Anomalous increase of SAW velocity due to conducting film on piezoelectric substrate

The influence of a thin conducting layer on the propagation of surface acoustic waves in a piezoelectric medium is investigated theoretically. It is generally believed that wave velocity decrease monotonically with increasing conductance of the layer. Our calculations show, however, that in the case of weakly inhomogeneous surface waves, such as Bleustein-Gulyaev and Love waves, there exists a certain conductance interval in which the wave velocity increases with increasing layer conductance. This anomalous behavior, referred to as the anomalous resisto-acoustic effect, is related to the penetration depth of the wave into the substrate. The anomalous effect is present if the penetration depth exceeds a certain critical value, and absent otherwise. The anomalous effect allows one to obtain value of Δv/v, the fractional velocity change, that is greater than the normally predicted value of Δv/v=(v₀ -v_m)/v ₀. For example, for Bleustein- Gulyaev waves propagating in Y-cut, X-propagation potassium niobate, values of Δv/v greater than 0.32 can be obtained, compared to the normally predicted value of 0.26