the magnetic shielding effectiveness of other types of scenarios besides lightning electromagnetic fields by adjusting the injected waveform of Helmholtz coil 3.

[0046] This embodiment represents only a preferred implementation of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention. Any lightning electromagnetic field shielding performance measuring device designed with similar technical features to the present invention will fall within the protection scope of the lightning electromagnetic field shielding performance measuring device for Helmholtz coil materials of the present invention.

[0047] Example 6 This embodiment provides a method for measuring the lightning electromagnetic field shielding performance of Helmholtz coil materials. The lightning electromagnetic field shielding performance measurement device of the Helmholtz coil material described in Embodiment 5 is used to measure the lightning electromagnetic field shielding performance of the shielding material under test. Figure 3 As shown, please follow these steps: Step 1: Calculate the waveform parameters of the injected current in Helmholtz coil 3 based on the lightning environment being measured; The waveform parameters of the injected current in Helmholtz coil 3 include the peak magnetic field strength at the center of Helmholtz coil 3, the rate of change of magnetic field strength, the time corresponding to the peak magnetic field strength, and the time corresponding to the maximum rate of change of magnetic field strength. The calculation process is as follows: Magnetic field strength at the center of Helmholtz coil 3 for:

[0048] In equation (11): Represents the permeability of free space. ; The radius of the Helmholtz coil; This represents the number of turns of the Helmholtz coil; This indicates the current passing through the Helmholtz coil. t Indicates time; For standard lightning current A-wave current :

[0049] In equation (12), Indicates the peak value of lightning current. This is the time constant during the rise phase of the lightning current. The time constant for the lightning current decay stage; Substituting equation (12) into equation (11), we get:

[0050] The rate of change of the magnetic field strength at the center of Helmholtz coil 3 is the first derivative of equation (13). :

[0051] When equation (14) is zero, the maximum magnetic field strength is obtained. t = :

[0052] The rate of change of the magnetic field strength at the center of the Helmholtz coil is monotonically decreasing during the rising phase. Considering the triggering range during experimental testing, we take... t = The rate of change of magnetic field strength at time t is the test benchmark. Substituting it into equation (14) yields...

[0053] because and Given a time constant, t = Substitution formula (13) t =0.2 The peak magnetic field strength and the rate of change of magnetic field strength at the center of Helmholtz coil 3 are obtained from equation (14); Select the control parameters for the injected lightning waveform according to the standard / test requirements.

[0054] According to the standard SAE ARP 5412A-2013 Aircraft Lightning Environment and Related Test Waveforms, α = 11354s. -1 β=647265s -1 , can be obtained =6.3581×10 -06 , =1.2716×10 -05 ,Will t = Substituting into equations (13) and (14), we obtain the magnetic field strength (at 10m from the lightning channel) as 3056 A / m and the magnetic field change rate as 9.138 × 10⁻⁶. 8 A / m / s.

[0055] It is well known in this art that magnetic flux density B reflects the actual total magnetic field strength inside a material / structure, and magnetic field strength H (unit: A / m) satisfies the following conditions: Relationship. Magnetic flux density B is used for theoretical derivation and numerical solutions. In engineering practice, the output signal of a high-precision magnetic field probe is the magnetic field density H, which is converted by an oscilloscope and recorded as a time-domain waveform.

[0056] Step 2: Measure the reference magnetic field; Step 2.1, as follows Figure 1 As shown, the Helmholtz coil 3 is placed on the insulating support 7; Step 2.2: Connect the output terminal and ground terminal of the impulse current generator 4 to the input and output terminals of the Helmholtz coil 3, respectively; Step 2.3: Place the signal measurement unit at the measurement position inside the shielded test box 1; Step 2.4: Operate the impulse current generator 4 and adjust the waveform according to the current waveform specified by the lightning electromagnetic field output in Step 1 until the peak value and rate of change of the magnetic field strength meet the test requirements. Ultimately, the rate of change of the magnetic field affects the response inside the shield or induction. When the peak value and rate of change of the magnetic field strength at the center of the Helmholtz coil 3 cannot be satisfied at the same time, the requirement of the rate of change of the magnetic field shall be satisfied first. Step 2.5: Record the output of the impulse current generator 4 under the reference magnetic field condition, as well as the peak magnetic field strength when unshielded. The average rate of change of magnetic field strength when unshielded .

