In this paper we have designed a FEM model of an electrowetting based printing head. The design and simulation were made taking into account the requirements of the new field "printable electronics". For computational modelling, coventor CFD and Ansys FLOTRAN, CFX and multiple Cosolver were used. The computed results show that the designed principle has good resolution, high aspect ratio, fast printing speed and high accuracy in droplet placement

The paper presents a theoretical study and simulations of the variation of the contact angle in the electrowetting phenomenon. We determine the droplet shape based on the fact that when the system is in equilibrium, the energy of the system reaches local minimum. The main parameter that characterizes the droplet shape is the wetting angle. We use a differential evolution algorithm to obtain the value of the wetting angle such that the energy of the system reaches its minimum value. Simulations using the CoventorWare 2005 software have been performed, to study the variation of the droplet shape for different voltage values. The results of the simulations are in good agreement with the theoretical model

Performances of a pneumatically actuated micropump are described. Simulation results combined to an analytical model are used to optimize the micropump design in order to obtain a working frequency of 10 Hz for pneumatic pressure varying between 0.1-6 bar. A pneumatic chamber is placed between a polymer membrane to be actuated, and microchannels connected to a vacuum system. Time for pressurizing cycle and vacuum cycle as function of design parameters and relative pressure are calculated.

The present paper introduces a statistic method for estimating the maximum number of generations needed for obtaining the solution by genetic algorithms (GAs) applied in optimization problems. The most common procedure used until now is based on observations and on the intuition of the programmer for choosing the number of iterations for which the algorithm runs. This can cause a deficit either in the precision of the solution or in the runtime of the algorithm if the choice is not proper. We propose an alternative method that estimates after what number of generations there appear no more significant differences in the variance of the algorithm's results. This method is tested on optimization problems of various types: continuous/discontinuous, convex/non-convex, deterministic/stochastic. ANOVA (analysis of variance) method is used to compare the means of two or more independent random variables with normal distributions. The GA is run several times, for various numbers of generations. By gradually applying the statistical test of the ANOVA method, it is determined the moment from which no significant differences appear in the results. This method provides an optimum balance between the precision of the solution and the run time of the algorithm.

The present work proposes a genetic algorithm (GA) based method for the optimization of geometrical parameters to obtain maximum heat transfer in a micro-channel structure. The works were directed to the specific problems related to thermal transfer performances of micro-cooling systems on chip. Silicon etched micro-channels and water as cooling fluid are considered in the analysis. The results are in good agreement with those in numerical simulations, analytical models, and experimental available data.

The surface component of reverse current of operating power PN junctions at high temperature, is a source of power dissipation concentrated in a very thin layer at the junction periphery. The resulted heat in this thin layer is removed towards the heat sink only through the peripheral part of the semiconductor die area. Typical commercial rectifier diodes exhibiting surface leakage current are considered to illustrate non-uniform junction temperature distribution. At higher applied reverse voltage, the surface component of reverse current flows non-uniformly around the junction perimeter. It is shown that the thermal resistance for the heat transfer from the junction periphery is significant higher than the corresponding one for the heat removal from the junction bulk. A simple evaluation indicates that the temperature of local hot spots near the junction peripheral surface may be at least 10 /spl deg/C higher than in the junction bulk. Junction temperature peaks were observed by infrared imaging microscopy. Influence on device reliability is possible.

This work presents an example of using the genetic algorithms (GAs) for the optimization of heat transfer in heat exchangers with application in electronics micro-cooling. First, the basic structure and operation principle of GAs in optimization problems are presented. Then, the results of their application in design and optimization of heat transfer in heat exchangers are exposed. The results are in good agreement with published experimental data and other simulations in the literature.

In the present work an analytical model for the excess surface currents related to the interface states in SiC junctions is proposed. Four contributions to the current are considered: generation of charge carriers associated with surface states localized at the SiC-SiO2 interface, generation of carriers associated with traps in the depletion layer, the diffusion of carriers in the neutral region near the depletion layer, and the channel effect due to surface charge. The surface charge can cause a surface inversion layer in the low doped region of the diode. In conditions of the reverse bias, a current flows through this region-giving rise to an additionally surface component of the leakage current (surface channel current). Our calculations take into account the incomplete ionization of dopants and use the results of the charge-sheet model for SiC inversion layers. Reported experimental results on surface effects on SiC junctions are considered for the evaluation of the model.