Radar Sub-surface Sensing for Mapping the Extent of Hydraulic Fractures and for Monitoring Lake Ice and Design of Some Novel Antennas
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Hydraulic fracturing, which is a fast-developing well-stimulation technique, has greatly expanded oil and natural gas production in the United States. As the use of hydraulic fracturing has grown, concerns about its environmental impacts have also increased. A sub-surface imaging radar that can detect the extent of hydraulic fractures is highly demanded, but existing radar designs cannot meet the requirement of penetration range on the order of kilometers due to the exorbitant propagation loss in the ground. In the thesis, a medium frequency (MF) band sub-surface radar sensing system is proposed to extend the detectable range to kilometers in rock layers. Algorithms for cross-hole and single-hole configurations are developed and tested based on simulations using point targets and realistic fractured rock models. A super-miniaturized borehole antenna and its feeding network are also designed for this radar system. The antenna makes use of a composite ferrite core and has dimensions of Î»0/35 — Î»0/1500 — Î»0/1500 that can fit within a borehole and shows a decent radiation efficiency of 10% even with a conducting cylinder passing through the center of the antenna.
Also application of imaging radars for sub-surface sensing frozen lakes at Arctic regions is investigated. The scattering mechanism of the lake ice is the key point to understand the radar data and to extract useful information. To explore this topic, a full-wave simulation model to analyze lake ice scattering phenomenology that includes columnar air bubbles is presented. The proposed model can handle complex interactions between high density air bubbles and rough ice surfaces. Based on this model, the scattering mechanism from the rough ice/water interface and columnar air bubbles in the ice at C band is addressed and concluded that the roughness at the interface between ice and water is the dominate contributor to backscatter and once the lake is completely frozen the backscatter diminishes significantly.
Radar remote sensing systems often require high-performance antennas with special specifications. Besides the borehole antenna for MF band subsurface imaging system, several other antennas are also designed for potential radar systems. Surface-to-borehole setup is an alternative configuration for subsurface imaging system, which requires a miniaturized planar antenna placed on the surface. Such antenna is developed with using artificial electromagnetic materials for size reduction. Furthermore, circularly polarized (CP) waveform can be used for imaging system and omnidirectional CP antenna is needed. Thus, a low-profile planar azimuthal omnidirectional CP antenna with dimensions of 0.5Î»0 — 0.2Î»0 — 0.06Î»0, gain of 1dB and bandwidth of 40 MHz is designed at 2.4 GHz by combining a novel slot antenna and a PIFA antenna.