Lead-free transducer for non-destructive evaluation

Lead-free piezoelectric ceramics with the formula 0.90(Bi _0.5Na_0.5)TiO₃∈-∈0.05(Bi _0.5K_0.5)TiO₃∈-∈0.015(Bi _0.5Li_0.5)TiO₃-0.05BaTiO₃ (abbreviated as BNKLBT-1.5) were prepared by a conventional mixed-oxide method. A disc of this material was fabricated and used to construct an ultrasonic transducer suitable for use in non-destructive evaluation (NDE). Using a laser vibrometer, it was observed that both BNKLBT and PZT exhibited a surface displacement pattern indicative of coupling of the radial mode vibration with the thickness mode vibration. This is consistent with the measurements of electrical impedance vs frequency which showed that for both discs a strong radial mode with many harmonics was clearly observed and many (usually undesired) modes existed near the thickness mode resonance frequency. The discs were mounted in stainless steel housings with appropriate electrical connections to form transducers. Tungsten/epoxy backing was incorporated to provide a very short ring-down time, a characteristic required for many NDE applications. The characteristics of the BNKLBT transducer were quite similar to that of a PZT transducer of similar structure, showing that this lead-free material has the potential to replace PZT in transducers for NDE applications.