Electromagnetic Properties Of Fiber Reinforced Epoxy Microwave Absorbing Composites

Microwave absorbing materials have broad application prospects in the stealth field due to their high efficiency,low cost and convenient use.With the goal of“thin,light,wide and strong”,research on absorbing materials has gradually turned to structural absorbing materials.In order to meet the adaptability under harsh conditions,structural absorbing composites not only need to meet the requirments of mechanical properties,but more importantly to meet the requirments of absorbing properties.In this paper,the carbonyl iron powder?CIP?absorbers with high efficience absorbing capability were employed to modify the epoxy resin?EP?to obtain novel absorbing bearing composites.Meanwhile,the EP was strengthened by glass fiber?GF?and carbon fiber?CF?to improve mechanical properties.First,the optimal process conditions of vacuum assisted resin infusion?VARI?were explored by orthogonal test and the rheological properties of CIP/EP reaction precursors were tested,as well as the effects of mass ratio of CIP to EP(m_CIP/m_EP)on electromagnetic properties of CIP/EP composites were studied.The results showed that the optimum conditions are as follows:temperature is 35?,m_CIP/m_EPP is 1.5:1,stirring time is 30 min and alcohol content is 5%and the CIP/EP reaction precursors with m_CIP/m_EP of 0³:1 can meet the operation time requirements of VARI process.When m_CIP/m_EP is 1:1,CIP/EP-2 with 2.2mm thickness exhibites a remarkable absorption performance,with a maximum reflection loss?RL?of-53.6dB at 8.9GHz and the band range below–10 dB?the corresponding bandwich?of 2.1GHz?8.2¹0.3GHz?.Second,on the basis of optimum conditions,CIP/GF/EP composties were prepared by VARI process,and the electromagnetic properties and absorbing methanisms were investigated.The electromagnetic properties indicate that the dielectric loss of the CIP/GF/EP composites basically unchange with the increase of frequency,and the magnetic loss decrease slightly with the increase of frequency.When m_CIP/m_EP is 2:1,CIP/GF/EP-4 composite with2.2mm thickness exhibites a remarkable absorption performance,with a maximum RL of-51.5dB at10.1GHz and the corresponding bandwich of 3.6GHz?8.8¹2.4GHz?.The superior microwave absorption properties of CIP/GF/EP composites are related to impedance matching,electronic polarization,interfacial polarization and resonance loss.Finally,CIP/GF/CF/EP composites were prepared by adding CF reflector layer on the basis of the above work,and the absorption properties and mechanical properties were explored by adjusting the GF layers.The CIP/GF/CF/EP composite with 7GF layers has better wave absorption and mechanical properties.CIP/GF/CF/EP-7 composite can reach the maximum RL of-34.2dB at 9.6GHz within the range of 8.2¹2.4GHz and the corresponding bandwich of 3.2GHz.The tensile strength and tensile modulus of CIP/GF/CF/EP-7 are 242.28MPa and22.39GPa,and its flexural strength and flexural modulus are 225.76MPa and 17.47GPa.