A MEMS sensor for stiffness change sensing applications based on three weakly coupled resonators

Abstract

Micro-electro-mechanical (MEM) resonator devices have been widely used to sense small changes in the properties of the resonator, namely the stiffness and mass of the resonator. Among these, sensing devices that detect stiffness change have been employed for many applications, including accelerometers, strain sensors, pressure sensors and force gradient sensors for imaging microscopy. In recent years, a new sensing approach, which utilises 2 degree-of-feedom (DoF) weakly coupled resonators has been proposed. By measuring the mode shape changes instead of the frequency shifts, it has been shown that this type of sensing devices has: 1) orders of magnitude higher sensitivity than conventional single DoF resonator sensors; 2) common mode rejection capabilities.

This thesis introduces a novel structure, based on three weakly coupled resonators (i.e. a 3DoF system), in which the stiffness of the resonator in the middle is at least twice the value compared to the other two identical resonators. The device is intended for sensing a change in stiffness. With the 3DoF resonator sensing device, another order of magnitude improvement in the stiffness sensitivity could be demonstrated.

In addition to the novel 3DoF coupled resonator structure, we have also investigated a few practical aspects of the coupled resonator sensing devices that have not been addressed in previous research. These aspects include the damping, dynamic range, nonlinearity and output metrics of the sensor. We have also found a trade-off between the sensitivity and the dynamic range. To solve this dilemma, a bias operation point has also been proposed. By using the bias operation point, it was shown in theory that the linearity of the sensors can also be improved.

Finally, we have also theoretically estimated the vibrational amplitudes and phase delays of each individual resonators within the 3DoF system at the out-of-phase mode frequency. Furthermore, based on these estimations, we have proposed a feasible self oscillating loop structure, which has the capability of automatically locking to the out-of- phase mode frequency.

More information

Identifiers

ORCID for Harold Chong: orcid.org/0000-0002-7110-5761

Catalogue record

Export record