Measurements of flow velocity in a microscopic region using a transmission grating: a differential type

Abstract

A method is described for measuring flow velocity in a microscopic region by means of a differential-type laser velocimeter with a transmission grating. The principle of this velocimeter is described on the basis of spatial filtering of the transmission grating. The filtering characteristics are theoretically analyzed using a power spectral density function. The velocimeter is used to measure flow velocities and their spatial distributions in a small (700-μm diam) glass tube. The theoretical and experimental results show that this differential-type velocimeter is more suitable and practical than the conventional one for measuring the flow velocity in a small probe.