Chest-Worn Health Monitor Based on a Bistatic Self-Injection-Locked Radar

Abstract

This paper presents wearable health monitors that are based on continuous-wave Doppler radar technology. To achieve low complexity, low power consumption, and simultaneous wireless transmission of Doppler information, the radar architecture is bistatic with a self-injection-locked oscillator (SILO) tag and an injection-locked oscillator (ILO)-based frequency demodulator. In experiments with a prototype that was operated in the medical body area network and the industrial scientific and medical bands from 2.36 to 2.484 GHz, the SILO tag is attached to the chest of a subject to transform the movement of the chest due to cardiopulmonary activity and body exercise into a transmitted frequency-modulated wave. The tag consumes a very low power of 4.4 mW. The ILO-based frequency demodulator, located 30 cm from the subject, receives and processes this wave to yield the waveform that is associated with the movement of the chest. Following further digital signal processing, the cardiopulmonary activity and body exercise are displayed as time-frequency spectrograms. Promisingly, the experimental results that are presented in this paper reveal that the proposed health monitor has high potential to integrate a cardiopulmonary sensor, a pedometer, and a wireless transmission device on a single radar platform.

Wrist Pulse Rate Monitor Using Self-Injection-Locked Radar Technology

“…However, compared to the vital signs, these interference signals are temporary and aperiodic, thus the joint time-frequency analysis can be utilized to establish a reliable spectrogram for long-term monitoring of the target signal with a wide range of physical activities [28]. Notably, since the modulation bandwidth of the active antenna worn on a moving subject’s wrist is generally less than 7 MHz, this remote frequency discriminator with gain-enhanced LNA could support up to 14 active antennas to concurrently detect vital signs of 14 users by simply switching the carrier frequency of the ILO.…”

“…The above experiment proves that the SIL radar offers better sensitivity and can reduce the number of active components to increase endurance. In addition, the SIL radar can be separated into two parts—SILO and frequency discriminator—for the detection of vital signs with a bistatic architecture [28], which further reduces the size of the wearable device and therefore provides improved comfort.…”

“…Furthermore, this technology allows the SIL oscillator (SILO) and the frequency discriminator, with an antenna installed for each of them, to be placed at different locations in a bistatic architecture [27]. Implementing the features above, a chest-worn health monitor was recently reported to be capable of monitoring the respiration, heart rate, and pace of an exercising subject at the same time by processing demodulated signals using joint time frequency analysis and moving average filtering [28]. …”

Physiological Driver Monitoring Using Capacitively Coupled and Radar Sensors

“…Remote radar-based vital signs sensing has been intensively investigated in the last two decades. The attention has been focused mainly on contactless vital signs monitoring in indoor environments [10][11][12][13][14][15][16][17][18]. Considerable research on multi-people vital signs sensing and tracking has been performed by imec [19][20][21][22][23][24], which also presented recently a Frequency-Modulated Continuous Wave (FMCW) integrated chip (IC) radar capable of detecting the vital signs up to a distance of 15 m while achieving a low-power consumption record of only 680 µW [24].…”

Short-Range Noncontact Sensors for Healthcare and Other Emerging Applications: A Review

“…With growing interest of employing radar for short-range applications, many researchers have been pushing the technology boundaries in every aspect to try to make its applications ubiquitous in our daily lives. In the past two decades, various radar hardware architectures have been proposed, including direct-conversion quadrature radar receiver [ 48 ], digital intermediate-frequency (IF) receiver [ 24 , 49 ], injection locking radar [ 50 , 51 ], six-port radar [ 52 ], CW-FMCW hybrid radar [ 44 , 45 ], and millimeter wave radar on-chip [ 46 , 53 ]. Each of the architectures has its pros and cons and is suitable for certain specific applications.…”