ELECTROMECHANICAL RESPONSE OF POLYMER-FILMS BY LASER-DOPPLER VIBROMETRY

A two-sided laser Doppler vibrometer (LDV) was designed to measure the d(33) electromechanical coupling coefficient of piezoelectric and ele ctrostrictive thin films. Optical fibers and optical fiber couplers we re used to split the light into multiple beams and to simultaneously i lluminate the same spot on both sides of the film. This probe measured the normal displacement on each side of the sample and allowed comput ation of the change in thickness by summing the two LDV signals. Data for PVDF films are presented to illustrate problems associated with th is type of measurement A large bending motion of the sample occurred w hich was responsible for a significant error in the measured thickness change. Reducing the amplitude of this motion by stacking films was a n efficient way to increase the accuracy of the data. An error analysi s was carried out to qualitatively explain these experimental observat ions. It was also discovered that the measurement accuracy improved wh en the ac driving voltage frequency was less than the bending resonanc e frequency of the sample. (C) 1998 Acoustical Society of America. [S0 001-4966(98)01303-4].