Preparation method of reversible electromagnetic function conversion material and application of obtained product

Abstract

According to the preparation method of the reversible electromagnetic function conversion material and the application of the obtained product, the impedance and thickness of hydrogel can be effectively adjusted by changing the water content, and the defects that electromagnetic shielding and microwave absorption cannot be converted, and the electromagnetic wave absorption frequency is fixed and single are overcome. The reversible dynamic adjustment electromagnetic performance conversion can be converted from the electromagnetic shielding performance to the microwave absorption performance and can also be converted from the microwave absorption performance to the electromagnetic shielding performance, and the reversible conversion process can be reversibly and dynamically adjusted along with the microwave absorption frequency band. The reversible electromagnetic function conversion material integrates reversible conversion of electromagnetic performance and dynamic adjustment of microwave absorption frequency band, opens up a new way for development of next-generation intelligent convertible electromagnetic equipment crossing different fields, and provides a theoretical basis.

Description

Technical Field

[0001] This invention relates to a method for preparing a reversible electromagnetic function conversion material and the application of the resulting product. Background Technology

[0002] Electromagnetic waves (EMWs) are fundamental to communications, medicine, defense, scientific research, and industrial production. A dynamic reversible EMW switch, capable of seamlessly switching between reflecting and absorbing electromagnetic waves, is a highly attractive design that enables precise dynamic control of EMW signals, opening up possibilities for next-generation EMW management. Frequency tuning of EMW absorption is also crucial for next-generation EMW management. This switching and frequency tuning provides a novel approach to dynamic spectrum allocation, significantly expanding applications in intelligent driving and sensing, robotics, and other fields. Furthermore, it not only overcomes the limitations of fixed-frequency radar, enabling real-time adjustment and self-adaptation of radar signals, but also simultaneously meets the diverse application requirements of stealth aircraft during combat, positioning during return, and landing. It also brings new possibilities to medical imaging, wireless power transfer, and antennas. In medical imaging, it can improve the performance of electromagnetic medical imaging equipment, achieving higher resolution and more accurate diagnostic results; in wireless power transfer, it can achieve precise control and broadening of power transfer frequencies, thereby improving the efficiency and safety of wireless charging systems. Therefore, reversible EMW switches will propel human society towards a more intelligent, efficient, and sustainable future. However, fabricating a dynamic reversible electromagnetic wave switch is an unprecedented challenge.

[0003] In principle, a prerequisite for realizing dynamic switching is impedance tunability. Specifically, electromagnetic waves are reflected at interfaces due to impedance mismatch, while they are absorbed and attenuated when they enter the interior of materials due to impedance matching. Typical electromagnetic materials have fixed electromagnetic parameters, making it difficult to dynamically adjust impedance. Therefore, since the impedance requirements for reflecting and absorbing electromagnetic waves are diametrically opposed, switchable switching is theoretically difficult to implement, and this area has remained unexplored to date. Summary of the Invention

[0004] Electromagnetic functional materials, with their fixed impedance, cannot simultaneously meet the impedance mismatch requirements of electromagnetic shielding materials and the impedance matching requirements of microwave absorbing materials, nor can they address the fixed microwave absorption frequency of traditional microwave absorbing materials. This invention provides a reversible electromagnetic function conversion material. By adjusting the water content, the electromagnetic shielding and microwave absorption properties of the hydrogel-based material can be reversibly switched. In practical applications, adjusting the water content achieves the reversible switching of electromagnetic functions—that is, the reversible switching between electromagnetic interference shielding and microwave absorption performance—accompanied by dynamic tuning of the microwave absorption frequency. Electromagnetic hydrogels can be applied in multiple fields such as radar stealth, electromagnetic interference resistance, intelligent military communications, industrial and consumer communications, and medical wearable devices, belonging to the field of nanomaterial preparation and application technology.

