3D printed re-entrant cavity resonator for complex permittivity measurement of crude oils

This paper presented a microwave resonator-based dielectric metrology technique using a new unified analytical model to extract complex permittivity of low-loss liquid materials. The main design drive of the modified re-entrant cavity is to confine the electric field and therefore enhance the interaction with the material under test while maintaining high quality factor of the cavity. This enables high sensitivity when measuring complex permittivity of low loss materials. The fabrication of the resonator was made easy by using stereo-lithography (SLA) 3D printing. The measured resonance frequency of the fabricated cavity is 2.09 GHz and the quality factor is 5250. The device was first validated using several common solvents. A unified analytical perturbation model based on simulations is developed for the extraction of the complex permittivity. The influence of the dielectric constant on the loss-tangent model has been fully taken into account. Results obtained agree very well with literature values. The device has subsequently been used in the measurement of crude oil samples and the correlation between permittivity measurement and crude oil category has been established.