Method and device for evaluating shielding effectiveness of magnetic shielding assembly

Abstract

The invention provides a method and device for evaluating the shielding effectiveness of a magnetic shielding assembly, and relates to the technical field of shielding effectiveness evaluation of magnetic shielding assemblies. The magnetic shielding assemblies are placed in the center of the axis of the Helmholtz coil, and the evaluation method comprises the steps that under the condition that the Helmholtz coil is no-load, magnetic field values in the N magnetic shielding assemblies are measured at a first set step length, and a no-load magnetic field value is obtained; controlling the constant current source to output current so as to enable the Helmholtz coil to generate a working magnetic field; under the condition that the Helmholtz coil generates the working magnetic field, the magnetic field values in the N magnetic shielding assemblies are measured again at the first set step length, and a loaded magnetic field value is obtained; calculating an internal magnetic field difference value of the magnetic shielding assembly according to the no-load magnetic field value and the loaded magnetic field value of the same position of the magnetic shielding assembly; and calculating a shielding effectiveness value of the magnetic shielding assembly according to the internal magnetic field difference value and the working magnetic field to determine whether the shielding effectiveness of the magnetic shielding assembly is qualified. According to the invention, high-efficiency and accurate evaluation before assembling of the magnetic shielding assembly can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic shielding assembly shielding effectiveness evaluation, in particular to a magnetic shielding assembly shielding effectiveness evaluation method and device. BACKGROUND

[0002] The core working principle of a hydrogen atomic clock is based on the energy level transition of a hydrogen atom, and the energy level transition frequency of the hydrogen atom has a clear correlation with the magnetic field strength of the magnetic environment in which it is located, and the specific relationship is: f = f0 + 2766H 2 (wherein, f is the actual transition frequency, f0 is the transition frequency in an ideal non-magnetic environment, and H is the magnetic field strength).

[0003] Further, the change of the external magnetic field will directly cause the fluctuation of the atomic transition frequency, and the fluctuation relationship can be expressed as: Δf = a*H*ΔH (wherein, Δf is the frequency fluctuation value, a is the proportional coefficient, and ΔH is the magnetic field strength change). As can be seen, the smaller the magnetic field strength sensed by the hydrogen atom, the weaker the magnetic field strength change, the higher the stability of the transition frequency, and the more excellent the magnetic sensitivity index of the hydrogen atomic clock.

[0004] In order to create an ideal working environment of "near zero magnetic" for hydrogen atoms, a special magnetic shielding assembly needs to be designed in the development process of a hydrogen atomic clock product to shield external magnetic field interference. The core index for evaluating the performance of the magnetic shielding assembly is the shielding effectiveness, which is defined as the ratio of the external magnetic field strength to the internal magnetic field strength of the magnetic shielding assembly, that is, S = H 外 / H 内 (wherein, S is the shielding effectiveness, H 外 is the external magnetic field strength, and H 内 is the internal magnetic field strength). There are many factors affecting the shielding effectiveness of the magnetic shielding assembly, mainly including: the initial magnetic permeability and thickness of the magnetic shielding material, the structural design of the magnetic shielding assembly, the heat treatment level of the magnetic shielding assembly, the demagnetization effect of the magnetic shielding assembly, and the assembly process of the magnetic shielding assembly. Any improper handling of the above steps will result in substandard shielding effectiveness of the magnetic shielding assembly.

[0005] In the prior art, the magnetic shielding assembly is directly assembled into the hydrogen atomic clock after being processed according to the design drawing and subjected to multiple process treatments; and the performance of the magnetic shielding assembly is indirectly reflected by testing the magnetic sensitivity index of the hydrogen atomic clock product after the development of the hydrogen atomic clock product is completed. This method has significant defects: if the magnetic sensitivity index is not up to standard, the magnetic shielding assembly inside the hydrogen atomic clock needs to be disassembled to troubleshoot the problem, which not only has problems such as difficult positioning and large rework workload, but also seriously affects the reliability and consistency of the hydrogen atomic clock product, and prolongs the development cycle.

[0006] Therefore, there is an urgent need for a technical solution that can accurately evaluate the shielding effectiveness of a magnetic shielding assembly before it is assembled into a hydrogen atomic clock, to solve the pain points of the prior art. SUMMARY

[0007] To solve at least one of the above problems, the present application proposes a method and device for evaluating the shielding effectiveness of a magnetic shielding assembly, which solves the problems of disassembly, rework, difficult problem positioning, and long development cycle of a hydrogen atomic clock caused by poor magnetic sensitivity index in the prior art, realizes efficient and accurate evaluation of the magnetic shielding assembly before assembly, and guarantees the consistency, reliability, and controllability of the development cycle of the hydrogen atomic clock product.

