全内反射测速技术(TIRV)中界面隐失波基准光强I0的确定

基于隐失波全内反射的测速技术TIRV (Total internal reflection velocimetry)是微纳流动中测量壁面附近几百纳米范围内速度的有效方法。隐失波的光强分布I (z)随离开壁面的高度z指数衰减。若荧光粒子位于光强分布中,其亮度也将符合此指数关系,通过测量粒子亮度可确定粒子的垂向位置z,而确定隐失波的基准光强I0是该技术的关键之一。基于粒子近壁Boltzmann浓度分布、粒子粒径不均匀性和隐失波光强公式,给出了粒子亮度概率密度分布的数值解。实验测量粒子统计亮度分布后,依据实验和理论分布相同原则可定量确定基准光强I0。采用φ100nm和φ250nm 荧光粒子验证此方法并定量分析了粒径分散性对确定 I0的影响。进一步采用φ100nm粒子进行近壁速度测量实验,结果验证了本方法的有效性。

Determination of the interfacial evanescent wave base intensity I0 in total internal reflection velocimetry (TIRV)

The total internal reflection velocimetry (TIRV)based on evanescent wave is an ef-ficient method for velocity measurement within a few hundred nanometers to the wall.The eva-nescent wave intensity,I(z),decays exponentially with the distance z away from the wall.When a nanotracer located in this field is illuminated by evanescent wave,its radiation intensity will also obey the exponential decay low,and thus it is possible to determine the nanotracer’s z position by its illuminated intensity.Obviously,one of the key issues of this technology is to determine the base intensity I0 . In this paper,a numerical solution of the nanotracer intensity probability density function is given to predict the intensity distribution according to the exponential decay of the evanescent wave,the tracer concentration distribution and the tracer size variation.By com-paring the measured intensity distribution with the theoretical prediction,the base intensity I0 can be quantitatively determined.Fluorescent polystyrene spheres ofφ100nm andφ250nm are used in the measurements.The validity of this method is verified.The effect of the nanotracer size variation on the determination of I0 is also analyzed.Furthermore,φ100nm nanotracers are used to measure the velocity close to the wall,and the result verifies the validity of our method.