SRR-Based Liquid-Level Sensor with Axial MIW Coupling for Opaque Containers

Abstract

This work presents a low-cost microwave sensor for liquid-level detection in opaque dielectric containers, with particular focus on olive oil. The proposed approach is based on a Square Split-Ring Resonator (SSRR) placed inside the container, whose resonance is modified depending on the presence of the liquid. Contactless interrogation is achieved through axial Magneto-Inductive Wave (MIW) coupling with an external SSRR connected to a microstrip transmission line. The system operates using a simple amplitude-based detection scheme with a fixed-frequency excitation and a Schottky-diode-based detector, enabling a compact and low-cost implementation. Full-wave electromagnetic simulations demonstrate a clear difference in the transmission response between empty and liquid-covered conditions, resulting in distinct output voltage levels. These results validate the proposed concept and highlight its suitability for real-time liquid-level sensing in opaque containers using simple interrogation electronics.