The study of modal sensors and actuators is motivated by their ability to control the resonance frequency and the vibration modes of mechanical structures. In this work, a non-homogeneous poling method to obtain a radial modal sensor from a piezoelectric disc is presented. The construction method for three modal elements is described and their electrical behavior is presented and analyzed in comparison to a uniform poled disc.

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Limited diffraction ultrasonic transducers are devices that have a large depth of acoustic field without important effects of diffraction, which make them optimal in applications of medical images, among others. This report details how this special type of piezoelectric device was designed by means of a simple technology using three electrodes in the form of concentric rings in both faces of a ferroelectric ceramic disk, which were used to apply a profile of non-homogeneous polarization. Once designed, the radiation fields emitted by these resonators were characterized experimentally by electro-acoustic and acousto-optic techniques and were compared with those emitted by conventional devices. As shown in the experimental characterizations, ultrasonic transducers with optimal properties for use in medical applications such as good collimation of the ultrasound beam, high lateral resolution, as well as little effects of diffraction were obtained.