High transmission loss of slit arrays for underwater sound

We report on the transmission loss of slit arrays under normal incidence. The role of the acoustical impedance ratio between the solid and the water in the transmission properties of slit arrays is studied numerically. Calculations predict large transmission loss up to 60 dB for low impedance ratio. Thus, the insertion loss of the slit-array is positive and could be useful in underwater sound applications. This counterintuitive result is discussed in terms of the hydrodynamic short-circuit, where the fluid and the solid interface vibrate out of phase resulting in sound transmission suppression.