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Sensitive readout of implantable microsensors using a wireless system locked to an exceptional point

Abstract

Exceptional points are degeneracies in physical systems at which both the underlying eigenvalues and eigenvectors of the system coalesce. They originated in theoretical explorations of quantum mechanics, but are of increasing value in photonics, acoustics and electronics because their emergence in physical systems with controlled gain and loss can dramatically alter the response of a system. In particular, systems biased at exceptional points can exhibit an amplified response to a small perturbation, enabling greatly enhanced sensitivity for certain resonant sensors. In biomedicine, implanted electronic sensors based on resonant inductor–capacitor (LC) circuits can be used to monitor internal physiological states, but their capabilities are currently limited by the low sensitivity of existing wireless interrogation techniques. Here we show that a reconfigurable wireless system locked to an exceptional point can be used to interrogate in vivo microsensors with a sensitivity 3.2 times the limit encountered by existing schemes. We use a controller that maximizes the abruptness of a parity–time-symmetry phase transition to operate a reconfigurable circuit at an exceptional point and maintain enhanced sensitivity. With this approach, we demonstrate robust readout of LC microsensors (with diameters of 900 μm) that are subcutaneously implanted in a rat, and show that it can be used for wideband sensor interrogation for measurement of the resonant frequencies of single and multiple sensors.

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Fig. 1: Implantable microsensor readout with a wireless system locked to an exceptional point.
Fig. 2: Readout mechanism and sensitivity enhancement at an EP.
Fig. 3: Experimental demonstration of enhanced sensitivity by EP locking.
Fig. 4: Microsensor readout in physiological environments.
Fig. 5: Wideband interrogation of single and multiple sensors.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

Pseudocode for the EP-locking algorithm is provided in the Supplementary Information.

References

  1. 1.

    Collins, C. C. Miniature passive pressure transensor for implanting in the eye. IEEE Trans. Biomed. Eng. 14, 74–83 (1967).

    Article  Google Scholar 

  2. 2.

    Chen, P.-J., Rodger, D. C., Saati, S., Humayun, M. S. & Tai, Y.-C. Microfabricated implantable parylene-based wireless passive intraocular pressure sensors. J. Microelectromech. Syst. 17, 1342–1351 (2008).

    Article  Google Scholar 

  3. 3.

    Abraham, W. T. et al. Wireless pulmonary artery haemodynamic monitoring in chronic heart failure: a randomised controlled trial. Lancet 377, 658–666 (2011).

    Article  Google Scholar 

  4. 4.

    Mannoor, M. S. et al. Graphene-based wireless bacteria detection on tooth enamel. Nat. Commun. 3, 763–768 (2012).

    Article  Google Scholar 

  5. 5.

    Chen, L. Y. et al. Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care. Nat. Commun. 5, 5028 (2014).

    Article  Google Scholar 

  6. 6.

    Hu, X. et al. Micrometer-scale magnetic-resonance-coupled radio-frequency identification and transceivers for wireless sensors in cells. Phys. Rev. Appl. 8, 014031–13 (2017).

    Article  Google Scholar 

  7. 7.

    Miri, M.-A. & Alu, A. Exceptional points in optics and photonics. Science 363, eaar7709 (2019).

    MathSciNet  Article  Google Scholar 

  8. 8.

    Feng, L., El-Ganainy, R. & Ge, L. Non-Hermitian photonics based on parity–time symmetry. Nat. Photon. 11, 752–762 (2017).

    Article  Google Scholar 

  9. 9.

    Wiersig, J. Sensors operating at exceptional points: general theory. Phys. Rev. A 93, 033809 (2016).

    Article  Google Scholar 

  10. 10.

    Liu, Z.-P. et al. Metrology with PT-symmetric cavities: enhanced sensitivity near the PT-phase transition. Phys. Rev. Lett. 117, 110802 (2016).

    Article  Google Scholar 

  11. 11.

    Hodaei, H. et al. Enhanced sensitivity at higher-order exceptional points. Nature 548, 187–191 (2017).

    Article  Google Scholar 

  12. 12.

