A silver nanoparticle-modified evanescent field optical fiber sensor based on a MEMS microchannel chip has been successfully fabricated. Experimental results show that the sensor response decreases linearly with increasing concentration of analyte. Over a range of methylene blue concentrations from 0 to 0.4 μmol/mL, the sensor response is linear (R = 0.9496). A concentration variation of 0.1 μmol/mL can cause an absorbance change of 0.402 dB. Moreover, the optical responses of the same sensing fiber without decoration and modified with silver nanoparticles have also been compared. It can be observed that the output intensity of the Ag nanoparticle-modified sensor is enhanced and the sensitivity is higher. Meanwhile, the absorbance spectra are found to be more sensitive to concentration changes compared to the spectra of the peak wavelength.

The electromagnetic (EM) scattering mechanism of dynamic oil spill–covered sea surface area is studied in this manuscript. Utilizing the theory of oil film diffusion combined with oil spill volume, a three–dimensional (3D) geometric model of dynamic oil spill–covered sea surface area is established. The changes of the geometric structure and statistical characteristics of the sea surface area under the influence of the oil film are also analyzed. The thinner the oil spill thickness, the more sensitive it is to the sea surface slope and wave height. The facet-based hybrid model and the multilayer dielectric scattering method are combined to measure the EM scattering on the sea surface when covered by dynamic oil spills. In addition, the hydrodynamic and tilt effect are discussed. The EM scattering mechanism of the dynamic oil spill–covered sea surface area is revealed, and the tilt modulation is greater than the hydrodynamic effect in the dynamic process of an oil spill. It provides an important reference for the remote sensing monitoring of oil.

Micromirrors with variable focal length are critical components in a lot of optical systems. Due to the limitation of microfabrication and actuation mechanism, it is very difficult to control the surface shape of varifocal mirror precisely. In this study a novel surface micromachined varifocal-piston micromirror is presented. By simulating quasi-simply supported boundary condition, an accurate focusing mirror is achieving. It is driven by a parallel-plate electrostatic actuator. When the micromirror is actuated, as the increase of the driving voltage, the micromirror will experience two stages. In the first stage, four beams that support the mirror are bent, which make the micromirror vertical translation. As the translation reaches its limit, the micromirror will enter the second stages. The micromirror will bend to concave shape and thus can focus light. The focus length can be adjusted from infinity to 2.11mm by the change of the driving voltage. At last, because of the existence of the two stages and the clear distinction between them, the developed mirror can also be employed as a digital-tuned spatial light modulator.

Tsunami bring great disasters to human beings. The focus of the research is to predict the feasibility of tsunami early warning by microwave radar scheme. In this paper, the electromagnetic (EM) scattering characteristics of the sea surface from the calm sea to the submarine earthquake are studied. Based on the high order Boussinesq wave model combined with the up and down movement of the two submarine plates, the three-dimensional (3D) geometric propagation model of the tsunami sea surface is established. The geometric structure and propagation characteristics of the sea surface under different earthquake magnitudes are analyzed. The higher the earthquake magnitude, the more obvious the effect on the sea wave height and sea surface slope. Secondly, the influence of wind velocity disturbance on sea surface roughness caused by tsunami is deduced. The EM scattering distribution of tsunami-affected sea surface is solved by combining the wind disturbance theory with the EM scattering method based on the surface element model. In addition, the distribution of EM scattering coefficients of tsunami sea surface under different radar parameters, background wind speed and earthquake magnitude are also discussed, providing an important theoretical basis for the rapid warning of tsunami by microwave radar.