Periodic crack-model of comb transducers: efficiency and optimization

A model for a comb transducer is investigated in which the
comb-sample interface is modeled by a periodic system of cracks. Leaky interface
crack waves are generated by a normal incident shear bulk wave beam or by an
equivalent excitation of the comb teeth at the interface. The generation
efficiency is analyzed in systems where both the comb and the sample halfspaces
are from the same material, steel or aluminium, for different teeth width and
period, and for the case of solid contact between the two halfspaces between
cracks; the other case of sliding contact is discussed briefly. Numerical
results show that up to 25% of the incident power can be transformed into
interface crack waves by a comb tooth. Optimal number of comb teeth is
estimated, and the transducer frequency response is discussed. Approximated
relationships are presented that may help designing a comb.