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Dynamic characterization of MEMS structures by ultrasonic wave excitation

A novel optical method for evaluating the natural frequency and the quality factor (Q) of a MEME structure is proposed in this paper. The proposed method is based on ultrasonic wave excitation which is a non-contact technique and does not impose undefined loadings. Images of the MEME structure vibrated ultrasonically are captured by a CCD camera at different frequencies. The vibrational amplitudes of the MEME structure are subsequently extracted using edge detection based on a Mexican hat wavelet transform and an amplitude-frequency spectrum is obtained from which the resonant frequency is determined. The damping characteristic is subsequently evaluated using a half-power-point method. A silicon MEME structure consisting of a perforated crossbeam (205 µm × 26 µm) and a cantilever beam (220 µm × 23 µm) is tested. The thickness of the MEME structure is approximately 3 µm. The experimental set-up is relatively simple and the results show that the proposed method is an effective approach for evaluating the dynamic characteristics of the MEME structure.