Finite element model updating of micromachined torsion structures using experimental eigendata

In this paper, the dynamic characteristics including natural frequencies and mode shapes of a cross-shaped torsion structure, fabricated by a micromachining process, are measured by using two full-field and non-contact experimental techniques: Electronic Speckle Pattern Interferometry and Stroboscopic Interferometry. In addition, the finite element method is also applied to analyze the microstructure. Since the mechanical properties of a microstructure are usually not accurately known and neither is its depth dimension, it is very likely that the measured and the predicted results show a significant inconsistency. This research performs a finite element model updating procedure to determine a set of much more reliable values for the mechanical properties and the thickness of the torsion structure. The result is a refined finite element model capable of accurately predicting the dynamic behaviors of the micromachined device and suitable for further design modification studies. Two updating cases both show significant improvements in frequency prediction. With the inclusion of the thickness parameter, the second case reduces the frequency differences from over 17 % to under 0.4 %.