Characterization of piezoelectric biopolymer nanofibers for energy harvesting applications

1. NGUYEN THAI CUONG
Nanoscale characterization of piezoelectric bio-
based polymers for their energy harvesting
applications
Supervisors: Philippe Leclere, Sophie Barrau
Mons - July 2021

2. 12 May 2023 PhD Defense - Mons 2
Evolution of smart wearables promotes the use of self-powered systems
"We don't want humans to be aware of
what they are wearing. It has to be
self-contained piece that can charge
itself, store energy and perform useful
functions."
Maksim Skorobogatiy, physicist at
Ecole Polytechnique de Montreal.
H-index: 53 with more than 10000
citations.
Phase 4
Implantable
Phase 1
Accessory
Phase 3
Patchable
Phase 2
Portable
2016 2017 2020 2025
• Body implantable
• Low weight
• Self-sustain
• Safety to human body
Source: ID Tech, Smart Wearables: Reflection and Orientation paper,
European Commission, 2016.
• Flexible/Stretchable
• Ultrathin
• Conformal to skin
• Textile-Integrated
• Reduced in size
• Integrated to electronic
• Accessory-type devices
• Low-power
• Conformal to body
Issues
and
Shapes

3. A typical ceramic-based
piezoelectric harvester
12 May 2023 3
Piezoelectric materials - great candidates for wearable, self-powered devices
Piezoelectric effect
Force
Biochemical
sources
Radiant
sources
Thermal
sources
Mechanical
sources
µW/cm
2
or
µW/cm
3
100µW
100000
10000
1000
100
10
1
0,1
Inorganic piezoelectric materials
1µW 10µW 100µW 1mW 10mW 100mW 1W+
Smart Watch
~5µW
LCD clock
~500µW
Hearing aids
~2mW
Headphone
~60mW
Smartphone
~2W
Maurya, D., Yan, Y. & Priya, S. J.et al. Adv. Mater. Clean Energy 50–71 (2015).
The need for alternative piezoelectric material which is
biocompatible, flexible and cheap!
Brittle
Toxic to human body (e.g., PZT)
Expensive, not easy to process
High piezoelectric coefficients
PhD Defense - Mons

4. 12 May 2023 4
Poly(L-lactic acid) as a promising piezoelectric biopolymer
Shear piezoelectricity without poling
Low piezoelectric constant (compared to
PVDF and PVDF-TrFE)
Easy to process and cheap
Biocompatible
Highest piezoelectric constant for
piezoelectric biopolymer
Piezoelectricity of crystallized PLLA film originates from the re-alignment
of the C=O dipole under external stress!
Applying stress
PhD Defense - Mons
PLLA
Li, X. et al. Energy Technol. 8, 1901252 (2020)
Shear piezoelectricity response of PLLA

5. 12 May 2023 5
Electrospinning - an efficient approach to induce ferroelectricty in PLLA
What about crystallized PLLA nanofibers? Do they exhibit better ferroelectricity?
High voltage
power supply
Syringe bump
Plastic bump
Collector
Our relative questions are:
Non-polar
polar
What is the response of PLLA composite nanofibers? Do they exhibit better piezoelectricity as we expected?
Sultana, A. et al. J. Mater. Chem. B 5, 7352–7359 (2017).
Amorphous
PLA nanofibers!
Amorphous PLLA electrospun fiber displays not only piezoelectricity but also ferroelectricity!
PhD Defense - Mons

6. 6
Outline of my thesis
12 May 2023
Crystallinity
Mechanical
Properties
Piezoelectric
Properties
Crystallized
PLLA fibers
Part 1
BTO/PLLA
nanofibers
Mechanical
Properties
Piezoelectric
Properties
Crystallinity
Part 2
Part 3 Synthesis and characterization of bio-based Non-Isocyanate Polyurethane with
ferroelectric potential
PhD Defense - Mons

