Method for manufacturing frequency-selective surface based on femtosecond laser-induced graphene

Abstract

The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene belongs to the field of frequency-selective surface manufacturing technology, and includes: (1) a graphene patterning step: using a femtosecond laser to induce the formation of a graphene periodic micro-nanostructure on the surface of a flexible substrate; (2) a frequency-selective unit structure design step: by stacking graphene resonance units of different geometric shapes in layers, a nested resonance structure is obtained to achieve selective transmission or reflection of multi-band electromagnetic waves; the graphene resonance unit is the graphene periodic micro-nanostructure; (3) a large-area manufacturing step: using femtosecond laser dynamic scanning and energy control technology to achieve an area greater than 10 cm 2 Frequency-selective surface processing. The present invention achieves large-area, multi-band frequency-selective characteristics by inducing local structural modification of graphene through femtosecond laser and combining it with metasurface design.

Description

Technical Field

[0001] The present invention belongs to the technical field of frequency selective surface manufacturing, and in particular relates to a method for manufacturing a frequency selective surface based on femtosecond laser induced graphene. Background Art

[0002] Frequency-selective surfaces (FSS) are artificial structures that can selectively control electromagnetic waves (e.g., reflect or transmit specific frequency bands). They are widely used in radar stealth, communication antennas, electromagnetic shielding, and other fields. With the growing demand for multi-band, reconfigurable, and lightweight modern electronic systems, the development of efficient, low-cost, and multi-band FSS manufacturing technologies has become a research hotspot.

[0003] Traditional FSS fabrication methods (such as photolithography, electron beam etching, and nanoimprinting) have significant limitations. They require multiple steps (resin coating, masking, etching, etc.), resulting in high costs and long production cycles. Furthermore, they rely on metal or semiconductor materials, making flexible or transparent devices difficult to achieve. Multi-band FSS require multi-layer stacking or complex unit designs, making it difficult to ensure precision and consistency using traditional processes. Chemical etching is also involved in the fabrication process, which can cause contamination.

[0004] Graphene is an ideal alternative material due to its high conductivity, mechanical flexibility, and tunability. However, traditional preparation methods (such as chemical vapor deposition (CVD)) require high temperature and high pressure environments and are prone to damage when transferred to flexible substrates. Femtosecond laser-induced graphene (FLIG) technology uses ultrafast lasers to directly carbonize a polymer surface to create a porous graphene structure, offering the following advantages:

[0005] No mask required: Directly program the laser path, enabling fast writing of complex patterns.

[0006] Environmentally friendly: carried out at room temperature and pressure, compatible with flexible substrates (such as polyimide).

[0007] High precision and controllability: extremely short pulses of femtosecond lasers ( seconds) to reduce thermal damage and regulate the conductivity of graphene.

[0008] However, the existing FLIG technology still faces the following challenges when applied to FSS:

[0009] Multi-band design: Requires complex micro-nanostructures, which are difficult to achieve efficiently with traditional laser processing.

[0010] Large-area uniformity: Laser scanning strategy and parameter control affect structural consistency.

[0011] Performance optimization: The coupling mechanism between graphene conductivity, pattern geometry and electromagnetic response needs to be further studied.

[0012] Currently, there are the following solutions for manufacturing large-area multi-band frequency-selective surfaces:

[0013] (1) Laser-induced graphene (LIG) for FSS: Graphene is generated on the surface of polyimide using a CO2 laser or nanosecond laser to form a conductive pattern. For example, a study prepared single-frequency FSS by adjusting the laser power and scanning speed. However, due to the limitations of the laser type, the processing accuracy is low, and multiple bands require multiple patterning, making it difficult to cover multiple bands.

[0014] (2) Multi-layer stacked metal FSS: Metal layers of different frequency bands are prepared by photolithography, and then stacked layer by layer to achieve multi-band response. For example, a patent uses three layers of metal patches corresponding to the Ku, K, and Ka bands respectively.

