291 results about "Absorption bandwidth" patented technology

The invention relates to the technical field of polymer composite materials, in particular to an aramid nanofiber low-frequency wave-absorbing composite material and a preparation method thereof. The aramid nanofiber low-frequency wave-absorbing composite material is prepared from the following raw materials: magnetic wave-absorbing fibers and aromatic polyamide nanofibers, the magnetic wave-absorbing fiber is prepared from a raw material system comprising FeCo magnetic wave-absorbing filler, aromatic polyamide fiber and a hyperbranched polysiloxane modifier. The aramid nanofiber low-frequency wave-absorbing composite material prepared by taking the magnetic wave-absorbing fibers and the aromatic polyamide nanofibers as raw materials not only has excellent mechanical properties (the tensile strength can reach 133 Mpa), but also has excellent wave-absorbing performance (the minimum reflection loss can reach-46.8 dB, and the low-frequency effective absorption bandwidth (EAB) is 2.24 GHz (5.52 GHz to 7.76 GHz). The method can be widely applied to the fields of communication and electronic equipment.

The invention provides an infrared broadband absorber. According to the invention, an efficient absorption structure is formed by introducing the non-antisymmetric Bragg structure layer and the metal material film with relatively high absorption rate. The phase change material and the dielectric material form an antisymmetric Bragg structure, the absorptivity of the device is further improved, and the MgF2 low-refractive-index layer is combined, and the materials and the thickness of each layer are optimized, so that effective reflection suppression and absorption enhancement of light with different wavelengths are realized. Compared with the prior art, the infrared broadband absorber is simple in structure, the absorption effect of 90% or above can be achieved within the ultra-wide range, the relative absorption bandwidth exceeds 152.8%, a great opportunity is provided for ultra-wide spectrum detection, a feasible technical approach is provided for ultra-wide spectrum confrontation and invisibility, and the infrared broadband absorber has the advantages of being high in practicability and wide in application range. And confrontation and stealth on active and passive composite sensing detection equipment are expected to be realized, and the application potential of the material in the fields of infrared absorption, infrared stealth, photothermal conversion, sensing and the like is expanded.

The invention discloses a silicon carbide / graphene composite material and a preparation method thereof, the composite material is of a three-dimensional network structure generated through in-situ reaction of multilayer graphene and silicon powder, silicon carbide nanowires in the structure are distributed on graphene sheets, the length of the silicon carbide nanowires is 1-5 microns, the diameter of the silicon carbide nanowires is 50-100 nm, and the silicon carbide nanowires are in a beta-SiC crystal form. The material is prepared through a carbon thermal reduction method, specifically, silicon carbide nanowires grow on the surface of graphene in situ, so that electromagnetic parameters and impedance matching characteristics of the material are optimized. The prepared composite material has the characteristics of light weight, high specific surface area, good dielectric loss and the like, and shows good broadband wave-absorbing performance in the frequency band of 2-18 GHz, the minimum reflection loss can reach-23.535 dB, and the effective absorption bandwidth reaches 1.498 GHz. The method is simple in process, low in energy consumption and suitable for large-scale production, and has wide application prospects in the fields of stealth technology, electromagnetic shielding and the like.

The invention provides N-O doped flower-like porous carbon microspheres as well as a preparation method and application thereof, and belongs to the technical field of electromagnetic wave absorbing materials. According to the invention, microspheres are coated by using a simple soap-free emulsion polymerization method, a complex multi-layer heterogeneous interface structure is realized, N and O atoms are introduced, and heteroatom doping is realized so as to improve the wave-absorbing performance; a unique flower-shaped structure is grown on the surface of the microsphere through a self-assembly process, and an exquisite flower-shaped porous carbon microsphere can be obtained through carbonization, so that an ingenious structure beneficial to multiple reflection and scattering generation is realized. Under the conditions that the mass ratio of the flower-like porous carbon microspheres to the paraffin is 1: 5 and the matching thickness is 2.5-3mm, the minimum reflection loss of the flower-like porous carbon microspheres is-40.8 to-48.0 dB, the optimal effective absorption bandwidth is 4.40 GHz, and the flower-like porous carbon microspheres have excellent electromagnetic wave absorption performance.

