Extreme impedance mismatch causes sound insulation at water–air interfaces, limiting numerous cross-media applications such as ocean-air wireless acoustic communication. Although quarter-wave impedance transformers can improve transmission, they are not readily available for acoustics and are restricted by the fixed phase shift at full transmission. Therefore, how to achieve high-efficiency wave manipulation across the water-air interface is an urgent problem in the engineering field.
Recently, the research team from Wave Mechanics and Control Laboratory of Tianjin University proposed impedance-matched hybrid metasurfaces assisted by topology optimization to solve this problem. Sound transmission enhancement and phase modulation across the water–air interface are achieved independently. Compared to the bare water–air interface, it is experimentally observed that the average transmitted amplitude through an impedance-matched metasurface at the peak frequency is enhanced by approximately 25.9 dB, close to the limit of the perfect transmission 30 dB. And nearly 42 dB amplitude enhancement is measured by the hybrid metasurfaces with axial focusing function. Various customized vortex beams are experimentally realized to promote applications in ocean-air communication. The physical mechanism of sound transmission enhancement is that the fluid–solid interactions induce the specific vibration modes of metasurface to dynamically satisfy the required impedance-matching condition. The proposed concept has potential applications in efficient transmission and free communication across dissimilar media. The study was published in Advanced Science under the title of ‘Hybrid Metasurfaces for Perfect Transmission and Customized Manipulation of Sound Across Water–Air Interface’. Full details can be found in
https://onlinelibrary.wiley.com/doi/10.1002/advs.202207181
The proposed concept of hybrid metasurfaces for perfect transmission and customized manipulation of sound across the water–air interface.
Enhanced water-air sound transmission under broadband pulse incidence
Enhanced water-air sound axial focusing by hybrid metasurfaces
By School of Mechanical Engineering
Editor: Sun Xiaofang
