Editing Humidity Detector Based on Quartz Crystal Oscillator (section)

=== Preparation of the Hygroscopic Sensing Layer ===
To functionalize the quartz crystal for humidity sensing, a sodium silicate (water glass) thin film was deposited onto its surface.

1. '''Dilution:''' 20μL original sodium silicate solution was diluted with 10 mL DI water to achieve a volume ratio of 1:500.

2. '''Drop-casting:''' Using a micropipette, approximately 6 μL of the diluted solution was carefully drop-cast onto the center region of the quartz crystal. The gold electrodes at the periphery were strictly left uncovered to prevent any interference with electrical conduction.

3. '''Curing:''' The coated crystal was placed on a hot plate to heat gradually to a temperature range of 60–80 °C. It was maintained under these conditions for approximately one hour to fully evaporate the solvent. Then it was cooled down natuarally to room temperature, resulting in the formation of a solid, hygroscopic thin film.
[[File:Solution-on-crystal.jpeg|500px|thumb|center|Dropped solution on the quartz crystal]]
[[File:Hot-plate.jpeg|500px|thumb|center|Heating on the hot plate]]