The invention provides a copper-doped silicon carbide composite material and a preparation method and application thereof, and relates to the technical field of electromagnetic wave absorbing materials. The preparation method of the copper-doped silicon carbide composite material provided by the invention comprises the following steps: performing arc plasma cracking on a precursor containing silicon and carbon to obtain the copper-doped silicon carbide composite material, the precursor containing silicon and carbon comprises organic chlorosilane; an anode adopted by the arc plasma cracking comprises copper. The prepared copper-doped silicon carbide composite material has excellent electromagnetic wave absorption performance and large effective absorption bandwidth.

The invention relates to the technical field of electromagnetic functional materials, in particular to a nested hexagonal resonant structure wave-absorbing metamaterial and a preparation method and application thereof. The wave-absorbing metamaterial with the nested hexagonal resonant structure sequentially comprises a metal resonant layer, a homogeneous wave-absorbing coating and a metal matrix layer, the metal resonance layer is formed by periodically arranging a plurality of metal resonance units on the surface of the homogeneous wave-absorbing coating in an array manner; each metal resonance unit is of a nested hexagonal structure formed by arranging a plurality of structural units, and each structural unit is a hollow hexagonal metal patch. Through the combination of the homogeneous wave-absorbing coating and the metal resonance layer, the wave-absorbing metamaterial with the nested hexagonal resonance structure not only can realize effective absorption of an S wave band under the sub-wavelength scale, but also is beneficial to widening the effective absorption bandwidth and improving the absorption efficiency, simplifies the complex layered stacking framework of a traditional broadband wave absorber from the structural design, and has the advantages of simple structure and low cost. The method has the engineering application advantages of high process adaptability, high preparation feasibility and the like.

The invention relates to a preparation method of a lightweight reduced graphene oxide-silicon dioxide electromagnetic wave absorbing material. The invention belongs to the technical field of electromagnetic wave absorbing materials. The invention solves the problems that the impedance of the existing reduced graphene oxide is mismatched, the density of the modified reduced graphene oxide composite wave-absorbing material is increased and the preparation method is complicated. The method comprises the following steps: performing chemical crosslinking on graphene oxide, silicon dioxide and a silane coupling agent to obtain a precursor; and drying and sintering the precursor. The material prepared in the invention has good impedance matching and abundant interface polarization and relaxation effects, can effectively reduce the reflection loss value of electromagnetic waves and increase the effective absorption bandwidth of the electromagnetic waves, and has excellent electromagnetic wave absorption performance. When the thickness of the material is only 1.5 mm, the RL of the material can reach-54.08 dB, and when the thickness of the material is 1.7 mm, the effective absorption bandwidth of the material can reach 5.12 GHz. In addition, the density of the material is only 0.083 g / cm < 3 >, the process is simple, and stable batch production can be realized.

The invention belongs to the field of protective materials, and particularly relates to a 3D printing high-performance porous silicon carbide ceramic wave-absorbing material and a preparation method and application thereof. The extrusion type 3D printing technology is combined with the reaction sintering and impregnation technology, the complex structure forming and the high-performance wave absorbing effect are achieved, the material prepared through the method has excellent mechanical performance and wave absorbing performance at the same time (the bending strength is larger than 15 MPa, the reflection loss minimum value at the frequency band of 2-18 GHz is larger than-25 dB, and the absorption bandwidth is larger than 3 GHz), and the material has the good application prospect. The method is suitable for military stealth engineering and other fields.

The invention discloses a broadband wide-angle polarization insensitive metamaterial wave absorber, which comprises three layers of structures, namely a microstructure unit layer, an FR-4 substrate layer and a metal bottom plate layer which are sequentially superposed from top to bottom, the whole microstructure unit layer is in axial symmetry and comprises four layers of structures, the four layers of structures sequentially comprise a rectangular metal resonance piece, four fan-shaped metal resonance pieces, a first opening metal resonance ring and a second opening metal resonance ring from inside to outside, the first opening metal resonance ring and the second opening metal resonance ring are concentric opening circular rings, and the circle centers of the first opening metal resonance ring and the second opening metal resonance ring are the centers of the rectangular metal resonance pieces. The circle centers of the four fan-shaped metal resonance sheets are located at the four corners of the rectangular metal resonance sheet respectively, the arc angles of the four fan-shaped metal resonance sheets are 90 degrees, and the edges of the four fan-shaped metal resonance sheets are located on the extension lines of the edges of the rectangular metal resonance sheet respectively. The first opening metal resonance ring and the second opening metal resonance ring are respectively provided with two openings along the transverse axis and the longitudinal axis, and the width of the openings is equal to the side length of the rectangular metal resonance piece. The wave-absorbing material has wider wave-absorbing bandwidth and better absorbing performance.

