Non-Contact Reflectance based Cardiac Pulse Detection from Forehead, Elbow and Finger-Tip using Terahertz Waves

A new methodology for radar based cardiac pulse detection is presented in the (sub) terahertz frequency ranges. This new method reports, for the first time, detecting blood volume changes in the dermis layer by measuring the reflectance of terahertz wave. Up to date, all radar based human vital signs experiment results are directly or indirectly relying on the known micro-Doppler effects, ranging from a few hundreds of megahertz to a few hundreds of gigahertz. Importantly, there is a noticeable analogy between the new discovery in terahertz wave and the remote imaging plethysmography. The latter is an established principle for pulse detection on exposed skin illuminated by light waves. In this study, the two non-contact reflectance based methods using terahertz radar system and optical system are discussed and compared experimentally. Further more, electromagnetic wave simulation with realistic skin properties is performed to validate the new terahertz results. Finally, terahertz wave reflectance measurement results from forehead, inner elbow and finger-Tip are provided with two types of pulse reference: contact reference and non-contact imaging plethysmography reference.