FAQ: The PiezoClamping® manual shows 245 pC/N as the recommended d33 of PZT8 and 45 MPa for the prestress; for PZT4, the recommended d33 shown is 290 pC/N and the prestress, 35 MPa. If so, is it the same recommended value regardless of the quantity of piezoelectric elements? And how can you further optimize the prestress value? Mr. K.T.Y
Obtaining the charge constant d33 by measuring the charge Q as a function of applied force F.
The d33 and prestress recommended values are the same regardless of the quantity of piezoelectric elements. The d33 charge constant is an intensive property of the PZT material and is not affected by the number of piezo elements. The ideal prestress value depends on the maximum mechanical stress supported by the piezoelectric material and on stress distribution, which is determined by mechanical design. The larger the ceramic rings, the higher the torque required and the force over the rings. However, the rings area is also larger and pressure is equal to force divided by area. Because of that (pressure equal to force divided by area), the prestress is constant. The suggested prestress values are based on our practical experience and the user may further refine the ideal prestress based on FEA/FEM analyses and experimentation, particularly with regards the stress distribution.
PS: We have customers that vary the prestress to fine adjust the transducer frequency (the higher the prestress, the higher the frequency because it increases the effective contact area). This variation should not be greater than ±5 MPa and may have side effects if the transducers operate at maximum power.
Learn more about prestress technology.