Development of Piezoelectric Nanocomposites for Energy ...Feb 23, 2010 · Development of...

Development of Piezoelectric Development of Piezoelectric Nanocomposites for Energy Nanocomposites for Energy Harvesting and SelfHarvesting and Self--SensingSensing

Kenneth J. LohAssistant Professor

Department of Civil & Environmental EngineeringUniversity of California, Davis

The Applied Power Electronics Conference and ExpositionSpecial Presentations

Palm Springs, CA

February 23, 2010

Development of Piezoelectric Nanocomposites for Energy HarvestinDevelopment of Piezoelectric Nanocomposites for Energy Harvesting and Selfg and Self--SensingSensing

The Applied Power Electronics Conference and Exposition – February 23, 2010

University of California, Davis

Slide 2/17

Motivation for Structural Health MonitoringMotivation for Structural Health Monitoring

� Structural systems susceptible to various types of structural damage:

� Excessive loading and natural hazards (e.g., earthquakes, wind, among others)

� Fatigue cracking

� Corrosion and stress-corrosion cracking

� Damage diminishes structural performance, reliability, and safety

Urgent need for long-term sensing technologies to

prevent catastrophic

structural failure




Slide 3/17

Current Inspection ApproachesCurrent Inspection Approaches

� National Bridge Insp. Program:

� Bi-annual inspection

� Inspections are generally visual

� Challenges of visual inspection:

� Subjective with rating variability

� Limited to accessible locations

� Expensive and labor intensive

Typical bridge inspection with crane

� Permanent monitoring systems reserved for “critical” structures:

� Cable-based monitoring systems

� High installation costs:

� $3,000 (US) per channel

� Lower sensor densities are poorly scaled to damage

Central Data

Repository

Simple Sensor

(e.g. accelerometer)

Cable-based structural monitoring system




Slide 4/17

Emerging Sensing TechnologiesEmerging Sensing Technologies

� Advantages:� Low cost

� Dense instrumentation

� Reconfigurable

� Disadvantages:� Point sensors

� Indirect damage detection

� Physics-based models

Wireless Sensors and Sensor Networks

Carbon Nanotube (CNT)-based Thin Films

WiMMS

Wang, et al. (2008)

Intel Imote2

Spencer, et al. (2007)

CNT buckypaper

Prasad, et al. (2004)

CNT Neuron sensor

Kang, et al. (2006)

� Advantages:� Multifunctional by nature

� “Bottom up” assembly

� Conformable

� Disadvantages:� Technology at its infancy

� Scalability

� High costs of nanomaterials

Micro-electromechanical Systems (MEMS)

AD iMEMS

Weinberg (1999)

3-axis accelerometer

Lemkin (1997)

� Advantages:� Miniaturized sensor designs

� Lower power consumption

� Complex sensors/actuators

� Disadvantages:� “Top-down” design

� Expensive fabrication

equipment

� High costs*

� Sensor sensitivity on par with

macro-scale counterpart

� Major drawbacks of these emerging technologies:

� Power demand: require constant power supplies (e.g., batteries or AC power)




Slide 5/17

Piezoelectric MaterialsPiezoelectric Materials

� Piezoelectricity is the transduction between mechanical and electrical energies

� Direct piezoelectric effect:

� Generation of electrical potential due to applied strain (energy harvesting and sensing)

� Inverse piezoelectric effect:

� Generation of applied strain due to applied electrical potential (actuation)

Piezoelectric Materials

Lead zirconate titanate (PZT)Poly(vinylidene fluoride)

(PVDF)

Strain Electric potential

Piezoelectric energy harvester

Rectifier Storage

Generation of electric potential due to strain

MFC piezoelectric actuatorStrain generation due to electric field

� Objective of this research:

� Developa piezoelectric nanocomposite that exhibits high piezoelectricity and mechanical flexibility




Slide 6/17

Zinc Oxide Nanoparticles & NanowiresZinc Oxide Nanoparticles & Nanowires

� Zinc oxide (ZnO) nanoparticles and nanowires:

