A Micromachined Torsional Electric Field Sensor
is a relatively new discipline within medicine and psychology that is used to study the
nervous system and can also help diagnose anomalies in cognitive functions.
Unfortunately, the most popular techniques available (i.e. magnetic resonance imaging)
are expensive, time-consuming, and inaccessible to most. Furthermore, emerging markets
in virtual reality and education ... read moreare also interested in creating new applications that
would primarily rely on brain sensing technology. This research project is part of an
internally funded program at Draper that is seeking to develop a sensor that would
measure electric fields that are emitted from the outermost layer of the brain (usually
~1mV/m around 10-12Hz). If successful, this method would be relatively cheaper than most
commercial techniques with the added benefits of being mobile and providing real-time
measurements. In this thesis, a system level model was developed for characterizing the
behavior of the device due to an electric field input as well as vibrations. A numerical
model is also added to complement the electrostatics to capture any flux diversion that
may influence the field strength near the device during operation. The micromachining
process as well as the assembly are described. Results show agreement with modeling
parameters. First, the expected resonant frequencies of the mechanical modes of the
device during each major of the fabrication process are well predicted. Second, the
scale factor of the device increases linearly with the amount of voltage applied to the
system, which agrees with the model. Results suggest that the sensor's Brownian
resolution limit with a 900V bias at resonance (2.5 kHz) will be 2.5
V/m/√Hz, and at low frequencies (~ 10 Hz) will be 1.5 mV/m/√Hz.
Due to room vibrations, which are not attenuated by the current single-point laser
vibrometry measurement method used for experiments, this resolution limit has not yet
been approached. However, if a more optimal measurement scheme were used, that could
approach the Brownian limit, which has been done in other MEMS systems, this resolution
limit may plausibly be achievable in the future. At resonance this resolution would be
nearly three orders of magnitude better than required for brain sensing applications. At
low frequencies, the Brownian limit is of the same order as the required resolution.
This thesis not only demonstrates the ability of the sensor to measure electric fields,
but also develops a model and offers insights on further modifications that can be made
to improve sensor performance.
Thesis (M.S.)--Tufts University, 2018.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Robert White.
Committee: James Bickford, and Jason Rife.
Keyword: Mechanical engineering.read less