Papers by Keyword: Reflectivity

Abstract: SiO2-SiC composite particles were prepared using a sol-gel process. BaTiO3 powders were synthesize through solid-state reaction. They were mixed as microwave absorbents with Fe3O4 powders to obtain the complex absorption. Epoxide resin (EP) was used as matrix and solidified with the mixtures. The techniques of DSC-TG, XRD were used to characterize the composite particles and the obtained compacts. A vector network analyzer was used to measure the reflectivity of the SiO2-SiC-based composites. The effects of the aborbents’ contents on the reflection of the microwave absorption materials were disscussed. It was found that SiO2-SiC composites could be prepared using sol-gel process and BaTiO3 powders could be synthesize through solid-state reaction. The results indicated that SiO2-SiC composite is contribute to absorb microwave, where SiO2-SiC: BaTiO3: Fe3O4 = 6:2:2 (vol %), the frequency region in which the maximum reflectivity is more than -10 dB is 5.4-7.6 GHz.

Abstract: Silver films were prepared on the glass substrate by electron-beam vapor deposition. The reflectivity of the Ag thin film was measured by a Perkin-Elmer Lambda spectrophotometer in the wavelength region of 450-680 nm. The experimental measurements of reflectivity were validated with the numerical results using the Essential Macleod software. The surface topology and microstructure of the film were examined by means of atomic force microscope (AFM). The effects of the thermal and humidity on the reflectivity of the Ag film were examined by the environmental test. Nanoindentation tests were employed to determine the hardness of the film. The measured hardness of the Ag thin film was found to depend on the penetration depth.

Abstract: Double-layer cementitious plates with absorbing microwave properties were designed, based on the impedance matching theory and electromagnetic wave propagation laws. The reflectivity of cementitious composites was measured in the frequency ranges from 8 GHz to 18GHz, and the influence of silica fume on the impedance of the composites surface was studied. Meanwhile, absorbing properties of cementitious plates, which used ferrite and carbon fiber composited ferrite as microwave absorbers, were also investigated respectively. It is shown that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Compared with the single-layer structure, the reflectivity of the double-layer cementitious plates decreased around 6 dB ~ 8 dB. The maximum reflection loss of double-layer cementitious plate employing carbon fiber and ferrite reached -16.2dB, while the absorption bandwidth under – 10 dB was from 9.6 to 18 GHz.

Abstract: We use two-dimensional FDTD (Finite difference time domain) method to simulate light transmitting in Si nano-pillar arrays and get some results. The Si nano-pillar array, with diameters, heights, intervals respectively 50-80nm, less than 480nm, 26-44nm, is used as the testifying structure. The reflectivities of both experiment and simulation match well either for bulk silicon or for structure silicon even though small deviations are caused by the uneven size of the pillar’s diameters, heights, and intervals. What’s more, we find reflectivity (ref) increases along with diameter’s (d) increasing for a single pillar with diameters of 20-100nm under a constant light of 600nm, and reaches 10.48% at d=100nm. And with a constant d equal to 20nm, an infinite aspect ratio (r) and a light 600nm, ref is decreasing when the intervals (i) of pillars are increasing. Finally, under the condition of different i, the relations between ref and r are investigated. The undulation of these curves shows that the reflective waves play an important role in sub-wave length optics. Analysis also reveals that there exists a best i for achieving the lowest ref, too large or too small i will cause high ref, even if r is great; moreover, the lager i is, the higher pillar is needed to achieve the lowest ref.

Abstract: Reflectometry technique in Centre de Recherché Nucléaire de Draria (CRND) is operational since 2002. The instrument is used for investigation of monochromators and supermirrors. In this communication, several monochromators: 10 and 40 nickel-titanium bilayers deposited on a float-glass substrate with different period are analysed. The investigation of magnetic multilayers (25 silicon-iron bilayers monochromator) is also performed. From the results, Bragg peaks were identified indicating the periodicity of the multilayers.

Abstract: Distributed Bragg reflector (DBR) porous silicons exhibiting unique reflectivity were successfully obtained by an electrochemical etching of silicon wafer using square wave currents. Optically encoded smart dust which retained optical reflectivity was obtained from DBR porous silicon film in organic solution by using ultra-sono method. The size of optically encoded smart dust was measured by field emission scanning electron micrograph (FESEM) and was about 500 nm to few microns depending on the duration of sonication. Investigation for the optical characteristics of smart dust revealed that smart dust could be useful for application such as chemical sensor for detecting organic vapors.