The use of this sensor is to measure drip. Dripping must happen at a precise location. Should be able to measure any liquid dripping. Dripping occurs from a precise location, through a 1 cm2 area. Dripping might occur from hot objects, and low dripping rates might not be visible, due to evaporation (I suppose we can define a no-dripping which includes this eventuality without having to measure the fluid loss to evaporation, just based on some assumptions, because temperature sensors are also installed on the same device).
The sensor must be small format, to fit within an enclosed space of a few cm3.
The sensor is used in an environment with potentially high EM (electromagnetic) noise.