Measurements of flow velocity in a microscopic region using a transmission grating: elimination of directional ambiguity

Abstract

This paper describes a method of eliminating the directional ambiguity in the flow velocity measured in a microscopic region using a transmission grating. The opposite directions of the flow are discriminated from the phase relation between two output signals obtained from the two photodetectors with transmission gratings. The method is applied to measurements of flow velocity in a small (3-mm diam) glass tube. The experimental results verify the usefulness of the method for determining the flow direction in transmission grating velocimetry.