synched e harvesting wireless sensors for sensors expo 2009 dist

Synchronized Energy Harvesting Sensor Networks

S.W. Arms*, J.H. Galbreath, C.P. Townsend,S.W. Arms*, J.H. Galbreath, C.P. Townsend,D L Ch hill N Ph ^D L Ch hill N Ph ^D.L. Churchill, Nam Phan^D.L. Churchill, Nam Phan^

^Division ^Division Head (Acting) Head (Acting) StructuresStructuresStructures DivisionStructures Division AIR 4 3 3 2AIR 4 3 3 2

* President, CEOMicroStrain Inc Structures Division Structures Division -- AIR 4.3.3.2AIR 4.3.3.2

Naval Naval Air Systems CommandAir Systems CommandPatuxentPatuxent River, MarylandRiver, Maryland

MicroStrain, IncWilliston, [email protected].

Proc. Sensors Expo, Rosemount, IL, June 9h, 2009 © microstrain, inc. 2009 all rights reserved

Sensing Sensing the Futurethe Futurethe Futurethe Future

Wireless sensors, in the billions, will become Wireless sensors, in the billions, will become deeply embedded within structures & deeply embedded within structures & machines. machines.

Sensed information will be automatically Sensed information will be automatically compressed & forwarded for condition compressed & forwarded for condition based maintenance.based maintenance.

© microstrain, inc. 2009

The Economist April 28th – May 4th

2007“We’re wearing out…plan to replace us soon”

2007

Problem:Problem:Problem:Problem:

B hB h ill lill l llllBut who But who will replace will replace all all thosethose dead batteries?dead batteries?those those dead batteries?dead batteries?


Solution:Solution:Solution:Solution:•• HarvestHarvest & store energy from strain& store energy from strain•• Harvest Harvest & store energy from strain, & store energy from strain,

vibrationvibration, , motion, thermal gradients, motion, thermal gradients, light electromagnetic fieldslight electromagnetic fieldslight, electromagnetic fieldslight, electromagnetic fields

•• UseUse power management to balance thepower management to balance the•• Use Use power management to balance the power management to balance the energy “checkbookenergy “checkbook””

•• Use Use embedded processors to compress embedded processors to compress data computedata compute fatigue lifefatigue lifedata, compute data, compute fatigue life fatigue life


Bell M412 InstallationBell M412 InstallationStrain Strain energy

harvesting wirelessharvesting wireless pitch link installed on Bell M412 Feb 2007 (1st time ever)(1st time ever)

© microstrain, inc. 2009Patents pending

FlightFlightFlight Flight TestTestResultsResults

•• Passed Passed –– inin--flight EMI evaluationsflight EMI evaluations–– rotor track & balance verificationrotor track & balance verification

•• Data were collected wirelessly on board the Data were collected wirelessly on board the aircraft with no indication of data lossaircraft with no indication of data loss


Objective:Objective: Demonstrate a synchronized, Demonstrate a synchronized, energy harvesting wireless structural healthenergy harvesting wireless structural healthenergy harvesting, wireless structural health energy harvesting, wireless structural health monitoring & reporting system for helicopters monitoring & reporting system for helicopters


D t il dD t il dDetailedDetailedObjectivesObjectivesObjectivesObjectives

•• Develop a wireless data aggregator (WSDA), capable ofDevelop a wireless data aggregator (WSDA), capable ofDevelop a wireless data aggregator (WSDA), capable of Develop a wireless data aggregator (WSDA), capable of synchronizing wireless/hardsynchronizing wireless/hard--wired sensor networks and wired sensor networks and aggregating data with open architecture communications aggregating data with open architecture communications to HUMSto HUMSto HUMS.to HUMS.

•• Document time synchronization accuracyDocument time synchronization accuracy•• Develop a high sample rate wireless sensor node forDevelop a high sample rate wireless sensor node forDevelop a high sample rate wireless sensor node for Develop a high sample rate wireless sensor node for

helicopter gearbox apps.helicopter gearbox apps.•• Demonstrate system compatibility with a scalable Demonstrate system compatibility with a scalable

t k f ti RFIDt k f ti RFIDnetwork of active RFIDs.network of active RFIDs.

