A Novel Vital-Sign Sensor Based on a Self-Injection-Locked Oscillator

Abstract

Abstract-A novel vital-sign sensor with a self-injection-locked oscillator and a frequency demodulator to reduce system complexity and improve sensitivity is proposed. The theory provides a delta-sigma model to account for the excellent signal-to-noise spectral density ratio in a parametric study of the sensitivity performance. Then, the experiments verify the sensing principle and the predicted performance. Accordingly, a prototype sensor with high sensitivity is realized for noncontact cardiopulmonary monitoring, achieving a long sensing distance without the need for a low-noise amplifier. The sensing distance can grow four times longer by doubling the operating frequency. Furthermore, the sensor using a swept frequency can eliminate the null detection points and the external radio interference. As an experimental result, the sensor, which is placed 4 m away from the subject, can reliably detect the heartbeat signal an the operating frequency of 3.6 GHz and an output power level of 0 dBm. Index Terms-Delta-sigma model, frequency demodulator, selfinjection-locked oscillator, vital-sign sensor.

Detection of Concealed Individuals Based on Their Vital Signs by Using a See-Through-Wall Imaging System With a Self-Injection-Locked Radar

“…9 and 12 that show the range and azimuth information, respectively, by the following equation in polar form: (25) where is derived from (12) as . The purpose of using the fourth power of the subtracted spectrum in (25) is to enhance the signal to clutter plus noise ratio of the constructed STW images. As dynamic FMCW spectra are measured per 0.1 s, this prototype can provide 10-Hz image rate to monitor the position information of concealed individuals in real-time.…”

“…In our previous works [25], [26], a new kind of CW radar has been introduced to detect vital signs. In its basic operation, an oscillator transmits a CW signal, which is partly reflected by a distant target, and then injected into the same oscillator to form a self-injection-locked (SIL) state.…”

“…1. Since the SIL radar can detect Doppler shifts introduced by the cardiopulmonary activity of a human subject with a high signal-to-noise ratio (SNR) gain [25], the proposed system can therefore monitor the vital signs of concealed individuals simultaneously. Fig.…”

Concurrent Vital Sign and Position Sensing of Multiple Individuals Using Self-Injection-Locked Tags and Injection-Locked I/Q Receivers With Arctangent Demodulation

“…The frequency variation that is caused by the SIL phenomenon, included in (1), has been demonstrated in [24]- [26]. The experimental results in these previous works indicate the satisfactory sensing of cardiopulmonary movements by SIL radar.…”

“…With the help of FMCW and stepped frequency CW (SFCW) technologies [22], [23], these radars can concurrently localize the subjects while monitoring their motion and health. Recently, the use of self-injection locked (SIL) radars for sensing vital signs has been developed as a method with favorable performance, low system complexity, high sensitivity, and high immunity against the clutter effect [24], [25]. Additionally, a hopping frequency can be used to solve the problems of null points and co-frequency interference.…”