Corona characteristics of transducer ceramics

Abstract

Transducers are frequently plagued by the presence of corona which can adversely affect the performance and lifetime of the unit. Sites at which corona can occur include the wiring, spacing, configuration, sharp electrode edges, etc., but these can be minimized with proper design and engineering. A fundamental limit below which one cannot reduce the appearance of corona lies with the transduction material, that is, the piezoelectric ceramic itself. The corona characteristics of over 2500 lead zirconate-lead titanate ceramic rings have been determined and the results used to model a much larger ring population from which predictions can be made about the corona performance of transducers assembled from these rings. A summary of the information to be presented is that: (1) Populations of “as-fired” ceramic rings have significantly higher corona inception voltages than rings with surfaces finished by machine grinding. (2) Two distinctively different types of corona have been identified, one of which can be partially “cured” by sulfur hexafluoride. (3) The corona data for the rings have been fit to a Weibull distribution model and applied to a “weak-link” model to predict the best performance that can be expected from the assembled transducer. [Work sponsored by the Sonar Transducer Reliability Improvement Program, NAVSEA.]