DEVELOPMENT OF OPTICAL SENSORS FOR LIQUID DENSITY USING A MICROMACHINING TECHNIQUE

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In order to develop an optical sensor for liquid density, following studies have been carried out.1) Resonance characteristics of a microcantilever vibrated photothermally was observed in water first. The resonance frequency decreased considerably compared with that in vacuum because of the reaction force from water. The theoretical analysis on resonance frequency was also performed.2) It was cleared experimentally and theoretically that the resonance frequency depended on the liquid density.3) The resonance sharpness Q in liquid was rather smaller than that in vacuum because of the viscosity drag force from liquid. It was believed than the optical sensing for liquid viscosity was possible using the photothermal vibration in liquid.4) It was very difficult to irradiate the microcantilever in liquid efficiently with the near-infrared radiation of the laser diode. In order to develop the practical sensors, the microcantilever which was attaced directly to an optical fiber was fabricated from a quartz core by etching a clad layr from the fiber tip. Optical systems were very simple compared with previous ones, and stable resonance characteristics were obtained.