  We report both experimentally and theoretically that the enhanced acoustic
transmission can occur in the subwavelength region through a thin but stiff
structured-plate without any opening. This exotic acoustic phenomenon is
essentially distinct from the previous related studies originated from, either
collectively or individually, the interaction of the incident wave with
openings in previous structures. It is attributed to the structure-induced
resonant excitation of the non-leaky Lamb modes that exist intrinsically in the
uniform elastic plate. Our finding should have impact on ultrasonic
applications.