The invention belongs to the technical field of preparation of wave-absorbing materials, and particularly relates to a cobalt-based nitrogen-doped carbon nano composite material with a hollow cubic structure as well as a preparation method and application thereof. Comprising the following steps: taking ZnCo-ZIF with a nano cubic structure as a core, coating ZnCo-ZIF with polydopamine by adopting a precipitation method to form a precursor with a core-shell structure, and carbonizing the precursor at 800-900 DEG C to obtain the cobalt-based nitrogen-doped carbon nano composite material with the hollow cubic structure. According to the invention, the dielectric loss capability can be enhanced by using the conductivity and interface polarization effect of the coated carbon layer, and the Co particles introduce strong magnetic loss; meanwhile, due to interface polarization caused by abundant heterogeneous interfaces existing between the Co particles and the coating carbon layer, between the magnetic particles and the carbon nanotubes and between the carbon matrix and the carbon nanotubes in the composite material, the impedance matching characteristic can be improved, and high reflection loss and wide effective absorption bandwidth can be achieved under the low matching thickness.

The invention relates to the technical field of wave-absorbing metamaterials, in particular to a lattice element sequential wave-absorbing metamaterial and a preparation method thereof.The wave-absorbing metamaterial comprises a substrate and a lattice structure layer, and the lattice structure layer is formed by arranging a plurality of structure units on the surface of the substrate in a periodic array mode; each structural unit is formed by arranging a plurality of dot matrix elements; the dot matrix elements are sheet-shaped magnetic dot matrix elements. The wave absorbing crest of the dot matrix superstructure moves towards high frequency, and RLlt; and the effective absorption bandwidth of-10dB is improved. The wave-absorbing strength and bandwidth are improved, and the problem that an existing homogeneous wave-absorbing coating is difficult to have the characteristics of small thickness and light weight while the bandwidth is improved is solved.

The invention discloses a preparation method of a Fe3O4 modified phosphorus-doped carbon-based porous wave-absorbing material constructed on the basis of a multi-component strategy. The preparation method comprises the following steps: firstly, preparing a phosphorus-doped carbon-based porous nano material through a freeze-drying method and a sacrificial template method, then obtaining a Fe3O4 intermediate through oil bath, and finally reducing for 6 hours in an Ar atmosphere to obtain the Fe3O4-modified phosphorus-doped carbon-based porous wave-absorbing material, namely Fe3O4 (at) P-NCP. Based on a good magnetic loss mechanism of the material, a synergistic effect of dielectric loss and magnetic loss is provided for electromagnetic wave absorption. And meanwhile, the porous structure ensures that incident electromagnetic waves can form multiple reflections in the porous structure. The material has the advantages of good microwave absorption performance, thin matching thickness, wide effective absorption frequency band and the like. A good foundation is provided for development of porous materials, and a good design thought is provided for preparation of electromagnetic wave absorbing materials. The good microwave absorption performance of the material can play a good role in electromagnetic radiation and pollution, and the material has a wide application prospect.

The invention discloses a carbonyl iron powder-graphite electromagnetic wave absorption composite material and a preparation method thereof. The carbonyl iron powder-graphite electromagnetic wave absorption composite material is composed of superfine spherical carbonyl iron powder and flake graphite. According to the method for preparing the carbonyl iron powder-graphite electromagnetic wave absorbing composite material, a room-temperature dry ball milling technology is utilized, various carbonyl iron powder-carbon composite wave absorbing materials can be flexibly prepared, the preparation process is simple, the condition is mild, consumed time is short, use of a large amount of solvent is avoided, and the method is economical and environmentally friendly. According to the method for preparing the carbonyl iron powder-graphite electromagnetic wave absorption composite material, cheap carbonyl iron powder and flake graphite are adopted as raw materials, the raw materials are cheap and easy to obtain, and the method is suitable for actual industrial application. The carbonyl iron powder-graphite electromagnetic wave absorption composite material provided by the invention has large reflection loss and absorption bandwidth under the condition of low thickness, and can effectively absorb electromagnetic waves.

