The disclosure relates to the field of electromagnetic field tests, and more particularly to an anechoic chamber and a construction method thereof.
A mirror monoconical system is an important system in a transient electromagnetic field, and has multipurpose in a defense electronics field. The minor monoconical system needs a surrounding with no reflection or low reflection. In this case, it is necessary to place the system in a very open outdoor, which is obviously not a good choice because the sun and rain will damage the equipment and problems of power supply and maintenance are also great. Another choice is to construct an anechoic chamber, and a main function of the anechoic chamber is to construct a monoconical transverse electromagnetic (TEM) cell with a low reflection. The traditional anechoic chamber is mostly rectangular in shape, with a shell made of steel plates, the steel plates themselves have a strong reflection effect on electromagnetic waves, resulting in strong multipath components with multiple reflections.
When the reflection effect is not suppressed, multiple reflections are generated on surfaces of the steel plates by a pulse electromagnetic field, so as to make the pulse electromagnetic field generate a strong inter-symbol interference characteristic, which is a serious negative factor. Therefore, in order to prevent this situation from happening, it is necessary to lay a matching structure with ferrite absorbing materials and pyramidal absorbing materials on the steel plates, and the matching structure can absorb most electromagnetic waves, so as to reduce a reflection level at a boundary of the matching structure.
In general, when an incident angle of the electromagnetic wave into the absorbing material is 0, a reflectivity of the absorbing material is lowest. Traditional rectangular anechoic chambers and cylindrical anechoic chambers have higher primary interface reflectivity in some cases, making it increasingly difficult to meet testing requirements.
For that, Chinese patent with publication NO. CN109884569B provides a generation device for a standard field with small reflection and broadband, which relates to a hemispherical semi-anechoic chamber, in a situation of a spherical anechoic chamber, an incident angle of the electromagnetic wave into the absorbing material is zero, which can fully reduce the reflectivity. However, a surface of the hemispherical anechoic chamber is a curved surface, a casting process or a polygonal steel frame splicing process is used to construct an anechoic chamber in the industry at present, for the hemispherical anechoic chamber, multiple curved surfaces need to be manufactured, and the curved surfaces are spliced to construct the anechoic chamber, costs of the cutting and splicing processes are expensive and the cutting and splicing processes are complicated to realize, it can be seen that the construction of the hemispherical anechoic chamber is almost impossible to achieve in engineering. Meanwhile, since a bottom surface of the absorbing material is a flat surface, for the hemispherical anechoic chamber, an inner wall is a curved surface, it is difficult to dispose the absorbing material on the inner wall of the hemispherical anechoic chamber. In summary, the patent is expensive in technical realization and difficult in construction, which is almost impossible to achieve.
In view of this, the disclosure provides an anechoic chamber and a construction method thereof, to solve a problem that a reflectivity of the anechoic chamber cannot be balanced with a difficulty of its construction at present.
According to a first aspect, an embodiment of the disclosure provides an anechoic chamber, and the anechoic chamber includes a top surface, multiple trapezoid surfaces, multiple rectangular surfaces and an absorbing material.
The top surface is a polygon.
The multiple trapezoid surfaces correspond to edges of the top surface, respectively, a length of an upper edge of each of the multiple trapezoid surfaces is equal to a length of the corresponding edge of the top surface, each of the multiple trapezoid surfaces is connected to the corresponding edge of the top surface through the upper edge of the trapezoid surface, the multiple trapezoid surfaces are sequentially connected along a circumferential direction of the top surface, and each of the multiple trapezoidal surfaces is at an angle to the top surface.
The multiple rectangular surfaces correspond to the multiple trapezoid surfaces, respectively, a length of an upper edge of each of the multiple rectangular surfaces is equal to a length of a lower edge of the corresponding trapezoid surface, each of the multiple rectangular surfaces is connected to the lower edge of the corresponding trapezoid surface through the upper edge of the rectangular surface, the multiple rectangular surfaces are sequentially connected along a circumferential direction of the lower edges of the multiple trapezoid surfaces, and each of the multiple rectangular surfaces is perpendicular to the top surface.
The absorbing material is disposed on the top surface, the multiple trapezoid surfaces and the multiple rectangular surfaces.
In an embodiment, the top surface is a regular polygon.
In an embodiment, the top surface is a regular hexdecagon.
In an embodiment, the length of the lower edge of each of the multiple trapezoid surfaces is 1.2 meters (m).
In an embodiment, a radius of a ring surrounded by the multiple rectangular surfaces is 3.0755 m.
In an embodiment, a difference between a radius of the top surface and the radius of the ring surrounded by the multiple rectangular surfaces is 0.93 m.
In an embodiment, a height difference between the top surface and the upper edge of each of the multiple rectangular surfaces is 0.8 m.
