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，进行了以下研究：1）首先在水中观察了光热振动微悬臂梁的共振特性。由于水的反作用力，谐振频率比真空中的谐振频率明显降低。从实验和理论上明确了谐振频率与液体密度的关系; 3）由于液体的粘性拖曳力，液体中的谐振尖锐度Q比真空中的小得多。利用液体中的光热振动进行液体粘度的光学传感是可行的。4）利用半导体激光器的近红外辐射有效地照射液体中的微悬臂梁是非常困难的。为了研制实用化的微悬臂梁传感器，我们采用了在石英纤芯上刻蚀包层的方法，制作了直接附着在光纤上的微悬臂梁。与以往的光学系统相比，光学系统非常简单，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.