[0008] According to a first aspect of the present application, at least one embodiment of the present application provides a method for evaluating the shielding effectiveness of a magnetic shielding assembly, the magnetic shielding assembly being placed at the center of the axis of a Helmholtz coil, the evaluation method comprising: measuring the magnetic field values inside N magnetic shielding assemblies at a first set step under the condition that the Helmholtz coil is unloaded, to obtain unloaded magnetic field values, wherein N is an integer greater than or equal to 2; controlling a constant current source to output a current to make the Helmholtz coil generate a working magnetic field; under the condition that the Helmholtz coil generates the working magnetic field, the magnetic field values inside the N magnetic shielding assemblies are measured again at the first set step to obtain loaded magnetic field values; calculating the internal magnetic field difference value of the magnetic shielding assembly according to the unloaded magnetic field value and the loaded magnetic field value at the same position of the magnetic shielding assembly; calculating the shielding effectiveness value of the magnetic shielding assembly according to the internal magnetic field difference value and the working magnetic field; and determining whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness value.

[0009] For example, in some embodiments of the present application, the shielding effectiveness value is calculated according to the following formula:

[0010] wherein, the shielding effectiveness value is the working magnetic field is the internal magnetic field difference value is the unloaded magnetic field value is the loaded magnetic field value is.

[0011] For example, in some embodiments of the present application, the axis of the magnetic shielding assembly is provided with a demagnetizing wire connected with a demagnetizing machine, and the evaluation method further comprises: loading multiple demagnetizing currents in the demagnetizing wire to perform demagnetization treatment on the magnetic shielding assembly before measuring the unloaded magnetic field value of the magnetic shielding assembly, wherein the multiple demagnetizing currents have different sizes.

[0012] For example, in some embodiments of the present application, the determining whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness values comprises: determining whether the number of the shielding effectiveness values higher than a first set threshold is greater than or equal to a second set threshold; and determining that the shielding effectiveness of the magnetic shielding assembly is qualified in the case that the number of the shielding effectiveness values higher than the first set threshold is greater than or equal to the second set threshold.

[0013] According to a second aspect of the present application, at least one embodiment of the present application provides an evaluation device for shielding effectiveness of a magnetic shielding assembly, which is used to perform the evaluation method as described in any one of the first aspect, and the evaluation device comprises: a Helmholtz coil for generating a working magnetic field; a constant current source connected with the Helmholtz coil for adjusting the current to make the Helmholtz coil generate the working magnetic field; a fluxgate magnetometer for measuring the magnetic field values inside N magnetic shielding assemblies at a first set step in the cases of no load of the Helmholtz coil and generation of the working magnetic field by the Helmholtz coil, to obtain no-load magnetic field values and loaded magnetic field values respectively, wherein N is an integer greater than or equal to 2; and an upper computer for calculating internal magnetic field difference values of the magnetic shielding assemblies according to the no-load magnetic field values and the loaded magnetic field values of the same positions of the magnetic shielding assemblies, and for calculating shielding effectiveness values of the magnetic shielding assemblies according to the internal magnetic field difference values and the working magnetic field, and for determining whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness values.

[0014] For example, in some embodiments of the present application, the Helmholtz coil comprises a two-dimensional or three-dimensional Helmholtz coil.

[0015] For example, in some embodiments of the present application, the upper computer is used to calculate the shielding effectiveness values according to the following formula:

[0016] wherein, is the shielding effectiveness value, is the working magnetic field, is the internal magnetic field difference value, is the no-load magnetic field value, is the loaded magnetic field value.

[0017] For example, in some embodiments of the present application, further comprising: a demagnetization wire arranged at an axis of the magnetic shielding assembly; and a demagnetization machine connected with the demagnetization wire for loading multiple demagnetization currents in the demagnetization wire to perform demagnetization treatment on the magnetic shielding assembly before measuring the no-load magnetic field value of the magnetic shielding assembly, wherein the multiple demagnetization currents have different sizes.

