915-MHz Continuous-Wave Doppler Radar Sensor for Detection of Vital Signs

Abstract

A miniaturized continuous-wave Doppler radar sensor operating at 915 MHz to remotely detect both respiration and heart rate (beats per minute) is presented. The proposed radar sensor comprises a front-end module including an implemented complementary metal-oxide semiconductor low-noise amplifier (LNA) and fractal-slot patch antennas, whose area was reduced by 15.2%. The two-stage inverter-based LNA was designed with an interstage capacitor and a feedback resistor to acquire ultrawide bandwidth. Two operating frequencies, 915 MHz and 2.45 GHz, were analyzed with regard to path loss for efficient operation because frequency affects detection sensitivity, reflected signal power from the human body, and measurement distance in a far-field condition. Path-loss calculation based on the simplified layer model indicates that the reflected power of the 915 MHz radar could be higher than that of the 2.45 GHz radar. The implemented radar front-end module excluding the LNA occupies 35 × 55 mm2. Vital signs were obtained via a fast Fourier transform and digital filtering using raw signals. In an experiment with six subjects, the respiration and heart rate obtained at 0.8 m using the proposed radar sensor exhibited mean accuracies of 99.4% and 97.6% with respect to commercialized reference sensors, respectively.

Doppler-Spectrum Feature-Based Human–Vehicle Classification Scheme Using Machine Learning for an FMCW Radar Sensor

“…Secondly, in order to measure the time variance of Doppler spectrum shape, we calculate the absolute distance in the number of Doppler reflection points between two successive frames. We newly define the feature as the SPD (scattering point difference), defined by Equation (5). That is, this feature indicates the degree of change of the Doppler spectra.…”

“…Recently, research on the detection of human activities and motions was conducted. Examples include hand gesture recognition [2], human gait indication [3], human fall detection [4], and human vital signal detection [5].…”

Speed Calibration and Traceability for Train-Borne 24 GHz Continuous-Wave Doppler Radar Sensor

“…In order to meet the extremely high safety requirements of CTCS-3 in railway passenger dedicated lines, the architecture of the train-borne speed measurement subsystem has changed from a single wheel speed sensor to the fusion of multiple speed sensors, which can take full advantage of redundant data and complementary information of multiple kinds of speed sensors with different working principles. With the advantage of high-accuracy, wide-range, long-lifetime, stability, and reliability [6][7][8][9], the 24 GHz continuous wave (CW) Doppler radar sensor (DRS) has been widely used in high-speed and urban rail trains, working together with some of the other conventional wheel speed sensors to directly measure the instantaneous speed of trains in real time by using a non-contact approach, which is not affected by wheel slip and spin. Unlike the dual-sided symmetrical structure of vehicle-borne dual-channel DRS with the Janus configuration, which is used as a mobile standard speed-measuring instrument for the field verification of traffic speed meters in road traffic [10][11][12], train-borne dual-channel DRSs usually adopt a single-sided asymmetric structure, which is a more common and complicated configuration than the Janus configuration used in vehicle-borne dual-channel DRSs and seeks no approximation methods for the solution on train speed calculation [10].…”

An EMD-Based Algorithm for Emboli Detection in Echo Doppler Audio Signals

“…Gas bubbles in liquids are strong reflectors of sound so ultrasound-based methods are well suited for detection of circulating vascular gas bubbles. Doppler [12] and in particular ultrasound Doppler [13,14] is employed both in medical and in industrial applications for estimating fluid velocity. Doppler systems are most commonly used [15] and ultrasonic detection of circulating VGE after diving is considered a useful index for safe decompression [16].…”