A broadband polarization-insensitive terahertz absorber based on ITO resistance loss

Abstract

The purpose of the present invention is to provide a broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss, which belongs to the technical field of terahertz absorbing materials and aims to solve the shortcomings of existing terahertz absorbing materials in terms of broadband absorption capacity, oblique incidence angle adaptability, polarization insensitivity and lightweight structure. The absorbing material includes four layers of ITO resistance loss layers composed of ITO patch units from top to bottom, each layer of ITO resistance loss layer is adhered to a PET double-sided adhesive layer and is divided by a PS foam medium layer. The structure realizes polarization insensitivity and eliminates the problem of existing absorbing materials relying on polarization angle.

Description

Technical Field

[0001] The invention belongs to the technical field of terahertz absorbing materials, and in particular relates to a broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency of 0.1-10 THz (wavelength 3mm-30μm). It has the advantages of both infrared and microwaves and also has a unique frequency band advantage. With the successful development of terahertz wave sources and detectors, terahertz technology has gradually matured, making security risks such as information leakage, electromagnetic interference and target exposure increasingly high, so the importance of terahertz stealth and detection technology has become more and more prominent. The stealth capability of traditional stealth fighters cannot meet the requirements of the terahertz band, and there is an urgent need to seek greater breakthroughs to achieve lightweight, transparent and broadband stealth effects. The emergence of metamaterials has ushered in a new era for stealth technology. How to better enable stealth materials to have excellent broadband terahertz band stealth performance has become a research focus.

[0003] The action range of metamaterials can span the entire spectrum. In theory, for different wavelengths, metamaterials that work in this spectrum range can be designed, and the scale and morphology of the structural characteristic unit are determined by the wavelength of the working band. The anisotropic characteristics of metamaterial structures can be used to achieve spatial dispersion control of electromagnetic waves, thereby potentially breaking through the limitations of the inherent properties of conventional natural materials and achieving absorbing materials that take into account both broadband and wide incident angle (wide angle) requirements. Overcoming the shortcomings of poor maintenance of traditional absorbing coatings is an important technical means for modern aircraft to achieve stealth. In 2006, JB Pinry's research team and U. Leonhardt independently proposed the concept and theory of transformation optics, making stealth from possibility to reality. In 2008, a metamaterial with an electrically open resonant ring, a dielectric layer and a metal wire as a unit structure was proposed by Boston College and Duke University. The research was supported by the Los Alamos National Laboratory and the Air Force Office of Scientific Research in the United States, and was the first to achieve perfect absorption with an absorption rate of up to 99% in the microwave frequency band. The advent of the "perfect metamaterial absorber" marks the entry of metamaterial stealth technology into the historical stage. Subsequently, the research on perfect absorption metamaterial stealth technology quickly expanded to the terahertz field. In 2008, Tao et al. designed a terahertz stealth metamaterial based on an electric ring resonator and a magnetic resonator for the first time, which achieved an absorption rate of 70% at 1.3 THz, but its stealth performance and coverage frequency range (i.e., absorption bandwidth) need to be improved. In 2014, Zhu et al. designed and synthesized a pyramid-like layered array, which achieved relatively broadband effective absorption through the size gradient effect between layers, and achieved an absorption rate of more than 80% in the range of 0.7~2.3 THz, achieving the purpose of increasing the effective stealth bandwidth, but the absorption intensity still needs to be improved. In 2018, Ding et al. proposed a multi-layer switchable terahertz absorption metasurface with an absorption rate of more than 90% in the range of 0.56~1.232 THz, but its absorption bandwidth needs to be improved. In 2023, W. Yu et al. proposed a broadband absorbing material based on a two-dimensional / three-dimensional hybrid structure by embedding a two-dimensional plane into a three-dimensional structure. It has the characteristics of low loss while achieving broadband absorption, but the device operating frequency band is still in the GHz band. At present, metamaterials have shown great advantages in achieving broadband absorption, but the bi-anisotropy of the single-layer structure easily leads to the deterioration of the absorption performance when the electromagnetic wave is obliquely incident, making it difficult to achieve wide-angle absorption. In summary, there are few studies on oblique incidence stability, lightweight, and full terahertz bands in the current research on terahertz stealth at home and abroad. There are still some urgent research topics in the application of multi-layer metamaterials in broadband and wide-angle absorption.

