Effects of leaky Lamb-like wave propagation in single-element high intensity focused ultrasound transducer by vibration analysis

In a spherical piezoceramic transducer for HIFU (High Intensity Focused Ultrasound) treatment, a mode of plate wave propagation within the ceramic were experimentally observed in addition to the pure thickness-mode vibration. In this study, we experimentally and numerically analyzed the vibration behavior of an air-backed single-element spherical PZT transducer. The acoustic pressure distribution on the ceramic surface was obtained in the experimental analysis using time reversal, and the numerical analysis was performed using FEM. In the two-dimensional Fourier analysis, the radial wavenumber spectrum showed a secondary peak, corresponding to a leaky Lamb-like mode. The leaked waves may have propagated into water and formed the relatively large lobes on the propagation axis. These unwanted near-side lobes may potentially cause additional near-field heating of the tissues which should not be treated.