Terahertz low-pass filter based on frequency selective surface

Abstract

The invention relates to the technical field of terahertz wave application, in particular to a terahertz low-pass filter based on a frequency selective surface, which comprises a first dielectric layer, a second dielectric layer, a third dielectric layer, a first metal layer and a second metal layer. The first dielectric layer, the second dielectric layer and the third dielectric layer are stacked in sequence; the first metal layer is arranged on the surfaces of the first dielectric layer and the third dielectric layer, and the first metal layer is formed by arranging four metal sheets in a square shape; the second metal layer is arranged between the first dielectric layer and the second dielectric layer and between the second dielectric layer and the third dielectric layer, and the second metal layer is of an annular structure with a through hole. According to the terahertz wave filter, the filtering effect on terahertz waves can be achieved, the working frequency band can cover a microwave band and a terahertz band, the cut-off frequency of the terahertz wave filter can be regulated and controlled, and the cut-off frequency range of the terahertz wave filter is 0.01-1 THz; the device is simple in structure and low in preparation difficulty; the band-pass filter has high transmissivity in a passband, and has a good stop-band suppression characteristic at a high frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz wave applications, and particularly to a terahertz low-pass filter based on a frequency selective surface. Background Art

[0002] Terahertz (full English name: Terahertz; English abbreviation: THz) waves refer to electromagnetic waves with frequencies in the range of 0.1 - 10 THz, corresponding to wavelengths of 0.03 - 3 mm. It lies between microwaves and infrared light, and has the characteristics of strong penetration, low photon energy, non-ionizing damage, and rich spectral information, which is of great significance in many fields such as communication technology, medical imaging, and material detection. Especially in the field of communication, terahertz technology, as the latest frontier science, is the focus of the current national defense science and technology field, and has important strategic significance in fields such as radar, detection, and weapon manufacturing. As a key part of terahertz wireless communication, filters with high transmittance, low loss, and easy processing have always been a research hotspot in the terahertz communication field. Currently, terahertz filters mainly include terahertz waveguide filters, photonic crystal filters, and filters based on frequency selective surfaces. However, for waveguide-type filters, general processing techniques are difficult to meet the processing requirements of terahertz band filters; while photonic crystal filters are easily affected by environmental factors. Electromagnetic metasurfaces, as a two-dimensional form of metamaterials, usually arrange sub-wavelength unit structures periodically or aperiodically to achieve the regulation of electromagnetic waves. Among them, frequency selective metasurfaces are one of the research hotspots in the field of terahertz filters.

[0003] In recent years, a large amount of work has been carried out to achieve the selective control of terahertz frequency electromagnetic waves based on frequency selective surfaces, such as terahertz band-pass filters, terahertz band-stop filters, etc. In comparison, the research progress of terahertz low-pass filters is slow, and there are problems such as low transmittance, narrow working frequency band coverage, and poor stopband suppression effect. Therefore, it is necessary to design a terahertz low-pass filter with a simple structure, high transmittance for incident waves, and good stopband suppression effect to meet the application requirements of higher performance. In addition, frequency selective surface units have the characteristic of controlling their cut-off frequencies by changing structural parameters, so they have unique advantages and broad development prospects in the terahertz band. Summary of the Invention

[0004] The present invention provides a terahertz low-pass filter based on a frequency selective surface to solve the defects of low transmittance, narrow working frequency band coverage, and poor stopband suppression effect in the prior art.

[0005] The present invention provides a terahertz low-pass filter based on a frequency selective surface, comprising: A first dielectric layer; A second dielectric layer; A third dielectric layer, with the first dielectric layer, the second dielectric layer, and the third dielectric layer stacked in sequence. Two first metal layers, one of the first metal layers is disposed on the surface of the first dielectric layer away from the second dielectric layer, and the other first metal layer is disposed on the surface of the third dielectric layer away from the second dielectric layer. Among them, the first metal layer is a planar structure in which N metal sheets are arranged in a square, and N is a positive integer greater than or equal to 2. Two second metal layers, one of the second metal layers is disposed between the first dielectric layer and the second dielectric layer, and the other second metal layer is disposed between the second dielectric layer and the third dielectric layer. Among them, the second metal layer is an annular structure with through holes.

