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Strain Energy Harvesting forStrain Energy Harvesting forWireless Sensor NetworksWireless Sensor Networks
D.L. Churchill, M.J. Hamel,D.L. Churchill, M.J. Hamel,
C.P. Townsend, S.W. ArmsC.P. Townsend, S.W. Arms
2003 MicroStrain, Inc.2003 MicroStrain, Inc.
Williston, Vermont, USAWilliston, Vermont, USAall rights reservedall rights reserved
www.microstrain.comwww.microstrain.com
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MicroStrain, Inc.
designs & manufactures
micro-miniature, wireless sensors.
MicroStrains Wireless Sensing Networks are Patent Pending
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Deployment of sensors is often limited byDeployment of sensors is often limited by
the high cost of installation & wiring.the high cost of installation & wiring.
Wireless networking enables remote, lowWireless networking enables remote, lowcost monitoring with large numbers ofcost monitoring with large numbers of
sensors.sensors.
IntroductionIntroduction
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Why go wireless with smart
structures?
Easy to retrofit existing structuresEasy to retrofit existing structures
Hardwiring is expensive and time consumingHardwiring is expensive and time consuming
The ingress/egress points of fiber optic tails are subject toThe ingress/egress points of fiber optic tails are subject tobreakagebreakageand get in the way during productionand get in the way during production
Fatigue of lead wires, especially at points of abrupt stiffnessFatigue of lead wires, especially at points of abrupt stiffness change, ischange, isa major headachea major headache
Connectors pose reliability problems in field deployments and caConnectors pose reliability problems in field deployments and cannintroduce high stresses on fibers and lead wiresintroduce high stresses on fibers and lead wires
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Power remains a major issue
Who will replace hundreds of deadWho will replace hundreds of deadbatteries?batteries?
RF transponders require close coupling ofRF transponders require close coupling of
powering/interrogation wandpowering/interrogation wand
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Previous work in piezoelectric
energy harvesting
MIT (Schenk et. al)MIT (Schenk et. al)
Penn State (Penn State (OttmanOttman, et. al), et. al)
UCUC--Berkeley (Roundy et. al)Berkeley (Roundy et. al)
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Objective
To demonstrate a robustTo demonstrate a robuststrain energy harvestingstrain energy harvesting
system for powering ansystem for powering an
embedded wireless sensorembedded wireless sensornetwork without batteries.network without batteries.
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Methods
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Strain Energy Harvesting
(MicroStrain, Inc. patents pending)
Strain energy is stored by rectifyingStrain energy is stored by rectifyingpiezoelectric fiber output into a capacitorpiezoelectric fiber output into a capacitor
bank. When the capacitor voltage reaches abank. When the capacitor voltage reaches a
preset threshold, power is transferred to anpreset threshold, power is transferred to anintegrated wireless sensor.integrated wireless sensor.
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System Block Diagram
(MicroStrain, Inc. patents pending)
Antenna
Mechanical
Energy
MicroControllerA/DConverter
SensorSensorSensorProgram& DataEEPROM
RF Comm.Link
Vcc
Raw DataPacketizedSamples
Energy harvesting,energy storage,
& load control
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Energy Harvesting Controller(MicroStrain, Inc. patent pending)
1 2
Piezo Device
1
2
47uF
1
2
1 2
1 2
1 2
Antenna
MOSFET N
+
Rectifier Storage CapVoltageSensingSwitch
StrainLinkTransmitter
Strain Energy
Vcc
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Piezo power output vs. loadOutput Power vs. Load & Frequency
Piezoelectric Fiber
0.0E+00
1.0E-04
2.0E-04
3.0E-04
4.0E-04
5.0E-04
6.0E-04
7.0E-04
100 1000 10000 100000 1000000 10000000
Ohms
Watts 60Hz
120Hz
180Hz
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Energy harvesting controller w/ buck
converter(MicroStrain, Inc. patent pending)
1 2
Piezo Device
1
2
0.1uF
1
2
1 2
1 2
1 2
Antenna
First Switch
S1
270uF
1
2
Second Switch
S2
Rectifier
Short TermStorage CapSmall valueHigh voltage
Monitoring Device
StrainLinkTransmitteror transceiver
Strain orVibrationEnergy
Vcc
MicroPower
DC-DCConverter
Long TermStorage CapLarge valueLow Voltage
+
C2 C1
Threshold 1
Controller
1. C2 is charged to peak piezo voltage
2. S2 Enables converter at threshold 1
3. Converter transforms high impedance charge inC2 to discharged C1
4. When C1 is charged to threshold 2,controller connects transmitter ortransceiver
