Magnetic-Driven Broadband Epsilon-Near-Zero Materials at Radio Frequency

Epsilon-near-zero (ENZ) materials, exhibiting unique physical characteristics such as near-zero refraction, have aroused extensive interest and exhibit great potentials in novel applications of perfect absorbers, high-harmonic generation, and nonlinear optical response. Here, for the first time, magnetic-driven broadband ENZ materials are designed by fabricating polyvinyl alcohol (PVA)/Ni@carbon nanotubes (CNTs) films. Dielectric properties including real permittivity (epsilon '), imaginary permittivity (epsilon ''), dielectric loss (tan delta), and impedance (Z) are investigated. When Ni@CNTs content reached 30 wt.%, negative permittivity transferred to positive permittivity at approximate to 11.5 MHz, and epsilon-near-zero (|epsilon '| < 1) is realized from approximate to 9 to 14 MHz, exhibiting broad ENZ bandwidth of approximate to 5 MHz. Theory calculations confirm that delocalized electrons are introduced from CNTs, which improve the carrier mobility and achieve low frequency dispersion behavior. Longer interfacial polarization electric fields between PVA and CNTs are also demonstrated by theory calculations, enhancing the positive permittivity response to offset negative permittivity response from Ni@CNTs. These two mechanisms result in broadband ENZ at radio frequency. This film also exhibits excellent magnetic actuation ability under magnetic field, broadening applications from ENZ materials to novel fields such as magnetically actuated robots with perfect absorption, magnetic-driven biomimetic aircrafts with shielding ability, magnetic-driven photodetectors, etc.