[0006] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the second metal layer is a polygonal ring structure, and the through hole is a polygonal hole.

[0007] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the second metal layer is a circular ring structure, and the through hole is a circular hole.

[0008] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the number of the metal sheets is four, and the four metal sheets form a cross-shaped gap, and the cross-shaped gap is opposite to the through hole. The through hole is located at the geometric center of the annular structure.

[0009] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the first dielectric layer, the second dielectric layer, and the third dielectric layer are made of one of polytetrafluoroethylene, quartz, glass, FR-4, polyimide, polydimethylsiloxane, and parylene as materials.

[0010] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the dielectric constants of the first dielectric layer, the second dielectric layer, and the third dielectric layer are 2 to 6, and the loss tangents are 0.0001 to 0.30. The thicknesses of the first dielectric layer, the second dielectric layer, and the third dielectric layer are 10 to 3000 microns.

[0011] For the terahertz low-pass filter based on frequency selective surface provided by the present invention, the thicknesses of the first metal layer and the second metal layer are 0.1 to 30 microns, and the first metal layer and the second metal layer are made of one of gold, silver, copper, and nickel as materials.

[0012] The terahertz low-pass filter based on a frequency selective surface provided by the present invention, the cross-sections of the first dielectric layer, the second dielectric layer, and the third dielectric layer are all regular polygons with side lengths of 50 to 5000 micrometers.

[0013] The terahertz low-pass filter based on a frequency selective surface provided by the present invention includes: a plurality of stacked units composed of the first dielectric layer, the second dielectric layer, the third dielectric layer, the first metal layer, and the second metal layer.

[0014] The terahertz low-pass filter based on a frequency selective surface provided by the present invention, a plurality of the stacked units are arranged horizontally and vertically and form a polygon array.

[0015] A terahertz low-pass filter based on a frequency selective surface provided by the present invention. The terahertz low-pass filter based on a frequency selective surface includes: a first dielectric layer, a second dielectric layer, a third dielectric layer, a first metal layer, and a second metal layer. The first dielectric layer, the second dielectric layer, and the third dielectric layer are stacked in sequence; two first metal layers, one first metal layer is disposed on the surface of the first dielectric layer away from the second dielectric layer, and the other first metal layer is disposed on the surface of the third dielectric layer away from the second dielectric layer, wherein the first metal layer is a planar structure in which N metal sheets are arranged in a square, and N is a positive integer greater than or equal to 2; two second metal layers, one second metal layer is disposed between the first dielectric layer and the second dielectric layer, and the other second metal layer is disposed between the second dielectric layer and the third dielectric layer, wherein the second metal layer is an annular structure with through holes. The terahertz low-pass filter based on a frequency selective surface provided by the present invention can achieve the filtering effect on terahertz waves, the working frequency band can cover the microwave band and the terahertz band, its cut-off frequency can be adjusted, and its cut-off frequency range covers 0.01 to 1 THz; the device structure of the present invention is simple and the preparation difficulty is low; it has a high transmittance in the passband and good stopband suppression characteristics at high frequencies. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present invention.

[0018] Figure 2 It is a transmittance curve of Embodiment 1 of the present invention.

[0019] Figure 3It is the transmittance curve of Embodiment 2 of the present invention.

[0020] Figure 4 It is a schematic structural diagram of Embodiment 3 of the present invention.

[0021] Figure 5 It is the transmittance curve of Embodiment 3 of the present invention.

[0022] Figure 6 It is a schematic structural diagram of Embodiment 4 of the present invention.

[0023] Figure 7 It is the transmittance curve of Embodiment 4 of the present invention.