[0018] For example, in some embodiments of the present application, the host computer is configured to determine whether the number of the N shielding effectiveness values that are higher than a first threshold is greater than or equal to a second threshold, and to determine that the shielding effectiveness of the magnetic shielding assembly is qualified when the number of the shielding effectiveness values that are higher than the first threshold is greater than or equal to the second threshold.

[0019] For example, in some embodiments of the present application, the magnetic shielding assembly is further configured to be assembled into the hydrogen atomic clock according to an assembly process of the magnetic shielding assembly in the hydrogen atomic clock.

[0020] Through the above example embodiments, the magnetic shielding assembly shielding effectiveness evaluation method and device provided by the present application have at least one of the following beneficial effects: The shielding effectiveness evaluation is completed before the magnetic shielding assembly is assembled into the hydrogen atomic clock, qualified assemblies can be screened in advance, the problem of disassembly and troubleshooting due to insufficient magnetic sensitivity after assembly is completely solved, the rework workload is reduced, and the development cycle of the hydrogen atomic clock is shortened.

[0021] Through the design of "magnetic tool simulation of actual assembly process", "multiple demagnetization at different currents", "Helmholtz coil providing stable and uniform magnetic field", and "multi-point coincidence measurement", the interference factors such as tool magnetism, assembly residual magnetism, and non-uniformity of the magnetic field are eliminated, and it is ensured that the shielding effectiveness calculation result can truly reflect the actual performance of the assembly.

[0022] Through the standardized evaluation process and clear qualification criteria, the performance of the mass-produced magnetic shielding assembly can be unified, and the overall consistency and working reliability of the hydrogen atomic clock product are improved, thereby providing protection for the stable operation of the hydrogen atomic clock.

[0023] It should be understood that the above general description and the following detailed description are only exemplary and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0024] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description of example embodiments thereof, taken in conjunction with the accompanying drawings. The drawings described below are only some embodiments of the present application, and are not limiting to the present application.

[0025] Figure 1 A schematic diagram of a magnetic shielding assembly shielding effectiveness evaluation device of an example embodiment is shown; Figure 2 A flowchart of a magnetic shielding assembly shielding effectiveness evaluation method of an example embodiment is shown; Figure 3 A structural schematic diagram of a magnetic shielding assembly of an example embodiment is shown. DETAILED DESCRIPTION

[0026] Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings. Example embodiments, however, can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the example embodiments to those skilled in the art. Like reference numerals refer to like elements throughout the several views.

[0027] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the

[0028] The flow charts shown in the drawings are only exemplary and do not necessarily have to include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be further broken down, and some operations / steps can be combined or partially combined, so the actual execution order can be changed according to actual conditions.

[0029] The terms "first", "second", and the like in the description and in the claims of the present application and the above drawings are used to distinguish between similar objects, not to describe a particular sequential order. In addition, the terms "comprises", "comprising", and the like are intended to cover non-exclusive inclusions. For example, processes, methods, systems, products, or devices that comprise a list of steps or units are not limited to the listed steps or units, but can optionally further include other steps or units not listed, or can optionally further include other steps or units inherent to such processes, methods, products, or devices.

[0030] Those skilled in the art can understand that the drawings are only schematic views of example embodiments, and the modules or flows in the drawings are not necessarily essential for implementing the present application, and therefore should not be used to limit the scope of protection of the present application.

[0031] Figure 1 A schematic diagram of an evaluation device for magnetic shielding effectiveness of a magnetic shielding assembly is shown.

[0032] As shown in Figure 1 The evaluation device for magnetic shielding effectiveness of a magnetic shielding assembly includes a Helmholtz coil 101, a constant current source 102, a fluxgate magnetometer 103, and a host computer 104.

[0033] The Helmholtz coil 101 is configured to generate a working magnetic field.

[0034] According to some embodiments, the Helmholtz coil comprises a two-dimensional or three-dimensional Helmholtz coil for generating a stable and uniform external magnetic field to provide a standard magnetic field environment for evaluating the shielding effectiveness of the magnetic shielding assembly. The uniform magnetic field region of the Helmholtz coil can cover a cylindrical space of φ200xH500mm, and the magnetic field inhomogeneity in the space is not more than ±5%, which can ensure the consistency of the external magnetic field conditions.

[0035] The constant current source 102 is connected to the Helmholtz coil 101 for adjusting the current to make the Helmholtz coil 101 generate a working magnetic field.