[0005] The specific technical solution of this invention is as follows: A reversible electromagnetic functional conversion material is disclosed, which achieves reversible conversion of electromagnetic shielding of hydrogel-based materials by adjusting the water content. The initial thickness of the hydrogel-based material is 0-5 cm and the water content is 0-90%.

[0006] Furthermore, the hydrogel-based material is a hydrogel or a system composed of a hydrogel and a filler.

[0007] The matrix of the hydrogel in this application includes, but is not limited to, polyvinyl alcohol, polyacrylic acid and its derivatives, polyethylene glycol and its derivatives, sodium alginate and its derivatives, bacterial cellulose or polypropylene ether and its derivatives.

[0008] The filler material for the hydrogel in this application is selected from, but is not limited to, dielectric fillers, magnetic materials, ceramic materials, and dielectric magnetic materials.

[0009] Furthermore, the filler is selected from one or more of the following: cobalt tetroxide, titanium oxide, zinc oxide, copper oxide, aluminum oxide, nickel oxide, reduced graphene oxide, carbon nanotubes, Mxene, silicon carbide, carbon fiber, carbon spiral, carbon cloth, molybdenum disulfide, and iron oxide.

[0010] Furthermore, the hydrogel-based materials are cobalt tetroxide / reduced graphene oxide / polyethylene hydrogels, cobalt tetroxide / reduced graphene oxide / polyacrylic acid hydrogels, cobalt tetroxide / reduced graphene oxide / polyethylene glycol hydrogels, cobalt tetroxide / reduced graphene oxide / sodium alginate hydrogels, cobalt tetroxide / reduced graphene oxide / bacterial cellulose hydrogels, cobalt tetroxide / reduced graphene oxide / polypropylene ether hydrogels, titanium dioxide / reduced graphene oxide / polyvinyl alcohol hydrogels, cobalt tetroxide / carbon nanotubes / polyvinyl alcohol hydrogels, or cobalt tetroxide / Mxene / polyvinyl alcohol hydrogels.

[0011] Due to their 3D internal cross-linked network and swelling properties, hydrogels can be repeatedly dehydrated and hydrated, allowing for the adjustment of conductivity and thickness by controlling the water content. When the hydrogel matrix used is polyvinyl alcohol, the resulting composite material can be represented as Co3O4@RGO / PVA.

[0012] A method for preparing a reversible electromagnetically switching hydrogel (the hydrogel-based material is cobalt tetroxide / reduced graphene oxide / polyethylene hydrogel) includes the following steps: (1) Cobalt tetroxide was deposited on the surface of reduced graphene oxide by atomic layer deposition to obtain cobalt tetroxide / reduced graphene oxide material; (2) Cobalt tetroxide / reduced graphene oxide and polyvinyl alcohol and boric acid solution were blended to obtain cobalt tetroxide / reduced graphene oxide / polyvinyl alcohol hydrogel.

[0013] Further, in step (1), graphene oxide is ultrasonically dispersed in an appropriate amount of ethanol for 15 minutes, then dropped onto an 8cm×8cm square quartz sheet, dried in air, and placed in the reaction chamber of the ALD device; CoCp2 and O3 are selected as deposition precursors, and high-purity N2 is used as carrier gas and purge gas; the temperature of the reaction chamber is 150 ℃; the temperature of CoCp2 is maintained at 70 ℃, and the number of cycles is 50-200.

[0014] Furthermore, in step (2), Co3O4@RGO is 6% of the amount of PVA added; the mass fraction of the PVA aqueous solution is 20%, and the concentration of the sodium tetraborate solution is 15.255 mg / ml.

[0015] This invention first deposits cobalt tetroxide on graphene oxide via atomic layer deposition, then mixes it with polyvinyl alcohol and boric acid to obtain a self-healing Co3O4@RGO / PVA hydrogel with reversibly switchable electromagnetic properties. In this composite material, the thickness of the cobalt tetroxide can be controlled by adjusting the number of deposition cycles; the electromagnetic properties of the hydrogel can be controlled by electromagnetic waves by adjusting the number of cobalt tetroxide deposition cycles; and the electromagnetic properties and absorption frequency of electromagnetic waves can be dynamically and reversibly switched and adjusted by changing the water content, showing great promise for future applications.

