Fauconnier Maxime, Karunakaran Bhuvaneshwari, Drago-González Alex, Wong William S Y, Ras Robin H A, Nieminen Heikki J
Medical Ultrasonics Laboratory (MEDUSA), Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland.
Department of Applied Physics, Aalto University, Espoo, Finland.
Nat Commun. 2025 Feb 12;16(1):1568. doi: 10.1038/s41467-025-55907-w.
The propagation of interfacial waves in free and constrained conditions, such as deep and shallow water, has been broadly studied over centuries. It is a common event that anyone can witness, while contemplating the ocean waves washing ashore. As a complementary configuration, this work introduces waves propagating on an interface restricted by its pinning to the solid microstructures of an underwater superhydrophobic surface. The latter has the ability to stabilize a well-defined microscale gas layer, called a plastron, trapped between the water and the solid phase. The acoustic radiation force produced with focused MHz ultrasound successfully triggers kHz "plastronic waves", i.e., capillary waves travelling on a plastron's gas-water interface. The exposed waves possess interesting features, i.e., (i) a high propagation speed up to 45 times faster than conventional deep water capillary waves of comparable wavelength and (ii) a relation of the propagation speed with the geometry of the microstructures. Based on this and on the observed variation of wave speed over time in conditions of gas-undersaturated or -supersaturated water, the usefulness of the plastronic waves for the non-destructive monitoring of the plastron's stability and the spontaneous air diffusion is eventually demonstrated.
几个世纪以来，人们广泛研究了界面波在自由和受限条件下的传播，如深水和浅水中的传播。当人们凝视着海浪冲上岸时，这是任何人都能目睹的常见现象。作为一种补充配置，这项工作介绍了在受其与水下超疏水表面的固体微观结构固定限制的界面上传播的波。后者能够稳定一个定义明确的微尺度气体层，称为气套，被困在水和固相之间。聚焦的兆赫兹超声产生的声辐射力成功地触发了千赫兹的“气套波”，即在气套的气 - 水界面上传播的毛细波。所呈现的波具有有趣的特征，即：（i）传播速度高达可比波长的传统深水毛细波的45倍；（ii）传播速度与微观结构的几何形状有关。基于此以及在气体未饱和或过饱和水条件下观察到的波速随时间的变化，最终证明了气套波在无损监测气套稳定性和自发空气扩散方面的实用性。
