Enhancement of inductive power transfer with flat spiral resonators

Puccetti Giovanni - Ciclo XXVII - 2015

Abstract - The aim of this thesis is to develop a depth analysis of the inductive power transfer (or wireless power transfer, WPT) along a metamaterial composed of cells arranged in a planar conguration, in order to deliver power to a receiver sliding on them. In this way, the problem of the eciency strongly aected by the weak coupling between emitter and receiver can be obviated, and the distance of transmission can signicantly be increased. This study is made using a circuital approach and the magnetoinductive wave (MIW) theory, in order to simply explain the behavior of the transmission coecient and e- ciency from the circuital and experimental point of view. Moreover, at spiral resonators are used as metamaterial cells, particularly indicated in literature for WPT metamate- rials operating at MHz frequencies (5-30 MHz). Finally, this thesis presents a complete electrical characterization of multilayer and multiturn at spiral resonators and, in par- ticular, it proposes a new approach for the resistance calculation through nite element simulations, in order to consider all the high frequency parasitic eects. Multilayer and multiturn at spiral resonators are studied in order to decrease the operating frequency down to kHz, maintaining small external dimensions and allowing the metamaterials to be supplied by electronic power converters (resonant inverters).

Fabrication, Electrical Characterization and Simulation of Thin Film Solar Cells: CdTe and CIGS Materials

Nima E. Gorji- Ciclo XXVI - 2014

Abstract - In this thesis we investigated thin film solar cells based on chalcogenide CdTe and Cu(In,Ga)Se2 (CIGS) materials. The CdTe devices were fabricated by R.F. Magnetron sputtering characterized electrically and optically and were numerically simulated for degradation studies. The role of defective surfaces, pinholes, CdCl2 treatment and surface modification was studied in order to increase the stability of these devices. The numerical analysis indicates that defect generation can degrade the electrical parameters mostly at the junction of CdS/CdTe. In another hand, we characterized the CIGS thin film devices by admittance spectroscopy and surface photovoltage spectroscopy. The shunt and series resistances, bulk defect levels, graded bandgap and interface states were extracted. We also proposed several graded bandgap profiles based on valence band grading. The simulations carried out indicate that the graded band gap can increase the photocurrent while the Auger generation can increase the thermodynamic efficiency of the device.

Metodi di ottimizzazione globale per problemi di sintesi elettromagnetica

Massimo Fabbri - Ciclo VIII - 1997 

Abstract - L’oggetto di questa tesi è l’analisi di alcuni metodi di ottimizzazione globale e la loro applicazione ad alcuni problemi di sintesi elettromagnetica. I metodi studiati sono tre:
- il metodo di ottimizzazione globale delle Search Trajectories (ST)
- il metodo di ottimizzazione globale delle Evolution Strategies (ES)
- il metodo di ottimizzazione globale delle Filled Functions (FF)
Le procedure di calcolo che sono state ottenute a partire dai suddetti metodi sono state prima testate su funzioni note e poi applicate ai problemi di sintesi elettromagnetica. Ogni metodo ha le sue particolarità che si sono evidenziate nella trattazione teorica e nella validazione con i problemi test. Sono stati effettuati confronti incrociati fra i risultati ottenuti dai tre metodi, in particolare per determinarne la convergenza al minimo globale.