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.
Highlights
Radar technology can detect vital signs such as respiration and heart rate without contact electrodes [1]
This paper introduces a 915 MHz CW Doppler radar sensor comprising an ultra-wideband low-noise amplifier (LNA) and fractal-slot patch antennas to obtain heart rate and respiration
The signal-to-noise ratio of the vital signals measured by the 915 MHz radar sensor at a distance of 80 cm could decrease under a near-field condition compared with a radar sensor at a distance of 80 cm could decrease under a near-field condition compared with a farfar-field condition [16]
Summary
Radar technology can detect vital signs such as respiration and heart rate without contact electrodes [1]. High-frequency signals have difficulty penetrating the inside of the human body, and attenuation loss can be significantly increased when electromagnetic (EM) waves are transmitted through high-dielectric materials, such as muscles and skin [8]. This paper introduces a 915 MHz CW Doppler radar sensor comprising an ultra-wideband low-noise amplifier (LNA) and fractal-slot patch antennas to obtain heart rate and respiration. The radar sensor operating in the 915 MHz industrial, scientific, and medical radio band can have high accuracy for detecting vital-sign information due to high penetration and low signal loss in the human body.
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