� Wide band gap (~ 3.4 eV) II-VI semiconductor

� High electron mobility

� Inherently piezoelectric

� Wurtzite asymmetrical crystal structure

� Relative displacement of Zn2+ with respect to O2-

during applied strain

Zinc oxide nanoparticles

Ni, et al. (2007)

ZnO piezoelectricity under different strain modes

Gao, et al. (2009)

Wurtzite crystal structure




Slide 7/17

Fabrication MethodologyFabrication Methodology

� Numerous techniques for fabricating ZnO-based thin films:

� Sputtering, chemical vapor deposition, as-grown nanowire arrays, among others

� Suffer from high fabrication costs, scalability, and limited thicknesses

� Fabrication based on thermal annealing and evaporation:

(a) Non-dispersed and (b) dispersed ZnO-PSS solutions

Low-temperature thermal evaporation

ZnO-PSS-PVA thin film




Slide 8/17

Thin Film MorphologyThin Film Morphology

� Utilize scanning electron microscopy to qualitatively evaluate deposited nanoparticle dispersion and density

� Pristine zinc oxide average particle diameter of 20 nm

� Observe adequate dispersion and dense deposition of nanoparticles




Slide 9/17

Piezoelectricity Experimental SetupPiezoelectricity Experimental Setup

� Experimental validation of ZnO-PSS-PVA thin film piezoelectricity:

� Affix nanocomposite onto Plexiglas cantilever beam

� Instrumented P(VDF-TrFE) piezoelectric polymer as control

� Simultaneously measured generated voltage when beam undergoes free vibration

ZnO-PSS-PVA and PVDF film affixed onto Plexiglas cantilevered beam

Generated potential measured using Agilent 54621D oscilloscope




Slide 10/17

Nanocomposite PiezoelectricityNanocomposite Piezoelectricity

� Free vibration of beam induced by introducing large initial displacement

� Strain gage near support measures strain at top surface of beam

� ZnO-PSS-PVA thin film piezoelectricity compared to commercial P(VDF-TrFE)

� Validated piezoelectric response of proposed thin film

� Exhibited comparable piezoelectricity with commercial P(VDF-TrFE) films

0 0.1 0.2 0.3 0.4 0.5 0.6-6000

-4000

-2000

0

2000

4000

6000

8000

Time [s]

Strain [

µε]

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Time [s]

Voltage [V

]

PVDF

ZnO-PSS

Flexural strain of beam during free vibration Overlay of ZnO-PSS and P(VDF-TrFE) thin film generated voltage




Slide 11/17

Strain Sensing Experimental ValidationStrain Sensing Experimental Validation

� Self-sensing strain sensor validation study:

� Direct piezoelectric effect

� Does not depend on external power supply (e.g., batteries or AC power)

� Self-sensing performance evaluated using free vibration of cantilevered beam

� Magnitude of generated voltage directly related to induced strain

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40.75

0.50

0.25

0

-0.25

-0.50

-0.75

Time [s]

Voltage [V

]

-7,500

-5,000

-2,500

0

2,500

5,000

7,500

Strain [

µε]

Strain

ZnO-PSS

ZnO-PSS-PVA films affixed onto PVC beam Overlay of ZnO-PSS-PVA voltage response v. applied strains




Slide 12/17

Optimization of PiezoelectricityOptimization of Piezoelectricity

� Optimize piezoelectric performance based on zinc oxide weight fraction, ffilm:

� Fabricate 16 unique types of thin films:

� Varied ZnO concentration in PSS solution

� Varied PSS dipersing agent’s concentration

� Fixed 1.0 wt.% poly(vinyl alcohol) solution concentration

%100⋅++

=PVAPSSZnO

ZnOfilm

www

wf

1.0 wt.% PSS 2.5 wt.% PSS 5.0 wt.% PSS

10 mg-mL-1

ZnO in PSSSample A:33.3%

Sample E:22.2%

Sample I:14.3%

20 mg-mL-1

ZnO in PSSSample B:50.0%

Sample F:36.4%

Sample J:25.0%

30 mg-mL-1

ZnO in PSSSample C:60.0%

Sample G:46.2%

Sample K:33.3%

40 mg-mL-1

ZnO in PSSSample D:66.7%

Sample H:53.3%

Sample L:40.0%




Slide 13/17

Comparison of Bulk Film PiezoelectricityComparison of Bulk Film Piezoelectricity

� Simultaneously measured thin film generated voltages during free vibration of the cantilevered beam

