Investigation of the air effect on the resonance frequency and damping of three small assembled structures using different adhesive materials (SU8 epoxy resin and compressed gold)

摘要

There has been growing interest in recent years in the understanding of microsystems and the mechanical properties essential for their design. In this context, an experimental technique is proposed to characterize the structures of small dimensions composed of both silicon and lithium niobate and assembled using three different adhesive materials (SU8 (5 and 1 mu m) and compressed gold) surrounded by various ambient air pressure levels. Dynamic tests were performed on three different structures used for the manufacturing of a harvesting energy microconverter. The assembled structure is mounted on a support and excited by a white noise signal via an electromagnetic shaker. The dynamic responses are recorded by a Doppler laser vibrometer and the modal parameters (obtained from the dynamic response) are identified in order to determine their evolution when the ambient air pressure inside the vacuum chamber is changed. A nonlinear modal identification is then performed. It is based on the logarithmic decrement method applied in the time-frequency domain using a wavelet transform of the time responses. The evolution of the equivalent modal frequencies and damping of the assembled structure versus time and vibration magnitude are identified for several pressure values ranging from a secondary vacuum to atmospheric pressure.