Comparison of actuator performance in lead-based and lead-free piezoelectric cymbals

Class V flextensional actuator named “cymbal” is composed of a ceramic disk that is sandwiched between two truncated conical metal endcaps. It has received considerable attention for sensor and actuator applications due to their high displacement and moderate generative force. It is well known that the strain/displacement of the piezoelectric ceramic correlated to the piezoelectric coefficient and external electric field applied (S = dE). According to the piezoelectric coefficient (d33) of KNN-LT-LS lead-free piezoelectric ceramic was comparable to PZT-8. Therefore, the purpose of this study was to investigate the effect of different ceramic driving elements (hard PZT and KNN-LT-LS ceramics) in the flextensional cymbal actuator on the strain amplification as well as the characteristic in strain-electric field loop response. The results showed that displacement of KNN-LT-LS cymbal (11.9±0.28 μm) were two times higher than that of PZT-8 cymbal (5.65±0.07 μm) at 10 kV/cm. Moreover, bi-polar S-E loop characteristic was larger in KNN-LT-LS cymbal compared to PZT-8 cymbal. This was due to easily domain reorientation in KNN-LT-LS ceramic observed by P-E loop. Under 10 kV/cm, P_r and E_c of KNN-LT-LS ceramic were 4.9 μC/cm² and 3.9 kV/cm whereas P_r and E_c of PZT-8 ceramic were 0.22 μC/cm² and 1.5 kV/cm, respectively.