A new concept of piezoceramic array transducer element using breathing mode has been proposed for therapeutic application. Finite element numerical simulation showed that a concave hemispherical piezoceramic shell with a diameter slightly larger than the wavelength in water is effective for obtaining good acoustic matching with water. A hemispherical piezoceramic element with an inner diameter of 4.0mm and a thickness of 0.2-0.4mm produced more than several times higher acoustic power output than a conventional thickness-mode element at the same drive voltage in the simulation. Its good acoustic matching with water is considered to be accomplished by the combined resonance with the spherical bulk of water half covered by the shell, because the resonance was very sensitive to the change in sound speed of the virtual material replacing water with the same acoustic impedance in simulation.
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