The invention provides a middle and far infrared broadband metamaterial absorber and a design method thereof. The middle and far infrared broadband metamaterial absorber comprises metamaterial absorption units which are arranged in a periodic array mode. The whole metamaterial absorption unit is square and comprises a top metal layer, a dielectric layer and a bottom metal layer from top to bottom in sequence. The top metal layer is attached to the upper surface of the dielectric layer and is formed by arranging eight metal sheets according to a certain arrangement mode, namely a circular metal sheet which is arranged at the central position of the upper surface of the dielectric layer, and the center of the circular metal sheet is aligned with the center of the upper surface of the dielectric layer; three annular metal sheets concentric with the circular metal sheet surround the periphery of the circular metal sheet, and gaps exist between the circular metal sheet and the annular metal sheet on the innermost layer and between the annular metal sheets on the adjacent layers from inside to outside. And the four metal square sheets with the same size are respectively arranged at four corners of the upper surface of the dielectric layer. The absorption bandwidth is greatly prolonged, and perfect absorption of a target wave band can be infinitely approached by adjusting geometric parameters of the absorber.

The invention discloses an aerogel metamaterial capable of switching electromagnetic wave absorption and deflection reflection wave beam and a preparation method thereof, and the preparation method is characterized in that a metamaterial unit with a loose structure is arranged and comprises a first layer of rectangular pyramid, a second layer of quadrangular frustum pyramid, a third layer of quadrangular frustum pyramid and an internal pyramid cavity; the first layer of rectangular pyramid, the second layer of quadrangular frustum pyramid, the third layer of quadrangular frustum pyramid and the internal pyramid cavity are on the same center line; the bottom surface of the internal pyramid cavity is close to the bottom surface of the third-time quadrangular frustum pyramid, and the vertex of the internal pyramid cavity is close to the vertex of the first-layer quadrangular pyramid; the preparation method comprises the following steps: pouring mixed dispersion liquid containing conductive / magnetic functional components and cellulose microfibers into a mold manufactured according to a set structure, freezing, and then freeze-drying to obtain the metamaterial unit. The obtained aerogel metamaterial solves the problems that the effective absorption bandwidth of aerogel with adjustable electromagnetic wave absorption performance is difficult to substantially break through, and the aerogel cannot have both electromagnetic wave absorption performance and deflection reflection beam performance at the same time.

The invention discloses a preparation method of a magnetic doped nanofiber derived carbon aerogel wave-absorbing material with a gradient pore structure and application of carbon aerogel, and belongs to the field of microwave wave-absorbing materials. The aerogel microstructure is controlled by regulating and controlling the parameters of the arched ice template and the content of the magnetic material precursor, and the lightweight carbon aerogel material is obtained through arched ice template freezing, freeze drying and carbonization. The gradient pore structure of the carbon aerogel improves impedance matching and promotes microwave reflection and scattering; the nano cellulose, the aramid nano fiber and the metal organic framework cooperatively optimize the polarization loss and magnetic loss performance by constructing a multi-element heterogeneous interface. Due to the characteristics, the carbon aerogel has excellent wave absorbing performance. According to the present invention, the carbon aerogel has the optimal reflection loss value of-57.03 dB when the frequency is 2-18 GHz and the thickness is 2.8 mm, and the effective absorption bandwidth (RL < =-10 dB) of the microwave absorption is 6.76 GHz, such that the carbon aerogel has the good application prospect in the electromagnetic wave field, and can simultaneously achieve the broadband and the strong absorption of the microwave under the low thickness.

The invention provides a broadband absorption and transmission integrated frequency selective surface with a high selection characteristic, which comprises a first loss layer, a second loss layer and a frequency selection layer, and is characterized in that the first loss layer and the second loss layer realize a transmission band with the high selection characteristic and the broadband characteristic at the same time by using dual-order resonance; the second loss layer and the frequency selection layer are cascaded to realize the absorption and transmission integrated characteristic, and the first loss layer is used for improving the low-frequency and high-frequency wave absorption characteristics and expanding the wave absorption bandwidth. Under the combined action of the first loss layer, the second loss layer and the frequency selection layer, wave transmission within the frequency band of 7.72-11.89 GHz and wave absorption within the frequency band of 1.96-7.12 GHz and the frequency band of 12.95-17.33 GHz are achieved. The antenna has high selection characteristics and broadband characteristics, can effectively suppress interference of external electromagnetic waves of other frequency bands or electromagnetic waves of a frequency band close to a communication frequency band on communication, can reduce the radar cross section of a target, and facilitates target stealth.

