Abstract
We propose a sub-1 Hz resonance frequency MEMS resonator that can be used for seismometers. The low resonance frequency is achieved by an electrically tunable spring with an ultra-small spring constant. Generally, it is difficult to electrically fine-tune the resonance frequency at a near-zero spring constant because the frequency shift per voltage will diverge at the limit of zero spring constant. To circumvent this issue, we propose a multi-step electrical tuning method. We show by simulations that the resonance frequency can be tuned by 0.008 Hz/mV even in the sub-1 Hz region. The small spring constant, however, reduces the shock robustness and dynamic range of the seismometer. To prevent this, we employ a force-balanced method in which the mass displacement is nulled by the feedback force. We show that the displacement can be obtained from the voltage that generates the feedback force.
Highlights
A seismometer is a sensor that detects ground motions [1]
Mechanical seismometers adopt a mass-spring-damper system with a low resonance frequency so that the proof mass behaves as a fixed point relative to the ground
In the case of Middlemiss’ gravimeter, which has a similar structure to a seismometer, the resonance frequency of 2.3 Hz was achieved by an ultra-small spring constant composed of two kinds of mechanical spring, one of them having a negative spring constant [4]
Summary
A seismometer is a sensor that detects ground motions [1]. Mechanical seismometers adopt a mass-spring-damper system with a low resonance frequency so that the proof mass behaves as a fixed point relative to the ground. To achieve a resonance frequency of about. In the case of Middlemiss’ gravimeter, which has a similar structure to a seismometer, the resonance frequency of 2.3 Hz was achieved by an ultra-small spring constant composed of two kinds of mechanical spring, one of them having a negative spring constant [4]. T. [6,7]
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