Converging acoustic waves through complex media with a four-phase metalens

Wavefront shaping is an established solution to converge acoustic waves through complex media. Discrete phase sampling is inevitable in practice because of manufacture resolution. Limited phase sampling undermines focusing performance, which is hardly improved by increasing the number of phase sections. We propose that such loss can be alleviated when the modulator is designed directly on discrete phases. The feedback-based wavefront shaping with the genetic algorithm has been taken here. The performance of the optimized four-phase metalens catches up with the continuous one and is robust to variations in complex media. Experiments have confirmed its function. These results have potential applications in acoustic focusing and imaging through complex media.