FEM modelling and experimental characterization of microbeams in presence of residual stress

Out-of-plane bending tests are here used to experimentally validate some numerical models of microbeams actuated by the electric field. Out-of-plane bending microcantilevers and clamped\u2013clamped microbeams often suffer the presence of residual strain and stress, respectively, which affect their static and dynamic behaviour and pull-in voltage. In case of microcantilever an accurate modelling has to include the effect of an initial curvature due to microfabrication process, while in double clamped microbeams constraints may impose a pre-loading caused by a tensile stress. So-called geometrical nonlinearity sometimes occurs, when microcantilever exhibits large displacement, or because of the mechanical coupling between axial and flexural behaviours in double clamped microbeams. Modelling this kind of nonlinearity is an additional goal of this study. Experiments demonstrated a good agreement with results of FEM approaches proposed. In the case of microbridges numerical models are used to identify the residual stress. A reverse analysis is implemented, the axial pre-stress is calculated by means of the measured pull-in voltage

Strain modulation spectroscopy

The technique of resonant strain modulation has been applied for the first time to the modulation of optical transitions occurring between levels of the 4f shell of lanthanide ions. This allows changes in signal strength of typically 0.01% of the maximum spectral line height, which results from spectral line shifts smaller than 10-²/(kg/mm²), to be easily detected. After a full description the method is used to obtain the orbit lattice parameters dB₀²/dδ of Pr³⁺ in CaF₂ and SrF₂ hosts. On the assumption of a local cubic lattice these are found to be (-4.5 ± 1.5) x 10 cm and (-5.4 ± 1.0) x 10 cm respectively. The shifts of some optical transitions of CaF₂:Er³⁺are also presented. Application of the method to shifts of the vibronic sided bans of MeF₂:sm²⁺, polarisation studies of the no phonon f-d transitions of Sm²⁺, and to Er³⁺ and Sm²⁺ in different site symmetries, is also discussed