[0024] Figure 8 It is a schematic structural diagram of Embodiment 5 of the present invention.

[0025] Figure 9 It is the transmittance curve of Embodiment 5 of the present invention.

[0026] Reference numerals: 1: First dielectric layer; 2: Second dielectric layer; 3: Third dielectric layer; 4: First metal layer; 41: Metal sheet; 5: Second metal layer. Detailed implementation manners

[0027] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the description of this implementation manner, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this implementation manner and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this implementation manner.

[0029] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of this embodiment, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0030] In this embodiment, unless otherwise clearly specified and defined, terms such as "arranged", "installed", "connected", "joined", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in this embodiment can be understood according to specific circumstances.

[0031] In the embodiments of the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0032] The following Figures 1-9 describes a terahertz low-pass filter based on a frequency selective surface of the present invention. The terahertz low-pass filter based on a frequency selective surface includes: a first dielectric layer 1, a second dielectric layer 2, a third dielectric layer 3, two first metal layers 4 and two second metal layers 5.

[0033] Among them, the first dielectric layer 1, the second dielectric layer 2 and the third dielectric layer 3 are arranged in a stacked manner in sequence; one first metal layer 4 is disposed on the surface of the first dielectric layer 1 away from the second dielectric layer 2, and the other first metal layer 4 is disposed on the surface of the third dielectric layer 3 away from the second dielectric layer 2. Among them, the first metal layer 4 is a planar structure in which N metal sheets 41 are arranged in a square, and N is a positive integer greater than or equal to 2; one second metal layer 5 is disposed between the first dielectric layer 1 and the second dielectric layer 2, and the other second metal layer 5 is disposed between the second dielectric layer 2 and the third dielectric layer 3. Among them, the second metal layer 5 is an annular structure with through holes.

[0034] Preferably, the first metal layer 4 consists of four metal sheets 41 arranged in a square pattern. The following embodiments will be described with this arrangement.

[0035] A terahertz low-pass filter based on a frequency selective surface provided by the present invention employs a stacked unit with a periodic interleaved arrangement of dielectric layers and metal layers. Specifically, an arrangement of four metal layers and three dielectric layers is adopted. The first layer is the first metal layer 4, the second layer is the first dielectric layer 1, the third layer is the second metal layer 5, the fourth layer is the second dielectric layer 2, the fifth layer is the second metal layer 5, the sixth layer is the third dielectric layer 3, and the seventh layer is the first metal layer 4.

[0036] The stacked unit composed of the above four metal layers and three dielectric layers can have multiple stacked units arranged to form this device. Depending on the actual situation, one or more stacked units can be selected.

[0037] The first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are dielectric layers. The first metal layer 4 is located outside the first dielectric layer 1 and the third dielectric layer 3, and the second metal layer 5 is located between the first dielectric layer 1 and the second dielectric layer 2, as well as between the second dielectric layer 2 and the third dielectric layer 3.

[0038] The first metal layer 4 and the second metal layer 5 can be made of the same material, but their structures are different. The first metal layer 4 is composed of four metal sheets 41 and has a square structure arranged in a 2×2 pattern. There are gaps between the four metal sheets 41, and the gaps can be adjusted according to the actual situation. Specifically, the four metal sheets 41 are arranged in a 2-row and 2-column pattern, forming a cross-shaped gap.

[0039] The second metal layer 5 adopts an annular structure, that is, it has a through hole in the center. The second metal layer 5 can be a circular ring structure or a polygonal ring structure.

[0040] Specifically, the two sides of the first dielectric layer 1 are in close contact with the first metal layer 4 and the second metal layer 5, the two sides of the second dielectric layer 2 are in close contact with the second metal layer 5, and the third dielectric layer 3 is in close contact with the second metal layer 5 and the first metal layer 4.

