“…There is a long history of using noncontact radar and dielectric spectroscopic methods to estimate moisture content in complex systems as the water content of soils, − and building materials such as concrete, masonry, composites, wood, and the asphalt material of roads, − and in a wide range of agricultural applications . In our previous work, we employed a high-resolution noncontact dielectric microwave cavity to quantify and control confinement of absorbed water in cellulose nanocrystal materials, hydration number of water-sensitive fluorogenic dyes, and to characterize dielectric properties of epitaxial 2D graphene. , Inspired by these prior studies, the present paper explores the potential of a noncontact resonant microwave cavity-testing method to precisely monitor the complex dielectric permittivity (ε * ) of PEI samples exposed to a mixture of N 2 and CO 2 gas under different controlled levels of relative humidity (RH).…”