MACES: A Miniature Cavity Enhanced Spectrometer capable of detecting NO2 Levels on a UAV - NOAA Chemical Sciences Laboratory
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NOAA Chemical Sciences Laboratory Senior Design Team 25 | Design Center Colorado mACES: A Miniature Cavity Enhanced Spectrometer capable of detecting NO2 Levels on a UAV Team 25: Star Fassler | Jake Leicht | Erin Bobby | Lucas McMahan | Aquzana Mejia 1
Table of Contents
Executive Summary 3
Project Requirements 4
Design Overview 5
Optical Cage Functionality 6
Testing 7-9
Overall Functionality of mACES 10
Final Developed Design 11
Meet the Team 12-13
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 2
Executive Summary
ACES mACES
Optical Engineering Mechanical Engineering Electrical Engineering
Nitrogen dioxide, better known as NO2, is a pollutant that primarily releases into the air from the burning of fuels. Not only
can breathing in high concentrations of NO2 irritate the respiratory system, it is a key factor in the formation of ozone and
particulate matter pollution contributing to climate change. The existing systems, including instruments on the surface and
airborne platforms, struggle to accurately measure the gradient in the lower troposphere, specifically near populated areas. These
systems are mostly capable of predicting what the upward profile of NO2 levels look like with respect to the ground.
Due to these persistent and detrimental effects to our environment and human health at large, Team 25 partnered up
with The National Oceanic and Atmospheric Administration (NOAA) Chemical Sciences Laboratory in an effort to build a miniature
cavity enhanced spectrometer for measuring NO2 levels on an unmanned aerial vehicle (UAV). NOAA has developed an existing
ground based system known as the Airborne Cavity Enhanced Spectrometer (ACES) that is capable of measuring the absorption
spectrum of NO2 as well as other chemical compounds. Due to its size and weight, ACES is mostly limited to ground based
measurements and sometimes large aircraft platforms that can't easily measure NO2 gradients in the lowest few hundred feet of
the troposphere. Miniaturizing this system is the first step in the overall impact this instrument can have on cleaning up the
environment and reducing NO2 pollution. NOAA has coined the name Miniature Airborne Cavity Enhanced Spectrometer or mACES
for the device our team is constructing. With a complex system that integrates an optical cavity, a broadband light source, and a
grating spectrometer, mACES is a lightweight, compact instrument that has been designed to be mounted to the DJI Matrice 600
drone for flight in the lower troposphere.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 3
Project Requirements
mACES should be able to accurately detect NO2 levels in the atmosphere relative to NOAA’s current
ACES system, with aspects that allow it to be attached as a payload under a drone for readings in the
lower troposphere. In order for the instrument to be mounted to a drone, the overall mass of the system
has to be drastically reduced from ~150 kg to ~5 kg. To achieve this goal, Team 25 divided the
engineering tasks into 3 primary structures and 3 subsystems.
Primary Structures
Optical Cage
Contains the main components of the instrument that will determine if mACES is
functioning properly and will accurately detect NO2 levels.
Drone Mounting
Designed for the dual purpose of attaching the entire payload to a drone to get data
from different elevations in the lower troposphere, as well as isolating the optical
cage from the shock and vibrations it may experience during flight.
Casing
Protects the system from dust as well as moisture. As with any other part of this
project, we had the added requirement of making this casing as light as possible
while achieving the previous needs of this structure.
Subsystems
Plumbing
Moves air samples into and out of the optical cage where light from the LED passes
through them to detect NO2 levels via the spectrometer. Tight seals, particle
filtering, and chemically neutral materials were a major focus.
Power & Temperature Control
Ensure that the system does not get above a certain temperature range (20 C -
35 C) during use, which would affect the efficiency of the LED as well as the
reliability and accuracy of the data.
Wiring
Takes into account all of the electronic components of the system to be wired to
the battery, PCB, and BeagleBone microcomputer for power and data collection.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 4
Design Overview
There were four primary design concerns in the development of mACES: functionality as a spectrometer,
vibration mitigation, weight reduction, and temperature control. Nearly half of the development time for mACES
was spent creating designs for the Optical Cage, Drone Mounting, and Casing systems that were lightweight,
resistant to vibration, and that maintained the integrity of the optical system employed on ACES. As is true for
many other experimental projects, it was important to establish a design, fabricate it, and move quickly into
functional testing. Running concurrently with testing was an iterative process of analysis of the systems
performance, refinement of the design, and refabrication of parts that were not performing to specifications.
