Study On Design And Performance Of Gypsum Based Electromagnetic Wave Absorbing Materials Based On 2D And 3D Grid Structures

The development and application of high performance electromagnetic(EM)wave absorbing building materials are of great significance for enhancing the EM protection capability and improving EM environment.Therefore,in this work,high performance EM wave absorbing building materials with different types of structures were designed and fabricated based on the two-dimensional(2D)grid structure and three-dimensional(3D)network structure.The EM wave absorbing properties and mechanisms were investigated and analyzed in details.The main contents are as follows:The 2D absorbing grids were prepared through surface treatment of fiberglass mesh using nano carbon black(CB),and grid structured gypsum EM wave absorbing plates was designed and fabricated based on this 2D absorbing grids.The results show that the EM wave absorbing proerpties in 2-4 GHz frequency range of gypsum based materials can be notably enhanced by embedding the 2D absorbing grids.In addition,the layered design of grid structured gypsum-base composites can ulteriorly improve its absorbing capacity.The RL of double layered specimen with 10 mm thickness can be lower than-8 dB in 2-4 GHz frequency range,and the lowest RL reaches-32 dB.Based on the 2D absorbing grids and lightwight absorbing mortar,and combined with the multi-layer structure characteristics of traditional exterior wall thermal insulation system,an external wall structure integrated with EM wave absorption property and thermal insulation property was designed.The EM wave absorption properties were tested in the frequency range of 1.1-5 GHz,the results indicate that when the(CB)content of 2D absorbing grids is 5%,the insulation layer thickness is 20 mm,the CB content and wave-transparent aggregate volume fraction of the mortar layer with 20 mm thickness are 2% and 50 vol.%,respectively,and the RL below-8 dB in 1.1-5 GHz.The RL peaks are caused by interference effect,and the effective bandwidth is determined by the EM attenuation capacity of absorbent,the multiple reflections between different interfaces,and the multiple reflection and scattering between wave-transparent aggregate particles in the mortar layer.The 3D grid structure has more complex internal structure than the 2D grid structure,the EM wave attenuation path of building materials can be increased by embedding 3D grid structures,leading to the improvement of EM wave absorption capacity.In this study,the 3D woven fabrics,with grid structure and 3D network structure,were used to fabricate gypsum based absorbing materials for the first time,and the EM properties were investigated.The results indicate that when CB particles coated on the 3D waven fabrics,the composites possess better EM wave absorption properties and wider effective bandwidth,and the dosage of CB is small.When the CB content of 6 mm 3D woven fabric is 24%,the bandwidth for-8 dB reaches 12.4 GHz in the frequency range of 2-18 GHz,and the lowest RL value is-28 dB.The paper honeycomb has the regular 3D periodic grid structure,and the continuous honeycomb walls can generate multiple reflections of EM waves,which is beneficial to the enhancement of EM wave absorbing performance.Honeycomb structured gypsum based materials for EM wave absorbing were prepared by embedding paper honeycomb coated with CB particles which is obtained by impregnation technology.The results indicate that the EM wave absorbing properties can be affected obviously by the size parameters of honeycomb structure and CB content.When the honeycomb edge length is 8 mm,honeycomb height is 9 mm,and CB content is 30%,the RL values are less than-8 dB in the whole frequency ranges.In addition,double layered honeycomb structure were designed and prepared in order to further enhance the EM wave absorbing properties,the testing results of EM wave absorption indicate that the EM wave absorbing performance can be effectively improved,especially the absorption performance of the low frequency band EM wave.All the structural EM wave absorbing materials devised and fabricated in this work exhibit multi-bands EM wave absorption performance,which indicates that increase the path of EM attenuation through structural design is an effective way to realize strong EM wave absorption of building materials.