Design of Uncoupled and Cascaded Array of Resonant Microwave Sensors for Dielectric Characterization of Liquids

In this article, we introduce an array of uncoupled and cascaded microwave sensors with a novel structure for the dielectric characterization of liquid samples for biomedical applications. The developed array consists of four cascaded resonators and can measure the complex permittivity of multiple samples simultaneously and independently, contributing to microwell plate measurements. The fabricated sensors consist of couplers and defected grounded interdigitated capacitors (IDCs), yielding a high sensitivity. Each sensor in the array acts as a resonator, with the resonance frequency and quality factor changing according to the material under test (MUT). We have used water/ethanol mixtures in different concentrations to calibrate the sensor and later relate the changes in resonance behavior to the one in dielectric permittivity. The corresponding fitting functions based on IDC’s model have a high $r$ -squared value and result in a high precision permittivity extraction of the liquids with the volume of 20 $\mu \text{L}$ in the frequency range of 3.87 GHz (for the sample with the highest permittivity) to 8 GHz.