Next-generation microwave and engineered electromagnetic sensor platforms for accurate non-invasive glucose monitoring

Non-invasive glucose monitoring has emerged as a major research focus owing to the limitations of conventional invasive techniques, including pain, infection risk, poor patient compliance, and the inability to provide continuous physiological information. This review presents a structured and critical assessment of recent advances in glucose sensing technologies, with particular emphasis on microwave and engineered electromagnetic sensor platforms. Relevant literature spanning the past two decades was critically reviewed, with emphasis on experimentally validated studies, recent advances in metamaterial-inspired sensing, and clinically relevant microwave biosensing technologies. The sensing approaches are comparatively analyzed based on operating principle, frequency of operation, sensing mechanism, sensitivity, clinical applicability, measurement accuracy, and implementation complexity. Particular attention is devoted to resonator-based, transmission-line, antenna-based, millimeter-wave, and metamaterial-inspired microwave sensors, highlighting how engineered electromagnetic field confinement improves dielectric sensitivity for glucose detection. Compared with many existing reviews, this work provides a more comprehensive critical comparison of sensing mechanisms, operating frequency selection, clinical translation challenges, motion artifacts, active sensing strategies, and emerging multifunctional electromagnetic platforms incorporating machine learning, energy harvesting, and advanced metamaterial engineering. The review further discusses key barriers to clinical implementation, including calibration stability, tissue heterogeneity, hydration effects, environmental interference, reproducibility, and limited human validation. Finally, future research directions toward wearable, low-power, self-powered, and clinically reliable non-invasive glucose monitoring systems are presented to support the translation of engineered electromagnetic sensing technologies from laboratory demonstrations to practical healthcare applications.