Broadband Flexible Sensor for Microwave Dielectric Spectroscopy of Liquids in Vials

Microwave dielectric spectroscopy (MDS) is a powerful technique for analyzing the electromagnetic properties of biological substances, offering advantages over lower-frequency methods such as impedometry, which are prone to concentration polarization effects. While flexible MDS sensors and broadband MDS sensors have been independently demonstrated, no prior work has successfully combined both capabilities into a single platform. In this work, we present the first flexible, broadband MDS sensor capable of measuring the complex permittivity of biological liquids directly within their original vials, across a frequency range of 2–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$19{\,}$</tex-math> </inline-formula>GHz. The novelty of this sensor is enabled by a theoretical framework that describes the excitation of waveguide modes in cylindrical coplanar waveguides (CCPWs). By accurately modeling the influence of these modes on the device’s scattering parameters, we establish a reliable method for extracting the complex permittivity of liquid samples contained within standard laboratory vials. The sensor’s mechanical flexibility allows it to conform to vials of varying shapes and sizes, facilitating noninvasive, contactless measurements. This feature is particularly advantageous for hazardous materials, where minimizing human exposure is essential, and for sensitive biological samples, which are susceptible to contamination if transferred from the containers in which they were originally collected. The proposed sensor addresses key limitations of existing MDS platforms, providing a safe, accurate, and practical solution for broadband dielectric characterization of biological and chemical substances.