7. 12 May 2023 7
Advanced AFM technique - Peakforce QNM for nanomechanical properties
Approach
Withdrawal
Peakforce
Force
Time
Tip trajectory
Tip-sample separation
Force
Approach
Withdrawal
Fit for modulus
adhesion
disspation
deform
Peakforce
Laser
Quadrant
Photodiode
z-signal
Feedback
Electronics
Scanner
Cantilever
Sample
Contact mechanic
Models
Hertz
JKR
DMT
Surface
forces
Attraction Attraction
Up to 8 channels:
1. Topography
2. Peakforce Error
3. Elastic Modulus
4. Log DMT
5. Adhesion
6. Indentation
7. Deformation
8. Dissipation
Dimension Icon (Bruker)
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8. 12 May 2023 8
Piezoresponse Force Microscopy for piezoelectricity and ferroelectricity at nanoscale
Vertical PFM Lateral PFM
Vertical
Direction
Rotation
P P
• Vertical PFM: detect out-of-plane polarization
• Lateral PFM: detect in-plane polarization
Imaging method
Vorpahl, S. M. et al. ACS Appl. Energy Mater. 1, 1534–1539 (2018).
Topography VPFM Amplitude VPFM Phase
• For many years, the presence of PFM hysteresis loops is the
clear evidence of ferroelectricity at nanoscale!
MFP-3D (Asylum Research)
• Able to go up to ±220 V bias.
• Able to apply DFRT-PFM.
• Easy to carry out.
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Switching Spectroscopy method
Sample bias (V)
PFM
Amplitude
(pm)
Sample bias (V)
PFM
Phase
(degrees)

9. 12 May 2023 9
Fabrication and characterization methods
Sample Preparation:
Characterization methods:
Electrospinning
• V= 24 kV
• d= 19 cm
PLLA nanofibers
on different substrates
Post-annealing
6%wt PLLA (L130) in
DCM/Acetonitrile
DSC XRD FTIR Advanced AFM techniques
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10. 12 May 2023 10
Effect of annealing process on the overall crystallinity
• As-spun sample: amorphous
• Annealed samples: semi-crystalline.
• Highest crystallinity at 160°C.
• Annealing time had little effect.
exo up
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11. 12 May 2023 11
Effect of annealing process on crystalline phases
• As-spun and fibers annealed at 60°C remained as
amorphous.
• Two prominent peaks at 16.7° and 19.1° proves the
increased crystallinity.
• Samples annealed at 140°C and 160°C: α-phase.
Samples annealed at 80-120°C : α'-phase.
• 955 cm-1: amorphous fraction.
• 921 cm-1: crystalline fraction (α' and α).
• Multiple band-splitting in the spectral region of
750-650 cm-1 : α-phase is dominant. No band-
splitting in 750-650 cm-1 : α'-phase is dominant.
Samples annealed at 160°C were selected as the representatives for crystallized PLLA nanofibers!
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12. 12 May 2023 12
Morphologies of PLLA nanofibers by Tapping AFM
Amorphous
Crystallized
Mesophase
Crystalline
phase
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13. 12 May 2023 13
Effect of annealing process on fiber diameter
Amorphous Crystallized
• Estimation of fiber diameter by measuring the its width is
poorly accurate due to tip convolution effect.
• Fiber diameter = distance from the substrate to the
highest point of the cross-section profile.
• Number of fibers for the calculation: N = 100.
• The decrease of the fiber diameter upon annealing
originates from the collapse of the pores and the merging
of crystallite domains.
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14. 12 May 2023 14
Local mapping of mechanical properties by Peakforce QNM
Amorphous
Crystallized
• Crystallized PLLA nanofibers consist of spherical crystallite domains surrounded by armorphous domains.
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15. 12 May 2023 15
Elastic and plastic deformation as a function of applied force
Amorphous Crystallized
• The onset of plastic deformation is 50 nN for as-spun and 100 nN for annealed PLLA nanofiber.
• In the elastic region, the contact modulus remains constant as the force increases.
• The elastic contact modulus values were chosen from the region where elastic deformation is dominant.
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Elastic Plastic
Elastic Plastic