Optical Cage Drone Mounting Casing
The Optical Cage houses all of the The Drone Mounting system The Casing serves as a protective
crucial functionality of mACES. serves as the critical interface barrier for the sensitive optical
The Optical Cage is designed to between mACES and its carrier equipment onboard mACES. The
provide a rigid frame for the drone. It features a vibration casing design on this prototype is
optical components along the damping system that mitigates preliminary and is manufactured
system’s “Critical Light Path”*. vibrations from the drone so that through rapid prototyping to show
Design calculations drove mACES they do not affect mACES’s ability what its final form might look like.
to be designed with a 15 cm to collect data. It utilizes carbon NOAA will be delivered a robust
optical cavity, the smallest it fiber reinforced plastic mounting list of recommendations for the
could be while meeting accuracy rods, and medium (50A) final instrument that keep in mind
requirements. Each component is durometer neoprene rubber weatherproofing, durability, mass,
designed to be as lightweight as vibration dampers to isolate and cost. Plausible options
possible while maintaining the mACES from any significant include injection molding or
systems structural integrity. vibrational frequencies from the urethane casting.
drone.
* In an optical instrument, such as mACES, the Critical Path is defined by the direct path of light through each optical component.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 5
Optical Cage Functionality
1. 455 nm light from the LED is directed into the optical cavity by the Off-Axis Parabolic
Mirror (OAP).
2. The light bounces off the two highly reflective cavity mirrors several thousand times,
creating a highly sensitive measurement in a small instrument footprint. NO2
concentrations are also being sampled in.
3. The light will then continue on its path out of the cavity where it is focused into the
Bandpass Filter.
4. The fiber coupler is connected to the Spectrometer via a fiber optic cable where the
data is then processed on a computer.
5. While the light continues on its path to be imaged by a Spectrometer, the NO2
concentration within the optical cavity is determined by how those molecules affect
the intensity of light. The various sensors measure the outflow which will be used in
further calculations.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 6
Testing - Functionality
Since mACES is an experimental device, the testing phase of this project was crucial to proving the
feasibility of this miniaturized system. There were 3 main categories of concern that each of the tests
fall under:
To test for leaks, all air was pumped out of the
optical cavity. Then, the team waited to see how
long it would take for the pressure in the cavity to
In order to ensure mACES is fully functional, increase. The longer the cavity went without
there must be no light or air leaks from the increasing, the tighter the seal on the flange
optical cavity. The primary point of concern interfaces. The results of the air leak test showed
for these leaks is centered around the that it took over 2 minutes for any pressure
flange interfaces, shown in the figure change to occur in the cavity, as seen in the figure
below. below, a graph that shows pressure change over
time. The nearly flat line in the graph indicates that
the seals around the flange interfaces created a
tight seal, and therefore a functional device.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 7
Testing - Heat
Since mACES is an experimental device, the testing phase of this project was crucial to proving the
feasibility of this miniaturized system. There were 3 main categories of concern that each of the tests
fall under:
Heat dissipation is essential to the functionality of
mACES in two ways: how it affects the alignment
of the optical cavity, and how it affects the LED.
The LED has a maximum temperature of 40 C
before its efficiency drops significantly and causes
the measurements taken to be less precise.
Typically, an LED heat management system is
composed of 2 additional components: a
thermoelectric cooler (TEC) and heat sink.
However, because our LED system is attached to a Although the copper mount adds another
2D-stage that controls the x, y, and z position of piece in the LED assembly that heat must
the LED, another component had to be added to pass through, its high thermal conductivity
make the system fit together: a copper mount. allows for better heat dissipation from the
system. However, the mount still adds more
interfaces between the TEC and heat sink,
therefore decreasing the thermal efficiency of
the whole system. This is why the selection
of the heat sink is very important. The figure
above shows 4 heat sink options, all of which
maintain the temperature of the LED except
for the smallest option shown in green.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 8
Testing - Vibration
Since mACES is an experimental device, the testing phase of this project was crucial to proving the
feasibility of this miniaturized system. There were 3 main categories of concern that each of the tests
fall under:
Since mACES will be mounted under a drone to collect and
analyze data, the team had to understand the effect that
vibration had on mACES, and test the vibration damping
system that was designed to protect it. mACES was placed
on a vibration table and vibrated from 10 Hz to 130 Hz to
simulate the vibration of a drone.