[0057] As is known in the art, Average rate of change of magnetic field strength = The average rate of change of magnetic field strength without shielding is calculated using this formula. The average rate of change of magnetic field strength after covering with the shielding material in step 3. .

[0058] Step 3: Measure the peak magnetic field strength after covering the opening 2 with the shielding material being tested. and the average rate of change of magnetic field strength The magnetic field shielding effectiveness is calculated based on the reference magnetic field and the magnetic field after the shielding material under test is covered. Step 3.1, as follows Figure 4 As shown, place the shielding material plate to be tested over the opening 2, press it down, and seal the edges with copper foil to avoid the influence of edge leakage on the test results. Place the entire measuring device in the calibrated position. Step 3.2: Operate the impulse current generator 4, set the parameters to 100% of the reference magnetic field recording value, output pulse current, and perform the test 3 or 5 times, taking the average value of the data. Step 3.3: Record the output of the impulse current generator under the magnetic field conditions after the shielding material is applied, as well as the peak value of the magnetic field strength after being shielded by the shielding material. and the average rate of change of magnetic field strength shielded by shielding material ; Step 3.4, Shielding Effectiveness (SE) is an indicator that measures the degree to which a shield attenuates electromagnetic waves. It is usually expressed in decibels (dB). The method to calculate shielding effectiveness is to compare the change in electromagnetic field intensity at a certain spatial location with and without a shield. The formula is: SE = 20lg (E1 / E2) or SE = 20lg (H1 / H2), where SE represents shielding effectiveness, E1 or H1 represents the incident electric field intensity, and E2 or H2 represents the transmitted electric field intensity. The higher the shielding effectiveness, the better the shielding effect. It is usually used to evaluate the ability to suppress electromagnetic interference.

[0059] Calculate the magnetic field shielding effectiveness of the shielding material under test in the time domain. Magnetic field shielding effectiveness, representing the efficiency of suppressing changes in field strength. :

[0060] .

[0061] This embodiment represents only a preferred implementation of the method for measuring the electromagnetic shielding performance of Helmholtz coil materials in this invention. Any method for measuring the electromagnetic shielding performance of Helmholtz coil materials designed with similar technical features to this invention will fall within the protection scope of the method for measuring the electromagnetic shielding performance of Helmholtz coil materials in this invention.

Claims

1. A device for measuring the shielding effectiveness of a material against lightning electromagnetic fields of a Helmholtz coil, characterized in that, The magnetic field generating device is provided with a shielding test box (1) in the magnetic field coverage range, the shielding test box (1) is provided with an opening (2), the opening (2) makes the magnetic field lines of the magnetic field generating device cross the shielding test box (1), the shielding test box (1) is provided with a signal measuring unit, and the signal measuring unit measures the magnetic field in the shielding test box (1); the magnetic field generating device is a Helmholtz coil (3), and the Helmholtz coil (3) is connected with an impulse current generator (4).

2. The Helmholtz coil material lightning electromagnetic field shielding performance measurement device according to claim 1, characterized in that, The Helmholtz coil (3) is arranged on both sides of the shielding test box (1), and the Helmholtz coil (3) is located outside the opening (2).

3. The Helmholtz coil material lightning electromagnetic field shielding performance measurement device according to claim 2, characterized in that, The Helmholtz coil (3) is two circular coils, one of which is located outside the opening (2), and the diameter D of the circular coil satisfies D >= 3L or D >= 4d, L is the length of the side of the shielding test box (1), d is the length of the diagonal of the shielding test box (1), and the distance s between the two circular coils is D / 2.

4. The Helmholtz coil material lightning electromagnetic field shielding performance measurement device of claim 1, wherein, The shielding test box (1) is a ferrous square shielding box, the opening (2) is located at the center of one side face of the shielding test box (1), and the opening (2) has two symmetrical square shapes at the opening and the bottom.

5. The Helmholtz coil material lightning electromagnetic field shielding performance measurement device of claim 1, wherein, The signal measuring unit is a high-precision magnetic field probe (5), and the frequency band coverage range of the high-precision magnetic field probe (5) is 0.1 kHz-30 MHz.

