Disclosure of Invention
In order to solve the above-mentioned defects in the prior art, the present invention provides an optically transparent electromagnetic super-surface with a reduced broadband and wide-angle RCS for solving the problem that the existing scattering suppression technology cannot meet the requirements of both optically transparent scenes and visual observation and scattering suppression, which is used for meeting the requirements of the prior art that the reduction of broadband and wide-angle RCS cannot be achieved and that special scenes such as platform windows and the like are also considered for optically transparent scenes or visual observation.
The invention is realized by the following technical scheme.
The invention provides an optical transparent electromagnetic super-surface for reducing broadband and wide-angle RCS (radar cross section), which comprises two PET (polyethylene terephthalate) medium layers and three ITO (indium tin oxide) layers, wherein a surface ITO layer is printed on the upper surface of the upper PET medium layer, a middle ITO layer is printed on the upper surface of the lower PET medium layer and is tightly attached to the lower surface of the upper PET medium layer; the bottom ITO layer is printed on the lower surface of the lower PET medium layer. The formed multilayer electromagnetic super surface is beneficial to reducing the Q value of the super surface so as to widen the bandwidth of the super surface.
The surface layer ITO layer and the middle layer ITO layer are respectively composed of N multiplied by N super surface modules which are arranged in a chessboard manner; the super-surface module is composed of M multiplied by M basic units, N is more than or equal to 2, M is more than or equal to 2, effective resonance can be generated on low-frequency-band incident waves, and the super-surface module is beneficial to the reduction performance of broadband RCS of the super-surface. Each adjacent super-surface module is distributed along the center in a clockwise rotating mode, the scattering energy is redirected by using the anti-phase characteristic between the adjacent super-surface modules, and effective RCS reduction can be achieved.
The three ITO layers made of the transparent conductive film are beneficial to absorbing and converting partial scattering energy into heat energy through ohmic loss, a mixed mechanism of an absorption mechanism and a polarization conversion mechanism is realized in the same structure, and the broadband and wide-angle RCS (remote control system) reduction performance of the super surface is realized.
Furthermore, the super-surface module I on the surface layer ITO layer is composed of M multiplied by M basic units I, and the basic units I are composed of a group of L-shaped patches I which are arranged on the upper surface of the upper layer PET medium layer along the diagonal line.
Furthermore, the super-surface module of the middle ITO layer is composed of M multiplied by M basic units II, and each basic unit II is composed of a group of L-shaped patches II which are distributed on the upper surface of the lower PET medium layer along the diagonal line and a group of middle bent arched strips which are symmetrically distributed relative to the adjacent diagonal line.
The structure is beneficial to simulating infinite period conditions so as to reduce the coupling effect between the basic units forming the super-surface module, is beneficial to generating resonance on the broadband incident wave, realizes effective RCS reduction performance under the broadband incident wave, and ensures that TE and TM waves in the broadband have the same frequency response and realize polarization stability due to the symmetrical distribution.
Furthermore, the arched strips are positioned between the L-shaped patches II, the length of the strips at the bending positions is the same as the width of the openings of the two arms of the L-shaped patches II, and the thickness of the strips at the bending positions is the same as that of the L-shaped patches II; the structure can reduce the structural parameters of the basic unit II and the complexity of structural design.
The distance between the strip at the bent part and the end parts of the two arms of the L-shaped patch is not less than the width of the single arm of the L-shaped patch, so that the coupling effect between the arched strip and the L-shaped patch is utilized, and the frequency response effect of the basic unit II on the medium-frequency-band incident waves is improved.
Furthermore, the periodic pitches P of the basic unit I and the basic unit II are the same, which is beneficial to forming the super-surface module I and the super-surface module II with the same size, so that the super-surface formed by clockwise rotating distribution of the center has symmetrical distribution characteristics, and the polarization stability of the super-surface is realized.
Furthermore, two arms of the L-shaped patch I and the L-shaped patch II are symmetrical about a diagonal, so that the L-shaped patch I and the L-shaped patch II have polarization insensitivity to TE and TM incident waves. The length and the width of the single arm of the L-shaped patch I are smaller than those of the single arm of the L-shaped patch II, and the difference of structural parameters is beneficial to improving the frequency response characteristic of high-frequency-band incident waves.
Furthermore, the surface layer ITO layer, the middle layer ITO and the bottom layer ITO layer are made of transparent conductive indium tin oxide materials, and the polarization conversion mechanism and the absorption mechanism can be integrated in the same structure by utilizing the characteristics of certain sheet resistance and conductivity of the transparent conductive indium tin oxide, so that the broadband and wide-angle RCS (remote control system) reduction performance and the optical transparency of the super surface are realized.
