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

Nature Electronicsvolume 1pages7478 (2018) | Download Citation


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.

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  1. 1.

    Patterson, R. P. Fundamentals of impedance cardiography. IEEE Eng. Med. Biol. Mag. 8, 35–38 (1989).

  2. 2.

    Payne, R. A., Symeonides, C. N., Webb, D. J. & Maxwell, S. R. J. Pulse transit time measured from the ECG: an unreliable marker of beat-to-beat blood pressure. J. Appl. Physiol. 100, 136–141 (2006).

  3. 3.

    Allen, J. Photoplethysmography and its application in clinical physiological measurement. Physiol. Meas. 28, R1 (2007).

  4. 4.

    Tamura, T., Maeda, Y., Sekine, M. & Yoshida, M. Wearable photoplethysmographic sensors—past and present. Electronics 3, 282–302 (2014).

  5. 5.

    Gong, S. et al. A wearable and highly sensitive pressure sensor with ultrathin gold nanowires. Nat. Commun. 5, 3132 (2014).

  6. 6.

    Pang, C. et al. A flexible and highly sensitive strain-gauge sensor using reversible interlocking of nanofibres. Nat. Mater. 11, 795–801 (2012).

  7. 7.

    Kindig, J. R., Beeson, T. P., Campbell, R. W., Andries, F. & Tavel, M. E. Acoustical performance of the stethoscope: a comparative analysis. Am. Heart J. 104, 269–275 (1982).

  8. 8.

    Liang, H., Lukkarinen, S. & Hartimo, I. Heart sound segmentation algorithm based on heart sound envelogram. Comput. Cardiol. (1997).

  9. 9.

    Frinking, P. J., Bouakaz, A., Kirkhorn, J., Cate, F. J. T. & Jong, N. Ultrasound contrast imaging: current and new potential methods. Ultrasound Med. Biol. 26, 965–975 (2000).

  10. 10.

    Lin, J. C. Noninvasive microwave measurement of respiration. Proc. IEEE 63, 1530 (1975).

  11. 11.

    Chen, K., Misra, D., Wang, H., Chuang, H. & Postow, E. An X-band microwave life-detection system. IEEE Trans. Biomed. Eng. 7, 697–701 (1986).

  12. 12.

    Li, C. et al. A review on recent progress of portable short-range noncontact microwave radar systems. IEEE Trans. Microw. Theory Tech. 65, 1692–1706 (2017).

  13. 13.

    Celik, N., Gagarin, R., Huang, G. C., Iskander, M. F. & Berg, B. W. Microwave stethoscope: development and benchmarking of a vital signs sensor using computer-controlled phantoms and human studies. IEEE Trans. Biomed. Eng. 61, 2341–2349 (2014).

  14. 14.

    Wolf, R. H., Lehner, N. D. M., Miller, E. C. & Clarkson, T. B. Electrocardiogram of the squirrel monkey Saimiri sciureus. J. Appl. Physiol. 26, 346–351 (1969).

  15. 15.

    Pereira-Junior, P. P., Marocolo, M., Rodrigues, F. P., Medei, E. & Nascimento, J. H. M. Noninvasive method for electrocardiogram recording in conscious rats: feasibility for heart rate variability analysis. An. Acad. Bras. Cienc. 82, 431–437 (2010).

  16. 16.

    Kamal, A. A. R., Harness, J. B., Irving, G. & Mearns, A. J. Skin photoplethysmography—a review. Comput. Methods Programs Biomed. 28, 257–269 (1989).

  17. 17.

    Chen, K., Huang, Y., Zhang, J. & Norman, A. Microwave life-detection systems for searching human subjects under earthquake rubble or behind barrier. IEEE Trans. Biomed. Eng. 47, 105–114 (2000).

  18. 18.

