Magnetic-driven and biocompatible radio frequency epsilon-near-zero film for wearable sensor

When the permittivity is equal to zero or very close to zero, unique physical properties are triggered in epsilon-near-zero (ENZ) materials, which have broad application prospects in perfect absorption, superlens, invisible cloak, and other fields. In this work, by doping high-entropy alloy (HEA) into reduced graphene oxide (HEA@RGO), ENZ performance at 19 MHz is realized from three-dimensional (3D) printed polydimethylsiloxane (PDMS)/HEA@RGO film when HEA@RGO content reaches 15 wt%. However, negative permittivity from 2 to 80 MHz is realized from 3D-printed PDMS/graphene film with 15 wt% graphene content. Theory calculations are used to explore the mechanism of ENZ performance at radio frequency. Compared with the band structure of graphene, when HEA is formed, the band of HEA@RGO is flatter, resulting in an increase in the effective electron mass, which causes a decrease in the plasma frequency, realizing radio frequency ENZ performance. Moreover, the 3D-printed PDMS/HEA@RGO ENZ film exhibits excellent magnetic actuation performance because of the strong saturation magnetization of HEA@RGO. Furthermore, the film exhibits good biocompatibility and is prepared into a wearable capacitive sensor device with a laminated structure, which realizes effective monitoring of human movement.