CN110489866A - A kind of prediction technique calculating closed cavity magnetic field shielding efficiency - Google Patents
A kind of prediction technique calculating closed cavity magnetic field shielding efficiency Download PDFInfo
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- CN110489866A CN110489866A CN201910768469.2A CN201910768469A CN110489866A CN 110489866 A CN110489866 A CN 110489866A CN 201910768469 A CN201910768469 A CN 201910768469A CN 110489866 A CN110489866 A CN 110489866A
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Abstract
The invention discloses a kind of prediction techniques for calculating closed cavity magnetic field shielding efficiency, which is characterized in that the prediction technique of the closed cavity magnetic field shielding efficiency is the following steps are included: step 1: calculating shield in a certain low frequency point f0Magnetic field shielding efficiency SH (f0Magnetic field after the preceding magnetic field/shielding of)=shielding；Step 2: form factor is calculatedWherein, c is shield form factor, and Δ is the thickness of shield metal material, and μ is magnetic conductivity, the π of ω=2 f0；Step 3: according to the anti-shield effectiveness expression formula for releasing entire frequency range of the form factor of step 2 are as follows: SH=| cosh (γ Δ)+c γ sinh (γ Δ) |；Step 4: the shield effectiveness under logarithmic form is calculated according to relational expression SE=20log10 (SH), draws shield effectiveness curve.
Description
Technical field
The present invention relates to technical field of electromagnetic compatibility, more particularly to the prediction side for calculating closed cavity magnetic field shielding efficiency
Method.
Background technique
Shield effectiveness of the shielding cavity under low frequency magnetic field is the problem of meriting attention.At present for spherical and unlimited oval
The magnetic field shielding efficiency of cylindricality shield has accurate analytic formula.And for the magnetic of other lock shield cavitys of different shapes
Field shield effectiveness calculates, then needs to be obtained with numerical method or other approach, in electromagnetic simulation software, generally require to whole
A frequency range calculate by frequency point, this, which will be expended, largely calculates the time.
Therefore, it is desirable to have a kind of prediction technique for calculating closed cavity magnetic field shielding efficiency to be able to solve to deposit in the prior art
The problem of.
Summary of the invention
The invention discloses a kind of prediction technique for calculating closed cavity magnetic field shielding efficiency, closed cavity magnetic field screens
Cover the prediction technique of efficiency the following steps are included:
Step 1: shield is calculated in a certain low frequency point f0Magnetic field shielding efficiency SH (f0After the preceding magnetic field/shielding of)=shielding
Magnetic field；
Step 2: form factor is calculatedWherein, c be shield shape because
Son, Δ are the thickness of shield metal material, and μ is magnetic conductivity, the π of ω=2 f0；
Step 3: according to the anti-shield effectiveness expression formula for releasing entire frequency range of the form factor of step 2 are as follows:
SH=| cosh (γ Δ)+c γ sinh (γ Δ) |；
Step 4: calculating the shield effectiveness under logarithmic form according to relational expression SE=20log 10 (SH), draws shielding effect
It can curve.
Preferably, the thickness of the shield is less than skin depth, and the step 1 calculates the magnetic field shielding effect of shield
When energy, frequency point f is chosen0Numerical value is between 1kHz-10kHz.
Preferably, when the shield is magnetic conductivity low material, the low frequency point f0 of the step 1 selects 1kHz-
Frequency point between 10kHz.
The invention proposes a kind of prediction techniques for calculating closed cavity magnetic field shielding efficiency, by solving a certain frequency point
The shield effectiveness of lower shield finds out the form factor c of shield by the shield effectiveness, is finally somebody's turn to do according to shielding factor
The shield effectiveness approximate formula of shield are as follows:
SH=| cosh (γ Δ)+c γ sinh (γ Δ) |
Method calculation amount of the invention is small, and time-consuming is few, in practical projects, has reference price to the fast design of shield
Value.
Detailed description of the invention
Fig. 1 is model schematic of the shielding cavity in COMSOL.
Fig. 2 is shielding cavity magnetic field shielding efficacy curve figure.
Fig. 3 is shielding cavity model schematic.
Fig. 4 is cavity magnetic field shielding efficacy curve figure.