[0015] (3) Tunable FSS based on variable materials: Liquid crystals, phase change materials, or voltage are used to control the graphene Fermi level to achieve dynamic adjustment of the FSS frequency. For example, one solution integrates a driving circuit on the graphene pattern and changes the resonant frequency through bias voltage.

[0016] However, the above method still has the following defects:

[0017] (1) Laser-induced graphene (LIG) for FSS: The nanosecond laser has a significant thermal effect and insufficient edge accuracy; the multi-frequency design depends on the complexity of the unit structure, making it difficult to process uniformly over a large area.

[0018] (2) Multi-layer stacked metal FSS: The process is complex, and the inter-layer alignment error affects the performance; the metal structure cannot be dynamically tuned, and the weight and thickness increase.

[0019] (3) Tunable FSS is based on variable materials: it relies on external control systems and has a complex structure; it is difficult to ensure uniformity over a large area, and it is difficult to control multiple independent frequency bands. Summary of the Invention

[0020] The present invention provides a method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene, which is used to overcome the defects in the prior art.

[0021] In order to solve the above technical problems, the present invention provides the following technical solution: a method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene, comprising:

[0022] (1) Graphene patterning step: using femtosecond laser to induce the formation of graphene periodic micro-nanostructures on the surface of a flexible substrate;

[0023] (2) Frequency-selective unit structure design steps: By stacking graphene resonant units of different geometric shapes in layers, a nested resonant structure is obtained to achieve selective transmission or reflection of multi-band electromagnetic waves; the graphene resonant unit is the graphene periodic micro-nano structure;

[0024] (3) Large-area manufacturing steps: Using femtosecond laser dynamic scanning and energy control technology to achieve an area larger than 10cm 2 Frequency selective surface processing.

[0025] Furthermore, the graphene periodic micro-nanostructure is a grid pattern, and the grid units are square, cross, double circular rings or fractal branches.

[0026] Furthermore, the square resonance unit is used to reflect low-frequency electromagnetic waves, the cross resonance unit is used to transmit medium-frequency electromagnetic waves, the double circular ring resonance unit is used to reflect high-frequency electromagnetic waves of different frequencies, and the fractal branch resonance unit is used to transmit millimeter-wave electromagnetic waves.

[0027] Furthermore, the nested resonant structure adopts a layered design, and each layer adopts a structure of a dielectric substrate and a metal layer. The dielectric substrate is the flexible substrate, and the metal layer refers to the graphene periodic micro-nano structure.

[0028] Furthermore, the FSS unit structure obtained in step (3) includes a multilayer structure from bottom to top: 1) a flexible substrate; 2) a graphene resonant unit layer, which is composed of a graphene periodic micro-nanostructure generated by laser induction; 3) a dielectric layer, which is composed of a zinc oxide nanowire array covered on the flexible substrate on which the graphene periodic micro-nanostructure has been formed; and 4) a protective layer.

[0029] Furthermore, before graphene patterning, the flexible substrate needs to be pretreated, ultrasonically cleaned with ethanol and acetone, and then carbonized to generate graphene periodic micro-nanostructures using a femtosecond laser galvanometer processing platform through femtosecond laser direct writing.

[0030] Furthermore, when laser direct writing is performed on the femtosecond laser galvanometer processing platform, multi-band electromagnetic response is performed, including conductivity control and geometric parameter control.

[0031] Further, the conductivity control process: 1) set the laser power gradient to perform local annealing or etching on the graphene surface; 2) quantitatively characterize the defect density by Raman spectroscopy; 3) measure the Hall effect or four-probe method to obtain the conductivity σ and establish σ-P laser Relationship curve; 4) Process FSS unit and test S parameters to verify f r The law of change with σ.

[0032] Further, the geometric parameter control process: 1) Based on the target frequency band, the formula λ=c / f r Calculate the initial size DD, where λ is the wavelength of the resonant wave corresponding to the target frequency band, c is the speed of light in vacuum, and f r1) Optimize the shape and size of the FSS unit using full-wave simulation to ensure conflict-free multi-band resonance; 2) Manufacture FSS units of different sizes using laser direct writing or photolithography; 3) Measure the frequency response curve and iteratively adjust the size DD until the target frequency band is covered.

