阅读说明：本技术 Ku波段的高透明柔性动态调频吸波表面结构及其制备方法 (Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure and preparation method thereof ) 是由 陆卫兵 刘震国 耿明扬 陈昊 于 2021-07-14 设计创作，主要内容包括：本发明公开了一种Ku波段的高透明柔性动态调频吸波表面结构及制备方法,属于微波器件技术领域,包括叠合设置的石墨烯电容、方形金属丝网阵列、PDMS介质层和金属丝网底板,所述的石墨烯电容包括上下两层叠合设置的PET衬底,在每层所述的PET衬底的内侧均设有单层周期石墨烯条带阵列,在所述的两层叠合设置的PET衬底之间均匀填充透明离子液。石墨烯的方阻能通过直流电压源对其施加不同的电压进行动态控制,具体功能包括对入射波进行完美吸收且中频吸波频点在Ku波段进行动态调谐,可用于透明隐身、光电太阳能电池等,为石墨烯在微波段的透明柔性应用铺设了道路。(The invention discloses a Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure and a preparation method thereof, belonging to the technical field of microwave devices. The square resistance of the graphene can be dynamically controlled by applying different voltages to the graphene through a direct-current voltage source, the specific functions include perfect absorption of incident waves and dynamic tuning of intermediate-frequency wave-absorbing frequency points in a Ku wave band, the graphene square resistance can be used for transparent stealth, photoelectric solar cells and the like, and a road is laid for transparent flexible application of the graphene in a microwave band.)

The high-transparency flexible dynamic frequency modulation wave-absorbing surface structure with the Ku waveband is characterized by comprising a graphene capacitor, a square metal wire mesh array, a PDMS dielectric layer and a metal wire mesh bottom plate which are sequentially overlapped;

the graphene capacitor comprises a first PET substrate, a first graphene strip array arranged on the first PET substrate, a second graphene strip array arranged on the second PET substrate and transparent ionic liquid filled between the first PET substrate and the second PET substrate in sequence;

the first PET substrate and the second PET substrate are arranged in an overlapped mode, and the first graphene strip array and the second graphene strip array are arranged on the inner surfaces of the first PET substrate and the second PET substrate respectively.

2. The Ku-waveband high-transparency flexible dynamic frequency-modulation wave-absorbing surface structure according to claim 1, wherein the first graphene strip array and the second graphene strip array have the same pattern;

the first graphene strip array and the second graphene strip array respectively comprise graphene strip units which are arranged at equal intervals in a periodic manner; the graphene strip units are rectangular, and the graphene strip units on the first graphene strip array correspond to the graphene strip units on the second graphene strip array one to one.

3. The Ku waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure as claimed in claim 1, wherein acetone glue is coated around the inner surface of the second PET substrate, and the first PET substrate is bonded with the second PET substrate through the acetone glue.

4. The Ku-band high-transparency flexible dynamic frequency-modulation wave-absorbing surface structure according to claim 3, wherein the thickness of the acetone gel is 100 microns.

5. The Ku-band highly transparent flexible dynamic frequency modulation wave-absorbing surface structure according to claim 1, wherein the square wire mesh array comprises periodically arranged wire mesh units, the wire mesh units and the graphene strip units are arranged in a one-to-one correspondence manner, and the center points of the wire mesh units and the graphene strip units are coincident.

6. The preparation method of the Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure according to claim 1, which comprises the following steps:

step 1, modeling a graphene capacitor, a square metal wire mesh array, a PDMS dielectric layer and a metal wire mesh bottom plate by utilizing a matlab and an equivalent circuit theory, and optimizing to obtain the optimal graphene strip unit size, the optimal graphene strip unit interval, the optimal graphene square resistance value and the optimal metal wire mesh unit size through parameter scanning;

step 2, growing graphene by using a copper foil, and transferring the graphene to a first PET substrate and a second PET substrate after the graphene grows;

etching the graphene on the first PET substrate and the graphene on the second PET substrate through laser to obtain a first graphene strip array attached to the first PET substrate and a second graphene strip array attached to the second PET substrate;

step 3, coating acetone glue on the periphery of the surface of the second PET substrate, wherein the acetone glue and the second graphene strip array are positioned on the same surface of the second PET substrate; filling transparent ionic liquid in the region surrounded by the third glue;

step 4, the first PET substrate is attached to and sealed with the second PET substrate through acetone glue, and the first graphene strip array faces the second PET substrate; forming a graphene capacitor;

step 5, respectively attaching a square metal wire mesh array and a metal wire mesh bottom plate to two surfaces of the PDMS medium layer;

and 6, attaching the graphene capacitor to a PDMS dielectric layer attached to the square wire mesh array and the wire mesh base plate, wherein the square wire mesh array is attached to the second PET substrate.

