A passive metamaterial radiator with wide-angle high emissivity

Abstract

The application belongs to the technical field of metamaterials, and particularly relates to a passive metamaterial radiator with wide-angle high emissivity, which comprises a plurality of periodically arrayed basic units, wherein the basic unit comprises, from top to bottom, a top dielectric layer, a first ITO layer, a middle dielectric layer, a second ITO layer, a bottom dielectric layer and a third ITO layer; the first ITO layer comprises a circular patch and at least two slotted rings with the same center as the circular patch and located at the periphery of the circular patch; the second ITO layer comprises a rectangular patch and at least two symmetrically arranged branch patches arranged on the rectangular patch; the passive metamaterial radiator maintains high emissivity characteristics in a wide-band and wide-angle range, thereby effectively reducing the radiation visibility of a target at different detection angles.

Description

Technical Field

[0001] This invention belongs to the field of metamaterials technology, specifically relating to a passive metamaterial radiator with wide-angle high emissivity. Background Technology

[0002] With the rapid development of passive microwave remote sensing technology, airborne microwave radiometers have been widely used in military reconnaissance and target identification. For ground-based metallic targets, their inherent high reflectivity results in a brightness temperature far lower than the surrounding background, creating a significant brightness temperature contrast during microwave radiometer detection. Therefore, effectively controlling the microwave radiation characteristics of ground-based metallic targets to reduce the brightness temperature difference between the target and the background has become an important research direction in the fields of electromagnetic stealth and radiation camouflage.

[0003] Metamaterials are a class of artificial composite materials that achieve unique electromagnetic response characteristics through subwavelength unit structures. Their electromagnetic properties can be precisely designed and controlled through structural geometric parameters, arrangement, and dielectric materials, thereby enabling the regulation of the absorption, transmission, or reflection characteristics of incident electromagnetic waves within a specific frequency range.

[0004] With the continuous advancement of metamaterials technology, passive metamaterial radiators have attracted attention in the field of microwave radiation modulation due to their ability to modulate the microwave thermal radiation of targets without external energy drive. Passive microwave radiation refers to the natural thermal radiation process of an object in thermal equilibrium, determined by its own temperature and electromagnetic properties, and its radiation power is closely related to the emissivity of the object. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a passive metamaterial radiator with high emissivity over a wide angle. The passive metamaterial radiator maintains high emissivity characteristics over a wide bandwidth and wide angle range, thereby effectively reducing the radiation visibility of the target at different detection angles.

[0006] This invention provides a passive metamaterial radiator with a wide-angle high emissivity, comprising multiple periodically arrayed basic units, wherein the basic units include a top dielectric layer, a first ITO layer, an intermediate dielectric layer, a second ITO layer, a bottom dielectric layer, and a third ITO layer distributed from top to bottom;

[0007] The first ITO layer includes a circular patch and at least two slotted rings located around the circular patch and arranged with the same center as the circular patch.

[0008] The second ITO layer includes a rectangular patch and at least two symmetrically arranged branch patches disposed on the rectangular patch.

[0009] The dielectric layer can be made of PMMA or other common materials that can be used as dielectric layers.

[0010] Preferably, the first ITO layer, the second ITO layer, and the third ITO layer are all attached to the substrate. The substrate can be a PET substrate or any other suitable substrate material. The orientation of the substrate and the ITO layers can be such that the substrate is above the ITO layers or below the ITO layers. For example, the first and second ITO layers are above the substrate, and the third ITO layer is below the substrate.

[0011] Multiple slotted rings and circular patches are set at the same center, meaning that the centers of multiple slotted rings and circular patches are the same, so the whole is symmetrical.

[0012] At least two symmetrically arranged branch patches mean that multiple branch patches are symmetrical about the center point of the rectangular patch. Therefore, the number of branch patches is an even number, i.e., 2, 4, or 6, preferably 4, and they are all set at the midpoint of the side of the rectangular patch.

[0013] Preferably, the number of slotted rings is two.