[0033] The beneficial effects achieved by this invention are: by inducing local structural modification of graphene through femtosecond lasers, combined with metasurface design, frequency-selective properties can be achieved over a large area and in multiple frequency bands (such as microwaves, terahertz, and infrared). This invention has the following advantages:

[0034] ① Multi-band compatibility: A single panel enables independent regulation of multiple frequency bands, reducing the complexity of traditional multi-layer structures.

[0035] ② High-precision processing: Femtosecond laser achieves submicron-level structural etching, avoiding the pollution problems of mechanical or chemical etching.

[0036] ③Flexibility: Graphene-based flexible substrate, suitable for curved surface conformal design (such as smart skin, 5G antenna cover).

[0037] ④Large area and high efficiency: scanning speed>100mm / s, processing area up to 30×30cm².

[0038] ⑤ Environmentally friendly and low-cost: no mask and chemical etching required. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0040] Figure 1 Schematic diagram of a square fractal branch resonance unit as an example of an embodiment of the present invention, in which a femtosecond laser galvanometer processing platform is used to process a large-area array pattern on a flexible substrate.

[0041] Figure 2 Schematic diagram of a square resonant unit as an example of an embodiment of the present invention, in which a femtosecond laser galvanometer processing platform is used to process a large-area array pattern on a flexible substrate.

[0042] Figure 3 is the Raman spectrum described in the Examples.

[0043] Figure 4 is the frequency response curve described in the embodiment. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0045] The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to the present invention comprises the following steps:

[0046] The first step is graphene patterning: using the high-precision processing capability of femtosecond lasers to induce graphene periodic micro-nanostructures on the surface of flexible substrates (such as polyimide);

[0047] The graphene periodic micro-nanostructure is a grid-like pattern, with grid units such as squares, crosses, double circular rings, and fractal branches. These periodic graphene micro-nanostructures form resonant units. By designing their geometry, size, and period, they can generate a resonant response (reflection or transmission) to electromagnetic waves of a specific frequency, thereby achieving frequency selection.

[0048] The geometric parameters and corresponding frequency bands of the graphene resonance unit are shown in Table 1 below, and the unit period of the graphene resonance unit is 10-11 mm and the line width is 0.05-0.1 mm.

[0049] Table 1 Geometric parameters of graphene resonant unit and corresponding frequency bands

[0050]

[0051] The second step is the structural design of the frequency-selective unit: by layering and stacking graphene resonance units of different geometric shapes, a nested resonance structure is obtained to achieve selective transmission or reflection of multi-band electromagnetic waves.

[0052] The nested resonant structure adopts a layered design, with each layer using a dielectric substrate + metal layer structure. The dielectric substrate is the flexible substrate described above, and the metal layer refers to the graphene periodic micro-nanostructure described above. The "metal layer" is a functional description of the graphene periodic micro-nanostructure. The distance between two adjacent dielectric substrates is d = 0.5 mm, which is achieved by a support structure or air layer. The layers from bottom to top are:

[0053] Layer 1 (bottom layer): dielectric substrate + square ring metal layer (reflects low frequency 2.4 GHz);

[0054] Layer 2: dielectric substrate + cross-patch metal layer (transmission intermediate frequency 5.8 GHz);

[0055] Layer 3: dielectric substrate + double circular ring metal layer (reflects high frequencies 10 GHz and 18 GHz);

[0056] Layer 4 (top layer): dielectric substrate + fractal branch metal layer (transmits millimeter waves 15 GHz).

[0057] The third step is large-area manufacturing: using dynamic scanning and energy control technology of femtosecond laser to ensure the consistency and efficiency of large-area (greater than 10cm²) processing.

