Associate Professor
Department of Electrical and Electronic Engineering, University of Dhaka, Bangladesh

Title of the Invited Talk: Microwave-Based Sensing Solutions for Detecting Nitrogenous Fertilizers and Heavy Metals in Water: Design, Evaluation and Lab Validation

Abstract: Water contamination by agricultural pollutants and heavy metals poses a significant environmental challenge, necessitating accurate and cost-effective detection methods. This work explores the design, development, and experimental evaluation of microwave-based sensing solutions for detecting two major categories of water contaminants: nitrogenous fertilizers and heavy metal ions. We demonstrate two distinct sensor designs optimized for these applications. The first sensor, a hairpin-based microstrip design operating at 6 GHz, targets nitrogen-based nutrients including ammonia, ammonium sulfate, and urea in water. Our proposed device demonstrates excellent performance in aqueous samples with detection limits of 12.79 mg/L for ammonia, 13.56 mg/L for ammonium sulfate, and 43.36 mg/L for urea. Notably, in multi-fertilizer scenarios with fixed total solvent density of 450 ppm, the sensor exhibits a significant resonant frequency shift of 1.65 GHz, demonstrating it’s capability for complex mixture analysis. Next, we present an interdigital complementary split ring resonator (ICSRR) incorporated structure, specifically designed for heavy metal detection. This compact 25 mm × 25 mm device effectively detects cadmium, chromium, silver, and lead ions in water. The optimized interdigital electrodes generate highly intense electric field distribution in free space, which may disrupt due to the presence of different heavy metal solutions. The sensor exhibits notch frequency shifts ranging from 12.66% to 33.03% relative to the unloaded state, with reasonably low detection limits of 0.634 mg/L for Pb²⁺, 0.714 mg/L for Ag⁺, 0.613 mg/L for Cd²⁺, and 0.533 mg/L for Cr³⁺. Both microwave sensors underwent comprehensive testing and validation, including design analysis, experimental trials, circuit modeling, simulations, and extensive measurement campaigns. Our future work aims to integrate these sensors with compact VNAs to develop portable monitoring systems, enabling on-site detection of nitrogen-based nutrients and heavy metals in water. This advancement would transform our laboratory-proven sensors into field-deployable devices, offering a significant breakthrough in environmental sensing through their reusable design and high sensitivity.