[0036] When the constant current source 102 is turned off, the Helmholtz coil 101 is in an unloaded state. When the constant current source 102 is turned on, the Helmholtz coil 101 generates a working magnetic field.

[0037] The fluxgate magnetometer 103 is used to measure the magnetic field values inside the N magnetic shielding assemblies 10 at a first set step under the conditions of the Helmholtz coil 101 being unloaded and the Helmholtz coil 101 generating a working magnetic field, respectively obtaining unloaded magnetic field values and loaded magnetic field values. Wherein, N is an integer greater than or equal to 2.

[0038] The host computer 104 is used to calculate the internal magnetic field difference value of the magnetic shielding assembly 10 according to the unloaded magnetic field value and the loaded magnetic field value of the same position of the magnetic shielding assembly 10. The host computer 104 is used to calculate the shielding effectiveness value of the magnetic shielding assembly according to the internal magnetic field difference value and the working magnetic field. The host computer 104 is also used to determine whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness value, including: judging whether the number of shielding effectiveness values higher than a first set threshold in N shielding effectiveness values is greater than or equal to a second set threshold; in the case that the number of shielding effectiveness values higher than the first set threshold is greater than or equal to the second set threshold, it is determined that the shielding effectiveness of the magnetic shielding assembly 10 is qualified.

[0039] According to an example embodiment, the host computer 104 is used to calculate the shielding effectiveness value according to the following formula:

[0040] Wherein, is the shielding effectiveness value, is the working magnetic field, is the internal magnetic field difference value, is the unloaded magnetic field value, is the loaded magnetic field value.

[0041] According to an example embodiment, the evaluation device further comprises a demagnetization guide wire and a demagnetization machine (not shown in the figure).

[0042] Before measuring the no-load magnetic field value of the magnetic shielding assembly, the demagnetizing wire passes along the axis of the magnetic shielding assembly 10. The demagnetizing machine is connected with the demagnetizing wire, and is used for loading multiple demagnetizing currents in the demagnetizing wire, so as to demagnetize the magnetic shielding assembly 10 before measuring the no-load magnetic field value of the magnetic shielding assembly 10, eliminate the residual magnetism in the magnetic shielding assembly, and avoid the influence of the residual magnetism on the shielding effectiveness evaluation result.

[0043] According to some embodiments, the multiple demagnetizing currents are different in size, so as to completely eliminate the residual magnetism in the material through "gradient demagnetization". For example, two demagnetizing currents are loaded, and the two demagnetizing currents are respectively about 100A and 50A.

[0044] According to an example embodiment, the evaluation device further comprises a non-magnetic matching tool (not shown in the figure).

[0045] The non-magnetic matching tool is used for assembling the magnetic shielding assembly according to the assembly process of the magnetic shielding assembly in the hydrogen atomic clock, so as to ensure that the evaluation state is consistent with the actual installation state.

[0046] According to some embodiments, the non-magnetic matching tool is made of non-magnetic material, which can avoid the magnetic interference of the tool itself on the magnetic field measurement.

[0047] As shown in Figure 3 , the three-layer magnetic shielding assembly of the hydrogen atomic clock is assembled according to the assembly process using the non-magnetic matching tool, and then the assembled magnetic shielding assembly is placed at the axis center of the Helmholtz coil 101, so as to perform the shielding effectiveness evaluation of the magnetic shielding assembly by using the evaluation method.

[0048] Figure 2 A flowchart of the evaluation method of the shielding effectiveness of the magnetic shielding assembly according to an example embodiment is shown.

[0049] As shown in Figure 2 , the evaluation method of the shielding effectiveness of the magnetic shielding assembly is performed by the evaluation device as described above, and the evaluation method comprises steps S201-S207.

[0050] In step S201, multiple demagnetizing currents are loaded in the demagnetizing wire to demagnetize the magnetic shielding assembly.

[0051] The demagnetizing machine loads multiple demagnetizing currents with different sizes to the magnetic shielding assembly through the demagnetizing wire, eliminates the residual magnetism in the assembly, and avoids the influence of the residual magnetism on the shielding effectiveness evaluation result. For example, two demagnetizing currents with different sizes can be loaded, and the number of times is not limited in the present application, which is only an example.

[0052] In step S202, the magnetic field values in the N magnetic shielding assemblies are measured at a first set step under the no-load condition of the Helmholtz coil, and the no-load magnetic field values are obtained, which are denoted as B 1N .

