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For an electrohydrodynamic (EHD) jet, variables such as the direction of the meniscus and the ejection stability need to be analyzed. Thus, the EHD jet should be observed three-dimensionally (3D) because the variables can only be obtained in the 3D field, especially in unstable modes. However, if the 3D field is reconstructed from multi-directional binary images, eliminating reconstruction errors caused by invisible areas is almost impossible, even when using a tomographic technique. To solve this problem, a new 3D reconstruction method including an ellipse estimation was developed in this study. The method was verified by numerical simulation and applied to estimate the jetting flow rate and the direction of an ethanol droplet ejected from a nozzle according to a voltage. more...

In this Letter, a three-dimensional (3D) optical correction method, which was verified by simulation, was developed to reconstruct droplet-based flow fields. In the simulation, a synthetic phantom was reconstructed using a simultaneous multiplicative algebraic reconstruction technique with three detectors positioned at the synthetic object (represented by the phantom), with offset angles of 30° relative to each other. Additionally, a projection matrix was developed using the ray tracing method. If the phantom is in liquid, the image of the phantom can be distorted since the light passes through a convex liquid-vapor interface. Because of the optical distortion effect, the projection matrix used to reconstruct a 3D field should be supplemented by the revision ray, instead of the original projection ray. The revision ray can be obtained from the refraction ray occurring on the surface of the liquid. As a result, the error on the reconstruction field of the phantom could be reduced using the developed optical correction method. In addition, the developed optical method was applied to a Taylor cone which was caused by the high voltage between the droplet and the substrate. more...