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Solid oxide fuel cell (SOFC) is the most efficient energy conversion technology of alltime in producing electricity from fuels. However, temperature-driven premature degradation is one of the biggest problems that impedes the widespread use of this technology. Understanding the temperature distribution of an operating SOFC is central to mitigate such degradations as well as to further enhance the performance. The published efforts on SOFC temperature sensing, except small button cells, are mainly confined to measure temperature only from the gas channels (fuel/ air) with relatively low spatial resolution. However, the electrodes' temperature distribution measured with an adequate spatial resolution is more desirable than the gas temperature to investigate a cells' behaviour and its correlation to a stack's performance. The insufficiency of technology to in situ monitor the cell surface temperature distribution with an adequate spatial resolution was identified as a crucial research gap in the SOFC development cycle. Therefore, this research is aimed at developing a sensing technology to monitor in situ the cell surface temperature distribution of an operating SOFC with an adequately high spatial resolution and applying that technology to get a better insight into SOFC operation.

In the past few years, microwave-photonics technologies have been investigated for optical fiber sensing. By introducing microwave modulation into the optical system, the optical detection is synchronized with the microwave modulation frequency. As a result, the system has a high SNR and thus an improved detection limit. In addition, the phase of the microwave-modulated light can be obtained and Fourier transformed to find the time-of-arrival information for distributed sensing. Recently, an incoherent optical-carrier-based microwave interferometry (OCMI) technique has been demonstrated for fully distributed sensing with high spatial resolution and large measurement range. Since the modal interference has little influence on the OCMI signal, the OCMI is insensitive to the types of optical waveguide. Motivated by the needs of distributed measurement in the harsh environment, in the first part of this paper, several OCMI-based sensing systems were built by using special multimode waveguides to perform sensing for heavy duty applications. Driven by an interest on the high-resolution sensing, in the second part of the paper, I propose a coherence-gated microwave photonics interferometry (CMPI) technique, which uses a coherent light source to obtain the optical interference signal from cascaded weak reflectors. The coherence length of the light source is carefully chosen or controlled to gate the signal so that distributed sensing can be achieved. The experimental results indicate that the strain resolution can be better than 0.6 µε using a Fabry-Perot interferometer (FPI) with a cavity length of 1.5 cm. Further improvement of the strain resolution to the 1 nε level is achievable by increasing the cavity length of the FPI to over 1m. The CMPI has also been utilized for distributed dynamic measurement of vibration by using a new signal processing method. The fast time-varying optical interference intensity change induced by the sub-scan rate vibration is recorded in the frequency domain. After Fourier transform, distinctive features are shown at the vibration location in the time domain signal, where the vibration frequency and intensity can be retrieved. The signal processing method supports vibration measurement of multiple points with the measurable frequency of up to 20 kHz.

The advancement of renewable energy technologies is critical due to the unsustainable nature of currently used energy sources and the need to meet increasing energy demands. A broad and diverse energy plan is important for long term energy independence and stability. Geothermal energy sources including hydrothermal systems and enhanced geothermal systems (EGS) should play a key role in this energy plan. Geothermal energy is the most reliable, currently developed, schedulable alternative energy source. It is estimated that improvements in these systems have the potential to provide at least 200,000 exajoules of energy to the U.S. in as little as 50 years [1]. The progress in developing this field is challenging in part due to the complex geochemical and geophysical properties of the subsurface environment. This dissertation reviews geothermal energy system limitations due to current well monitoring technologies and introduces microelectromechanical systems (MEMS) sensors as a means of optimizing well performance. Harsh environment MEMS offer an ideal alternative to macro-scale sensors due to their harsh environment material compatibility, the ability to couple MEMS with wireless RF transmission systems, and their small footprint.In this work, harsh environment MEMS encapsulation materials are tested in simulated geothermal environments to determine their survivability. The sensors must be encapsulated to provide protection from oxidation, erosion, surface roughening, and other chemical attacks. Encapsulation materials such as silicon carbide, sapphire, vitreous carbon, and poly-crystalline diamond were tested in multiple simulated geothermal environments to determine a suitable protective layer for these MEMS devices. Once appropriate materials are determined, two temperature sensors are designed, optimized, fabricated, and tested. The first sensor improves upon existing out-of-plane MEMS capacitive temperature sensor devices by utilizing harsh environment materials. The second sensor is a novel in-plane design optimized to linearize capacitive output. These sensors are tested up to over 650 °C.[1] Massachusetts Institute of Technology. The future of geothermal energy: Impact of enhanced geothermal systems (egs) on the united states in the 21st century. 2006