MIPD

Small-scale energy harvesting device

LIUJIN

MIPD

Contents

Introduction1

Thermoelectric power generation2

Vibration power generation3

RF power generation4

Conclusion

4

5

Introduction

Application of wireless sensors network

Life time

size

Energy harvesting devices

A directly to sensor

B to a secondary battery in node

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Emerging types

Thermo-electric power

generation

T gradient, heat flows

Low T difference feasible ；

Vibration power conversion

Mechanical vibrations

Kinetic energy->AC power

RF power conversion

Background radiation

Thermoelectric part

Seebeck effect

(coefficient α=v2-v1/δT ， highest observed in semiconductor)

Thermocouples

Characterize thermo materials

Z=α2/RK

(K:parellel thermal conductance)

Why semiconductor is good?

A charge carrier concentration

B High electrical conductivity

C low thermal conductivity

Through-plane module

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12 thermocouples ， 60uw/cm2,△T=5Kn ： Bi2Te3 ， p ：（ Bi ， Sb ） 2Te3 ， single element ：

20*40*80um3 ，Length<100um

In-plane module

Advantage: L& higher aspect ratio, more thermocouples per unit, cheaper fab tech

Design diff: substrate(bridge) removed or low thermal and electrical conductivity

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In-plane module ： a different design

One type of semiconductor was used,1000 elements, dT=10K, 1.5uw,2v

Thermocouple 7 um wide and 500 um long

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Thermoelectric materials

limitation: Wiedemann-Franz law:

electrical conductivity ~electronic component of thermal conductivity

RT:Bi2Te3(ZT~1,bulk material)

Other way: phonon transport

Low dimension: quantum confinement

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Vibration power generation

AC power- need rectification

Power origin: wide range of frequency (fundamental: 13-385HZ,a:0.1~12) strong maximum output at resonant

frequency(f increases when size decreases)

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Generic Model:

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Trade off between the bandwidth and powerComparison Unit (P/a2 per unit)

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Strain->Materials electrical potential gradient

relative motion of magnet and coil

variable capacitor

Three mechanisms

Electromagnetic Piezoelectric Electrostatic

Electromagnetic

Assuming constant magnetic field:

Challenge:A V<100mv, 1cm3

B compatibility of magnetic materialsC magnetic field interfere electronics

component

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Volume:~4mm3 f=4.4khz a=380m/s2 P=0.3uw Membrane:7um housing GaAs

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Best performance:Four magnetic configuration:F=52HZ,a=0.59m/s2,v=0.15cm3

p=46uw

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Piezoelectric

33mode: compressive strain perpendicular to electrode

mode

31mode: strain perpendicular to electrode

d33>d31, but d31 is easier to implement

Bimorph configuration

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F=85HZ, p=210uw,v=10v

Electrostatic

Advantage: compatible &easily integrated

Disadvantage: 1. initial voltage 2.power generation lost by accident

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In-plane overlap-varying converter

A:finger:7um wide, 512um deep, 400each side, 15*5*1mm3,predicted:2.5khz,8.6uw.8vB:20*20*2mm3,10hz,3.9m/s2,200v,6uw, electret coated on electrode

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In-plane gap-closing closing converter

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optimized, 2.25m/s2,120hz, 1cm3,116uw(predicted)

Out-of-plane gap closing converter

36uw,2.4v,6hz, compressed volume 13.5cm

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RF power generation

Incident power density (plane wave): S=E2/RDistance restrictionRF source：A commercial radio and tv broadcast

antennas(<3km,2.6uw/cm2)B Base stations for cellphone serviceC WLANS (wirless local area networks)

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RFID

Actively provide rf power to wirless sensors DC-RF-transmission-collect-(AC-DC

conversion)

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conclusion

Thermo: most compatible; aspect ratio, lower resistance, n of

thermal couples

Vibration: resonant frequency problem size decreases, f increases

RF: RFID tags not typical harvesting device

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