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LIUJIN. Small-scale energy harvesting device. 1. Introduction. 2. Thermoelectric power generation. 3. Vibration power generation. 4. 4. RF power generation. Conclusion. Contents. 5. Introduction. - PowerPoint PPT Presentation
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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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