[0041] In one embodiment of the present invention, the second metal layer 5 is a polygonal ring structure and the through hole is a polygonal hole. In this embodiment, the shape of the through hole is the same as that of the polygonal ring structure, but the size is reduced in proportion. Preferably, the polygonal ring structure can be, for example, Figure 4 as shown in the square ring structure, and its through hole is also a square through hole; or it can be, for example, Figure 8 as shown in the hexagonal ring structure, and its through hole is also a hexagonal hole.

[0042] In one embodiment of the present invention, as Figure 6 shown, the second metal layer 5 is a circular ring structure and the through hole is a circular hole.

[0043] In one embodiment of the present invention, the number of metal sheets is four, and the four metal sheets form a cross-shaped gap, and the cross-shaped gap is opposite to the through hole; the through hole is located at the geometric center of the annular structure. In this embodiment, the geometric centers of the first metal layer 4 and the second metal layer 5 are on the same straight line.

[0044] In one embodiment of the present invention, the first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are made of one of polytetrafluoroethylene, quartz, glass, FR-4, polyimide, polydimethylsiloxane, and parylene. It can be understood that FR-4 is a widely used glass fiber-reinforced epoxy resin composite material; FR stands for "Flame Retardant", meaning that this material has flame retardant properties, and the number "4" represents a specific type or grade of the material.

[0045] In one embodiment of the present invention, the dielectric constants of the first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are 2 to 6, the loss tangent is 0.0001 to 0.30, and the thicknesses of the first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are 10 to 3000 microns.

[0046] In one embodiment of the present invention, the thicknesses of the first metal layer 4 and the second metal layer 5 are 0.1 to 30 microns, and the first metal layer 4 and the second metal layer 5 are made of one of gold, silver, copper, and nickel.

[0047] In one embodiment of the present invention, the cross-sections of the first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are all regular polygons with side lengths of 50 to 5000 microns.

[0048] In one embodiment of the present invention, the terahertz low-pass filter based on the frequency selective surface includes: a plurality of stacked units composed of the first dielectric layer 1, the second dielectric layer 2, the third dielectric layer 3, the first metal layer 4, and the second metal layer 5.

[0049] In one embodiment of the present invention, a plurality of stacked units are arranged in the transverse and longitudinal directions and form a polygon array, which can be a square array or a hexagonal array, etc. That is to say, a terahertz low-pass filter based on the frequency selective surface provided by the present invention is composed of stacked units of the first dielectric layer 1, the second dielectric layer 2, the third dielectric layer 3, the first metal layer 4, and the second metal layer 5, and the stacked units form an N×N array, where N is any positive integer.

[0050] The beneficial effects of the present invention are demonstrated through the following three embodiments: Embodiment 1: As Figure 1As shown, the stacked unit is a square unit, including a first dielectric layer 1, a second dielectric layer 2, a third dielectric layer 3, a first metal layer 4, and a second metal layer 5. Among them, the metal layer is in close contact with the dielectric layer. The first metal layer 4 is four square metal sheets 41 with side length p1; the second metal layer 5 is a square ring with an outer side length of p2 and an inner side length of p3.

[0051] In Example 1, the dielectric layers are all polytetrafluoroethylene with a dielectric constant of 2.1 and a loss tangent of 0.0003. The first dielectric layer 1 and the third dielectric layer 3 have the same thickness of D1, and the second dielectric layer 2 has the same thickness of D2. The side length of the stacked unit structure in Example 1 is p.

[0052] In Example 1, the metal layer material used is copper with a conductivity of 5.8×10 7 S / m, and the thickness of each metal layer is the same, all being h. The structural dimensions used in Example 1 are shown in Table 1.

[0053] Table 1 This embodiment is a low-pass filter with a cut-off frequency of 0.065 THz. The transmittance of the terahertz low-pass filter in Example 1 is shown in Figure 2 , as shown in the figure. The transmittance of the incident electromagnetic wave reaches more than 90% in the range of 0.028 - 0.065 THz, and 0.065 - 0.4 THz is the stopband of this filter. This filter has the characteristics of a low-pass filter, and it has a high transmittance and a wide stopband within its working range.

