Reversible Switching Between Microwave Absorption and EMI Shielding of VO 2 Composite Foam.

Developing lightweight composite with reversible switching between microwave (MW) absorption and electromagnetic interference (EMI) shielding is promising yet remains highly challenging due to the completely inconsistent attenuation mechanism for electromagnetic (EM) radiation. Here, a lightweight vanadium dioxide/expanded polymer microsphere composites foam (VO 2 /EPM) is designed and fabricated with porous structures and 3D VO 2 interconnection, which possesses reversible switching function between MW absorption and EMI shielding under thermal stimulation. The VO 2 /EPM exhibits MW absorption with a broad effective absorption bandwidth of 3.25 GHz at room temperature (25 °C), while provides EMI shielding of 23.1 dB at moderately high temperature (100 °C). This reversible switching performance relies on the porous structure and tunability of electrical conductivity, complex permittivity, and impedance matching, which are substantially induced by the convertible crystal structure and electronic structure of VO 2 . Finite element simulation is employed to qualitatively investigate the change in interaction between EM waves and VO 2 /EPM before and after the phase transition. Moreover, the application of VO 2 /EPM is demonstrated with a reversible switching function in controlling wireless transmission on/off, showcasing its excellent cycling stability. This kind of smart material with a reversible switching function shows great potential in next-generation electronic devices.