V. H. Salazar
Cinvestav I.P.N., Dept. of Electrical Eng., Bioelectron. Section, AV. IPN 2508 Mexico D. F.
O. Perez-Martinez (Cuba)
The conventional materials, such as PZT ceramics, show a high electromechanical coupling factor; however, they must be acoustically matched to tissue in order to facilitate transmission and reception over a broad frequency band. Application of this ceramic in linear arrays entails additional complexity. Each element in an array must be subdivided into several subelements to suppress coupling unwanted lateral modes. Thus piezoelectric ceramics with large electromechanical anisotropies (the electromechanical coupling factor for thickness dilatational vibration K[sub t] is much large than that for planar extensional vibration K[sub p]) have recently come to be developed for use as high-frequency ultrasonic transducer materials. PbTiO[sub 3] ceramics modified with alkaline metals or rare earth have been extensively investigated because of their promise as a piezoelectrical materials for high-frequency and high-temperature applications. In Pb[(Co[sub 1/2]W[sub 1/2])[sub 0.04]Ti[sub 0.96]]O[sub 3] ceramics Yamashita et al. reported that the electromechanical coupling factor for thickness dilatational vibration K[sub t] increasing of poling field but coupling factor for planar extensional vibration K[sub p] was negligibly small. In (Pb[sub 0.88]Ln[sub 0.08])(Ti[sub 0.98]Mn[sub 0.02]) ceramics (Ln=La, Nd, Sm, and Gd) Takeuchi et al. found that the Sm ion was excellent in the substitution of the Pb ion to make large electromechanical anisotropy between longitudinal and transverse mode vibration. Electromechanical properties of PbTiO[sub 3] ceramics modified by the partial substitution of Eu for Pb and Mn for Ti are examined, and the results are compared with the partial substitution of Sm and other elements of the lanthanides group.