Wenwei Zheng

Infrared thermochromic properties of VO2 thin films prepared through aqueous sol-gel process

The stoichiometric vanadium(IV) oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 °C for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.

Analysis of Polarimetric Scattering for Backgrounds and Camouflage Materials

Recent investigations into the use of new method of polarization remote sensing for the detection of camouflage targets in complex backgrounds have led to the need to understand the optical properties of military objects and backgrounds. The use of polarimetric signatures in remote sensing has been the subject of much study particularly; an understanding of camouflage materials properties and their variations is critical to detect the existence of these targets. Our study examined spectral polarization degree of camouflage materials within a meadow environment and presented a description of polarimetric scattering of materials. The result indicates that the polarimetric degree of camouflage materials is influenced by conditions of the incidence, azimuth angle and the surface roughness. Therefore, a spectral phenomenological model for the polarimetric scattering of camouflage materials was developed for the visible and infrared band to study these issues in more detail; the model considered the effects of solar rays and surface refractive index. From the model, it is clear that scattering light from the camouflage materials can be divided into two parts, surface scattering and volume scattering. Surface scattering acts as a function of polarization but volume scattering acts as a function of depolarization, and the method of polarization remote sensing can improve the understanding of camouflage detection.

Analysis of polarimetric characteristics of camouflage targets

The performance of camouflage targets recognition using visible and infrared images is limited by the low contrast in intensity for complex backgrounds. We are developing a polarization imaging technique where, in each image pixel, the polarization data is used to recognize camouflage targets. In the paper, the rationale of detection equipment is demonstrated and we analysis, using polarization images will significantly improve the performance of camouflage targets detection. Images are generated by using polarization degree and polarization angle of scattered light from the surface of camouflage targets. By using Multispectral CCD Polarization Camera, polarimetric characteristics of camouflaged targets and clutter background are measured and images of polarization degree and polarization angle are taken. Results indicate that polarimetric characteristics of scattering light from camouflaged targets are very different from that of natural backgrounds. Polarimetric imaging can eliminate the influence of backgrounds and enhance the efficiency of reconnaissance. Compared with reflectance images, polarization images have advantages in camouflage targets detection.

Thermophysical properties and stability of paraffin microemulsions as latent functionally thermal fluid

Paraffin microemulsions are multifunctional thermal fluid consisting of water as the continuous phase and paraffin as the dispersed phase. They can store or transfer a large amount of thermal energy by using the latent heat capacity of the paraffin during the phase transition as well as the sensible heat capacity of water. In this study, hexadecane O/W microemulsions were emulsified by an ionic surfactant SDS and a co-surfactant butanol. The phase behavior, effective stability, droplet size and thermophysical properties, such as latent heat and dynamic viscosity, were investigated experimentally. The results showed the prepared microemulsion with 30 wt.% hexadecane has expected high heat capacity about 93.4 J/g and low viscosity about 21 mpa·s. The average droplet size is 73 nm. The results indicate that they have potential applications in thermal energy storage and transfer.