[0053] Turn off the constant current source, and the Helmholtz coil has no external magnetic field. Place the demagnetized magnetic shielding assembly at the center of the Helmholtz coil axis. Insert the probe of the fluxgate magnetometer into the magnetic shielding assembly, and measure the internal magnetic field value along the axis of the magnetic shielding assembly. When measuring, start from the farthest end of the magnetic shielding assembly, and collect the magnetic field data of several points at the set step length, to ensure that the data cover the key areas inside the magnetic shielding assembly.

[0054] In step S203, control the constant current source to output current, so that the Helmholtz coil generates a working magnetic field.

[0055] The constant current source is electrically connected with the Helmholtz coil. By adjusting the size of the output current, the Helmholtz coil generates a working magnetic field with a preset intensity, denoted as B0.

[0056] According to some embodiments, the preset working magnetic field in this application is preferably 2Gs or 1Gs. 2Gs or 1Gs can accurately simulate the external weak magnetic field interference that may actually be encountered, so that the "external loaded magnetic field" in the evaluation process is consistent with the "real external magnetic field" that the magnetic shielding assembly needs to shield after installation - avoiding the evaluation results from being unable to reflect the shielding capability under weak magnetic field due to the magnetic field being set too strong (such as tens of Gs), or the external magnetic field change being unable to effectively drive the internal magnetic field response due to the magnetic field being set too weak (such as 0.1Gs), ultimately ensuring that the evaluation results can directly determine whether the assembly meets the installation requirements; and can avoid the demagnetization operation of step S201 being invalid due to the magnetic shielding assembly being reloaded with a magnetic field after the input current.

[0057] According to some embodiments, steps S202 and S203 can be exchanged in order, and this application only takes the example of first performing step S202 and then performing step S203, but is not limited thereto.

[0058] In step S204, under the condition that the Helmholtz coil generates a working magnetic field, the magnetic field value inside the N magnetic shielding assemblies is measured again at the first set step length, to obtain the loaded magnetic field value, denoted as B 2N .

[0059] Turn on the constant current source to make the Helmholtz coil generate a preset magnetic field B0; keep the position of the magnetic shielding assembly unchanged. Insert the probe of the fluxgate magnetometer into the magnetic shielding assembly, and measure the internal magnetic field value again along the axis of the magnetic shielding assembly by following the same path as step S202. When measuring, start from the farthest end of the magnetic shielding assembly, and collect the magnetic field data of several points at the set step length, to ensure that the data cover the key areas inside the magnetic shielding assembly.

[0060] In step S205, calculate the internal magnetic field difference value of the magnetic shielding assembly according to the no-load magnetic field value and the loaded magnetic field value at the same position of the magnetic shielding assembly.

[0061] The internal magnetic field difference value of the same position is calculated according to the following formula:

[0062] wherein, is the internal magnetic field difference value, which can reflect the influence degree of the external magnetic field change on the internal magnetic field of the magnetic shielding assembly, is the empty load magnetic field value, is the loaded magnetic field value.

[0063] In step S206, the shielding effectiveness value of the magnetic shielding assembly is calculated according to the internal magnetic field difference value and the working magnetic field.

[0064] According to the example embodiment, the shielding effectiveness value is calculated according to the following formula:

[0065] wherein, is the shielding effectiveness value.

[0066] In step S207, whether the shielding effectiveness of the magnetic shielding assembly is qualified is determined according to the shielding effectiveness value.

[0067] It is judged whether the number of shielding effectiveness values higher than the first set threshold value is greater than or equal to the second set threshold value among the N shielding effectiveness values; the shielding effectiveness S of the measurement point and the qualified point number are taken as the criterion: in the case that the number of shielding effectiveness values higher than the first set threshold value is greater than or equal to the second set threshold value, it is determined that the shielding effectiveness of the magnetic shielding assembly is qualified; in the case that the number of shielding effectiveness values higher than the first set threshold value is less than the second set threshold value, it is determined that the shielding effectiveness of the magnetic shielding assembly is unqualified.

[0068] For example, it is required that the shielding effectiveness S of no less than 15 points among 20 measurement points is not less than 1x10 5 , that is, it is determined that the magnetic shielding assembly is qualified and has the condition of being assembled to the hydrogen atomic clock.

