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.

Ultra-Miniature Power Management for Microsystem Platforms

High density passive components (inductors, transformers, capacitors) are developed and integrated with high frequency (100-500 MHz) CMOS switching power conversion circuits. The  mm3-scale integrated converter will be capable of delivering >20 V from a battery source to enable mobile microsystems such as micro air vehicles and microrobots.

High-inductance-density air core inductors and transformers have been fabricated using a three-dimensional copper electroforming process. These devices have measured inductance densities > 100 nH/mm2  and quality factors > 20. Optimal performance is achieved in the range of 50 MHz - 500 MHz to enable next generation switching converters operating at very high frequencies.

SEM image of three-dimensional, stacked, air-core microinductor.

A Grazing Flow Impedance Facility For Engine Nacelle Acoustic Liners

Acoustic liners remain the standard for providing a method to reduce environmental noise from aircraft engine nacelles. To aid in their development, facilities are required that are capable of accurately educing the acoustic impedance in the presence of mean flow. The Grazing Impedance Tube at NASA LaRC possesses these capabilities and was donated to the University of Florida. Improvements have been made to enable optical flow diagnostics, provide an increased speed range, and reduce turbulence levels. This facility provides a testbed to improve upon current liner impedance eduction methods as well as facilitate development of novel design approaches and studies into fundamental liner flow physics.

Grazing Flow Impedance Tube Profile

Metric Value
Dimensions 2" x 2"

Maximum Mach Number

Maximum SPL

130 dB @ Ma = 0.5

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

Development of a MEMS Piezoelectric Microphone for Aeroacoustic Applications


Boeing Dreamliner

Passenger expectations for a quiet flight experience [1] coupled with concern about long-term noise exposure of flight crews [2] drive aircraft manufacturers to reduce cabin noise in flight. Cabin noise has traditionally been limited using insulating panels and skin dampers on the fuselage. Unfortunately, these thin panels are not effective at reducing low frequency (long wavelength) noise and cannot be made thicker due to weight concerns [1]. Treating the noise at its source shows potential for reduction of low frequency noise and weight savings compared to insulating panels. With fuel costs rapidly increasing, reduction of excess weight and subsequent maximization of the "revenue-generating payload" [3] is more important than ever.

In order to identify noise sources and assess the impact of noise reduction technologies during the design process, aircraft manufacturers require robust, low cost microphones. Measuring primary sources of cabin noise, such as shockcell noise, is difficult under simulated cruise conditions in test facilities [1] and establishes the need for microphones that can be used in full-scale tests at altitude. Their use on the fuselage exterior requires extremely small packaged sizes, in addition to the ability to withstand moisture and freezing conditions at flight altitudes. Microelectromechanical systems (MEMS) microphones show promise for meeting the stringent performance requirements of aircraft manufacturers at reduced size and cost, made possible using batch fabrication technology [4-9].