Identification of Mechanical Pre-Stressing Degradation in Piezoelectric Transducers

The degradation of the mechanical pre-stressing in piezoelectric transducer is a drawback that reduces the performance of these devices. The behavior of the transducer is affected by the pre-stress and can be identified through of the impedance curves, mostly by the resonance deviations. In this work, we have proposed a circuit that allow us to know if the pre-stress is kept at a suitable level after the transducer operation. This circuit works based on the relation of pre-stress to phase difference between voltage and current in the transducer. The circuit provides an electric signal whose duty cycle and the average voltage can be used to identify small variations of pre-stress. The tests were conducted in three transducers originally pre-stressed at a reference level (52.8 MPa). Afterwards, the pre-stressing was deliberately degraded in 8.1 MPa and the tests repeated. The sensitivity of the system was around 0.23 V/MPa. The circuit is simple, low cost and can be used out of specialized laboratories.