Large signal dielectric losses in electrostrictive materials

摘要

The dielectric loss factor tan delta is a critical parameter in transducer design and performance prediction, as it is directly related to the electrical energy lost to Joule heating. A method for calculating the equivalent loss factor of "quasilinear" materials from a measured major polarization vs. field loop by extending the standard definition of tan delta for a linear lossy capacitor to nonlinear materials is presente.d To extract effecitve loss tangents for minor loops from the the major loops, an area correction algorithm was implemented. This algorithm proves to be nearly exact for all bias and drive levels in the case of an ideal linear capacitor. In most cases, the effective tan delta calculated from a major loop agrees fairly well with that calculated from a directly measured minor loop. Finally, the behavior of the loss tangent as a function of the dc bias field, ac drive field, prestress level and temperature will be examined. It shall be shwon that, in general, the effective loss factor of lead magnesium niobate-lead titanate decreases with increasing temperature, consistent with its transition fro ma piezoelectric to an electrostrictive material, but increases with prestress. At a fixed temperature and prestress level, the loss factor increases as the bias or drive levels decreases. However, at certai nbias levels, the loss tangent is practically the same, regardless of the drive level.