Engineering Commons^™

Physics-Based And Behavioral Models For Fuel Cells, Charles Chima Anyim

Theses and Dissertations

In recent times there has been renewed interest in fuel cells for electricity production, especially for transportation applications. Fuel cells are attractive because the electricity production process from chemical energy does not cause pollution, and no carbon emissions occur. In this work, we will focus on Proton Exchange Membrane (PEM) fuel cells that use hydrogen and oxygen to generate electricity, producing only electricity, heat and water. If hydrogen can be produced in a green, non-polluting way, fuel cells can truly be an environmentally benign energy source.

In this work, we will look at the modeling of a fuel cell system. …

Increased Detectivity And Low Temperature Performance Analysis Of Sub-20Μm Micropixel Array A1gan Uv Photodiodes, Samia Islam

Theses and Dissertations

This thesis is divided into two sections. At first, we demonstrate ~1.5x detectivity increase in AlGaN photodiodes on sapphire using distributed micropixel arrays with 5-15 µm pixel diameter. This is due to the ~10x larger chip footprint of the 5um diameter micropixel arrays compared to planar control structures with identical p contact area. The responsivity of the larger areas was the same as that of the control structure despite the larger footprint while the dark currents, an indicator of noise, remained unchanged. The photocurrent generated between pixels was collected due to transmission line effects connecting the pixels separated by 5um, …

Electromagnetic Modeling Of Gan Varactor Microwave Switches, Yi-Hsuan Yang

Theses and Dissertations

Microwave switches are important components which have been widely used in many microwave systems, such as electronic products, satellites communications, antennas, and radars etc. Traditionally, microwave switches are fabricated using pin diodes or MEMS, Si MOSFETs or GaAs HEMTs. These devices, due to the material limitations are suffering from a low breakdown voltage and are unable to handle high power. III-Nitride based varactor microwave switches provide opportunities for high power microwave devices, due to highly conducting 2D electron gas in the channel and high breakdown electric field.

Designing microwave switches typically involves modeling and simulation using tools such as MATLAB, …