Magnetics Business & Technology - March/April 2023 - 14

FEATURE ARTICLE
Optically Pumped Magnetometers from QuSpin Guide Drones & Brain Imaging
change in the transparency of the atoms. The resulting change in
the photocurrent gives a measure of the magnetic field signal.
QuSpin's new OPM sensor for magnetic anomaly detection. Sensor
head is at left and electronic control unit at right.
Optically pumped magnetometers have an edge over even some
superconducting devices for precision magnetic field detection
since they don't need cryogenic cooling. QuSpin, a company
focused on developing atomic devices, has come out with its
second-generation sensor for integration into compact aerial and
underwater drones. Meanwhile, Cerca Magnetics, a medtech
startup is applying QuSpin's OPM technology to open new capabilities
in neurologic imaging.
" Our second-generation QTFM sensor is now ready, " reports Jeff
Orton, senior engineer for QuSpin. " The G2 has been redesigned
from the ground up to enable advanced magnetometry
applications requiring uncompromising sensitivity in a rugged,
small, low-power package. The design choices for G2 focused
on magnetometer integration on compact unmanned aerial and
underwater platforms. "
The G2 is a rubidium optically pumped atomic magnetometer
based on free induction decay. It represents a significant
upgrade over the company's G1 sensor launched in 2017. The
new device is significantly more robust and ruggedized for use in
challenging geophysical applications. There is no slew rate limitation,
it can tolerate an arbitrarily noisy, fast-changing magnetic
field environment without unlocking. Deadzone is negligible.
While the G1 had a large planar deadzone, G2 only has a negligible
axial deadzone so it can be used at any latitude without
orientation concerns. While in many high-performance magnetic
anomaly detection applications, external vector magnetometers
are needed to remove internal and external heading errors, in the
G2 a small triaxial attachment over the sensor head converts the
unit from a pure scalar magnetometer to a hybrid scalar+3-axis
vector magnetometer for hybrid performance.
Total-field OPMs can operate in Earth's field with high accuracy.
The atoms in the OPM vapor cell have a well-defined precession
frequency that is directly proportional to the magnitude of
the background field. In QTFM Gen-2, the precession frequency
is directly measured with a high resolution frequency counter to
obtain the value of background magnetic field.
Meanwhile, medtech startup Cerca
Magnetics has been making progress
in its efforts to commercialize a wearable
brain imaging research system
that uses optically pumped magnetometers
from QuSpin. The system
was developed by researchers at the
University of Nottingham, who currently
are working on development of
a 128-channel wearable system. The
company is a joint venture between
the university and Magnetic Shields
Ltd which provides specialized electromagnetic
interference shielding for the
system.
Cerca Magnetics' wearable
brain imaging
research device vies with
SQUID technology
Magnetoencephalography with optically pumped magnetometers
(OPM-MEG) is a new way to non-invasively assess brain function.
Like conventional MEG, it measures magnetic fields generated
by current flow in neural assemblies, and thus provides
assessment of brain function in health and disease. However,
unlike conventional systems it doesn't require cryogenically
cooled sensors.
Cerca was named best medtech startup of 2021 in the prestigious
OBN Awards held in the UK for innovative achievement
in the life sciences in recognition for developing and bringing
to market the first commercial, wearable MEG device. Since
the company was formed in September 2020, its systems have
already been installed at the Hospital for Sick Children in Toronto
for research into autism and in a special diagnostic suite at the
Young Epilepsy facility in Surrey, UK where it is being used to
improve how the epilepsy is diagnosed and treated.
Traditionally, explains Cerca, the only way to detect the extremely
small magnetic fields generated by the brain (a billion times
smaller than the Earth's magnetic field) was to exploit superconducting
sensors known as SQUIDs. SQUIDs must be kept at
cryogenic temperatures (-269 °C), and this means that sensors
in a conventional MEG system must be immersed in liquid helium.
This, in turn, makes scanners heavy, cumbersome and very
expensive. This has proven a significant barrier to widespread
uptake of MEG.
Basically, OPMs are passive magnetic field sensors comprised
of three main components: (1) a laser, (2) a glass vapor cell containing
'sensing' atoms in a gaseous state, and (3) a photodetector.
QuSpin makes both zero-field OPMs and total-field OPMs.
Zero-field OPMs exhibit extreme sensitivity when the magnetic
background is small. When the field is nearly zero, the atoms
in the vapor cell become mostly transparent allowing maximum
light onto the photodetector. Any change in the field induces a
14 Magnetics Business & Technology * March/April 2023
Recent breakthroughs in physics have enabled the development
and fabrication of OPMs that exploit the quantum properties of
alkali atoms to measure very small magnetic fields. OPM sensitivity
rivals that of superconducting devices, but OPMs do not
require cryogenic cooling. Moreover, their size is no larger than
a Lego brick. OPMs thus provide a perfect building block for their
integrated wearable MEG system, explains Cerca.
www.MagneticsMag.com
http://www.MagneticsMag.com
Magnetics Business & Technology - March/April 2023

Table of Contents for the Digital Edition of Magnetics Business & Technology - March/April 2023
