Graphene (top) and carbon materials of different structures: fullerenes (bottom left); carbon nanotubes (lower middle); graphite (bottom right)
Absorbing mechanism diagram of multi-component graphene-based multifunctional composite absorbing material.
With the development of electronic information technology and the popularity of electronic products, electromagnetic waves are widespread in people's daily lives. Electromagnetic pollution is formed when electromagnetic radiation exceeds the upper limit of the human body and the environment. In the military field, radar is still the usual means of searching for targets in modern warfare. Developing radar stealth materials that can absorb electromagnetic waves efficiently is one of the effective ways to improve the viability of weapon systems. Therefore, absorbing materials have extensive research value and application prospects in civil and military fields.
A new type of electromagnetic wave absorbing material - graphene
Graphene is a new type of two-dimensional nanomaterial discovered in 2004. Its magical two-dimensional structure gives it unique physical and chemical properties.
Graphene is currently the best known conductive material. The speed of electron movement in graphene can reach 1/300 of the speed of light. The valence band and conduction band of graphene intersect at the Fermi level, which gives graphene a unique zero-gap semiconductor performance, twice the highest mobility of indium telluride. In the future, graphene may replace silicon to make ultra-micro transistors, increasing the computational speed of computer processors by a factor of 100.
The strength of graphene is equivalent to more than 100 times the strength of the best steel at present, and the hardness even exceeds that of diamonds.
The material with the strongest strength, but its density is very small. At room temperature, the thermal conductivity of graphene is ten times that of commonly used metal heat conductive materials such as gold, silver and copper, and is more than twenty times that of aluminum.
Graphene also has other special properties, such as ultra-high specific surface area. The theoretical specific surface area of ​​monoatomic graphene can reach astonishing 2,630 m 2 /g, which is 2 to 3 times the specific surface area of ​​activated carbon, and can be used for adsorption and desorption of various macromolecules and small particles. The optical transmittance of graphene reaches 97.7%, which makes graphene have potential for application in transparent electrodes of solar cells.
The above characteristics make it possible for graphene to replace traditional carbon materials into a new type of electromagnetic wave absorbing material. However, it is unavoidable that, similar to other carbon-based materials, the main electromagnetic wave attenuation mechanism of simple graphene is electrical loss, and thus the absorbing performance is insufficient. good.
The combination of carbon materials with ferrite and electric loss type metal compound nanoparticles is an effective way to improve the absorbing properties. Graphene has a large specific surface area and is suitable as a carrier for loading nanoparticles. It not only can effectively solve the problem of poor dispersion of nanoparticles and self-agglomeration, but also can design and optimize its structure and properties at the nanometer scale. Graphene-based multifunctional composite absorbing materials of specific composition, structure and properties.
Absorbing mechanism of graphene
When electromagnetic waves encounter any medium of shape during propagation, reflection and transmission phenomena occur at the incident surface or interface of the electromagnetic wave. Since the wave impedance of the original propagation medium does not match the wave impedance of the material, a portion of the electromagnetic waves are reflected and the other portion is transmitted into the interior of the medium. The less the impedance matches, the more electromagnetic waves are reflected. Only when the wave impedance of the original propagation medium and the wave impedance of the material match each other, the electromagnetic wave is incident into the material with maximum efficiency. Electromagnetic waves interact with materials during their internal propagation and are converted into other forms of energy (such as mechanical energy, electrical energy, and thermal energy), that is, electromagnetic wave losses. Therefore, the absorbing properties of the absorbing material are mainly determined by two conditions: one is the impedance matching characteristic, that is, the reflection of electromagnetic waves on the surface of the material or the electromagnetic wave can be maximized into the interior of the material; the second is the attenuation characteristic, that is, the electromagnetic wave enters After the material is inside, the material can effectively absorb or lose electromagnetic waves and reduce the secondary reflection of electromagnetic waves.
Multi-component graphene-based absorbing materials pass through the microstructure and synergistic effect of composite hybrid particles, and study the loading density, morphology, structure, content of each component and the synergistic effect between the components of the absorbing materials. The influence of electromagnetic parameters, while utilizing the special structure of graphene and the special properties caused by the combination of graphene and nano-particles, the effects of interfacial polarization, electron relaxation polarization and dipole polarization are used to lose electromagnetic waves. A lightweight, high-strength, broadband absorbing material structure system with various electromagnetic wave loss mechanisms and adjustable performance.
Research Status and Enlightenment of Graphene Absorbing Materials
In recent years, researchers have done a lot of valuable work in the research of graphene absorbing materials.
The design and preparation of multi-system graphene-based composite absorbing materials and the study of electromagnetic wave absorption properties have been carried out internationally. High specific surface area, excellent electrical properties and special two-dimensional structure all give the excellent potential of graphene as an ideal building block for new composite absorbing materials, but the comprehensive absorbing properties of graphene-based composite absorbing materials remain to be determined. improve.
The multi-component nano-particles are combined with graphene to alleviate the agglomeration of the graphene sheets to a certain extent, and more importantly, the prepared multi-component composite materials are multifunctional, and for the absorbing materials, each The materials of the components have different electromagnetic wave absorption characteristics, and the materials of the plurality of components can be combined with the advantages of the materials to achieve the complementary advantages. However, the disadvantages of the multi-component composites during preparation are also obvious, for example, poor compatibility of different interfaces, dispersibility and uniformity of multi-component materials are difficult to control, and the like.
Nevertheless, the design and preparation of multi-system graphene-based composite absorbing materials will continue to be the focus of research on new absorbing materials in the future. Graphene as a new substrate will also promote the development of stealth materials and electromagnetic protection. Research provides a greater role.
Aluminum Awning Window,Triple Glazed Windows,Basement Awning Window,Aluminum Awning Window Shades
Foshan City JBD Home Building Material Co.,Ltd. , https://www.jbdhome.com