Anwar Ahmed

A Characterization of the Performance of a MEMS Gyroscope in Acoustically Harsh Environments

Microelectromechanical systems (MEMS) gyroscopes are typically smaller and less expensive than their macroscale counterparts. For this reason, they are being used in many new applications, including in harsh environments. It has been well documented that the performance of unprotected MEMS gyroscopes can be deleteriously affected by exposure to mechanical shock or high-frequency vibrations. The results of this investigation experimentally demonstrate that MEMS gyroscopes are also susceptible to high-power high-frequency acoustic noise when acoustic energy frequency components are close to the resonating frequency of the gyroscopes proof mass. Additionally, due to microfabrication tolerances and the resulting differences between otherwise identical devices, there can be significant differences in the acoustically sensitive bandwidth between otherwise identical MEMS gyroscopes. This phenomenon is characterized for the ADXRS300 MEMS gyroscope.

Topological model of flow regimes in the plane of symmetry of a surface-mounted obstacle

Flow visualization between Reynolds numbers of 2000 and 6500 in the end-wall region of an obstacle mounted on a flat plate revealed presence of a multiple vortex system. Three Reynolds-number dependent regimes were identified. With increasing Reynolds number the vortex system transitioned from a static system to a to-and-fro oscillating system and finally to a shedding-splitting system. These observations have been used to infer flow topologies in the plane of symmetry of the juncture from start-up through all three regimes.

On the Degradation of MEMS Gyroscope Performance in the Presence of High Power Acoustic Noise

Due to their reduced size, cost, and power requirements relative to traditional gyroscopes, MEMS gyroscopic sensors are finding increasing use in many applications. It is well known that unshielded MEMS gyroscopes can be vulnerable to both mechanical shock and high frequency vibrations. The results of this investigation indicate that MEMS gyroscopes are also susceptible to high power, high frequency content acoustic noise. Acoustic energy frequency components that are close to the resonating frequency of the proof mass in the MEMS gyroscope can produce undesirable motion of the proof mass, resulting in corruption in the angular rate measurement. If the acoustic signals possess enough power in the vicinity of the sensor resonating frequency, the resulting degradation in sensor performance can be severe enough to render the angular rate measurements useless.

Control of Cylinder Wake Using Three Dimensional Disturbances

Wake of a circular cylinder subjected to acoustically driven disturbances introduced from sinusoidal slits was investigated at Reynolds number of 24,000 and 40,000. Results showed that the amplitude of the primary shedding frequency was eliminated when the forcing frequency was twice the fundamental frequency. This is attributed to the mechanism of redistribution of energy from the large coherent structures to the smaller ones. Furthermore, the introduction of three dimensional disturbances accelerated the separating shear layers which narrowed the wake and made it uniform in terms of mean velocity and reduced drag.

Effect of Geometric Modifications on the Flow Field of a Turret

Results of the effects of the passive flow control techniques to modify the flow field over a generic turret model are reported. The baseline turret model consisted of a cylindrical base and a hemispherical top with a truncated side similar to an optical aperture used in laser beam propagation. Control surfaces placed on or around the base model were used to delay the flow separation and improve the quality of flow over the aperture and wake. Tests consisted of surface oil-flow visualization, surface pressure fluctuations, and PIV. Preliminary results indicate that the control surfaces were successful in reducing the wake and modifying the flow in the vicinity of the laser aperture. PIV measurements supported the observations of a reduction in the wake and unsteadiness.

The Underwater Effects of High Power, High Frequency Acoustic Noise on MEMS Gyroscopes

Unlike their macroscale counterparts, MEMS gyroscopes use a vibrating proof mass rather than a rotational mass to sense changes in angular rate. They are also smaller and less expensive than traditional gyroscopes. For this reason, MEMS gyroscopes are being used in many new applications, some of which include operation in harsh environments. There has been much research on the negative effects of the performance of MEMS gyroscopes in environments that experience mechanical shock, high frequency vibration, and high frequency acoustic noise in air. However, MEMS gyroscopes are beginning to be used in underwater applications such as autonomous underwater vehicles, digital compasses, and torpedo guidance systems. The results of this experiment demonstrate that MEMS gyroscopes submerged in water are susceptible to high power, high frequency acoustic noise at and near the resonant frequency of the proof mass. These effects are demonstrated using the ADXRS300 MEMS gyroscope.Copyright