6. The Helmholtz coil material lightning electromagnetic field shielding performance measurement device according to claim 5, characterized in that, The shielding test box (1) is provided with a positioning support (6) made of plastic, the high-precision magnetic field probe (5) is fixed on the positioning support (6), and the high-precision magnetic field probe (5) is located at the center of the opening (2).

7. A method for measuring lightning electromagnetic field shielding performance of a material of a Helmholtz coil, which measures lightning electromagnetic field shielding performance of a shielding material to be measured using the lightning electromagnetic field shielding performance measuring device for a material of a Helmholtz coil according to claim 2, characterized in that, Specifically, the following steps are implemented: Step 1, according to the lightning environment to be measured, the current waveform parameters of the Helmholtz coil (3) are calculated; Step 2, the reference magnetic field is measured; Step 3, the magnetic field after the opening (2) is covered with the shielding material to be measured is measured, and the magnetic field shielding efficiency is calculated according to the reference magnetic field and the magnetic field after the opening (2) is covered with the shielding material to be measured.

8. The method of measuring the shielding effectiveness of a material against an electromagnetic field of a lightning of a Helmholtz coil according to claim 7, characterized in that, The step 1 is specifically that the current waveform parameters of the Helmholtz coil (3) include the magnetic field strength peak value at the center of the Helmholtz coil (3), the magnetic field strength change rate, the time corresponding to the magnetic field strength peak value and the time corresponding to the maximum magnetic field strength change rate, and the calculation process is as follows: The magnetic field strength at the center of the Helmholtz coil (3) Is: In formula (11), represents the vacuum permeability, ; is the radius of the Helmholtz coil; is the number of turns of the Helmholtz coil; represents the current through the Helmholtz coil, t represents time; For standard lightning current A-wave current : In formula (12), denotes the lightning current peak value, is the time constant of the lightning current rise phase, is the time constant of the lightning current decay phase; The formula (12) is brought into the formula (11) to obtain: The rate of change of the magnetic field strength at the center of the Helmholtz coil (3) is the first derivative of equation (13) : When the formula (14) is zero, the magnetic field strength maximum is obtained, at this time, t = 0 : The monotone decreasing rate of the magnetic field strength rising section at the center of the Helmholtz coil is considered, and the trigger range is taken into account when testing t = The magnetic field strength change rate at the moment is the test reference, and the formula (14) is substituted Since and is a known time constant, we have t = Substituting into equation (13), t =0.2 and equation (14) gives the peak magnetic field strength and the rate of change of magnetic field strength at the center of the Helmholtz coil (3). According to the standard / test requirements, the control parameters of the injected lightning waveform are selected.

9. The method of measuring the shielding effectiveness of a material against an electromagnetic field of a lightning of a Helmholtz coil according to claim 7, wherein, The step 2 is specifically: Step 2.1, the Helmholtz coil (3) is placed on the insulating support (7); Step 2.2, the output end and the grounding end of the impulse current generator (4) are connected with the input and output ends of the Helmholtz coil (3) respectively; Step 2.3, the signal measuring unit is placed in the measuring position in the shielding test box (1); Step 2.4, the impulse current generator (4) is operated, the current waveform of the specified lightning magnetic field is output according to the current waveform parameters of the Helmholtz coil in step 1, the waveform is adjusted until the magnetic field strength peak value and the change rate meet the test requirements; Step 2.

5. Record the output of the impulse current generator (4) at the reference magnetic field condition, and the peak magnetic field strength without shielding and the average rate of change of magnetic field strength without shielding .

10. The method of measuring the shielding effectiveness of a material against an electromagnetic field of a lightning of a Helmholtz coil according to claim 9, wherein, The step 3 is specifically: Step 3.1, cover the opening (2) with the shielding material plate to be tested, press tightly, use copper foil to seal the edges to avoid edge leakage affecting the test results, and place the entire measuring device in the calibrated position; Step 3.2, operate the impulse current generator (4), set the parameters to 100% of the reference magnetic field recording value in step 2, output pulse current, test at least 3 times, and take the average value; Step 3.3, record the output of the impulse current generator under the magnetic field condition after the shielding material is placed on the cover, and the peak value of the magnetic field intensity shielded by the shielding material and the average rate of change of the magnetic field intensity shielded by the shielding material ; Step 3.4, calculating the magnetic shielding effectiveness of the measured shielding material in the time domain and the magnetic shielding effectiveness representing the field strength change rate suppression efficiency : 。

Images