Elevation resolution is an important indicator in tomographic SAR imaging as it represents the ability to discriminate closed targets in elevation. In general, the elevation resolution is proportional to the length of the elevation aperture. However, as the elevation aperture increases, the geometric consistency of the image will undesirably deteriorate and hence fails the image coregistration approach required by the traditional super-resolution tomographic imaging. In this paper, a new super-resolution tomographic imaging method is proposed to overcome the inconsistency problem caused by the large elevation aperture. The core strategy is to get rid of two-dimensional image coregistration by applying a three-dimensional (3D) back projection like imaging manner: the 3D space is firstly divided into a 3D imaging grid, each of which is individually imaged via compressive sensing for super-resolution. The effectiveness of the proposed approach is evaluated by both computer simulations and real P-band UAV SAR data.

Light-emitting diodes (LED) chip scale packages (CSPs) have been promoted as a new light source with many advantages in smaller package size, lower material and process cost, and better heat dissipation effect. However, as it is exposed in harsh environments such as high temperature, high humidity, and high blue light irradiation, silicone material used in LED CSPs always suffers deterioration, which will seriously affect the LED's reliability and working life. Thus, the preparation of high reliable silicone has practical significance to promote the application of LED CSPs in lighting. In this research, titanium was introduced into the molecular chain of phenyl silicone by using the hydrolysis condensation method. A high temperature aging test was then performed to the prepared silicone before and after modification, and their optical, thermomechanical, and dielectric properties were characterized to evaluate their reliabilities. The results show that: (1) the Arrhenius function with the dielectric property as an aging characterization can be used as a temperature accelerated life model to predict the service life of the prepared silicone and (2) the titanium modified silicone can advance the high temperature stability on optical properties, thermomechanical, and dielectric properties and enhance the life expectancy. The major contributions of this study are to support the improvement of the novel LED CSP packaging materials and processes, and also to provide the technical guidance on the fast, accurate, and cost-effective reliability assessment for high-quality LED light sources.

In a high-power white light emitting diode (LED) package, the phosphor/silicone composite is typically used for photometric and colorimetric conversions, ultimately producing the white light. However, the phosphor/silicone composite is always exposed under harsh environments with high temperature, high blue light irradiation and high moisture when the LED operates. Therefore, its reliability issue has become one of the critical bottlenecks to improve the lifetime of a high-power white LED package. As the curing process and mechanical behavior of phosphor/silicone composite essentially determine its reliability, this paper firstly uses an in situ viscosity monitoring approach combined with Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) analysis to explain the curing mechanism of a phosphor/silicone composite by taking the effects of temperature and phosphor mass fraction into consideration. Then, the mechanical properties of phosphor/silicone composites aged under a long-term high moisture condition are evaluated by using the tensile test. Meanwhile, the finite element (FE) simulations, the Mori-Tanaka theoretical estimations and the microstructure analysis are applied to investigate the high moisture induced degradation mechanisms. The results show that: (1) the in situ measured isothermal viscosity curves of both pristine silicone and phosphor/silicone composites follow the Arrhenius empirical model, and high temperature and high phosphor mass fraction can increase the curing rate; (2) the hydrosilylation reaction between silicones determines the curing mechanism of phosphor/silicone composite; (3) the tensile test, FE simulation and Mori-Tanaka theoretical prediction results confirm that the Young's modulus of phosphor/silicone composite increases by gradually adding phosphors; and (4) the Young's modulus of phosphor/silicone composite increases after the high moisture ageing test, which can be attributed to the oxidation and cross-linking reaction of silicone and the hydrolysis of phosphor powders.