[0058] Through the above-mentioned preparation process, the FSS unit structure prepared in this embodiment includes a multi-layer structure from bottom to top:

[0059] 1. Substrate: flexible polyimide film, thickness 10-50 μm;

[0060] 2. Graphene resonant unit layer: composed of laser-induced graphene periodic micro-nanostructure;

[0061] 3. Dielectric layer: zinc oxide nanowire array, used to enhance dielectric control;

[0062] 4. Protective layer: Polydimethylsiloxane (PDMS) encapsulation layer, thickness <5μm, plays a protective role, preventing the prepared FSS unit structure from being affected by external environmental factors (such as moisture, mechanical damage, etc.) and maintaining its stable performance.

[0063] The dielectric layer is overlaid on a flexible substrate with a periodic graphene micro-nanostructure, forming a stacked structure. Common methods for depositing dielectric layers on micro-nanostructures include physical deposition (such as electron beam evaporation and magnetron sputtering), chemical deposition (chemical vapor deposition and solution spin coating), and self-assembly. In the self-assembly method, interactions between nanomaterials (such as electrostatic and van der Waals forces) are exploited to allow zinc oxide nanowires to spontaneously assemble and align on the surface of the graphene micro-nanostructure in a solution environment, forming an ordered dielectric layer.

[0064] In the above preparation process, before the first step of graphene patterning, the substrate needs to be pretreated. The PI film is ultrasonically cleaned with ethanol and acetone to remove oil, dust and other impurities on the surface of the PI film, improve the surface cleanliness and adhesion, and then the PI film is carbonized by femtosecond laser direct writing using a femtosecond laser galvanometer processing platform to generate graphene periodic micro-nanostructures.

[0065] The femtosecond laser galvanometer processing platform is a high-precision processing equipment based on ultrafast laser technology and a high-speed galvanometer scanning system. Its core components include:

[0066] 1. Femtosecond laser source, parameters: pulse width < 1ps (typically 100-500fs), wavelength 1030nm or 515nm (frequency-doubled), repetition rate 10kHz-1MHz. Function: Ultrashort pulse width enables "cold working" and reduces the heat-affected zone (HAZ), making it suitable for brittle materials and high-precision micro-nano processing.

[0067] 2. Galvo Scanner System, consisting of: XY-axis high-speed galvanometers, F-theta focusing lens, and dynamic focusing module. Performance: Scanning speed >2 m / s, positioning accuracy ±1 μm, field of view 100 × 100 mm² to 300 × 300 mm².

[0068] 3. Motion control platform, multi-axis linkage: Z-axis lifting platform (accuracy ±0.5μm) + rotation axis (optional) for 3D structure processing. Synchronous control: galvanometer and motion platform coordinated control to achieve large-area splicing and complex surface processing.

[0069] 4. Optical path and cooling system, optical path modules: beam expander, energy attenuator, beam shaper (such as DOE). Cooling system: water cooling / air cooling to ensure stable operation of the laser, with a temperature control accuracy of ±0.1°C.

[0070] 5. Monitoring and feedback system, real-time monitoring: Confocal sensor or CCD camera for processing position calibration and defect detection. Closed-loop control: Adjust laser parameters (power, focus depth) and scanning path through feedback.

[0071] The present invention utilizes a laser galvanometer platform, which enables dynamic focusing, improves aspect ratio processing capability (sidewall steepness of deep holes / grooves increased by >30%), and supports vertical stacking processing of multi-layer FSS structures. It achieves one-time forming of complex three-dimensional structures (such as fractal branches and double-ring nesting) through multi-axis collaboration, reducing splicing errors. During the processing, the laser energy (10~500μJ) and pulse train mode (Burst Mode) are adjusted in real time based on the material reflectivity to improve the processing efficiency of copper / dielectric substrates and avoid excessive ablation of the metal layer or carbonization of the dielectric. Through image recognition technology, processing defects (such as edge burrs and microcracks) are automatically detected to improve the yield rate.