[0014] Preferably, the thickness of the slotted ring (i.e., the difference between the outer diameter and the inner diameter of the ring; the inner diameter in this application refers to half of the hollow part inside the ring, i.e., the radius of the circle of the hollow part; the outer diameter in this application refers to the radius of the circle of the outer edge of the ring) is 50-80% of the radius of the circular patch; the distance between the slotted ring and the circular patch (referring to the radial distance between the inner circle of the slotted ring and the outer edge of the circular patch) is 30-40% of the radius of the circular patch; and the distance between the slotted rings (referring to the radial distance between the outer edge of one slotted ring and the inner edge of the adjacent slotted ring on the periphery) is 30-40% of the radius of the circular patch.

[0015] Preferably, the slotted ring has at least two slots symmetrically arranged around the center of the circular patch. These slots are gaps.

[0016] Preferably, the number of grooves is 4, and the width of the groove is 50-120% of the thickness of the slotted ring.

[0017] Preferably, the slotted ring includes an inner slotted ring and an outer slotted ring. The inner slotted ring has four inner slots, and the outer slotted ring has four outer slots. The inner and outer slots are located on the radial axis of the circular patch. The radial axis is the line connecting any point on the circular patch to the center of the circle.

[0018] Preferably, the width of the inner groove is smaller than the width of the outer groove.

[0019] Preferably, the side length of the rectangular patch is 70-80% of the side length of the base unit, and the branch patch is rectangular and is disposed at the center of the side of the rectangular patch. The long side of the branch patch is perpendicular to the rectangular patch, and the length of the long side of the branch patch is 10-15% of the side length of the rectangular patch. Preferably, the length of the long side of the branch patch is twice the length of the short side.

[0020] Preferably, the first ITO layer has a sheet resistance of 150 Ω / sq, the second ITO layer has a sheet resistance of 80 Ω / sq, and the third ITO layer has a sheet resistance of 6 Ω / sq.

[0021] The beneficial effect of this invention is that it can achieve high emissivity characteristics over a wide bandwidth and wide angle range. Simulation results show that when TE and TM polarized electromagnetic waves are incident perpendicularly, this invention can achieve a high emissivity of over 90% in the 4.54-26.11 GHz range, with a relative bandwidth of up to 140.75%. For TE polarization, this invention achieves a high emissivity of 80% in the incident angle range of 0° to 60°; for TM polarization, it achieves a high emissivity of 80% in the incident angle range of 0° to 70°. When electromagnetic waves with different polarization angles are incident, this invention can achieve results consistent with those of TE and TM polarized electromagnetic waves when incident perpendicularly in the polarization angle range of 0° to 90°, indicating that this invention has polarization insensitivity characteristics.

[0022] The passive metamaterial radiator with wide-angle high emissivity designed in this invention possesses characteristics of broadband high emissivity, wide-angle high emissivity, polarization insensitivity, and optical transparency, while also offering advantages such as low profile, lightweight, ease of fabrication, and low cost. This invention can effectively control the emissivity of ground-based metallic targets, significantly reducing the brightness temperature difference between the target and the background, and is suitable for scenarios such as radiation stealth and passive radiation camouflage. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the passive metamaterial radiator of the present invention.

[0024] Figure 2 This is a side view of the overall structure of the passive metamaterial radiator of the present invention.

[0025] Figure 3 This is a structural diagram of the first ITO layer of the passive metamaterial radiator patterned according to the present invention.

[0026] Figure 4 This is a structural diagram of the second ITO layer of the passive metamaterial radiator patterned according to the present invention.

[0027] Figure 5 This is a structural diagram of the unpatterned third ITO layer of the passive metamaterial radiator of the present invention.

[0028] Figure 6 This is the emissivity curve of the passive metamaterial radiator of the present invention when TE and TM polarized electromagnetic waves are incident perpendicularly.

[0029] Figure 7 This is the emissivity curve of the passive metamaterial radiator of the present invention under oblique incidence of TE-polarized electromagnetic waves.

[0030] Figure 8 This is the emissivity curve of the passive metamaterial radiator of the present invention under oblique incidence of TM polarized electromagnetic waves.

[0031] Figure 9 The present invention presents the emissivity curves of the passive metamaterial radiator under electromagnetic wave incident at different polarization angles.

