A Low-noise MEMS Seismograph Based on Symmetric Buckling Beams

Abstract

MEMS seismographs are able to achieve lower noise performance by increasing the mass, reducing the resonant frequency, and increasing the quality factor (Q), which allows they can be used in the field of seismology. In this design, we propose a novel beam-mass design that incorporating two types of buckling beams (BBs), one of which will exhibits negative stiffness characteristic when the gravity of the proof mass is greater than its buckling load, while the other still exhibits positive stiffness characteristic. Through effective stiffness compensation, simulation results show that this MEMS seismograph owns a quasi-zero stiffness characteristic (0.15 N/m) and a low resonant frequency of 8.89 Hz. Previous studies of positive stiffness beams usually used folded beams, curved-beams with single-end constraints, etc, however, it is important to note that changes in the width of beams by the microfabrication directly impact the stiffness characteristic of the MEMS seismographs, and may even result in the loss of quasi-zero stiffness characteristics. Nevertheless, the simulation results of our design reveal that this MEMS seismograph maintain a quasi-zero stiffness characteristics and low resonant frequency (<10 Hz) within an angle from the horizontal (2.7° - 177.3°), although the width of BBs is smaller than the specified dimensions because of the effects of microfabrication errors. Finally, comprehensive testing reveals that this MEMS seismograph possesses a resonant frequency of 8.6 Hz at an angle of 84° from the horizontal, noise power spectral density of 20 ng/√Hz from 0.42 Hz to 3 Hz.