Method and device for evaluating shielding effectiveness of a magnetic shielding assembly

Abstract

The application provides a kind of magnetic shielding assembly shielding effectiveness evaluation method and device, it is related to magnetic shielding assembly shielding effectiveness evaluation technical field.Magnetic shielding assembly is placed in the axis center of helmholtz coil, and evaluation method includes: in the case where helmholtz coil is unloaded, with first set step, the magnetic field value inside N magnetic shielding assembly is measured, and unloaded magnetic field value is obtained;Control constant current source output current, so that helmholtz coil generates working magnetic field;In the case where helmholtz coil generates working magnetic field, first set step is measured again, and the magnetic field value inside N magnetic shielding assembly is obtained, and loading magnetic field value is obtained;According to the unloaded magnetic field value and loading magnetic field value of the same position of magnetic shielding assembly, the internal magnetic field difference value of magnetic shielding assembly is calculated;According to internal magnetic field difference value and working magnetic field, the shielding effectiveness value of magnetic shielding assembly is calculated, to determine whether the shielding effectiveness of magnetic shielding assembly is qualified.The application can realize efficient and accurate evaluation before magnetic shielding assembly assembly.

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 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 whole machine after the hydrogen atomic clock product is developed. 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 as follows:

[0010]

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] For example, in some embodiments of the present application, the Helmholtz coil comprises a two-dimensional or three-dimensional Helmholtz coil.

[0016] 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:

[0017]

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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:

[0023] 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.

[0024] Through the design of "magnetic tool simulation of actual assembly process", "multiple different current demagnetization", "Helmholtz coil providing stable and uniform magnetic field", "multi-point coincidence measurement", and the like, interference factors such as tool magnetism, component 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.

[0025] 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.

[0026] It should be understood that the foregoing general description and the following detailed description are only exemplary and are not limiting of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which example embodiments of the present application are shown by way of illustration. The drawings described below are only some embodiments of the present application, and are not limiting of the present application.

[0028] Figure 1 A schematic diagram of a magnetic shielding assembly shielding effectiveness evaluation device of an example embodiment is shown;

[0029] Figure 2 A flowchart of a magnetic shielding assembly shielding effectiveness evaluation method of an example embodiment is shown;

[0030] Figure 3 A structural schematic diagram of a magnetic shielding assembly of an example embodiment is shown. DETAILED DESCRIPTION

[0031] 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.

[0032] The described features, structures, or characteristics can be combined 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

[0033] The flow charts shown in the drawings are merely examples and do not necessarily include all of the content and operations / steps, nor are they necessarily performed 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 order of execution can be changed according to actual conditions.

[0034] The terms "first", "second", and the like in the description and in the claims of the present specification and the above drawings are used to distinguish between similar objects, not to describe a particular sequential order. Moreover, the terms "include", and "have", and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a list of steps or units are not necessarily limited to the listed steps or units, but can optionally further include additional steps or units not expressly listed or can also include additional steps or units inherent in such process, method, product, or apparatus.

[0035] 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 to implement the present disclosure, and therefore should not be used to limit the scope of protection of the present disclosure.

[0036] Figure 1 A schematic diagram of an evaluation device for magnetic shielding effectiveness of a magnetic shielding assembly is shown.

[0037] 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.

[0038] The Helmholtz coil 101 is used to generate a working magnetic field.

[0039] According to some embodiments, the Helmholtz coil includes 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.

[0040] 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.

[0041] 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.

[0042] The fluxgate magnetometer 103 is used to measure the magnetic field values inside the N magnetic shielding assemblies 10 at a first set step when the Helmholtz coil 101 is unloaded and when the Helmholtz coil 101 generates 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.

[0043] 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.

[0044] According to an example embodiment, the host computer 104 is used to calculate the shielding effectiveness value according to the following formula:

[0045]

[0046] 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.

[0047] According to an example embodiment, the evaluation device further comprises a demagnetization wire and a demagnetization machine (not shown in the figure).

[0048] 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.

[0049] According to some embodiments, the multiple demagnetizing currents are different in size, so as to completely eliminate the residual magnetism in the material by "gradient demagnetization". For example, two demagnetizing currents are loaded, and the two demagnetizing currents are respectively about 100A and 50A.

[0050] According to an example embodiment, the evaluation device further comprises a non-magnetic matching tool (not shown in the figure).

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Figure 2 A flowchart of the evaluation method of the shielding effectiveness of the magnetic shielding assembly according to an example embodiment is shown.

