MIPD Small-scale energy harvesting device LIUJIN

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

MIPD 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=v 2 -v 1 /δT ， highest observed in semiconductor)  Thermocouples

Characterize thermo materials  Z=α 2 /RK (K:parellel thermal conductance)  Why semiconductor is good? A charge carrier concentration B High electrical conductivity C low thermal conductivity

Through-plane module MIPD LAB 12 thermocouples ， 60uw/cm2, △ T=5K n ： Bi2Te3 ， p ：（ Bi ， Sb ） 2Te3 ， single element ： 20*40*80um 3 ， 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 MIPD LAB

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

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

Vibration power generation  AC power- need rectification  Power origin: wide range of frequency (fundamental: HZ,a:0.1~12) strong maximum output at resonant frequency(f increases when size decreases) MIPD LAB

Generic Model: MIPD LAB Trade off between the bandwidth and power Comparison Unit (P/a 2 per unit)

MIPD 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, 1cm 3 B compatibility of magnetic materials C magnetic field interfere electronics component MIPD LAB

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

 Best performance: Four magnetic configuration: F=52HZ,a=0.59m/s 2, v=0.15cm 3 p=46uw

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

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

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

In-plane overlap-varying converter  A:finger:7um wide, 512um deep, 400each side, 15*5*1mm3, predicted:2.5khz,8.6uw.8v B:20*20*2mm3,10hz,3.9m/s2,200v,6uw, electret coated on electrode MIPD LAB

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

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

RF power generation  Incident power density (plane wave): S=E 2 /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

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

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

MIPD