Jutta Mohaupt

Dielectric, elastic and piezoelectric properties of porous pzt ceramics

Abstract Porous ceramics with type 3–3 connectivity were prepared and investigated with a view to their application for ultrasound transducers. Ceramics with a porosity in the order of 0.4 to 0.5 exhibit sufficiently high permittivity (≈ 500), a thickness coupling factor equalling that of dense material (≈ 0.5), a low transverse coupling factor, a low vibrational Q (≈ 20) and low acoustic impedance (≈ 9·106kg/m2·s), all of which indicates their eminent suitability as a material for the fabrication of transducers as used in medical diagnostics. The experimentally determined influence of the porosity on the dielectric constants of these materials was used for the critical testing of various theories for calculating the constants of multiphase materials. It was found that the dielectric and elastic constants of porous piezoelectric ceramics can be very satisfactorily described on the basis of Bruggemans theory, which has fallen somewhat into obscurity. Their piezoelectric properties are discussed with refer...

Anisotropic piezoelectric effect in modified PbTiO/sub 3/ ceramics

Experimental and theoretical investigations of the electromechanical anisotropy of ceramics modified with Ca, Ni-Nb, and Mn are presented. It is demonstrated that the large anisotropy of these ceramics is neither a bulk property of the PbTiO/sub 3/-crystallites nor a domain wall effect. The anisotropy is caused by the statistical orientation of the crystallites in the ceramics and by the material properties due to this orientation. The ratio of electrostrictive coefficients and the ratio of single-crystal permittivities in these ceramics also play a decisive role. The result enables one to comprehend easily the dependence of the ceramics electromechanical anisotropy on the material composition, the degree of poling, and the temperature.<<ETX>>

Method for the manufacture of an ultrasonics antenna array

A method for the manufacture of a linear or annular ultrasonics antenna array for the megahertz range, which consists in providing a laminate of alternating layers of unsintered ceramic and spacing layers, the spacing layers being composed of a filler material which is heat fugitive at the sintering temperature of the ceramic, the spacing material also including refractory grains distributed therein of a size which corresponds to the spacing desired between the ceramic layers, sintering the laminate to thereby liberate the filler material and leave voids between the refractory grains, impregnating the resulting laminate with a polymerizable resin to bond the sintered ceramic layers together, and separating the resulting laminate into individual transducer elements.