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Small-scale energy harvesting device

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.

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Small-scale energy harvesting device

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  1. LIUJIN Small-scale energy harvesting device

  2. 1 Introduction 2 Thermoelectric power generation 3 Vibration power generation 4 4 RF power generation Conclusion Contents 5 MIPD

  3. Introduction • Application of wireless sensors network Life time size • Energy harvesting devices A directly to sensor B to a secondary battery in node

  4. Vibration power conversion Thermo-electric power generation RF power conversion T gradient, heat flows Low T difference feasible ； Mechanical vibrations Kinetic energy-> AC power Background radiation Emerging types MIPD

  5. Thermoelectric part • Seebeck effect (coefficient α=v2-v1/δT，highest observed in semiconductor) • Thermocouples

  6. 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

  7. Through-plane module 12 thermocouples，60uw/cm2,△T=5K n：Bi2Te3，p：（Bi，Sb）2Te3，single element：20*40*80um3， Length<100um MIPD LAB

  8. 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 MIPD LAB

  9. 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 MIPD LAB

  10. 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 MIPD LAB

  11. 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) MIPD LAB

  12. Generic Model: Trade off between the bandwidth and power Comparison Unit (P/a2 per unit) MIPD LAB

  13. Three mechanisms Piezoelectric Electromagnetic Electrostatic relative motion of magnet and coil Strain->Materials electrical potential gradient variable capacitor MIPD

  14. Electromagnetic • Assuming constant magnetic field: • Challenge: A V<100mv, 1cm3 B compatibility of magnetic materials C magnetic field interfere electronics component MIPD LAB

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

  16. Best performance:Four magnetic configuration:F=52HZ,a=0.59m/s2,v=0.15cm3p=46uw MIPD LAB

  17. Piezoelectric mode 31mode: strain perpendicular to electrode 33mode: compressive strain perpendicular to electrode d33>d31, but d31 is easier to implement MIPD

  18. Bimorph configuration F=85HZ, p=210uw,v=10v MIPD LAB

  19. Electrostatic • Advantage: compatible &easily integrated • Disadvantage: • 1. initial voltage • 2.power generation lost by accident MIPD LAB

  20. 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 MIPD LAB

  21. In-plane gap-closing closing converter optimized, 2.25m/s2,120hz, 1cm3,116uw(predicted) MIPD LAB

  22. Out-of-plane gap closing converter • 36uw,2.4v,6hz, compressed volume 13.5cm MIPD LAB

  23. RF power generation • Incident power density (plane wave): S=E2/R Distance restriction RF source： A commercial radio and tv broadcast antennas(<3km,2.6uw/cm2) B Base stations for cellphone service C WLANS (wirless local area networks) MIPD LAB

  24. RFID • Actively provide rf power to wirless sensors • DC-RF-transmission-collect-(AC-DC conversion) MIPD LAB

  25. 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 MIPD LAB

  26. Thank you!

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