[0016] This electromagnetic functional hydrogel is composed of cobalt tetroxide / reduced graphene oxide / hydrogel material. Its preparation process is simple, and the cobalt tetroxide coating thickness can be easily controlled by adjusting process parameters, thereby regulating the electromagnetic properties of the hydrogel. Furthermore, due to its three-dimensional interconnected internal network and swelling characteristics, the hydrogel of this invention has an adjustable water content. By adjusting the water content, the conductivity and thickness of the composite material can be changed, thereby adjusting the impedance. This achieves reversible adjustment of electromagnetic properties and microwave absorption frequency, overcoming the shortcomings of traditional electromagnetic materials that cannot achieve dynamic switching between electromagnetic shielding and microwave absorption, and the limitations of traditional microwave absorbing materials whose fixed absorption performance cannot be adjusted in a timely manner according to changes in the external environment.

[0017] The Co3O4@RGO / PVA hydrogel material obtained by this invention can dynamically switch electromagnetic properties and adjust electromagnetic wave absorption properties in a timely manner according to changes in the external environment. It has self-healing properties, adhesion, and tensile conductivity stability. It has great application prospects in smart electronic devices, radar stealth, and modern medical devices. It overcomes the shortcomings of traditional electromagnetic materials, such as the inability to dynamically switch electromagnetic wave absorption materials, passive absorption, and limited color.

[0018] When other hydrogel or hydrogelatin-based materials are used, the electromagnetic shielding and microwave absorption properties of hydrogel-based materials can be reversibly converted by controlling the water content.

[0019] Compared with the prior art, the advantages of the present invention are as follows: 1. This invention achieves reversible conversion of the electromagnetic shielding and microwave absorption properties of hydrogel-based materials by controlling the water content.

[0020] 2. The Co3O4@RGO / PVA hydrogel prepared by this invention can effectively achieve reversible conversion of properties, namely, reversible conversion of electromagnetic shielding performance and microwave absorption performance, by adjusting the water content. It is also accompanied by reversible and effective adjustment of microwave absorption frequency, which solves the shortcomings of traditional electromagnetic materials that cannot switch electromagnetic shielding and microwave absorption performance in real time according to actual application needs, as well as the fixed absorption performance of microwave absorbing materials.

[0021] 3. The Co3O4@RGO / PVA hydrogel prepared by this invention can adjust the reversible conversion of electromagnetic properties and microwave absorption frequency band simply by adjusting the water content. It is simple to operate, economical, environmentally friendly and pollution-free, and has good self-healing properties. In practical applications, it can effectively save on usage costs and reduce waste caused by material damage. It has broad application prospects in intelligent electronic devices, radar stealth and military communications. Attached Figure Description

[0022] Figure 1 The images shown are transmission electron microscope (TEM) images of the samples of this invention: a. TEM image of Co3O4@RGO; b. Elemental distribution image of the samples of this invention. Figure 2 Scanning electron microscope image of the Co3O4@RGO / PVA sample; Figure 3 An optical photograph of the gel state transition process of the sample of this invention; Figure 4 The electromagnetic parameters of Co3O4@RGO / PVA in this invention at different water contents are: a. conductivity, b. reflection coefficient and absorption coefficient, c. real part of dielectric, d. imaginary part of dielectric, e. real part of magnetic permeability, f. imaginary part of magnetic permeability; Figure 5 Electromagnetic properties of Co3O4@RGO / PVA hydrogel under different water contents: a. Electromagnetic properties during dehydration, b. Bandwidth tuning during dehydration, c. Electromagnetic properties during hydration, d. Bandwidth tuning during hydration. Figure 6 Electromagnetic properties of PVA hydrogels at different water contents: a. Electromagnetic properties during dehydration, b. Bandwidth tuning during dehydration, c. Electromagnetic properties during hydration, d. Bandwidth tuning during hydration. Figure 7 To determine the electromagnetic properties of RGO / PVA hydrogels at different water contents, consider: a. Electromagnetic properties during dehydration; b. Bandwidth tuning during dehydration; c. Electromagnetic properties during hydration; d. Bandwidth tuning during hydration.

