Lead-free Piezoelectric KNN-based Pin Transducers for Structural Monitoring Applications

A 2.4 mm diameter piezoelectric ceramic disc was used to construct a spring-loaded pin-type transducer for intelligent monitoring of systems. Two types of lead-free KNN-based ceramics (0.95K_0.5Na_0.5(Nb_0.94Sb_0.06)O₃— 0.05LiTaO₃+ 1.25 mol% BaO and K_0.5Na_0.5NbO₃-0.75 mol% K_5.4Cu_1.3Ta₁₀O₂₉) were selected as a sensing element of the pin. The piezoelectric spring-loaded pins were mounted on the corners of the aluminum plate for the performance evaluation using a laser ultrasonic technique. The signals detected by transducers with different sensing elements including lead-based ceramics have been compared. The capability of impact detection of the lead-free transducers was shown to be comparable to that of the lead-based one. It is envisaged that lead-free piezoelectrics will become the important transducer materials in the next generation nondestructive evaluation technology.