Theoretical and experimental investigations of lateral modes in 1-3 piezocomposites

Materials with a periodic microstructure show resonances caused by the elastic wave Bragg diffraction. This paper presents a simple approach to describe these resonances (called lateral resonances) in 1-3 piezoelectric composite materials which have a 2-D periodicity. Our model is based on the analysis of the propagation of transverse waves in a 2-D periodic medium of infinite thickness and takes into account the periodic and interfacial boundary conditions. This model predicts the displacement field vectors and frequencies of lateral resonances from which the phase velocity of lateral waves is determined. The theoretical and experimental variations of this velocity versus the ceramic rod width to pitch ratio are compared. It is shown that the first lateral mode frequency is maximum when the ceramic volume fraction is around 0.65. Theoretical predictions of the mechanical displacement at the composite surface are compared with measurements obtained by an interferometric laser technique. A good agreement is observed, showing that lateral waves are mainly vertically polarized.