Listening to immersed superhydrophobic surfaces: Acoustic inspection of air plastron layers

When immersed in water, a solid coated with a superhydrophobic surface traps an air layer, called a plastron, that shields it from liquid contact. This layer enables underwater respiration in animals and provides drag reduction, anti-corrosion, and antifouling effects. However, plastrons are sensitive to external disturbances and can destabilize. This study demonstrates how plastron acoustic resonance can be used to monitor and measure the trapped air layer volume. Validated against direct observations, the method is portable, noninvasive, and effective for studying plastron stability under realistic conditions and various flow conditions.