Optically Controlled Microwave Sensors for Biomedical Diagnostics

This book presents the design, development, and validation of an innovative optically controlled microwave sensor for non-invasive, real-time detection of urea concentration in human urine, addressing critical limitations of conventional biochemical assays that are costly, time-consuming, and unsuitable for point-of-care applications. The proposed sensor operates at 1.22 GHz and uniquely integrates three synergistic design elements: a circular spiral inductor (CSI) combined with an interdigital capacitor (IDC) to form a high-Q resonant structure that concentrates electromagnetic fields in the sensing region; Hilbert fractal stubs that minimize diffraction effects and optimize impedance matching; and a light-dependent resistor (LDR) that enables a novel hybrid optical-microwave transduction mechanism, wherein the optical transparency of urine-inversely correlated with its urea concentration-modulates the LDR resistance and thereby directly alters the insertion loss magnitude (S¿¿) at the fixed resonance frequency. Numerical validation using CST Microwave Studio and experimental testing on human urine samples from 15 patients.