Microwave-Based Detection of Heavy Metals in Water Using an Interdigital Electrode-Integrated Complementary Split Ring Resonator Sensor

This letter presents a highly sensitive microwave sensor for detecting four heavy metals (Ag
$^+$
, Pb
$^{2+}$
, Cd
$^{2+}$
, and Cr
$^{3+}$
) in water. The sensor incorporates an interdigital electrode integrated complementary split ring resonator (IECSRR) to enhance electric field confinement and achieve higher sensitivity. Performance of the device has been examined for various aqueous metal solutions by assessing the changes in the stopband center frequency from scattering parameters and the limit of detection (LoD). The results obtained from simulations, experimental measurements, and circuit simulations using extracted parameters demonstrate strong agreement. The presence of Pb
$^{2+}$
, Ag
$^+$
, Cd
$^{2+}$
, and Cr
$^{3+}$
causes a 12.66%, 15.04%, 19.5%, and 33.03% maximum fractional sensitivity, respectively. Additionally, the detection limits (in mg/L) for these substances are 0.634, 0.714, 0.614, and 0.533, respectively. Such a multipurpose miniature sensor with a 25
$\times$
25 mm footprint is suitable for applications related to environmental security.