Communicating gWirelesslyy

MicroStrain’sMicroStrain’s Wireless Sensor NetworksWireless Sensor Networks(( ))(IEEE (IEEE 802802..1515..44))

Time Division Multiple Access (TDMA) &

Frequency Division Multiple Access (FDMA)


( )Carrier Sense

Multiple Access (CSMA)

How many nodes will thisHow many nodes will thisHow many nodes will this How many nodes will this low power TDMA system low power TDMA system

support?support?

Aggregate sample rate (Hz): Aggregate sample rate (Hz): 10 000/total no sensor channels10 000/total no sensor channels~10,000/total no. sensor channels~10,000/total no. sensor channels

i 100 i li 100 i l hh ddi.e.: ~100 single i.e.: ~100 single chch nodes can nodes can transmit data at 100 samples/sectransmit data at 100 samples/sec


Methods:Methods:Timing Engine Timing Engine

Previous WorkPrevious WorkPrevious WorkPrevious Work

•• Le Cam, V., “Synchronization of Wireless Sensors: Le Cam, V., “Synchronization of Wireless Sensors: Review of Methodologies, Experience Feedback of the Review of Methodologies, Experience Feedback of the Very Precise GPS Solution” Third European WorkshopVery Precise GPS Solution” Third European WorkshopVery Precise GPS Solution , Third European Workshop Very Precise GPS Solution , Third European Workshop on Structural Health Monitoring, July 5on Structural Health Monitoring, July 5--7, Granada, 7, Granada, Spain, July 5Spain, July 5--7, 20067, 2006

Placed GPS receivers at each wireless node Placed GPS receivers at each wireless node to achieve absolute precision of 1 to achieve absolute precision of 1 microsecondmicrosecond

Data Aggregator collects gg gtime synchronized dataw/ 4 GB removable flash memory

All wireless nodes use precision nano-power real time clock p p(RTC) with +/- 3 ppm (-40 to +85 deg C) time reference.

Wired inertial sensor uses same time reference as DataWired inertial sensor uses same time reference as Data Aggregator.

’ C Gl b l SData Aggregator’s RTC uses Global Positioning System (GPS) as time reference. Data Aggregator sends beacons to update time sensing node’s time keepersp g p


Timing Engine OverviewTiming Engine OverviewTiming Engine OverviewTiming Engine Overview

•• Ti iTi i i id thi id th•• Timing Timing engine provides the engine provides the following:following:•• 11pulse per second pulse per second

(PPS) (PPS) Synch ClockSynch Clock•• Trigger LineTrigger Line

CANController

CAN NodesCAN NodesCAN NodesCAN Nodes

GPSReceiver

Ti iTrigger LineTrigger Line•• Extremely accurate Extremely accurate

absolute time keeperabsolute time keeper

•• The The 1 1 PPS synchronization PPS synchronization Wireless Wireless NodesWi l N d

Wireless Controller

Wireless NodesWireless NodesWireless NodesWireless NodesTiming Engine

yyclock is distributed to CAN clock is distributed to CAN and and 802802..1515..4 4 network network controllers. (green)controllers. (green)

•• In turn network controllersIn turn network controllers

µP Corerunning Linux

Wireless Controller

Wireless NodesWireless NodesWireless NodesWireless Nodes

USB Node

USB N d

SYNCH CLK & TRIG•• In turn, network controllers In turn, network controllers

propagate the propagate the 11PPS clock to PPS clock to nodes through a highnodes through a high--priority priority broadcast beacon packet. broadcast beacon packet. (blue and orange)(blue and orange)

RS-232 Node

RS-232 Node

USB Node

Wireless Synch Beacon

CAN Synch Mechanism


Harvesting gEnergygy

Vibration vs. Strain Energy Vibration vs. Strain Energy Harvesters:Harvesters:gygy

G b R t EGearbox Resonant Energy Harvester Output: 37 mWVolume: 4.3 cc Weight: 38 gramsWeight: 38 grams

