When waves impinge on a disordered material they are back-scattered and form a highly complex interference pattern. Suppressing any such distortions of a wave’s free propagation is a challenging task with many applications in a number of different disciplines. In a recent theoretical proposal, it was pointed out that both perfect transmission through disorder as well as a complete suppression of any variation in a wave’s intensity can be achieved by adding a continuous gain–loss distribution to the disorder. Here we propose a practical discretized version of this abstract concept and implement it in a realistic acoustic system. Our prototype consists of an acoustic waveguide containing several inclusions that scatter the incoming wave in a passive configuration and provide the gain or loss when being actively controlled. Our measurements on this non-Hermitian acoustic metamaterial demonstrate the creation of a reflectionless scattering wave state that features a unique form of discrete constant-amplitude pressure waves. In addition to demonstrating that gain–loss additions can turn localized systems into transparent ones, we expect our proof-of-principle demonstration to trigger interesting new developments, not only in sound engineering, but also in other related fields such as in non-Hermitian photonics.
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The authors would like to thank M. Paolone and the Distributed Electrical Systems Laboratory at Ecole Polytechnique Fédérale de Lausanne (EPFL) for lending us the National Instrument CompactRIO-9068 platform for the experiment.
The authors declare no competing interests.
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Rivet, E., Brandstötter, A., Makris, K.G. et al. Constant-pressure sound waves in non-Hermitian disordered media. Nature Phys 14, 942–947 (2018). https://doi.org/10.1038/s41567-018-0188-7
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