[0023] Figure 8 To determine the electromagnetic properties of CNT / polyacrylic acid hydrogel at different water contents when the CNT content is 5%, we consider: a) electromagnetic properties during dehydration; b) frequency band tuning during dehydration; c) electromagnetic properties during hydration; and d) frequency band tuning during hydration.

[0024] Figure 9 To determine the electromagnetic properties of polyethylene glycol hydrogels at different water contents, consider: a) electromagnetic properties during dehydration; b) frequency band tuning during dehydration; c) electromagnetic properties during hydration; and d) frequency band tuning during hydration.

[0025] Figure 10 The electromagnetic properties of cobalt tetroxide / reduced graphene oxide / sodium alginate hydrogels under different water contents are: a. electromagnetic properties during dehydration; b. frequency band tuning during dehydration; c. electromagnetic properties during hydration; d. frequency band tuning during hydration.

[0026] Figure 11 The electromagnetic properties of cobalt tetroxide / reduced graphene oxide / bacterial cellulose hydrogels under different water contents are: a. electromagnetic properties during dehydration; b. frequency band tuning during dehydration; c. electromagnetic properties during hydration; d. frequency band tuning during hydration.

[0027] Figure 12 To determine the electromagnetic properties of zinc oxide / polypropylene ether hydrogels under different water contents, consider: a) electromagnetic properties during dehydration; b) frequency band tuning during dehydration; c) electromagnetic properties during hydration; and d) frequency band tuning during hydration. Detailed Implementation

[0028] The present invention will be described in detail below through specific embodiments. However, the purpose and use of these illustrative embodiments are only for explaining and illustrating the present invention, and do not constitute any limitation on the actual protection scope of the present invention, nor are they intended to limit the protection scope of the present invention to these embodiments.

[0029] Example 1: Preparation of Co3O4@RGO Atomic layer deposition (ALD) was used to deposit cobalt tetroxide (CTO) in an ALD apparatus. Cobalt dicene and water were used as precursors during ALD, the deposition temperature was 150°C, and high-purity N2 was used for purging. A series of samples were prepared by adjusting the number of cycles to 50, 100, and 200 cycles, and the resulting product was named nCo3O4@RGO, where n represents the number of cycles.

[0030] The morphology of Co3O4@RGO prepared by ALD deposition was characterized by transmission electron microscopy. Figure 1a, b). Energy dispersive X-ray spectroscopy (EDS) of the obtained product revealed that Co, C, and O were uniformly deposited on the RGO surface, proving the homogeneity of RGO on Co.

[0031] Example 2: Preparation of Co3O4@RGO / PVA hydrogel 0.9 g of Co3O4@RGO and 15 g of PVA powder were dispersed in 60 mL of deionized water and reacted at 98 °C for 2 hours to obtain a Co3O4@RGO / PVA aqueous solution.

[0032] Sodium tetraborate (1.14375 g) was then dissolved in 75 ml of water and added to the Co3O4@RGO / PVA solution and stirred until homogeneous to obtain Co3O4@RGO / PVA hydrogel.

[0033] The unique 3D interconnected network and swelling properties of the Co3O4@RGO / PVA hydrogel enable it to achieve electromagnetic property conversion during changes in water content. This unique 3D interconnected network of the Co3O4@RGO / PVA hydrogel is also confirmed by electron microscopy images. Figure 2 Its unique swelling properties were also... Figure 3 Confirmed.

