strain energy harvesting

8/8/2019 Strain Energy Harvesting

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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


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


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

strain energy harvesting

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