Flexible and tunable microwave absorption structures using carbonyl iron@polydimethylsiloxane pillar arrays

Abstract

The flexible absorbers with artificially engineered micro-structures are promising microwave-shielding materials applied to flexible electronic devices. However, the deformation of flexible absorbers has a great impact on their microwave-absorption properties, which needs more intensive researches. Herein, the flexible absorbers of periodically arrayed polydimethylsiloxane (PDMS) pillars mixed with carbonyl iron particles (CIPs) were fabricated via a template-casting method and deformed by vertically applied forces. As the bending angles of pillars increase between 0 and 70 degrees, the frequencies of the absorption peaks exhibit a linear redshift in 11.69-10.53 GHz. The shifting rates are -0.00543, -0.00235, and -0.00681 GHz per degree for the 2 mm period arrays, and -0.00432, -0.00324, and -0.00412 GHz per degree for the 3 mm period arrays, when the mass ratios of CIPs are 40%, 50%, and 60%, respectively. The shift of the peaks results from the increased imaginary part of permeability and the permittivity when the pillars bend, giving rise to the increase of propagation constant in the effective medium and the enhancement of the first-order Fabry-Perot resonance. The results demonstrate a simple and feasible pathway to manipulate microwave absorption dynamically through deformation.