Specific embodiment
To keep the purposes, technical schemes and advantages of the invention implemented clearer, below in conjunction in the embodiment of the present invention
Attached drawing, technical solution in the embodiment of the present invention is further described in more detail.In the accompanying drawings, identical from beginning to end or class
As label indicate same or similar element or element with the same or similar functions.Described embodiment is the present invention
A part of the embodiment, instead of all the embodiments.The embodiments described below with reference to the accompanying drawings are exemplary, it is intended to use
It is of the invention in explaining, and be not considered as limiting the invention.Based on the embodiments of the present invention, ordinary skill people
Member's every other embodiment obtained without creative efforts, shall fall within the protection scope of the present invention.
If a shield meets: the radius of inside and outside wall is significantly greater than skin depth；The radius of inside and outside wall is obviously big
In the thickness of shield metal material, then there is the expression formula of magnetic field shielding efficiency:
1) for spherical shield body
2) for infinitely long cylinder, axis of the external magnetic field perpendicular to cylindrical body
3) for infinitely long cylinder, external magnetic field is parallel to the axis of cylindrical body
Wherein:
Δ is the thickness of shield metal material；
r0For the radius of ball or the radius of cylindrical body；
δ is skin depth.
μrFor relative permeability, μ0For space permeability.
When frequency is lower, i.e., | γ Δ | when → 0, the expression formula of three above magnetic field shielding efficiency is approximately: respectively
When material relative permeability is not high, ignore μrΔ/r0, the expression formula of three above magnetic field shielding efficiency at this time
Further it is approximately:
In fact, the magnetic field shielding efficiency of different shape shield has unified approximate expression, indicate are as follows:
SH=| 1+jc ω μoσΔ|
Wherein c is defined as form factor, that is, depends on the shape and size of shield.
The present invention is by being quickly obtained different shape shield magnetic field shielding efficiency from the magnetic field shielding efficiency of a frequency point
Simplification method, steps are as follows:
Step 1: go out shield in a certain frequency point f by electromagnetic simulation software or other numerical calculations0Under magnetic field
Shield effectiveness SH (f0Magnetic field after the preceding magnetic field/shielding of)=shielding；
Step 2: form factor is calculatedWherein, the π of ω=2 f0；
Step 3: according to shape therefore the anti-shield effectiveness expression formula for releasing entire frequency range are as follows:
SH=| cosh (γ Δ)+c γ sinh (γ Δ) |
Step 4: calculating the shield effectiveness under logarithmic form according to relational expression SE=20log10 (SH), draws shielding effect
It can curve.
In step 1 and step 2, the use premise of approximate formula is that the thickness of shield is less than skin depth, therefore
When carrying out shield effectiveness calculating with electromagnetic simulation software, choosing frequency point numerical value be should be as small as possible.But material lower for magnetic conductivity
Expect (such as common aluminium) in 100Hz or less, it is difficult to show shield effectiveness.Therefore selection 1kHz-10kHz between frequency point into
Row, which calculates, is more suitable for.
Embodiment 1:
Take specification be 10cm × 10cm × 10cm rectangle closed cavity, thickness 0.5mm, material be copper (σ=5.8 ×
107S/m, μr=1) shield effectiveness calculating is carried out.When seeking form factor c, it is ensured that material thickness is less than skin depth.
Skin depth is 2.09mm under 1kHz, is greater than material thickness.
Step 1: as shown in Figure 1, establishing model in software COMSOL, it is 1kHz that setting, which calculates frequency, carries out frequency domain and asks
Solution, obtains SH=2.66.
Step 2: form factor is calculated
Step 3: the magnetic field shielding efficiency in entire frequency range can be obtained according to form factor are as follows:
SH=|+0.0108 γ sinh (γ Δ) of cosh (γ Δ) |
Wherein, Δ is the thickness of shield metal material；
Step 4: the shield effectiveness under logarithmic form is calculated according to relational expression SE=20log 10 (SH), draws shielding
Efficacy curve, as shown in Figure 2.
Embodiment 2:
Taking shape is the shielding cavity of two double cones docking, and single cone height h=0.1m, bottom surface radius r=0.1m are thick
Degree is 0.1mm, and material is copper (σ=5.77 × 107S/m, μr=1).Model will be protected as shown in figure 3, when seeking form factor c
It demonstrate,proves material thickness and is less than skin depth.Skin depth is 2.09mm under 1kHz, is greater than material thickness.
