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Nano wave absorbing composites and their applications in stealth aircraft

nanotechnology refers to the arrangement and composition of atoms/molecules on the surface of nanoparticles through specific technical design, so that they produce a special structure and perform special technical performance or function. The emergence of nanotechnology shows that the objects of production and scientific research in the future will develop to a smaller size and deeper level, from the micron level to the nano level. The future development goal of nanotechnology is to manipulate atoms and molecules to build nanoscale devices or products with certain functions according to the needs of checking that the dust cover should be intact. The FRP industry is our largest utilization market. In this system composed of a small number of electrons, atoms or molecules, the understanding of new laws and how to manipulate or combine them have become one of the main directions of nanotechnology research

nano wave absorbing composite

1 definition

in composite materials, there is usually a continuous phase, which is called matrix; The other phase is dispersed phase, which is called reinforcing material. Nano functional composite material refers to a multiphase solid material composed of two or more substances with different physical or chemical properties, at least one of which is nano particles, grains, films or fibers in the one-dimensional direction. Such nano particles, grains, films or fibers must have unique properties different from ordinary large-scale materials, and the composites composed of these materials are usually called nanocomposites. This kind of composite material is also called nano functional composite material because it has some peculiar functions. Nano wave absorbing composites are a kind of nano functional composites that can absorb the electromagnetic wave energy projected onto its surface and convert the electromagnetic wave energy into heat energy or other forms of energy through the dielectric loss of materials

2 working principle of nano absorbing composites

radar waves are first transmitted to the free space with impedance Z0, and then projected onto the surface of the material with impedance Z1. At this time, radar waves are partially reflected. The reflection coefficient r is obtained from the following formula:

r= (z0-z1)/(z0+z1)

where, Z0=( μ 0/ε 0)1/2,Z1=( μ 1/ε 1)1/2。 μ 0 μ 1 is the permeability of free space and absorbing material respectively; ε 0 and ε 1 is the dielectric constant of free space and microwave absorbing material respectively. In order not to generate reflection, the reflection coefficient must be zero, that is, z0=z1 or μ 0/ε 0= μ 1/ε 1。 This is the impedance matching principle of ideal absorbing materials. Due to the material in reality μ Often less than μ 0, and ε Far greater than ε 0, it is difficult to meet the above requirements, so the impedance gradual transition and multi-layer structure design methods are often used in actual design to approximately achieve impedance matching

3 characteristics of nanocomposites

nanocomposites have a large proportion of interface components, a high proportion of atoms on the surface of particles, and an increase in unsaturated bonds and hanging bonds. The existence of a large number of dangling bonds polarizes the interface and widens the absorption band. High specific surface area causes multiple scattering. The quantum size effect of nano materials makes the energy levels of electrons split, and the split energy level spacing is in the energy range of microwave, creating a new microwave absorption channel for nano materials. Under the radiation of microwave field, the movement of atoms and electrons in nano materials intensifies, which increases the efficiency of converting electromagnetic energy into heat energy, thus improving the absorption performance of electromagnetic waves

application of nano wave absorbing composites

the stealth technology of modern aircraft, in addition to using thermal infrared and self electromagnetic stealth methods, the main means is to use new wave absorbing materials. Nano absorbing composites are being developed as a new generation of stealth materials. According to its material forming process and bearing capacity, nano absorbing composites can be divided into structural type and coating type

1 structural nano radar absorbing composites

structural nano radar absorbing composites are structural composites formed by dispersing absorbers in structural composites reinforced by special fibers (such as quartz fiber, glass fiber, etc.), which have the dual functions of carrying and absorbing radar waves. Figure 1 shows a wave absorbing composite structure for the leading edge of an aircraft wing. Its skin is made of glass fiber reinforced plastic with a thickness of 0.76mm, and its aerodynamic shape is guaranteed by rigid foam material without absorbent; The inner side of the rigid foam is coated with a coating filled with aluminum powder, which can scatter part of the incident electromagnetic waves to other directions without returning to the radar receiving station; The foam material is filled with absorbent and has a certain gradient in order to better attenuate the incident electromagnetic wave; The whole structure is mainly supported by wing beams. The leading edge of the aircraft wing shown in Figure 2 is a broadband absorbing structure. The structural absorbing material is a three-layer structure, and its inner and outer skin is very thin (0.5 ~ 1.5mm). The inner skin is made of reinforced plastic composed of resistance fabric. The inner skin under stress in the structure is usually made of metal plated glass cloth. Light absorbing materials are filled between the inner and outer skin, and absorbing components are added in the manufacturing process. The filler concentration in the interlayer can be changed to obtain a good match

Figure 3 shows the structure of the absorbing grid used in the inlet of the jet engine. Among them, the absorbing band is made of resin matrix composites reinforced by glass fiber and impregnated with absorbent, and the protective layer is general FRP material. The whole grid structure is fixed at the inlet lip, which can effectively attenuate the incident radar wave

2 coated nano radar absorbing composite material

is usually coated on the target surface after mixing absorbent and binder to form a radar absorbing composite coating. Coating nano microwave absorbing composites can be made by coating this kind of coating on the target surface. At present, the multi-layer coating microwave absorbing materials that are widely studied are 2-layer and 3-layer microwave absorbing coatings composed of electric loss and magnetic loss materials. In order to cope with the different working methods of different radars, stealth aircraft have begun to selectively use nano radar absorbing materials, that is, nano powders are evenly dispersed into the aircraft surface coating to enhance the efficiency of absorbing radar electromagnetic waves. Some developed countries are carrying out research on active cancellation technology, that is, using radar absorbing materials to absorb most of the radar waves first, leaving a small amount of reflected waves, and then using the main spar dynamic cancellation technology to cancel them all, so that the radar will completely lose its function. The United States has developed a series of thin-layer ferrite absorbing composites, which have been successfully applied to the fuselage, wing and V-shaped vertical tail outer surface of F-117A stealth fighter, and achieved good stealth effect. In the 1991 Gulf War, F-117A dispatched more than 1000 sorties without any damage, so as to maximize the purpose of making stealth aircraft kill enemy personnel and protect their own safety


in recent years, with the advent of new advanced detectors such as advanced infrared/ultraviolet detectors and millimeter wave radar, new and more severe challenges have been posed to the original aircraft stealth technology. One type of material has been difficult to meet the comprehensive requirements of "thin, light, wide and strong" proposed by aircraft stealth technology. Instead, a variety of microwave absorbing materials need to be combined in various forms to obtain the best stealth effect. Nano particles such as ferromagnetic materials Mn Zn, Ni Zn ferrite and ferroelectric BaTiO3 can greatly improve the microwave absorption performance; Using the organic-inorganic nano material composite technology, the electromagnetic parameters of the composite can be easily adjusted to meet the requirements of impedance matching and achieve weight reduction to the greatest extent. Therefore, nano microwave absorbing composites will become an important field in the research and development of microwave absorbing composites in the future. (end)

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