Design and validation of liquid permittivity sensor based on RCRR microstrip metamaterial

In this paper, based on the microstrip metamaterial composed of two coupled square rings, a novel liquid permittivity sensor is designed and fabricated. The sensor takes advantage of the coupling between two square rings connected by an interdigital capacitor. It realizes a relatively high sensitivity, and the bandwidth is less than 100 MHz at a working frequency of 900 MHz. The resonance frequency shifts from 810 MHz to 689.5 MHz when the real part of the sample's relative permittivity shifts from 1 to 78. The experimental results are in good agreement with simulated results. The designed sensor with compact dimensions and operating frequency paves the way for application to the Internet of Things.