Noncontact RF Vital Sign Sensor for Continuous Monitoring of Driver Status

Jin Kwan Park, Yunseog Hong, Hyunjae Lee, Chorom Jang, Gi Ho Yun, Hee Jo Lee, Jong Gwan Yook

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)


In this paper, a radio frequency vital sign sensor based on double voltage-controlled oscillators (VCOs) combined with a switchable phase-locked loop (PLL) is proposed for a noncontact remote vital sign sensing system. Our sensing system primarily detects the periodic movements of the human lungs and the hearts via the impedance variation of the resonator. With a change in impedance, both the VCO oscillation frequency and the PLL feedback voltage also change. Thus, by tracking the feedback voltage of the PLL, breath and heart rate signals can be acquired simultaneously. However, as the distance between the body and the sensor varies, there are certain points with minimal sensitivity, making it is quite difficult to detect vital signs. These points, called impedance null points, periodically occur at distances proportional to the wavelength. To overcome the impedance null point problem, two resonators operating at different frequencies, 2.40 and 2.76 GHz, are employed as receiving components. In an experiment to investigate the sensing performance as a function of distance, the measurement distance was accurately controlled by a linear actuator. Furthermore, to evaluate the sensing performance in a real environment, experiments were carried out with a male and a female subject in a static vehicle. To demonstrate the real-time vital sign monitoring capability, spectrograms were utilized, and the accuracy was assessed relative to reference sensors. Based on the results, it is demonstrated that the proposed remote sensor can reliably detect vital signs in a real vehicle environment.

Original languageEnglish
Article number8676362
Pages (from-to)493-502
Number of pages10
JournalIEEE Transactions on Biomedical Circuits and Systems
Issue number3
Publication statusPublished - 2019 Jun

Bibliographical note

Funding Information:
Manuscript received September 28, 2018; revised January 29, 2019 and March 18, 2019; accepted March 23, 2019. Date of publication March 29, 2019; date of current version May 24, 2019. This work was supported in part by MSIT (Ministry of Science and ICT), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2017-2013-0-00680) supervised by IITP (Institute for Information & Communications Technology Promotion), and in part by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2017R1A2B2011724). This paper was recommended by Associate Editor H. Yu. (Corresponding author: Jong-Gwan Yook.) J.-K Park, H. Lee, C. Jang, and J.-G. Yook are with the Department of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, South Korea (e-mail:,;; chorom@yonsei.;

Publisher Copyright:
© 2007-2012 IEEE.

All Science Journal Classification (ASJC) codes

  • Biomedical Engineering
  • Electrical and Electronic Engineering


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