Effect of agarose concentration on coated micro-bottle resonators for humidity detection

Agarose is a stable hydrophilic material commonly used for relative humidity sensing application. Agarose porous nature causes changes in its refractive index as relative humidity change. Micro bottle resonators are a promising choice for sensing applications due to their good quality factor. In this work, the effect of agarose gel concentration on micro-bottle ability to detect relative humidity changes was investigated. The agarose gel coating was made in two different concentrations 0.5% and 1%. These two concentrations were used as coating for microbottle resonators with the diameter of 190 μm. The micro-bottle samples were made by the soften-and-compress technique. In the humidity range of 35%–85% RH, the 0.5% agarose gel coated microbottle had a sensitivity of 0.1077 dB/RH%. The microbottle resonator coated with the 1% solution showed a lower sensitivity of 0.0899 dB/RH%. This improvement in sensitivity with lower agarose gel concentration is due to the pore size of agarose gel. Yet, both concentrations showed improvement in sensitivity compared to the bare micro-bottle showing that agarose can be a potential choice for building sensitive efficient relative humidity sensors.