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Review
. 2020 Mar 6;20(5):1454.
doi: 10.3390/s20051454.

Human Vital Signs Detection Methods and Potential Using Radars: A Review

Mamady Kebe  1 , Rida Gadhafi  1   2 , Baker Mohammad  1 , Mihai Sanduleanu  1 , Hani Saleh  1 , Mahmoud Al-Qutayri  1
Affiliations
Review

Human Vital Signs Detection Methods and Potential Using Radars: A Review

Mamady Kebe et al. Sensors (Basel). .

Abstract

Continuous monitoring of vital signs, such as respiration and heartbeat, plays a crucial role in early detection and even prediction of conditions that may affect the wellbeing of the patient. Sensing vital signs can be categorized into: contact-based techniques and contactless based techniques. Conventional clinical methods of detecting these vital signs require the use of contact sensors, which may not be practical for long duration monitoring and less convenient for repeatable measurements. On the other hand, wireless vital signs detection using radars has the distinct advantage of not requiring the attachment of electrodes to the subject's body and hence not constraining the movement of the person and eliminating the possibility of skin irritation. In addition, it removes the need for wires and limitation of access to patients, especially for children and the elderly. This paper presents a thorough review on the traditional methods of monitoring cardio-pulmonary rates as well as the potential of replacing these systems with radar-based techniques. The paper also highlights the challenges that radar-based vital signs monitoring methods need to overcome to gain acceptance in the healthcare field. A proof-of-concept of a radar-based vital sign detection system is presented together with promising measurement results.

Keywords: heart rate; radars; respiration rate; sensors; vital signs.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Twelve-lead clinical electrocardiogram (ECG) system; (b) ambulatory ECG system; (c) representation of ECG signal.
Figure 2
Figure 2
(a) Photoplethysmogram (PPG) measurement setup; (b) effect of light on different tissues of human body [37]; (c) description of PPG waveform.
Figure 3
Figure 3
CO2 measurement techniques: (a) sidestream; (b) mainstream; (c) description of a capnogram [47].
Figure 4
Figure 4
(a) General setup for breath airflow-based vital signs monitoring system; (b) time response of a thermistor sensor for breath rate (BR) acquisition; (c) humidity variation with time [59].
Figure 5
Figure 5
Strain-based sensing methods of breath rate: (a) resistive sensing, (b) capacitive sensing, (c) inductive sensing and (d) fiber-optic sensing.
Figure 6
Figure 6
(a) Impedance pneumography setup; (b) 3D movement sensor setup for breath rate acquisition. The sensor can be an accelerometer, a gyroscope, a magnetometer or a combination of them.
Figure 7
Figure 7
Systolic and diastolic blood pressure (BP) measurement using cuff [101].
Figure 8
Figure 8
(a) Measurement setup of cardiac sound; (b) comparison of phonocardiography (PCG) and ECG signals.
Figure 9
Figure 9
(a) Block diagram of vital signs Doppler. Basic transceiver architectures: (b) zero intermediate frequency (IF); (c) heterodyne.
Figure 10
Figure 10
Flow chart of (a) arctangent demodulation (AD) signal processing and (b) complex signal demodulation (CSD) signal processing.
Figure 11
Figure 11
Frequency-modulated continuous-wave (FMCW) signal: (a) frequency variation over time, (b) instantaneous chirp signals.
Figure 12
Figure 12
General algorithm used to extract the vital signs of multiple subjects using radar techniques.
Figure 13
Figure 13
Algorithms used in (a) [138], (b) [140] and (c) [141] to retrieve the range and vital signs of subjects-under-test (SUTs).
Figure 14
Figure 14
Stepped-frequency continuous-wave radar (SFCW) signal: (a) frequency variation over time, (b) instantaneous chirp signals.
Figure 15
Figure 15
(a) Time-domain SFCW radar data with presence of human subject after applying inverse fast Fourier transform (IFFT); (b) vital signs after cancelling the clutter effect [146]; (c) algorithm used to obtain the range-Doppler profile [145].
Figure 16
Figure 16
(a) Time domain and (b) spectrum of an ultra-wideband (UWB) signal; (c) basic block diagram of a UWB radar.
Figure 17
Figure 17
Vital signs retrieval algorithm for the ultra-wideband (UWB) radar in (a) [140] and (b) [131].
Figure 18
Figure 18
Federal Communication Commission (FCC) and European Electronic Communication Commission (ECC) masks for UWB application [166].
Figure 19
Figure 19
(a) Random body movement (RBM) cancellation using two identical transceivers [111]; (b) self-injection radar for RBM cancellation [128].
Figure 20
Figure 20
Beat-to-beat intervals (BBIs) obtained from one subject in comparison with an ECG reference [172].
Figure 21
Figure 21
(a) Setup of the vector network analyzer (VNA)-based continuous-wave (CW) radar for vital signs measurement; BR and heart rate (HR) of (b) Male volunteer and (c) female volunteer.
Figure 22
Figure 22
Algorithm used to process the experimental data.
See this image and copyright information in PMC

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