Contactless Liquid Interface Measurement based on a Hollow Coaxial Cable Resonator


This paper reports a contactless liquid interface sensor based on a microwave Fabry-Perot resonator. A hollow coaxial cable is employed as the sensing platform, in which air serves as the dielectric layer. By shorting the inner and outer conductors of the hollow coaxial cable, two reflectors with high reflectivity (>70%) are created to form a microwave Fabry-Perot resonator. An open groove is engineered on the resonator allowing the electromagnetic wave to interact with the medium outside the cavity. When a container, filled with different layers of liquids, is placed near the groove edge of the sensor, the leaked electromagnetic wave will interact with the liquids inside the container. By correlating the relative permittivity of the liquid mixture to the resonant frequency of the Fabry-Perot resonator, the interface between different liquids can be unambiguously determined. In the demonstration experiment, the water-oil interface and oil-ethanol interface were measured. Meanwhile, the sensor could also be employed to measure the relative permittivity of different liquids in a non-contact fashion. The presented sensor offers a robust, cost-effective, and real-time configuration for contactless liquid interface detection, which has potential applications in the oil and chemical industries.


Electrical and Computer Engineering

Research Center/Lab(s)

Intelligent Systems Center

Keywords and Phrases

Chemical detection; Chemical industry; Circular waveguides; Coaxial cables; Containers; Cost effectiveness; Electromagnetic waves; Liquids; Microwave resonators; Microwave sensors; Natural frequencies; Permittivity; Reflection; Contactless measurement; Fabry-Perot resonators; High reflectivity; Liquid interface; Measurement-based; Relative permittivity; Sensing platforms; Water oil interface; Fabry-Perot interferometers; Hollow coaxial cable

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


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© 2019 Elsevier, All rights reserved.

Publication Date

01 Jan 2019