Ultrasonic cleaning enhances productivity in the industry and therefore reduces emissions. To this end, optimizing ultrasonic power delivery through metal walls is essential. Attaching a piezoelectric power ultrasound transducer to a metal wall dampens the fundamental resonance of the transducer. The metal wall alters the boundary condition at the transducer head from free to rigid, and therefore the antinode required for the fundamental resonance is not born at the head. To solve this limitation, we propose a novel contact interface, an airgap contact coupling (ACC).