CN113194704A - Method for protecting working circuit in cavity - Google Patents
Method for protecting working circuit in cavity Download PDFInfo
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- CN113194704A CN113194704A CN202110509211.8A CN202110509211A CN113194704A CN 113194704 A CN113194704 A CN 113194704A CN 202110509211 A CN202110509211 A CN 202110509211A CN 113194704 A CN113194704 A CN 113194704A
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- cavity
- metal strip
- resonance
- shielding box
- rectangular
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0007—Casings
- H05K9/0049—Casings being metallic containers
Abstract
The invention belongs to the technical field of electromagnetic protection, and relates to a method for inhibiting a cavity resonance mode, which is characterized by comprising the following steps: at least comprises the following steps: 1) obtaining the size l multiplied by a multiplied by b of an inner cavity of the rectangular shielding box; wherein l, a and b are the length, width and height of the inner cavity; 2) finding out a resonance point close to the frequency of the working circuit and a resonance point of the rectangular shielding box which has the largest influence on the circuit; 3) designing a corresponding metal frame according to the resonance points obtained in the step 1), and fixing the metal frame at the bottom of the shielding box cover plate through welding to inhibit the resonance points of the resonant cavity; 4) checking whether the box body is assembled properly, finishing properly and improperly, cutting off partial materials of the box body, and returning to the step 4). Aiming at the defect of the shielding efficiency of a rectangular metal shielding box at a resonant frequency point, the method for inhibiting the resonant mode of the cavity is low in cost and convenient to process, so that the circuit working at the resonant frequency point of the cavity can be protected.
Description
Technical Field
The invention belongs to the technical field of electromagnetic protection, and relates to a method for protecting a working circuit in a cavity, which can be used for protecting a circuit working at a special frequency point in a shielding cavity.
Background
The presence of a large number of sensitive electronic components in an electronic device, typically a low noise amplifier, may be disturbed by an external complex electromagnetic environment and may not function properly, or may even be damaged.
In order to protect the circuit, protective measures have to be introduced. Metal with high conductivity (such as aluminum) has good reflection to external electromagnetic waves and low cost enough, so that the metal can be made into a cavity for shielding the electromagnetic waves to protect a circuit. Rectangular metal shield boxes are widely used to protect electrical circuits.
But the rectangle metal shielding box has the gap certainly because of the problem of processing simultaneously, and when the shielding box received electromagnetic pulse irradiation, the electromagnetic wave can get into inside the metal cavity through the gap coupling, forms different resonant modes at specific frequency point, to the electronic components and parts of work at these frequency points, the electromagnetic resonance in the cavity can produce serious interference even, and pure rectangle shielding cavity can't play effectual guard action, probably causes the destruction to the circuit because the resonance electromagnetic environment in the cavity on the contrary.
Disclosure of Invention
Aiming at the defect of the shielding efficiency of the rectangular metal shielding box at the resonant frequency point, the invention provides the method for protecting the working circuit in the cavity, which has low cost and convenient processing, so as to protect the circuit working at the resonant frequency point of the cavity.
The object of the invention is achieved in that a method for protecting a working circuit inside a cavity is characterized in that: at least comprises the following steps:
1) obtaining the size l multiplied by a multiplied by b of an inner cavity of the rectangular shielding box; wherein l, a and b are the length, width and height of the inner cavity;
2) finding out a resonance point close to the frequency of the working circuit and a resonance point of the rectangular shielding box which has the largest influence on the circuit;
3) designing a corresponding metal frame according to the resonance points obtained in the step 1), and fixing the metal frame at the bottom of the shielding box cover plate through welding to inhibit the resonance points of the resonant cavity;
4) checking whether the box body is assembled properly, finishing properly and improperly, cutting off partial materials of the box body, and returning to the step 4).
The length, the width and the height of the inner cavity are l, a and b in the step 1), and the conditions are met (l is more than a and more than b).
The step 2) comprises the following steps:
(1) the top surface of the cavity in the rectangular shielding box is formed by the bottom surface of the box cover, and the top surface of the inner cavity is arranged to be a multiplied by l; a rectangular coordinate system is established by taking a vertex of the bottom surface of the inner cavity as an original point, the axis of the wide edge of the bottom surface is the + x axis, the axis of the high edge of the inner cavity is the + y axis, the axis of the long edge of the bottom surface is the + z axis, and the electric field in the cavity obeys the wave equation:
wherein
Is the vector of the electric field in the cavity,
in order to be the laplacian operator,
k is the angular frequency, mu, of the corresponding electric field0Is the magnetic permeability in vacuum, epsilon0Is the dielectric constant in vacuum.
