Novel concept of array transducer element using combined resonance between oscillations of hemispherical piezoceramic shell and bulk water

For therapeutic ultrasound array transducers, it is required to reduce the electrical impedance of their elements so that the transducer can produce high ultrasonic power at a relatively low drive voltage. For this purpose, we are investigating a new concept of piezoceramic element using its breathing mode. Numerical simulation showed that a concave hemispherical piezoceramic shell with a diameter on the order of a wavelength in water is effective for obtaining good acoustic matching with water. High acoustical coupling was achieved by utilizing the combined resonance between the breathing-mode oscillation of the piezoceramic shell and the volume oscillation of a water sphere half enclosed by the shell.