[0072] Specifically in this embodiment, during the laser-induced graphene patterning process, the laser parameters are: wavelength 1030 nm, pulse width 250~300 fs, repetition frequency 500 kHz~1 MHz; dynamic control: power (10~20 W), scanning speed (100~800 mm / s), defocus (±50 μm); scanning path: spiral progressive filling (to avoid heat accumulation); post-processing: printing ZnO nanowires (temperature 400°C, time 1 h); spin coating PDMS encapsulation (rotation speed 3000 rpm, curing temperature 80°C).

[0073] like Figure 1 (a) and (b) show the real-time process of processing large-area (30×30 cm) array patterns using a femtosecond laser galvanometer processing platform. Figure 1 (c) and (d) are the actual pictures of the processed samples, and it can be seen that the processing consistency is very good.

[0074] Figure 2 (a) and (b) are the actual pictures of the processed resonance unit. Figure 2 As can be seen from the local enlarged image of (c), the unit structure is highly consistent.

[0075] When performing laser direct writing on a femtosecond laser galvanometer processing platform, multi-band electromagnetic response is required, including conductivity control and geometric parameter control.

[0076] 1. Regarding conductivity control, increasing laser power reduces the graphene defect density, which in turn increases the conductivity, causing the resonant frequency to shift toward higher frequencies. Therefore, by adjusting the femtosecond laser power, the defect density and conductivity of graphene are altered, ultimately controlling the resonant frequency of the frequency selective surface (FSS).

[0077] The principle of conductivity regulation is:

[0078] (1) Relationship between laser power and defects: When the laser power is high (e.g. >5 W), the thermal effect of the femtosecond laser is sufficient to trigger local annealing of graphene, repair lattice defects (e.g. vacancies, edge disorder), and reduce the defect density; when the laser power is low (e.g. <2 W), the laser energy is insufficient to repair defects and may increase defects by ablation or oxidation (e.g. forming carboxyl or epoxy groups).

[0079] According to the Drude model, graphene conductivity is related to carrier mobility and carrier concentration: reduced defect density → fewer scattering centers → increased carrier mobility and carrier concentration → increased conductivity. Therefore, it can be seen that when the laser power is high, the conductivity increases, and when the laser power is low, the conductivity decreases.

[0080] (2) Relationship between conductivity and resonant frequency: According to the Drude model, the increase in conductivity reduces the surface impedance of graphene, causing the resonant frequency of FSS to shift toward high frequency (conversely, it shifts toward low frequency).

[0081] Conductivity control process: Step 1: Set the laser power gradient (e.g., 2-10W) to perform local annealing or etching on the graphene surface; Step 2: Quantitatively characterize the defect density by Raman spectroscopy (D peak to G peak intensity ratio ID / IG); Step 3: Measure the conductivity σ by Hall effect or four-probe method. The relationship between scan rate, laser power, and conductivity is shown in Table 2. Establish the conductivity σ and laser power P laser σ-P laser Relationship curve; Step 4: Process the FSS unit and test the S parameters to verify the target resonant frequency f r The law of change with σ.

[0082] Table 2 Relationship between scan rate, laser power and conductivity

[0083]

[0084] Figure 3 The Raman spectrum is given. In the figure, the core characteristic peaks and their physical meanings are:

[0085] ‌ (1) D peak (~1350 cm -1 )‌,‌ Source‌: Related to carbon ring defects (such as five-membered / seven-membered rings), vacancies, and edge structures, and belongs to the double resonance scattering process (defects are required to break the momentum conservation).

[0086] ‌ (2) G peak (~1580 cm -1 ), Source: sp² carbon atom in-plane stretching vibration (E2g symmetry), a common peak in all graphene.

[0087] ‌ (3) 2D peak (‌G' peak, ~2700 cm -1 )‌,‌ Source‌: Double-phonon resonance scattering peak, graphene characteristic peak.

[0088] 2. Geometric parameter control: The goal is to directly control the resonant wavelength λ by adjusting the structural dimension D of the resonant unit to cover multiple frequency bands. The relationship between resonant wavelength and dimension: By varying D, single-band coverage is achieved (e.g., D1 = 28 mm, D1 = 28 mm → 2.4 GHz, D2 = 7.2 mm, D2 = 7.2 mm → 10 GHz). Composite structure design: Nesting substructures of different sizes (e.g., a square ring + a double circular ring) within the same FSS unit can stimulate multi-frequency resonances (2.4 / 10 / 18 GHz).

