Fingertip Pulse Signals Enhanced by Using Intermodulation Multiplication of Active High-Sensitivity Split-Ring Resonator

This paper presents a novel active split ring resonator (SRR) for detecting the wrist and fingertip pulse signals. Though fingertip signal is extremely tiny in general, the proposed intermodulation multiplication technology can improve the sensitivity by more than 400%. The frequency shift of sensing can be multiplied to highly sensitive by measuring the 3^rd, 5^th, 7th and 9^th intermodulation (IM) components. The pulse signal can be measured from the frequency deviations of SRR by interfering the coupling path on the surface of the sensor. In this work, the highest component can be achieved to 9^th IM. The frequency shift of measuring the wrist pulse signal is increased from 3.5 MHz to 16 MHz. The fingertip signal is first measured by a microwave sensor and can achieve high accuracy of less than 0.75% error.