Design and Experimental Realization of Ultra-High Green Index Electromagnetic Interference Shields With Opposing Magnetic and Conductivity Gradients.

Absorption-dominant electromagnetic interference (EMI) shields with shielding effectiveness (SE) exceeding 60 dB, characterized by a high green index (GI, the ratio of absorbance over reflectance), are in high demand. Achieving high SE together with GI >10 has proven to be challenging. A multitude of complex loss mechanisms determining EM wave absorption and reflection, and the limitations of each candidate material in some aspect of shielding, have led to the construction of layered structures with a gradient of desirable properties that can leverage the best attributes of each constituent material. Herein, a layered shield, consisting of a top absorption layer of Ni nanochain-decorated MXene nanoribbons embedded in a poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) aerogel and a bottom reflection layer of PEDOT:PSS film atop of silver (Ag) nanowire film, was fabricated based on theoretical predictions. With opposing magnetic and conductivity gradients, this shield provides a phenomenally high GI of 355 with an exceptional average GI of 64 and SE of 90 dB over X-band. Theoretical estimates of reflection loss, electromagnetic simulations, absorption cross-section calculations and density functional theory simulations support the absorption-reflection-reabsorption mechanism. This study paves the way for next-generation absorption-dominant EMI shields by offering a theoretical basis that supports their systematic and optimized design.