3D-printed pumpkin-shaped cavity resonator to determine the complex permittivity of liquids

This article presents a novel 3D-printed cavity resonator, adopted for the extraction of complex dielectric permittivity of liquid chemicals. The proposed structure consists of a spherical cavity slightly compressed at the poles (similar to a pumpkin), which embeds a thin pipe, where the liquid material under test flows. When the liquid is injected into the pipe, the resonance frequency and the quality factor of the fundamental cavity mode change, and their measurement allows retrieving the complex dielectric permittivity of the liquid. The device is entirely realized by 3D-printing and subsequently metalized by electroplating. The flexibility of the 3D-printing technique allows to implement cavities with unconventional shapes. In this case, the shape is selected to achieve a high quality factor, and it permits to find a good compromise between high sensitivity and good accuracy in the determination of the complex dielectric permittivity. The device was tested with several liquids, and the results were compared to characterizations performed using a commercial coaxial probe.