[0034] Example 3: Preparation of PVA hydrogel PVA was synthesized using a simple one-pot method. PVA powder (15 g) was dispersed in 60 mL of deionized water and incubated at 98 °C for 2 hours to obtain an aqueous PVA solution.

[0035] Then, sodium tetraborate (1.14375g) was dissolved in 75ml of water and added to the PVA solution and stirred until homogeneous to obtain PVA hydrogel.

[0036] Example 4: Preparation of RGO / PVA hydrogel 0.9 g of RGO and 15 g of PVA powder were dispersed in 60 mL of deionized water and reacted at 98 °C for 2 hours to obtain an RGO / PVA aqueous solution.

[0037] Sodium tetraborate (1.14375 g) was then dissolved in 75 ml of water and added to the Co3O4@RGO / PVA solution and stirred until homogeneous to obtain RGO / PVA hydrogel.

[0038] Application of Co3O4@RGO / PVA composite material in electromagnetic wave absorption To obtain the microwave absorption properties of the Co3O4@RGO / PVA composite material, the electromagnetic shielding performance of the hydrogel in the 8.2–12.4 GHz and 12.4–18 GHz frequencies, and the electromagnetic parameters in the 2–18 GHz frequency range were measured using a Ceyear 3672B-S network analyzer. The test samples for electromagnetic shielding performance in the 8.2–12.4 GHz range were fabricated with length and width dimensions of 24 mm and 11 mm, respectively, while the test samples in the 12.4–18 GHz range had length and width dimensions of 17 mm and 9 mm, respectively. The electromagnetic parameter test samples for microwave absorption performance were directly cut into rings with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm (thickness of 2.00 mm). Each ring was placed on a vector mesh analyzer to measure the electromagnetic parameters of the composite material.

[0039] The test results for 100 Co3O4@RGO / PVA are as follows: Figure 4 As shown in the figure, the conductivity of the 100 Co3O4@RGO / PVA hydrogel decreases with decreasing water content, then suddenly increases and decreases again at a water content of 24%. Simultaneously, its reflection coefficient R gradually decreases, while its absorption coefficient A gradually increases. This is because as the water content decreases, the thickness and conductivity decrease, impedance matching gradually increases, and more electromagnetic waves can enter the hydrogel and be reflected rather than absorbed. The electromagnetic properties gradually transform from electromagnetic shielding performance to microwave absorption performance. During the gradual decrease in water content, the real part ε′ and imaginary part ε″ of the dielectric of 100 Co3O4@RGO / PVA gradually decrease, and these values ​​decrease with increasing frequency. This is mainly attributed to the changes in electromagnetic parameters, losses, conductivity, thickness, and impedance during the change in water content, which is beneficial for optimizing impedance matching. This is highly advantageous for achieving wide-frequency tunable electromagnetic wave absorption performance.

[0040] The electromagnetic wave absorption performance of each sample was analyzed using transmission line theory.

[0041] Where the scattering parameter (S) 11 and S 21 ), calculate the reflection coefficient (R), absorption coefficient (A), and transmission coefficient (T), and the total EMISE (SE). T ), absorption coefficient (SE) A ) and reflectance coefficient (SE) R ); where Z in Z0 is the input impedance of the absorber, Z0 is the free space impedance, and μ is the input impedance of the absorber. r relative complex permeability (μ) r=μ′-iμ"),ε r The complex permittivity (ε) r =ε′-iε"), where d is the thickness of the absorber, and c and f are the speed and frequency of light, respectively.

