A Microwave Sensor System for the Unattended Control of Corrosion in Urban Metallic Infrastructures

This article presents a microwave sensor system (including the electromagnetic module and the associated electronics for signal generation and processing) useful for unattendedly monitoring the corrosion level in urban metallic infrastructures, particularly, streetlights and traffic lights. The electromagnetic module consists of a microstrip line loaded with a slot resonator, the sensitive element, transversely etched in the ground plane. To make the electromagnetic module conformal, a necessity for the intended application, the slot-loaded line has been implemented in a narrow (and hence flexible) low-loss microwave substrate. To adapt it to the circular shape of the metallic infrastructure, streetlights with different curvature shapes in the reported example cases, a conformal 3-D-printed piece of polylactic acid (PLA) has been fabricated. By sandwiching the electromagnetic module between such PLA piece and the surface of the streetlight subjected to corrosion control, perfect contact of it with the sensing element is achieved. The output variable of the sensor is the magnitude of the transmission coefficient of the slot-loaded line at a specific frequency (correlated with the level of corrosion of the surface) converted to a voltage by means of an envelope detector. The functionality of the proposed sensor is validated by means of a complete system, including the associated electronics.