A High-Bandwidth Heat Flux Sensor for Measurements in Hypersonic Flows

Understanding the character and dynamics of hypersonic boundary layers poses a considerable challenge to the design of hypersonic vehicles.  Specifically, being able to predict the location of laminar-to-turbulent transition is of critical concern as it affects heating rates, aerodynamic loading, and skin-friction drag, therefore impacting the design of the thermal protection system and thus the overall weight and performance of the vehicle.

Zero-Power Magnetic Field Sensors Using Magnetoelectric Nanowires

We seek to develop a platform that allows magnetic field sensing using a small footprint, in the absence of an external power supply. Our approach uses magnetoelectric nanofibers to create a zero-power magnetic field sensor. The challenge is to develop methods to assemble these materials into devices that leverage their unique anisotropic properties.

The figure of merit for magnetoelectric materials is the magnetoelectric coefficient, a measure of the amount of voltage generated with respect to the magnitude of the applied magnetic field. Bulk magnetoelectrics and thin films are limited by defects and substrate clamping respectively.  To overcome the limitations of thin-film based composite magnetoelectrics we have developed magnetoelectric bilayer structures on a single nanofiber, i.e., 1D magnetoelectrics. These materials are theoretically predicted to have magnetoelectric coupling coefficients that are orders of magnitude greater than their thin film counterparts. 

Magnetoelectric materials can be employed in a wide variety of applications including magnetic field sensors and tunable resonance energy harvesters.  By optimizing for material system and architecture, drastic increases in magnitude of voltage generated with decreased size can be achieved. This could allow for more sensitive magnetic field sensors appropriate for a wider array of applications and decreased size to allow for easier integration into ICs.

Levitated Microfactories for High-speed Adaptive Microassembly

The overall goal of UF’s effort on this DARPA Atoms to Products program (under sub-contract to SRI International) is to manufacture the micro-robots for demonstration of a massively parallel (1,000+) micro-robot factory. Each micro-robot comprises at least one magnetic base and one end effector. The magnetic base is configured with a pattern of north and south poles. A starting design is a 3 mm x 3 mm x 0.4 mm thick base that is arranged into a 9-pole checkerboard pattern. The simplest end effector is a simple mechanical rod attached to the top of the magnetic case.

The micro-robot platforms (magnetic bases and end effectors) will be mass manufactured using a combination of precision manufacturing and microfabrication techniques. Rather than assembling discrete magnets into specific pole patterns, selective magnetization techniques will be used to “imprint” the desired pole pattern into mechanically contiguous layers. These methods will eliminate the need for assembly, and also facilitate the massive batch manufacture of many magnetic bases in parallel. Concurrently, end effectors will be microfabricated using suitable microfabrication technologies. The bases and end effectors will be combined together via monolithic co-fabrication or via wafer-scale batch-assembly processes.  

High Temperature Optical Sapphire Pressure Sensors for Harsh Environments

The primary objective of this research is to develop a high-bandwidth pressure sensor to provide benchmark, time-resolved, dynamic pressure data in high-temperature combustion environments. Specifically, these sensors will be designed to be embedded within a system and provide remote interrogation which will enable pressure to be measured in situ and on line under extreme conditions. Ultimately, this sensing technology will lead to better understanding and increased efficiency of complex power generation systems. In order to achieve this objective, research in sapphire laser micromachining and thermocompression bonding via spark plasma sintering technology will be conducted to enable fabrication of a fiber optic lever pressure sensor that uses a sapphire optical fiber for transduction of the pressure-induced diaphragm deflection. The proposed project will result in instrumentation-grade, high-temperature sensors that enable flush mounted measurements without sensor cooling. Furthermore, the use of optical techniques enables “passive” device operation, with electronics located remotely from the sensor. After fabrication and packaging, the pressure sensor will be rigorously characterized in acoustic plane wave tubes under both ambient and high-temperature conditions to determine its performance as a quantitative measurement device.

A Flush-Mount Piezoelectric MEMS Microphone for Aeroacoustic Flight Testing Applications

In their effort to locate, understand and mitigate the impact of noise sources on an aircraft, aeroacousticiansare in need of a high performance, low cost microphone to combat the increasing noise restrictions on commercial aircraft. Existing commercial sensors, even with their relatively high cost, in some cases constrain the quality and type of measurement that may be achieved. One such constraint is that the physical size and characteristics of the sensors limit the optimal locations in which the sensors may be placed. Previous generations of MEMS aeroacoustic microphones have failed to address the need for a sensor that can be packaged and installed with a smooth front surface to be used for boundary layer measurements in a fuselage array at cruise conditions. Additionally, these microphones must meet demanding requirements, including the sensing of high sound pressure levels (>160 dB) with low distortion (<3%) and high sensitivity stability (with respect to moisture and freezing) over temperatures from -60°F to 150°F. This work addresses the limitations of existing MEMS piezoelectric microphones used in aeroacoustic applications by incorporating through-silicon vias(TSVs) into the fabrication to eliminate the use of wirebondsthat affect the flow field and create an overall flush-mount microphone package.

A MEMS-based Fast-response Five-hole Probe with Optical Pressure Transducers

The goal of this research is to develop a MEMS-based Five-hole Probe(5HP) that is able to measure the localized velocity vector (both the velocity magnitude and direction) and the static and dynamic pressure, in steady and/or unsteady flow fields. Five optical pressure sensors located on the hemisphere tip of the 5HP provide all information that is needed to resolve the flow. This 5HP is expected to be able to provide high spatial resolution, high frequency response and is compatible with elevated temperature environments. A primary focus of this research is on the microfabrication and micromachining of a die that incorporates five optical transducers and its successive packaging process. The completed sensors will be tested in flow cells and wind tunnels at UF for the final calibration.

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.

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.