Shaping Microwave Fields using Non-Linear Unsolicited Feedback: Application to Enhanced Energy Harvesting

Wavefront Shaping has emerged over the past decade as a powerful tool to control wave propagation through complex media, initially in optics and more recently also in the microwave domain with important applications in telecommunication, imaging and energy transfer. The crux of implementing wavefront shaping concepts in real life is often its need for (direct) feedback, requiring access to the target to focus on. Here, we present the shaping of a microwave field based on indirect, unsolicited and blind feedback which may be the pivotal step towards practical implementations. With the example of a radiofrequency harvester in a metallic cavity, we demonstrate tenfold enhancement of the harvested power by wavefront shaping based on non-linear signals detected at an arbitrary position away from the harvesting device.