[0055] 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.

[0056] In step S201, multiple demagnetizing currents are loaded in the demagnetizing wire to demagnetize the magnetic shielding assembly.

[0057] 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.

[0058] 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 value is obtained, which is denoted as B 1N .

[0059] 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.

[0060] In step S203, the constant current source outputs current to make the Helmholtz coil generate a working magnetic field.

[0061] The constant current source is electrically connected with the Helmholtz coil. By adjusting the output current, the Helmholtz coil generates a working magnetic field with a preset intensity, denoted as B0.

[0062] According to some embodiments, the preset working magnetic field in the present 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), and finally ensuring that the evaluation results can directly determine whether the assembly meets the installation requirements; and it can also 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.

[0063] According to some embodiments, steps S202 and S203 can be exchanged in order, and the present application only takes the example of performing step S202 first and then performing step S203, but it is not limited thereto.

[0064] 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 .

[0065] 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 along the same path as in 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.

[0066] In step S205, the internal magnetic field difference value of the magnetic shielding assembly is calculated according to the no-load magnetic field value and the loaded magnetic field value at the same position of the magnetic shielding assembly.

[0067] The internal magnetic field difference value of the same position is calculated according to the following formula:

[0068]

[0069] 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.

[0070] 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.

[0071] According to an example embodiment, the shielding effectiveness value is calculated according to the following formula:

[0072]

[0073] wherein, is the shielding effectiveness value.

[0074] In step S207, whether the shielding effectiveness of the magnetic shielding assembly is qualified is determined according to the shielding effectiveness value.

[0075] It is judged whether the number of shielding effectiveness values higher than the first set threshold value in the N shielding effectiveness values is greater than or equal to the second set threshold value; 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.

[0076] For example, it is required that the shielding effectiveness S of no less than 15 points in 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.

[0077] The application provides a hydrogen atomic clock magnetic shielding assembly shielding effectiveness evaluation device and method, which can screen qualified components in advance, avoids the need to disassemble and troubleshoot the magnetic shielding assembly after installation due to substandard effectiveness, solves the pain points of difficult problem positioning and repeated rework in the prior art, ensures controllable hydrogen atomic clock development cycle; through non-magnetic tooling, multiple gradient demagnetization and coincidence measurement, and uniform working magnetic field, the interference of tooling magnetism and component residual magnetism is eliminated, the shielding effectiveness calculation is ensured to be real, and the reliability of the evaluation result is improved; the component effectiveness difference is accurately distinguished, the experience judgment error is avoided, and the consistency of batch production of hydrogen atomic clock magnetic shielding assemblies is improved; without relying on a complex test system of a hydrogen atomic clock complete machine, the module device can be used for efficient evaluation, the hardware environment dependence is reduced, and the influence of component disassembly on the structural reliability of the hydrogen atomic clock is reduced; the device component is modularized, the measurement step and demagnetization current can be adjusted, the magnetic shielding evaluation requirements of different models of hydrogen atomic clocks are adapted, large-scale hardware modification is not needed, and the system upgrading and operation and maintenance difficulty is reduced.

[0078] Taking a three-layer magnetic shielding assembly of a passive hydrogen atomic clock as an evaluation object, the shielding effectiveness is evaluated based on the evaluation device and method of the application, and the specific process is as follows:

[0079] 1. A matched tooling made of non-magnetic aluminum alloy is used, and the three-layer magnetic shielding assembly is assembled into a complete unit according to the assembly process of the inner magnetic shielding assembly of the hydrogen atomic clock.

[0080] 2. A demagnetization wire is arranged along the axis of the assembled magnetic shielding assembly, and the wire is connected to a demagnetization machine at both ends; a demagnetization current of 100 A is first loaded for 30 s, and then a demagnetization current of 50 A is loaded for 20 s to complete demagnetization.

[0081] 3. The probe of a fluxgate magnetometer is fixed at the center of the axis of the Helmholtz coil, a constant current source is turned on, and the current is adjusted; when the fluxgate magnetometer displays a magnetic field value of 2Gs, the constant current source current is recorded as 0.78 A, and the current value is locked.

[0082] 4. The constant current source is turned off, and the demagnetized magnetic shielding assembly is placed at the center of the axis of the Helmholtz coil; the probe of the fluxgate magnetometer is inserted from the top end (the farthest end) of the magnetic shielding assembly, and the magnetic field values of 20 points are measured in turn from the top end to the bottom end at a step of 1 cm, and are recorded as B1.

