Industrial and Social Applications of Wireless Sensor Nets with “Energy Scavenging”
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Transcript of Industrial and Social Applications of Wireless Sensor Nets with “Energy Scavenging”
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Industrial and Social Applications of Wireless Sensor Nets with “Energy Scavenging”
With a case study on “battery-less” tiny-temperature nodes for “smart building applications”
Paul Wright, Jan Rabaey, David Culler, Eli Leland, Elaine Lai, Sue Mellers, Michael Montero, Jessy Baker, Brian Otis, Rob Scewczyk, and Shad Roundy (now at The Australian National University)
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Energy Scavenging
GOAL: Design an ‘infinite life’ power source for a sensor node
APPLICATION: Wireless Sensor Networks in Buildings
VISION: Millions of self-powered sensor/transceivers, each the size of a speck of dust, will infiltrate a building and create a smart environment
PROOF OF CONCEPT: To power a Mica2Dot Mote using vibrations from a wooden stairway in the Naval Architecture Building
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Continous Power / cm3 vs. Life Several Energy Sources
0
1
10
100
1000
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Years
mic
roW
atts
Lithium
Alkaline
Lithium rechargeableZinc air
NiMH
Solar
Vibrations
Battery, Solar, and Vibrational Energy
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Vibration SourceFrequency
of Peak (Hz)
Peak Acceleration
(m/s2)
Kitchen Blender Casing 121 6.4
Clothes Dryer 121 3.5
Door Frame (just after door closes) 125 3
Small Microwave Oven 121 2.25
HVAC Vents in Office Building 60 0.2-1.5
Wooden Deck with People Walking 385 1.3
Bread Maker 121 1.03
External Windows (size 2ftx3ft) next to a Busy Street
100 0.7
Notebook Computer while CD is Being Read
75 0.6
Washing Machine 109 0.5
Second Story of Wood Frame Office Building
100 0.2
Refrigerator 240 0.1
Common Sources of Vibrations
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The Piezoelectric Effect
• Constitutive Equations
dEY
dED = strain = stressY = Young’s modulusd = piezoelectric coeff.D = electrical displacement = dielectric constantE = electric field
Usable Modes of PZT
V-
+
3
12
33 Mode
31 Mode
FV+-
3
12
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Tungsten proof mass, glued base, PZT bender Pirelli Piezoelectric Device Staircase Piezoelectric device
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Piezoelectric Bimorph Generators
Loa d
Vs
C Rs
Piezoelectric generator
2
2
4 T
eAmP
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Wooden Stairs
Power generator must match peak frequency of vibration source for max power output
FFT of frequencies
Vibrations from walking down stairs
Peak Frequency at 26.8 Hz
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Bender Design
Characteristics
• Piezoelectric: PZT
• Tungsten Alloy Mass: 52 g
• Beam Dimensions:
1.25” x 0.5” x 0.02”
Behavior
• Resonant Frequency: 26.8 Hz
• Power Output: 450 μW
40V peak–to-peak output from bender
when someone walks down the stairs
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Tiny Temp
Piezoelectric Power Generator
Storage Capacitor
Thermistor
Power Circuit
Mote
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6600μF
Enable
Co
mp
ara
tor
Re
gu
lato
r
Vout = 3.3V DC
CST
~ VIN
Piezo Bender
Rectifier
Voltage Out to Mote Voltage In
from Bender
Voltage Regulator
Comparator (3.5V – 5V)
Storage Capacitor
Power Circuit
Re
ctifi
er
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Load Requirements
• Mica2Dot Mote
• 3.3 Input Voltage
• 800 ms ‘Startup Time’
• 45 mW to take temperature reading and transmit information
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Bender Platform
Temperature Sensor Hole
PCB Holder
Upper Case
Capacitor Holders
Case TabsLower Case
Bridge
FDM Packaging
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Proof of Concept #1 (CEC)Procedure
• 3 people ran on the stairs for 40 minutes
Capacitor Discharging
Power Out
816 ms
5 V
3.5 V
Results
• 3.28 V for 816 ms
• 2 temperature readings transmitted
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Proof of Concept #2 (Fire)
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Proof of Concept #2 (Fire)
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Next Steps: Short Term
Efficiency
Cha
rge
Up
Tim
e
Mica2dot mote
PicoRadio-based node
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Next Steps: Long Term
Design a variable resonant frequency MEMS bender which adapts to vibration sources with different peak frequencies.
SiSiO2
PDMSTMSM
Si SiO2
Si3N4
PZT Platinum
Aluminum
Inertial Mass
Substrate
Cantilever Beam
Flip and Bond Assembly
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• Thanks to CITRIS, NSF & the California Energy Commission for their sponsorship
Many Thanks!