Water detection using bi-wires as sensing elements: Comparison between capacimetry-based and Time-of-Flight-Based Techniques

It is known that bi-wires can be employed as passive distributed sensing elements (SE), to accurately locate water infiltrations in soil, concrete materials, etc., using standard TDR instrumentation and proper signal processing. The present work examines the possibility of using the same kind of SE’s with simpler techniques and cheaper hardware, in order to trigger an alert in case of water infiltrations. Two techniques are examined: the first measures the SE capacitance, and the second the Time-of-Flight (ToF) of electromagnetic waves in the SE. The performance of the techniques is comparatively evaluated, in terms of (i) sensitivity to the presence of water, and (ii) influence of temperature variations. The capacitance-based technique is found to be more sensitive to the presence of water, but also more prone to the influence of temperature, as long as the temperature variations are of modest entity (below 10 °C). For higher temperature variations, the capacimetric method appears to be advantageous. The results of the paper are useful to practically implement the monitoring of, e.g., water leaks in a large set of buried pipes, water infiltrations in a large concrete structure, etc.