Design guidelines of 1-3 piezoelectric composites dedicated to ultrasound imaging transducers, based on frequency band-gap considerations
Résumé
Periodic piezoelectric composites are widely used for imaging applications such as biomedical imaging or non destructive evaluation. We propose to view these structures as phononic crystals and investigate in this frame their properties with respect to periodicity. This approach is based on the investigation of band gaps, that strongly depend on the properties of the considered composites (geometry, size, nature of materials). It is motivated by the fact that band gaps in principle allow one to excite the thickness mode without exciting other parasitic waves. The plane-wave-expansion (PWE) method that we use has already been applied to periodic piezoelectric composites, but in contrast to previous approaches we consider not only waves propagating in the symmetry plane of the composite, but also waves propagating with a non-zero angle of incidence. The method is applied to a representative 1-3 connectivity piezocomposite in order to demonstrate its potentialities for design. The evolution of band gaps is explored with respect to the angle of incidence. All bulk waves that contribute to the setting-up of plate modes in the vicinity of the thickness mode are found and identified.