    Chen, W., Özdemir, S. K., Zhao, G., Wiersig, J. & Yang, L. Exceptional points enhance sensing in an optical microcavity. Nature 548, 192–196 (2017).

    Article  Google Scholar 

  13. 13.

    Zhao, H., Chen, Z., Zhao, R. & Feng, L. Exceptional point engineered glass slide for microscopic thermal mapping. Nat. Commun. 9, 1764 (2018).

    Article  Google Scholar 

  14. 14.

    Schindler, J., Li, A., Zheng, M. C., Ellis, F. M. & Kottos, T. Experimental study of active LRC circuits with PT symmetries. Phys. Rev. A 84, 040101 (2011).

    Article  Google Scholar 

  15. 15.

    Schindler, J. et al. PT-symmetric electronics. J. Phys. A 45, 444029 (2012).

    Article  Google Scholar 

  16. 16.

    Assawaworrarit, S., Yu, X. & Fan, S. Robust wireless power transfer using a nonlinear parity–time-symmetric circuit. Nature 546, 387–390 (2017).

    Article  Google Scholar 

  17. 17.

    Chen, P.-Y. et al. Generalized parity–time symmetry condition for enhanced sensor telemetry. Nat. Electron. 1, 297–304 (2018).

    Article  Google Scholar 

  18. 18.

    Sakhdari, M. et al. Ultrasensitive, parity–time-symmetric wireless reactive and resistive sensors. IEEE Sens. J. 18, 9548–9555 (2018).

    Article  Google Scholar 

  19. 19.

    Hajizadegan, M., Sakhdari, M., Liao, S. & Chen, P.-Y. High-sensitivity wireless displacement sensing enabled by PT-symmetric telemetry. IEEE Trans. Antennas Propag. 67, 3445–3449 (2019).

    Article  Google Scholar 

  20. 20.

    Grebennikov, A. RF and Microwave Transistor Oscillator Design (Wiley, 2007).

  21. 21.

    Langbein, W. No exceptional precision of exceptional-point sensors. Phys. Rev. A 98, 023805 (2018).

    Article  Google Scholar 

  22. 22.

    Chen, C., Jin, L. & Liu, R.-B. Sensitivity of parameter estimation near the exceptional point of a non-hermitian system. Preprint at https://arxiv.org/abs/1809.05719 (2018).

  23. 23.

    Zhang, M. et al. Quantum noise theory of exceptional point sensors. Preprint at https://arxiv.org/abs/1805.12001 (2018).

  24. 24.

    Lau, H.-K. & Clerk, A. A. Fundamental limits and non-reciprocal approaches in non-Hermitian quantum sensing. Nat. Commun. 9, 4320 (2018).

    Article  Google Scholar 

  25. 25.

    Hwang, S. W. et al. A physically transient form of silicon electronics. Science 337, 1638–1640 (2012).

    Article  Google Scholar 

  26. 26.

    Luo, M., Martinez, A. W., Song, C., Herrault, F. & Allen, M. G. A microfabricated wireless RF pressure sensor made completely of biodegradable materials. J. Microelectromech. Syst. 23, 4–13 (2014).

    Article  Google Scholar 

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Acknowledgements

The authors thank A. Bansal, Z. Xiong and G. Gammad for their assistance with the in vivo experiments and Z. Goh for the art in Fig. 1. J.S.H. acknowledges support from the National Research Foundation Singapore (NRFF2017-07), Ministry of Education Singapore (MOE2016-T3-1-004), and Institute for Health Innovation and Technology grants.

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J.S.H. and C.-W.Q. conceived and planned the research. Z.D. performed the simulations and designed the wireless system. Z.D., Z.L. and F.Y. characterized the system and performed the experiments. J.S.H. and Z.D. wrote the paper with input from all the authors.

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Correspondence to John S. Ho.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Notes A–F and Supplementary Figs. 1–11

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Dong, Z., Li, Z., Yang, F. et al. Sensitive readout of implantable microsensors using a wireless system locked to an exceptional point. Nat Electron 2, 335–342 (2019). https://doi.org/10.1038/s41928-019-0284-4

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