Furthermore, the upper PET medium layer and the lower PET medium layer are made of polyethylene glycol terephthalate materials, so that the super-surface optical transparency is realized.
Furthermore, the upper PET medium layer and the lower PET medium layer are the same in thickness, the relative dielectric constant is 2.5-4.5, the loss tangent is 0.01-0.03, the moderate relative dielectric constant is beneficial to realizing a basic unit structure with a low Q value, the broadband RCS reduction performance of the super surface is realized, the large loss tangent can reduce the amplitude of scattered waves through dielectric loss, and the broadband RCS reduction performance of the super surface is beneficial to.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
the optical transparent electromagnetic super-surface integrates two mechanisms of absorption and polarization conversion of electromagnetic waves into the same unit structure, completes the structural design of a mixed mechanism of the super-surface, has symmetry simultaneously, enables the unit to have higher incident angle stability, effectively expands the reduction bandwidth of RCS by a two-layer structure nesting method, and can realize RCS reduction of more than 10dB in a wide frequency range of 7.47-30.06 GHz. The absorption conversion rate ACR of the hybrid super-surface is more than 90% in the frequency range of the co-polarization reflection coefficient less than-10 dB, and the polarization conversion rate is more than 0.8 in the frequency ranges of 8-16GHz, 20.5-24GHz and 26.5-30.5 GHz. Meanwhile, the traditional metal patch is replaced by a transparent conducting film such as ITO (indium tin oxide) and the like, and the traditional opaque medium substrate is replaced by a transparent material such as PET (polyethylene terephthalate) and the like, so that the super-surface structure has good optical transparency, and can be applied to scenes needing to give consideration to both optical transparency or visual observation and RCS (radar cross section) reduction and low scattering characteristics.
Detailed Description
The present invention will now be described in detail with reference to the drawings and specific embodiments, wherein the exemplary embodiments and descriptions of the present invention are provided to explain the present invention without limiting the invention thereto.
Referring to fig. 1, the optically transparent electromagnetic super surface of the present embodiment includes three transparent conductive indium tin oxide ITO layers 1, 2, 3 and two polyethylene terephthalate PET dielectric layers 4, 5; the surface layer ITO layer 1 is printed on the upper surface of the upper layer PET medium layer 4; the middle ITO layer 2 is printed on the upper surface of the lower PET medium layer 5 and is tightly attached to the lower surface of the upper PET medium layer 4; the bottom ITO layer 3 is printed on the lower surface of the lower PET layer 5; the thicknesses of the two layers of PET medium layers are the same, and a 60mm multiplied by 4mm super-surface whole body is formed.
Referring to fig. 2(a), the surface ITO layer 1 is composed of 2 × 2 super surface modules i 11; the super-surface module I11 is composed of 5 multiplied by 5 basic units I111, adjacent super-surface modules are distributed along the center in a clockwise rotating mode, 0 and 1 in the drawing respectively represent two adjacent different super-surface modules, and the super-surface module 0 is a super-surface module 1 after being rotated by 90 degrees clockwise.
Referring to fig. 2(b), the basic unit i 111 of the super-surface module i 11 is composed of a group of L-shaped patches i 1111 arranged along the diagonal line on the upper surface of the upper PET dielectric layer. In this embodiment, the two arms of the L-shaped patch I1111 are symmetrical with respect to the diagonal, the single arm has a length L1 of 1.0mm to 3.0mm, a width W1 of 0.2mm to 0.8mm, and a unit period pitch P of 4mm to 10 mm. This embodiment uses, but is not limited to, L1-2.05 mm, W1-0.4 mm, and P-6 mm.
Referring to fig. 3, the super-surface structure module ii 21 is composed of 2 × 2 super-surface modules ii 21; the super-surface module II 21 is composed of 5 × 5 basic units II 211, adjacent basic unit structures are distributed along the center in a clockwise rotation mode, similarly, "0" and "1" in the drawing respectively represent two adjacent different structural basic units, and after the "0" basic unit structure is rotated by 90 degrees clockwise, the "1" basic unit structure is formed.
As shown in fig. 4, the basic unit ii 211 is composed of a group of L-shaped patches ii 2111 arranged on the upper surface of the lower PET medium layer along the diagonal line and a group of middle bent arched strips 2112 symmetrically distributed about the adjacent diagonal line, the arched strips 2112 are located between the L-shaped patches ii 2111, the length L3 of the bent strips is the same as the width of the openings of the two arms of the L-shaped patches ii 2111, and the thickness W3 of the bent strips is the same as the thickness W2 of the L-shaped patches ii 2111; the distance between the strip at the bent part and the end parts of the two arms of the L-shaped patch II 2111 is not less than the width of the single arm of the L-shaped patch II 2111.
