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"High-frequency electromagnetic induction sensing for buried utility detection and mapping"

Abstract

Detecting and locating underground metallic and non-metallic utilities infrastructure is an important problem for utility maintainers and digging crews. Deteriorating or leaky gas distribution pipes pose a public safety and environmental hazard but can be difficult to locate due to poor record keeping or broken tracing wires. Many geophysical sensing techniques have been used to detect buried pipes and wires including acoustic methods, ground penetrating radar and low frequency electromagnetic induction. Each of these techniques has success in some environments or circumstances, but no sensing technique is completely robust. This thesis investigates a new technique for detecting subsurface pipes and wires: high frequency electromagnetic induction (HFEMI) sensing. Utilizing a frequency range of 10 kHz - 10 MHz, HFEMI has been used successfully for detecting and locating low-conducting subsurface targets such as improvised explosive devices (IED). In this thesis we show that HFEMI can be used to detect buried pipes and wires.

To model the electric currents induced on buried targets we use the Method of Moments. Using this technique, we examine the impact of soil conductivity, target diameter and length, and excitation frequency on the signal produced by buried targets. We study the performance of a bistatic gradiometer utility detection system and quantify its effectiveness at suppressing the transmitter field. Example data from a prototype system is presented and inverted for target depth. In addition, the surface impedance boundary condition (SIBC) is used to model corrosion along a pipe. Sommerfeld integral techniques are used to study the role of the air-soil interface in the target excitation and detection. Finally, studies are done of the target-to-transmitter signal ratio for several frequencies and excitation geometries. These studies inform the feasible operating regions for a gradiometric utility detection system.

Committee Members:

• Professor Fridon Shubitidze, PhD (Chair)
• Professor Colin Meyer, PhD
• Professor Benjamin Barrowes, PhD