A Keyhole-Shaped Microwave Resonator for Hematocrit Sensing Toward Dengue Monitoring

Rapid and continuous monitoring of blood hematocrit (HCT) levels is critical for detecting hemoconcentration and plasma leakage associated with dengue virus progression. This paper presents a label-free, metamaterial-based microwave sensor designed to detect dielectric variations corresponding to changes in HCT. The proposed structural design utilizes a keyhole-shaped resonator. The sensor’s transmission coefficients (S21) were numerically evaluated using simulated dielectric properties representing an extended modelled HCT range of 0% to 80%. The simulated analysis demonstrates a systematic response, linear in resonance frequency (R2 = 0.996) and curved in magnitude (R2 = 0.812), achieving a resonance shift sensitivity of 4.5 MHz/%HCT and a magnitude sensitivity of 0.0599 dB/%HCT. Based on these simulations, a 20% relative rise from a patient’s baseline HCT (assuming = 50%) corresponds to a 45 MHz resonance shift and a −0.599 dB magnitude deviation. As an initial proof of concept, the prototype was tested with alcohol–water mixtures. Over 0–40% alcohol the resonance moved to lower frequencies, whereas above 60%, it reversed. This compact microwave sensor is a candidate framework for point-of-care HCT monitoring, subject to validation on blood.