Flexible Strain Harvester Output:~14 uW per sq cm (90 uW per sq in)@ 200 uE p-p, 4.3 Hz@ p p,On Bell 412 Pitch Link 12 patches delivered ~ 1 uW/lb (200-400 uW)Weight: 4.3 gr/patch*12 patches = 52 gr


Sensing strainSensing strain, force pressureforce, pressure, torque vibrationtorque, vibration,

temperaturetemperature

WirelesslyWirelessly

MicroStrain’s embedded firmware MicroStrain’s embedded firmware optimized for strain gaugesoptimized for strain gauges

•• Wireless offset adjust Wireless offset adjust •• Wireless gain adjustWireless gain adjust•• Wireless control of sample ratesWireless control of sample ratese ess co t o o sa p e atese ess co t o o sa p e ates•• Wireless shunt cal Wireless shunt cal –– bits to bits to microstrainmicrostrain•• LowLow tempco’stempco’s::•• Low Low tempco stempco s: :

offset: offset: --.007%/C , span: .007%/C , span: ..015%/015%/C C •• Mux’dMux’d pulsed & regulated bridge excitationpulsed & regulated bridge excitation•• Mux dMux d, pulsed & regulated bridge excitation, pulsed & regulated bridge excitation


Wireless Pitch Link StrainWireless Pitch Link Strain& Load Sensing Nodes& Load Sensing Nodes

Fractal antennas

Shear-Link ™


Patents Pending

Pitch Link Consumption for Various Pitch Link Consumption for Various O ti M dO ti M dOperating Modes:Operating Modes:

•• Mode 1: Wait until stored energy crosses thresholdMode 1: Wait until stored energy crosses threshold:: nanoampnanoamp•• Mode 1: Wait until stored energy crosses thresholdMode 1: Wait until stored energy crosses threshold: : nanoampnanoampcomparator turns circuit “on”. Predetermined amount of data comparator turns circuit “on”. Predetermined amount of data transmitted. transmitted. Consumption varies with available energy, timekeeper Consumption varies with available energy, timekeeper draws 9 microwatts.draws 9 microwatts.

•• Mode 2: Data logged to memory:Mode 2: Data logged to memory: Download Download at at end end of test. of test. Consumption @ 32 samples/sec: ~100 Consumption @ 32 samples/sec: ~100 uwattsuwatts

•• Mode 3: Transmit if energy allows:Mode 3: Transmit if energy allows: Log 100 samples, check stored Log 100 samples, check stored energy, transmit if possible. energy, transmit if possible. Consumption with 32 samples/sec: ~250 Consumption with 32 samples/sec: ~250 uWuW, drops to 100 , drops to 100 uWuW without radio transmission.without radio transmission.

•• Mode 4: Real Time Transmission:Mode 4: Real Time Transmission: Log 100 samples, then transmit. Log 100 samples, then transmit. Consumption with Consumption with 32 samples/sec: ~250 32 samples/sec: ~250 uwattsuwatts..


Wireless Wireless Bridge (Strain) Bridge (Strain) S tS t DiDiSystem System DiagramDiagram

Timekeeper

© microstrain, inc. 2009(patents pending)

High Speed Wireless NodeHigh Speed Wireless NodeHigh Speed Wireless NodeHigh Speed Wireless Node•• Programmable sample rates, Programmable sample rates, g pg p

offsetsoffsets, gains, , gains, & anti& anti--aliasing aliasing filtersfilters

•• A/D resolution:A/D resolution: 1616 bitsbits•• A/D resolution: A/D resolution: 16 16 bitsbits

•• 100 KHz A/D 100 KHz A/D sampling sampling rate (3 rate (3 chch, simultaneous, full diff), simultaneous, full diff)

•• Event consists of 125,000 Event consists of 125,000 samples (or 0.4 seconds at samples (or 0.4 seconds at 100 KHz sample rate)100 KHz sample rate)100 KHz sample rate)100 KHz sample rate)

• Stores 1 million samples on 2 MB embedded, non-volatile memory

© microstrain, inc. 2009Patents Pending

Energy Energy ConservationConservation::

work to balance the work to balance the “ h kb k”“ h kb k”“energy checkbook”“energy checkbook”