7. The preparation method of the Ku-band high-transparency flexible dynamic frequency modulation wave-absorbing surface structure according to claim 6, wherein in the step 1, modeling is performed on a graphene capacitor, a square wire mesh array, a PDMS dielectric layer and a wire mesh bottom plate by using matlab and an equivalent circuit theory, and when incident electromagnetic waves are vertically incident, the graphene strip array is equivalent to series connection of a resistor, a capacitor and an inductor; the square wire mesh array is equivalent to a capacitor; the PET substrate, the PDMS dielectric layer and the metal mesh bottom plate are characterized by respective standard transmission line models.

8. The preparation method of the Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure is characterized in that the graphene strip units optimized in the step 1 are rectangles with the size of 5.0mm by 5.4mm, the interval of the graphene strip units is 0.4mm, and the size of the wire mesh units is 3.6mm by 5.4 mm.

Technical Field

The invention belongs to the technical field of microwave devices, and relates to a Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure and a preparation method thereof.

Background

The electromagnetic stealth and electromagnetic protection of the optical transparent component in the national defense field have extremely important application scenes and are always one of the research key points and difficulties of a combat platform system. Research data shows that the transparent component contributes a great proportion to the overall RCS of the battle platform. For example, the transparent cockpit is one of three electromagnetic scattering sources of an airplane, and the RCS contribution to the nose direction accounts for 1/4 of the whole airplane. Taking the water surface operation platform which is mainly used for sea, anti-diving, near shore and air defense operation as an example, the electromagnetic stealth and electromagnetic protection are needed, and the electromagnetic stealth and protection also comprises various transparent parts such as a ship cockpit, a porthole, a lamp shade, an equipment window and the like besides various frequency devices. Therefore, electromagnetic stealth and electromagnetic protection of the transparent part on the weapon platform are realized by designing the electromagnetic wave-absorbing structure with the optical transparent characteristic, and the improvement of the survival capability and the operational efficiency of the whole weapon platform has important theoretical significance and engineering application value.

In addition, in order to improve the detection capability, the working frequency of the radar is often changed dynamically, so that weapon platforms such as future fighters and ships need to have corresponding changing means to adapt to the changing means, so as to better meet the requirement of electromagnetic countermeasure and increase the battlefield viability. For the transparent component, the wave-absorbing amplitude and the working frequency band of the transparent electromagnetic wave-absorbing structure are required to have certain dynamic adjustable functions. The existing transparent materials such as ITO can only realize certain electromagnetic shielding and electromagnetic wave absorbing functions, and cannot realize dynamic regulation and control of electromagnetic wave absorption. Therefore, the demand for developing a novel transparent electromagnetic wave-absorbing material with dynamically adjustable wave-absorbing rate and working frequency is urgent, and the problem to be solved is urgent for the development of a new generation platform and equipment electromagnetic stealth and countermeasure technology.

In recent years, with the Development of nano-fabrication technology, Transparent Flexible wave-absorbing surface research is carried out by combining specially-fabricated wire mesh with some Transparent Flexible media PDMS (t.jang and l.j.guo. "Transparent and Flexible Polarization-Independent Microwave Absorber," ACS Photonics, vol.1, No.3,2014), PET (y.okano, s.ogino and k.ishikawa, "Development of optical transmission ultra Microwave Absorber for ultra high-Frequency RF Identification System," IEEE transmission.micro.door.tech, vol.60, No.8,2012), and the research direction is mainly focused on wave-absorbing bandwidth enhancement and the like. However, once the topological shape of the metal wire mesh in the wave-absorbing surface is fixed, the wave-absorbing surface structure is difficult to change, so that the function of the wave-absorbing surface structure is determined, and dynamic regulation cannot be realized.

Graphene, as an emerging two-dimensional planar material, exhibits outstanding properties in mechanical, electrical, optical, biochemical and the like, such as single-layer graphene with light transmittance close to 97.7%, fastest electron mobility (15000cm2/v/cm), ultrahigh charge carrier mobility (200000cm2/v/s) without temperature control and efficient fermi speed (106m/s) close to the speed of light. Graphene also has excellent mechanical properties, its young's modulus is 1.0TPa, and in addition, it has excellent electronic conductivity and flexibility.

