A Fringing Field Based Screen-Printed Flexible Capacitive Moisture and Water Level Sensor

A simple, low cost, screen-printed flexible capacitive sensor for moisture, and water level detection is presented in this paper. The sensor is fabricated on the flexible polyamide substrate. The interdigitated structure electrodes are screen printed on the substrate to form the capacitive fingers using carbon paste. The relative permittivity of the medium changes due to the water vapors on the sensor, which in turn changes the capacitance of the sensor due to the fringing field. A novel auto-nulling based signal conditioning circuit was utilized to measure the capacitance of the sensor. The flexible nature of the sensor enhances the use of the fabricated capacitive sensor in applications such as diaper wetness monitoring, soil moisture monitoring, body hydration monitoring.