The vibration table test was performed to
determine the effect of vibration on the optical
system. Although vibration has minimal effect
on the quality of data collected by mACES, it
still may have an effect on additional
components in the system. The vibration
dampers placed at each of the connection
points between the drone and mACES, shown in
the figure above, were tested to confirm the
efficacy of our original VDS design. The result of
After vibrating mACES on the vibration table, the team this test indicated that 50A durometer rubber
determined that vibration had no effect on the number of dampers successfully decreased vibration in
signal counts that mACES was able to detect. This is shown mACES.
in the figure above, where there is a flat line between peaks
indicating no change in counts as vibration changed.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 9
Overall Functionality of mACES
Team 25 and NOAA Chemical Sciences Laboratory accomplished their
goal of determining if mACES can accurately detect NO2 levels, which
has been validated by our client, Dr. Caroline Womack.
Precision Mirror Reflectivity
The smaller spectrometer can produce precise data, mACES has a mirror reflectivity of 0.9999. The closer it is
specificallyFinal Developed Design
Due to the complexity of mACES and the restrictions in place from the COVID-19 pandemic,
Team 25 developed a well thought out and clearly documented plan that outlined how to
prioritize the critical aspects involved in the functionality of mACES. Not all structures and
subsystems were essential to ensure the system’s functionality, so the team split up
manufacturing into Phase 1 and Phase 2. Phase 1 focused on the optical functionality while
Phase 2 focused on redesign and nonfunctioning mechanical rapid prototyping components
to see the final form factor.
Phase 1 Phase 2
Design Functional Prototype Testing and Analysis Redesign
Spider Mount Plate Manufacturing and Alignment Individual components, not
Mirror Mount Plate Component Loads the entire system
Bandpass Filter Mount Assembly Vibe/Shock
Heat Sink Mount Is mACES functioning per our
Optical Cavity Length Deep Focus on Optical Cage specs?
Optical Cavity Flanges Vibration Damping System
Carbon Fiber Rods Casing
Vibration Damping System Heat Management
System Casing
Miniaturization Recommendations
General Layout
and Delivery
Hand off working Optical
Cage System to NOAA
Provide recommendations
for future improvements
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 11Meet the Team
Star Fassler - Project Manager
Optical Cage System Sub-Team Lead
Member of Plumbing and Wiring Sub-Teams
Aside from my Mechanical Engineering degree, I will also
be graduating with a Biomedical Engineering option and
am eager to expand my knowledge and technical skills. I
eventually aspire to be a motivational speaker and use
all my past, present, and future experiences to help
guide the future STEM leaders of our world.
Jake Leicht - Logistics Manager/Manufacturing Engineer
Drone Mounting Sub-Team Lead
Member of Optical Cage System and Wiring Sub-Teams
After graduation, I will be commissioning as a 2nd
lieutenant in the Air Force and attending Euro Nato
Joint Jet Pilot Training.
Erin Bobby - Test/Systems Engineer
Power/Temperature Control Sub-Team Lead
Member of Drone Mounting and Plumbing Sub-Teams
I will graduate with a degree in Mechanical Engineering
and a minor in Entrepreneurial Business.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 12Meet the Team
Lucas McMahan - CAD Engineer
Wiring Sub-Team Lead
Member of Drone Mounting and Power/Temperature
Control Sub-Teams
After getting my Mechanical Engineering Degree, I will
pursue a career in product development in the
biomechanical sphere. With several years of experience
in the engineering field, I am then planning to get a law
degree to become a patent attorney.
Aquzana Mejia - Financial Manager
Plumbing Sub-Team Lead
Member of Optical Cage System and
Power/Temperature Control Sub-Teams
I will be graduating with a major in Mechanical
Engineering and a minor in Engineering Management. I
worked at the BOLD Center throughout my time at CU
Boulder and I hope to gain experience in the engineering
field and return to work with students in the future.
A special thank you to our client, Dr. Caroline Womack, the NOAA
team, and our director, Andrew Goldstein, for all their guidance
and support throughout the ideation and development of
mACES. We would also like to thank Shirley Chessman, Julie
Steinbrenner, Daria Kotys-Schwartz, Greg Potts, Chase Logsdon,
Patrick Maguire, Mark Eaton, Victoria Lanaghan, Lauren Wheeler,
Yvonne Garcia, Keith Regner, Branden Adams, Spencer Green,
Ryan Weatherbee, Sean Wilcox, and Jackson Hootman.
Senior Design Team 25: mACES | May 2021 NOAA Chemical Sciences Laboratory 13You can also read
