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Beth Stadler
Electrical and Computer Engineering
Magnified image of nickel nanowires
Magnified image of glass beads prior to tin oxide application
Magnified image of photonic crystals: tin oxide lattice
left after removing glass beads
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PHOTOS COURTESY OF BETH
STADLER AND ANAND GOPINATH
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About the Sensing and Automation Research Center
The Sensing and Automation Research Center (SARC)
integrates sensor technology research with practical algorithm
developments in micro-electro-mechanical systems (MEMS), systems
on-a-chip, wireless sensor networks, and computer science
to enable the next generation of intelligent embedded systems
that solve practical industrial problems. The center primarily
focuses on advances in: industrial productivity; energy management;
healthcare automation; environmental monitoring; and food
safety, security, quality, and process efficiency.
SARC's vision is to bring together industry and academe to
apply intelligent systems towards providing integrative sensing
and automation solutions in safety, security, efficiency,
and quality applications in these areas by focusing on multi-disciplinary
research involving electrical engineering, computer science,
mechanical and chemical engineering, material science, food
science, and public health. To date, eight companies have
provided letters of endorsement for the SARC and have been
involved in its formation. The SARC is a part of the Center
for the Development of Technological Leadership
(CDTL) at the University of Minnesota. CDTL's mission is to
serve the high-tech community through education, research,
and consulting in technological leadership and management.
INFORMATION COURTESY OF MASSOUD AMIN, CDTL DIRECTOR
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Except for TV screens, creators of modern technology seem obsessed
with miniaturization of their products. The word nano
even became a household word this past year when Apple used it to
name its latest, smallest-to-date iPod portable music device. But
when scientists say nano, how small do they mean? A nanometer is
one-billionth of a meter (with a meter being slightly longer than
a yardstick). Looking at it another way, it takes 60,000 nanometers
(nm) to stretch across the width of a human hair. Nanotechnology
is the term used to describe the constellation of research
and development work in the nanometer range, and is one of the hottest
fields at the University of Minnesota today. Drawing faculty from
many disciplines, nanotechnology research at the University holds
the promise to bring us advances as diverse as new drug delivery
systems, energy-saving lighting devices, and engineered tissues.
Beth Stadler may give us the next such advance. Stadler, an assistant
professor of electrical and computer engineering, uses nanotechnology
to create sensors for sound and smell. Nanostructures are used to
provide the quality of the sensors she builds: the sensors for sound
detection use magnetic wires (ranging in size from 10-350 nm in
diameter) and the gas sensors for environmental detection use a
three-dimensional lattice resembling a sponge (with the sponge's
pores ranging in size from 300-900 nm in diameter).
Tiny combs
The acoustic sensing nanowires that Stadler constructs mimic the
tiny hairs (called cilia) that vary in length--like the
teeth of a comb--along the curled-up cochlea in the ear. When a
sound enters the ear, the cilia of the length that detect that particular
pitch's resonance frequency vibrate and generate an electrochemical
signal to the nerve. The nerve interprets this information and in
turn sends a specific signal to the brain, which can translate the
signal into the appropriate sound. "If you uncurl the cochlea,
you would see something like what we are making, except that our
cilia are much smaller," says Stadler. "We are making
a two-dimensional acoustic comb so small that it would take 600-2000
nanowires [representing the comb's teeth] to go across the diameter
of a human hair."
Although such an acoustic comb could hold promise for replacing
cochlear implant technology, which has issues of nontunability and
background noise interference, the immediate application of these
"artificial ears" may be for sonar uses or medical ultrasound.
By mimicking the lateral line sensory system found on
the skin of fish that uses cilia to pick up vibrations, Stadler's
acoustic sensors could be used to line the suits of divers so they
can find their way in dark or turbid waters. For medical ultrasound,
tiny acoustic sensors could be introduced into the body via catheters
to take improved pictures, such as for echocardiography. Stadler
imagines the eventual development of a transducer smaller than an
aspirin being attached to a catheter, which could be swallowed and
guided to the correct location needed to generate high-quality images
for diagnostic purposes.
Stadler's recent acoustic sensor studies include work on a new material
called Galfenol, which is a gallium-iron alloy. Galfenol
exhibits high sensitivity, generating a significant magnetic field
in response to a signal, and yet it has the excellent mechnical
properties of iron. Stadler's lab is now growing organized arrays
of Galfenol nanowires mounted perpendicular to a base containing
magnetic sensors (see upper photo on the left). To aid in her work,
Stadler has established a collaboration with a local company, Nonvolatile
Electronics (NVE), to obtain sensors for her nanowires. She is pairing
the cutting-edge sensors that NVE fabricates with her nanowires
to look for a match that could provide a leap forward in her sensor
development work.
Sense of smell
Stadler's research on artificial olfactory sensors is not for the
purpose of building a true "artificial nose" that could
find clinical use, but rather to sense the release of a gas for
applications such as homeland security, food protection, and leak
detection. The gas sensors rely on photonics, the science
of manipulating the smallest units of light known as photons.
In brief, photonic crystal structures can be built so
as to control light, allowing or prohibiting certain colors of light
[based on their wavelength] from penetrating the structure. To begin
making these photonic crystals, Stadler uses a lattice of glass
beads that are packed tightly together by her colleague, Professor
Anand Gopinath. Stadler fills in the space around the glass beads
with tin oxide and then removes the beads to leave behind a sponge-like
tin oxide lattice with an ordered arrangement of nano-sized spherical
holes (see lower two photos on the left).
These tin oxide photonic crystals serve as an atomic sieve for light,
with the size of the glass beads used to create the structures determining
which colors of light can pass through them. Traditionally, scientists
like Stadler have examined how the electrical properties (such as
resistivity) of tin oxide change in a given type of environment.
However, these optical structures are very sensitive to changes
in the dielectric constant, so this new technology will be able
to not just detect the presence of a gas, but also to fingerprint
the gas detected. According to Stadler, "it goes beyond giving
us just one number [yes or no].instead, it generates a whole rainbow,
with more information. For example, rather than just knowing if
an environment is oxidizing or reducing, we can tailor the size
of the spheres to look for the particular peaks of a specific gas."
Instead of calling it an artificial nose, it may be more accurate
to call it an optical nose, because "it uses optical properties
to smell gasses," explains Stadler.
Keeping it small
Nanotechnology appears to be critical to the building of the next
generation of sensors. "These sensors wouldn't work without
nanostructures," notes Stadler. For the gas sensors, for example,
"the optical properties we are going to exploit only occur
at the scales we are working with.the structures need to have periodicity
on the same scale as [the wavelengths] of light."
Stadler may benefit from being in the right place at the right time.
Her most recent venture is as one of the faculty members involved
in the University of Minnesota's new Sensing and Automation Research
Center (SARC; see box to the left), which will bring University
researchers together with industry interested in developing new
sensor technology.
For Stadler, the pieces of the puzzle appear to be in place to do
big things with the science of small things.
For more information:
Beth Stadler's home page: www.ece.umn.edu/users/stadler/
University of Minnesota Nanotechnology Coordinating Office:
www.nano.umn.edu
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