Detection of Air Bubbles and Liquid Droplet in a Dielectric Tube by Thermo-Elastic Optical Indicator Microscopy

A new method based on microwave near-field imaging for the detection of water droplets and air bubbles in a dielectric tube is presented. The present method is based on the optical visualization of the microwave near-field distribution excited around a dielectric tube containing water droplets and air bubbles. In this study, the microwave near-field distribution of a dielectric tube containing air bubbles and water droplets of various sizes was visualized analyzed through the thermo-elastic optical indicator microscope. From the experimental results, it was shown that the present method can measure size and distribution of millimeter-scale bubbles and water droplets in an optically opaque dielectric tube (diameter: 1.0 mm) in a non-contact, non-invasive, and non-destructive manner.