Development of Flexible Moisture Sensors Based on the Corrosion and Degradation of Conductive Substrates

Water and moisture sensing are becoming essential features measured in clean energy and transportation applications. In this study, we develop sensors with the ability to detect moisture through two distinct conductive technologies: (1) a change in morphology using water-soluble polymer composite foams and (2) a rust-induced change or resistance change caused by the corrosion of a metal substrate. Five different foam sensors were successfully fabricated, tested, and determined as functional moisture sensors following their time and relative humidity responses. The sensors’ sensitivity was calculated, and a maximum sensitivity of 3.61 kΩ/RH % was achieved. The electrical properties, foam morphologies, and chemical, thermal, and mechanical properties of the foams were measured and compared. The second sensing technology encompasses a magnesium–copper galvanic system which when in contact with water for extended periods of time will corrode (i.e., convert the metal into metal oxide), causing an irreversible change through an increase in resistance, subsequently alerting the user of possible water flooding. The metallic sensors were tested at three different outdoor temperatures (0, 23, and 50 °C) in order to characterize the influence of temperature. They were also tested with a direct force where corrosion was accelerated. Chipless microwave resonators were utilized as platforms for investigation of the performance of the developed sensors. Both technologies presented act as both the substrate and sensing material.