[0004] Looking at the current research results in the field of terahertz wave absorption and stealth, there are still two prominent problems that are difficult to overcome in metamaterials in terms of taking into account broadband and wide-angle absorption at the same time: (1) Polarization divergence of wave absorption performance when electromagnetic waves are incident obliquely: Generally speaking, TM polarization is easier to achieve large incident angles, while under TE polarization, the electromagnetic performance of the metasurface generally changes rapidly when the incident angle is above 45°; (2) Broadband and wide angle are incompatible: metasurfaces with effective incident angles above 60° are generally narrowband, while the electromagnetic performance of broadband metasurfaces generally changes significantly after the incident angle exceeds 45°. In order to solve the above problems, researchers have proposed a variety of design schemes to improve the wave absorption performance of metasurfaces at large incident angles, but their designs are difficult to take into account both polarizations. With the rapid development of micro-nano manufacturing technology, multi-layer metamaterials can be designed in three-dimensional space, with greater control space and design freedom. In particular, its spatial dispersion characteristics provide a possible way to realize the preparation of broadband terahertz stealth metamaterials, solve the impedance matching deviation under oblique incidence, and thus achieve broadband and wide-angle absorption and stealth. Summary of the invention

[0005] The purpose of the present invention is to provide a broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss, aiming to solve the shortcomings of existing terahertz absorbing materials in terms of broadband absorption capacity, oblique incidence angle adaptability, polarization insensitivity and lightweight structure, and provide a selection scheme for conductive, insulating or dielectric materials in the field of terahertz absorbing. The application target of the present invention is to meet the strict requirements for ultra-wideband and wide-angle absorption in the fields of military stealth, aerospace and communications.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss, which includes four ITO resistance loss layers composed of conductive material ITO patch units from top to bottom, each ITO resistance loss layer is adhered to a dielectric material PET double-sided adhesive layer and is divided by a dielectric material PS foam medium layer;

[0008] The ITO patch unit located in the top ITO resistance loss layer adopts a square block pattern design with two in the horizontal direction and two in the vertical direction, the patch spacing is O2, and the patch width is L3;

[0009] The ITO patch unit of the second ITO resistance loss layer from top to bottom is a square ring structure, which is composed of a square with a side length of L2 minus a square with a side length of O1 in the middle;

[0010] The ITO patch unit of the third ITO resistance loss layer from top to bottom adopts a square continuous plane structure with a side length of L1;

[0011] The ITO patch unit of the bottom ITO resistance loss layer is a square with a side length of P, which is the reflection layer of the entire absorbing material piece and is close to an ideal conductor.

[0012] Furthermore, the dielectric constant of the dielectric material PET double-sided adhesive layer is 2.62, and the loss tangent is 0.014; the dielectric constant of the PS foam dielectric layer is 1.1, and the loss tangent is 0.018.

[0013] Furthermore, from top to bottom, the sheet resistance of the ITO resistance loss layer is 200Ω, 220Ω, 230Ω, and 150Ω, respectively.

[0014] Furthermore, P = 50 μm, L1 = 49 μm, L2 = 43 μm, L3 = 17.5 μm, O1 = 10 μm, O2 = 8 μm; the thickness of the PS foam medium layer is 12.5 μm, and the thickness of the PET double-sided adhesive layer is 1 μm.

[0015] The working principle of the absorbing material is as follows: The absorption rate calculation formula of the absorbing material is: A=1-RT, where A is the absorption power, R is the reflectivity, and T is the transmittance. Since the bottom ITO resistance loss layer is thick enough, the transmittance T=0. At this time, the absorbing formula can be expressed as: A=1-R.

[0016] The broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss of the present invention is polarization-insensitive to the incident electromagnetic wave. When the electromagnetic wave is incident vertically / obliquely, the ITO high-resistance surface with a certain conductivity is prepared, which means that the free electrons in the material will encounter greater resistance during the movement. When the terahertz electromagnetic wave enters the interior of the material, it will interact with the free carriers (such as free electrons) in the material. These carriers move under the action of the electric field and generate heat due to the resistivity of the material, thereby converting electromagnetic energy into thermal energy. And based on the multiple refraction losses of the porous structure of the dielectric material PS foam inside the dielectric layer and between the PS and PET layers, the absorption bandwidth of the absorbing material is widened, thereby realizing the ultra-wideband absorption of the absorbing material in the terahertz band.

[0017] The present invention has the characteristic of polarization insensitivity, that is, there is no significant change in the absorption effect of TE wave (transverse electric wave) and TM wave (transverse magnetic wave) incident.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. The selection of this material achieves an absorption rate of more than 90% in a wide range of 0.84~7.1 THz, and the peak absorption efficiency reaches 99.9%, overcoming the shortcomings of narrow bandwidth and low absorption efficiency of existing technologies.

