Fiber optic sensors and digital signal processing in displacement measurements
Various techniques such as resonance, LVDT, strain gauge and interferometry methods have been used widely to measure field-induced strain in piezoelectric materials. Among these measurement techniques, optical interferometers have been suitable for non-contact measurements and are applicable over wide frequency ranges. Although interferometry is an optimal method for room temperature strain determination, it is impractical for temperature dependant situations due to its inability to operate in environments with mechanical noise. Vibrometer is also an optimal method for such measurements but is less portable as compared to the MTI Fotonic(TM) Sensor. In this research, the use of fiber optic technique for the measurement of displacement of different piezoelectric samples was investigated. The strain and the piezoelectric coefficients were measured using the MTI 2000 Fotonic(TM) Sensor, which works on the principle of the optical lever. This thesis reports the systematic study of the measured displacements using the Fotonic Sensor, the corresponding frequency components of the obtained displacement signals, and the approach to obtain maximum displacement values in contrast to the average values otherwise obtained. Piezoelectric d33 and d31 coefficients associated with the converse piezoelectric effect are derived and compared with other frequency dependent strain measurements such as the vibrometer and Michelson inteferometry methods.