Powering down between Powering down between ggsamples greatly reduces samples greatly reduces power consumptionpower consumptionpower consumptionpower consumption


Embedded routines allowEmbedded routines allowEmbedded routines allowEmbedded routines allowmicroelectronics tomicroelectronics to

adapt to adapt to th t f il blth t f il blthe amount of available the amount of available

energyenergyenergy energy


Average power consumption Average power consumption g p pg p p((mWmW) for 50 ) for 50 kSPSkSPS data data

i itii itiacquisitionacquisition

Acquisition Interval Sample 1 min 10 min 1 hour 1 daySample duration (sec)

y

0.1 1.67 0.22 0.09 0.060.5 8.09 0.86 0.19 0.071 0 16 1 1 66 0 33 0 07


1.0 16.1 1.66 0.33 0.07

Results:

Wireless Network Timing -

How quickly are broadcast commands processed?

Broadcast Synchronization Results (4 nodes)

• Waveform at right shows Scope tracesg4 captured waveforms representing the start of sampling for each of the 4 p gnodes.

• Note that each node• Note that each node starts sampling at slightly different times. In this specific case the lastspecific case, the last node started sampling ~3.4 microseconds (µsec) after the first nodeafter the first node.


Broadcast Synchronization Results

Scope traces• After repeating the

broadcast trigger d 250 ti th

Scope traces

command 250 times, the timing differences are bound within an envelope of ±4 µsec. This represents the initial synchronization accuracysynchronization accuracy for the group of nodes.


Results:Results:Results:Results:

Wired & Wireless Network Wired & Wireless Network Timing: Timing:

How well syncedHow well synced w/w/How well synced How well synced w/ w/ beaconing?beaconing?gg

Saw tooth Input, room temp.2 d 2 h @ t t2 nodes, 2 hours @ room temperature,

clock drift: ~325 us (45 ppb) between the two sensor nodesTiming beacon sent once – at start of test only.

Node 1 & Node 2 Sensor Data Overlay

2

2.5

3

(V)

1

1.5

2

ensor Inp

ut

0

0.5

7199 94 7199 96 7199 98 7200 00 7200 02 7200 04 7200 06 7200 08

Se

7199.94 7199.96 7199.98 7200.00 7200.02 7200.04 7200.06 7200.08

Time (seconds)


Saw Tooth Input, -40 to +85 deg C 2 nodes 2 hours w/ 10 Hz Sawtooth: clock drift 5 71 msec (793 ppb)2 nodes, 2 hours, w/ 10 Hz Sawtooth: clock drift 5.71 msec (793 ppb)

w/ 1 Hz Sawtooth: clock drift 5.04 msec (700 ppb)Timing beacon sent once – at start of test only.

Node 1 & Node 2 Sensor Data Overlay

2

2.5

3

(V)

1

1.5

2

Sensor In

put

0

0.5

7199.70 7199.72 7199.74 7199.76 7199.78 7199.80 7199.82 7199.847199.70 7199.72 7199.74 7199.76 7199.78 7199.80 7199.82 7199.84

Time (seconds)


Timing Results SummaryTiming Results Summary

• Synch beacon sent once at start of test only providedSynch beacon sent once - at start of test only - provided ~5 ms timing accuracy over 2 hours, subjected to -40 to +85 C.

• Synch w/ periodic (60 sec) beacon provided +/- 50 us timing accuracy over 13 hours, subjected to -40 to +85 C.g y , j

• Conservative approach: send resync beacon every 5 minutes to achieve sub millisecond timing accuracy whenminutes to achieve sub-millisecond timing accuracy when temperatures are extreme and changing rapidly.


ConclusionsConclusions

•• Accurate time synch developed for wirelessAccurate time synch developed for wireless

Conclusions Conclusions

Accurate time synch developed for wireless Accurate time synch developed for wireless sensor nets that doesn’t require GPS.sensor nets that doesn’t require GPS.