[0042] An electromagnetic shielding effectiveness (EMI SE) greater than 10 dB and a reflection loss (RL) value less than -10 dB indicate that the electromagnetic waves can be reflected and absorbed by 90% respectively, which can meet the usage requirements. Figure 5 The figure shows the electromagnetic properties (EMI SE and RL) at different water contents. As can be seen from the figure, the 100 Co3O4@RGO / PVA can be adjusted by the water content. With a hydrogel thickness of 6.5 mm, the electromagnetic properties can be effectively adjusted by changing the water content, from electromagnetic shielding performance (EMI SE = 34.26 dB to RL = -60.42 dB) during the dehydration stage, and from RL = -57.58 dB to EMI SE = 31.7 dB during the hydration stage. During both dehydration and hydration processes, the electromagnetic wave absorption frequency changes from the C-band (4-8 GHz) to the Ku-band (12-18 GHz).

[0043] Furthermore, both PVA and RGO / PVA hydrogels can achieve electromagnetic property conversion and frequency tuning. With an initial thickness of 6.5 mm, the electromagnetic properties of the PVA hydrogel change from electromagnetic shielding performance (EMI SE = 32 dB) to RL = -50.42 dB during the dehydration stage, and from RL = -51.25 dB to EMI SE = 31.65 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency occurs during both the dehydration and hydration processes. Figure 6 The electromagnetic properties of RGO / PVA hydrogel change from electromagnetic shielding (EMI SE=32 dB) to microwave absorption (RL=-50.42 dB) during the dehydration stage, and from RL=-51.25 dB to microwave absorption (EMI SE=31.65 dB) during the hydration stage. This change is influenced by the tuning of the electromagnetic wave absorption frequency during both dehydration and hydration processes. Figure 7 ).

[0044] The water content control method is generally applicable to hydrogels regardless of the type of hydrogel or the initial thickness. Furthermore, CNT / polyacrylic acid hydrogels can also achieve electromagnetic property conversion and frequency tuning. At an initial thickness of 7 mm, the electromagnetic properties of CNT / polyacrylic acid hydrogels change from electromagnetic shielding performance (EMI SE=35 dB) to RL=-55 dB during the dehydration stage, and from RL=-53 dB to EMI SE=32 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency is achieved during both the dehydration and hydration processes. Figure 8 ).

[0045] Polyethylene glycol hydrogels can also achieve electromagnetic property conversion and frequency tuning. With an initial thickness of 10 mm, the electromagnetic properties of polyethylene glycol hydrogel change from electromagnetic shielding performance (EMI SE=45 dB) to RL=-40 dB during the dehydration stage, and from RL=-41 dB to EMI SE=39 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency occurs during both the dehydration and hydration processes. Figure 9 ).

[0046] Cobalt tetroxide / reduced graphene oxide / sodium alginate hydrogels can also achieve electromagnetic property conversion and frequency tuning. With an initial thickness of 12 mm, the electromagnetic properties of the cobalt tetroxide / reduced graphene oxide / sodium alginate hydrogel change from electromagnetic shielding performance (EMI SE=55 dB) to RL=-58 dB during the dehydration stage, and from RL=-59 dB to EMI SE=54 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency is achieved during both the dehydration and hydration processes. Figure 10 ).

[0047] Cobalt tetroxide / reduced graphene oxide / bacterial cellulose hydrogels can also achieve electromagnetic property conversion and frequency tuning. With an initial thickness of 15 mm, the electromagnetic properties of the cobalt tetroxide / reduced graphene oxide / bacterial cellulose hydrogel change from electromagnetic shielding performance (EMI SE=65 dB) to RL=-55 dB during the dehydration stage, and from RL=-59 dB to EMI SE=54 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency is achieved during both the dehydration and hydration processes. Figure 11 ).

[0048] Zinc oxide / polypropylene ether hydrogels can also achieve electromagnetic property conversion and frequency tuning. With an initial thickness of 20 mm, the electromagnetic properties of the zinc oxide / polypropylene ether hydrogel change from electromagnetic shielding performance (EMI SE=76 dB) to RL=-35 dB during the dehydration stage, and from RL=-30 dB to EMI SE=73 dB during the hydration stage. Tuning of the electromagnetic wave absorption frequency is achieved during both the dehydration and hydration processes. Figure 12 ).

