Technique for accurate determination of tensor properties of materials used in medical transducers

Modern design tools for ultrasound transducers, such as finite element modeling, require the knowledge of all property tensor elements for the materials. The mechanical moduli of isotropic materials can be determined from the longitudinal and shear wave sound velocities as well as the density. This paper describes a new method for measuring the velocities in matching layer and backing materials used in medical transducers. For the longitudinal velocity measurement, the spectrum of the signal reflected by a flat sample in a water tank is evaluated. The accuracy is hereby 1-2%. For the shear wave velocity measurement, laminates of PZT and the material under investigation are fabricated. The transducer resonates in a thickness-shear mode. Finite element code is used to simulate and fit the electrical impedance of the ceramic to the experimental curve, thereby accurately determining the shear wave velocity of the material sample laminated to the ceramic. The tensor coefficients for the PZT material determine the accuracy of the method and should be known when applying this technique