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2. ENGINEERING AND TECHNOLOGY
In this paper we report on a novel approach to implementing a compact humidity sensor that utilizes whispering gallery mode (WGM) phenomena in a silica microsphere coated with Agarose hydrogel. The spectral positions of the WGM resonances for such a sensor depend strongly on the refractive index and thickness of the coating. The WGM’s spectral shift occurs due to adsorption/desorption of the water vapor in response to changes in ambient humidity and also due to the corresponding changes of the coating thickness. We experimentally investigated the WGMs spectral shift for a 100 μm diameter silica microsphere coated with Agarose hydrogel over a wide range of relative humidity (RH) values from 30%RH to 70%RH at a constant temperature. Six dip coating cycles of 2.25% wt. /vol. Agarose hydrogel were carried out in sequence with a characterization of the sensor performed for each coating thickness. A resonance shift of 16 nm is achieved in our experiment for the six-layer Agarose hydrogel coating sensor
Mallik, A., Liu, D., & Kavungal, V. (2017). Compact humidity sensor based on a multi-layer Agarose hydrogel coated silica microsphere resonator. Researchgate.net. doi:org/10.1117/12.2263529.