According to a second aspect, the embodiment of the disclosure provides a construction method for anyone of the anechoic chambers described in the first aspect, and the construction method includes:
In an embodiment, the determining a reflectivity equation of the anechoic chamber includes:
In an embodiment, the reflectivity equation of the anechoic chamber is expressed as follows:
The embodiment of the disclosure provides a novel equation, that is the reflectivity equation of the anechoic chamber, the sizes of the top surface, the rectangular surfaces, the trapezoid surfaces of the anechoic chamber, a number of polygonal edges of the top surface, the number of the trapezoid surfaces and the number of the rectangular surfaces can be determined by the reflectivity equation of the anechoic chamber, the anechoic chamber is obtained by splicing the top surface, the multiple trapezoid surfaces and the multiple rectangular surfaces, and the anechoic chamber is easy to process, and is easy to dispose the absorbing material, meanwhile, a reflectivity of the anechoic chamber can be effectively reduced.
In order to provide a clearer explanation of technical solutions in embodiments of the disclosure or related art, drawings required in the embodiments will be simply introduced below. Apparently, the drawings in the following description are merely some of the embodiments of the disclosure, for those skilled in the art, other drawings can be obtained according to the drawings without creative work.
Descriptions of embodiments of the specification should be combined with corresponding drawings, and the drawings should be a part of the complete specification. In the drawings, a shape or a thickness in the embodiments can be expanded, and be marked with simplification or convenience. Moreover, parts of each structure in the drawings will be described separately for explanation, it is worth noting that components not shown in the drawings or not described through text are known to those skilled in the art.
The description of the embodiments here, any reference to direction and orientation, is only for convenience of description and cannot be understood as any limitation on a scope of protection of the disclosure. The following description of the embodiments will involve combinations of features that may exist independently or in combination, and the disclosure is not particularly limited to the embodiments. The scope of the disclosure is defined by claims.
The anechoic chamber can be constructed by the following method, sizes of the top surface, the trapezoid surfaces, the rectangular surfaces of the anechoic chamber, a number of polygonal edges of the top surface, a number of the trapezoid surfaces and a number of the rectangular surfaces are determined according to a reflectivity equation of the anechoic chamber, and the top surface, the trapezoid surfaces and the rectangular surfaces are spliced to construct the anechoic chamber.
The embodiments of the disclosure provide a novel equation, that is the reflectivity equation of the anechoic chamber, the equation can be used to design and construct the anechoic chamber, and a derivation process of the reflectivity equation of the anechoic chamber is as follows.
A center of a ring surrounded by the rectangular surfaces is taken as an origin of a coordinate system (i.e., spherical coordinate system), a radius of the ring surrounded by the rectangular surfaces is taken as an x-axis, and a height direction is taken as a z-axis to construct a spherical coordinate system.
A radius of a bottom of a mirror monocone in the anechoic chamber is recorded as rc, specifically, the mirror monocone is installed in the anechoic chamber through a way of a monoconical feed point proximate to ground, and the monoconical feed point is located at the z-axis of the spherical coordinate system.
A height of the anechoic chamber is recorded as H, and the radius of the ring surrounded by the rectangular surfaces is recoded as W, and a thickness of the absorbing material is recorded as L.
The top surface includes a relevant area and an irrelevant area, the irrelevant area is a part of the top surface covered by a projection of the mirror monocone on the top surface along the height direction, and the relevant area is a part of the top surface that is not covered by the projection of the mirror monocone on the top surface along the height direction.
As shown in
As shown in
The reflectivity of the absorbing material is expressed as a function of an incident angle α, the function is recoded as R(α), and an expression of the function R(α) is expressed as follows:
The expression of R(α) is converted to a linear power dimension, and the expression of R(α) is expressed as follows:
An electric field of the mirror monocone is expressed as follows:
In general, Zd=Zc. in engineering, therefore, Zd=Zc is uses as an example to describe in the embodiment, however, this is not intended to limit the embodiment (those skilled in the art can reasonably deduce results when Zd and Zc are not equal based on the records of the embodiment), make Zd=Zc. here, and the electric field of the mirror monocone is expressed as follows:
It should be noted that the above expressions are rule formulas of a minor monocone with an infinite length, and there is no analytical solution for a mirror monocone with a finite length at present. The following simulation is made through a simulation analysis to obtain simulation results in a case of the minor monocone with the finite length.
Therefore, when analyzing a total reflection power ratio of the anechoic chamber, the straight line CO1 should not be included, and only three straight lines , , and are analyzed.
In the spherical coordinate system, a coordinate of the point A is A=(W, 0), and an incident angle θA of the point A is θA=0.
In the spherical coordinate system, a coordinate of the point C is C=(rc, H), and an incident angle θC of the point C is θC=angle (rc+jH).
