Date of Award

Fall 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Leland W. Weiss

Abstract

Increasing focus on alternative energy sources has produced significant progress across a wide variety of research areas. One particular area of interest has been solar energy. The sun represents sustainable and renewable energy source capable of meeting present energy needs without compromising the ability of future generations to meet theirs. Energy from the sun can be utilized in multiple ways. Direct rise in modern power generation typically involves either photovoltaic systems or large-scale solar thermal energy installations. While large-scale solar thermal energy generation is well advanced, there has been comparatively little research on smaller scale thermal energy collection and application. This work presents investigations into micro solar thermal energy development and use for MEMS-based power applications. This approach is divergent from traditional micro solar photovoltaic devices, relying on transforming incoming solar energy to heat for use by devices like thermoelectric generators (TEG) and other heat engines. The ability to maximize temperature gain from the sun's heat energy while minimizing heat losses is critical for a system that relies on solar energy for useful mechanical or electrical work output. The use of a manometer-scale solar selective absorber coating to enhance the performance of a TEG module in solar thermal energy harvesting is presented. The thin film coating is fabricated by electrochemical deposition of a bimetallic layer of tin and nickel on copper substrate. Further, the use of vacuum packaging to limit heat losses from the collector plate is examined. Limiting heat losses is shown to improve the overall efficiency of these devices. Also, a thermal scavenging technique that relies on phase change within the working fluid in a micro capillary channel heat exchanger is presented. These devices have the potential to provide autonomous power for micro electronics, and represent sustainable alternatives to battery-powered MEMS-based devices.

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