    Kao, T. J., Yan, Y., Shen, T., Chen, A. Y. & Lin, J. Design and analysis of a 60-GHz CMOS Doppler micro-radar system-in-package for vital-sign and vibration detection. IEEE Trans. Microw. Theory Tech. 61, 1649–1659 (2013).

  19. 19.

    CST Microwave Studio (Computer Simulation Technology, 2017);

  20. 20.

    Zubal, I. G. et al. Computerized three‐dimensional segmented human anatomy. Med. Phys. 21, 299–302 (1994).

  21. 21.

    Yu, F., Lyon, K. G. & Kan, E. C. A novel passive RFID transponder using harmonic generation of nonlinear transmission lines. IEEE Trans. Microw. Theory Techn. 58, 4121–4127 (2010).

  22. 22.

    Patron, D. et al. On the use of knitted antennas and inductively coupled RFID tags for wearable applications. IEEE Trans. Biomed. Circuits Syst. 10, 1047–1057 (2016).

  23. 23.

    Gordon, P. H., Chen, R., Park, H. & Kan, E. C. Embroidered antenna characterization for passive UHF RFID tags. Preprint available at (2017).

  24. 24.

    Ma, Y., Hui, X. & Kan, E. C. Harmonic-WISP: a passive broadband harmonic RFID platform. Proc. Microw. Symp. (IMS), 2016 IEEE MTT-S Int. 1–4 (IEEE, 2016).

  25. 25.

    Hui, X., Ma, Y. & Kan, E. C. Real-time code-division multi-tag localization with centimeter accuracy. Proc. IEEE RFID Conf. 110–116 (IEEE, 2017).

  26. 26.

    Ma, Y., Hui, X. & Kan, E. C. 3D real-time indoor localization via broadband nonlinear backscatter in passive devices with centimeter precision. Proc. 22nd Int. Conf. Mobile Comput. Network. 216–229 (ACM, 2016).

  27. 27.

    Li, C., Lubecke, V. M., Boric-Lubecke, O. & Lin, J. A review on recent advances in Doppler radar sensors for noncontact healthcare monitoring. IEEE Trans. Microw. Theory Techn. 61, 2046–2060 (2013).

  28. 28.

    Adib, F., Mao, H., Kabelac, Z., Katabi, D. & Miller, R. C. Smart homes that monitor breathing and heart rate. Proc. 33rd ACM Conf. Hum. Fact. Comput. Syst.837–846 (ACM, 2015).

  29. 29.

    Pinheiro, E., Postolache, O. & Girão, P. Theory and developments in an unobtrusive cardiovascular system representation: ballistocardiography. Open Biomed. Eng. J. 4, 201–216 (2010).

  30. 30.

    Sakoe, H. & Chiba, S. Dynamic programming algorithm optimization for spoken word recognition. IEEE Trans. Acoust. Speech Signal Process 26, 43–49 (1978).

  31. 31.

    Kim, C. et al. Ballistocardiogram: mechanism and potential for unobtrusive cardiovascular health monitoring. Sci. Rep. 6, 31297 (2016).

  32. 32.

    Geddes, L. A., Voelz, M. H., Babbs, C. F., Bourland, J. D. & Tacker, W. A. Pulse transit time as an indicator of arterial blood pressure. Psychophysiology 18, 71–74 (1981).

  33. 33.

    Mukkamala, R. et al. Toward ubiquitous blood pressure monitoring via pulse transit time: theory and practice. IEEE Trans. Biomed. Eng. 62, 1879–1901 (2015).

  34. 34.

    Yeager, D. J., Sample, A. P. & Smith, J. R. in RFID Handbook: Applications, Technology, Security, and Privacy (eds Ahson, S. & Ilyas, M.) 261–278 (CRC Press, Boca Raton, 2008).

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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.

Author information


  1. School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA

    • Xiaonan Hui
    •  & Edwin C. Kan


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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.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Xiaonan Hui.

Electronic supplementary material

  1. Supplementary Information

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

  2. Supplementary Video 1

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

  3. Supplementary Video 2

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

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