Monitoring vital signs over multiplexed radio by near-field coherent sensing

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Abstract

Monitoring the heart rate, blood pressure, respiration rate and breath effort of a patient is critical to managing their care, but current approaches are limited in terms of sensing capabilities and sampling rates. The measurement process can also be uncomfortable due to the need for direct skin contact, which can disrupt the circadian rhythm and restrict the motion of the patient. Here we show that the external and internal mechanical motion of a person can be directly modulated onto multiplexed radiofrequency signals integrated with unique digital identification using near-field coherent sensing. The approach, which does not require direct skin contact, offers two possible implementations: passive and active radiofrequency identification tags. To minimize deployment and maintenance cost, passive tags can be integrated into garments at the chest and wrist areas, where the two multiplexed far-field backscattering waveforms are collected at the reader to retrieve the heart rate, blood pressure, respiration rate and breath effort. To maximize reading range and immunity to multipath interference caused by indoor occupant motion, active tags could be placed in the front pocket and in the wrist cuff to measure the antenna reflection due to near-field coherent sensing and then the vital signals sampled and transmitted entirely in digital format. Our system is capable of monitoring multiple people simultaneously and could lead to the cost-effective automation of vital sign monitoring in care facilities.

Fig. 1: CST Microwave Studio simulation model for monitoring vital signs over radio transmission by near-field coherent sensing.
Fig. 2: Schematics of harmonic RFID system for near-field coherent sensing.
Fig. 3: The vital signals from NCS measurements.
Fig. 4: Blood pressure measured by NCS.

Change history

  • 29 June 2020

    The Supplementary Video files initially published online were corrupted and were replaced on 26/06/2020.

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Acknowledgements

This project was supported by the US Department of Energy (DoE) under Advanced Research Projects Agency – Energy (ARPA-E) project no. DE-AR0000528. The authors thank F. Rana and J. Fan for their comments on critical applications and technical presentation, as well as H. Park for assistance with the embroidered antenna.

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X.H. formulated the NCS theory, performed the electromagnetic simulation and designed the experimental procedure for conceptual demonstration and calibration. E.C.K. envisioned the NCS principle, set the project goals and coordinated other project activities.

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Correspondence to Xiaonan Hui.

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Supplementary Information

Supplementary Figures 1–9 and a description of each figure.

Supplementary Video 1

The electromagnetic simulation of near-field coherent sensing by CST Microwave Studio.

Supplementary Video 2

The real-time heartbeat and pulse monitoring experiment and signal details.

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Hui, X., Kan, E.C. Monitoring vital signs over multiplexed radio by near-field coherent sensing. Nat Electron 1, 74–78 (2018). https://doi.org/10.1038/s41928-017-0001-0

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