Fundamental understanding of piezoelectric strain sensors

This paper investigates the behavior of piezoelectric elements as strain se nsors. Strain is measured in terms of the charge generated by the element a s a result of the direct piezoelectric effect. Strain measurements from pie zoceramic (PZT) and piezofilm (PVDF) sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are discussed, along with their limitations. The sensors are surface bonded to a beam and are calibrated over a frequency range of 5-500 Hz. Correctio n factors to account for transverse strain and shear lag effects due to the bond layer are analytically derived and experimentally validated. The effe ct of temperature on the output of PZT strain sensors is investigated. Addi tionally, design of signal conditioning electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of pi ezoelectric sensors compared to conventional strain gages in terms of sensi tivity and signal to noise ratio is demonstrated.