Surface concavity enhances ultrasonic transmission from air to liquid

We reveal a unique effect in which the ultrasonic transmission efficiency from the air to the liquid is significantly enhanced by the liquid surface concavity induced by ultrasound. The surface concavity acts as a special geometry-controllable transducer to transmit ultrasound into the liquid, where the sound transmission efficiency exhibits a relationship with the concavity depth: τ ∼ d².