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)

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

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

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

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

Tungsten proof mass, glued base, PZT bender Pirelli Piezoelectric Device Staircase Piezoelectric device

Piezoelectric Bimorph Generators

Loa d

Vs

C Rs

Piezoelectric generator

2

2

4 T

eAmP

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

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

Tiny Temp

Piezoelectric Power Generator

Storage Capacitor

Thermistor

Power Circuit

Mote

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

Load Requirements

• Mica2Dot Mote

• 3.3 Input Voltage

• 800 ms ‘Startup Time’

• 45 mW to take temperature reading and transmit information

Bender Platform

Temperature Sensor Hole

PCB Holder

Upper Case

Capacitor Holders

Case TabsLower Case

Bridge

FDM Packaging

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

Proof of Concept #2 (Fire)

Proof of Concept #2 (Fire)

Next Steps: Short Term

Efficiency

Cha

rge

Up

Tim

e

Mica2dot mote

PicoRadio-based node

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

• Thanks to CITRIS, NSF & the California Energy Commission for their sponsorship

Many Thanks!