[0032] Figure 10 The passive metamaterial radiator of this invention replaces the patterned first ITO layer structure with a circular patch (i.e., Comparative Example 1), and shows the emissivity curves when electromagnetic waves are obliquely incident, where Figure (a) shows TE polarization and Figure (b) shows TM polarization.

[0033] Figure 11 The passive metamaterial radiator of this invention replaces the patterned first ITO layer structure with a circular patch plus four L-shaped right angles (i.e., Comparative Example 2), and shows the emissivity curves when electromagnetic waves are obliquely incident. Figure (a) shows TE polarization, and Figure (b) shows TM polarization.

[0034] Figure 12 The passive metamaterial radiator of this invention replaces the patterned first ITO layer structure with a circular patch plus a slotted circle (i.e., Comparative Example 3), and shows the emissivity curves when electromagnetic waves are obliquely incident, where Figure (a) shows TE polarization and Figure (b) shows TM polarization.

[0035] Figure 13 The passive metamaterial radiator of this invention replaces the patterned second ITO layer structure with a square patch (i.e., Comparative Example 4), and shows the emissivity curves when electromagnetic waves are obliquely incident, where Figure (a) shows TE polarization and Figure (b) shows TM polarization.

[0036] In the figure, 1 is the top dielectric layer, 2 is the first ITO layer, 3 is the middle dielectric layer, 4 is the second ITO layer, 5 is the bottom dielectric layer, 6 is the third ITO layer, 7 is the substrate, 21 is the circular patch, 22 is the inner slotted ring, 221 is the inner slot, 23 is the outer slotted ring, 231 is the outer slot, 41 is the rectangular patch, and 42 is the branch patch. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the present invention.

[0039] Example 1

[0040] like Figure 1 , 2 As shown, a passive metamaterial radiator with wide-angle high emissivity comprises multiple periodically arrayed basic units, each basic unit being square with a side length of [missing information]. p It is 10mm.

[0041] The basic unit includes, from top to bottom, a top dielectric layer 1, a first ITO layer 2, a middle dielectric layer 3, a second ITO layer 4, a bottom dielectric layer 5, and a third ITO layer 6.

[0042] The top dielectric layer 1, the middle dielectric layer 3, and the bottom dielectric layer 5 have a relative permittivity of 2.25, a loss tangent of 0.001, and a thickness of [missing information]. h It is made of 3mm PMMA material.

[0043] The first ITO layer 2 has a pattern and uses an ITO conductive film with a sheet resistance of 150Ω / sq. The second ITO layer 4 has a pattern and uses an ITO conductive film with a sheet resistance of 80Ω / sq. The third ITO layer 6 does not have a pattern and is a whole layer of ITO material, using an ITO conductive film with a sheet resistance of 6Ω / sq.

[0044] The first ITO layer 2, the second ITO layer 4, and the third ITO layer 6 are all disposed on the substrate 7, so as to Figure 1-2 The orientation relationship is such that the first ITO layer 2 and the second ITO layer 4 are located above the substrate 7, and the third ITO layer 6 is located below the substrate 7. That is, the basic unit includes, from top to bottom, the top dielectric layer 1, the first ITO layer 2, the substrate 7, the middle dielectric layer 3, the second ITO layer 4, the substrate 7, the bottom dielectric layer 5, the substrate 7, and the third ITO layer 6.

[0045] The substrate 7 is a PET substrate with a relative permittivity of 3.2, a loss tangent of 0.003, and a thickness of [missing information]. t It is 0.125mm.

[0046] like Figure 3 As shown, the first ITO layer 2 includes a circular patch 21 and two slotted annexes located around the circular patch 21 and concentrically positioned around it. The slotted annexes include an inner slotted annexes 22 and an outer slotted annexes 23. The inner slotted annexes 22 have four inner slots 221, and the outer slotted annexes 23 have four outer slots 231. The inner and outer slots 221 are located on the radial axis of the circular patch 21. The four inner slots 221 and the four outer slots 231 are equidistantly positioned, i.e., positioned directly above, below, to the left, and to the right of the slotted annexes. Therefore, it exhibits both central symmetry and rotational symmetry.

