Electromagnetic interference (EMI) and electromagnetic radiation are the two main sources of severe pollution in the rapidly growing 5G and intelligent electronics industries. These pollutions not only degrade the functionality of electronics but also have negative effects on human health. As a result, there is an urgent need to develop EMI shielding materials with high shielding efficiency and strong absorption capacity. Minimal thickness and lightweight properties are also required for advanced EMI shielding materials. From the EMI shielding principle, the electromagnetic attenuation effectiveness and the overall shielding capability of a material depend on its magnetic and dielectric characteristics. In other words, integrating appropriate dielectric and magnetic components is an emerging and potential approach for developing EMI shielding materials with exceptional features.
Based on the above principle, numerous research work focusing on designing diverse electromagnetic composites have been reported. While most of the resulting composites are either microparticles or nanoparticles, converting them into monolithic materials suitable for practical EMI applications without degrading the overall performance of the host devices or systems remains a big challenge. Another challenge is to effectively and economically obtain desirable EMI shields from the components and their associated functional characteristics.
In recent studies, constructing heterostructures has emerged as an effective and economical strategy for using the functional components for practical shielding applications. To further achieve outstanding shielding performance while maintaining the high absorption capability, it is critical to rationally design three-dimensional (3D) porous architectures based on metal foams. As a result, it becomes even more imperative to utilize suitable dielectric components to design the metal foam-based heterostructures. Polyaniline (PANI) is an ideal dielectric candidate for EMI shielding applications owing to its remarkable advantages, including low density, cost-effectiveness and tunable electrical conductivity. Nevertheless, the underlying shielding mechanism of these kinds of heterostructures, especially for pre-constructed conductive frameworks, remains largely underexplored.
Herein, Mr. Han Gao, Miss Chenhui Wang, Miss Zhangjing Yang and Professor Yang Zhang from Beijing Technology and Business University designed and fabricated a 3D porous nickel metal foam (NF)/PANI heterostructure with strong EMI shielding and outstanding absorption performance based on a pre-constructed macroscopic conductive framework. Using a facile in-situ polymerization technique, PANI coating layer was intertwined on the NF substate framework. As a result, Ni/PANI composite foam (NPF) with and unique 3D porous heterostructure was formed. The dielectric behaviors, structure and EMI shielding performance of this structure were systematically investigated. The work is currently published in the journal, Composites Science and Technology.
The authors’ findings showed that the rich interface coupled with the enhanced interfacial polarization and absorption-dominated shielding mechanism resulted in significantly enhanced shielding capabilities. With only 2.7% increase in the pristine NF thickness, the shielding performance of the NPF heterostructure significantly improved. Compared with the previously reported shielding materials, the present NPF proved that using a rationally designed structure, outstanding shielding performance of about 93.8 dB (~99.99999996% radiation can be shielded) and remarkable absorption capacity per unit thickness of about 147.64 dB/mm can be simultaneously achieved. Such extraordinary performance was attributed to the benefits of the 3D porous heterostructure, dielectric-magnetic integration and presence of abundant interfaces in the NPF system, which was responsible for improved dipole relaxation, multiple reflections, interfacial and dielectric polarization. Moreover, the shielding effectiveness remains very stable with only a 5.95% decline even after 5000 bending cycles.
In summary, the researchers developed a facile, efficient and cost-effective strategy for fabricating innovative 3D porous heterostructure EMI shielding material by incorporating PANI into nickel metal foam. The results demonstrated the significance of rationally designed 3D heterostructure in achieving extraordinary electromagnetic capabilities, endowing it with great application possibilities. The approach is effective and scalable and applies to other metal foams for large-scale advanced shielding applications. In a statement to Advances in Engineering, Professor Yang Zhang pointed out that the obtained novel 3D porous heterostructure is an ideal candidate for next-generation as well as large-scale EMI shielding systems that require thin thickness and outstanding performance.
Gao, H., Wang, C., Yang, Z., & Zhang, Y. (2021). 3D porous nickel metal foam/polyaniline heterostructure with excellent electromagnetic interference shielding capability and superior absorption based on pre-constructed macroscopic conductive framework. Composites Science and Technology, 213, 108896.