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IMG Seminar: Capacitive shear stress sensor and its interface circuitry

Submitted by John Griffin on Mon, 11/15/2010 - 4:05pm
Event date: 
Wed, 11/17/2010 - 9:00pm to 10:00pm

Speaker: Jessica Meloy

Introduction: The time-resolved characterization of complex wall-bounded flow fields is difficult and unachievable with the current set of research tools. At the University of Florida the Interdisciplinary Microsystems Group (IMG) has teamed with FCAAP to develop the next generation of instrumentation grade sensors for aerospace applications. Specifically, microelectromechanical systems (MEMS) technology is being used to develop sensor systems for reliable direct time-resolved shear stress measurement and fill this instrumentation void. IMG has developed a robust miniaturized package for integration into flow control studies currently being conducted at both the Advanced Aero-Propulsion Laboratory at Florida State University and at IMG wind tunnel facilities at the University of Florida. The specific sensor system being utilized in these studies is capable of measuring shear stress values as low as 1mPa with a sensitivity of 1.7mV/V/Pa and at least 80dB rejection to cross sensitivities. In this seminar the sensor system’s circuitry and package development will be discussed.

Capacitive Shear Stress Sensors

This project focuses on the development of a non-intrusive, direct, time-resolved wall shear stress sensor system for low-speed applications. The goals of the project include the fabrication and packaging of a 2-D wall-shear stress sensor with backside wire bond contacts to ensure hydraulic smoothness in flow environments. A differential capacitance transduction scheme is utilized with interdigitated comb fingers on each side of a suspended floating element, allowing for measurements to be made in both the positive and negative x- and y-directions.  A synchronous modulation-demodulation circuit is employed to simultaneously capture both mean and fluctuating shear content. Both AC and DC calibrations are performed to determine sensor sensitivity in both directions of transduction. This is the most successful effort of shear sensor development in published literature. 

Development of a MEMS Piezoresistive Aeroacoustic Microphone

Increases in air traffic and tighter restrictions on noise pollution in and around airports have motivated research to reduce the aeroacoustic noise generated by aircraft.  Aeroacoustic testing with microphone arrays is used to identify and help design acoustic treatments on new and existing aircraft in order to reduce the noise signature of the aircraft.  The performance of a microphone array is a function of the number of microphones used, which is traditionally limited by the cost of each sensor.  Piezoresistive MEMS microphones take advantage of batch fabrication wafer processing to reduce sensor cost and achieve higher sensor packing densities in aeroacoustic arrays.  Thus, an increase in performance can be achieved for an equivalent, or possibly reduced, cost.

Optical Shear Stress Sensor

Design, fabricate, calibrate, and test time-resolved, direct shear stress sensors capable of measuring stresses in harsh environments using miniaturized optics.  Optical gratings on the floating element sensor generate Moire fringe patterns for optical amplification of the floating element displacements due to applied shear stress.

MEMS-based Optical Sensors for High Temperature Applications

The goal of this research is to develop a pressure sensor and shear stress sensor that are able to provide continuous, time-resolved flow measurements within high temperature environments such as those seen in hypersonic wind tunnels and turbines.  A primary focus of this research is on the micromachining of sapphire using a picosecond laser.  Sapphire’s mechanical and thermal properties make it an ideal material for high temperature measurements.  Each sensor operates by mechanically deflecting under either a pressure or shear stress.  These deflections can then be detected using an opto-mechanical transduction scheme.  The completed sensors will be tested in flow cells and wind tunnels at UF as well as in other transonic and hypersonic facilities.

J-355PS Picosecond Laser Micromachining Workstation from Oxford Lasers