In this embodiment, the two arms of the L-shaped patch 2111 are symmetrical about a diagonal, with a single arm length L2 of 1.0mm to 3.0mm and a width W2 of 0.2mm to 0.8 mm; the middle arched strip 2112 is positioned between the L-shaped patches 2111, the length L3 of the strip at the bending part is 1.5mm-3.2mm, the width W3 is 0.2mm-0.8mm, the length L4 of the strip at the two sides is 1.0mm-2.0mm, and the width W4 is 0.5mm-1.5 mm. This example uses, but is not limited to, 2.26mm for L2, 0.5mm for W2, 2.3mm for L3, 0.5mm for W3, 1.65mm for L4, and 0.7mm for W4.
In the embodiment, the period pitch P of the basic unit I111 is the same as that of the basic unit II 211; the two arms of the L-shaped patch I1111 and the L-shaped patch II 2111 are symmetrical about a diagonal line, and the length and the width of one arm of the L-shaped patch I1111 and the L-shaped patch II 2111 are the same. The upper PET medium layer and the lower PET medium layer have the same thickness, the relative dielectric constant is 2.5-4.5, and the loss tangent is 0.01-0.03. The sheet resistance of the ITO film is 5-20 omega, but the sheet resistance adopted in the embodiment is not limited to 6 omega.
The working principle of the embodiment is as follows:
the optical transparent electromagnetic super-surface can convert incident electromagnetic waves into cross polarized waves by utilizing a polarization conversion principle, the working bandwidth of the optical transparent electromagnetic super-surface is expanded by a structure nesting method, the super-surface module rotates clockwise along the center of a structure, the reflection phase inversion of adjacent modules can be realized, and scattered beams can be redirected to the directions of four corners according to a phase cancellation principle; meanwhile, the ITO thin film material with a specific resistance value is adopted to replace the traditional metal material, ohmic loss is introduced to realize the conversion from electromagnetic energy to heat energy, the effective absorption of incident electromagnetic waves can be realized in a specific frequency range, the echo energy in a threat angle range is reduced, and the purpose of RCS reduction is achieved; in addition, because the floor also adopts the ITO film, and the medium substrate adopts the PET material with optical transparency, the super surface has high optical transparency as a whole, and the super surface can be applied to scenes which need optical transparency or perspective observation and RCS reduction at the same time.
The specific principle of the design of the mixing mechanism of the optically transparent electromagnetic super-surface of the embodiment is as follows:
the mixing mechanism of the optical transparent electromagnetic super-surface of the embodiment is mainly analyzed by two parts, namely a wave-absorbing principle and a polarization conversion principle:
according to the wave absorption principle analysis, the absorptivity of the super-surface unit can be expressed as:
wherein
And
co-polarized and cross-polarized reflection coefficients and transmission coefficients, respectively. Since the reflective plate employs the ITO film with low impedance, the electromagnetic wave is almost totally reflected, the transmission coefficients of the two polarizations can be approximated to 0, and the absorption rate of the super-surface unit can be defined as:
according to the polarization Conversion principle, Conversion is defined as the ratio of polarization Conversion of incident waves into cross-polarized waves, which is expressed as:
considering both the absorbed and converted electromagnetic energy, the absorption conversion ACR of a super-surface unit can be defined as:
as can be seen from the formula (4), for the super-surface unit of this embodiment, the absorption conversion rate is composed of two parts, one part is from the wave-absorbing effect of the wave-absorbing principle, and the other part is from the conversion effect of the polarization conversion principle, which indicates that the super-surface unit realizes the mixing of the two mechanisms.
The technical effects of the invention are further explained by combining simulation experiments as follows:
simulation software: full-wave simulation software HFSS — 15.0.
Simulation content and results:
simulation 1, the results of simulation calculation of co-polarized and cross-polarized reflection coefficients and transmission coefficients of the super-surface unit of this embodiment in the frequency range of 6GHz-34GHz are shown in fig. 5 (a).
As can be seen from FIG. 5(a), the super surface unit of this embodiment has a transmission coefficient of less than-25 dB in the frequency range of 6GHz-34GHz, because the lowest layer employs an ITO film with low impedance, and the electromagnetic wave is almost totally reflected. And in the frequency range of 7.44GHz-31.31GHz, the co-polarization reflection coefficient is less than-10 dB, and the cross-polarization reflection coefficient is not close to 0. It follows that the incident electromagnetic wave energy is divided into three components, reflected waves, absorbed waves and converted into cross-polarized waves.