[0089] Geometric parameter control process: Step 1: Based on the target frequency band (such as 2~18GHz), calculate the initial size DD of the resonant ring using the formula λ=c / fr, where λ is the resonant wave wavelength corresponding to the target frequency band, c is the speed of light in vacuum, and f is the initial size DD of the resonant ring. r The target resonant frequency is obtained. Step 2: Optimize the shape and size of the FSS unit using full-wave simulation (CST / HFSS) to ensure conflict-free multi-band resonance. Step 3: Fabricate FSS units of different sizes using laser direct writing. Step 4: Measure the frequency response curve and iteratively adjust the size DD until the target frequency band is covered.

[0090] Among them, when the target frequency band is 2~18GHz, the corresponding resonant wavelength range (in air) of this frequency band is λ = c / f， but:

[0091] fmin = 2 GHz, then λ max = c / 2×10 9 ≈150 mm;

[0092] f max = 18 GHz, then λ min = c / 18×10 9 ≈16.67 mm.

[0093] Target resonant frequency ( f r ) and initial size DD: here f r Refers to the center frequency at which the structure is expected to resonate, as determined for the preliminary design. DD refers to the characteristic dimension of the key substructure that has the most direct relationship to the resonant frequency.

[0094] A more practical initial value setting: Considering that the unit period P needs to be much smaller than the wavelength to avoid grating lobes (usually P < λ / 2, for 2.4 GHz, λ / 2 ≈ 62.5 mm), and the simulation optimization space, the initial value of the side length of the outer square ring can be set in the range of 28-32 mm for trial.

[0095] 3. Collaborative optimization strategy: Material-structure joint design: Fine-tune f by controlling conductivity at a fixed frequency band (e.g., 5.8 GHz) r (±5%), and then roughly adjust the geometric parameters to cover adjacent frequency bands.

[0096] The essence of geometric coarse tuning is to achieve a significant resonant frequency shift (typically >10%) by significantly modifying key FSS unit geometry (e.g., ±5% or more), quickly covering adjacent frequency bands near the target frequency band (e.g., 5.8 GHz → 5.0 GHz or 6.5 GHz). During geometric coarse tuning, dimensions that are linearly sensitive to the resonant frequency and easy to manufacture are selected for coarse adjustment. For example, given the geometric parameters in Table 1, the arm length L2 of the cross-patch resonator unit can be coarsely adjusted by ±(8-15)%, resulting in a frequency shift from 5.8 GHz to 5.0 GHz and 6.5 GHz, covering an adjacent frequency band of 5.8 GHz to 5.0 GHz. Alternatively, the side length L1 of the square ring can be coarsely adjusted by ±10%, resulting in a frequency shift from 2.4 GHz to 2.2 GHz and 2.6 GHz, covering an adjacent frequency band of 2.4 GHz to 2.6 GHz.

[0097] Compared with the prior art, the present invention has the following advantages:

[0098] (1) Single-step large-area manufacturing: Through femtosecond laser direct writing, multi-scale graphene structures are generated on flexible substrates at one time without the need for masks or etching, significantly reducing costs.

[0099] (2) Multi-band integrated design: Using laser parameters to control the microscopic morphology of graphene (such as porosity and number of layers), units with different resonant characteristics are designed in the same plane.

[0100] The physical mechanism of controlling the micromorphology of graphene by using laser parameters is shown in Table 3.

[0101] Table 3 Relationship between scan rate, laser power and conductivity

[0102]

[0103] In the table above, 1) When the laser power is low (≤2 W): the photon energy is insufficient to completely destroy the carbon-carbon bond, and the surface adsorbates are only removed by local thermal effects or slightly oxidized, resulting in low porosity.

