Tech Briefs Magazine - September 2021 - 64

SPINOFF
E
verything in the atmosphere can
make a sound - volcanoes rumble
and waterfalls crash - but there's more
to that sound than what our ears perceive.
Much like how infrared light consists
of frequencies that aren't visible to
the naked eye, there's an audio analogue
called infrasound that consists of
pitches too low (0.001 to 20 hertz) to be
heard by the human ear.
The sudden turbulence sometimes
experienced when flying is called clearair
turbulence, so named because there
are no visible clouds or atmospheric features
to warn of the disruption. Tur -
bulent invisible air can seemingly come
out of nowhere and wreak havoc on aircraft.
Though
it isn't easily detected visually,
clear-air turbulence has a definite infrasound
signature. Researchers Qamar
Shams and Allan Zuckerwar at NASA's
Langley Research Center in Hampton,
VA realized that if air traffic controllers
or pilots could listen to
these whirling vortices
before airplanes en -
counter them, an al -
ternate route could be
plotted.
Their experiments be -
gan in 2007 but initial
tests showed them that
they couldn't grab just
any off-the-shelf microphone
and expect it to
work with infrasound.
The long-wave frequencies
get overpowered by
higher-frequency
sounds, which results in
interference.
NASA's special infrasound microphone can pick
up the ultra-low frequencies generated by turbulence
in the skies. This technology is now
being tested on the Stratodynamics HiDRON
glider for both turbulence detection and aeronautical
research. (Credit: NASA)
Spinoff is NASA's annual publication featuring
successfully commercialized NASA technology. This
commercialization has contributed to the development
of products and services in the fields of health and
medicine, consumer goods, transportation, public safety,
computer technology, and environmental resources.
Microphone Detects Turbulence Hundreds of Miles Away
A NASA microphone that detects unseen air turbulence is lofted to high heights aboard a
stratospheric glider.
tern around Langley's runway, they were
able to pick up and locate atmospheric
turbulence more than 300 miles away.
By 2017, the technology had won the
NASA Commercial Invention of the Year
award, been tested on the ground for
the Department of Defense, and been
researched at Sandia National Laboratories
to validate its performance but it
hadn't flown aboard any aircraft. In -
terest in turbulence detection from
Stratodynamics Lewes, DE, would soon
change that.
Stratodynamics realized the microphone
system had significant potential
as an in-flight turbulence detection sensor
and looked for opportunities to test
the technology. After licensing the
patents from NASA, the company began
to implement the sensor on an un -
crewed stratospheric glider known as the
HiDRON.
Typically launched by a weather balloon, the HiDRON has soared to more than
100,000 feet in the air. (Credit: Stratodynamics)
The pair began developing something
that could listen to these low frequencies
in high fidel ity. Microphones use a moving
dia phragm to pick up audio where
sound waves cause the surface to vibrate.
The researchers used a low-tension dia -
phragm with a wide radius paired with a
large, sealed air chamber behind it to
64
Cov
allow the microphone to hear these
ultra-low sound waves that travel great
distances. The infrasonic microphones
are manufactured by PCB Piezotronics of
Depew, NY under contract with Langley.
With the sensor completed, testing
began. When the microphones were
placed in an equidistant triangular patwww.techbriefs.com
ToC
Stratodynamics
has lifted their balloonlaunched
HiDRON glider to heights of
more than 100,000 feet,
from which it slowly
makes its way back down
to Earth. With the assistance
of the infrasound
microphone and wind
probe, the UAV measures
the intensity of turbulence
in its path at a
distance and may possibly
detect thermal col -
umns to keep the plane
sailing longer. Currently,
more work is underway
to design the algorithms
required to understand
the turbulent signature's
intensity and range.
The researchers hope the data provided
by the infrasonic microphone
will become ubiquitous in detecting
and forecasting turbulence, air traffic
control decision-making, and aviation
route planning.
Visit https://spinoff.nasa.gov/turbulencemicrophone.
Tech
Briefs, September 2021
https://spinoff.nasa.gov/turbulence-microphone http://www.techbriefs.com http://www.abpi.net/ntbpdfclicks/l.php?202109TBNAV
Tech Briefs Magazine - September 2021

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