Highly Sensitive Microwave Sensor Based on SIW Using an AxialCapacitive Extension (ACE) with IDC Loaded CSRR for Wrist PulseDetection

This paper presents a noninvasive microwave wrist pulse sensor that integrates a circular substrate integrated waveguide (SIW) cavity with an interdigitated capacitor (IDC) loaded complementary split ring resonator (CSRR) and an axial capacitive extension (ACE). The proposed resonant architecture provides enhanced electric-field confinement and an expanded high-sensitivity region, achieving a dielectric sensitivity of 5.85% under material loading. Wrist pulses arise from periodic capillary vibrations that induce small permittivity variations, which allows the system to extract pulse information using a simple, low-cost measurement setup that demodulates the output variation of the sensor. Experimental results confirm accurate wrist pulse detection, yielding a heart rate estimation error of only 0.35% relative to a BIOPAC reference. These results demonstrate that the proposed sensor achieves high sensitivity with reliable wrist pulse extraction, and suitability for reliable noninvasive pulse sensing.