TinyTemp Node

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TinyTemp Node
Eli Leland and Elaine Lai
Professor Paul Wright, Sue Mellers, Michael
Montero, Brian Otis, Rob Scewczyk, and Shad Roundy
BWRC Winter Retreat 2004
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Energy Scavenging
GOAL Design an infinite life power source for a
sensor node APPLICATION Wireless Sensor
Networks 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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Battery, Solar, and Vibrational Energy
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Common Sources of Vibrations
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The Piezoelectric Effect

• Constitutive Equations

Usable Modes of PZT
d strain s stress Y Youngs modulus d
piezoelectric coeff. D electrical
displacement e dielectric constant E electric
field
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Piezoelectric Bimorph Generators
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Wooden Stairs
Peak Frequency at 26.8 Hz
FFT of frequencies
Power generator must match peak frequency
of vibration source for max power output
Vibrations from walking down stairs
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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 peakto-peak output from bender when someone
walks down the stairs
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Tiny Temp
Storage Capacitor
Power Circuit
Mote
Piezoelectric Power Generator
Thermistor
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Power Circuit
Voltage Out to Mote
Voltage In from Bender
Rectifier
Voltage Regulator
Storage Capacitor
Comparator (3.5V 5V)

Regulator
Enable
VIN Piezo Bender
Vout 3.3V DC
Comparator





CST
6600µF
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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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FDM Packaging
Upper Case
Temperature Sensor Hole
Capacitor Holders
PCB Holder
Bridge
Bender Platform
Power Circuit PCB
Case Tabs
Lower Case
Capacitors
Mote PCB
Bender Mass
PZT Bender
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Proof of Concept

• Procedure
• 3 people ran on the stairs for 40 minutes

• Results
• 3.28 V for 816 ms
• 2 temperature readings transmitted

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Next Step Short Term
Mica2dot mote
Charge Up Time
PicoRadio-based node
Efficiency
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Next Step Long Term
Design a variable resonant frequency MEMS bender
which adapts to vibration sources with different
peak frequencies.
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Many Thanks!

• Thanks so much to Professor Paul Wright, Sue
  Mellers for their support and help!
• Thanks also to Brian Otis, Rob Szewczyk, Mike
  Montero, Elizabeth Reilly, and Shad Roundy for
  their advice and continuous support!
• Thanks to the California Energy Commission for
  their sponsorship