Solar radiation estimation using artificial neural networks

Artificial Neural Network Methods are discussed for estimating solar radiation by first estimating the clearness index. Radial Basis Functions, RBF, and Multilayer Perceptron, MLP, models have been investigated using long-term data from eight stations in Oman. It is shown that both the RBF and MLP models performed well based on the root-mean-square error between the observed and estimated solar radiations. However, the RBF models are preferred since they require less computing power. The RBF model, obtained by training with data from the meteorological stations at Masirah, Salalah, Seeb, Sur, Fahud and Sohar, and testing with those from Buraimi and Marmul, was the best. This model can be used to estimate the solar radiation at any location in Oman.     

Design of resonant-cavity-enhanced photodetectors using geneticalgorithms

Expressions of quantum efficiency of resonant-cavity-enhanced (RCE) PIN photodetectors reported in the literature are based on the assumption of constant reflectivities of the quarter-wave stacks (QWS) at the ends of the cavity. The quantum efficiency is formulated in a closed analytical form that includes the structural parameters of the photodetector and takes into account the wavelength dependence of the reflectivities and the active region absorption coefficient. The variation of the QWS reflectivity and, in particular, its phase constant with wavelength has a significant influence on the resulting quantum efficiency spectra, as demonstrated in this paper. The results are in very good agreement with recently published experimental data which show a dominant peak at the operating wavelength. This behavior has not been predicted by previous simulation results. Since the quantum efficiency spectra are not periodic, the use of the finesse, defined as the ratio of the free spectral range to the full width at half maximum, as a measure of wavelength selectivity is not valid. The conventional quality factor definition used for filter design is thus adopted as a measure of selectivity. A genetic algorithm-based optimization and design procedure for RCE photodetectors have also been developed with the quantum efficiency, quality factor, and frequency bandwidth as input design parameters     

Design of ultra-fast dual-wavelength resonant-cavity-enhancedSchottky photodetectors

A systematic optimization procedure for the design of RCE Schottky photodetectors to achieve maximum quantum efficiency and high speed operation at 1.3 and 1.55 μm wavelengths is presented. The quantum efficiency formulation used includes the structural parameters of the photodetector and takes into account the wavelength dependence of the top and bottom mirrors reflectivities. The results have shown that the value of the thickness of the antireflection coating layer has a major influence in selecting the width of the photodetector to simultaneously achieve maximum quantum efficiency and high bandwidth at the two wavelengths. Simulated values of 270 and 40 GHz were obtained, respectively, for the 3-dB carrier-transit time-limited bandwidth and bandwidth-efficiency product for an RCE Schottky photodetector with a 0.02-μm gold layer     

Axial cross polarization in reflector antennas with surface errors of large correlation diameter

Equations for boresight cross polarization and isolation of axisymmetric and offset antennas in the presence of surface errors are derived in terms of numerically computable integrals. Computations revealed that 1) for root mean square (rms) error< lambda/4cross polarization increases monotonically with increasing rms error; and 2) maximum cross polarization occurs when the correlation diameter is 0.5Dfor axisymmetric antennas (0.8Dfor offset antennas). For rms error>lambda/4boresight cross polarization remains almost constant. Furthermore, results revealed that for given correlation diameter and rms error, axisymmetric antennas offer better boresight isolation in comparison with offset antennas having the same polarization efficiency.     

Optimization procedure for the design of ultrafast, highlyefficient and selective resonant cavity enhanced Schottky photodiodes

An expression of quantum efficiency for high-speed resonant-cavity-enhanced (RCE) Schottky photodiodes is derived. This expression includes the structural and the physical parameters of the photodetector and takes into account the parameters of the metallic Schottky mirror and the wavelength dependence of the reflectivities. The metal layer thickness sets the maximum achievable quantum efficiency as it decays exponentially with it. The antireflection coating layer, on the other hand, determines the photodetector selectivity and the optimum absorption layer thickness that maximizes its quantum efficiency. An algorithm for the design and optimization of RCE Schottky photodetectors has been developed. Theoretical values of 647 GHz and 129 GHz were obtained, respectively, for the carrier-transit time limited 3-dB bandwidth and bandwidth-efficiency product for an RCE Schottky photodetector with a 0.02 μm gold layer     

Contour maps for sunshine ratio for Oman using radial basis function generated data

Contour maps for sunshine hours and sunshine ratios for Oman have been generated. The data to generate these maps were obtained using an RBF neural network model. This model estimates sunshine hours and ratios for a given point based on its latitude, longitude, altitude and month of the year. Data from 25 locations were used to plot the contour maps. These maps provide a needed reference for the spatial distribution of sunshine hours and sunshine ratios on a monthly basis for the whole of Oman from which estimates can be made for any location.     

Effect of profile errors with large correlation diameter on axisymmetric antenna crosspolarisation

The effect of profile errors with large correlation diameter on the boresight crosspolarisation of axisymmetric antennas is investigated. An expression for boresight isolation as a function of the correlation diameter, the r.m.s. surface error and the polarisation efficiency of the antenna is given. Curves of isolation as a function of the r.m.s. surface error and the correlation diameter are given for polarisation efficiencies of 0.99 and 0.999 (i.e. for antennas with peak off-axis cross-polarisation of ?25.3 dB and ?35.4 dB, respectively).     

Characteristic analysis of resonant-cavity-enhanced (RCE)photodetectors

Analyses of light field distribution within a lossy resonant-cavity-enhanced (RCE) p-i-n photodetector is performed. A new expression for the field distribution inside the cavity is derived. This expression is used to derive an expression for the quantum efficiency taking into account the standing wave effect. The field distribution expression is also used in the continuity equations to derive and evaluate the frequency response of the RCE photodetector