On the Application of the Incomplete QR Algorithm to the Analysis of Microstrip Antennas

In this paper, we provide some insight into the usage of fast, iterative, method-of-moments (MoM) solution of integral equations (IE) describing antennas and other metallic structures immersed in a planar multilayered environment. Based on the form of multilayered media Green's functions, we extract free-space terms, associated with direct rays within the analyzed structure, reducing the number of significant interactions required to describe the rest of MoM matrix. Next, we show that it is possible to construct a hybrid algorithm, where the fast multipole method (FMM) is used to the free-space matrix part, while the reduced rank incomplete QR (iQR) decomposition is applied to the remaining portion of the MoM matrix. This HM-iQR (hybrid multipole - incomplete QR) method is applied to a relatively large (in terms o f the number of unknowns) problem of plane wave scattering by a finite array of rectangular microstrip patches printed on a grounded dielectric slab. Computation results from the new algorithm are compared to literature data and to the results of the pure low rank IE-QR method

The influence of the specific surface of grains on the luminescence properties of Nd3+ -doped Y3Al5O12 nanopowders

Nd3+: Y3Al5O12 (Nd: YAG) powders were prepared by the Pechini method in the temperature range of 800 to 1400 degrees C. The pure garnet phase of the obtained materials was confirmed by XRD studies. The size of the grains was controlled by the annealing temperature of the samples. Their morphologies were investigated by TEM and porosity measurements ( BET). The effect of annealing temperature on the morphology and luminescence properties of Nd: YAG nanocrystallites was studied, and the results were compared to the properties of a Nd: YAG single crystal. A significant enhancement of the F-4(3/2) -> (4) I-9/2/F-4(3)/2 -> (4) I-11/2 intensity ratio with decreasing grain size was observed. It was found that the decay times of the Nd3+ luminescence depends on the specific surface and is significantly longer for well crystallized nanocrystalline grains than for single crystals having the same concentration of Nd3+ ions. The role of crystallinity and specific surface on the radiative processes is analyzed