Step 1: establishing model in software MagNet, due to cavity axial symmetry, can be solved with two-dimensional axial symmetric.
It is 1kHz that setting, which calculates frequency, carries out strip method, obtains SH=1.4.
Step 2: form factor is calculated
Step 3: the magnetic field shielding efficiency in entire frequency range can be obtained according to form factor are as follows:
SH=|+0.0215 γ sinh (γ Δ) of cosh (γ Δ) |
Wherein, Δ is the thickness of shield metal material；
Step 4: the shield effectiveness under logarithmic form is calculated according to relational expression SE=20log 10 (SH), draws shielding
Efficacy curve, as shown in Figure 4.
Finally it is noted that the above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations.To the greatest extent
Present invention has been described in detail with reference to the aforementioned embodiments for pipe, those skilled in the art should understand that: it is still
It is possible to modify the technical solutions described in the foregoing embodiments, or part of technical characteristic is equally replaced
It changes；And these are modified or replaceed, the essence for technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution
Mind and range.
Claims (3)
1. a kind of prediction technique for calculating closed cavity magnetic field shielding efficiency, which is characterized in that the closed cavity magnetic field shielding
The prediction technique of efficiency the following steps are included:
Step 1: shield is calculated in a certain low frequency point f0Magnetic field shielding efficiency SH (f0Magnetic after the preceding magnetic field/shielding of)=shielding
；
Step 2: form factor is calculatedWherein, c is the form factor of shield, and Δ is shielding
The thickness of body metal material, μ are magnetic conductivity, the π of ω=2 f0；
Step 3: according to the anti-shield effectiveness expression formula for releasing entire frequency range of the form factor of step 2 are as follows:
SH=| cosh (γ Δ)+c γ sinh (γ Δ) |；
Step 4: the shield effectiveness under logarithmic form is calculated according to relational expression SE=20log10 (SH), it is bent to draw shield effectiveness
Line.
2. the prediction technique according to claim 1 for calculating closed cavity magnetic field shielding efficiency, it is characterised in that: the screen
The thickness for covering body is less than skin depth, when the step 1 calculates the magnetic field shielding efficiency of shield, chooses frequency point f0Numerical value exists
Between 1kHz-10kHz.
3. the prediction technique according to claim 2 for calculating closed cavity magnetic field shielding efficiency, it is characterised in that: the screen
When to cover body be magnetic conductivity low material, the low frequency point f of the step 10Select the frequency point between 1kHz-10kHz.
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| CN111125610A (en) * | 2019-12-26 | 2020-05-08 | 华北电力大学 | Magnetic field shielding effectiveness prediction method and system |
| CN114340370A (en) * | 2022-01-11 | 2022-04-12 | 西安理工大学 | Design method of multilayer multi-material shield body with wide frequency range |
| CN117015224A (en) * | 2023-09-28 | 2023-11-07 | 国网江苏省电力有限公司营销服务中心 | Electromagnetic shielding device and system for keeping superconducting state of Josephson junction |
| CN117347734A (en) * | 2023-10-08 | 2024-01-05 | 东南大学 | Method for selecting position of special-shaped shielding shell shielding effectiveness test antenna |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111125610A (en) * | 2019-12-26 | 2020-05-08 | 华北电力大学 | Magnetic field shielding effectiveness prediction method and system |
| CN111125610B (en) * | 2019-12-26 | 2022-02-15 | 华北电力大学 | Magnetic field shielding effectiveness prediction method and system |
| CN114340370A (en) * | 2022-01-11 | 2022-04-12 | 西安理工大学 | Design method of multilayer multi-material shield body with wide frequency range |
| CN117015224A (en) * | 2023-09-28 | 2023-11-07 | 国网江苏省电力有限公司营销服务中心 | Electromagnetic shielding device and system for keeping superconducting state of Josephson junction |
| CN117015224B (en) * | 2023-09-28 | 2024-02-20 | 国网江苏省电力有限公司营销服务中心 | Electromagnetic shielding device and system for keeping superconducting state of Josephson junction |
| CN117347734A (en) * | 2023-10-08 | 2024-01-05 | 东南大学 | Method for selecting position of special-shaped shielding shell shielding effectiveness test antenna |
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