� Results show only certain films exhibit good piezoelectric performance

� Optimal ZnO weight fraction is approximately 33% to 37%

� High ZnO weight fraction thin films have high noise floors due to agglomeration

1 1.5 2 2.5 3-10

0

10

[mV-cm]

Sample E

1 1.5 2 2.5 3-10

0

10

[mV-cm]

Sample F

1 1.5 2 2.5 3-10

0

10

[mV-cm]

Sample G

1 1.5 2 2.5 3-10

0

10

Time [s]

[mV-cm]

Sample H

1 1.5 2 2.5 3-40-200

2040

[mV-cm]

Sample I

1 1.5 2 2.5 3-40-200

2040

[mV-cm]

Sample J

1 1.5 2 2.5 3-40-200

2040

[mV-cm]

Sample K

1 1.5 2 2.5 3-40-200

2040

Time [s]

[mV-cm]

Sample L

1.5 1.7 1.9 2.1 2.3 2.5-15

-10

-5

0

5

10

15

Time [s]

[mV-cm]

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

Strain rate [

∆ε-s-1]P

Sample K

Strain rate

1.4 1.6 1.8 2 2.2 2.4-25

-20

-15

-10

-5

0

5

10

15

20

25

Time [s]

[mV-cm]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

Strain rate [

∆ε-s-1]

Strain rate

Sample F




Slide 14/17

LayerLayer--byby--Layer Thin Film FabricationLayer Thin Film Fabrication

� Sequential assembly of oppositely-charged nanomaterials onto a charged substrate

� Bottom-up fabrication methodology

� Incorporation of a wide variety of nanomaterials

� 2.5-dimensional nano-structuring to design multifunctional composites

� Excellent physical, mechanical, and electrical properties:

� Enhance thin film homogeneity

� Alignment of zinc oxide nanowires in polymeric matrix

1. Polycationic monolayerPVA, PANI, etc.

2. Polyanionic monolayerZnO Nanowires-PSS




Slide 15/17

Poling and Molecular AlignmentPoling and Molecular Alignment

� Current piezoelectric materials undergo high-voltage poling during fabrication:

� Alignment of molecular dipole moments to elicit high piezoelectricity

� ZnO-based nanocomposites do not need poling to attain piezoelectricity:

� Future work: employ high voltage (kV) poling to further enhance nanocomposite performance

Poling




Slide 16/17

Summary of Results & Path ForwardSummary of Results & Path Forward

� Zinc oxide nanoparticles as a viable novel material for the development of piezoelectric nanocomposites:

� ZnO inherently piezoelectric

� Dispersed in polyelectrolyte solutions

� Thermal annealing and evaporation for thin film fabrication

� Preliminary results confirm ZnO-PSS-PVA thin film piezoelectricity:

� Affixed nanocomposites to cantilevered Plexiglas and PVC beams

� Measured generated potential under free vibration of the beam

� Validated comparable piezoelectricity with commercial PVDF-based films

� Optimized zinc oxide weight fraction to find optimal 33% to 37% concentrations

� Future research directions:

� High-electric field poling to further enhance piezoelectricity

� Generated potential can find applications in ambient energy harvesting

� Need to enhance its electrical and mechanical properties for actuation/active sensing

Thank You! Thank You! –– QQUESTIONSUESTIONS??

Acknowledgements:

This research is supported by the College of Engineering, University of California, Davis

The authors would also like to express their gratitude to:

�Ms. Yingjun “Irene” Zhao (M.S. Student): Piezoelectric testing

�Mr. Donghyeon Ryu (Ph.D. Student): SEM imaging

�Ms. Donghee Chang (Undergrad): Nanocomposite fabrication

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