[0083] 5. The constant current source is turned on (maintaining an output of 0.78 A), and the Helmholtz coil generates a magnetic field of 2Gs; the position of the magnetic shielding assembly is kept unchanged, and the same path (step 1 cm, and the measurement points are completely coincident with step 4) of step 4 is used to measure the magnetic field values of 20 points again, and the values are recorded as B2.

[0084] 6. The ΔB of each point is calculated, and the shielding effectiveness S is calculated according to the formula S=2Gs / ΔB.

[0085] 7. Count the S value of 20 measuring points.

[0086] 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.

[0087] 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 the hydrogen atomic clock product.

[0088] 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.

[0089] 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.

[0090] The exemplary embodiments of the application are specifically shown and described above. It should 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 of evaluating the shielding effectiveness of a magnetic shielding assembly, characterized by, The magnetic shielding assembly is placed in the center of the axis of the Helmholtz coil, and the evaluation method comprises: In the case of no load of the Helmholtz coil, the magnetic field values inside N magnetic shielding assemblies are measured at a first set step to obtain no-load magnetic field values, wherein N is an integer greater than or equal to 2; The constant current source outputs current to make the Helmholtz coil generate a working magnetic field; In the case 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; According to the no-load magnetic field values and the loaded magnetic field values of the same position of the magnetic shielding assembly, the internal magnetic field difference value of the magnetic shielding assembly is calculated; According to the internal magnetic field difference value and the working magnetic field, the shielding effectiveness value of the magnetic shielding assembly is calculated; According to the shielding effectiveness value, it is determined whether the shielding effectiveness of the magnetic shielding assembly is qualified.

2. The assessment method of claim 1, wherein, The shielding effectiveness value is calculated according to the following formula: wherein, is the shielding effectiveness value, is the working magnetic field, is the internal magnetic field difference, is the unloaded magnetic field value, is the loaded magnetic field value.

3. The assessment method of claim 1, wherein, The axis of the magnetic shielding assembly is provided with a demagnetizing wire connected with a demagnetizing machine, and the evaluation method further comprises: Multiple demagnetizing currents are loaded in the demagnetizing wire to demagnetize the magnetic shielding assembly before measuring the no-load magnetic field value of the magnetic shielding assembly, wherein the multiple demagnetizing currents have different sizes.

4. The evaluation method of claim 1, wherein, The determination of whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness value comprises: It is determined 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 is qualified.

5. An apparatus for evaluating the shielding effectiveness of a magnetic shielding assembly, characterized by: The evaluation device for performing the evaluation method as claimed in any one of claims 1-4 comprises: a Helmholtz coil for generating a working magnetic field; a constant current source connected with the Helmholtz coil for adjusting 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 case of no load of the Helmholtz coil and in the case that the Helmholtz coil generates the working magnetic field to obtain no-load magnetic field values and loaded magnetic field values respectively, wherein N is an integer greater than or equal to 2; a host computer for calculating the internal magnetic field difference value of the magnetic shielding assembly according to the no-load magnetic field values and the loaded magnetic field values of the same position of the magnetic shielding assembly, and for calculating the shielding effectiveness value of the magnetic shielding assembly according to the internal magnetic field difference value and the working magnetic field, and for determining whether the shielding effectiveness of the magnetic shielding assembly is qualified according to the shielding effectiveness value.

6. The evaluation device according to claim 5, characterized in that The Helmholtz coil comprises a two-dimensional or three-dimensional Helmholtz coil.

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

8. The evaluation device according to claim 5, characterized in that Further comprising: a demagnetizing wire provided at the axis of the magnetic shielding assembly; A demagnetization machine connected with the demagnetization wire, used for loading multiple demagnetization currents in the demagnetization wire to demagnetize 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.

9. The evaluation device according to claim 5, characterized in that The host computer is configured to determine whether the number of the shielding effectiveness values that are higher than a first set threshold value is greater than or equal to a second set threshold value, and 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 set threshold value is greater than or equal to the second set threshold value.

10. The evaluation device according to claim 5, characterized in that Further comprising: A non-magnetic matching tool configured to assemble the magnetic shielding assembly according to an assembly process of the magnetic shielding assembly in a hydrogen atomic clock. A non-magnetic matching tool configured to assemble the magnetic shielding assembly according to an assembly process of the magnetic shielding assembly in a hydrogen atomic clock.

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