Pyroelectric conversion: Harvesting Energy from

Pyroelectric conversion: Harvesting Energy from Temperature Fluctuations Dr. Àngel Cuadras Instrumentation, Sensors and Interfaces Group Castelldefels School of Technology Universitat Politècnica de Catalunya (UPC) 1

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

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

2

INTRODUCTION Thermal energy •Present everywhere •Thermodynamical restrictions Sun Fire

Sources

Industry Hot Pipes Engines

Thermal to electrical conversion – Thermoelectricity: thermal gradients – Pyroelectricity: from thermal time-dependent fluctuations 3

OUTLINE • • • • • •

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

4

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… 5

PHYSICAL DESCRIPTION • Crystalline structures

∆

Cations (Pb,Ti,Ca,Ta…) Anions (O)

Cubic structure 6

PHYSICAL DESCRIPTION • Crystalline structures • Point symmetry

Cations (Pb,Ti,Ca,Ta…) Anions (O)

Tetragonal structure 7


•Mechanical stress Structure Deformation ∆

•Thermal stress •Electrical stress

Piezoelectric Pyroelectric Ferroelectric Tetragonal structure 8




Pyroelectric

Tetragonal structure 9




∆ ∆T

+++++++++++++++++++++ ∆V Pyroelectric --------------------

Tetragonal structure

Ion displacement due to ∆T Æ Induced charge 10




T>TC Paraelectric

Cubic structure

Ion symmetry Æ no induced charge 11

PYROELECTRIC EFFECT •Temperature increase TGS

•Polarization 0

•Dependence of p on T ps =

250

150

-4

p P

100

-15

-2

-10

P(µC m )

200

-2

-1

p (10 C m K )

-5

dPs dT

•Maximum temperature Æ Curie temperature, phase transition

-20

50 TCurie

0 300

305 T (K)

310

-25 315

•Induced current as a function of T I=

dQs dPs dT = = Sps dt dt dt

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

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

LiTaO3

• Polymers – PVDF-Polyvinylidene Difluoride – Growth methods: Chemical processing TGS 13

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 p FoM = cV ε 0 ε r Material

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

TGS

εr (1 kHz)

TC (ºC)

cv (J cm-3 K-1)

3.5

35

49

2.5

LiTaO3

2.3

46

665

3.2

PZT

1.6

1350

320

PVDF

0.3

12

80

2.4 14

OUTLINE • • • • • •


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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 16

APPLICATIONS: HARVESTERS

R. B. Olsen, D. A. Bruno, and J. M. Briscoe, "Pyroelectric Conversion Cycles," J. Appl. Phys. 58 (1985) 4709 17

PYROELECTRICITY: YES OR NOT? YES?

NOT? • Low power generation • Low conversion efficiency • Temperature fluctuations

• Low cost • Infinite thermal sources

Estimation: S = 10 cm2 λ= 10-4 C m-2K-1

⇒

I = 1 µA

dT/dt= 10 K s-1 18

MODELING CONVERSION I = S · p·

W

RT

CT

T

I

Thermal model

dT dt Re

Ce

V ∆V =

S ·p ·∆T Ce

Electrical model

Harvester critical parameters RT and CT : thermal conductivity and thermal capacitance Re and Ce : electrical losses and electrical capacitance Efficiency (< 1 %) 19

OUTLINE • • • • • •


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

Thermal measurement •SMD Thermistor •Fast thermal response •Sensitivity up to 0.01 K

Current Measurement Rf I VO

Acquisition System Agilent

Voltage measurement Electrometer Keithley 616

Resistance measurement Electrometer Keithley 616 R up to 1014 Ω 21

PZT STUDIED HARVESTERS 4 cm

4 cm

Technology

PZT

•Ceramic powder

Alumina Substrate

•Screen printing. •Firing •Poling

Bottom electrode PdAg (contact)

Sample ID

Target Thickness (µm)

Poling Field (MV/m)

1

60

5

2

60

7

3

100

5

4

100

7

22

PZT FORMATION Tpoling + -

Random orientation of dipoles

DC field application: poling

Remanent polarization

Dipole orientation

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PZT CONVERTERS dT/dt (K/s)

I T dT/dt

0,3

I (µA)

0,2

T (K) 350

1,0

340

• Step function

0,5

330

• Large thermal inertia

0,0

320

Pyrocurrent follows dT/dt

0,1 0,0 310 -0,5

-0,1 0

50

100

150 Time (s)

200

250

Air Heating:

300 300

Imax = 0.3 mA

Generated charge density Q = 0.75 C·cm-2 24

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 25

PZT CONVERTERS 1 3

Constant poling field 5 MV/m

0.3

Technological dependence:

I (µA)

0.2

• Poling Field 0.1

• Thickness

0.0

Optimized design

-0.1 0

20

40 60 Time (s)

80

100

26

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 0.4

0.0

•

Warm air flow/fan

•

Temperature fluctuation (298 K Æ 335 K)

-2

-0.2

3.60 cm

-2

7.44 cm -0.4 0

10

20

4

30 40 Time (s)

50

•

Peak current

•

Generated Charge density

60

Q = 0.24 C·cm-2 •

3 dT/dt (K/s)

I (µA)

0.2

2

Symmetry in heating and cooling

1 0 0

10

20

T im e ( s )

30

28

IMPROVING HARVESTERS

• Cell association • Energy storage • Thermal cycling

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PARALLEL ASSOCIATION Parallel Cell Association

0,4 3 4 3||4

I (µA)

0,3

0,2

Current addition

0,1

0,0 0

25

50 time (s)

75

100

Stacked structures 30

ENERGY STORAGE

Ce

•Impedance matching overcome •Low power systems strategy •Rectification + storage

•Energy loss at diodes •Capacitor charge 31

THERMAL CYCLING

10

6 330

V (V)

8 320

6 4

310

2

340

T (K)

330

5 4

320

3 310

2 1

300

V (V) 0 0

50

300 100 150 200 250 300 350

0 0

100

time (s) N ⎡ ⎛ ⎞ QS CL − Ce ⎤ S·p·∆T ⎢1 − ⎜ Vo ( N ) = ⎟ ⎥= 2Ce ⎢ ⎝ CL + Ce ⎠ ⎥ 2Ce ⎣ ⎦

Temperature (K)

12

V(V)

V T

PVDF

340

Temperature (K)

PZT

⎡ ⎛ C − C ⎞N ⎤ e ⎢1 − ⎜ L ⎟ ⎥ ⎢⎣ ⎝ CL + Ce ⎠ ⎥⎦

200

300 Time (s)

400

500

Vo,max ( N → ∞ ) =

S·p·∆T 2Ce 32

BEYOND PYROELECTRICITY 0,3

I T

360

I (µA)

0,1

340

0,0

320

-0,1 -0,2 -0,3

300 0

100

200 Time (s)

300

Temperature (K)

0,2

•Materials sensitive to external influences. •Generated current from a PZT when illuminated. •Current is not proportional to dT/dt.

400

•Combination of different effects in a single harvester •Piezoelectrical response – when undergo mechanical stresses •Semiconductor – heated with light 33

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?

Av. Canal Olimpic s/n 08860 Castelldefels (Barcelona), Spain, [email protected]

Castelldefels School of Technology (EPSC), Universitat Politècnica de Catalunya (UPC) 35