DOI: 10.1109/TMTT.2024.3461568   IEEEXplore: https://ieeexplore.ieee.org/document/10704920

Photoresponsive microwave split-ring resonator (SRR) sensor for optical density and dielectric analysis of liquids.

2 GHz, 390 - 700 nm (460 nm blue light and 630 nm red light) in this demonstration.

The integration of a CdS photoresistor on each ring of a magnetically coupled split ring resonator pair mounted above a half wavelength microstrip feedline allows for the simultaneous sensing of dielectric properties and color absorption by measuring |S21| resonant frequency and amplitude in an EM field while exposing the sensor through the analyte sample with a colored light source.

Sensor applications are found in chemical, biological, pharmaceutical, and food processing industries with a requirement or advantage from concurrent measurement of dielectric characteristics with microwave sensing and colorant characteristics with optical density sensing .

−0.57 dB per log10(Colorant Volume) sensitivity for red-light illumination passing through blue-colored samples −0.17 dB per log10(Colorant Volume) sensitivity for the blue-light illumination in red-colored liquids