[0104] 2) When the laser is of medium power (2-5 W): the energy exceeds the graphene destruction threshold, and the upper layer of multilayer graphene is selectively removed by ablation, forming controllable holes.

[0105] 3) When the laser power is high (>5W): Excessive energy density causes carbon atoms to vaporize (sublimation temperature ~4500℃), triggering severe ablation and forming a disordered porous structure.

[0106] (3) Dynamically adjustable potential: The electrical conductivity of graphene can be flexibly adjusted through laser processing parameters or subsequent doping, laying the foundation for the realization of adjustable FSS in the future.

[0107] It should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. The terms used in the description of this application are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to this application.

Claims

1. A frequency-selective surface fabrication method based on femtosecond laser-induced graphene, characterized in that: include: (1) Graphene patterning step: using femtosecond laser to induce the formation of graphene periodic micro-nanostructures on the surface of a flexible substrate; The graphene periodic micro-nanostructure is a grid pattern, and the grid units are square, cross, double circular ring and fractal branches; (2) Frequency-selective unit structure design steps: By stacking graphene resonant units of different geometric shapes in layers, a multi-band stacked resonant structure is obtained to achieve selective transmission or reflection of multi-band electromagnetic waves; The graphene resonant unit is the graphene periodic micro-nano structure; the multi-band stacked resonant structure adopts a layered design, and each layer adopts a structure of a dielectric substrate and a metal layer, the dielectric substrate is the flexible substrate, and the metal layer refers to the graphene periodic micro-nano structure; The square resonant unit on the first layer is used to reflect low-frequency electromagnetic waves, the cross-shaped resonant unit on the second layer is used to transmit medium-frequency electromagnetic waves, the double circular ring resonant unit on the third layer is used to reflect high-frequency electromagnetic waves of different frequencies, and the fractal branch resonant unit on the fourth layer is used to transmit millimeter-wave electromagnetic waves. (3) Large-area manufacturing steps: Using femtosecond laser dynamic scanning and energy control technology to achieve an area larger than 10cm 2 Frequency selective surface processing.

2. The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to claim 1, characterized in that: The FSS unit structure obtained in step (3) includes a multilayer structure from bottom to top: 1) a flexible substrate; 2) a graphene resonant unit layer, which is composed of a graphene periodic micro-nanostructure generated by laser induction; 3) a dielectric layer, which is composed of a zinc oxide nanowire array covered on the flexible substrate on which the graphene periodic micro-nanostructure has been formed; and 4) a protective layer.

3. The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to claim 1, wherein: Before graphene patterning, the flexible substrate needs to be pretreated and ultrasonically cleaned with ethanol and acetone. Then, a femtosecond laser galvanometer processing platform is used to carbonize the flexible substrate through femtosecond laser direct writing to generate graphene periodic micro-nanostructures.

4. The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to claim 3, wherein: When performing laser direct writing on the femtosecond laser galvanometer processing platform, multi-band electromagnetic response is performed, including conductivity control and geometric parameter control.

5. The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to claim 4, characterized in that: Conductivity control process: 1) Set the laser power gradient to perform local annealing or etching on the graphene surface; 2) Quantitatively characterize the defect density through Raman spectroscopy; 3) Measure the Hall effect or four-probe method to obtain the conductivity σ ,Establish σ -P laser Relationship curve; 4) Process FSS unit and test S parameters to verify the target resonant frequency f r With conductivity σ The law of change.

6. The method for manufacturing a frequency-selective surface based on femtosecond laser-induced graphene according to claim 4, characterized in that: Geometric parameter control process: 1) Based on the target frequency band, through the formula λ = c / f r Calculate initial size DD ,in λ is the resonant wave wavelength corresponding to the target frequency band, c is the speed of light in vacuum, f r 1) Optimize the shape and size of the FSS unit using full-wave simulation to ensure conflict-free multi-band resonance; 2) Manufacture FSS units of different sizes using laser direct writing or photolithography; 3) Measure the frequency response curve and iteratively adjust the size. DD Until the target frequency band is covered.

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