Electromagnetic Time-Reversal Imaging of Pinholes in Pipes

We have designed and implemented a structural health monitoring (SHM) system to detect and localize multidefects in semi-infinite cylindrical metal pipelines simultaneously. The system utilizes electromagnetic decomposition of the time-reversal operator (known under French acronym DORT) signal processing method. The magnificent performance of the DORT detector against signal-to-noise ratio (SNR), and its ability to detect and localize multidefects simultaneously, are the main advantages of the DORT time-reversal method. In the DORT time-reversal method, the reversed wave would precisely retrace back the exact intricate received path to converge coherently at the original source location by using the proper Green's function. We have utilized the operating frequencies which are far enough from the (highly dispersive) band near the waveguide TE
₁₁
cut-off frequency. The radius of the pipe is assumed to be a = 10 cm. Hence, in order to excite the first two modes, frequency bandwidth is considered to be 300 MHz at the center frequency of 1.15 GHz. This system is tested to localize two rectangular holes of the area (0.13 λ
₀
)
²
, where λ
₀
is the free-space wavelength at the central frequency. In addition, required parameters such as the minimum number of antennas for detection, the DORT detector performance analysis, the equivalent reflection coefficients of the holes with different sizes and shapes, and the maximum distance of detection of small holes are calculated.