Large signal dielectric losses in sonar transducers

The dielectric loss factor tan<th>δ is a critical parameter in transducer design and performance prediction, as it is directly related to the electrical energy lost to Joule heating. For an ideal linear material, tan<th>δ is a constant irrespective of the operating conditions. However, electrostrictive materials such as lead magnesium niobate/lead titanate (PMN/PT) exhibit significantly nonlinear behavior. It is, therefore, expected that tan<th>δ (as well as the other material constants) will be a strong function of the transducer operating conditions. In this paper we will present three different methods for calculating the loss factor of ‘‘quasilinear’’ materials. It will be shown that, in the limit of small signals about a bias point, the three methods are consistent with the standard linear definition. These three methods will be applied to material measurements taken at NAVSEA Newport on PMN/PT. The behavior of the loss tangent as a function of the dc bias field, ac drive field, prestress level, and temperature will be examined. Finally, the predicted response of stacks and transducers using tan<th>δ calculated from the material measurements will be compared with experimental results. [Work sponsored by PEO(USW)‐P and the Office of Naval Research.]