16. 12 May 2023 16
Mapping of adhesion force proves the onset of plastic deformation
50 nN 90 nN back to 50 nN 100 nN back to 50 nN
Amorphous
Crystallized
30 nN 50 nN back to 30 nN 60 nN back to 30 nN
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17. 12 May 2023 17
Comparison of contact modulus between as-spun and annealed PLLA nanofibers
Amorphous
Crystallized
crystallized
PLLA film
Amorphous PLLA film
• A common trend for both amorphous and crystallized PLLA
nanofibers: The smaller the diameter, the higher the contact
modulus.
• After 300 nm, the contact modulus reach the values of bulk
materials.
• All heat-treated nanofibers show enhanced contact modulus
compared to that of the pristine ones.
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18. 12 May 2023 18
P(VDF-co-TrFE) thin film as a reference sample for PFM measurement
P(VDF-co-TrFE) 70/30
-(VDF)- -(TrFE)-
• A well-studied ferroelectric polymer
• A popular material for flexible
piezoelectric harvesting application
P(VDF-co-TrFE)
in MEK
P(VDF-co-TrFE)
thin film
140°C
2h
1
2
3
4
Spin
Coating
ITO substrate
Before annealing After annealing
0 10 20 30 40
0
100
200
300
400
Height
(nm)
Distance (µm)
168
170 nm
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19. 12 May 2023 19
Ferroelectric analysis of P(VDF-co-TrFE) thin film by Piezoresponse Force Microscopy
Spectroscopy method
• Both methods indicate a PFM amplitude of ~ 500 pm, proving
that a consistent result can be achieved by both methods.
• Hysteresis PFM loops prove the ferroelectric nature of the
P(VDF-co-TrFE).
• Coercive voltage Vc = ±14 V.
+30V
-30V
+30V
-30V
Imaging method
PFM
Amplitude
PFM
Phase
0 2 4 6 8 10 12 14
-50
0
50
100
150
Phase
(°)
Distance (mm)
130°
-50°
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20. 12 May 2023 20
Local hysteresis loops of amorphous PLLA fibers by PFM
Fibre 175nm Fibre 228nm Fibre 305nm
Vc = ±44 V Vc = ±50 V Vc = ±60 V
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21. 12 May 2023 21
Local hysteresis loops of crystallized fibers by AFM
Fibre 168nm Fibre 235nm Fibre 352nm
Vc = ±33 V Vc = ±37 V Vc = ±46 V
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22. 12 May 2023 22
Comparison of local piezoelectricity between PLLA nanofiber and PVDF copolymer
• Mean and standard deviation values were calculated from 15 different nanofibers (n=15).
• Annealed nanofibers show increased piezoelectric response compared to as-spun samples.
• The piezoresponse of crystallized nanofibers are still low compared to PVDF-TrFE thin film.
PhD Defense - Mons

23. 12 May 2023 23
• Post-annealing process show a positive effect on crystallinity, mechanical and piezoelectric properties of electrospun PLLA nanofibers.
• Electrospun nanofibers show better mechanical properties than their film counterpart, but only in a certain range of diameter.
• The piezoelectric response of crystallized PLLA nanofibers are still much lower than that of PVDF-TrFE → room for improvement →
Part 2.
Conclusions for part 1
Amorphous
Crystallized
crystallized
PLLA film
Amorphous PLLA film
PhD Defense - Mons

24. 12 May 2023 24
Outline of my thesis
Crystallinity
Mechanical
Properties
Piezoelectric
Properties
Crystallized
PLLA fibers
Part 1
BTO/PLLA
nanofibers
Mechanical
Properties
Piezoelectric
Properties
Crystallinity
Part 2
Part 3 Synthesis and characterization of bio-based Non-Isocyanate Polyurethane with
ferroelectric potential
PhD Defense - Mons

25. 12 May 2023 25
Characterization of Barium Titanate nanoparticles
• Barium Titanate is a good piezoelectric ceramic (d33 =
350-460 pm/V) with non-toxic elements.
• Commercial BTO nanoparticles purchased from Inframat
(France).
• Average diameter (N= 200): 240 ± 62 nm.
• The presence of a doublet at 2θ = 45° confirms the
ferroelectric nature of the BTO powder.
Barium Titanate powder
(Inframat)
Cubic
(Paraelectric)
Tetragonal
(Ferroelectric)
PhD Defense - Mons