Due to these properties of graphene, great attention has been paid to researchers. After a decade of development, Graphene has been used by many researchers for absorption control of electromagnetic waves (Osman Balci, emery o. polar, nurbek kakenov and coskun kocabas. "Graphene-enabled electrically switchable radar-absorbing surfaces," nat. commun. 2015). However, these operations are mainly based on theory and the ehz band is abundant. In the Microwave band commonly used in the current communication technology, the dynamic tuning work by using Graphene is very little, and for this reason, the characteristic of Graphene in the Microwave band is equivalent to a layer of adjustable resistive film, and the imaginary part of the impedance is very small, so that the Graphene needs to be Patterned so as to obtain an "equivalent imaginary part" (Da Yi, Xing-Chang Wei, and Yi-Li Xu., "Tunable Microwave Absorber base Patterned Graphene," IEEE trans. micro w.thermal technique, vol.65, No.8, pp.2819-2826, and aug.2017); in addition, the microwave band application requires the graphene to have a large size, and the growth and patterning of the large-area graphene become a difficulty that hinders the practical application of the graphene. In 2018, the subject group solved the problem of large-area Graphene patterning in the work (Chen H., Lu W.B., Liu Z.G., Zhang J., Zhang A.Q., Wu B.Experimental modification of Microwave Absorber Using Large area Multilayer-Graphene based Frequency Selective Surface, IEEETrans. micro.thermal technique, 66,3087,2018), and provided possibility for utilizing Graphene to dynamically tune the wave-absorbing Surface in the Microwave section.

Disclosure of Invention

The technical problem to be solved by the invention is to realize dynamic regulation and control of the resonance frequency of the wave-absorbing surface by utilizing graphene in a microwave band. The invention provides a Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure, which comprises a graphene capacitor, a square metal wire mesh array, a PDMS dielectric layer and a metal wire mesh bottom plate which are sequentially overlapped; all the layers of the wave-absorbing surface structure are transparent and flexible, and the light transmittance of the wave-absorbing surface structure at the position of 550nm is close to 75%.

The graphene capacitor comprises a first PET substrate, a second PET substrate, a first graphene strip array arranged on the first PET substrate, a second graphene strip array arranged on the second PET substrate, and transparent ionic liquid filled between the first PET substrate and the second PET substrate;

the first PET substrate and the second PET substrate are arranged in an overlapped mode, and the first graphene strip array and the second graphene strip array are arranged on the inner surfaces of the first PET substrate and the second PET substrate respectively.

Further, the first graphene strip array and the second graphene strip array have the same pattern; the first graphene strip array and the second graphene strip array respectively comprise graphene strip units which are arranged at equal intervals in a periodic manner; the graphene strip units are rectangular, and the graphene strip units on the first graphene strip array correspond to the graphene strip units on the second graphene strip array one by one;

further, acetone glue is coated on the periphery of the inner surface of the second PET substrate, the thickness of the acetone glue is 100 micrometers, and the first PET substrate is bonded with the second PET substrate through the acetone glue.

Furthermore, the square wire mesh array comprises wire mesh units which are arranged periodically, each wire mesh unit is arranged in one-to-one correspondence with the graphene strip units, and the center points of the correspondingly arranged wire mesh units are coincided with the center points of the graphene strip units.

The preparation method of the high-transparency flexible dynamic frequency modulation wave-absorbing surface structure of the Ku waveband comprises the following steps:

step 1, modeling is carried out on a graphene capacitor, a square metal wire mesh array, a PDMS dielectric layer and a metal wire mesh bottom plate by utilizing matlab and an equivalent circuit theory, and the size of a graphene strip unit, the interval of the graphene strip unit, the square resistance of graphene and the size of the metal wire mesh unit with the optimal dynamic frequency modulation function are obtained through parameter scanning and optimization.

Step 2, obtaining a graphene square resistance value according to the step 1, growing graphene by using a copper foil, wherein the growing method is a CVD (chemical vapor deposition) method, and transferring the graphene to a first PET (polyethylene terephthalate) substrate and a second PET substrate after growth;

according to the size of the graphene strip units and the interval of the graphene strip units obtained in the step 1, etching the graphene on the first PET substrate and the graphene on the second PET substrate through laser to obtain a first graphene strip array attached to the first PET substrate and a second graphene strip array attached to the second PET substrate;

step 3, coating acetone glue on the periphery of the surface of the second PET substrate, wherein the acetone glue and the second graphene strip array are positioned on the same surface of the second PET substrate; filling transparent ionic liquid in the region surrounded by the third glue;