Claims

1. A reversible electromagnetic function conversion material, characterized by, The reversible conversion of electromagnetic shielding and microwave absorption performance of the hydrogel-based material is realized by adjusting the water content, the initial thickness of the hydrogel-based material is 0-5 cm, and the water content is 0-90%.

2. A reversible electromagnetic function conversion material according to claim 1, characterized in that, The hydrogel-based material is a hydrogel or a system composed of a hydrogel and a filler.

3. A reversible electromagnetic function conversion material according to claim 2, characterized in that The base of the hydrogel is polyvinyl alcohol, polyacrylic acid and its derivatives, polyethylene glycol and its derivatives, sodium alginate and its derivatives, bacterial cellulose, or polyacrylic ether and its derivatives.

4. The reversible electromagnetic function transducing material of claim 2, wherein The filler is selected from one or more of dielectric fillers, magnetic materials, ceramic materials, and dielectric magnetic materials.

5. The reversible electromagnetic function conversion material according to claim 2, characterized in that, The filler is selected from one or more of tricobalt tetroxide, titanium oxide, zinc oxide, copper oxide, aluminum oxide, nickel oxide, reduced graphene oxide, carbon nanotubes, Mxene, silicon carbide, carbon fiber, carbon spiral, carbon cloth, molybdenum disulfide, and ferroferric oxide.

6. The reversible electromagnetic function conversion material according to claim 2, characterized in that, The hydrogel-based material is tricobalt tetroxide / reduced graphene oxide / polyethylene hydrogel material, tricobalt tetroxide / reduced graphene oxide / polyacrylic acid hydrogel, tricobalt tetroxide / reduced graphene oxide / polyethylene glycol hydrogel, tricobalt tetroxide / reduced graphene oxide / sodium alginate hydrogel, tricobalt tetroxide / reduced graphene oxide / bacterial cellulose hydrogel, tricobalt tetroxide / reduced graphene oxide / polyacrylic ether hydrogel, titanium oxide / reduced graphene oxide / polyvinyl alcohol hydrogel, tricobalt tetroxide / carbon nanotube / polyvinyl alcohol hydrogel, or tricobalt tetroxide / Mxene / polyvinyl alcohol hydrogel.

7. The reversible electromagnetic function conversion material according to claim 2, characterized in that, The hydrogel-based material is tricobalt tetroxide / reduced graphene oxide / polyethylene hydrogel, and the preparation method comprises the following steps: (1) depositing tricobalt tetroxide on reduced graphene oxide by atomic layer deposition method to obtain tricobalt tetroxide / reduced graphene oxide material Co3O4@RGO; (2) blending tricobalt tetroxide / reduced graphene oxide with polyvinyl alcohol and sodium tetraborate solution to obtain tricobalt tetroxide / reduced graphene oxide / polyethylene hydrogel.

8. The reversible electromagnetic function conversion material according to claim 7, wherein, In step (1), graphene oxide is ultrasonically dispersed in an appropriate amount of ethanol for 15 minutes, then dropped onto an 8cm×8cm square quartz sheet, dried in air, and then placed in the reaction cavity of the ALD device; CoCp2 and O3 are selected as deposition precursors, high-purity N2 is used as carrier gas and purge gas; the temperature of the reaction cavity is 150 ℃; the temperature of CoCp2 is maintained at 70 ℃, and the cycle number is 50-200.

9. A reversible electromagnetic function conversion material according to claim 8, characterized in that In step (2), the PVA addition amount of Co3O4@RGO is 6%; the mass fraction of PVA aqueous solution is 20%, and the concentration of sodium tetraborate solution is 15.255 mg / ml.

10. Application of the reversible electromagnetic function conversion material according to any one of claims 1-6 in the fields of radar stealth equipment and military communication equipment, medical treatment, and civilian electronic equipment.

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