Tech Briefs Magazine - February 2023 - 30

Manufacturing &
Prototyping
(a)
Pogo
Pins
RPA
Cap
Pogo Pin
Holder
(b)
RPA Cap
RPA Shroud
Pogo Pin Holder
Electrode Housing
Electrode Stack
Set Screw
Electrode
Stack
(c)
Electrode
Housing
Deflection Spring
Pogo Pin PassThrough
Hole
Electrode
Housing
Set Screw
Blind Hole
RPA Inlet
This figure shows how the meshes fit inside the RPA housing, which aligns the meshes. (Image: MIT researchers)
traditional sensor materials (e.g., silicon
and thin-film coatings). Using the glass-ceramic
in a fabrication process that was developed
for 3D printing with plastics enabled
the team to create sensors with
complex shapes that could withstand the
wide temperature swings a spacecraft
would encounter.
" Additive manufacturing can make a big
difference in the future of space hardware, "
said Luis Fernando VelásquezGarcía,
Principal Scientist, MIT's Microsystems
Technology Laboratories. " Some
people think that when you 3D-print something,
you have to concede less performance.
But we've shown that is not always
the case. Sometimes there is nothing to
trade off. "
An RPA was first used in a space mission
way back in 1959. How it works is the sensors
detect the energy in ions, or charged
particles, that are floating in plasma.
Aboard an orbiting spacecraft, they measure
energy and conduct chemical analyses
that can help scientists predict the weather
or monitor climate change.
The sensors contain a series of electrically
charged meshes dotted with tiny holes.
As plasma passes through the holes, elec30
trons
and other particles are removed until
only ions remain. These ions then create
an electric current measured and analyzed
by the sensor.
The housing structure that aligns the
meshes must be electrically insulating
while also being able to withstand sudden,
drastic temperature swings. The
team used Vitrolite - a printable,
glass-ceramic
material.
neered in the early 20th
Vitrolite, piocentury,
was often
used in colorful tiles that became a
common sight in art deco buildings; it
can withstand temperatures as high as
800 °C without breaking down. Conversly,
polymers used in semiconductor RPAs
start to melt at 400 °C.
" When you make this sensor in the
cleanroom, you don't have the same degree
of freedom to define materials and
structures and how they interact together, "
said Velásquez-García. " What made this
possible is the latest developments in additive
manufacturing. "
The team used vat polymerization, a decades-old
process for additive manufacturing
with polymers or resins. With vat polymerization,
a 3D structure is built one
layer at a time by submerging it repeatedly
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into a vat of liquid material - Vitrolite, in
this instance.
UV light is used to cure the material after
each layer is added before the platform
is submerged again. Each layer is only 100
microns thick - about the diameter of a
human hair - which enables the creation
of smooth, pore-free, complex ceramic
shapes.
Since the sensors were cheap and easy to
produce, the team prototyped four designs.
One design was especially effective at
capturing and measuring a wide range of
plasmas, a la a satellite in orbit, while another
was well-suited for sensing extremely
dense and cold plasmas.
Going forward, the team wants to enhance
the fabrication process. Reducing
the thickness of layers or pixel size in
glass-ceramic vat polymerization could create
complex hardware that is even more
precise. Also, fully additively manufacturing
the sensors would make them compatible
with in-space manufacturing. The
team also hopes to explore the use of
artificial intelligence to optimize sensor
design for specific use cases.
For more information, contact Abby
Abazorius at abbya@mit.edu; 617-253-2709.
Tech Briefs, February 2023
RPA
Shroud
Housing Groove
Collector
Electrode
Second ElectronRepelling
Grid
Ion-Retarding
Grid
First ElectronRepelling
Grid
Floating Grid

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Tech Briefs Magazine - February 2023

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