Determination of electromechanical coupling coefficients in transducer materials with high mechanical losses

An important problem in transducer design is the accurate determination of electromechanical coupling coefficients for piezoelectric materials. The authors report on novel methods for determining both k_t the thickness mode coefficient, and k₃₁, an important parameter for transducer arrays. The coupling coefficients are computed near piezoelectric resonances using Krimholtz-Leedom-Matthaei (KLM) equivalent circuit models. These models have been modified to account for the mechanical losses of the material through an effective attenuation coefficient which can be estimated independently of the coupling coefficient. This measurement theory is applied to three different transducer materials: PVDF (polyvinylidene fluoride), PZT5A and a PZT (lead zinc titanate)/epoxy composite