RESUMEN
Novel radar-wave absorption nanocomposites are developed by filling the nanoscaled ferrites of strontium ferroxide (SrFe12O19) and carbonyl iron (CIP) individually into the highly flexible liquid silicone rubber (LSR) considered as dielectric matrix. Nanofiller dispersivities in SrFe12O19/LSR and CIP/LSR nanocomposites are characterized by scanning electronic microscopy, and the mechanical properties, electric conductivity, and DC dielectric-breakdown strength are tested to evaluate electrical insulation performances. Radar-wave absorption performances of SrFe12O19/LSR and CIP/LSR nanocomposites are investigated by measuring electromagnetic response characteristics and radar-wave reflectivity, indicating the high radar-wave absorption is dominantly derived from magnetic losses. Compared with pure LSR, the SrFe12O19/LSR and CIP/LSR nanocomposites represent acceptable reductions in mechanical tensile and dielectric-breakdown strengths, while rendering a substantial nonlinearity of electric conductivity under high electric fields. SrFe12O19/LSR nanocomposites provide high radar-wave absorption in the frequency band of 11~18 GHz, achieving a minimum reflection loss of -33 dB at 11 GHz with an effective absorption bandwidth of 10 GHz. In comparison, CIP/LSR nanocomposites realize a minimum reflection loss of -22 dB at 7 GHz and a remarkably larger effective absorption bandwidth of 3.9 GHz in the lower frequency range of 2~8 GHz. Radar-wave transmissions through SrFe12O19/LSR and CIP/LSR nanocomposites in single- and double-layered structures are analyzed with CST electromagnetic-field simulation software to calculate radar reflectivity for various absorbing-layer thicknesses. Dual-layer absorbing structures are modeled by specifying SrFe12O19/LSR and CIP/LSR nanocomposites, respectively, as match and loss layers, which are predicted to acquire a significant improvement in radar-wave absorption when the thicknesses of match and loss layers approach 1.75 mm and 0.25 mm, respectively.
Asunto(s)
Radar , Elastómeros de Silicona , Electricidad , Hierro/química , EstroncioRESUMEN
Mn1-x Zn x Fe2O4 ferrofluids were produced from natural sand for magnetic sensors and radar absorbing materials. The X-ray diffraction data showed that the Zn partially substituted the Mn and Fe ions to construct a spinel structure. The increasing Zn composition decreased the lattice parameters of the structure. The transmission electron microscopy images showed that the filler Mn1-x Zn x Fe2O4 nanoparticles tended to agglomerate in three dimensions. Lognormal and mass fractal models were used to fit the small-angle X-ray scattering data of the ferrofluids demonstrated that the ferrofluids formed chain-like structures with a fractal dimension of 1.12-1.67 that was constructed from primary particles with sizes of 3.6-4.1 nm. The filler, surfactant, and carrier liquid of the ferrofluids were confirmed by the functional groups of the metal oxides, tetramethylammonium hydroxide, and H2O, respectively. The secondary particles contributed to the saturation magnetization of the Mn1-x Zn x Fe2O4 ferrofluids. The Mn1-x Zn x Fe2O4 ferrofluids demonstrated excellent performance as magnetic sensors with high stability, especially compared with MnFe2O4 ferrofluids. Furthermore, the ferrofluids exhibited excellent radar absorbing materials. The Mn1-x Zn x Fe2O4 ferrofluids prepared in this work may serve as a future platform for advancing magnetic sensors and radar absorbing materials.