1

Pyroelectric conversion: Harvesting Energy from

Temperature Fluctuations

Dr. Àngel Cuadras

Instrumentation, Sensors and Interfaces GroupCastelldefels School of Technology

Universitat Politècnica de Catalunya (UPC)

2

COLLABORATIONS

• University of Brescia. (Dept. Electronics for Automation and INFM)– A. Ghisla, V. Ferrari, M. Ferrari

• Instrumentation, Sensors and Interfaces GroupCastelldefels School of Technology– Dr. Gasulla, Dr. Pallàs

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INTRODUCTIONThermal energy

•Present everywhere

•Thermodynamical restrictions

Sun

Fire

Thermal to electrical conversion– Thermoelectricity: thermal gradients– Pyroelectricity: from thermal time-dependent fluctuations

Industry Hot PipesEngines

Sources

4

OUTLINE

• History• Pyroelectric Effect• Materials• Applications: Sensors and Harvesters• Experimental harvesters• Conclusions

5

HISTORY

• Phenomenon observation– Classic Greeks: Theophrastus (314 BC)– XVIIIth and XIXth: phenomenon observation

• Description and quantification– Classical explanation: Lord Kelvin– Quantical explanation: Born

• Researchers: – Schrödinger, Röntgen and P. Curie, among others

• Applications:– Sensors: Yeou Ta…– Harvesters investigated by Olsen et al., Ikura…

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PHYSICAL DESCRIPTION

• Crystalline structures

∆

Cubic structure

Cations (Pb,Ti,Ca,Ta…)

Anions (O)

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PHYSICAL DESCRIPTION

• Crystalline structures• Point symmetry

Tetragonal structure

Cations (Pb,Ti,Ca,Ta…)

Anions (O)

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PHYSICAL DESCRIPTION

Structure Deformation ∆

•Mechanical stress

•Thermal stress

•Electrical stress

• Crystalline structures• Point symmetry

Tetragonal structure

Piezoelectric

Pyroelectric

Ferroelectric

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PHYSICAL DESCRIPTION

Structure Deformation ∆

•Mechanical stress

•Thermal stress

•Electrical stress

• Crystalline structures• Point symmetry

Tetragonal structure

Pyroelectric

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PHYSICAL DESCRIPTION

• Crystalline structures• Point symmetry

Structure Deformation ∆

•Mechanical stress

•Thermal stress

•Electrical stress

Tetragonal structure

+++++++++++++++++++++

- - - - - - - - - - - - - - - - - - - -Pyroelectric

∆ ∆T∆V

Ion displacement due to ∆T Induced charge

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PHYSICAL DESCRIPTION

Structure Deformation ∆

•Mechanical stress

•Thermal stress

•Electrical stress

• Crystalline structures• Point symmetry

ParaelectricT>TC

Ion symmetry no induced chargeCubic structure

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PYROELECTRIC EFFECT

300 305 310 3150

50

100

150

200

250

p

T (K)

p (1

0-4 C

m-2 K

-1)

-25

-20

-15

-10

-5

0

TCurie

P(µ

C m

-2)

P

s ss

dQ dP dTI Spdt dt dt

= = =

ss

dPpdT

=

•Temperature increase•Polarization

•Dependence of p on T

•Maximum temperature Curie temperature, phase transition

•Induced current as a function of T

TGS

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PYROELECTRIC MATERIALS

LiTaO3

• Crystal materials – CaTiO3,LiTaO3,PbTiO3– Triglycine sulfate (TGS)– Growth methods: Czochralki, water dissolution

• Ceramics – PZT - Lead zirconate titanate – Growth methods: Screen printing– Poling

• Polymers – PVDF-Polyvinylidene Difluoride– Growth methods: Chemical processing

TGS

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MATERIALS DESCRIPTION• Pyroelectric coefficient (p)

– Thermal energy conversion to electrical conversion • Thermal capacitance (cV)

– Thermal energy stored in the lattice• Electrical permittivity (ε= ε0εr)

– Electrical energy stored in the lattice• Figure of Merit

0V r

pFoMc ε ε

=

Material p(10-4 C m-2 K-1)

εr(1 kHz)

TC(ºC)

cv(J cm-3 K-1)

TGS 3.5 35 49 2.5LiTaO3 2.3 46 665 3.2

PZT 1.6 1350 320

PVDF 0.3 12 80 2.4

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OUTLINE

• History• Pyroelectric Effect• Materials• Applications: Sensors and

Harvesters• Experimental harvesters• Conclusions

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APLICATIONS: SENSORS

• Proposed by Yeou Ta in 1938

• Application: IR sensors, burglar alarms

• Advantages– Wide thermal and electromagnetic

sensitivity– Fast response (0 to 10 Hz) – Low-cost– Good signal to noise ratio– Work at ambient temperature

• Scientific and commercial development

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APPLICATIONS: HARVESTERS

R. B. Olsen, D. A. Bruno, and J. M. Briscoe,

"Pyroelectric Conversion Cycles," J. Appl. Phys. 58 (1985) 4709

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PYROELECTRICITY: YES OR NOT?

YES?

• Low cost• Infinite thermal sources

NOT?

