A slideshow detailing a MEMS Accelerometer for use in arrows

1. Smart Projectiles:
Using MEMS Accelerometers to
Capture and Examine Arrow
Behavior
Austin R. Sams
ES 176 Final Project
Harvard University

2. Problem Statement
• Limited options for collecting arrow flight data
• Current methods:
– Expensive
– Inaccurate
– Disrupt normal flight dynamics An accelerometer attached
externally to an arrow shaft.
[1]

3. Solution
• Capacitive MEMS
accelerometer attached to a
normal arrow nock
– Compatible with all arrows
– Usable by professionals and
recreational archers alike
– Low weight and placement
minimizes flight disruption
– Minimal material and
fabrication cost
– Comb formation ensures
reliable measurement
Port for
charging
and data
collection
Normal
arrow nock
MEMS
accelerometer and
electrical
components

4. Application
Archer
shoots
Device
records
data
Archer
retrieves
arrow and
device
Archer
analyzes
data
Archer
improves
technique
• Archers can use data
recorded from device to
improve their form and
technique
• Extremely useful for
beginners
– Technique is harder to fix
once learned
• And professionals
– Allows for fine-tuning of
form in ways previously
impossible

5. 1
4
2 3
6 7
9 10
8
14 15 16
17 18
11 12
5
13
19
Fabrication (X and Y Axes)
Photoresist
Metal
Nitride
Silicon

6. 21
24
22 23
25 26 27 28
29 3130 32
33 34 35 36
37 38 39 40
41 42 43 44
Fabrication (Z Axes)Photoresist
Metal
Sacrificial Layer
Silicon

7. Device Measurement
• Fixed voltage applied to metal
combs
• Current = Signal
• Collected via connection
to yellow metal comb shown
in cross section
• Mass is removed from
mobile comb
(orange) to calibrate
Metal
Silicon
Silicon
tethers
[2]

8. Summery
• Capacitive 3-axis comb accelerometer
• Attached to nock
– Accelerometer fits inside arrow shaft
• Measures forces experienced by arrows
• Data used to perfect technique
• Manufactured primarily with silicon and metal

9. Achievements
• Unimpeded flight dynamics
• Improved Measurement Accuracy
– Calibrated for accelerative forces experienced by
arrows
• Unprecedented compatibility
– Archer can place and reuse the device in any
arrow

10. References
[1] http://www.gcdataconcepts.com/images/setup1.jpg
[2] http://ic-garden.cn/wp-content/uploads/3-axis-Accelerometer.png (With edits)
[3] Zhang, D., & Wei, B. (2017). Advanced Mechatronics and MEMS Devices II. Cham: Springer
International Publishing.
[4] http://www.gracey.co.uk/downloads/accelerometers.pdf
[5] F. Chollet, H. Liu, A (not so) short introduction to MEMS (http://MEMScyclopedia.org/
introMEMS.html (18.2.2008))
[6] Andrejašicˇ, M. (2008). MEMS ACCELEROMETERS. Lecture presented at the University of Ljubljana.
[7] Habbal, F. (2017, November). Capacitance Sensing and Actuation. Lecture presented in Harvard
University.
[8] http://www.analog.com/en/products/MEMS/accelerometers/adxl346.html#product-overview
[9] Donahoe, R. V., Vcelak, J., Sabin, P. C., & Avis, J. E. (2015). U.S. Patent No. 9,005,057. Washington, DC:
U.S. Patent and Trademark Office.
[10] Frequenztechnik, M. (2001). Piezoelectric Accelerometers: Theory and Application. Retrieved
from http://www.gracey.co.uk/downloads/accelerometers.pdf
[11] Meyer, H. O. (n.d.). Applications of Physics to archery. Retrieved November 6, 2017, from https://
arxiv.org/pdf/1511.02250.pdf