PIEZOELECTRICIDAD

Author: CASALS MIRONES JORGE ALEJANDRO.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: Facultat d'Informàtica,Campus Nord.
Place of preparation: EDIFICI B5 DESPATX B5-011 NORD.

Summary: Systems Test No. Destructivo (END) use among the variety of existing techniques, ultrasonic pulses at high frequencies for the diagnosis and characterization of materials. In these systems the trials pingers more piezoelectric transducers are used because they have a high factor acoplo electromechanical. Generally, these systems which enable the analysis of 100% of the samples are used in liquid media to significantly reduce the difference between the acoustic impedances piezoelectric resonator and the environment, as well as between the middle and the object of analysis. To reduce the impedance acoustic transducer and improve the alignment of impedances are used composites piezoelectric type 1-3. These piezocomposites are formed by bars of piezoelectric ceramics working on ways separated by a thick epoxy resin. The advantages of using these composite materials, in addition to reducing its acoustic impedance, are: increasing factor acoplo electromechanical the resonator (increasing the amplitude of the wave emitted), and increase the bandwidth of resonance, which is necessary to deliver pulses Shorts. In order to do an analysis simpler and faster and be able to study objects which by their nature can not wet, has been carried out the study of a piezoelectric transducer with composites for the issuance of ultrasound in the air. Due to the difference in acoustic impedances between the transducer and air, the noise energy emitted to the environment is very weak, being necessary to implement major powers. The application of high electric fields or large deformation generates nonlinear behavior typical of the devices power that can not be predicted by the constitutive equations for the linear theory. For this reason, this thesis work is fundamental objective study of the non-linearities in power transducers using composites. The acoustic wave which is transmitted to the medium needs to be intense for that information bearing ensure a full inspection of the entire volume of the workpiece or material that we are interested in analyzing, thus requiring large deformations are obtained with transducers working short pulses with resonance. The actions associated with these deformities were carried out at frequencies close to the resonance frequency (fs). The characterization nonlinear regime stationary in the composites and ceramics used in the manufacture thereof, as well as a comparison between them has revealed that the composite be used, ie material (hard or soft) and that fraction of ceramics (fc) is the best. An accurate and complete characterization requires not only able to predict the behavior at high signal but also the analysis of pulsed regime transducer, thus preventing the thermal evolution of the transducer due to the application of electrical signals high. For characterization nonlinear signal has been used both to burst into the queue of free oscillations as in the regime of stationary resonator. To reduce the difference in acoustic impedances between air and piezoelectric resonator have added one or more layers of adaptation to the quarter-wave resonator. In this research paper discusses some of the results obtained using surface adapter in ceramics and composites 1-3 r 8 ealizado 2b8 s piezoelectric material with hard and soft