In the spherical coordinate system, a coordinate of the point D1 is D1=(xD1, zD1)=(W, H−BD−L sin βC), and an incident angle θD1 of the point D is θD1=angle (xD1+jzD1).
In the spherical coordinate system, a coordinate of the point E1 is E1=(xE1, zE1)=(W−BE−L cos βc, H), and an incident angle θE1 of the point E is θE1=angle (xE1+jzE1).
A complementary angle of the incident angle of the point C is
An incident angle of an electromagnetic wave is recorded as α, on the straight line , α=θ, and ρ=W; on the straight line , a unit vector of a vector is expressed as , and a formula of the incident angle α is expressed as follows:
and
On the straight line , α=90−θ, and ρ=H cot θ; and a formula of a feed power is expressed as follows:
Meanwhile, it takes into account that θ is actually a variable in the spherical coordinate system, and a formula of a surface integral is expressed as follows:
ds=2πx√{square root over ((dx)2+(dz)2.)}
On the straight line , z=x tan θ, dx=0, ds=2πx2 sec2 θdθ, where θ∈[θA, θD1).
On the straight line ,
On the straight line , dz=0, x=z cot θ, ds=2πxz csc2 θ, and
where θ∈[θE1, θC).
The reflectivity equation of the anechoic chamber can be expressed as follows:
It should be noted that in the above derivation processes, attention should be paid to in the engineering, Zd=Zc, for example, Zd=Zc=50 Ω. Meanwhile, attention should be paid to normalization of the feed power, that is, in a situation that the feed power is 1 watt (W), the formula of the feed power is expressed as follows:
Therefore, according to parameters (e.g., the radius and the height of the mirror monocone, which are known parameters) of a tested mirror monocone and parameters (e.g., the height of the anechoic chamber and the thickness of the absorbing material, which are known parameters) of the anechoic chamber, and the above parameters are substituted into the above formulas to obtain a relationship between the reflectivity of the anechoic chamber and size parameters of the anechoic chamber. Specifically, the known data such as the parameters of the mirror monocone is substituted into the above formulas to obtain length values of BE and BD, and the size parameters of the top surface, the trapezoid surfaces and the rectangular surfaces, the number of the polygon edges of the top surface, the number of the trapezoid surfaces and the number of the rectangular surfaces are determined by those skilled in the art combining actual engineering needs (e.g., a size of a site and a size of an inner space of the anechoic chamber), so as to design a corresponding cutting solution, and the cutting solution refers to construct the anechoic chamber through a steel plate cutting process and a splicing technology, that is to construct the anechoic chamber through splicing the top surface, the trapezoid surfaces and the rectangular surfaces. The following example illustrates an operation example of constructing an anechoic chamber according to the above formulas.
As shown in
In terms of engineering implementation, the trapezoid surfaces and the rectangular surfaces can be spliced with the top surface through a splicing method to construct the anechoic chamber, the top surface, the trapezoid surfaces and the rectangular surfaces are flat surfaces, which can reduce costs (include cutting costs and manufacturing costs), moreover, it is easy to process, and is easy to dispose the absorbing material. Compared to the hemispherical anechoic chamber in the related art, the hemispherical anechoic chamber uses a hemispherical surface as a curved surface, which is difficult to cut and splice, and the absorbing material is difficult to be disposed on the curved surface, therefore, the embodiment has apparent advantages.
Furthermore, it should be understood that the embodiment takes the construction of the regular hexdecagon anechoic chamber as the example to describe, which is not intended to limit the embodiment, those skilled in the art can freely design the shape of the anechoic chamber based on the reflectivity equation of the anechoic chamber in the embodiment and combined with practical engineering needs, which can be an arbitrary polygonal anechoic chamber.
The embodiment of the disclosure provides a design method of the anechoic chamber, especially deriving a completely novel equation, that is, the reflectivity equation of the anechoic chamber. The relationship between the size parameters (e.g., lengths of BD and BE) of the anechoic chamber and the reflectivity of the anechoic chamber can be calculated through the reflectivity equation of the anechoic chamber, so as to determine the length values of BD and BE that balance the size and reflectivity of the anechoic chamber, determine the size parameters of the top surface, the trapezoid surfaces, the rectangular surfaces of the anechoic chamber, the number of the edges of the top surface, the number of the trapezoid surfaces and the number of the rectangular surfaces, and provide data and theoretical basis for the construction of the anechoic chamber. The anechoic chamber of the embodiment of the disclosure combines low cost and low reflection, which can better satisfy the testing requirements of the anechoic chamber in engineering.
The above descriptions are merely the embodiments of the disclosure and is not intended to limit the disclosure, any modifications, equivalent substitutions, improvements and the like made within spirit and principles of the disclosure should be included in a scope of protection of the disclosure.
Number | Date | Country | Kind |
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2022113966772 | Nov 2022 | CN | national |