Video of a conference talk:
Cryogenic Operation of MEMS Microphones for Superconducting Magnet Quench Detection
Collaboration with Luisa Chiesa in the Superconductivity Lab at Tufts, Makoto Takayasu at MIT Plasma Physics Lab, and Michael Emerling, Amish Desai and Steve Chau of Tanner Research
Students: Zijia Zhao, Casey Owen, Mischael Anilus, Jillian Stern
A linear array of MEMS acoustic sensors operating in the coolant space of a force-cooled CICC (Cable In-Conduit Conductor) is an attractive alternative to conventional quench detection techniques. MEMS acoustic sensors are particularly suited for HTS conductors as they can provide high detection speed, good sensitivity, and the ability to localize quench events. In order to implement such a system, MEMS acoustic sensors that can operate in cryogenic fluids (77 K liquid nitrogen, low temperature gaseous and liquid helium) are required. In this work, commercial MEMS microphones and microphone preamplifiers are characterized in cryogenic gaseous helium at static pressures between 0.5 and 1.5 bar, and temperatures down to 20 K, as well as in liquid nitrogen at 1 bar and 77 K. Calibrated acoustic sources are used to deliver plane pressure waves into the cryogenic acoustic media in a plane wave tube geometry. Frequency response data is gathered for several MEMS options: three capacitive MEMS microphones, one piezoelectric MEMS microphone, and a reciprocal electrostatic MEMS speaker used as a sensing element. Distinctions among those MEMS options are drawn regarding the impact of the cryogenic environment on the transducer itself, and on the performance of the required preamplifier electronics. Recommendations of a linear MEMS sensor array method are made for a quench detection and its localization tool in high-current HTS CICC cables and magnets.
Video of a conference talk:
MEMS Surface Shear Sensors for Aerodynamic Applications
This project aims to develop "direct" surface shear stress measurement sensors that can provide real time measurement of the time resolved local shear stress at the surface of a wind tunnel model or vehicle during ground or flight testing. The goal is to provide spatial resolution of 1 mm, bandwidth of 100 kHz, and to cover the shear stress range of 0.1 Pa to 1000 Pa. Our approach is to micromachine floating element style MEMS shear stress sensors in arrays, and to integrate these with high performance capacitance to digital converters in a small form factor package. There are challenges associated with low topology packaging of the sensors, and sensitivity to other variables such as fluctuating pressures, pressure gradients, and environmental variables such as temperature and humidity. Collaborators have included industry and government partners.
The current design employs 256 "floating element" style sensors on a 1 cm x 1 cm chip. The sensor has been able to measure shear stresses from approximately 0.5 Pa to approximately 15 Pa in laminar flow cell and turbulent boundary layer environments. Current bandwidth is limited to about 10 Hz. Sensitivity to pressure gradient has been characterized. Additional characterization of environmental sensitivities to temperature, humidity, vibration, and fluctuating pressures are needed. Additional developments to improve resolution and bandwidth, as well as reduce surface topology, are under way.
We have applied the array to the measurement of boundary layer shear in a flat plate subsonic wind tunnel study. We are interested in extending our applications areas to additional wind tunnel studies with structured models, flight testing, and turbomachinery.
This project aims to develop and characterize MEMS ultrasound transmit and receive array-on-a-chip devices for navigation and flow sensing applications. The goal is to demonstrate the ability to measure 3D velocity and distance to an acoustic reflector using frequency modulated continuous wave Doppler ultrasound or pulsed chirps. The project includes design, microfabrication, and testing.
The current system has been successful at measuring 1D velocity of a moving reflector with 60 velocity updates per second, at a resolution of approximately 0.5 cm/s and a maximum measurable range to the reflector of 1.5 meters. Work is ongoing in increase resolution, increase range, extend the technology to measur 3D velocities and distance veotors, and reduce package size and power for portable applications. We are interested in collaborating with potential end users who would find a low power, low weight distance and velocity measurement system useful. We can imagine applications in mobile robotics and personal navigation systems.
Images of the packaged ultrasound array chip (left), and a microscope image of a few sensor elements (right).
Microelectronics and MEMS Packaging
Our group gets involved in a variety of electronics packaging problems, often either as we try to package our MEMS sensors, or as we work with partners such as Draper Labs on system packaging problems.
Aerosol Jet Printing of Transceiver Circuit
with Peter Lewis, Brian Smith and others at Draper Labs
This research employs aerosol jet printing to rapidly manufacture a multilayer PCB with COTs component integration. Specifically, this research provides a method to making a system-on-a-chip (SOC) circuit on a variety of substrates with novel integration methods. This fits well into the recent research phenomenon deemed "Internet of Things" (IoT). By advancing the manufacturing capabilities for a system that can measure and transmit data, one can integrate such circuits with minimal spatial and geometric interference to the broader device. A unique manufacturing process was developed for non-embedded components which involves the building up of the circuit around the system's microprocessor. The transceiver circuit and its microprocessor, based off a commercially available circuit, has been successfully programmed and has shown to be working. The matching network is still being worked on, however, the goal is to have it working by the conference. To the best of the researchers' knowledge, this research is novel in that it is the most complicated multilayer circuit that has been built using aerosol jet printing technology. Rapid ageing tests for a silver and a CNT ink were done and analyzed to determine the reliability of an aerosol jet printed circuit board. Results show adhesion is the primary mechanism of device failure as opposed to conductor degradation.
