Printed Self-Resonant Sensor on Building Envelope for Wall Integrity Monitoring

A screen printed self-resonant sensor is designed and printed on Tyvek® substrates to monitor the relative humidity (RH) and moisture level change inside the walls for early detection of moisture-related building problems. The highly sensitive sensor is based on the detection of the major resonant frequency shift in the reflection spectrum of the printed structure, which is highly sensitive to water. Tyvek® made by flash spinning extremely fine high-density polyethylene fibers allows for water vapor permeability and has been commonly used as house wrap in the walls. Two designs of the self-resonant sensors are modeled using 3-D finite element method and are printed within the Tyvek® envelope patch to monitor the RH level difference in a controlled chamber. Both modeling and experimental results have proven the effectiveness of the passive sensors to detect a small water droplet of 50 μL and RH change of as small as 10% variation.