High permittivity and shielding effectiveness of microwire composites with optical transparency

Flexible composites with optical transparency were fabricated with glass-coated nanocrystalline ferromagnetic microwires and transparent silicone matrix. Free space method was employed to measure the effective permittivity and shielding effectiveness of samples fabricated from 4 to 20 GHz. Due to resonance phenomena of the embedded microwires with certain lengths, both dielectric permittivity and loss of the composite are quite high at designed microwave frequency. Broadband shielding effectiveness (SE) of the transparent shielding layer with 0.5 wt% of microwires and thickness less than 0.75 mm can be 10 to 14 dB. The maximum SE of combining two layers of sheets (~1.5 mm) with microwires of different length could be better than 20 dB.