Image: A microcontroller and RF transceiver circuit created entirely using aerosol jet printing of both dielectric and interconnect layers.
Co-fabrication of Micro-Coaxial Interconnects and Substrate Junctions for Multi-Chip Microelectronic Systems
with Daniela Torres, Caprice Gray, Tony Kopa and others at Draper Labs
Low inductance micro-coaxial cables for power distribution as well as micro-coaxial cables for signal distribution have been fabricated using an in-situ fabrication and attachment strategy. These cables have been fabricated to expedite characterization of different wires for the Miniature Multi-Wire Systems (MMS) IR&D at Draper. MMSmain goal is to create a microelectronic packaging technology that will greatly reduce the time required to design and fabricate multi-chip modules and other complex electronic assemblies. This technology will be based on the use of shielded micro-wires (micro-coax) for all component interconnects to eliminate the lengthy layout and fabrication processes associated with today's high-density packaging technologies. The first type of cable is a low inductance cable made with 1 Mil wire bonded Gold, 1 5m Parylene dielectric, and 5 5m Gold shield. The second set of cables are also low inductance cables made with 1 Mil wire bonded Gold, 100 nm Hafnium (HfO2) dielectric, and 5 5m Gold shield. The third set of cables are signal coaxial cables made of 1 Mil wire bonded Gold, 38 5m of Parylene dielectric, and 5 5m Gold shield. The characteristic impedance of these wires are measured to be 2.0-3.5O Ohm, 0.07-0.13O Ohm, and 44.6-51.5O Ohm respectively. Further characterization of these wires will also be discussed in this presentation, which will include cross-talk integrity and thermal shock reliability.
(Left) SEM image of the attachment end of a micro-coax wire where the core has been exposed for contact. (Right) SEM of a FIB cross-section of the micro-coax showing the shield, dielectric, and core.
Students: Martin Majkut, Nikolas Kastor
Our group has recently been working on two concepts in robotics. The first is design and control of soft foam robots. A motor tendon actuated soft robot was built from castable polyurethane foam with a low cost and robust manufacturing method. This method can produce a robot in less than one hour with lower cost and greater durability than 3D printing. The robot produced by this method exhibits the ability to change shape, by compressing and folding, allowing it to perform complex locomotion. Hard components, such as motors and sensors, are sutured into cavities in the foam body in order to facilitate the construction process and reduce interaction with the soft body. This highly deformable robotic platform will be useful in evaluating factors that affect locomotion including material selection, structural design and control methodologies.
A tendon driven foam robot design. The calibrated weight is critical for controlling ground interaction and variable friction. Read the paper!
The second topic we worked on recently is vibration communication and sensing in robots. Structure-borne vibrations in a one dimensional structure were examined as a means of communication and sensing for networks of robots. The concept was inspired by the observation that insects use structural vibrations to communicate and to detect features of their environment. A 12 x 5 x 6 cm mobile robot capable of traversing an acoustically favorable structure was developed. A technique for measuring distance between robots and communicating commands to robots using vibrations generated on a common one dimensional substrate were demonstrated
The autonomous robot pictured was developed to navigate a rail system (one-dimensional environment). The robot can communicate with an external computer and sense distance by sending structural vibrations along a "third rail". (a) Robot navigating the track (b) a close-up of the three-rail system (c) a cross-section of the rail system with labels.
A microelectromechanical systems (MEMS) based microphone array on a chip has been developed and applied to aeroacoustic measurements. The array is designed to measure the fluctuating pressures present under a turbulent boundary layer (TBL). Each chip measures 1 cm2 and contains 64 individually addressable capacitively sensed microphones, with a center to center pitch of approximately 1.25 mm. Surface topology, including the packaging, is kept to less than 0.13 mm. Element to element sensitivity variation in the array is less than 12.5 dB from least to most sensitive, and phase variation is less than 16.5 degrees (at 1 kHz). The microphone 3dB bandwidth is 300 Hz to 100 kHz, and the microphones are linear to better than 0.3% at sound pressure levels up to 150 dB SPL. A unique switched architecture system electronics and packaging method are employed to reduce data acquisition channel count requirements, and to maintain a low surface roughness.
The array was recently applied to the measurement of multi point turbulence spectra under a flat plate TBL in a low speed, low turbulence intensity wind tunnel at the University of Toronto Institute for Aerospace Studies (UTIAS). Testing was at a maximum speed of 30 m/s, and maximum Reynolds numbers based on plate length of approximately 106. Evidence of turbulent structures was gathered by examining coherence data between rows of array elements spaced apart in the flow direction. Coherence decreased with distance in the 300 Hz to 2 kHz band, indicating an ability to separate turbulent structures from acoustic pressure fluctuations in this band, even at the low speeds achievable in the UTIAS tunnel.
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