A new vibration mode for medical imaging arrays

Abstract

The possibility of designing medical imaging arrays using a new transducer vibration mode is analyzed. The vibration mode, that we call ‘‘width mode'', is studied theoretically and experimentally and compared to the classical ‘‘array mode''. Starting from the constitutive equations for piezoelectric materials and with proper boundary conditions, the propagation velocity for the new mode is first found for the case of mono-dimensional propagation approximation. Then an approximate theory for vibrating systems which possess only two degrees of freedom is used in order to express dispersion curves for the propagation velocity for the two modes of interest. Theoretical results are then compared with experimental data obtained for PZT5-A and PZT4 ceramic materials. The new oscillation mode shows some advantages such as a smaller degree of wave velocity dispersion, a smaller absolute value of wave velocity propagation and a lower electrical impedance. Plots of input electrical admittance show that with a proper choice of the geometrical ratio w/t a good separation between the width and other unwanted modes can be obtained. Some advantages of the proposed lapping technology for obtaining transducers of the desired dimensions are also reported.