Dynamic torsion of laminar beams as a working principle for sensors

Abstract

A method is presented in order to put planar structures in a pure torsion, by directly acting from their surfaces where a stress state is induced, taking advantage of piezoelectric layers that are integral with them. An experimental investigation was carried out on alumina beams which, in a portion of their faces, support two ferroelectric layers of lead zirconate titanate created using conventional thick-film technology processes. A suitable system of coplanar electrodes, embedded in the layers, promotes piezoelectric deformations parallel to the substrate, induced by a voltage across them. At the layer–substrate interfaces, completely in-plane stresses are created, and when they are conveniently oriented, the beam is prompted into pure torsion, which takes on the characteristics of a vibration following the application of alternated voltage. Besides describing the design and realization of the sample beams, this study reports on their dynamic behaviour in torsion, the experimental set-ups and the procedures for its characterization. The results are discussed and highlighted in order to outline the potential of the method with regard to using the realized beams as primary sensors for physical quantities. To this end, proposals for possible devices are considered, and an application of beams in a force sensor is also reported.