 The research team developed a new method to increase the efficiency of sound transmission between two different media, such as air and water. This method involves using a combination of impedance-matched metamaterials and topology optimization to create a device that can amplify sound waves across the interface. The result was a significant improvement in the amount of sound energy transferred from one medium to another, which could have important implications for underwater communications. This article was authored by Hongtao Zhou, Xiao Zeng Zhang, Tong Zhu, and others.