5. When charge in C1 is depletedbelow threshold voltage 3,controller disconnects load
LTC1934-1
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Wireless Sensing Node (WSN)(MicroStrain, Inc. patents pending)
Sensor Inputs
multiplexer, PGinstrumentation
amplifier
A/D converter
(16 bit resolution)
Radio Frequency(RF) transmitter
or transceiver
8-bit , low
power,
microcontroller
micropower
voltage regulator
with energy
harvesting
power source
Flash EEPROM
for sensor logging
Sensor signal
conditioning
RF powercontrol
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WSN microtransmitters
(MicroStrain, Inc. patents pending)
Small outline digital wireless sensorSmall outline digital wireless sensor
nodenode
45mW power when transmitting,45mW power when transmitting,
5mW processing, 15 microwatts5mW processing, 15 microwatts
sleepingsleeping AA LiAA Li--Ion battery life 2Ion battery life 2--5 years5 years
D LiD Li--Ion 7Ion 7--10 years10 years
Wireless networking protocolWireless networking protocol
implemented in firmwareimplemented in firmware
16 bit A/D resolution16 bit A/D resolution
Transmission range 1/3 mile LOSTransmission range 1/3 mile LOS
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Software programming (gains, offsets)Software programming (gains, offsets)allows one hardware design to operate withallows one hardware design to operate with
many sensor typesmany sensor types
thermocouples, strain gauges,thermocouples, strain gauges,
magnetometers, capacitive/inductivemagnetometers, capacitive/inductivesensors, magnetic sensors, temperature &sensors, magnetic sensors, temperature &
humidity sensorshumidity sensors
WSN microtransmitters
are programmable
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Test methodology
A composite material specimen wasA composite material specimen waslaminated with unidirectional alignedlaminated with unidirectional aligned
piezoelectric fibers (PZT5A, 250 um,piezoelectric fibers (PZT5A, 250 um,
overall size 13x10x.38 mm). The fibersoverall size 13x10x.38 mm). The fiberswere embedded within a resin matrix forwere embedded within a resin matrix for
damage tolerance (Advanceddamage tolerance (Advanced CerametricsCerametrics,,Lambertville, NJ).Lambertville, NJ).
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Test methodology (continued)
A foil strain gauge (MicroA foil strain gauge (Micro--Measurements,Measurements,Raleigh, NC) was bonded to theRaleigh, NC) was bonded to thepiezoelectric fiber and shunt calibrated.piezoelectric fiber and shunt calibrated.
The specimen was loaded in three pointThe specimen was loaded in three pointcyclic bending (75 to 300cyclic bending (75 to 300 microstrainmicrostrain) using) usinganan electrodynamicelectrodynamic actuator (60,120, andactuator (60,120, and180 Hz).180 Hz).
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Strain energy harvesting setup
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Strain energy harvesting demo
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Strain energy harvesting demo
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Results
The times required for energy storage &The times required for energy storage &data transmission for 10mW of powerdata transmission for 10mW of power
transfer were recorded.transfer were recorded.
For peak strains of 150For peak strains of 150 microstrainmicrostrain, the time, the time
to transmit was 30 to 160 seconds (for 180to transmit was 30 to 160 seconds (for 180to 60 Hz tests).to 60 Hz tests).
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Results
Energy Harvesting Demonstration.Charging Time vs. Frequency and Applied Strain
Peak Applied Strain ()50 100 150 200 250 300 350
Timeto
ReachFullC
ha
rge(Sec.)
0
20
40
60
80
100
120
140
160
180180 Hz Vibration
120 Hz Vibration
60 HZ Vibration
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Applications
smart aerospace, civil, and medicalsmart aerospace, civil, and medicalstructuresstructures
machine monitoringmachine monitoring
smart tiressmart tires
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Navy Applications
Damage controlDamage control
Condition based maintenance ofCondition based maintenance of
electrical and mechanical systemselectrical and mechanical systems
Ship and aircraft structural monitoringShip and aircraft structural monitoring
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Acknowledgments
NSF SBIR Phase II & IIBNSF SBIR Phase II & IIB
Navy SBIR Phase INavy SBIR Phase I BoeingBoeingPhantom WorkPhantom Works Dans Dan ClingmanClingman
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Thank You!Thank You!
To download an MPEG video of
MicroStrains patent pending
strain energy harvestingwireless sensor demo
link to our server at:
http://www.microstrain.com/MSdemoHI.mpeg