• Low power generation• Low conversion efficiency• Temperature fluctuations

Estimation:

S = 10 cm2

λ= 10-4 C m-2K-1 ⇒

dT/dt= 10 K s-1

I = 1 µA

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MODELING CONVERSION

W RTCT

T VI ReCe

Thermal model Electrical model

· ·dTI S pdt

=

e

· ·S p TVC

∆∆ =

Harvester critical parameters

RT and CT : thermal conductivity and thermal capacitance

Re and Ce : electrical losses and electrical capacitance

Efficiency (< 1 %)

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OUTLINE

• History• Pyroelectric Effect• Materials• Applications: Sensors and Harvesters• Experimental harvesters• Conclusions

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EXPERIMENTAL SETUP

Heating– 298 K to 370 K– Warm air – Halogen lamp

Current Measurement

Voltage measurementElectrometer Keithley 616

Resistance measurementElectrometer Keithley 616

R up to 1014 Ω

RfI

VO AcquisitionSystem Agilent

Thermal measurement•SMD Thermistor

•Fast thermal response

•Sensitivity up to 0.01 K

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PZT STUDIED HARVESTERS

Alumina Substrate

Bottom electrode PdAg (contact)

PZT Technology

•Ceramic powder

•Screen printing.

•Firing

•Poling

Sample ID Target Thickness (µm)

Poling Field (MV/m)

1 60 5

2 60 7

3 100 5

4 100 7

4 cm

4 cm

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PZT FORMATION

Tpoling

+-

Random orientation of

dipoles

Remanent polarizationDC field application:

poling

Dipole orientation

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PZT CONVERTERS

0 50 100 150 200 250 300

-0,1

0,0

0,1

0,2

0,3

I

I (µA

)

Time (s)

300

310

320

330

340

350

T

T(K)

-0,5

0,0

0,5

1,0 dT/dt

dT/dt (K/s)

Air Heating:

• Step function

• Large thermal inertia

Pyrocurrent follows dT/dt

Imax = 0.3 mA

Generated charge density

Q = 0.75 C·cm-2

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PZT CONVERTERS

Air Heating:

• Step function

• Large thermal inertia

Pyrocurrent follows dT/dt

Imax = 0.3 mA

Generated charge density

Q = 0.75 C·cm-2

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PZT CONVERTERS

Technological dependence:

• Poling Field

• Thickness

0 20 40 60 80 100

-0.1

0.0

0.1

0.2

0.3 Constant poling field5 MV/m

1 3

I (µA

)

Time (s)

Optimized design

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PVDF CONVERTERS

Measurement Specialties Inc.

Piezoelectrical Film

PVDF large area technology

Sample ID

Thickness (µm)

Area(cm-2)

C (nF)

A1 70 3.6 0.740

A2 40 7.44 2.78

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PVDF CONVERTERS

0 10 20 30 40 50 60-0.4

-0.2

0.0

0.2

0.4

3.60 cm-2

7.44 cm-2

I (µA

)

Time (s)

• Warm air flow/fan

• Temperature fluctuation

(298 K 335 K)

• Peak current

• Generated Charge density

Q = 0.24 C·cm-2

• Symmetry in heating and cooling

0 1 0 2 0 3 0

0

1

2

3

4

dT/

dt (K

/s)

T im e ( s )

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IMPROVING HARVESTERS

• Cell association• Energy storage• Thermal cycling

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PARALLEL ASSOCIATION

0 25 50 75 1000,0

0,1

0,2

0,3

0,4 3 4 3||4

I (µA

)

time (s)

Parallel Cell Association

Current addition

Stacked structures

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ENERGY STORAGE

•Low power systems strategy

•Rectification + storage

•Impedance matching overcome

•Energy loss at diodes

•Capacitor charge

Ce

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THERMAL CYCLING

0 100 200 300 400 5000

1

2

3

4

5

6

V (V)

Time (s)V(

V)

300

310

320

330

340

Tem

pera

ture

(K)

T (K)

PZT PVDF

0 50 100 150 200 250 300 3500

2

4

6

8

10

12

V

V (V

)

time (s)

300

310

320

330

340

Tem

pera

ture

(K)

T

( ) · ·1 12 2

N N

S L e L eo

e L e e L e

Q C C C CS p TV NC C C C C C

⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞− −∆⎢ ⎥ ⎢ ⎥= − = −⎜ ⎟ ⎜ ⎟+ +⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦( ),max

· ·2o

e

S p TV NC∆

→ ∞ =

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BEYOND PYROELECTRICITY

0 100 200 300 400-0,3

-0,2

-0,1

0,0

0,1

0,2

0,3

I

I (µA)

Time (s)

300

320

340

360

Tem

pera

ture

(K)

T •Materials sensitive to external influences.

•Generated current from a PZT when illuminated.

•Current is not proportional to dT/dt.

•Combination of different effects in a single harvester

•Piezoelectrical response – when undergo mechanical stresses

•Semiconductor – heated with light

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CONCLUSIONS

• Pyroelectricity has been revisited• PZT and PVDF cells have been developed and

modeled.• Parallel association increases the current.• Energy can be effectively transferred and stored in

capacitors.• Further research in order to effectively power low power

systems.

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QUESTIONS?

Castelldefels School of Technology (EPSC),Universitat Politècnica de Catalunya (UPC)

Av. Canal Olimpic s/n08860 Castelldefels (Barcelona), Spain,

angel.cuadras@upc.edu