26. 12 May 2023 26
Fabrication and characterization methods of BTO/PLLA electrospun nanofibers
BTO/PLLA nanofibers
on different substrates
BTO/PLLA
Solution
PLLA in
DCM/Acetonitrile
5%wt BTO
DSC XRD SEM Advanced AFM methods
Post-annealing
160°C 2h
Sample Preparation:
Characterization methods:
Electrospinning
• V= 24 kV
• d= 15 cm
PhD Defense - Mons

27. 12 May 2023 27
Morphologies of BTO/PLLA nanofibers by SEM
6 wt% 10 wt% 15 wt% 20 wt%
PLLA
PLLA/BTO
• The addition of BTO significantly change the morphologies of the resulting fibers, compared to pure PLLA.
• The condition of 15 wt% of PLLA was selected as the optimum condition for electrospinning of BTO/PLLA composites.
PhD Defense - Mons

28. 12 May 2023 28
Effect of BTO addition and annealing process on the BTO/PLLA fiber diameter
As-spun
Annealed
PLLA 15%wt BTO 5%wt /PLLA 15%wt BTO 5%wt /PLLA 15%wt
• Size distribution is calculated from 100 individual nanofibers for each case.
• The addition of BTO nanoparticles lead to a decrease in the average diameter.
• Further heat-treatment at 160°C reduced the average diameter of the hybrid nanofibers, a similar trend as observed in the previous part.
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29. 12 May 2023 29
BSE and EDX results confirm the presence of BTO nanoparticles
As-spun
Annealed
• EDX spectra prove the existence of BTO
particles.
• BTO particles appear as brighter spots
compared to PLLA fiber due to higher Z
number.
• BSE images reveal that BTO particle are
embedded deeply inside the PLLA
nanofibers.
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30. 12 May 2023 30
Crystallinity and crystalline phase of BTO/PLLA nanofibers
• Pristine BTO/PLLA mostly amorphous with : χc = 4.7 %. Annealed BTO/PLLA highly crystallized: χc = 75.2 %
• Annealed BTO/PLLA sample mostly contains α-crystalline phase.
• The presence of a doublet at 2θ = 45° confirms the ferroelectric nature of the BTO nanoparticles after the fabrication
and post-treatment process.
• χc = 4.7 %
• χc = 75.2 %
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BTO
BTO
BTO
BTO

31. 12 May 2023 31
Local mechanical properties of BTO/PLLA fibers
Modulus Deformation Cross-section Profile
Amorphous
Crystallized
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32. 12 May 2023 32
Local mechanical properties as a function of applied force
50nN 70nN 90nN 100nN
120nN 150nN 170nN 200nN 220nN
50nN 70nN 90nN 100nN
120nN 150nN 170nN 200nN 220nN
Modulus
Deformation
• The influence of BTO nanoparticle become
more remarkable at high applied forces.
• A modulus value of ~ 90GPa is observed at
220 nN in the region embedded with BTO
nanoparticles.
• The results prove the increased impact
strength of the PLLA nanofibers by the
addition of BTO.
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33. 12 May 2023 33
Local piezoelectricity by PFM of BTO/PLLA nanofibers-Q factor and Resonant frequencies
4
3
1
2
• For the areas covered by pure PLLA nanofibers, there are no significant changes for Q factor and contact resonance frequencies.
• The increase in quality (Q) factor of the green region results from changes in the elastic and damping properties of BTO nanoparticles.
• The amplitude response of the cantilever increase signifcantly on the region embedded with BTO particles, which is an qualitative
indication of a better electroactive response.
Crystallized BTO/PLLA fiber
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34. 12 May 2023 34
Effect of BTO nanoparticles on the local piezoelectric response of PLLA fiber
3
1
2
Spot 3
Spot 2
Spot 1
• The piezoresponse of PLLA regions
embedded with BTO particle is much higher
than the pure PLLA regions.
• The PFM amplitude is improved by 7 times.
• The coercive bias Vc is about 24 V, much less
than pure PLLA fiber.
Crystallized BTO/PLLA fiber
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35. 12 May 2023 35
Comparison of local piezoelectricity between PLLA nanofiber and PVDF copolymer
PhD Defense - Mons
• BTO/PLLA nanofibers show enhanced piezoelectric and ferroelectric activities compared to P(VDF-co-TrFE) thin film!