step 4, the first PET substrate is attached to and sealed with the second PET substrate through acetone glue, and the first graphene strip array faces the second PET substrate; forming a graphene capacitor;

step 5, respectively attaching a square metal wire mesh array and a metal wire mesh bottom plate to two surfaces of the PDMS medium layer; the size of the wire mesh units in the square wire mesh array is the same as that of the wire mesh units obtained in the step 1;

step 6, attaching the graphene capacitor to a PDMS dielectric layer attached to the square wire mesh array and the wire mesh base plate, wherein the square wire mesh array is attached to the second PET substrate;

has the advantages that: the invention provides a Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure, which is based on a laser etching large-area graphene strip array technology, utilizes patterned graphene, proves the possibility of dynamic regulation and control of the wave-absorbing surface of the graphene in a microwave band from theory to experiment, and lays a solid foundation for large-scale application of the graphene in the microwave band; meanwhile, a 100-micron closed space is formed by acetone gel, so that the ionic liquid is directly filled between two graphene electrodes without short circuit, the problem of low transparency of the graphene capacitor due to the diaphragm paper is solved, and a new idea is provided for the application of the graphene in a microwave-band transparent electromagnetic protection scene.

The Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface is simple in structure, the sheet resistance of the graphene can be controlled by applying different voltages to the graphene through a direct-current voltage source, and a dynamic method, namely a direct-current bias device is used for dynamically regulating and controlling the impedance of the grown graphene, so that dynamic verification is performed. The specific functions of the invention include perfect absorption of incident waves and dynamic tuning of intermediate frequency wave-absorbing frequency points in Ku wave band, and the invention can be used for applications such as transparent stealth and photoelectric solar cells, and spreads a way for transparent flexible application of graphene in microwave band.

Drawings

FIG. 1 is a schematic diagram of a structure of a high-transparency flexible dynamic frequency-modulation wave-absorbing surface of a Ku waveband;

FIG. 2 is a cross-sectional view of a Ku band highly transparent flexible dynamic frequency modulation wave-absorbing surface structure;

FIG. 3 shows the test results of the wave-absorbing rate of the wave-absorbing surface structure of the present invention under different DC voltages.

1, a graphene capacitor; 11. a first PET substrate; 12. the device comprises a second PET substrate, 13, a first graphene strip array, 14, a second graphene strip array, 15 and transparent ionic liquid; 2. a square wire mesh array; 3. a PDMS dielectric layer; 4. a wire mesh base plate.

Detailed Description

The structure and performance of the present invention will be further explained with reference to the accompanying drawings.

As shown in fig. 1, the Ku-band highly transparent flexible dynamic frequency modulation wave-absorbing surface structure includes a graphene capacitor 1, a square wire mesh array 2, a PDMS dielectric layer 3, and a wire mesh bottom plate 4, which are sequentially stacked;

the graphene capacitor 1 comprises a first PET substrate 11, a second PET substrate 12, a first graphene strip array 13 arranged on the first PET substrate 11, a second graphene strip array 14 arranged on the second PET substrate 12, and a transparent ionic liquid 15 filled between the first PET substrate 11 and the second PET substrate 12; for example, the transparent ionic liquid 15 may be trifluoromethanesulfonimide salt.

The first PET substrate 11 and the second PET substrate 12 are disposed in an overlapping manner, and the first graphene strip array 13 and the second graphene strip array 14 are disposed on the inner surfaces of the first PET substrate 11 and the second PET substrate 12, respectively.

The first graphene strip array 13 and the second graphene strip array 14 have the same pattern; the first graphene strip array 13 and the second graphene strip array 14 each include graphene strip units arranged periodically at equal intervals; the graphene strip units are rectangular, and the graphene strip units on the first graphene strip array 13 correspond to the graphene strip units on the second graphene strip array 14 one by one;

acetone glue is coated around the inner surface of the second PET substrate 12, the thickness of the acetone glue is 100 microns, and the first PET substrate 11 is bonded with the second PET substrate 12 through the acetone glue.

The square wire mesh array 2 comprises wire mesh units which are periodically arranged, each wire mesh unit is in one-to-one correspondence with the graphene strip unit, and the central points of the wire mesh units and the graphene strip units are overlapped.