[0047] The radius r1 of the circular patch 21 is 1.5mm.

[0048] The inner diameter r2 of the slotted ring 22 is 2mm, the outer diameter r3 is 3mm, and the length of the slot is... 1 (its thickness is the same as that of the inner slotted ring 22) is 1mm, and its width is... w 1 is 0.6mm.

[0049] The inner diameter r4 of the externally slotted ring 23 is 3.5mm, the outer diameter r5 is 4.5mm, and the length of the slot is... 2 is 1mm, width w 2 represents 1 mm.

[0050] like Figure 4 As shown, the second ITO layer 4 includes a rectangular patch 41 and four symmetrically arranged branch patches 42 disposed on the rectangular patch 41. The rectangular patch 41 is a square with a side length of [missing information]. 3 is 7.88mm. The branch patch 42 is rectangular, and its length is perpendicular to the rectangular patch 41. The length of the branch patch 42... 4 is 1mm, width w 3 is 0.5mm.

[0051] like Figure 5 As shown, the third ITO layer 6 is completely located below the substrate 7, and its size is the same as that of the substrate 7.

[0052] Example 2

[0053] use Figure 1 The emissivity of the basic unit structure of the passive metamaterial radiator shown is obtained from simulations using the commercial electromagnetic simulation software CSTStudio Suite, ranging from 1 to 30 GHz. The horizontal axis represents frequency, and the vertical axis represents emissivity. Figure 6 As shown. By Figure 6It can be seen that the proposed passive metamaterial radiator can achieve a broadband high emissivity characteristic of 90% in the range of 4.54–26.11 GHz under the incidence of TE and TM polarized waves. Due to the symmetry of the proposed structure, the emissivity results for vertically incident TE and TM polarized waves are consistent.

[0054] The emissivity performance of Embodiment 1 of the present invention was measured under TE polarization at different oblique incidence angles, such as... Figure 7 As shown. By Figure 7 It can be seen that as the incident angle increases, the emissivity gradually decreases, while the emissivity bandwidth widens towards higher frequencies. In particular, when the electromagnetic wave is incident at a wide angle of 60°, the proposed passive metamaterial radiator can still achieve a high emissivity of over 80%. Therefore, this invention can achieve high emissivity performance with a wide bandwidth and wide angle up to 60° under TE polarization.

[0055] The emissivity performance of Embodiment 1 of the present invention was measured under TM polarization at different oblique incidence angles, such as... Figure 8 As shown. By Figure 8 It can be seen that as the incident angle increases, the amplitude of emissivity remains basically unchanged, but the emissivity bandwidth gradually shifts towards higher frequencies, while the relative bandwidth remains basically unchanged. In particular, when the electromagnetic wave is incident at a wide angle of 70°, the proposed passive metamaterial radiator can still achieve a high emissivity of more than 80%. Therefore, this invention can achieve high emissivity performance with a wide bandwidth and wide angle of up to 70° under TM polarization.

[0056] The emissivity performance of Embodiment 1 of the present invention under different polarization angles was measured, such as... Figure 9 As shown. By Figure 9 As can be seen, with the increase of the incident polarization angle, the present invention can maintain emissivity performance that is essentially identical to that when the electromagnetic wave is incident perpendicularly. This result is attributed to the symmetrical structure of the proposed passive metamaterial radiator, which exhibits consistent results for arbitrary polarization wave incidence. Therefore, the present invention possesses polarization insensitivity characteristics.

[0057] Comparative Example 1

[0058] Based on Embodiment 1 above, the patterned first ITO layer 2 was replaced with a circular patch with a radius of 1.5 mm, i.e., the slotted ring was removed. Its emissivity characteristics were analyzed under TE and TM polarization, respectively.

[0059] like Figure 10 As shown in (a), for TE polarization, when electromagnetic waves are incident at an angle of 0° to 60°, its emissivity can achieve a high emissivity of 80% in the range of 0° to 30°. However, its emissivity gradually decreases in the high-frequency band.

