Acknowledgements

response upon striking the graphene/air interface. Nitrogen-doping and side polar groups induced strong polarization effects in GAC. Higher extent of reduction of the grapheme sheets in GAT left a smaller amount of side polar groups and formed more sp2 graphitic lattice, both favored π-π stacking between the adjacent graphene sheets. The enhanced polarization effects and the increased electrical conductivity of GAT contributed to better EMI shielding performance. Bi further investigated the effect of porosity on EMI shielding mechanisms compressing the aerogel (GA9) into thin film (GA9F), as shown in Figure 10b. The highly connected conducting network resulted in a significant increase in the electrical conductivity of GA9F, while the EMI SE remained unchanged at constant rGO content. The observation was contradictory to the previous outcomes that higher electrical conductivity or better-connected network contributed to higher EMI SE. Hence, the fact can be believed that the EMI SE is highly dependent on the effective amounts of materials response to the EM waves. Despite the similar intrinsic properties of rGO, the amount of absorption of EM waves in GA9 was much higher than that in GA9F when the EM waves penetrated through the porous structure. The cavities within the highly porous GA absorbed the EM waves through multiple internal reflections and eventually depleted the energy. Hence, the tightly connected conducting network within GA9F changed

Generally, EMI shielding is defined as the prevention of the propagation of EM waves from one region to another by using shield materials. With the development of electronic industry, weight reduction is an additional technical requirement besides the good EMI shielding performance. Metal as a traditional EMI shielding material has been

replacing with lighter materials, such as polymer-based composites, foams and aerogels. This chapter reviewed various types of lightweight materials with their EMI SEs corresponding to their EMI shielding mechanisms. To verify the benefits of using lightweight materials for EMI shielding applications, a comprehensive comparison was performed as shown in Figure 11. All the data in Figure 11 were collected from the

Comparison of EMI SEs of lightweight materials as a function of density of materials.

the EMI shielding mechanism from absorption to reflection.

4. Conclusions

Electromagnetic Materials and Devices

Figure 11.

226

Liying Zhang would like to acknowledge the support by the initial research funds for young teachers of Donghua University. Shuguang Bi would like to acknowledge the financial support of Wuhan Engineering Center for Ecological Dyeing & Finishing and Functional Textiles, Key Laboratory of Textile Fiber & Product (Wuhan Textile University), Ministry of Education, Hubei Biomass Fibers and Eco-dyeing & Finishing Key Laboratory. Zhang and Bi would also thank the funding support by State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University (KF1827). Ming Liu would like to acknowledge the support from School of Materials Science and Engineering at Nanyang Technological University for this work.