[0069] This application provides a device and method for evaluating the shielding effectiveness of a hydrogen atomic clock magnetic shielding component. It allows for the early screening of qualified components, avoiding the need for disassembly and troubleshooting after installation due to substandard performance. This addresses the pain points of difficult problem localization and repeated rework in existing technologies, ensuring a controllable development cycle for the hydrogen atomic clock. Through non-magnetic tooling, multiple gradient demagnetization and overlap measurements, and a uniform working magnetic field, interference from tooling magnetism and component residual magnetism is eliminated, ensuring accurate shielding effectiveness calculations and improving the reliability of evaluation results. It accurately distinguishes component performance differences, avoiding errors from empirical judgments and improving the consistency of mass production of hydrogen atomic clock magnetic shielding components. It eliminates the need for a complex testing system for the entire hydrogen atomic clock, enabling efficient evaluation through a modular device, reducing hardware environment dependence and minimizing the impact of component disassembly on the structural reliability of the hydrogen atomic clock. The modular design of the device allows for adjustment of parameters such as measurement step size and demagnetization current, adapting to the magnetic shielding evaluation needs of different hydrogen atomic clock models without large-scale hardware modifications, reducing the difficulty of system upgrades and maintenance.

[0070] Taking the three-layer magnetic shielding assembly of a certain type of passive hydrogen atomic clock as the evaluation object, the shielding effectiveness was evaluated based on the evaluation device and method of this application. The specific process is as follows: 1. Using a matching tooling made of non-magnetic aluminum alloy, the three-layer magnetic shielding components are assembled into a complete unit according to the assembly process of the magnetic shielding components inside the hydrogen atomic clock of this model.

[0071] 2. Thread the demagnetizing wire along the axis of the assembled magnetic shielding assembly, and connect both ends of the wire to the demagnetizer; first apply a demagnetizing current of 100A for 30s, then apply a demagnetizing current of 50A for 20s to complete the demagnetization.

[0072] 3. Fix the probe of the fluxgate magnetometer at the center of the Helmholtz coil axis, turn on the constant current source and adjust the current; when the fluxgate magnetometer displays a magnetic field value of 2Gs, record the constant current source current as 0.78A and lock the current value.

[0073] 4. Turn off the constant current source and place the demagnetized magnetic shielding assembly at the center of the Helmholtz coil axis; insert the fluxgate magnetometer probe from the top (farthest end) of the magnetic shielding assembly, and measure the magnetic field value at 20 points from top to bottom in 1cm increments, and record it as B1.

[0074] 5. Turn on the constant current source (maintain 0.78A output) to generate a 2Gs magnetic field in the Helmholtz coil; keep the position of the magnetic shielding component unchanged, and measure the magnetic field value at 20 points again along the same path as in step 4 (step size 1cm, measurement points completely coincide with step 4), and record it as B2.

[0075] 6. Calculate ΔB for each point, and then calculate the shielding effectiveness S using the formula S=2Gs / ΔB.

[0076] 7. Count the S value of 20 measuring points.

[0077] For example, where S of 18 points is greater than or equal to 1 x 10 5 , the criterion of "not less than 15 points qualified" is met, and the magnetic shielding assembly is determined to be qualified and can be assembled to the hydrogen atomic clock.

[0078] It can be seen from the embodiment that the evaluation device and method of the application can efficiently and accurately complete the shielding effectiveness evaluation of the hydrogen atomic clock magnetic shielding assembly, and provide reliable guarantee for the development of hydrogen atomic clock products.

[0079] It should be clearly understood that the application describes how to form and use specific examples, but the application is not limited to any details of these examples. Instead, based on the teachings of the disclosure of the application, these principles can be applied to many other embodiments.

[0080] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the application, and are not for limiting purposes. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be executed synchronously or asynchronously, for example, in multiple modules.

[0081] The exemplary embodiments of the application are specifically shown and described above. It can be understood that the application is not limited to the detailed structure, arrangement or implementation method described herein; on the contrary, the application is intended to cover various modifications and equivalent arrangements included in the object and scope of the appended claims.

