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New for September 2023, thanks to Dr. Fabian Michler. Radar technology has emerged as a game-changer in diverse sectors, including healthcare. One groundbreaking application is radar-based vital sign detection. This innovative approach offers a non-intrusive solution for real-time vital sign sensing, enhancing patient care and medical research.
A key advantage is radar's non-contact nature. Unlike attaching sensors or electrodes, radar enables discomfort-free continuous monitoring. This is crucial for long-term patient observation and situations like pandemics, where limited physical contact is essential. Many light materials such as bedding and clothes are almost transparent to radars, simplifying an integration of the sensing system into beds and seats. Due to the high frequencies which are typically used as transmit signals, the skin effect limits the penetration depth of the electromagnetic wave into the human body. Typically, the penetration depth is less than a millimeter for frequencies at 24 GHz or above. Due to this and the low transmit power used, there is no biologic interaction.
Working principle
Radar-based vital sign detection utilizes the principles of radio waves to measure and analyze the subtle movements of the human body. By emitting low-power radiofrequency signals and capturing their reflections, radar systems can detect even the tiniest movements caused by breathing, heartbeat, and body movement. Most of the published systems are operating in the license-free ISM bands around 24 GHz or 61 GHz, where a short wavelength allows for a high phase resolution. On the other hand, the impact of motion artifacts is still acceptable since the body surface still appears as a more or less even surface to these frequencies.
Figure 1: Basic operation principle: A radar system is placed in vicinity to the human body
and measures the chest displacement caused by respiration and heartbeat. ©Sykno GmbH
The simplest radar architecture to be used is the continuous-wave (CW) radar, where a sinusoidal transmit signal is used. The target displacement Δx of the human body's surface is then derived by comparing the phase angle Δφ between transmit and receive signal:
This radar technology stands out for its simplicity, allowing for a very computationally and power-efficient design and a high measurement precision in the single-digit micrometer range at the same time.
Since the CW radar approach cannot separate different targets in range domain, frequency-modulated CW (FMCW) and frequency-shift keying (FSK) radars have been used for vital sign detection as well.
Vital sign extraction
Typically, the displacement signal is a superposition of respiratory movement, heartbeat vibration and unwanted random body movements. Using digital filtering of the displacement signal, these components can be separated.
Figure 2:Raw displacement data as captured with a CW vital sign sensing radar. It is the
superposition of respiration,heartbeat, and body movements. ©Sykno GmbH
Figure 3: Extracted vital sign signals after digital filtering of the raw displacement signal. ©Sykno GmbH
The classification of individual respiration and cardiac phases can be performed with advanced de-noising and peak detection algorithms or even AI-based processing. For a person at rest, the accuracy of the wired gold standard ECG can be reached for the detection of the heartbeat using a fully contactless radar-based measurement system.
Conclusion
In conclusion, radar-based vital sign detection represents a significant breakthrough in healthcare monitoring. Its non-intrusive nature, high accuracy, and versatility make it a valuable tool for medical professionals and researchers alike. As technology continues to evolve, radar-based systems have the potential to enhance patient care, improve medical research, and shape the future of healthcare monitoring. As we move forward, it is likely that radar technology will play an increasingly pivotal role in revolutionizing how we monitor and assess vital signs in the pursuit of better health outcomes.
References
If you want more info, there's a full paper from the journal Sensors from MDPI Publishing in Switzerland:
A Clinically Evaluated Interferometric Continuous-Wave Radar System for the Contactless Measurement of Human Vital Parameters
Or, if you happen to have IEEExplore access, you can check out:
Microw(h)att?! Ultralow-Power Six-Port Radar: Realizing Highly Integrated Portable Radar Systems with Good Motion Sensitivity at Relatively Low Cost
FMCW-Radar-Based Vital-Sign Monitoring of Multiple Patients
24-GHz Impedance-Modulated BPSK Tags for Range Tracking and Vital Signs Sensing of Multiple Targets Using an FSK Radar].