| Pipes are still used nowadays as a vital transporting means for gas, fuel and other goods. It is very necessary to maintain pipes to avoid lethal leaks and financial losses. This work provided a new noninvasive technique for evaluating the condition of buried pipes based on the scattered fields received by the ground penetrating radar (GPR).;Several electromagnetic simulations were studied to understand this problem. The commercial electromagnetic simulator FEKO was used in this thesis. The simulated model constituted of a pipe buried in sand illuminated by a broadband antenna (Vivaldi) with bandwidth 3GHz --- 10GHz. The involved method of moments requires meshing only the surfaces of the different geometrical structures, which reduced the computational requirements.;The electrical signature of a 2 cm circular crack in a 50 cm long metallic pipe was investigated. The pipe was buried at 30 cm below the interface of sand, clay, silt and loam. Also humus concentrations up to 10% were considered. The results showed that the crack signature is significant when fields were received right above the soil interfaces, depending on the attenuation level in the soil.;The interesting phenomenon of the natural frequencies was explored to detect cracks in buried pipes. It turned out that cracks exhibit additional resonances (to the pipe's main resonance) when observed in the far scattered fields. An algorithm based on the Matrix Pencil Method (MPM) was developed in order to extract these resonances to be expressed as poles. The poles were dependent only on the size and shape of the pipe's cracks. Once a crack existed in the pipe, additional poles were present. These poles indicate to the existence of a crack(s). Unfortunately, this method does not provide information about the number of cracks, it does provide information only about the presence of these cracks. An additional imaging technique can be used in localized positions where these cracks are detected.;A motorized scanning system was built to collect data from a buried pipe in a controlled environment. Measurements were first conducted in a 1 m 3 anechoic chamber to verify the numerical results. The simulations showed that the algorithm was capable of extracting the crack's poles with a signal to noise ratio SNR = 10 dB. The experimental data showed an SNR of -5 dB. It is believed that the available anechoic chamber does not provide accurate far field measurements due to its small size. Future research is necessary to improve the experiment set up and the sensitivity of the proposed algorithm to the inevitable noise. |
