High-voltage power transmission in electrical grids requires reliable and durable dielectric polymers for wire insulation1,2. Electrical treeing caused by high, local electric fields is a damaging process that leads to structure degradation and electrical conduction of dielectric materials, and ultimately, to catastrophic failure of the devices3,4,5. Here, we demonstrate that the addition of less than 0.1 volume per cent of superparamagnetic nanoparticles into a thermoplastic polymer enables the repair of regions damaged by electrical treeing and the restoration of the insulating properties. Under the application of an oscillating magnetic field, the embedded nanoparticles migrate to the electrical trees and generate a higher local temperature, which heals the electrical tree channels in the polymer. Our method allows us to regenerate the dielectric strength and electrical resistivity over multiple cycles of tree formation and healing, which could be used to increase the lifespan and sustainability of power cables for electronics and energy applications.

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This work was supported by the Program of National Key Basis and Development Plan (973) (grant 2014CB239505 to J. He). The scanning transmission electron microscopy was performed in Beijing Neurosurgical Institute (China). The authors thank C.J. Cao (Carl Zeiss Co. Ltd, Shanghai, China) for sample mounting method and imaging technology support in the computed micro-X-ray tomography tests, and Z.X. Cao (Object Research Systems Inc., Montreal, Canada) for assistance with 3D reconstruction and analysis.

Author information


  1. State Key Laboratory of Power System, Department of Electrical Engineering, Tsinghua University, Beijing, China

    • Yang Yang
    • , Jinliang He
    • , Qi Li
    • , Lei Gao
    • , Jun Hu
    • , Rong Zeng
    •  & Shan X. Wang
  2. Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    • Jian Qin
  3. Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA

    • Shan X. Wang
  4. Department of Electrical Engineering, Stanford University, Stanford, CA, USA

    • Shan X. Wang
  5. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA

    • Qing Wang


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J. He, Q.L., Q.W. and Y.Y. conceived and designed the experiments. Y.Y., Q.L., L.G. and J. Hu carried out the experiments. Y.Y. and J.Q. performed simulations. Y.Y., J. He, Q.L., R.Z., Q.W. and S.X.W. analysed the data. Q.L., Q.W. and J.He wrote the manuscript. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Jinliang He or Qi Li or Qing Wang.

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