Frequency changes in aerodynamically excited resonating micromachined beams

The resonant frequency of micromachined structures is primarily dependent upon the mass and stiffness of the device. This paper examines some of the second-order effects that may affect the resonant frequency of micromachined beams. A series of clamped-clamped micromachined beams were fabricated using a standard CMOS process with wet chemical etch postprocessing. The beams were aerodynamically excited using compressed air and the oscillations of the beams were optically measured using a non-contact laser reflectance system. The measured resonance frequency of the beams decreased with decreasing width. The measured frequencies were as high as 42 kHz and the change in frequency was as large as 25%.