  While wired-power-transfer devices ensure robust power delivery even if the
receiver position or load impedance changes, achieving the robustness of
wireless power transfer (WPT) is challenging. Conventional solutions are based
on additional control circuits for dynamic tuning. Here, we propose a robust
WPT system in which no additional tuning circuitry is required for robust
operation. This is achieved by our systematically designing the load and the
coupling link to be parts of the feedback circuit. Therefore, the WPT operation
is automatically adjusted to the optimal working condition under a wide range
of load and receiver positions. In addition, pulsed oscillations instead of
single-harmonic oscillation are adopted to increase the overall efficiency. An
example system is designed with the use of a capacitive coupling link. It
realizes a virtual, nearly-ideal oscillating voltage source at the load site,
giving efficient power transfer comparable to that of the ideal
wired-connection scenario. We numerically and experimentally verify the
robustness of the WPT system under the variations of load and coupling, where
coupling is changing by our varying the alignment of aluminum plates. The
working frequency and the transferred power agree well with analytical models.
The proposed paradigm can have a significant impact on future high-performance
WPT devices. The designed system can also work as a smart table supporting
multiple receivers with robust and efficient operation.
