| The serious electromagnetic wave pollution caused by the surge of electronic devices has promoted the huge demand and rapid development of electromagnetic interference（EMI）shielding materials and technologies.At present,the development trend of EMI shielding materials is embodied in dimensional large,mechanical flexibility,and structural lightweight.Based on the application demand and development trend of EMI shielding materials,this paper takes the warp-knitted metal mesh as the textile substrate material and carries out research from the aspects of yarn knittability evaluation,warp-knitted structure optimization,multi-phase composite system construction,and EMI shielding performance simulation.The main research contents include the optimization of the knittability of ultra-fine metal wire,the structural design of warp-knitted metal mesh,the preparation of metal-carbon-polymer composites,and the finite element analysis of the EMI shielding performance of the warp-knitted metal mesh and its composites.（1）The knittability of ultra-fine wire was studied,the characterization method of bending stiffness of ultra-fine wire was comprehensively discussed,the influence rule of yarn structure parameters and dynamic cyclic load on the knittability of metal wire was clarified,the monofilament diameter,number of twist strands and twist pitch parameters of metal wire were optimized,and the stiffness evolution and performance attenuation mechanism of ultra-fine wire under dynamic loading were explored.Based on typical elastic mechanic theory and dynamic bending response behavior,a dynamic three-point bending model was established.The three-point bending method can accurately simulate the bending load of metal wire at each stage of the actual knitting process and is suitable for evaluating the bending behavior of metal wire.The bending stiffness of the metal wire is positively correlated with the wire diameter in an exponential order.The appropriate ultra-fine diameter design is conducive to optimizing the knittability of the metal wire.To meet the requirements of the successful knitting of the metal wire,the wire diameter is optimized to 0.027 mm.The plying and twisting process can effectively improve the knittability of ultra-fine metal wires.For double-stranded and triple-stranded ultra-fine metal wires,the twist pitch of 4.5 mm is conducive to the smooth knitting of the yarn.In addition,under cyclic bending and reciprocating friction loading,the ultra-fine metal wire exhibits plastic deformation,irreversible structural response,and performance degradation.Mono-strand and triple-stranded metal wire possess good performance stability under dynamic loading and meet the requirements of smooth knitting,which is conducive to being the candidate yarn type for EMI shielding fabrics.（2）Four novel warp-knitted structures with two bars of one in one out threading mode have been designed.The metal mesh composed of continuous ultra-fine metal wire was prepared through warp knitting technology.The EMI shielding mechanism of the warp-knitted metal mesh was investigated.The effects of the warp-knitted structure of the metal mesh,the material of the metal wire,and the parameters of warp run-in on the mechanical properties,electrical properties,and microwave shielding properties of the flexible warp-knitted metal mesh are systematically investigated.When the structure of the metal mesh is open warp satin,metal mesh fabric exhibits the thinner thickness（0.15 mm）,the lightest weight（22.51 g/m2）,the outstanding mechanical isotropy（λ=0.045）,the strong normal external bearing capacity（20.20 N）,the excellent mechanical flexibility（17.96 MPa）,the lowest resistivity(3.85×10-3 ohm/sq),and the strongest EMI shielding ability（-19.29 d B）.Thanks to the excellent conductivity and EMI shielding performance,gold-plated molybdenum wire mesh and stainless-steel wire mesh can be used in the field of wearable protection and engineering protection,respectively.The parameters of warp run-in can adjust the EMI shielding effectiveness of the warp-knitted metal mesh.When the warp run-in parameter is set to 2580 rack,the prepared metal mesh shows the highest average EMI shielding effectiveness（-25.52 d B）.In addition,even under the large strain tensile deformation and the periodic bending and torsion deformation,the retention rate of EMI shielding efficiency of warp-knitted metal mesh is always greater than 70%,showing ideal EMI shielding stability.The conductive warp-knitted metal mesh fabric has a yarn diameter of the micrometer scale and a structural unit of the millimeter scale.It has the characteristics of the lightweight structure,industrial production scale,good mechanical stability,excellent flexibility,permanent conductivity,and excellent microwave reflection attenuation,which shows great potential in flexible EMI shielding devices for clothing and engineering.（3）A metal/polymer/carbon three-phase composite structure was designed.The warp-knitted metal mesh-based composite fabric was prepared by solution mixing and blade coating process using stainless steel（SS）warp-knitted mesh fabric,polyurethane（TPU）matrix,and carbon nanotube（CNT）filler particles as raw materials.The effects of CNT filler concentration and TPU/CNT coating thickness on the electrical property,EMI shielding property,electrothermal conversion property,and mechanical property of the composite fabric were systematically studied.The addition of CNT contributes to constructing a unique inter-connected conductive and reinforcement network in the TPU polymer matrix on the SS warp-knitted fabric substrate,and can effectively adjust the mechanical performance,EMI shielding effectiveness,electrical conductivity,and electrothermal conversion capability of the composite fabric.The heterogeneous composites combine the microwave-reflecting characteristic of the metal mesh and the microwave-absorbing features of the CNT nanofiller.The effective EMI shielding efficiency of22.01 d B in the X-band frequency（8.2-12.4 GHz）is achieved,and the corresponding shielding efficiency enhancement exceeds 263%relative to pure metal mesh.After repeated 1000 bending-relaxing deformations,the EMI shielding effectiveness of the composite fabric maintains nearly90%of the initial value.In addition,the collaborative conductive network has excellent conductivity（1348 S/m）and outstanding electrothermal conversion capability（91.1℃）.The construction of multi-scale carbon-metal heterostructure contributes to endowing the composite fabric with excellent electrical conductivity,effective EMI shielding performance,excellent mechanical performance,and efficient electrothermal conversion performance,which opens a new path for the structural design of flexible,lightweight,large-scale,and multi-functional EMI shielding materials for architecture canopy.（4）A modeling method of scanning the key points of textile structure was developed,and the three-dimensional（3D）high-precision models of warp-knitted metal mesh and its composite fabric were constructed.The influence of warp-knitted structure,wire material,and microstructure parameters on the EMI shielding performance of warp-knitted metal mesh and its composite fabric was analyzed using the electromagnetic field simulation software HFSS.The 3D fabric model is highly similar to the real warp-knitted structure,which lays the foundation for the accuracy of subsequent electromagnetic performance simulation.The simulation value of the EMI shielding effectiveness of the open lap atlas metal mesh is the highest（-18.24 d B）.Each wire interwoven area is a possible micro-shielding field,which is always the area with the largest electric field intensity and is prone to internal multiple reflection effects.The EMI shielding performance of the metal mesh is positively correlated with the conductivity of the metal wire material.The gold-plated molybdenum wire mesh exhibits excellent electromagnetic wave attenuation capability（-23.69 d B）.The simulation value of EMI shielding effectiveness of composite fabric with CNT loading of 10 wt%and TPU/CNT coating thickness of 0.20 mm is 22.23 d B,which is 212%higher than that of uncoated SS warp-knitted mesh,which verifies the effectiveness of metal/polymer/carbon three-phase hybrid system in shielding electromagnetic waves.The visualization function of EMI shielding performance in the finite element simulation software is helpful to explore the electromagnetic response mechanism of fabrics.The mean value of EMI shielding effectiveness simulated by the finite element model is close to the measured mean value.The predicted influence mechanisms of the fabric structure,wire material,and microstructure parameters on the EMI shielding performance of warp-knitted metal mesh and its composite fabric are consistent with the experimental results.The feasibility and effectiveness of the finite element simulation method in the structural design and performance prediction of warp-knitted metal mesh and its composite fabric are verified. |
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