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Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Optimization of Multistage Depressed Collectors by using FEM and METEO Salvatore Coco (1) , Antonino Laudani (1) , Giuseppe Pulcini (2) , Francesco Riganti Fulginei (2) , Alessandro Salvini (2) (1) University of Catania, DIEES Catania, Italy – e-mail: alaudani@diees.unict.it (2) Roma Tre University, Department of Applied Electronics - Roma, Italy Specialized 3-D simulators are required by TWT multistage depressed collector (MDC) designers to help them to analyze and test new and arbitrarily shaped geometries for high efficiency TWTs. To perform such a task a Finite Element (FE) approach can be pursued, since it allows a very flexible meshing and gives the possibility of using irregular meshes to fit properly the MDC’s geometry; in such a way complex geometries can be accurately simulated [1]. Unfortunately, the use of optimization techniques in the design process of these devices is rarely used [2], because of the high number of parameters and the high computational cost of efficiency evaluation (the fitness function). In this paper the authors present the application of a novel metaheuristics technique called METEO (Metric-Topologicalevolutionary-Optimization) [3], to optimize the performance of multistage collectors, simulated by means of Finite element collector and electron gun simulator COLLGUN [4]. METEO [3] is a hybrid algorithm composed by three different heuristics: FSO (Flock of Starlings Optimization) [5], PSO (Particle Swarm Optimization), and BCA (Bacterial Chemotaxis Algorithm); it performs the optimization using both the topological as the metric rules. In fact the mentioned heuristics own a different performance taken alone, in particular FSO presents a high degree of exploration, and a good capability to escape from local minima, whilst PSO, and BCA own a good proprieties of convergence. Besides, they offer a natural parallel implementation that allows speeding up the whole process of optimization. This characteristic can be useful exploited in order to obtain the desired target with an acceptable computational cost. References [1] S. Coco, F. Emma, A. Laudani, S. Pulvirenti, M. Sergi, “COCA: A Novel 3-D FE Simulator for the Design of TWTs Multistage Collectors”, IEEE trans. on electron devices, 48 , 24-31, 2001. [2] T. K. Ghosh, R.G. Carter, “Optimization of Multistage Depressed Collectors”, IEEE trans. on electron devices, 54 , 2031-2039, 2007. [3] G. Pulcini, F. Riganti Fulginei, A. Salvini, “Metric-Topological-Evolutionary Optimization”, OIPE2010 Proceedings, Sofia - Bulgaria, Sept. 14-18 2010, pp. 3-4. [4] S. Coco, S. Corsaro, A. Laudani, G. Pollicino, R. Dionisio, and R. Martorana, “COLLGUN: A 3D FE simulator for the design of TWT's electron guns and multistage collectors”, Scientific Computing in Electrical Engineering, Mathematics in Industry, Springer-Verlag, 9, 175-180, 2006 [5] F. R. Fulginei, A. Salvini, “Model identification by the Flock-of-Starlings Optimization”, Int. Journal of applied Electromagnetics and Mechanics, vol. 30, n. 3-4, pp. 321-331, 2009. 50
Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Parametric bandwidth analysis of an Artificial Magnetic Conductor surface D. Ramaccia, F. Bilotti and A.Toscano University RomaTre, Department of Applied Electronics Rome, Italy – E-mail: davide.ramaccia@gmail.com In this contribution we show a possible application of Finite Integral Technique for the parametric analysis of the bandwidth of an Artificial Magnetic Conductor (AMC) made by a periodic array of metallic patches on a dielectric grounded substrate. As is well know, these structures mimic the perfect magnetic conductor condition in a small frequency range [1-3]. A typical AMC surface with square patches, its equivalent circuit representation are shown in Figure 1a and 1b respectively. a) b) Figure 1: HIS a) typical structure with square patches. b) equivalent circuit model. Consider an incident electromagnetic wave normally. If the surface is made by a Perfect electric conductor, the wave is reflected back with a 180 degree phase shift, so it is opposite in phase with respect to the incident one. If the surface is made by an AMC, the reflected wave is in phase with respect to the incident one. As mentioned before, this particular behavior is only in a small frequency range that is defined as the range within the phase shift is inside the interval [-90°;+90°]. The geometric and electrical parameters of the structure allow us to modify the values of the lumped elements and consequently the bandwidth of the structure as show in Fig. 2. Figure 2: Increased Bandwidth around 20 GHz for a AMC with periodicity D=7mm and substrate permittivity ε = 3 . References [1] O. Luukkonen et al., "Simple and Accurate Model of Planar Grids and High–Impedance Surfaces Comprising Metal Strips or Patches," IEEE Trans. Antennas Propag., 56, 1624–1632, 2008. [2] D. Sievenpiper et al., "High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band," IEEE Transaction Microwave Theory Tech., 47, 1999. [3] F.Costa et al., “On the Bandwidth of High-Impedance Frequency Selective Surfaces,” IEEE Antennas and Prop. Lett., 8, 2009. 51
Page 1 and 2: Meta 2010 & FEM 2010 - Rome, 13-15
Page 3 and 4: Meta 2010 - Committees Chairmen Met
Page 7 and 8: Meta 2010 Foreword Ladies and Gentl
Page 9 and 10: FEM 2010 Foreword Ladies and Gentle
Page 25 and 26: Session FEM-1 Magnetic device model
Page 43 and 44: Session FEM-3 Methods and solvers M
Page 47 and 48: Session FEM-4 Design and applicatio
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Page 67 and 68: Author Index Meta 2010 & FEM 2010 -

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