[0054] Example 2: The stacked unit structure of this Example 2 is the same as that of Example 1, that is, the materials of the dielectric layers are the same, the materials of the metal layers are the same, and the patterns of the dielectric layers and the metal layers are the same. Only the structural parameters of the unit are changed. The structural dimensions used in Example 2 are shown in Table 2.

[0055] Table 2 The transmittance of Example 2 is as shown in Figure 3 , its cut-off frequency is 0.01 THz, and the transmittance reaches more than 90% in the frequency band range of 0.004 - 0.01 THz, and 0.01 - 0.06 THz is the stopband of this filter.

[0056] Example 3: The unit structure of this low-pass filter is as shown in Figure 4 , the dielectric layer is hexagonal. The materials of the dielectric layer and the metal layer are the same as those in Example 1 and Example 2. The dielectric layer uses polytetrafluoroethylene with a dielectric constant of 2.1 and a loss tangent of 0.0003, and the metal layer material used is copper with a conductivity of 5.8×10 7Copper of S / m.

[0057] For the stacked unit of Example 3, the side length parameter r is 62 μm, and the other structural parameter dimensions are shown in Table 3.

[0058] Table 3 The transmittance of Example 3 is as Figure 5 shown. Its cut-off frequency is 1 THz. The frequency band from 0 to 1 THz is the passband of this low-pass filter, and the passband transmittance is greater than 70%. In the frequency band range of 0.4 - 1 THz, the transmittance reaches more than 90%. The frequency band from 1 to 6 THz is the stopband of this low-pass filter.

[0059] Example 2 and Example 3 can prove that the present invention can adjust the cut-off frequency of the low-pass filter by adjusting the periodic arrangement mode, structural parameters, etc. of the unit. The adjustable range is 0.01 THz - 1 THz, covering the microwave frequency band and the terahertz frequency band, and having broad application prospects.

[0060] Example 4: The structure of the stacked unit in this example is as Figure 6 shown. The dielectric layer is a square unit. Different from Example 1, the second metal layer 5 and the third metal layer are a ring with an outer radius of r1 and an inner radius of r2; the dimensions are: r1 = 400 μm, r2 = 150 μm.

[0061] The transmittance of Example 4 is as Figure 7 shown. Its cut-off frequency is 0.08 THz. The frequency band from 0 to 0.08 THz is the passband of this low-pass filter, and the passband transmittance is greater than 70%. In the frequency band range of 0.08 - 0.2 THz, it is the stopband of this low-pass filter.

[0062] Example 5: The structure of the stacked unit in this example is as Figure 8 shown. The dielectric layer is a square unit. Different from Example 1, the second metal layer 5 and the third metal layer are a hexagonal ring with an outer side length of r1 and an inner side length of r2; the dimensions are: r1 = 400 μm, r2 = 150 μm.

[0063] The transmittance of Example 5 is as Figure 9 shown. The frequency band from 0 to 0.088 THz is the passband of this low-pass filter, and the passband transmittance is greater than 60%. In the frequency band range of 0.088 - 0.2 THz, it is the stopband of this low-pass filter.

[0064] Example 4 and Example 5 can prove that the metal layer structure of the present invention can be various ring structures.

[0065] According to the above five embodiments, the terahertz low-pass filter based on frequency selective surface of the present invention can achieve the transmission of electromagnetic waves in the low-frequency band, covering the microwave band and the terahertz wave band; at the same time, its cut-off frequency can be adjusted by at least one of the following methods: adjusting the parameters of the stacked unit structure (including size and shape), the materials of the dielectric layer or the metal layer, and the arrangement of the stacked units.

