Dynamic Variation in a Resonating MEMS Shear Stress Sensor
Open Access
- Author:
- Ziegler, Todd Damian
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Michael Lester Jonson, Thesis Advisor/Co-Advisor
Md Amanul Haque, Thesis Advisor/Co-Advisor - Keywords:
- MEMS
resonator
dynamics
variation
shear stress - Abstract:
- Fluid shear stress is an important parameter in the understanding and control of viscous drag, laminar to turbulent transition, flow separation, and turbulent eddies. Laminar flow theory is well defined and understood while turbulent flows are difficult to describe due to their random nature. The measurement of turbulent or fluctuating wall shear stress would contribute to the fundamental understanding of turbulence as well as applications in aerospace, automotive, marine, and biomedical fields. Existing shear stress sensors lack the capability of resolving turbulent flow due to spatial and temporal averaging effects. Micro-electro-mechanical systems (MEMS) can be advantageous for such applications because of their small sizes, tight dimensional tolerances, and enhanced dynamic characteristics. However, concerns regarding bulk micro-machining accuracy and precision, dynamic variation for batch fabrication, and deflection measurement schemes must be resolved before sensor development can continue. This research utilizes scanning electron microscope linewidth techniques to evaluate the manufacturing accuracy and precision by measuring individual beam widths to develop mean and 95% confidence intervals. The beam dimension measurements exhibited a relative error of 1.75% from design dimensions with a relative uncertainty of 2.83% for the bulk micro-machining process. Dynamic characterization of the out-of-plane resonance is performed using laser doppler vibrometry techniques to determine the resonant frequency variation and investigate laser doppler vibrometry as a deflection measurement scheme. The resonant frequency 95% confidence relative uncertainty is 1.44% averaged from 18 micro-fabricated devices with exactly identical design parameters. Laser doppler vibrometry offers reasonable measurement resolution limited by probe volume and fringe spacing. Range and bandwidth capabilities are limited by the signal processing equipment. However, the technique requires bulky and sensitive components for measurement limiting the application potential. Further investigation and development of a 2-beam in-plane laser doppler vibrometer will better characterize the resolution and system packaging potential for applications.