Simulation 2, simulation calculation is performed on the Absorption rate Absorption, the Conversion rate Conversion and the Absorption Conversion rate ACR of the super-surface unit in the range of the frequency 6GHz-34GHz, and the result is shown in FIG. 5 (b).
As can be seen from fig. 5(b), the absorption conversion rate ACR of the super-surface unit in this embodiment is greater than 90% in the frequency range where the co-polarization reflection coefficient is less than-10 dB, so that the super-surface unit has a higher polarization conversion rate in the frequency range where the wave absorption rate is lower and a higher wave absorption rate in the frequency range where the polarization conversion rate is lower, and the electromagnetic wave regulation performance is significantly improved due to the synergistic effect of the two mechanisms.
Simulation 3, the polarization Conversion ratio PCR and the Conversion ratio Conversion of the super-surface unit of this example were simulated in the frequency range of 6GHz-34GHz, and the results are shown in FIG. 6 (a).
As can be seen from FIG. 6(a), the polarization conversion rate of the super-surface unit in this embodiment is greater than 0.8 in the frequency ranges of 8-16GHz, 20.5-24GHz and 26.5-30.5GHz, and represents the ratio of the incident wave converted into its cross-polarized wave to the residual energy not containing absorbed and dissipated part of the energy.
Simulation 4, in the frequency range of 6-34GHz, the reflection phase of the super-surface unit of this embodiment and the reflection phase of the mirror super-surface unit after the super-surface unit rotates 90 degrees with respect to its center are simulated and calculated, and the result is shown in fig. 6 (b).
As can be seen from FIG. 6(b), the reflection phase difference of the super-surface unit of the present embodiment and the mirror super-surface unit after the super-surface unit rotates 90 degrees from its central symmetry is within 180 + -37 deg. in the frequency ranges of 7-23GHz and 28-30.5GHz, so that the phase cancellation of the scattered waves can be realized, and the scattering peak in the threat angle range is reduced.
Simulation 5, which simulates the wave-absorbing conversion rate of the super-surface unit of this embodiment at TE and TM wave incidence with an incident angle from 0 ° to 60 ° (step angle 15 °), respectively, in the frequency range of 6-34GHz, and the result is shown in fig. 7. Fig. 7(a) shows the TE wave incident condition, and fig. 7(b) shows the TM wave incident condition.
As can be seen from fig. 7(a) and (b), in the range of 0 ° to 45 °, the wave-absorbing conversion rate is greater than 80% (in the case of TM wave incidence, it exceeds 90%), and although the wave-absorbing conversion rate is reduced at approximately 60 °, a significant absorbing conversion effect is still exhibited, indicating that the super-surface unit of the present embodiment has a high incident angle stability.
Simulation 6, in the range of 6-34GHz, TE wave incidence and TM wave incidence are respectively adopted, and simulation calculation is performed on the reduction of the section of the single-station radar (compared with a metal plate with the same size) under the condition that the electromagnetic wave of the super-surface of the embodiment is vertical and has five different incidence angles of 15 °, 30 °, 45 ° and 60 °, and the results are shown in fig. 8(a) and (b).
As can be seen from FIGS. 8(a) and (b), the super-surface of the present embodiment achieves a broadband RCS reduction effect for both TE and TM waves at different incident angles, and achieves an RCS reduction effect of more than 10dB in the 7.47-30.06GHz band for normal incidence. Fig. 8(a) shows the TE wave incident condition, and fig. 8(b) shows the TM wave incident condition.
Simulation 7, selecting 5 frequency points such as 9GHz, 14GHz, 19GHz, 24GHz, 29GHz and the like under the TE wave vertical incidence condition, and performing simulation calculation on the three-dimensional scattering directional diagrams of the super surface and the metal plate with the same size in the embodiment, where the results are shown in fig. 9(a) and fig. 9(b), where fig. 9(a) is the scattering directional diagram of the super surface in the embodiment, and fig. 9(b) is the scattering directional diagram of the metal plate with the same size.
As can be seen from fig. 9(a), (b), compared with the metal plate, due to the clockwise arrangement of the super-surface modules, a reflected wave phase difference of 180 ± 37 ° is introduced between adjacent modules, so that the three-dimensional scattering pattern of the super-surface of the present embodiment is in a four-beam shape, and at the same time, the intensity of the reflected wave is lower than that of the reflected wave of the metal plate, because part of the energy is absorbed by the super-surface of the present embodiment, thereby also proving the correctness and effectiveness of the mixing mechanism of the super-surface of the present embodiment.
The present invention is not limited to the above-mentioned embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative efforts according to the disclosed technical contents, and these substitutions and modifications are all within the protection scope of the present invention.