Simultaneous multitarget vital signs measurement has become a hot issue for noncontact vital signs perception. However, there is still challenge in the multitarget heartbeat measurement due to the weakness of heartbeat signal and interference from complex environment. In this article, a new multiple-input–multiple-output (MIMO) continuous-wave (CW) radar system equipped with 2-D digital beamforming (DBF) is presented to measure the respiration and heartbeat of multiple human subjects at unknown positions simultaneously. Through 2-D beam scanning of the whole scene, a 2-D radar image is generated. From the image, the chest motion of multiple targets is accurately located. Then, the vital signs of targets are obtained through forming individual beams focusing on the chests of targets. Moreover, the low intermediate frequency (low-IF) architecture is adopted to minimize the impact of flicker noise in low-frequency amplifier stages. The experimental results demonstrate that the proposed MIMO 2-D imaging radar system can locate chest areas of multiple targets, suppress the clutters, and make vital signs measurement, heartbeat measurement in particular, more robust compared with single-input–multiple-output (SIMO) radar system in complex environment.

Remote vital sign detection using Doppler radar has gained increasing interest over the years. However, challenges remain in improving radar system sensitivity to extend the detection range. In this article, we analyze noise contributions in a dual-PLL low-IF Doppler radar system and identify RF leakage/coupling as a major component of the system noise floor. This effect results in negligible SNR improvement when the transmit output power is increased beyond a certain threshold. By applying RF leakage/coupling cancellation through phase and magnitude adjustments, we demonstrate significant improvements to radar system performance. Furthermore, we propose and validate an automatic RF leakage cancellation scheme. The proposed technique is shown to achieve a vital-sign-sensing range of $4$ m under a very low transmit power of $-$ 31 dBm and with a high confidence level of three beats per minute against the ground truth measured by an oximeter sensor.

This article proposes an effective way to use self-injection locking (SIL) in a radar system to detect human chest cavity movement for vital signs monitoring with minimal hardware. The proposed approach expands the idea of using a phase-locked loop (PLL) system as a demodulator and a single antenna, making the system more compact. The system includes on-chip dc offset cancellation for system initialization. This work investigates and compares an $LC$ -based voltage-controlled oscillator (LCVCO) and a ring voltage-controlled oscillator (RVCO) in terms of primary sensitivity for motion detection and phase noise. A study of injection-locking of both the LCVCO and RVCO is also established. The study shows that the RVCO is superior to the LCVCO in terms of sensitivity while the phase noise does not differ significantly as the frequencies of interest are very small, i.e., heart rate and respiration are bandwidth-limited to a few hertz. To verify the proposed idea, a design of both systems, an LCVCO-based PLL and an RVCO-based PLL, was implemented in 65 nm CMOS technology at 1.5 GHz. The simulation and measurement results confirm the idea proposed: the RVCO shows better performance across all metrics, e.g., higher sensitivity by 4 dB, lower power consumption by 30%, and reduced area (almost half) compared to the LCVCO.

Conventionally, high dynamic-range (HDR) imaging is based on taking two or more pictures of the same scene with different exposure. However, due to a high-speed relative motion between the camera and the scene, it is hard for this technique to be applied to push-broom remote sensing cameras. For the sake of HDR imaging in push-broom remote sensing applications, the present paper proposes an innovative method which can generate HDR images without redundant image sensors or optical components. Specifically, this paper adopts an area array CMOS (complementary metal oxide semiconductor) with the digital domain time-delay-integration (DTDI) technology for imaging, instead of adopting more than one row of image sensors, thereby taking more than one picture with different exposure. And then a new HDR image by fusing two original images with a simple algorithm can be achieved. By conducting the experiment, the dynamic range (DR) of the image increases by 26.02 dB. The proposed method is proved to be effective and has potential in other imaging applications where there is a relative motion between the cameras and scenes.

This article introduces an innovative Doppler radar system designed for remote displacement sensing: the envelope detection and self-injection-locked (ENVSIL) radar system. First, we conduct the theoretical analysis of the amplitude modulation (AM) mechanism in continuous-wave (CW) Doppler radar sensors. Our study reveals that in the presence of transmit (TX)–receive (RX) leakage, target motion can produce an effective AM of the carrier whose relative magnitude can be as large as that of the phase modulation (PM). Theoretical derivation, numerical simulation, and experimental validation are provided with excellent agreement between each other. This theoretical advancement presents new possibilities for radar receiver design employing envelope detectors. Moreover, guided by the AM theory, we develop the ENVSIL system to leverage the complementary relationship between AM and PM for IQ plot construction. The ENVSIL system exhibits notable performance, achieving a root mean square error (RMSE) of 0.66 mm for a 5-cm linear motion and an RMSE of 2.26% when measuring a 4-mm motion displacement at a distance of 2.7 m. The absence of a mixer in this architecture reduces the signal power requirement to 0 dBm, contributing to high power efficiency.

A new wake-up receiver (WuRx) designed in 0.13 μm CMOS process is hybrid-integrated with a micro-electromechanical system (MEMS) RF resonator. While only consuming 166 nW of power (18.8 nW for the comparator and 147 nW for periphery), the WuRx is capable of detecting RF signals as weak as -60 dBm. In order to achieve this sensitivity, a passive voltage-boosting network comprised of a high quality factor (high-Q) piezoelectric MEMS resonator is utilized, in place of an inductor, to amplify the received voltages applied to a CMOS rectifier. The output of the rectifier is then applied to a low-power comparator used to set a logical bit that indicates when an RF signal has been detected. The trade-offs in designing the voltage boosting network are explained and an equation for the optimum number of rectifier stages is derived.