Claims

1. A method for evaluating the shielding effectiveness of a magnetic shielding assembly, characterized in that, The magnetic shielding assembly is placed at the center of the Helmholtz coil's axis, and the evaluation method includes: When the Helmholtz coil is unloaded, the magnetic field values ​​inside N of the magnetic shielding components are measured with a first set step size to obtain the unloaded magnetic field value, where N is an integer greater than or equal to 2; The output current of the constant current source is controlled to generate a working magnetic field in the Helmholtz coil. When the Helmholtz coil generates the working magnetic field, the magnetic field value inside the N magnetic shielding components is measured again with the first set step size to obtain the loaded magnetic field value; The internal magnetic field difference of the magnetic shielding component is calculated based on the unloaded magnetic field value and the loaded magnetic field value at the same location of the magnetic shielding component. The shielding effectiveness of the magnetic shielding component is calculated based on the internal magnetic field difference and the working magnetic field. Based on the shielding effectiveness value, determine whether the shielding effectiveness of the magnetic shielding component is qualified.

2. The evaluation method as described in claim 1, characterized in that, The shielding effectiveness value is calculated according to the following formula: in, The shielding effectiveness value is... The working magnetic field, The difference in the internal magnetic field. The unloaded magnetic field value is... The applied magnetic field value.

3. The evaluation method as described in claim 1, characterized in that, The magnetic shielding assembly has a demagnetizing conductor along its axis, the demagnetizing conductor being connected to a demagnetizing machine, and the evaluation method further includes: Multiple demagnetizing currents are applied to the demagnetizing conductor to demagnetize the magnetic shielding assembly before measuring the unloaded magnetic field value of the magnetic shielding assembly, wherein the magnitudes of the multiple demagnetizing currents are different.

4. The evaluation method as described in claim 1, characterized in that, The step of determining whether the shielding effectiveness of the magnetic shielding component is qualified based on the shielding effectiveness value includes: Determine whether the number of shielding effectiveness values ​​higher than a first preset threshold among the N shielding effectiveness values ​​is greater than or equal to a second preset threshold; If the number of shielding effectiveness values ​​higher than the first set threshold is greater than or equal to the second set threshold, the shielding effectiveness of the magnetic shielding component is determined to be qualified.

5. A device for evaluating the shielding effectiveness of a magnetic shielding assembly, characterized in that, The evaluation apparatus for performing the evaluation method as described in any one of claims 1-4 includes: Helmholtz coils are used to generate a working magnetic field; A constant current source, connected to the Helmholtz coil, is used to adjust the current so that the Helmholtz coil generates the working magnetic field; A fluxgate magnetometer is used to measure the magnetic field values ​​inside N magnetic shielding components with a first set step size when the Helmhertz coil is unloaded and when the Helmhertz coil generates the working magnetic field, respectively obtaining the unloaded magnetic field value and the loaded magnetic field value, where N is an integer greater than or equal to 2; The host computer is used to calculate the internal magnetic field difference of the magnetic shielding component based on the unloaded magnetic field value and the loaded magnetic field value at the same position of the magnetic shielding component, and to calculate the shielding effectiveness value of the magnetic shielding component based on the internal magnetic field difference and the working magnetic field. It is also used to determine whether the shielding effectiveness of the magnetic shielding component is qualified based on the shielding effectiveness value.

6. The evaluation apparatus as described in claim 5, characterized in that, The Helmholtz coil includes a two-dimensional or three-dimensional Helmholtz coil.

7. The evaluation apparatus as described in claim 5, characterized in that, The host computer is used to calculate the shielding effectiveness value according to the following formula: in, The shielding effectiveness value is... The working magnetic field, The difference in the internal magnetic field. The unloaded magnetic field value is... The applied magnetic field value.

8. The evaluation apparatus as described in claim 5, characterized in that, Also includes: A demagnetizing conductor is positioned along the axis of the magnetic shielding assembly; A demagnetizer, connected to the demagnetizing conductor, is used to apply multiple demagnetizing currents to the demagnetizing conductor to demagnetize the magnetic shielding assembly before measuring the unloaded magnetic field value of the magnetic shielding assembly, wherein the magnitudes of the multiple demagnetizing currents are different.

9. The evaluation apparatus as described in claim 5, characterized in that, The host computer is used to determine whether the number of shielding effectiveness values ​​higher than the first set threshold is greater than or equal to the second set threshold among the N shielding effectiveness values, and to determine that the shielding effectiveness of the magnetic shielding component is qualified when the number of shielding effectiveness values ​​higher than the first set threshold is greater than or equal to the second set threshold.

10. The evaluation apparatus as claimed in claim 5, characterized in that, Also includes: A non-magnetic tooling is used to assemble the magnetic shielding component according to the assembly process of the magnetic shielding component in the hydrogen atomic clock.

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