[0020] 2. The selection of this material has the advantages of compact structure, simplicity and easy processing.

[0021] 3. The selection of this material achieves polarization insensitivity and eliminates the problem of existing absorbing materials' dependence on polarization angle.

[0022] 4. The selection of this material achieves an absorption rate of more than 90% in the range of 0~45° incident angle and more than 80% in the range of 0~60° incident angle, improving the phenomenon that the performance of the absorbing material is significantly reduced at large angles.

[0023] 5. The absorbing material can achieve a stable absorption rate of more than 80% covering the entire frequency range of 1 to 10 THz within the oblique incidence angle range of 45 to 60 degrees. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the wave absorbing material of the present invention;

[0025] Figure 2 It is a schematic diagram of the structure of the top ITO resistance loss layer;

[0026] Figure 3 It is a schematic diagram of the structure of the second ITO resistance loss layer;

[0027] Figure 4 It is a schematic diagram of the structure of the third ITO resistance loss layer;

[0028] Figure 5 is a side view of the absorbing material of the present invention;

[0029] Figure 6 This is a schematic diagram of the broadband absorption spectrum of the absorbing material obtained by simulation using the simulation software CST STUDIO SUITE2020 when the TE wave is incident at an incident angle of 0-60°;

[0030] Figure 7 This is a schematic diagram of the broadband absorption spectrum of the absorbing material of the present invention obtained by simulating the simulation software CST STUDIO SUITE2020 when the TM wave is incident at an incident angle of 0-60°;

[0031] Figure 8 It is a schematic diagram of the superposition of multiple reflected waves;

[0032] Among them: 1-the uppermost ITO resistance loss layer; 2-PET double-sided adhesive layer; 3-PS foam dielectric layer; 4-the second ITO resistance loss layer; 5-the third ITO resistance loss layer; 6-the bottommost ITO resistance loss layer. DETAILED DESCRIPTION

[0033] The invention is composed of dielectric material polystyrene foam (PS), polyethylene terephthalate (PET) double-sided adhesive and conductive material indium tin oxide (ITO) conductive layer. The wave absorbing material includes four layers of ITO resistance loss layers, each layer is sequentially adhered to the dielectric material PET double-sided adhesive layer and separated by the dielectric material PS foam.

[0034] like Figure 1-5 As shown, the ITO patch unit of the topmost ITO resistance loss layer 1 is designed with a square block pattern of two in the horizontal direction and two in the vertical direction, the patch spacing is O2, and the overall width is L3.

[0035] The ITO patch unit of the second ITO resistance loss layer 4 is a square ring structure, which is composed of a square with a side length of L2 minus a square with a middle side length of O1.

[0036] The ITO patch unit of the third ITO resistance loss layer 5 adopts a square continuous plane structure with a side length of L1.

[0037] The ITO patch of the bottom ITO resistance loss layer 6 is a square with a side length of P, which is the reflection layer of the entire absorbing material piece, close to an ideal conductor, and localizes the terahertz wave in the terahertz frequency band to the PET+PS dielectric layer.

[0038] Each ITO resistance loss layer is attached to the corresponding dielectric material PET double-sided adhesive layer 2 and is separated by the PS foam dielectric layer 3.

[0039] Regarding parameter settings, in CST STUDIO SUITE 2020, the basic parameters of the three materials are set as follows: PET dielectric constant 2.62, loss tangent 0.014; PS dielectric constant 1.1, loss tangent 0.018; from top to bottom, the square resistance of the ITO resistor loss layer is 200Ω, 220Ω, 230Ω, and 150Ω. The dimensions of the above devices are: P = 50 μm, L1 = 49 μm, L2 = 43 μm, L3 = 17.5 μm, O1 = 10 μm, O2 = 8 μm. The thickness of the PS layer is 12.5μm, and the thickness of the PET layer is 1μm.

[0040] The present invention has polarization insensitivity, that is, the absorption effect of TE wave (transverse electric wave) and TM wave (transverse magnetic wave) incident does not change significantly. The present invention provides a selection scheme of conductive, insulating or dielectric materials in the field of terahertz absorbing materials. Figure 6 , 7 shown.

