Traversal time of acoustic plate waves through a tunneling section

Experimental evidence is given for the unnoticeable time delay undergone by an acoustic Lamb wave pulse in penetrating a forbidden barrier, represented by a narrowed plate region in the propagation path. Measurements, which use a technique unique to Lamb waves overcoming typical objections made in wave packet experiments, have been performed in various aluminium plates far several frequencies and different barrier lengths and show a value of the traversal time close to zero that appears to be independent from the barrier length.