The invention provides a broadband wave-absorbing material with a multilayer structure, and the broadband wave-absorbing material with the multilayer structure is formed by depositing a conductive carbon-based material or a carbon-based magnetic composite material on the surface of an insulating substrate material to form wave-absorbing sheets, and then stacking the prepared wave-absorbing sheets to construct the broadband wave-absorbing material with the multilayer structure. The broadband wave-absorbing material with the multilayer structure prepared by the invention has excellent broadband wave-absorbing performance, and can effectively absorb microwaves in S, C, X and Ku frequency bands (2-18GHz) (RL is less than-10dB) at the same time. According to the invention, the problem that the impedance matching of the wave-absorbing material is poor due to the fact that electromagnetic waves cannot enter the material due to good conductivity of a carbon-based material is solved, the problems that the existing wave-absorbing material is complicated in process, narrow in effective absorption bandwidth, incapable of simultaneously realizing multi-band effective absorption and the like are solved, and a wide prospect is provided for the design and application of a novel wave-absorbing material.

The invention discloses a method for preparing wave-absorbing integrated SiC / Si3N4 composite ceramic with high strength and toughness in a short period. Silicon nitride, silicon carbide, a sintering aid and other powder are mixed and dispersed for a short time through high-strength mechanical vibration, and the high-strength and high-toughness wave-absorbing composite ceramic is prepared after direct sintering. According to the preparation process, the preparation steps of ball milling, drying, sieving and the like are avoided, the preparation process period of the SiC / Si3N4 composite ceramic can be shortened from 1 week to 1 day, and the labor intensity is reduced; according to the preparation process, an organic solvent and a grinding medium do not need to be introduced, and pollution to samples and the environment is avoided; more importantly, the preparation process can effectively disperse the nano-powder and the whiskers, avoids the damage of a grinding medium to the powder such as particles and the whiskers, and enhances the strength and toughness of the ceramic material. The bending strength of the prepared SiC / Si3N4 composite ceramic can reach up to 1007 MPa, the fracture toughness reaches 11.63 MPa.m < 1 / 2 >, the minimum reflection loss of electromagnetic waves is-27 dB, and the wave absorbing bandwidth is 2.28 GHz.

The invention discloses a combined rectangular cavity broadband wave-absorbing structure loaded with a gradient metal band array, the wave-absorbing structure is formed by sequentially arranging a plurality of wave-absorbing units, and each wave-absorbing unit comprises four rectangular cavities with different sizes, the gradient metal band array and an NDDP3 wave-absorbing material; the four rectangular cavities with different sizes are sequentially arranged according to the sizes; the NDDP3 wave-absorbing material is impregnated on the surfaces of the four rectangular cavities; and the gradient metal strip arrays are respectively loaded on four side surfaces of the three rectangular cavities with smaller sizes. The absorption bandwidth of the wave absorber can be widened by combining the rectangular cavities of different sizes, meanwhile, the problem that the wave absorbing performance of the combined rectangular cavity in a low-frequency band is poor can be solved by loading the gradient metal band array, and the wave absorber has good wave absorbing performance in the frequency band of 2-40 GHz; and meanwhile, under the condition of large-angle oblique incidence, the microwave absorbing material still has a relatively wide microwave absorbing bandwidth.

The invention relates to an ultra-wideband flexible transparent ultra-thin metamaterial wave absorber, which solves the problems of low profile, wide bandwidth and insensitive polarization and angle of the wave absorber, and belongs to the field of electromagnetic metamaterials. The antenna comprises a first dielectric layer, a second dielectric layer and a third dielectric layer which are sequentially arranged from bottom to top, the first dielectric layer and the third dielectric layer are PET substrates; the second dielectric layer is a PVC layer; the upper surface of the third dielectric layer is provided with conductive film units which are arranged periodically, and the lower surface of the first dielectric layer is covered with a conductive film. The upper surface of the third dielectric layer is provided with four conductive thin film units which are periodically arranged, and each conductive thin film unit is an ITO resistive thin film with a cross-shaped pattern. According to the invention, the flexible PVC is used as the dielectric substrate, the PET is used as the reflection bottom plate and the resonance layer, and the conductive film pattern of the resonance layer is optimally designed, so that the absorption performance of which the absorption rate is greater than 90% is realized within the frequency range of 12.02-102.91 GHz, and the relative absorption bandwidth can reach 158.1%.

