Efficient microwave traps with markedly enhanced interfacial polarization and impedance matching enabled by dual-shelled, dual-cavity magnetic@dielectric hollow nanospheres

Abstract

The ability to create robust microwave absorbing materials renders efficient protection of electromagnetic radiation. The combination of magnetic and dielectric losses has emerged as an appealing strategy to yield high-performance microwave absorbers. In this context, dual-shelled hollow nanospheres composed of magnetic Fe₃O₄ inner shell and dielectric TiO₂ outer shell (denoted DS-Fe₃O₄@TiO₂-HNs) are, for the first time, crafted by rationally introducing a sacrificial intermediate shell. Notably, such unique dual-shelled nanostructures with a relatively large hollow interior within the Fe₃O₄ inner shell and an additional cavity between the Fe₃O₄ inner shell and the TiO₂ outer shell (i.e., dual-cavity) manifest an advantageous attribute for producing lightweight absorbers. Intriguingly, the reflection loss (RL) of −60.17 decibel (dB) at 10 GHz and the effective bandwidth of microwave absorption of 10.5 GHz at RL ≤ −10 dB, representing 90% absorption, are achieved for DS-Fe₃O₄@TiO₂-HNs with a thickness of only 1.8 mm. The outstanding microwave absorption performance of DS-Fe₃O₄@TiO₂-HNs can be attributed to the synergy of efficient trapping of the incident wave, markedly enhanced interfacial polarization, and greatly improved impedance matching. As such, judiciously crafted uniform dual-shelled, dual-cavity nanospheres possessing optimal magnetic and dielectric losses hold great promise as highly efficient lightweight microwave absorbers for use in electromagnetic interference shielding, including mobile communication devices, AM radio, and radar, among other areas.