[0041] The specific absorption is as follows:

[0042] 1. When the TE wave (transverse electric wave) is incident vertically, the absorbing material achieves broadband absorption with a bandwidth of 6.39 THz and more than 90% in the 0.84~7.23 THz band, among which the absorption peak achieves an absorption efficiency of 99.9% at 1.23~1.28 THz; and achieves broadband absorption with a bandwidth of 7.62 THz and more than 80% in the 0.74~8.36 THz band.

[0043] 2. When the TE wave (transverse electric wave) is obliquely incident at an angle of 15° with the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 6.7 THz in the 0.85~7.55 THz band, among which the absorption peak achieves an absorption efficiency of 99.7% at 1.21~1.34 THz; and broadband absorption of more than 80% with a bandwidth of 7.83 THz in the 0.74~8.57 THz band.

[0044] 3. When the TE wave (transverse electric wave) is obliquely incident at an angle of 30° with the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 7.21 THz in the 0.88~8.09 THz band, among which the absorption peak achieves an absorption efficiency of 98.9% at 1.25~1.38 THz; and broadband absorption of more than 80% with a bandwidth of 8.37 THz in the 0.77~9.14 THz band.

[0045] 4. When the TE wave (transverse electric wave) is incident at an angle of 45° to the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 6.96 THz in the 0.96~7.92 THz band, among which the absorption peak achieves an absorption efficiency of 96.3% at 1.33~1.42 THz; and broadband absorption of more than 80% with a bandwidth of 9.18 THz in the 0.82~10 THz band.

[0046] 5. When the TE wave (transverse electric wave) is incident at an angle of 60° with the plane normal, the absorbing material achieves broadband absorption of more than 80% with a bandwidth of 9.03 THz in the 0.97~10 THz band.

[0047] 6. When TM wave (transverse magnetic wave) is incident vertically, the absorbing material achieves broadband absorption with a bandwidth of 6.39 THz and more than 90% in the 0.84~7.23 THz band, among which the absorption peak achieves an absorption efficiency of 99.9% at 1.22~1.29 THz; and achieves broadband absorption with a bandwidth of 7.61 THz and more than 80% in the 0.74~8.35 THz band.

[0048] 7. When the TM wave (transverse magnetic wave) is incident at an angle of 15° to the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 6.71 THz in the 0.85~7.56 THz band, among which the absorption peak achieves an absorption efficiency of 99.7% at 1.2~1.34 THz; and broadband absorption of more than 80% with a bandwidth of 7.82 THz in the 0.75~8.57 THz band.

[0049] 8. When the TM wave (transverse magnetic wave) is incident at an angle of 30° to the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 7.21 THz in the 0.88~8.09 THz band, among which the absorption peak achieves an absorption efficiency of 98.9% at 1.25~1.49 THz; and broadband absorption of more than 80% with a bandwidth of 8.37 THz in the 0.77~9.14 THz band.

[0050] 9. When the TM wave (transverse magnetic wave) is incident at an angle of 45° to the plane normal, the absorbing material achieves broadband absorption of more than 90% with a bandwidth of 6.95 THz in the 0.96~7.91 THz band, among which the absorption peak achieves an absorption efficiency of 96.3% at 1.31~1.45 THz; and broadband absorption of more than 80% with a bandwidth of 9.18 THz in the 0.82~10 THz band.

[0051] 10. When the TM wave (transverse magnetic wave) is incident at an angle of 60° to the plane normal, broadband absorption of more than 80% with a bandwidth of 9.03 THz is achieved in the 0.97~10 THz band.

[0052] This characteristic has wide application value in the fields of electromagnetic compatibility, stealth technology, electromagnetic shielding, etc. In stealth technology, polarization-insensitive absorbing materials can absorb radar waves more effectively, thereby reducing the radar scattering cross section of the target and improving the stealth effect. In the field of electromagnetic compatibility, polarization-insensitive absorbing materials can be used to reduce the interference between electromagnetic waves in different polarization states and improve the stability and reliability of the system.

[0053] like Figure 8 As shown, the interlayer interface of the second ITO resistance loss layer, the lower PET double-sided adhesive layer adhered to the second ITO resistance loss layer, and the PS foam medium layer adhered to the lower PET double-sided adhesive layer adhered to the second ITO resistance loss layer from top to bottom is defined as interface one, and the space above interface one is defined as space one;

[0054] The interlayer interfaces of the third ITO resistance loss layer, the upper PET double-sided adhesive layer to which the third ITO resistance loss layer adheres, and the PS foam medium layer to which the upper PET double-sided adhesive layer to which the third ITO resistance loss layer adheres are defined as interface 2, and the space between interface 1 and interface 2 is defined as space 2;

[0055] Multiple interference reflections mainly occur in the three PS foam dielectric layers. Due to the multi-layer structure design, the electromagnetic waves are localized between the top ITO resistance loss layer and the bottom ITO resistance loss layer, realizing electromagnetic loss + interference loss and wave absorption.

