NANOENGINEERING RESEARCH AT UH A MAGNET
FOR DEFENSE DEPARTMENT GRANT
Quest to Build Most Powerful Magnetic Field Sensor Could Reap Military,
HOUSTON, Feb. 5, 2007 – Whether you’re a soldier navigating
a minefield or a doctor examining a tumor, how well you know the
territory can make all the difference in the outcome.
That’s why military and medical personnel increasingly rely
on magnetic field sensors to help map their respective terrains
– and why the U.S. Department of Defense (DOD) has awarded
a University of Houston researcher and his team a grant worth up
to $1.6 million to build the most powerful magnetic field sensor
Stanko Brankovic, an assistant professor of electrical and computer
engineering with the Cullen College of Engineering at UH, and co-principle
investigator Paul Ruchhoeft, also a UH assistant professor of electrical
and computer engineering, will use the grant to create a new type
of magnetic field sensor that, if successful, will be hundreds –
perhaps thousands – of times more sensitive than anything
On the military front, hundreds of thousands or more of these
sensors could be the key components in a low-cost system that maps
minefields quickly and accurately. In the medical arena, the sensors
could be applied to magnetic resonance imaging, yielding highly
detailed images of, for example, a tumor or an injured knee.
The funding for the project, “Single Ferromagnetic Nanocontact-Based
Devices as Magnetic Field Sensors,” will be delivered in two
stages. The first stage, valued at $100,000 for one year, requires
a proof of concept, in which Brankovic and Ruchhoeft must construct
a working sensor. To do this, they will utilize new ideas in the
nanoengineering of novel materials and the development of nanofabrication
processes for devices smaller than 10 nanometers.
Should they succeed, the DOD will consider awarding them an extra
$1.5 million to complete an entire system that incorporates multiple
sensors, data-transmission equipment, and equipment and software
that translate data into an easily understandable format.
The team’s sensors will be based upon the phenomenon known
as “ballistic magnetoresistance,” which is the effect
of a magnetic field on the ability of electrons to flow between
magnetic electrodes through a nanocontact – a tiny wire measuring
billionths of a meter that forms naturally between magnetic electrodes.
If the two electrodes’ magnetic orientations (the direction
in which a material’s magnetism pushes or pulls) are different,
some of the electrons flowing between them will be repelled by the
spot in the nanocontact where the two different magnetizations meet,
“When exposed to a magnetic field, however, the resulting
change in magnetic orientation of the electrodes affects electrons’
ability to travel through the nanocontact,” he said. “Depending
on the size and material of the nanocontact and magnetization of
the electrodes, the electrons will flow through either more or less
This change can be measured by simple tools such as a voltmeter.
On the bulk scale, magnetoresistance – the change in electrical
resistance of a conductor when a magnetic field is applied –
is only one factor in determining how easily electrons travel between
electrodes. On the nanoscale, in which these magnetic field sensors
will be constructed, magnetoresistance is the only cause of fluctuation
in the flow of electrons.
The heart of Brankovic’s system will consist of two magnetic
electrodes, connected by a very small magnetic nanocontact. When
exposed to a magnetic field, the flow of electrons through the nanocontact
will change, yielding a measurable result.
Exactly how magnetoresistance works on this scale is unknown and
will be one of the subjects of Brankovic’s research. Two of
the main theories to explain the phenomenon – both of which
are supported by limited physical evidence – are incompatible.
Brankovic has developed his own hypothesis that, if correct, would
account for both sets of evidence.
“In my hypothesis, the nanocontact connecting the two electrodes
is composed of non-conductive metal oxide that has metal channels
that act as conductive pathways for electrons,” Brankovic
said. “When exposed to a magnetic field, some, but not all,
of the channels of conductive material are altered either by the
magnetic domain wall or by magnetostriction – the phenomena
of a material’s shape changing slightly when exposed to a
magnetic field. Either of these explanations would result in a small
but measurable change in the flow of electrons.”
Whether this supposition proves correct or magnetic resistance
on the nanoscale works in some other manner, Brankovic’s goal
will remain the same: to build a first-of-its kind magnetic field
sensor that is far more powerful than any other sensor to date.
If he succeeds, his invention will create a fundamental change in
the arena of magnetic field detection.
About the University of Houston
The University of Houston, Texas’ premier metropolitan research
and teaching institution, is home to more than 40 research centers
and institutes and sponsors more than 300 partnerships with corporate,
civic and governmental entities. UH, the most diverse research university
in the country, stands at the forefront of education, research and
service with more than 35,000 students.
About the Cullen College of Engineering
UH Cullen College of Engineering has produced five U.S. astronauts,
ten members of the National Academy of Engineering, and degree programs
that have ranked in the top ten nationally. With more than 2,600
students, the college offers accredited undergraduate and graduate
degrees in biomedical, chemical, civil and environmental, electrical
and computer, industrial, and mechanical engineering. It also offers
specialized programs in aerospace, materials, petroleum engineering
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