The invention belongs to the technical field of electromagnetic wave absorption, and particularly relates to a heterogeneous electromagnetic wave absorption composite nanofiber and a preparation method thereof, and the composite nanofiber comprises a matrix formed by carbon nanofibers and CoS2 nanoparticles dispersed on the surface or inside the carbon nanofibers in an embedded form. The composite nanofiber disclosed by the invention shows excellent electromagnetic wave absorption performance in a relatively wide frequency range, the minimum reflection loss reaches-59.84 dB, the effective absorption bandwidth is 4.9 GHz, and particularly, the composite nanofiber shows excellent wave absorption performance in an X wave band (8-12 GHz). Therefore, the material is suitable for electromagnetic wave interference suppression and information security protection of electronic equipment. In addition, the material is prepared through electrostatic spinning and a high-temperature treatment process, the process is simple and extensible, large-scale production is easy to achieve, and the material has high industrial application potential.

The invention discloses a nano (FeCoNiCuMn) 3O4-FeNi / rGO composite wave-absorbing material as well as a preparation method and application thereof, and belongs to the technical field of wave-absorbing composite materials. According to the (FeCoNiCuMn) 3O4-FeNi / rGO composite wave-absorbing material prepared by the preparation method provided by the invention, the graphene structure is complete, the particle size of oxide particles is uniform and ranges from 50nm to 300nm, and abnormal growth of oxide crystal grains / coarsening of the oxide particles is effectively avoided; meanwhile, the wave-absorbing coating has the advantages of being low in thickness, high in wave-absorbing capacity and wide in absorption bandwidth, the minimum reflection loss is-40.6 dB when the thickness is 2 mm, the absorption bandwidth is 5.4 GHz, and the application requirement of the wave-absorbing coating can be met; the preparation method is simpler, easy to operate and suitable for large-scale production; a new thought can be provided for further improving the wave-absorbing performance of the wave-absorbing material.

The invention discloses an ultra-wideband three-dimensional metamaterial wave absorber with large angular domain stability, which comprises M * N wave absorber units, and is characterized in that M is more than or equal to 10 rows, N is more than or equal to 10 columns, and each wave absorber unit sequentially comprises an upper-layer three-dimensional vertical resistive film patch cylindrical structure, a bottom square resistive film structure or a metal bottom plate II from top to bottom, a lower-layer three-dimensional vertical resistive film patch cylindrical structure and a lower-layer square resistive film patch cylindrical structure from top to bottom. And the cylindrical structure of the upper-layer three-dimensional vertical resistive film patch is adhered to the bottom square resistive film structure through optical cement or adhered to the metal bottom plate II. According to the invention, the effects of ultra-wide absorption bandwidth, large angular domain stability and polarization insensitivity can be realized.

The invention relates to the technical field of aerogel materials, in particular to a carbon-rich SiC-coated Si3N4 double-network aerogel and a preparation method thereof. The double-network aerogel comprises an inner framework and an outer framework, the inner framework is a SiC network, the outer framework is a Si3N4 network, the double-network aerogel is formed by interweaving the SiC network and the Si3N4 network, the SiC network and the Si3N4 network are rich in in-situ carbon, and the content of the in-situ carbon in the Si3N4 network is far smaller than that of the in-situ carbon in the SiC network. The aerogel disclosed by the invention successfully integrates multiple key properties, wherein high porosity and low thermal conductivity ensure excellent thermal insulation capability; the reflection loss reaches-60dB to the minimum, and the effective absorption bandwidth reaches 5GHz, so that the excellent broadband wave-absorbing performance is proved; the compressive strength of the material can reach 14 MPa or above, excellent mechanical reliability is shown, and an ideal solution is provided for electromagnetic protection and thermal management of high-end equipment.

The invention relates to an ablation-resistant, heat-insulation and wave-absorbing integrated fiber-reinforced silicon resin composite material, which belongs to the technical field of wave-absorbing materials, and comprises a heat-insulation area and a wave-absorbing area which are sequentially arranged from top to bottom, the wave absorbing area comprises a magnetic modified fiber single sheet and / or an electric modified fiber single sheet; each electrically-modified fiber single sheet comprises electrically-modified fibers and matrix resin, wherein the peripheries of the electrically-modified fibers are coated with electrically-coated modified layers, and gaps of the electrically-modified fibers are filled with the matrix resin; each magnetic modified fiber single sheet comprises a magnetic modified fiber and matrix resin, wherein the periphery of the magnetic modified fiber is coated with a magnetic coating modified layer, and gaps of the magnetic modified fiber are filled with the matrix resin. The modified layer is coated on the periphery of the fiber to form regular and ordered wave-absorbing areas, regular and ordered refraction and reflection areas are formed in gaps among the fibers, interfaces with different absorptivity are formed between the wave-absorbing areas and the refraction and reflection areas due to different materials, the absorption effect is improved, the absorptivity and the absorption bandwidth are improved, and the service life of the fiber is prolonged. And meanwhile, the problems of poor dispersion uniformity and low production efficiency of the wave-absorbing material are solved.