36. 12 May 2023 36
• Post-annealing process at controlled temperature can improve the crystallinity and crystalline phase of the electrospun PLLA
nanofiber. Consequently, its mechanical and piezoelectric properties can also be improved.
• The addition of inorganic BTO nanoparticles has positive effects on the piezoelectric and ferroelectric properties of the PLLA
nanofibers.
• These results proves the potential of PLLA nanofibers and PLLA composites for self-sustained wearable applications.
Final conclusions
PhD Defense - Mons

37. 12 May 2023 37
Perspectives for future work
nano-PUND for direct piezoelectric
measurement
non-destructive PFM for soft,
piezoelectric materials
PhD Defense - Mons

38. 12 May 2023 38
People
• Prof. Philippe Leclère
• Prof. Valerie Gaucher
• Dr. Sophie Barrau
• Dr. Liam Collins
• Dr. Alexandre Fadel
• Dr. Malo Dufay
• Dr. Anthony Ferri
• Dr. Antonio Da Costa
• Dr. Nicolas Tabary
• Dr. Valentina Sessini
Institutions
o University of Lille
o University of Mons (UMONS)
o University of Artois
Laboratories
o UMET
o CMN
o SMPC
o Materia Nova
Acknowledgements
PhD Defense - Mons

39. 12 May 2023 PhD Defense - Lille 39
Thank you for
your attention!

40. 12 May 2023 PhD Defense - Lille 40
• Studies of mechanical and piezoelectric properties of electrospun
PLLA nanofibers with post-annealing process
• A correlation between crystallinity, crystalline phase, and the
resulting physical properties was studied.
Part 1
• Effects of piezoelectric inorganic nanoparticles incorporation on the
mechanical and piezoelectric properties of a single PLLA nanofibers
were studied.
Part 2
• Study the nanostructure and its effect on mechanical and
piezoelectric properties of Non-isocyanate polyurethane (NIPU)
films.
Part 3

41. 12 May 2023 PhD Defense - Lille 41
Synthesis routes for NIPUs
• Several NIPUs were synthesized from Resorcinol (RBC) and two diamines.
• Amino-telechelic oligoamide (bioATO) was used as a bio-based chain extender.
• Total of 3 samples: RBC-CAD, RBC-PUTR and RBC-CAD-bioATO.

42. 12 May 2023 PhD Defense - Lille 42
Morphologies of NIPU by Tapping AFM
RBC-CAD RBC-PUTR RBC-CAD-bioATO

43. 12 May 2023 PhD Defense - Lille 43
Morphological changes of NIPUs as a function of temperature
25 °C 30 °C 35 °C 40 °C
45 °C 50 °C 55 °C 60 °C
65 °C 70 °C 75 °C 25 °C

44. 12 May 2023 PhD Defense - Lille 44
Local mechanical mapping of NIPUs
RBC - CAD RBC - PUTR RBC – CAD - bioATO
Height
Modulus
Adhesion

45. 12 May 2023 PhD Defense - Lille 45
Quantitative contact modulus of NIPUs by AFM
RBC-CAD RBC-PUTR
RBC-CAD-bioATO

