Slide-film Damping Research Articles

Design of a Novel Micromachined Gyroscope with Compensatory Capacitance

This paper presents a novel bulk micromachined gyroscope with the compensatory capacitance. Independent driving and sensing beams and a dual-frame structure are adopted to decouple mechanically for stable operation. The method of electrostatic push-pull drive and capacitive sense combs based on the slide film damping are applied to obtain a large driving force and high quality factors. The compensatory capacitance is designed to compensate the deviations of sensing differential capacitance from fabrications. The designed gyroscope has matched resonant frequencies of 2187Hz and 2206Hz for the drive and sense modes, respectively. Considering the noise of interface circuits, the gyroscope system sensitivity can reach 14.2mv/o/s, theoretically.

Numerical analysis of fluid–structure interaction effects on vibrations of cantilever microstructure

The operation of microelectromechanical systems (MEMS) with movable parts is often strongly affected by a fluid–structure interaction. Microelectromechanical devices often operate in ambient pressure, therefore air functions as an important working fluid. The influence of air in MEMS devices manifests as viscous air damping, which can be divided into two categories: slide-film damping and squeeze-film damping. The former occurs in laterally moving devices (e.g. comb drives), while the latter is characteristic for MEMS devices, in which a microstructure moves or bends towards a rigid surface with a thin air film in-between (as in microswitch). This paper reports results of numerical analysis of squeeze-film damping effects on free and forced vibrations of cantilever microstructure. Three separate finite element models are used for simulations. Each model is based on different form of Reynolds equation: nonlinear, linearized and linearized incompressible. Squeeze-film damping is associated with displacements of microstructure by using weak formulations of the equations that are coupled to lower surface of the microstructure, which is represented in three-dimensional (3D) and is treated as flexible in the analysis. Both small- and large-amplitude motions are considered. Comparison of results obtained with different models is presented and suggestions are given regarding the usage of particular form of Reynolds equation for modelling air-damping effects in the case of developed electrostatic microswitch.

A microfabricated metal grating oscillator for electric field detection

This letter proposes a novel design of a Micro Electro Mechanical System (MEMS) device featuring a metal grating vibratory microstructure driven by electrostatic force to sense the spatial electric field. Due to the advantages in slide-film damping and large vibration amplitude, such a device makes atmospheric packaging a low-cost option for practical manufacture. In this letter, we present the operating principles and specifications, the design structure, as well as the finite element simulation. Computational analysis shows that our design obtains good results in device parameters setting, while its simplicity and low-cost features make it an attractive solution for applications.

A novel tuning fork gyroscope with high Q-factors working at atmospheric pressure

In this paper, we report the design and fabrication of a novel micromachined electro-magnetically driven tuning fork type gyroscope with bar structure proof masses working at atmospheric pressure. The applied angular rate is sensed by detecting the differential change of capacitance between the bar structure electrodes and the fixed electrodes on the glass substrate. Instead of common squeeze-film damping, slide-film damping in the gap between proof masses and glass substrate plays a dominant role, which enables it to achieve high Q-factors and thus eliminate vacuum packaging. The measured Q-factors for driving and sensing modes are 965 and 716, respectively. The sensor obtained a sensitivity of 6 mV/°/s and a non-linearity of less than 0.5%.

A novel bulk micromachined gyroscope with slots structure working at atmosphere

Abstract Design, fabrication and testing of a novel silicon micromachined gyroscope prototype with slots structure are presented. The device structure which we called “slots gyroscope” consists of a proof mass with slots linked up to substrate by suspend springs and is fabricated by silicon–glass bonding and deep reactive ion etching (DRIE). The gyroscope makes use of electrostatic driving and capacitive sensing. As the proof mass used as the movable electrodes is parallel to the plane of fixed driving and sensing electrodes, there is only slide film damping in the driving and sensing mode. The gyroscope can operate at atmospheric pressure due to almost same high quality factor in the sensing direction and driving direction. The experiment result shows that the drive and sense mode resonant frequencies are 460.4 and 549.6 Hz, respectively, and the quality factor of the drive and sense are 102.5 and 106.5, respectively at atmospheric pressure. The scale factor and non-linearity of the micromachined gyroscope are 20 mV/(° s) and 0.56%, respectively at atmospheric pressure.

Slide film damping in laterally driven microstructures

Slide film damping occurs when two parallel plates are in relative tangential motion. Viscous energy dissipation in the fluid between the two plates becomes a representative damping mechanism in laterally driven microdevices. In this paper, we investigate the slide film damping both theoretically and experimentally. A new physical model has been proposed for the characterization of slide film damping. Dynamic characteristics of a fluid film have been described in terms of velocity profiles, damping mechanisms, and levels of viscous energy dissipation. Simplified analytical damping formulae have been developed for practical Q estimation. The theoretical Q compares well with the experimental Q. Data reported by previous investigators are also analyzed and compared with the Q value estimated in the present study. It is concluded that our theoretical model offers simple and reasonably good quantitative prediction of Q. Possible sources of error in the theoretical Q prediction are discussed. The effects of fluid-film thickness and microstructure geometry on Q are investigated, so that the results can be used in the damping design for laterally driven microtransducers.