Liquid density sensing by using a photothermal vibration

Abstract An optical sensing system for measuring liquid density, which uses the resonance frequency shift of a membrane vibrated by the photothermal effect in liquid, is described. On increasing the liquid density from 0.79 to 1.18 g/cm 3 , the resonance frequency for the membrane with a cantilever structure decreased monotonically from 1940 to 1700 Hz by sound radiation from the vibrating membrane.