Single-Conversion Self-Injection-Locked Radar for Underground Pipeline Leak Detection

A type of single-conversion self-injection-locked (SCSIL) radar for sensing underground pipeline leakage through moist soil is proposed. In the implemented prototype, a 5.8-GHz output signal from a self-injection-locked (SIL) oscillator (SILO) is down-converted to a 0.433-GHz transmit signal, and the echo signal is up-converted to the injection signal for the SILO. With experiments, the SCSIL radar, the conventional 5.8-GHz SIL radar, and the conventional 0.433-GHz SIL radar were compared under the same conditions, which included a 25-cm-thick soil barrier. The system sensitivity and penetration could both be improved by increasing the SILO’s locking range and decreasing the wireless propagation loss. To understand the behavior of the negative pressure wave (NPW) caused by pipeline leakage, simulations were conducted using MATLAB, and the detection principles were evaluated. In noncontact underground pipeline leakage detection, the standard deviation (STD) of demodulated signals can be used to estimate a leak’s location. Leakage detection and localization were successfully achieved by making measurements at different measurement points; furthermore, variables such as the leak size and diameter of the pipeline were investigated.