The invention belongs to the field of electromagnetic wave absorbing materials, and particularly relates to a thin broadband composite wave absorber based on a frequency selective surface. According to the invention, the wave-transparent layer is added in the middle of the multi-layer magnetic material, the mindset of simply stacking the same type of materials in the traditional multi-layer wave-absorbing structure is broken, and the wave-transparent layer is introduced to change the original characteristic that the impedance gradually changes in sequence; meanwhile, a magnetic wave-absorbing material, a frequency selection surface and a medium matching layer are subjected to composite design, the frequency selection surface generates an electromagnetic coupling effect at high frequency, phase and impedance conversion of electromagnetic waves in a multi-layer structure is controlled, and efficient impedance matching and electromagnetic wave energy dissipation in a broadband are achieved through electromagnetic absorption and interference cancellation; and an excellent wave absorbing effect is achieved. The total thickness of the composite wave absorber ranges from 0.064 lambda to 0.1 lambda, the-10 dB absorption bandwidth ranges from 3.3 GHz to 18 GHz, and the relative bandwidth reaches 138%; and meanwhile, the wave absorber has a wide angular domain characteristic under oblique incidence, and a novel thin broadband composite wave absorber scheme is provided.

The present invention belongs to the field of electromagnetic wave absorbing materials, and specifically provides a multifunctional terahertz wave absorbing fabric based on MXenes materials and a preparation method thereof, aiming to solve the problems of narrow absorption bandwidth, single function, and easy oxidation existing in MXenes absorbing materials; based on the fiber microstructure in the matrix, combining the conductance loss and Ohmic loss of MXenes materials, waterborne polyurethane (WPU) is sprayed on the surface of the absorbing fabric for modification to realize a multifunctional terahertz absorbing material. The absorption efficiency can reach 100% under electromagnetic waves of 0.3 - 1.2 THz. At the same time, the water contact angle and rolling angle reach 151.3° and 0° respectively, with good self-cleaning performance, and the absorption performance of the fabric remains above 99% after self-cleaning. In addition, it has excellent acid and alkali resistance and environmental adaptability.

The invention relates to the technical field of coatings for absorbing electromagnetic waves, and discloses a preparation method of an NZSP wave-absorbing coating with a three-dimensional periodic structure, and the preparation method comprises the following steps: step 1, obtaining NZSP spherical powder; step 2, spraying NZSP spherical powder on the substrate to obtain a first coating; 3, determining the shape of the periodic unit; the plurality of periodic units are arranged into a periodic structure according to a regular space array; step 4, performing laser sintering on the NZSP spherical powder spread on the first coating; 5, laying powder layer by layer, and carrying out accumulative sintering until a preset height is reached, so as to obtain a second coating; and 6, forming the NZSP wave-absorbing coating with a three-dimensional periodic structure by the first coating and the second coating. The first coating and the second coating are manufactured on the basis of the NZSP spherical powder, and the method has outstanding advantages in weight reduction application; the absorption bandwidth of the NZSP wave-absorbing coating is expanded through the macroscopic design of the periodic structure, the wave-absorbing performance is improved, and the NZSP wave-absorbing coating is suitable for the field of aerospace.

To provide an electromagnetic wave absorber having a high electromagnetic wave absorption characteristic, and a wide absorption band width.SOLUTION: An electromagnetic wave absorber includes a structure that a first dielectric body and a second dielectric body are laminated, and in which a complex dielectric constant in a maximum absorption frequency of the first and second dielectric bodies satisfies the following formulas (1) and (2): 8≤ε1'-ε2'≤40...(1), and 5.5≤ε1"-ε2"≤25...(2) (In formula (1), ε1' is a real part of the complex dielectric constant of the first dielectric body, and ε2' is a real part of the complex dielectric constant of the second dielectric body. In formula (2), ε1" is an imaginary part of the complex dielectric constant of the first dielectric body, and ε2" is an imaginary part of the complex dielectric constant of the second dielectric body.)SELECTED DRAWING: None