Tech Briefs Magazine - December 2022 - 35

out a laser beam that continually shifts between
different frequencies. When the detector
gathers light to measure its reflection
time, it can distinguish between the
specific frequency pattern and any other
light source, allowing it to work in all kinds
of lighting conditions with very high
speed. It then measures any phase shift
against unimpeded beams, which is a
much more accurate way to determine distance
than current LiDAR systems.
Most previous work using LiDAR has relied
on rotating mirrors to scan the laser
over the landscape. While this approach
works well, it is fundamentally limited by
the speed of the mechanical mirror, no
matter how powerful the laser it's using.
The Duke team instead uses a diffraction
grating that works like a prism,
breaking the laser into a rainbow of frequencies
that spread out as they travel
away from the source. Because the original
laser is still quickly sweeping through
a range of frequencies, this translates
into sweeping the LiDAR beam much
faster than a mechanical mirror can rotate.
This allows the system to quickly
cover a wide area without losing much
depth or location accuracy.
While OCT devices are used to profile
microscopic structures up to several millimeters
deep within an object, robotic
3D vision systems only need to locate the
surfaces of human-scale objects. To accomplish
this, the researchers narrowed
the range of frequencies used by OCT,
and only looked for the peak signal generated
from the surfaces of objects. This
costs the system a little bit of resolution,
but with much greater imaging range
and speed than traditional LiDAR.
The result is an FMCW LiDAR system
that achieves submillimeter localization accuracy
with data-throughput 25 times
greater than previous demonstrations. The
results show that the approach is fast and
accurate enough to capture the details of
moving human body parts in real-time.
For more information, contact University
Communications department at
dukenews@duke.edu; 919-684-2823.
Reflection-Reducing Imaging System for Machine Vision
Applications
The technology can be used in wind tunnel testing, thermal systems management, gas flow
imaging, and heat transfer measurements.
Langley Research Center, Hampton, VA
N
ASA researchers have developed a
compact, cost-effective imaging system
using a co-linear, high-intensity LED
illumination unit to minimize window
reflections for background-oriented
schlieren (BOS) and machine vision
measurements. The imaging system tested
in NASA wind tunnels can reduce or
eliminate shadows that occur when using
many existing BOS and photogrammetric
measurement systems; these shadows
occur in existing systems for a variety of
reasons, including the severe back-reflections
from wind tunnel viewing port
windows and variations in the refractive
index of the imaged volume.
The imaging system is comprised
of a small CMOS camera fitted with a
C-mount lens affixed to a 3D-printed
mount. Light from the high-intensity
LED is passed through a lens that both
diffuses and collimates the LED output,
and this light is coupled onto the cameras
optical axis using a 50:50 beam-splitting
prism.
Use of the collimating/diffusing lens
to condition the LED output provides
for an illumination source that is of similar
diameter to the cameras imaging
lens. This is the feature that reduces or
eliminates shadows that would otherwise
be projected onto the subject plane as
a result of refractive index variations in
the imaged volume.
Tech Briefs, December 2022
LED Heat Sink
Printed Circuit Board
Camera
Beamsplitter Cube
3D-Printed
Post Mount
12V Power
Cord
NASA's imaging system is comprised of a small CMOS camera fitted with a C-mount lens affixed to
a 3D-printed mount. (Image: NASA)
By coupling the light from the LED
unit onto the camera's optical axis, reflections
from windows, which are often
present in wind tunnel facilities to allow
for direct views of a test section, can
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be minimized or eliminated when the
camera is placed at a small angle of incidence
relative to the windows surface.
Due to its compact size, the system can
easily fit in the space behind a typical wind
35

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Tech Briefs Magazine - December 2022

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