This paper reviews recent advances in biomedical and healthcare applications of Doppler radar that remotely detects heartbeat and respiration of a human subject. In the last decade, new front-end architectures, baseband signal processing methods, and system-level integrations have been proposed by many researchers in this field to improve the detection accuracy and robustness. The advantages of noncontact detection have drawn interests in various applications, such as energy smart home, baby monitor, cardiopulmonary activity assessment, and tumor tracking. While many of the reported systems were bench-top prototypes for concept verification, several portable systems and integrated radar chips have been demonstrated. This paper reviews different architectures, baseband signal processing, and system implementations. Validations of this technology in a clinical environment will also be discussed.

A Review on Recent Advances in Doppler Radar Sensors for Noncontact Healthcare Monitoring

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. The FMCW mode is responsible for range detection while the interferometry mode is responsible for life activities (respiration, heart beat, body motion, and gesture) monitoring. Such cooperation is built on each mode's own strength. Beam scanning is employed to determine azimuth information, which enables the system to plot 360° 2-D maps on which the room layout and objects' location can be clearly identified. Additionally, the transmitted chirp signal is coherent in phase, which is very sensitive to physiological motion and allows the proposed technique to distinguish human from nearby stationary clutters even when the human subjects are sitting still. Hence, the proposed radar is able to continuously track the location of individuals and monitor their life activities regardless of the complex indoor environment. A series of experiments have been carried out to demonstrate the proposed versatile life activity monitoring system.

A Hybrid FMCW-Interferometry Radar for Indoor Precise Positioning and Versatile Life Activity Monitoring

In this paper, analyses on sensitivity and link budget have been presented to guide the design of high-sensitivity noncontact vital sign detector. Important design issues such as flicker noise, baseband bandwidth, and gain budget have been discussed with practical considerations of analog-to-digital interface and signal processing methods in noncontact vital sign detection. Based on the analyses, a direct-conversion 5.8-GHz radar sensor chip with 1-GHz bandwidth was designed and fabricated. This radar sensor chip is software configurable to set the operation point and detection range for optimal performance. It integrates all the analog functions on-chip so that the output can be directly sampled for digital signal processing. Measurement results show that the fabricated chip has a sensitivity of better than -101 dBm for ideal detection in the absence of random body movement. Experiments have been performed successfully in laboratory environment to detect the vital signs of human subjects.

High-Sensitivity Software-Configurable 5.8-GHz Radar Sensor Receiver Chip in 0.13- $\mu$ m CMOS for Noncontact Vital Sign Detection

In this paper, we experimentally realized a steering antenna using a type of active metamaterial with tunable refractive index. The metamaterial is realized by periodically printed subwavelength metallic resonant patterns with embedded microwave varactors. The effective refractive index can be controlled by low direct-current (dc) bias voltage applied to the varactors. In-phase electromagnetic waves transmitting in different zones of such metamaterial slab experience different phase delays, and, consequently, the output direction of the transmitted wave can be steered with progressive phase shift along the interface. This antenna has a simple structure, is very easy to configure the beam direction, and has a low cost. Compared with conventional phased-array antennas, the radome approach has more flexibility to operate with different feeding antennas for various applications.

Low-DC Voltage-Controlled Steering-Antenna Radome Utilizing Tunable Active Metamaterial

In this paper, a pair of integrated circuits for general purpose contactless measurement of diverse analog quantities, such as temperature, pressure, humidity, etc., is designed and fabricated in low-cost CMOS process. With one master and one slave chip, the chipset works on the principle of near-field communication (NFC), in which the master chip transmits magnetic energy to power up the slave chip and reads back digitized data via impedance modulation. Compared with traditional NFC-based radio-frequency identification systems, the self-locking operating frequency range is significantly extended from 8 to 12 MHz, providing a robust self-adaptive stability in impedance-varying environments. Apart from an analog port digitized by a built-in 12-bit self-calibrated analog-to-digital converter, up to three switch quantity ports are simultaneously integrated, enabling the chipset to monitor the change of static binary voltages, and provide additional control functions. The fabricated chipset has been successfully characterized and applied to contactless temperature measurement and the switch's on-off detection in a mass-produced household appliance product, showing great potential in various industrial and instrumental applications.

Wireless Sensing System-on-Chip for Near-Field Monitoring of Analog and Switch Quantities

A direct conversion 5.8 GHz radar sensor chip with 1GHz bandwidth was designed and fabricated. This radar sensor chip is software configurable to set the operation point and detection range for optimal performance. It integrates all the analog functions on-chip so that the output can be directly sampled for digital signal processing. Important design issues for direct conversion non-contact vital sign detection sensors, such as the effect of baseband flicker noise and gain budget, have been discussed. Experiments have been performed successfully in lab environment to detect the vital signs of human subject seated at a distance of up to 1.5 meter.

Software configurable 5.8 GHz radar sensor receiver chip in 0.13 µm CMOS for non-contact vital sign detection

This paper introduces a new radar system, using a type of Linear Frequency Modulation (LFM) signal which lacks components around zero frequency. Because it does not comprise zero frequency bands, this new type of signal may overcome DC offsets directly. Simulations in Matlab prove the feasibility of this new signal as well as how to improve its performance, mainly by enlarging the bandwidth and adding window functions. In this case, the performance of zero-IF transceivers may be improved and the efficiency of distance range resolution can still be guaranteed.

Dong Li

Papers

High-Sensitivity Software-Configurable 5.8-GHz Radar Sensor Receiver Chip in 0.13- $\mu$ m CMOS for Noncontact Vital Sign Detection

Low-DC Voltage-Controlled Steering-Antenna Radome Utilizing Tunable Active Metamaterial

Wireless Sensing System-on-Chip for Near-Field Monitoring of Analog and Switch Quantities

Software configurable 5.8 GHz radar sensor receiver chip in 0.13 µm CMOS for non-contact vital sign detection

The performance of LFM signals without components around zero frequency in pulse compression radar