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Max Perez

MicroSystems LabMechanical and Aerospace Engineering

University of California, IrvineIrvine, CA

perezma@uci.eduhttp://mems.eng.uci.edu

Micromachined Optical Accelerometers for Serial Sensor Networks

University of California - IrvineUniversity of California - Irvine

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Micro-Opto-Electro-Mechanical Systems(MOEMS)

Manipulating the world at the level of the wavelength

For Optical Communications For Consumer Electronics

MotivationMotivation

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Project Goals

Light OSAPower DAQ

• Conventional Systems– Electrical– Multiple power /detection lines– Subject to EM interference

– Low Sensitivity

A Distributed Acceleration SensorDistributed Acceleration Sensor network

100mVg

• Proposed System– All Optical– Single source/signal line– Immune to EM interference

– High Sensitivity 15Vg

Monitor

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Applications

A system of arrayed inertial sensors that are:

•Highly Sensitive Highly Sensitive •Spatially DistributableSpatially Distributable

•SimpleSimple•RobustRobust

Vibration Monitoring

Structure System Identification

Structural Health Monitoring

MotivationMotivation

Could be used for:

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FPI-based Accelerometer Concepts

Broadband Light

INi f OUTcSignal

Ao

I I

A

Ao

FPI-Based Accelerometer•Proof mass (m) suspended (stiffness k) relative to reference plate (damping c)•Reference plate attached to measured structure

System Operation•Interferometric fringe peak placement indicates inertial load (acceleration)

BackgroundBackground

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Device Fabrication

FabricationFabrication

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PDMS Elastomeric Suspension

Elastomeric Suspension: •Low Stress

Minimize plate bowing•No surface deposited mechanical layers

Minimize surface roughness

PDMS Elastomer: •High Compliance (E ~ 1MPa)•Stable (Tg ~ -125C)•Cleanroom compatible•Tough

Unstreched / Stretched PDMS Elastomer

FabricationFabrication

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The Trunnion Mode

Reference

Sense

Sense Mode•Normal or ‘out-of-plane’ mode

•Desire low stiffness for sensitivity

Trunnion Mode•Out-of-plane tosional mode•Activated by:

•Asymmetric suspensions (sense mode coupled)•Rotational Acceleration

I

Reference

Sense

highk highk

lowklowklowk

lowk

BackgroundBackground

Most Pressing Concern => Dynamic parallel plate error

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Composite Fabrication

~ACV

FAiMTa: •Field-Aided Micro-Tailoring technology•Electrically aligned particles in a polymer matrix act as short fibers

•Developed by Geun Hyung Kim and Yuri M. Shkel (U. Wisconsin-Madison)Polymeric composites tailored by electric fieldsJournal of Materials ResearchVol. 19, #4, No. 4, Apr 2004

FabricationFabrication

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Composite Results

Alignment: •Simple application of voltage results in particle alignment with structure geometry

•Iron fillings •500-900V, ~0.5mm gap, 5Hz•10% Fe : PDMS

~

500-900V @5Hz

ResultsResults

=> 8000X increase in 8000X increase in trunnion stiffness trunnion stiffness

=> 2X increase in 2X increase in sense stiffness sense stiffness

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Serialization Concepts

Serialized Operation: •Define sensor channels of R-high for each FPI •Creates an Intrinsic Wavelength Division sensor Network

INi f OUTcSignals

I I

A B

Ao B

oR

Ao B

o

R

Ao B

o

Sensed VibrationsBackgroundBackground

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Funding/Acknowledgments

•The National Science Foundation Grant CMS-0223050, program manager Dr. Shih-Chi Liu.

•Duration: Three years (Currently at 2/3 completion)

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Questions?

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The Composite Shear Suspension

Characteristics•Low volume fractions

=>greatest effects!•Minimal effect on sense axis stiffness

torsional v Hk k k

BackgroundBackground

0.5 mm

0.25 mm 1.0 mm

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

1

2

3

4

5

6x 10

4

Inclusion volume fraction

k Mo

de/k

Mo

de

(vf=0

)

Fractional Change in Modal Stiffness

In-Plane

Out-of-Plane

Trunnion