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The bionic flapping wing aircraft realizes flight by imitating the structure and flapping mode of birds. In this paper, a three-dimensional composite motion aerodynamic analysis model of a bionic flapping wing is established. The diverting field and flapping wing grid are divided up using dynamic hybrid grid technology. The flow field of the flapping wing is analyzed by solving the Navier–Stokes (N–S) equation combined with the Boussinesq hypothesis. The lift of the flapping wing under different flutter frequencies and incoming wind speeds is studied under the asymmetric flutter condition. In order to verify the accuracy of the aerodynamic simulation results, a flapping-wing shrinking-ratio model prototype is made, and low-speed wind tunnel experiments are carried out to test the changes in the flight lift of the wing at different flutter frequencies and angles of attack. A comparative analysis of the wind tunnel experiment and the aerodynamic simulation results shows that when the flapping frequency (1–5 Hz) and incoming wind speed (1–5 m/s) increase, the lift force generated by the wing flapping increases. Due to the deviation between the experimental sample airfoil area and the simulated airfoil area, as well as the wing-driven fuselage vibration during the experiment, a sensor error is produced, resulting in a deviation of about 1 N between the experimental result curve and the simulation result curve. However, the aerodynamic characteristics obtained from the aerodynamic simulation analysis are basically consistent with the aerodynamic change law measured in the wind tunnel experiment.

10.5μm thick Sn-doped silica films were prepared by the modified chemical vapor deposition followed by the solution-doping method. The films were exposed to 248 and 266nm laser light, respectively. Positive refractive index change up to 2×10−4 at 1550nm was observed by measuring the reflectivity based on Fresnel formulas. The data of UV absorption spectra suggest that the photosensitivity of the Sn-doped silica film under high energy density laser irradiation should be mainly due to the bond breaking of oxygen deficient defects, while under relatively low energy density laser irradiation, the refractive index change probably originates from photoconversion of optically active defects.

We have used electron microscopy to investigate the microstructure of Ni80Fe20/Cu magnetic multilayers which were synthesized by dc magnetron sputtering. Columnar structure was found in the specimen with and without giant magnetoresistance (GMR). All the columnar crystallites (CCs) originate from the Fe buffer layer on silicon wafer or glass substrate and penetrate though all the multilayers up to the surface of the film. The lateral size of the CCs ranges from 10 to 30 nm. Cross-sectional high-resolution electron microscopy study shows that the CCs are single-crystal-like with fcc structure resulting from the epitaxial growth of NiFe and Cu sublayers. Electron diffraction contrast imaging and electron energy filtered elemental mapping confirmed that multilayer nature is maintained throughout the entire NiFe/Cu film. Grain boundaries between CCs can be the most likely place where NiFe or Cu bridging will occur. Columnar structure was also found in a Ta/NiFe/Cu/NiFe/FeMn/Ta spin valve film. The possible in...

Organic/inorganic hybrid glass waveguides were fabricated by the sol-gel technique followed by direct ultraviolet patterning. The thermo-optic coefficient (dn/dT) of the hybrid material was measured by a prism-coupling method and was found to be −1.44×10−4/°C, comparable to those of typical polymer materials. In order to investigate the possibility of using this hybrid glass material as a thermo-optic waveguide material, a 2×2 Mach–Zehnder interferometric optical switch was fabricated on a silicon wafer. At the wavelength of 1.55 μm, the switch response time was measured to be less than 4.2 ms, and the switching power was 9.3 mW. Experimental results show that this hybrid material is very suitable for application in integrated thermo-optic components.

We report the fabrication and optical properties of an organic light-emitting microcavity. The cavity is a laser dye-doped polycarbonate film sandwiched between two Bragg reflectors, fabricated by alternately depositing TiO2 and SiO2 sol-gel thin films. Reflectivity up to 98% was achieved using the Bragg reflectors. The cavity has a photonic band gap between 597 and 789 nm with a defect state inside the gap. Narrow-band optical pumped light emission from the cavity and its polarization dependence were observed. A cavity quality factor as high as 354 was achieved. Angular and polarization dependence of light emission were analyzed using the transfer matrix method. All experimental results agree well with theoretical calculations.

The transient electroluminescence behavior of a Au/porous silicon/silicon/aluminum structure is investigated by a doubly injected short voltage pulse method. It is found that the electroluminescence response of porous silicon diode is very similar to that of an ordinary p‐n junction light‐emitting diode. A delay time and a rise time at the ‘‘on’’ side and a fall time at the ‘‘off’’ side are observed. The mechanism of electroluminescence is explained as the carrier injection through the Au/porous silicon Schottky barrier and the porous silicon/p‐Si heterojunction into the corrugated Si nanostructures, where the radiative recombination of carriers occurs. From the fall edge of electroluminescence transient response, the recombination lifetime of the injected carriers is found to be in the order of 30 ns. The major time constant of the diode structure is the delay time which ranges from 10−7 to 10−6 s and is determined by the quality of the Au/porous silicon contact.

Second-order nonlinearity (SON) of thermally poled PbO/B2O3 glass was investigated. The SON distribution within the glass was obtained by repeatedly grinding the poled glass and measuring its Maker fringes. After grinding away up to one third of the thickness of the poled sample, i.e., about 300 μm, clear fringes with the interference minimum not equal to zero could still be observed, indicating that the area of SON was not confined within thin layers near the two surfaces. Cathode side grinding and anode side grinding had quite different influences on the SON of the poled sample. A model of the anode-charge-layer dependent bulk electric field distribution was proposed and this electric field was regarded as playing a key role in the generation of a nonuniform bulk SON distribution in PbO/B2O3 glass.

Hemicyanine‐doped silica film was fabricated by sol–gel technique. Time evolution of structural changes in hemicyanine and their influence on the second‐order optical nonlinearity were investigated through UV‐visible absorption and second‐harmonic generation (SHG) measurements. We found that the conversion of protonated hemicyanine to monomeric and aggregated hemicyanine occurred within 4 h after film deposition. During this period of time the SHG signal continued to rise and finally reached the maximum. The growth of optical nonlinearity was mainly due to deprotonation of hemicyanine molecules. Blueshift of the absorption peaks for both aggregate and monomer were found during the drying of the film.

Pyroelectricity of the optical nonlinear hemicyanine dye in organized molecular films has been demonstrated by using the electric polarization and second harmonic generation measurements. The typical hysteresis loop of the samples confirmed existence of the remnant polarization of hemicyanine molecules which is 600 μC m−2. The pyroelectric coefficient of hemicyanine was found to be 12 μC m−2 K−1 at room temperature and enhanced with increasing temperature monotonically which was well explained by using a molecular dipole reorientation model.