DEVELOPMENT OF OPTICAL SENSORS FOR LIQUID DENSITY USING A MICROMACHINING TECHNIQUE

为了研制一种液体密度光学传感器，本文进行了以下研究。1)首先在水中观察了微悬臂梁光热振动的共振特性。由于水的反作用力，共振频率比真空中的共振频率大大降低。对谐振频率进行了理论分析。2)实验和理论证明了共振频率与液体密度的关系。3)由于液体的黏性阻力，液体中的共振锐度Q比真空中的要小。认为利用液体中的光热振动实现液体粘度的光学传感是可行的。4)激光二极管的近红外辐射很难有效地照射液体中的微悬臂梁。为了开发实用的传感器，在石英芯上刻蚀光纤尖端的包层，制成了直接附着在光纤上的微悬臂梁。光学系统与以前的光学系统相比非常简单，并且获得了稳定的谐振特性。

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.