APEC 2018 – Thin Self-Resonant Structures for Wireless Power Transfer

The high-Q achievable by self-resonant structures increases the range and efficiency of wireless power transfer (WPT). However, to date implementations of this structure have been thick, which limits their practical implementations. In the attached paper, we explore the design of thin self-resonant structures.

We describe:
1) a computationally efficient 2-D optimization algorithm is proposed to design thin
resonant structures and illustrate the trade-offs in the design, and
2)a new magnetic core shape is proposed which shapes the magnetic field lines to be parallel to the conductive layers and reduces current crowding.

These advances results in a prototype 3.5 mm thick self-resonant structure, which has a measured quality factor of 560 despite having a diameter of only 6.6 cm; this provides a 3.03× improvement over the state-of-the-art WPT coils in the literature.

APEC 2017 High-Q Self-Resonant Structure for Wireless Power Transfer

At APEC 2017 we presented a resonant structure that improves the range and efficiency of wireless power transfer.  High quality factor in resonant coils is essential for both goals, so developed a new technology that achieves Q values that weren’t previously possible. The new structure integrates inductive and capacitive effects to behave as an LC resonator.  It’s made by stacking alternating layers of thin foil and dielectric material in a magnetic core.  The high-Q is achieved through these effects:

  • Thin foil layers mitigate proximity effect.
  • Inductive coupling of sections and integration of capacitance eliminates terminations in high-current paths.
  • Capacitive ballasting forces equal current sharing between all layers.

We experimentally validated this structure and measured a Q of 1173 at 7 MHz despite a coil diameter of only 6.6 cm.    Next, we integrated 2 of the structures into a wireless power transfer system.  We were able to improve the range over which we could maintain efficiency above 94% by a factor of two when compared to the current state-of-the art.  For more details see our presentation slides linked here, or our paper linked here.