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Low-frequency electromagnetic fields for the detection of buried objects in the shallow sub-surface

Cross, James Dorian (2014)
Ph.D. thesis, University of Birmingham.

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Abstract

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.

Type of Work:Ph.D. thesis.
Supervisor(s):Atkins, Phil
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Electronic, Electrical and Computer Engineering
Subjects:TK Electrical engineering. Electronics Nuclear engineering
Institution:University of Birmingham
ID Code:4996
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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