Design Of Low Reflection Fibre Reinforced Electromagnetic Shielding Composites And Thermal Conductivity Functionalization

Electromagnetic radiation and electromagnetic pollution caused by wireless communications are becoming increasingly serious,seriously affecting the accuracy and lifetime of electronic equipment and endangering human health.Due to the rapidly growing demand for electronics in industry,military and aerospace,there is an urgent need for durable,high-performance electromagnetic shielding materials with adjustable electromagnetic interference（EMI）shielding properties.Fibre-reinforced polymer composites（FRPC）,which are lightweight,flexible in processing and easy to design with fabric layered structures,offer potential advantages in replacing heavy and corrosion-prone metals to protect humans and sensitive electronic equipment from electromagnetic radiation and external strikes.However,due to the fixed electromagnetic properties of continuous fabrics,tuning the electromagnetic properties of FRPC to achieve tunable and absorption-based electromagnetic shielding performance remains a great challenge.Here,super-efficient fibre-reinforced electromagnetic shielding composites with extremely low reflectivity,tunable electromagnetic shielding properties and strong mechanical properties are fabricated through a convenient modular assembly design of progressive conductive fabrics,and construct phonon transport channels to give the composites excellent heat transfer capabilities.Details of the research are as follows:（1）A simple method of modifying continuous fabrics with electromagnetic functional particles and a modular assembly of progressive conductive fabrics are used to achieve multilayer fibre-reinforced epoxy composites with extremely low reflectivity,tunable electromagnetic shielding and good impact resistance.Thanks to the orderly construction of aramid fibre（AF）-loaded triiron tetroxide（Fe₃O₄）hysteresis loss modules,UHMWPE fibre（UF）-loaded carbon nanotube（CNTs）dielectric loss modules and carbon fibre（CF）high-reflectivity modules,the impedance matching of the composite surface is effectively improved and the multiple reflection and absorption of electromagnetic waves within the material is enhanced.As a result,the fibre-reinforced resin matrix composite achieves extremely low electromagnetic wave reflection characteristics with ultra-high electromagnetic shielding efficiency,reaching an excellent electromagnetic shielding efficiency of 78.6 d B in the X-band frequency range with a low reflectivity of 0.06.In addition,due to the asymmetric structure of the high-performance fibre layers,the composite also exhibits excellent mechanical properties,with tensile strength of 283.1 MPa,bending strength of 141.2 MPa,and a low reflectivity of0.05.The composite also exhibits excellent mechanical properties with a tensile strength of283.1 MPa,a flexural strength of 141.2 MPa and a good impact resistance with an energy absorption of 15.9 J at 20 J impact.（2）The magnetic gradient of the impedance matching module is adjusted by controlling the loading of Fe₃O₄ magnetic nanoparticles on the surface of the Fe₃O₄@AF fabric to investigate the effect of the change of magnetic gradient on the impedance matching and electromagnetic shielding performance of the composite material with air.The effect of the change of magnetic gradient on the impedance matching degree and electromagnetic shielding performance of the composite material was investigated.The CNTs@UF fabric with different loading of CNTs was used to adjust the conductive gradient of the dielectric loss module to investigate the effect of the change of conductive gradient on the electromagnetic wave absorption ability of the composites.The composite material is used as a reflective module with high conductivity CF at the bottom for ensuring excellent electromagnetic shielding efficiency and enabling the return of electromagnetic waves.By regulating the conductive gradient and magnetic gradient of each functional module,a positive electromagnetic gradient is formed inside the composite material along the direction of electromagnetic wave incidence,which regulates the electromagnetic characteristics of the composite material and further validates the absorption-based electromagnetic shielding mechanism.The composite exhibits significant low reflection characteristics with R-values as low as 0.05 and a maximum electromagnetic shielding efficiency of 77.8 d B under changes in the electrical and magnetic gradients of the conductivity.At the same time,the composite material maintains good mechanical properties,with a tensile strength of 222.3 MPa,a flexural strength of 133.4 MPa and an energy absorption of 14.8 J at 20 J impact,demonstrating impact resistance.（3）Thermal conductivity is an important requirement for composites to be used in a wider range of applications.Therefore,based on the previous work,the structure of"A4U6C4"with the best shielding performance was chosen to explore the thermal conductivity of the composite.The h BN/STG thermal conductivity reached a maximum of 0.83 W·m^-1 K^-1.h BN/STG was pre-set on the surface of the modified fabric by spraying to form a coherent phonon transmission channel and encapsulated with epoxy resin to obtain a low-reflective composite with thermal conductivity.A multi-layer fibre-reinforced electromagnetic shielding composite with thermal conductivity was obtained.Thanks to the excellent thermal conductivity of the carbon-based material in the composite,a three-dimensional thermal conductivity network has been successfully built up internally as a bridge between the interlayer phonon transport channels,resulting in an interlayer thermal conductivity of up to 0.75 W·m^-1 K^-1.At the same time,with the progressive conductive modular design,the composite still maintains excellent electromagnetic shielding performance and low reflection characteristics of 75.8 d B and 0.09respectively,achieving a combination of low reflection,ultra-efficient shielding and interlayer thermal conductivity in FRPC.In addition,STG improves the impact resistance of the composite,achieving an energy absorption of 17.1 J at an impact of 20 J,demonstrating excellent protection against low velocity impacts.