[0060] like Figure 10 As shown in (b), for TM polarization, when electromagnetic waves are incident obliquely at angles from 0° to 70°, its emissivity can achieve a high emissivity of 80% within the range of 0° to 70°. However, its emissivity in the high-frequency band also shows a gradual decreasing trend.

[0061] Therefore, it can be concluded that the contrast structure (i.e., the circular patch) exhibits polarization mismatch for wide-angle incident waves with TE polarization, resulting in a gradual decrease in emissivity at high frequencies and thus unstable radiation characteristics at high frequencies. For TM polarization, although it can achieve a high emissivity of 80% in the 0° to 70° range, it also shows a gradual decrease in emissivity at high frequencies, limiting its stability over a wide bandwidth.

[0062] Comparative Example 2

[0063] Based on the above embodiment 1, the patterned first ITO layer 2 was replaced with a circular patch with a radius of 1 mm and four L-shaped right angles with a length of 1.5 mm and a width of 0.5 mm were added (the L-shaped right angle includes two vertical straight line segments of equal length, and the length of the outer edge of the straight line segment is 1.5 mm). Its emissivity characteristics were analyzed under TE and TM polarization respectively.

[0064] like Figure 11 As shown in (a), for TE polarization, when electromagnetic waves are incident at an angle of 0° to 60°, its emissivity can achieve a high emissivity of 80% in the range of 0° to 40°. However, the overall emissivity of this structure is low, especially in the high-frequency band where the emissivity shows a significant decreasing trend.

[0065] like Figure 11 As shown in (b), for TM polarization, when electromagnetic waves are incident at an angle of 0° to 70°, a high emissivity of 80% can be achieved in the range of 0° to 70°. However, the emissivity is lower in the range of 0° to 40° of incident angle, and the relative bandwidth gradually decreases with the increase of the incident angle.

[0066] Therefore, it can be concluded that although this comparative structure (i.e., a circular patch with an L-shaped right angle) can achieve high emissivity within a certain incident angle range under both TE and TM polarization, this structure suffers from emissivity instability across the entire frequency band. For TE polarization, especially in the high-frequency range, the emissivity drops significantly, limiting its radiation performance over a wide bandwidth. Under TM polarization, although it can maintain a high emissivity of 80% in the range of 0° to 70°, its relative bandwidth gradually narrows with increasing incident angle, and its emissivity is lower in the low-frequency range.

[0067] Comparative Example 3

[0068] Based on Embodiment 1 above, the patterned first ITO layer 2 was replaced with a circular patch with a radius of 1 mm, and an outer ring with an inner diameter of 2.5 mm and an outer diameter of 3 mm was added. Four rectangular slots with a length of 0.5 mm and a width of 0.6 mm were made on the ring. Its emissivity characteristics were analyzed under TE and TM polarization respectively.

[0069] like Figure 12 As shown in (a), for TE polarization, when electromagnetic waves are incident obliquely at 0° to 60°, its emissivity can achieve a high emissivity of 80% in the range of 0° to 40°, but the overall emissivity level is low and there is a significant decrease in the high frequency band.

[0070] like Figure 12 As shown in (b), for TM polarization, when electromagnetic waves are incident obliquely at angles from 0° to 70°, its emissivity can achieve a high emissivity of 80% within the range of 0° to 70°. However, there are emissivity troughs in both the low-frequency and high-frequency regions, and a relatively high emissivity is only achieved in the mid-frequency band, which limits its broadband stable transmission characteristics.

[0071] Therefore, it can be concluded that this comparative structure can only achieve high emissivity within a relatively small incident angle range under TE polarization, and there is a problem of performance degradation in the high-frequency range. Under TM polarization, although the structure has a large angular response range, its emissivity in the low-frequency and high-frequency regions is insufficient, resulting in limited overall broadband transmission performance.

[0072] Comparative Example 4

[0073] Based on the above embodiment 1, the patterned second ITO layer 4 was replaced with a square patch with a side length of 7mm, and its emissivity characteristics were analyzed under TE and TM polarization respectively.

[0074] like Figure 13 As shown in (a), for TE polarization, when electromagnetic waves are incident at an angle of 0° to 60°, its emissivity can achieve a high emissivity of 80% in the range of 0° to 40°. However, its emissivity has a trough in the low-frequency band, making it difficult to achieve stable broadband emissivity characteristics.

