Multi-target vital sign and location detection using metamaterial integrated radar architectures

Abstract

Over the past decades, microwave and millimeter-wave radar sensors have been widely used for vital sign detection in the medical field, based on the doppler effect coming from periodic cardiac activity of human target, with the development of semiconductor devices. Compared with conventional cardiac monitoring devices, such as smart watches, electrocardiography (ECG) devices or finger pulse oximeters, radar sensors raise much interest owing to its noncontact and high accuracy characteristics. Besides it, radar sensors have been implemented on location tracking due to its noncontact, high accuracy, and robustness against harsh environment characteristics. In this dissertation, metamaterial (MTM) leaky wave antennas (LWAs) based on different radar architectures, such as self-injection locked (SIL) and super-regenerative oscillator (SRO) architectures, will be presented for vital sign detection and location tracking of multiple targets at different locations. The proposed radar sensors possess the frequency-dependent beam scanning capability and high accuracy with low system complexity compared with conventional radar sensor architectures. Firstly, the state-of-the-art techniques for vital sign detection and location tracking will be summarized. Secondly, the design of the proposed SIL-based MTM LWA will be described, which consists of a one-dimensional (1D) MTM LWA with the beam-scanning angle from -50 ° to +30 ° for multi-target interrogation and the voltage-controlled oscillator (VCO) for the operation frequency range from 2.04 GHz to 2.48 GHz. Based on it, a microwave differentiator and a quadrature coupler followed by two envelope detectors are included to convert frequency-modulated (FM) signals into amplitude-modulated (AM) signals for vital sign extraction. Furthermore, the frequency-shift keying (FSK) method is adopted for location tracking of single target. Then, to improve the sensitivity of radar sensor for vital sign detection, the fundamental theory and circuit implementation of SRO-based radar sensor for vital sign detection is provided. Based on it, SRO-based MTM pulsed radar is proposed for multi-target vital sign and location detection. In this configuration, an envelope detector is employed at the output of radar sensor for vital sign extraction, while the time domain cross-correlation method is used for location tracking. For the proof of concept, two targets at different locations are detected using the proposed SRO-based MTM pulsed radar. Experiment results show that proposed radar sensor can detect multi-target locations as well as their corresponding vital sign signals accurately. Furthermore, compared with conventional or SIL-based radar sensors, SRO-based radar sensors exhibit high sensitivity and low system complexity characteristics. To this end, the time-domain cardiogram from fingertip is detected using the near-field sensor based on SRO architecture without any direct contact.