The preparation method of the Ku-waveband high-transparency flexible dynamic frequency modulation wave-absorbing surface structure comprises the following steps of:

step 1, modeling a graphene capacitor 1, a square metal wire mesh array 2, a PDMS dielectric layer 3 and a metal wire mesh bottom plate 4 by utilizing matlab and an equivalent circuit theory, and when incident electromagnetic waves are vertically incident, enabling a graphene strip array to be equivalent to series connection of a resistor, a capacitor and an inductor; the square wire mesh array 2 is equivalent to a capacitor; the PET substrate, the PDMS dielectric layer 3 and the metal wire mesh bottom plate 4 are represented by respective standard transmission line models;

the equations for equivalent resistance, inductance, and capacitance can be found in Luukkonen O, Simovski C, Granet G, Simple and effective analytical model of planar grid and high-impedance manufacturing metallic strips or latches, IEEE transactions and antenna Probe.56, 1624,2008, and Costa, F., Monorchio, A., & Manara, G.analysis and design of ultrasonic electromagnetic composites sampled high impedance manufacturing probes, IEEE transactions Probe.58, 1551,2010.

And optimizing to obtain the optimal graphene strip unit size, the optimal graphene strip unit interval, the optimal graphene square resistance value and the optimal wire mesh unit size through parameter scanning.

When the size of each graphene strip unit is 5.0mm by 5.4mm in a rectangular shape, the interval of each graphene strip unit is 0.4mm, and the size of each wire mesh unit is 3.6mm by 5.4mm, the wave-absorbing surface structure has a good dynamic frequency modulation function.

Meanwhile, the thickness of the PET substrate 2 adopted in the invention is 120 μm, and the relative dielectric constant is 2.8; the PDMS dielectric layer 3 has a relative dielectric constant of 2.8 and a thickness of 1 mm; the structural period of the graphene strip unit is 5.4 mm; the square wire mesh array 2 is a periodic structure, wherein the period of the structure is 5.4 mm.

Step 2, obtaining a graphene square resistance value according to the step 1, growing graphene by using a copper foil, wherein the growing method is a CVD (chemical vapor deposition) method, and transferring the graphene to a first PET (polyethylene terephthalate) substrate 11 and a second PET substrate 12 after growth;

according to the size of the graphene strip unit and the interval of the graphene strip unit obtained in the step 1, etching the graphene on the first PET substrate 11 and the second PET substrate 12 through laser to obtain a first graphene strip array 13 attached to the first PET substrate 11 and a second graphene strip array 14 attached to the second PET substrate 12;

step 3, coating acetone glue on the periphery of the surface of the second PET substrate 12, wherein the acetone glue and the second graphene strip array 14 are located on the same surface of the second PET substrate 12; filling transparent ionic liquid 15 in the region surrounded by the third glue;

step 4, the first PET substrate 11 is attached and sealed with the second PET substrate 12 through acetone glue, and the first graphene strip array 13 faces the second PET substrate 12; forming a graphene capacitor 1;

step 5, respectively attaching the square metal wire mesh array 2 and the metal wire mesh base plate 4 to two surfaces of the PDMS medium layer 3; the size of the wire mesh units of the square wire mesh array 2 is the same as that of the wire mesh units obtained in the step 1;

step 6, attaching the graphene capacitor 1 to a PDMS dielectric layer 3 attached to a square wire mesh array 2 and a wire mesh base plate 4, wherein the square wire mesh array 2 is attached to a second PET substrate 12;

modeling a designed model by using commercial software CST, simulating a graphene array by using a time domain simulation method, simulating patterned graphene by using an impedance boundary condition with zero thickness, taking values of sheet resistance of the graphene in a region of 700-2100 omega/sq at equal intervals according to the stepping of 50 omega/sq, and simulating to obtain the characteristics of the super surface of the graphene, such as transmission coefficient, reflection coefficient and the like, wherein the boundary condition applied to the model is an open boundary;

after the dynamic frequency modulation wave-absorbing surface structure is prepared according to the method, the wave-absorbing rate characteristic of the dynamic frequency modulation wave-absorbing surface structure is tested. The sheet resistance of the graphene can be controlled by applying different voltages to the graphene through a direct current voltage source, a dynamic method is utilized, namely, the impedance of the grown graphene is dynamically regulated and controlled through a direct current bias device, as shown in fig. 3, direct current voltages of 5V, 1.5V and 0V are respectively added to two ends of the graphene, when the sheet resistance of the graphene is increased from 700 omega/sq to 2100 omega/sq, the central frequency of a wave-absorbing surface is increased from 14.6GHz to 16.7GHz, meanwhile, wave-absorbing rate peak values corresponding to the central frequency are both greater than 0.95 and approximate to perfect absorption, and based on the situation, the dynamic regulation and control of the wave-absorbing surface in a microwave band, namely a Ku wave band, are realized.