A monopole transmitter for a sonic well tool includes an axial tube, a piezoceramic cylinder surrounding the axial tube, an endcap disposed at each end of and firmly contacting the cylinder, and an apparatus for holding the endcaps firmly against the axial tube. The endcaps firmly contact the axial tube...http://www.google.de/patents/US5043952?utm_source=gb-gplus-sharePatent US5043952 - Monopole transmitter for a sonic well tool
