An ultrasonic transducer assembly for making measurements within a fluid, the assembly including a transducer, a backing member and a matching member all supported within a cylindrical metal housing with the transmitting face of the housing being sealed with a thin sealing element formed of a non-resilient...http://www.google.com.tw/patents/US4297607?utm_source=gb-gplus-share專利 US4297607 - Sealed, matched piezoelectric transducer
