In this preliminary paper, we present a spatial filtering technique based on the wave equation for an one-dimensional waveguide and apply it to extract an acoustic leak signal, which is a symptom of a leak from a pipeline system, embedded in severe background noises. Two sets of sensor array, each of which consists of a pair of PVDF film elements, are installed at the both ends of the monitoring interval, so that the measured wave motions are decomposed into positive and negative traveling wave components. After an appropriate processing of these traveling waves, the background noises, which come from outside of the monitoring interval, are canceled and only the leak signal remains. Some preliminary experiments show that the proposed method can provide 10–100 times progress in the S/N ratio even if both the leak signal and the background noise are in the same frequency band.

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