•• System supports high sample rate (50 KHz) System supports high sample rate (50 KHz) sensor nodes, and active RFID tagssensor nodes, and active RFID tags

•• Provides open architecture interface to HUMS Provides open architecture interface to HUMS to eliminate wires and enable reductions into eliminate wires and enable reductions into eliminate wires and enable reductions in to eliminate wires and enable reductions in weight and complexity.weight and complexity.

Patents pending © microstrain, inc. 2009

Conclusions (continued)Conclusions (continued)

•• High sample rate nodes can operateHigh sample rate nodes can operate

Conclusions (continued) Conclusions (continued)

•• High sample rate nodes can operate High sample rate nodes can operate perpetually, without batteries, from gearbox perpetually, without batteries, from gearbox vibration alone.vibration alone.

•• Supports remote reporting over mobile phone Supports remote reporting over mobile phone networks (satellite reporting currently under networks (satellite reporting currently under development)development)development). development).

•• These capabilities, coupled with appropriate These capabilities, coupled with appropriate wireless security methods, will enable criticalwireless security methods, will enable criticalwireless security methods, will enable critical wireless security methods, will enable critical structural sensor data to be managed remotely, structural sensor data to be managed remotely, securely, and automatically.securely, and automatically.

Patents pending © microstrain, inc. 2009

Need More Info?Need More Info?Need More Info?Need More Info?

•• Sensors Expo Booth 1005Sensors Expo Booth 1005

•• www.microstrain.comwww.microstrain.com

•• www.microstrain.com/customerwww.microstrain.com/customer--docs.htmdocs.htm

•• [email protected]@microstrain.com@@

Acknowledgements:Acknowledgements:

Navy/NAVAIR Navy/NAVAIR SBIR PH II SBIR PH II ONR BAAONR BAAONR BAA ONR BAA

Bell HelicopterBell Helicopterpp

Thank You!Thank You!

References:References:•• M.J. Hamel et al., Energy Harvesting for Wireless Sensor Operation and Data M.J. Hamel et al., Energy Harvesting for Wireless Sensor Operation and Data

Transmission, Transmission, US Patent Appl. Publ. US 2004/0078662A1, filed March US Patent Appl. Publ. US 2004/0078662A1, filed March 20032003

D L Ch hill l S i E H i f Wi l S N k• D.L. Churchill et al., Strain Energy Harvesting for Wireless Sensor Networks, Smart Structures and Materials, SPIE, vol. 5005, pp. 319–327, 2003

•• S.W. Arms et al., Shaft Mounted Energy Harvesting System for Wireless S.W. Arms et al., Shaft Mounted Energy Harvesting System for Wireless dd l bll bl

g gg gSensor Operation and Data Transmission, Sensor Operation and Data Transmission, US Patent Appl. Publ. US US Patent Appl. Publ. US 2005/0017602A1, filed Jan 2004 2005/0017602A1, filed Jan 2004

• S.W. Arms et al., Wireless Strain Measurement Systems for Aircraft TestWireless Strain Measurement Systems for Aircraft Test, , yy ,Aerospace Test Expo, Anaheim, CA, Nov 2006

• S.W. Arms et al., Energy Harvesting Wireless Sensors for Helicopter Damage Tracking, American Helicopter Society Annual Forum, Phoenix, AZ, May 2006g, p y , , , y

•• S.W. Arms, C.P. Townsend, D.L. Churchill, M. S.W. Arms, C.P. Townsend, D.L. Churchill, M. AugustinAugustin, , D.YearyD.Yeary, P. Darden, , P. Darden, N. Phan, N. Phan, Tracking Pitch Link Dynamic Loads with Energy Harvesting Wireless Tracking Pitch Link Dynamic Loads with Energy Harvesting Wireless SS AHS 63 d A l F Vi i i B h VA M 2007AHS 63 d A l F Vi i i B h VA M 2007Sensors, Sensors, AHS 63nd Annual Forum, Virginia Beach, VA, May 2007AHS 63nd Annual Forum, Virginia Beach, VA, May 2007

synched e harvesting wireless sensors for sensors expo 2009 dist

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