Adjustable radio-frequency negative permittivity in graphite-PDMS elastomer metacomposites

Abstract

Metacomposites with tunable negative permittivity find wide range of applications such as in novel electrical devices, flexible invisibility cloaks, stretchable sensors, etc. In the work reported here, the superior tunable negative permittivity of Polydimethylsiloxane (PDMS)-Graphite nanocomposites, over graphite and neat PDMS has been demonstrated. The ac conductivity and impedance of PDMS composites with varying graphite loading are studied as a function of frequency (100 Hz–100 MHz). Interesting phenomenon like capacitive-inductive transition and positive to negative switching of permittivity are observed and interrelationships between them is discussed here. The negative permittivity which is mainly due to the inductive conductive networks formed within the composites, is explained based on interband transition and Drude theory of metals. For 30 wt% composite maximum positive permittivity of 280.4 and maximum negative value of -29.87 is observed at 100 Hz and 3.35 × 107 Hz respectively. For higher graphite loading the permittivity switching frequency is found to shift to lower frequency region due to increased inductive behavior of the composites.