Graham S. Wood

A Three Degree-of-Freedom Weakly Coupled Resonator Sensor With Enhanced Stiffness Sensitivity

This paper reports a three degree-of-freedom (3DoF) microelectromechanical systems (MEMS) resonant sensing device consisting of three weakly coupled resonators with enhanced sensitivity to stiffness change. If one resonator of the system is perturbed by an external stimulus, mode localization occurs, which can be detected by a change of modal amplitude ratio. The perturbation can be, for example, a change in stiffness of one resonator. A detailed theoretical investigation revealed that a mode aliasing effect, along with the thermal noise floor of the sensor and the associated electrical system ultimately limit the dynamic range of the sensor. The nonlinearity of the 3DoF sensor was also analyzed theoretically. The 3DoF resonator device was fabricated using a silicon on insulator process. Measurement results from a prototype device agreed well with the predictions of the analytical model. A significant, namely 49 times, improvement in sensitivity to stiffness change was evident from the fabricated 3DoF resonator sensor compared with the existing state-of-the-art 2DoF resonator sensors, while the typical nonlinearity was smaller than ±2% for a wide span of stiffness change. In addition, measurements indicate that a dynamic range of at least 39.1 dB is achievable, which could be further extended by decreasing the noise of the device and the interface electronics.

A sensor for stiffness change sensing based on three weakly coupled resonators with enhanced sensitivity

This paper reports on a novel MEMS resonant sensing device consisting of three weakly coupled resonators that can achieve an order of magnitude improvement in sensitivity to stiffness change, compared to current state-of-the-art resonator sensors with similar size and resonant frequency. In a 3 degree-of-freedom (DoF) system, if an external stimulus causes change in the spring stiffness of one resonator, mode localization occurs, leading to a drastic change of mode shape, which can be detected by measuring the modal amplitude ratio change. A 49 times improvement in sensitivity compared to a previously reported 2DoF resonator sensor, and 4 orders of magnitude enhancement compared to a 1DoF resonator sensor has been achieved.

A Comparative Study of Output Metrics for an MEMS Resonant Sensor Consisting of Three Weakly Coupled Resonators

This paper systematically investigates the characteristics of different output metrics for a weakly coupled three degree-of-freedom microelectromechanical systems resonant sensor. The key figures-of-merit examined are sensitivity and linear range. The four main output metrics investigated are mode frequency shift, amplitude difference, amplitude ratio, and eigenstate shift. It is shown from theoretical considerations, equivalent RLC circuit model simulations and electrical measurements, that there is a strong tradeoff between sensitivity and linear range. For instance, the amplitude difference has the best sensitivity but the worst linear range, whereas frequency shift has the widest linear range but the lowest sensitivity. We also show that using the vibrational amplitude ratio as an output metric provides the best balance between sensitivity and linear range. [2016-0077].

Comparative study of different output metrics for a three weakly coupled resonator sensor

This paper, for the first time, investigates the characteristics of different output metrics for a three degree-of-freedom (DoF) coupled resonator sensor. The main aspects examined are sensitivity and linear range. It is shown from theoretical estimations, equivalent RLC circuit model simulations and electrical measurements that using the vibration amplitude ratio as an output signal provides improved sensitivity and linearity range, compared to other methods such as shift in eigenstate, mode frequency or amplitude difference.

Atmospheric pressure mode localization coupled resonators force sensor

This paper reports on a 3-DoF mode localization resonant sensor experimentally evaluated under atmospheric conditions. It was demonstrated that using amplitude ratio as an output signal, even when the device is operated in air, yields a higher sensitivity compared to frequency variation sensitivity when assuming vacuum conditions.

An Investigation of Structural Dimension Variation in Electrostatically Coupled MEMS Resonator Pairs Using Mode Localization

If a pair of MEMS resonators is electrostatically coupled together, the vibration amplitude ratios at the resonant frequencies of the resulting coupled system are sensitive to stiffness perturbation. An imbalance between the two resonators causes the confinement of vibration energy when the system is resonating, an effect known as mode localization. The degree of localization can be determined by extracting the amplitude ratio of the resonators through capacitive transduction. In this paper, we have fabricated MEMS devices, using a dicing-free silicon-on-insulator process, consisting of pairs of closely spaced microresonators. Each resonator consists of a clamped-clamped beam with a wider section in the middle, which is the location of the electrostatic coupling, instituted through the dc biasing of the resonators. Several devices have been fabricated, with the length of the anchor beams being varied, which influences the frequency of resonance. Stiffness imbalance between the resonators has been introduced through electrostatic spring softening, with the sensitivity of the amplitude ratio of the resonant-mode shape being greater for the higher frequency, shorter anchor devices. The sensitivities of the devices in this paper have been found to be nine times greater than the state-of-the-art two-degree-of-freedom mode-localized sensors.