Design and Fabrication of Flexible Woodpile Structured Nanocomposite for Microwave Absorption Using Material Extrusion Additive Technique

The explosive growth of electronics and the widespread use of transient power sources have given rise to an undesirable and uncontrolled consequence of electromagnetic interference (EMI). It is crucial to address and mitigate the issues caused by EMI by developing effective shielding techniques. The material extrusion additive technique provides a solution through its versatile 3D printing of polymeric ink, offering advantages such as design flexibility, structural complexity, and environmental sustainability. The primary objective of this study is to investigate the rheological properties, electromagnetic properties, and thermal stability of nanocomposites consisting of Polydimethylsiloxane (PDMS) and Multi-Walled Carbon Nanotubes (CNTs). The aim is to utilize these findings for the design and 3D printing of a microwave absorber with high efficiency. Composite inks containing 50 vol% (C50) and 60 vol% (C60) of CNTs exhibit favorable shear-thinning behavior and shape retention. On the other hand, lower CNT percentages result in inconsistent viscosity, rendering the inks non-printable. Thermogravimetry analysis reveals that an increase in CNT vol% leads to a decrease in the thermal stability of 3D-printed PDMS-CNT nanocomposites. Higher CNT proportion enhances electric polarization, and attenuation capacity, as evidenced by measurements of complex permittivity and dielectric loss tangent. X-Ray Diffraction analysis was employed to examine the effect of CNT inclusion in the composites. A woodpile-structured metamaterial microwave absorber based on gradient index (GWMMA) was designed by manipulating geometric parameters and CNT vol%. Fifteen unit cell configurations were generated and subsequently chosen based on their exceptional attenuation capabilities, low impedance, and narrower filament width for simulations. The GWMMA demonstrates exceptional absorption performance, surpassing reflection loss values of −10dB. Incorporating a third filament stacking into the woodpile structure augments its efficacy, yet further additions of stackings result in diminishing returns. Experimental validation of a selected 3D-printed GWMMA structure of C60 with a width of 0.75 mm confirms its absorption capabilities, closely aligning with the simulated results. The GWMMA exhibits promising performance for microwave absorption, with absorption values exceeding 90%. Simulations indicate the adjustability of the GWMMA's bandwidth and absorption capabilities through alterations in array periodicity and cell size. Its spatial scale aligns with sub-wavelength structures, establishing it as a representative Metamaterial Absorber (MMA).