基于CNTs/PLA的多层宽频超材料吸波结构设计与优化

Design and Optimization of Multilayer Broadband Metamaterial Absorbing Structure Based on CNTs/PLA

目的 解决传统超材料吸波结构密度大以及对入射角度敏感的问题。方法 采用机械搅拌法和熔融共混法制备碳纳米管/聚乳酸(CNTs/PLA)复合吸波材料,通过CST电磁仿真软件开展多层超材料吸波结构设计,利用熔融沉积3D打印制备了设计的超材料吸波结构。通过扫描电子显微镜、矢量网络分析仪对制备材料和设计结构的微观形貌和电磁特性进行表征分析。结果 在机械搅拌和熔融共混的共同作用下,碳纳米管在聚乳酸中分布均匀。碳纳米管含量为10%时,复合材料的综合性能达到最佳。当其厚度为1.7 mm时,有效带宽达到最大为3.9 GHz;当厚度为3.2 mm时,反射率达到最低值约为–53.1 dB。设计的多层超材料吸波结构均具有极佳的宽频吸波特性;当R=11 mm时,圆形多层超材料结构的吸波性能最佳,反射率最低值为–53.9 dB,有效带宽为33.1 GHz,而平均反射率为–17.1 dB。此外对于TE极化的电磁波入射角在0°~60°范围内,而对于TM极化电磁波在入射角0°~70°范围内,圆形多层超材料结构具有宽角域吸波性能。结论 将碳纳米管与聚乳酸复合,在此基础上开展多层超材料结构设计,通过微观复合材料和宏观结构设计的共同作用,实现了轻质宽频的应用需求,能够为超材料吸波结构的设计及工程应用提供理论和技术支撑。

The designability of electromagnetic properties of the metamaterial structure provides it a broad range of potential application in the fields of electromagnetic wave absorption,electromagnetic shielding and wireless communication.In order to address the issues with traditional metamaterial structure,such as high density and sensitivity to oblique incident angle,a new three-dimensional multilayer broadband metamaterial absorbing structure was designed and prepared from the perspectives of micro-composite absorbing materials and macro-structure.In this work, the carbon nanotubes and polylactic acid (CNTs/PLA) composite absorbing material was prepared by mechanical stirring and melt blending method. The electromagnetic simulation software CST was used to design, simulate and optimize the proposed multilayer absorbing metamaterial structure through the obtained electromagnetic parameters. The structural parameters of metamaterial structure were optimized by the parameter sweep function in CST. Meanwhile, the absorption mechanism of the metamaterial structure was revealed and demonstrated through the analysis of the effective impedance and the distribution of electric field, magnetic field and power loss. The proposed absorbing metamaterial structure was fabricated by the fused deposition modeling (FDM) of 3D printing technology. The microscopic morphology and electromagnetic properties of the prepared materials and metamaterial structure were characterized by the scanning electron microscope (SEM) and vector network analyzer (VNA). The CNTs were uniformly distributed in PLA due to the combination of mechanical stirring and melt blending. When the CNTs content of composite filaments was 10%, the mechanical properties and electromagnetic wave absorption capability of the composite filaments were relatively good, and the overall performance of composite filaments reached its optimum. When the thickness of composite absorbing material was 1.7 mm, the effective bandwidth reached a maximum of 3.9 GHz. When the thickness was 3.2 mm, the reflectivity reached the lowest value of -53.1 dB. The excellent broadband electromagnetic wave absorption performance could be found through the design of multilayer metamateial structure, which was based on the composite filaments with the 10% CNTs content. Furthermore, the metamaterial absorbing structures in different shapes had various coupling relationships to incident electromagnetic waves. The circular multilayer metamaterial absorbing structure had the optimum electromagnetic absorption performance when R=11 mm, with the minimum reflectivity RLmin= -53.9 dB, the effective bandwidth EAB=33.1 GHz and the average reflectivity RLaverage= -17.1 dB. Moreover, this proposed circular multilayer metamaterial absorbing structure also could maintain the broadband and strong microwave absorption with the incident angle from 0° to 60° for TE polarization and 0° to 70°for TM polarization. In conclusion, through the combination of PLA with good biocompatibility and CNTs with excellent absorption performance, the composite filaments with both outstanding electromagnetic waves absorbing capability and mechanical property can be successfully produced by varying the mixing ratio. This process provides the basis for the design of the multilayer metamaterial absorbing structure. The multilayer design greatly improves the impedance matching characteristics of the metamaterial absorbing structure, while the symmetrical structure is beneficial to its wide-angle electromagnetic wave absorption. In general, the multilayer metamaterial absorbing structure design for electromagnetic wave absorption realizes the application needs of light weight and broadband absorption through the joint action of micro-composite materials and macro-structure design. It can provide theoretical and technical support for the engineering application of lightweight broadband metamaterial absorbing structures.