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Robust and efficient wireless power transfer using a switch-mode implementation of a nonlinear parity–time symmetric circuit


Stationary wireless power transfer has been deployed commercially and can be used to charge a variety of devices, including mobile phones and parked electric vehicles. However, wireless power transfer set-ups typically suffer from an inherent sensitivity to the relative movement of the device with respect to the power source. Nonlinear parity–time symmetric circuits could be used to deliver robust wireless power transfer even while a device is moving rapidly, but previous implementations have relied on an inefficient gain element based on an operation-amplifier circuit, which has inherent loss, and hence have exhibited poor total system efficiency. Here we show that robust and efficient wireless power transfer can be achieved by using a power-efficient switch-mode amplifier with current-sensing feedback in a parity–time symmetric circuit. In this circuit, the parity–time symmetry guarantees that the effective load impedance on the switch-mode amplifier remains constant, and hence the amplifier maintains high efficiency despite variation of the transfer distance. We experimentally demonstrate a nonlinear parity–time symmetric radiofrequency circuit that can wirelessly transfer around 10 W of power to a moving device with a nearly constant total efficiency of 92% and over a distance from 0 to 65 cm.

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Fig. 1: Circuit design for efficient and robust wireless power transfer based on nonlinear PT symmetry.
Fig. 2: Power-efficient switch-mode amplifier operation.
Fig. 3: Efficient switch-mode amplifier as a resonator’s gain element.
Fig. 4: Experimental wireless power transfer system and measurements.

Data availability

The datasets generated and analysed during the current study are available at


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This work was supported by a Vannevar Bush Faculty Fellowship (grant no. N00014-17-1-3030) from the US Department of Defense.

Author information




S.A. performed the simulations and measurements. S.F. supervised the project. Both authors contributed to writing the manuscript.

Corresponding author

Correspondence to Shanhui Fan.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–4 and discussion.

Source data

Source Data Fig. 1

Simulated total system efficiencies.

Source Data Fig. 2

Ideal amplifier waveforms.

Source Data Fig. 3

Calculated switching efficiency (Fig. 3a) and oscillation frequency and effective load impedance (Fig. 3b).

Source Data Fig. 4

Measured oscillation frequency, delivered power, total efficiency and the amplifier’s waveforms.

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Assawaworrarit, S., Fan, S. Robust and efficient wireless power transfer using a switch-mode implementation of a nonlinear parity–time symmetric circuit. Nat Electron 3, 273–279 (2020).

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