Measurement of in-plane motion of thin-film structures using videogrammetry

An electrodynamic shaker was used to apply a 1-Hz, 1.5-mm-amplitude, in-plane harmonic excitation to a thinfilm gossamer material mounted in an aluminum fixture. Using a two-camera videogrammetric setup that simultaneously imaged the test article at 75 frames per second (per camera), the x, y, and z motion components of two points on the thin film (F1 and F2) as well as of two points on the aluminum holder (R1 and R2) were tracked for a total of 4 s. The in-plane motion components of each tracked point closely corresponded to the excitation provided by the shaker. The presence of modally induced in-plane film deformation was confirmed by tracking the change in distance between points F1 and F2. The standard deviation of the value of the measured distance between these two points was found to be about 57 μm. This value was well above the noise floor for this measurement, 11 μm, experimentally determined by calculating the standard deviation of the measured distance between points R1 and R2 on the aluminum film holder, which was considered to be rigid and hence was not expected to undergo in-plane deformation.