[0066] In summary, the present invention provides a terahertz low-pass filter based on frequency selective surface. The terahertz low-pass filter based on frequency selective surface includes: a first dielectric layer 1, a second dielectric layer 2, a third dielectric layer 3, a first metal layer 4, and a second metal layer 5. The first dielectric layer 1, the second dielectric layer 2, and the third dielectric layer 3 are stacked in sequence; the first metal layer 4 is respectively disposed on the surface of the first dielectric layer 1 away from the second dielectric layer 2 and on the surface of the third dielectric layer 3 away from the second dielectric layer 2, and the first metal layer 4 is a square arrangement of four metal sheets 41; the second metal layer 5 is respectively disposed between the first dielectric layer 1 and the second dielectric layer 2 and between the second dielectric layer 2 and the third dielectric layer 3, and the second metal layer 5 is an annular structure with through holes. The terahertz low-pass filter based on frequency selective surface provided by the present invention can achieve the filtering effect on terahertz waves, the working frequency band can cover the microwave band and the terahertz band, its cut-off frequency can be adjusted, and its cut-off frequency range covers 0.01~1 THz; the device structure of the present invention is simple and the preparation difficulty is low; it has a high transmittance in the passband and good stopband suppression characteristics in the high frequency.

[0067] The device embodiments described above are merely illustrative, where the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0068] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A terahertz low-pass filter based on a frequency selective surface, characterized in that: include: A first dielectric layer (1); A second dielectric layer (2); A third dielectric layer (3), wherein the first dielectric layer (1), the second dielectric layer (2) and the third dielectric layer (3) are sequentially stacked; Two first metal layers (4), one of the first metal layers (4) being arranged on a surface of the first dielectric layer (1) away from the second dielectric layer (2), and the other of the first metal layers (4) being arranged on a surface of the third dielectric layer (3) away from the second dielectric layer (2), wherein the first metal layer (4) is a planar structure of N metal sheets (41) arranged in a square shape, N being a positive integer greater than or equal to 2; Two second metal layers (5), one of the second metal layers (5) is arranged between the first dielectric layer (1) and the second dielectric layer (2), and the other of the second metal layers (5) is arranged between the second dielectric layer (2) and the third dielectric layer (3), wherein the second metal layer (5) is a ring structure having a through hole.

2. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The second metal layer (5) is a polygonal ring structure, and the through hole is a polygonal hole.

3. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The second metal layer (5) is a circular ring structure, and the through hole is a circular hole.

4. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The number of the metal sheets (41) is four, and a cross-shaped gap is formed between the four metal sheets (41), and the cross-shaped gap is opposite to the through hole; The through hole is located at the geometric center of the annular structure.

5. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The first dielectric layer (1), the second dielectric layer (2) and the third dielectric layer (3) are made of one of polytetrafluoroethylene, quartz, glass, FR-4, polyimide, polydimethylsiloxane and polyparaxylene.

6. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The dielectric constant of the first dielectric layer (1), the second dielectric layer (2) and the third dielectric layer (3) is 2 to 6, the loss tangent is 0.0001 to 0.30, and the thickness of the first dielectric layer (1), the second dielectric layer (2) and the third dielectric layer (3) is 10 to 3000 micrometers.

7. The terahertz low-pass filter based on the frequency selective surface according to claim 1, characterized in that: The thickness of the first metal layer (4) and the second metal layer (5) is 0.1 to 30 micrometers, and the first metal layer (4) and the second metal layer (5) are made of one of gold, silver, copper and nickel.

8. The terahertz low-pass filter based on a frequency selective surface according to claim 1, characterized in that: The cross-sections of the first dielectric layer (1), the second dielectric layer (2) and the third dielectric layer (3) are all regular polygons with side lengths of 50 to 5000 micrometers.

9. The terahertz low-pass filter based on a frequency selective surface according to any one of claims 1 to 8, characterized in that: include: A plurality of stacked units consisting of the first dielectric layer (1), the second dielectric layer (2), the third dielectric layer (3), the first metal layer (4) and the second metal layer (5).

10. The terahertz low-pass filter based on the frequency selective surface according to claim 9, characterized in that: A plurality of the stacking units are arranged in the horizontal direction and the vertical direction to form a polygonal array.

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