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Title: Low-frequency electromagnetic fields for the detection of buried objects in the shallow sub-surface
Author: Cross, James
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2014
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This thesis explores the application of low-frequency electromagnetic fields, which may be excited within a buried pipe, for the detection of underground utilities. Low-cost network analyser technology, which can be applied to field-measurements of the relative-permittivity of soil, is evaluated. These technologies are compared to laboratory-grade alternatives whose cost prohibits their use for field work. Methodologies for the measurement of the relative-permittivity of soil are discussed with reference to the low-cost technology, including use of a novel coaxial cavity which incorporates a step-discontinuity. It is shown that there is potential for use of low-cost network analysers in measuring relative-permittivity, but that further research is required to formulate a complete methodology. The propagation of electromagnetic waves in layered media is discussed. The recent literature relating to this field is extensively reviewed, with several errors and omissions highlighted. A new calculation is presented which allows the calculation of the electromagnetic field due to a vertical electric dipole in a four-layered medium. Example results, including an approximation of a leaking pipe, are presented. Finally, two sets of field trials are reviewed. The first field trials looked to observe waves propagating with low-velocity in the ground, by measuring the phase change along an array of receiving probes. Waves, propagating with low-velocity, were observed. However, direction of arrival measurements were not achievable due to a combination of signal-to-noise ratio, and the expected phase change at the observed propagation-velocity, across an array of realistic size. The second field trials measured low-frequency electromagnetic fields, excited within a buried pipe, which were used to detect the location of the pipe with good correspondence to the ground truth. Furthermore, comparison with a ground-penetrating radar survey indicated that some anomalous results in the low-frequency electromagnetic survey corresponded to shallow targets detected using ground-penetrating radar.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering