An inexpensive and highly accurate “spintronic” magnetic field sensor developed at the University of Utah is shown here. The entire device, on a printed circuit board, measures about 0.8 inches by 1.2 inches. But the part that actually detects magnetic fields is the reddish-orange thin-film semiconductor—essentially “plastic paint”—near the center-right of the device. Photo Credit: Christoph Boehme, University of Utah |
University
of Utah physicists developed an inexpensive, highly accurate magnetic
field sensor for scientific and possibly consumer uses based on a
“spintronic” organic thin-film semiconductor that basically is “plastic
paint.”
The
new kind of magnetic-resonance magnetometer also resists heat and
degradation, works at room temperature and never needs to be
calibrated, physicists Christoph Boehme, Will Baker and colleagues
report online in the Tuesday, June 12 edition of the journal Nature Communications.
The
magnetic-sensing thin film is an organic semiconductor polymer named
MEH-PPV. Boehme says it really is nothing more than an orange-colored
“electrically conducting, magnetic field-sensing plastic paint that is
dirt cheap. We measure magnetic fields highly accurately with a drop of
plastic paint, which costs just as little as drop of regular paint.”
The
orange spot is only about 5-by-5 mm (about one-fifth inch on a side),
and the part that actually detects magnetic fields is only 1-by-1 mm.
This organic semiconductor paint is deposited on a thin glass substrate
which then is mounted onto a circuit board with that measures about
20-by-30 mm (about 0.8 by 1.2 inches).
The
new magnetic field sensor is the first major result to come out of the
new Materials Research Science and Engineering Center launched by the
University of Utah last September: a six-year, $21.5 million program
funded by the National Science Foundation, the Utah Science Technology
and Research initiative and the university.
University
of Utah physics professor Brian Saam, one of the center’s principal
investigators, says the new magnetometer “is viewed widely as having
exceptional impact in a host of real-world science and technology
applications.”
Boehme
is considering forming a spinoff company to commercialize the sensors,
on which a patent is pending. In the study, the researchers note that
“measuring absolute magnetic fields is crucial for many scientific and
technological applications.”
As
for potential uses in consumer products, Boehme says it’s difficult to
predict what will happen, but notes that existing, more expensive
magnetic-field sensors “are in many, many devices that we use in daily
life: phones, hard drives, navigation devices, door openers, consumer
electronics of many kinds. However, Joe Public usually is not aware when
he uses those sensors.”
“There
are sensors out there already, but they’re just not nearly as
good—stable and accurate—and are much more expensive to make,” Saam
says.
Boehme
believes the devices could be on the market in three years or less—if
they can be combined with other new technology to make them faster.
Speed is their one drawback, taking up to a few seconds to read a
magnetic field.
Boehme,
the study’s senior author, conducted the research with University of
Utah physics doctoral students Will Baker (the first author), Kapildeb
Ambal, David Waters and Kipp van Schooten; postdoctoral researcher
Hiroki Morishita; physics undergraduate student Rachel Baarda; and two
physics professors who remain affiliated with the University of Utah
after moving elsewhere: Dane McCamey of the University of Sydney,
Australia, and John Lupton of the University of Regensburg, Germany.
The
study was funded by the U.S. Department of Energy, National Science
Foundation, David and Lucile Packard Foundation and Australian Research
Council.
Sensor based on organic spintronics
The
sensors are based on a field of science named spintronics, in which
data is stored both electronically in the electrical charges of
electrons or atomic nuclei and in what is known as the “spin” of those
subatomic particles.
Described
simply, spin makes a particle behave like a tiny bar magnet that is
pointed up or down within an electron or a nucleus. Down can represent 0
and up and represent 1, similar to how in electronics no charge
represents 0 and a charge represents 1. Spintronics allows more
information—spin and charge—to be used than electronics, which just uses
charge.
The
new magnetic field sensor paint contains negatively charged electrons
and positively charged “holes” that align their spins parallel or not
parallel in the absence or presence of a magnetic field—but only if
radio waves of a certain frequency also are applied to the semiconductor
paint.
So
an electrical current is applied to the new device. Electrical contacts
in the device act as tiny broadcast antennas to bombard the plastic
paint with radio waves, which the researchers gradually change in
frequency. If a magnetic field is present, the spins in the polymer
paint will flip when the frequency of the radio waves matches the
magnetic field. The change of spin in the paint is converted to an
electrical current the researchers then read to determine magnetic field
strength.
Because the paint is an organic polymer, the sensor is known as an organic spintronics device.
Device works even if ‘old and crusty’
The
new magnetometer can detect magnetic fields ranging from 1,000 times
weaker than Earth’s magnetic field to tens of thousands times stronger—a
range that covers intermediate to strong magnetic fields, Boehme says.
He
says the new magnetometer cannot measure very weak magnetic fields,
which now are measured by devices known as SQUIDS. It can measure strong
magnetic fields, and although conventional magnetic resonance devices
do that very well, they are bulky and expensive—such as those used in
medical MRI machines—so the low cost and small size of the new
magnetometers may give them some advantages. But the major use of the
new devices is for intermediate strength magnetic fields, for which no
existing device works as well, Boehme says.
Boehme’s
new sensor is known as an organic magnetic resonance magnetometer or
OMRM. Its one disadvantage is it is slow, taking up to a few seconds to
detect a magnetic field. Boehme hopes to combine his technology with
similar developing magnetometer technology known as an organic
magnetoresistant sensor, or OMAR, which is more than 100 times faster
but requires calibration, isn’t very accurate, detects only weak to
moderate magnetic fields and is vulnerable to temperature fluctuations
and material degradation.
The
new device “can literally get old and crusty, and as long as it can
carry a detectable current, the magnetic field can be measured
accurately,” Boehme says.
Boehme
says new experiments will determine how much smaller the 1-m2 sensing
area can be made and still have it accurately detect magnetic fields. He
is aiming for 1 million times smaller: “It’s a matter of
microfabrication.”
Source: University of Utah