(2) As can be known from the theory of resonant cavity, the electric field longitudinal field component in the resonant cavity is obeyed
m, n and p are non-negative integers and are respectively the half period number of the electric field in the length, width and height directions, and at least two positive integers are arranged in the m, n and p, and different m, n and p correspond to different resonance modes;
(3) recording different resonance frequency points as fmnp，
Wherein c the speed of light: 3X 108m/s, finding the resonance point close to the working circuit frequency, and finding the resonance point with the maximum influence on the circuit, namely min (| f)mnp-f0L) |), take note of f at that timemnpIs FMNP。
And 3) designing a corresponding metal frame according to the resonance point, and fixing the metal frame at the bottom of the shielding box cover plate by welding to inhibit the resonance point of the resonant cavity.
The metal frame is composed of two different types of rectangular metal strips, and comprises M strips with length of about l and width of about l
The length of the P pieces is about a, and the width of the P pieces is about a
The type II metal strip of (1).
The first metal strip is parallel to the long edge of the box cover, and two ends of the first metal strip are aligned with two wide edges of the box cover.
The x coordinate of the geometric center of the straight metal strip is
k is a positive odd number; the length of the P roots is about a.
The two-type metal strip is parallel to the wide edge of the box cover, and two ends of the two-type metal strip are aligned with two long edges of the box cover.
Of said two types of metal stripThe z coordinate of the geometric center is
k is a positive odd number.
The thickness of the metal strips of the first type metal strip and the second type metal strip is h, the size of the metal strips of the first type metal strip and the second type metal strip can be reasonably selected according to the space allowance in the shielding box, and the two types of metal strips are mutually vertically embedded to jointly form a metal frame with the total thickness of h.
Compared with the shielding box which is used only, the shielding box has the following advantages:
1) the cost is low, and the device has the advantages of low cost,
the material required for improving the shielding effectiveness is metal, and can be metal materials such as aluminum, iron, steel and the like, and the amount of the material required for modification is small.
2) Convenient processing
Only the cover of the shielding box is processed, and the specific resonance mode is restrained by using the space allowance of the shielding box so as to protect the circuit.
Simulation results show that the method improves the shielding effectiveness of frequency points needing to be protected.
Drawings
FIG. 1 is a flow chart of an implementation of the present invention;
fig. 2 is an open cover structure of a rectangular shield case;
FIG. 3 is a general structure of a shield case lid welded with a metal frame;
FIG. 4 shows the rectangular shielding box with the inner cavity size of 90X 30X 160 and the unit of mm, the invention is used for restraining f101Graph comparing the shielding effectiveness at the center of the cavity for the mold and without the present invention;
FIG. 5 shows the rectangular shielding box with the inner cavity size of 90X 30X 160 and the unit of mm, the invention is used for restraining f102Graph comparing the shielding effectiveness at the center of the cavity for the mold and without the use of the present invention.
Detailed Description
Referring to fig. 1 and 2, the specific implementation steps of the present invention are as follows:
step 1: obtaining the size of a cavity in the rectangular shielding body;
assuming that the size l multiplied by a multiplied by b, a, b and l of an inner cavity of the rectangular shielding box is the length, width and height of the inner cavity (l is more than a and more than b), the top surface of the rectangular inner cavity is formed by the bottom surface of the box cover, the top surface of the inner cavity is set to be a multiplied by l, a rectangular coordinate system is established by taking a vertex of the bottom surface of the inner cavity as an origin, the axis of the wide side of the bottom surface is the + x axis, the axis of the high side of the inner cavity is the + y axis, and the axis of the long side of the bottom surface is the + z axis.
Step 2: calculating the frequency f of the circuit to be protected0A proximate cavity resonance point;
setting the frequency f of the circuit to be protected0Calculating the sum f0Close cavity resonance points, different resonance points being denoted fmnpM, n and p are respectively the number of the resonant standing waves in the length, width and height directions, m, n and p are non-negative integers, and at least two positive integers are provided
Wherein the speed of light c is 3 × 108m/s, finding a resonance point close to the frequency of the operating circuit, i.e. m, n, p makes | fmnp-f0Minimum, | remember f at this timemnpIs FMNP。
And step 3: and designing a corresponding metal frame according to the resonance mode, and welding the metal frame to the bottom of the cover plate of the shielding box.
The metal frame is made up of two different types of rectangular metal strips.
As shown in FIG. 3, M pieces having a length of about l and a width of about l are included
The first metal strip is parallel to the long edge of the box cover, two ends of the first metal strip are aligned with two wide edges of the box cover, and the geometric center of the first metal strip isxThe coordinates are
The length of the P root is about a, and the width of the P root is about a
The second type metal strip is parallel to the wide edge of the box cover, two ends of the second type metal strip are aligned with two long edges of the box cover, and the z coordinate of the geometric center of the second type metal strip is
The thickness of the two types of metal strips is h, the size of the two types of metal strips can be reasonably selected according to the space allowance in the shielding box, and the two types of metal strips are vertically embedded to jointly form a metal frame with the total thickness of h.