46. 12 May 2023 PhD Defense - Lille 46
Ferroelectric-like behaviour of RBC-CAD-bioATO
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Pr
= 0.05 mC cm
-2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.01
0.00
0.01
Current
density
(
m
A
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.02
-0.01
0.00
0.01
0.02
Current
density
(
m
A
cm
-2
)
Electric Field (kV mm
-1
)
a) b)
c) d)
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Pr
= 0.05 mC cm
-2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.01
0.00
0.01
Current
density
(
m
A
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.02
-0.01
0.00
0.01
0.02
Current
density
(
m
A
cm
-2
)
Electric Field (kV mm
-1
)
a) b)
c) d)
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Pr
= 0.05 mC cm
-2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0
-0.10
-0.05
0.00
0.05
0.10
Current
density
(
m
A
cm
-2
)
Electric Field (kV
a) b)
-20 -10 0 10 20
-0.2
-0.1
0.0
0.1
0.2
Pr
= 0.05 mC cm
-2
Polarization
(
m
C
cm
-2
)
Electric Field (kV mm
-1
)
-20 -10 0 10 20
-0.10
-0.05
0.00
0.05
0.10
Current
density
(
m
A
cm
-2
)
Electric Field (kV mm
-1
)
Ec
= 11 kV mm
-1
a) b)
RBC-CAD RBC-PUTR RBC-CAD-bioATO
A piezoelectric coefficient of 2 pC.N-1 was obtained for RBC-CAD-bioATO!

47. 12 May 2023 PhD Defense - Lille 47
A new trend in designing piezoelectric generators
Perovskite Materials
PVDF nanofiber
Copper
Aluminum foil
Old types of piezoelectric generator:
• Based on ceramic piezoelectric materials
• Toxic to human body
• Expensive
• Micro-sized
New types of piezoelectric generator:
• Biocompatible piezoelectric materials
• Eco-friendly and renewable
• Flexible and cheap
• Nano-sized

48. 12 May 2023 PhD Defense - Lille 48
Human motions- a great energy source for wearable, self-powered devices
Human is actually great source of energy.
Body Heat
Breathing
Finger
Motions
Footfalls
Arm
Motion
Sources
Harvesting energy from human motions is
more capable than from body heat.
6.9-19mW
2.4-4.8W
1.0W
60W
67W
Potential
Energy
Maurya, D., Yan, Y. & Priya, S. J.et al. Adv. Mater. Clean Energy 50–71 (2015).
Khalid, S., Raouf, I., Khan, A. et al. Int. J. of Precis. Eng. and Manuf.-Green Tech. 6,
821–851 (2019).

49. 12 May 2023 PhD Defense - Lille 49
Piezoelectric material-a key factor for self-powered, wearable devices
Basic building blocks of a self-powered, wearable devices:
Wearable Devices
Sensing unit
Data Processing unit
Communication unit
Human movements Energy Harvesting System
Piezoelectric
Harvester
Power
Management
Energy
Storage
Bottom Electrode
Flexible substrate
Top Electrode
Piezoelectric layer
Flexible substrate
Piezoelectric materials act as the core of all
piezoelectric harvesters!
Liu, Y., Khanbareh, H., Halim, M. A.. et al. Nano Sel. (2021) doi:10.1002/nano.202000242.

50. 12 May 2023 PhD Defense - Lille 50
Piezoelectricity and Piezoelectric coefficients
Piezoelectric
Force
Inverse Piezoelectric
Electric
stimuli
Mechanical
vibrations
32 crystallographic point group
20 non-centrosymmetric
piezoelectric
Less than 10 reversible polar
ferroelectric
(e.g., quartz)
(e.g., PZT,
PVDF, BTO)

51. 12 May 2023 51
Ferroelectricity: ferroelectric hysteresis and butterfly loop
Dielectric
Piezoelectric
Pyroelectric
Ferroelectricity
Electric
field
Ps
E
Ec
-Ec
-Pr
Pr
Ps
P
Polarization versus E
(Hysteresis loop)
Ps : Saturated polarization
Pr : Remanent polarization
Ec : Coercive field
P : Polarization
E : Electric field
S
E
-Ec Ec
Strain versus E
(Butterfly loop)
The presence of P-E and S-E loop
are often undeniable evidence for
piezoelectricity and ferroelectricity
at macro- and nanoscale!
PhD Defense - Mons