Generation of very high pressure pulses at the surface of a sandwiched piezoelectric material.

New clinical concepts in lithotripsy demand small shock heads. Reducing the size of piezoelectric shock heads will only be possible if the pressure generated at the surface of each transducer can be increased so that the total pressure at the focus remains very high. We propose for the first time to increase the pressure without increasing the transducer voltage by using sandwiched transducers, which are a combination of several stacked transducers. When excited at appropriate time intervals, the pressure waves generated by each one reinforce when they reach the load. This new technique has been successfully tested. A pressure of 2.5 MPa was generated with two stacked, 5 mm-thick 1-3 piezocomposite transducers operating at an excitation voltage of 8 kV. No transducer damage was detected after 10(6) shocks, which corresponds approximately to the treatment of 500 patients.