And 4, step 4: the shielding box after welding the metal frame can be cut off part of materials properly so as to facilitate the assembly of the box body.
The effects of the present invention can be further verified by the following simulation experiments.
Experiment 2, when the internal size of the rectangular shielding box is 90 × 30 × 160 and the unit is mm, the working mode f is suppressed by adopting the invention102I.e., the shielding effectiveness at about 2.5Ghz needs to be improved, the simulated shielding effectiveness is shown in fig. 5. Suppression of f with the invention102After resonance, the shielding effectiveness at 2.5Ghz is improved from-21.7 dB to 27.8 dB.
The experiments show that the electromagnetic resonance of the cavity in the shielding box can be obviously inhibited after the shielding box is adopted, and the shielding efficiency is improved.
Claims (10)
1. A method for protecting a working circuit in a cavity is characterized in that: at least comprises the following steps:
1) obtaining the size a multiplied by b multiplied by l of an inner cavity of the rectangular shielding box; wherein, a, b and l are the length, width and height of the inner cavity;
2) finding out a resonance point close to the frequency of the working circuit and a resonance point of the rectangular shielding box which has the largest influence on the circuit;
3) designing a corresponding metal frame according to the resonance points obtained in the step 1), and fixing the metal frame at the bottom of the shielding box cover plate through welding to inhibit the resonance points of the resonant cavity;
4) checking whether the box body is assembled properly, finishing properly and improperly, cutting off partial materials of the box body, and returning to the step 4).
2. The method of claim 1, wherein the method further comprises: the length, the width and the height of the inner cavity body of the step 1) are defined as follows (l is more than a and more than b).
3. The method of claim 1, wherein the method further comprises: the step 2) comprises the following steps:
(1) the top surface of the cavity in the rectangular shielding box is formed by the bottom surface of the box cover, and the top surface of the inner cavity is arranged to be a multiplied by l; a rectangular coordinate system is established by taking a vertex of the bottom surface of the inner cavity as an original point, the axis of the wide edge of the bottom surface is the + x axis, the axis of the high edge of the inner cavity is the + y axis, the axis of the long edge of the bottom surface is the + z axis, and the electric field in the cavity obeys the wave equation:
wherein
Is the vector of the electric field in the cavity,
in order to be the laplacian operator,
k is the angular frequency, mu, of the corresponding electric field0Is the magnetic permeability in vacuum, epsilon0Is the dielectric constant in vacuum.
(2) As can be known from the theory of resonant cavity, the electric field longitudinal field component in the resonant cavity is obeyed
m, n and p are non-negative integers and are respectively the half period number of the electric field in the length, width and height directions, and at least two positive integers are arranged in the m, n and p, and different m, n and p correspond to different resonance modes;
(1) recording different resonance frequency points as fmnp，
Wherein c the speed of light: 3X 108m/s, finding the resonance point close to the working circuit frequency, and finding the resonance point with the maximum influence on the circuit, namely min (| f)mnp-f0L) |), take note of f at that timemnpIs FMNP。
4. The method of claim 1, wherein the method further comprises: and 3) designing a corresponding metal frame according to the resonance point, and fixing the metal frame at the bottom of the shielding box cover plate by welding to inhibit the resonance point of the resonant cavity.
5. The method of claim 4, wherein the method further comprises the steps of: the metal frame is composed of two different types of rectangular metal strips, and comprises M strips with length of about l and width of about l
The length of the P pieces is about a, and the width of the P pieces is about a
The type II metal strip of (1).
6. The method of claim 5, wherein the method further comprises: the first metal strip is parallel to the long edge of the box cover, and two ends of the first metal strip are aligned with two wide edges of the box cover.
7. The method of claim 5, wherein the method further comprises: the x coordinate of the geometric center of the straight metal strip is
k is a positive odd number.
8. The method of claim 5, wherein the method further comprises: the two-type metal strip is parallel to the wide edge of the box cover, and two ends of the two-type metal strip are aligned with two long edges of the box cover.
9. The method of claim 5, wherein the method further comprises: the z coordinate of the geometric center of the two-type metal strip is
k is a positive odd number.
10. The method of claim 5, wherein the method further comprises: the thickness of the metal strips of the first type metal strip and the second type metal strip is h, the size of the metal strips of the first type metal strip and the second type metal strip can be reasonably selected according to the space allowance in the shielding box, and the two types of metal strips are mutually vertically embedded to jointly form a metal frame with the total thickness of h.
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