[0056] The superposition of multiple reflected waves can be expressed as:

[0057]

[0058]

[0059]

[0060] According to the Smith parameter inversion method, when an incident electromagnetic wave enters the upper layer of the metamaterial from the external space, part of the electromagnetic wave will be reflected back into the air due to the impedance matching principle. The reflection coefficient can be expressed as S 11 e (iθ11) The rest of the material will enter the metamaterial, and the transmission coefficient can be expressed as S 21 e (iθ21) After the forward propagating transmission wave reaches the second interface, it will be totally reflected due to the obstruction of the lower metal film and produce a propagation phase β. In this case, the reflection coefficient on the second interface is S 23 =-1. Similarly, when the electromagnetic wave reflected by interface 2 continues to propagate and reaches interface 1, transmission and reflection will also occur. The reflection coefficient at this time is expressed by S 12 e (iθ12) The transmission coefficient can be expressed as S 22 e (iθ22) It means that the reflected wave will generate a propagation phase β. Therefore, the incident terahertz band electromagnetic wave enters the metamaterial absorber and undergoes a series of reflection and transmission phenomena. Finally, the electromagnetic waves that return to the air multiple times inside the absorber are superimposed to form the total reflected wave S 11total The total reflected wave is expressed as above.

[0061] Where S 11 , S 22 and S 23 is the reflection coefficient, S 12 and S 21is the transmission coefficient, β represents the propagation phase of the incident electromagnetic wave entering the absorbing material, k and d in the figure are usually considered to be the propagation wave number and propagation distance, and t represents the thickness of the dielectric layer.

[0062] In summary:

[0063] 1. The selection of this material achieves an absorption rate of more than 90% in a wide range of 0.84~7.1 THz, overcoming the shortcomings of narrow bandwidth and low absorption efficiency of existing technologies.

[0064] 2. The material achieves polarization insensitivity, eliminating the problem of existing absorbing materials' dependence on polarization angle.

[0065] 3. The material achieves an absorption rate of more than 90% in the range of 0~45° incident angle and more than 80% in the range of 0~60° incident angle, improving the phenomenon that the performance of absorbing materials is significantly reduced at large angles.

[0066] 4. The material achieves a unit weight of only 0.6 kg / m 2 , avoiding the problem of excessive weight of existing absorbing materials.

[0067] 5. This material achieves efficient and large-scale preparation, breaking through the bottleneck of existing terahertz absorbing materials that are difficult to process and difficult to mass produce.

Claims

1. A broadband polarization-insensitive terahertz absorbing material based on ITO resistance loss, characterized in that: The absorbing material can achieve an absorption rate greater than 90% in a wide range of 0.84 to 7.1 THz; The absorbing material includes four ITO resistance loss layers composed of conductive material ITO patch units from top to bottom, each ITO resistance loss layer is adhered to a dielectric material PET double-sided adhesive layer and is divided by a dielectric material PS foam medium layer; The ITO patch unit located in the top ITO resistance loss layer adopts a square block pattern design with two in the horizontal direction and two in the vertical direction, the patch spacing is O2, and the patch width is L3; The ITO patch unit of the second ITO resistance loss layer from top to bottom is a square ring structure, which is composed of a square with a side length of L2 minus a square with a side length of O1 in the middle; The ITO patch unit of the third ITO resistance loss layer from top to bottom adopts a square continuous plane structure with a side length of L1; The ITO patch unit of the bottom ITO resistance loss layer is a square with a side length of P, which is the reflection layer of the entire absorbing material piece and is close to an ideal conductor; The dielectric constant of the dielectric material PET double-sided adhesive layer is 2.62, and the loss tangent is 0.014; the dielectric constant of the dielectric material PS foam medium layer is 1.1, and the loss tangent is 0.018; From top to bottom, the square resistance of the ITO resistance loss layer is 200Ω, 220Ω, 230Ω, and 150Ω; P = 50 μm, L1 = 49 μm, L2 = 43 μm, L3 = 17.5 μm, O1 = 10 μm, O2 = 8 μm; the thickness of the dielectric material PS foam medium layer is 12.5 μm, and the thickness of the PET double-sided adhesive layer is 1 μm.

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