Laminated ultrasonic transducer - with porous piezo-ceramic and electrodes, giving good electrical and acoustic match and high coupling factor

摘要

Ultrasonic transducer has several layers (1) of porous piezo-ceramic (I), alternating with electrodes (II) (2). Alternate (II) are connected in turn to one of 2 terminals (31,32). Pref. each (I) layer has a porosity gradient, with min. porosity at the interface with the adjacent (II). (I) is based on Pb, Ti, Zr, Ni, Nb and O, whilst (II) contain Ag, Pd and/or Pt. ADVANTAGE - The transducer ensures a good electrical match in addn. to a good acoustic match and high coupling factor. Lamination reduces the electrical impedance at the same permittivity, e.g. by a factor of 16 with 4 layers. This more than counterbalances the redn. in permittivity with increasing porosity, allowing the thickness to be reduced to about a third the normal value, e.g. from ca. 3 mm to 1 mm for a lambda/4 transducer. (6pp Dwg.No.1/4)