A model to describe the behaviour of a laterally radiating piezoelectric loudspeaker

Abstract

A laterally radiating piezoelectric loudspeaker, or “spiral transducer”, is a new kind of transducer which meets specific industrial requirements. It consists of a piezopolymer diaphragm and a rigid foil, both rolled around a cylindrical core, each side of the diaphragm being loaded with a thin fluid layer. An electrical field, applied on both metallized faces of the piezopolymer film, creates a longitudinal elongation of the film in such a way that it produces a lateral acoustical flow at each end of the cylinder. The aim of the work presented here is to provide an accurate description of the dynamic behaviour of this transducer using an appropriate analytical model developed for this purpose, based on fundamental equations of acoustics and mechanics, which takes into account the complex coupling between the mechanical and acoustical parts, and the effects of viscosity and heat conduction. The behaviour of such a loudspeaker when used as an earphone is then studied. An electrical network equivalent to the earphone is given and compared to a classical lumped elements network. Numerical results obtained from these models are also compared.