LED光源微質點影像測速儀之發展與應用

Development and Application of an LED Micro-PIV System

本研究旨在發展以發光二極體（light-emitting diode, LED）為光源的微質點影像測速儀，並應叫於微流場量測。由高功率LED所發出的光、以光纖導入裝置於顯微鏡上之環狀聚光鏡，此環狀聚光鏡提供離軸照明式圓錐形光路，只讓微流場中的質點散射光進入顯微鏡，免除因入射光直接照射量測區所造成的背景雜訊，故可拍攝得高對比、低雜訊、極為清晰的流場質點影像。LED具有高閃頻的特性，以數位訊號驅動，兩次閃爍之間的時間差可短至100微秒，故測速的動態範圍足以涵蓋大多數微流場的應用。LED便宜、耐用、且對眼睛不會造成傷害，與環狀聚光鏡配合應用，可組合成量測效果極佳的微質點影像測速儀。研究中以此LED微質點影像測速儀量測微渠道流場、均勻流通過圓柱流場、與流體動力聚焦流場，均獲得良好的量測結果。 A micro-PIV system using LED (light-emitting diode) as the light source is proposed in this study. LED is safe to human eyes and has much higher flashing rate than pulsed laser, which makes it a good candidate for the light source of micro PIV systems. The defect of low output power of LED is overcome by adopting a cardioid annular condenser in the microscope to enhance image quality. Clear, dark background particle images were captured from the micro-PIV system proposed. The LED micro-PIV system developed was then applied to measure channel flow, flow past circular cylinder, and hydrodynamic focusing flow in micro channel. It is found that satisfactory results were obtained for all the flow fields measured.