[0075] like Figure 13 As shown in (b), for TM polarization, when electromagnetic waves are incident at an angle of 0° to 70°, its emissivity can achieve a high emissivity of 80% in the range of 0° to 60°. However, its emissivity is low in the low-frequency band and there is an emissivity trough in the 15-20 GHz range, which limits its broadband high emissivity characteristics.

[0076] Therefore, it can be concluded that this contrast structure (i.e., the square patch) can only achieve a high emissivity of 40° in TE polarization, and it suffers from low emissivity troughs at low frequencies and unstable emissivity at high frequencies. For TM polarization, although it can achieve a high emissivity of 80% in the range of 0° to 60°, the emissivity is lower in the low-frequency band, which limits its high emissivity characteristics in this frequency band.

[0077] In summary, the passive metamaterial radiator designed in this invention exhibits excellent high emissivity characteristics under different polarization conditions, and can achieve stable high emissivity over a wide frequency and incident angle range. Specifically, under TE polarized wave incidence, this invention can achieve 80% high emissivity over a wide angle range of 0° to 60°, and maintain good radiation characteristics even at incident angles up to 60°; under TM polarized wave incidence, this invention can achieve 80% broadband high emissivity over a wide angle range of 0° to 70°. Furthermore, this invention exhibits good polarization angle stability for different polarization waves, indicating that the designed structure has polarization insensitivity. These characteristics make this invention suitable for scenarios such as broadband and wide-angle high emissivity target radiation stealth and passive radiation camouflage.

[0078] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0079] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A passive metamaterial radiator with wide-angle high emissivity, characterized in that, The base unit comprises a top medium layer (1), a first ITO layer (2), a middle medium layer (3), a second ITO layer (4), a bottom medium layer (5) and a third ITO layer (6) arranged in sequence from top to bottom. The first ITO layer (2) comprises a circular patch (21) and two slotted rings (22, 23) arranged with the same center as the circular patch (21). The two slotted rings comprise an inner slotted ring (22) and an outer slotted ring (23), the inner slotted ring (22) is provided with four inner slots (221), and the outer slotted ring (23) is provided with four outer slots (231), the inner slots (221) and the outer slots (231) are located on the radial axis of the circular patch (21); the four inner slots (221) are equidistantly arranged, and the four outer slots (231) are equidistantly arranged. The second ITO layer (4) comprises a rectangular patch (41) and at least two branch patches (42) arranged symmetrically on the rectangular patch (41); the first ITO layer (2), the second ITO layer (4) and the third ITO layer (6) are attached to the substrate (7). The third ITO layer (6) is completely located below the substrate (7), and the size of the third ITO layer (6) is consistent with the size of the substrate (7).

2. The passive metamaterial radiator of claim 1, wherein, The thickness of the inner slotted ring (22) and the outer slotted ring (23) is 50-80% of the radius of the circular patch (21), the distance between the inner slotted ring (22) and the circular patch (21) is 30-40% of the radius of the circular patch (21), the thickness of the slotted ring is the difference between the inner diameter and the outer diameter of the ring, and the distance between the slotted rings is 30-40% of the radius of the circular patch (21).

3. The passive metamaterial radiator of claim 1, wherein, The width of the inner slot (221) is 50-120% of the thickness of the inner slotted ring (22), and the width of the outer slot (231) is 50-120% of the thickness of the outer slotted ring (23); the thickness of the slotted ring is the difference between the inner diameter and the outer diameter of the ring.

4. The passive metamaterial radiator of claim 1, wherein, The width of the inner slot (221) is less than the width of the outer slot (231).

5. The passive metamaterial radiator of claim 1, wherein, The length of the long side of the branch patch (42) is 10-15% of the length of the side of the rectangular patch (41).

6. The passive metamaterial radiator of claim 1, wherein, The sheet resistance of the first ITO layer (2) is 150Ω / sq, the sheet resistance of the second ITO layer (4) is 80Ω / sq, and the sheet resistance of the third ITO layer (6) is 6Ω / sq.

Images